Technical program

Transcription

Technical program

LPSO2014
International Symposium on
Long-Period Stacking Ordered Structure
and Its Related Materials 2014
- Symposium Guide
- Technical Program
- Abstracts
October 5 - 8, 2014, Kumamoto, Japan
Hotel Nikko Kumamoto
Edited by
Y. Kawamura
http://www.msre.kumamoto-u.ac.jp/LPSO2014/
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Overview and Welcome Message
A new magnesium-base alloy has been developed in Japan and is now the focus of wide
attention in many parts of the world because of its novel structure called “Synchronized
Long-Period Stacking Ordered Structure”, which features synchronization with respect to
chemical and structural modulation. Owing to its unique atomic arrangement, Mg alloys with
synchronized long-period stacking ordered (LPSO) structure have a great potential to
exhibit many advantageous material properties including high strength. On the other hand,
much remains to be learned concerning the fundamentals of this alloy, such as its
mechanical properties and the mechanisms of atomic arrangement and strengthening.
The 2nd International Symposium on Long-Period Stacking Ordered Structure and Its
Related Materials (LPSO2014) will provide an important forum for international scientists
and researchers to present and discuss new findings and ideas concerning the
fundamentals and applications of the LPSO structure and LPSO-related materials. During
this symposium, various experimental, theoretical, and computational approaches for:
1) Determining the unique crystallography of the synchronized LPSO structure
2) Elucidating the principles of LPSO formation
3) Clarifying the strengthening mechanisms of LPSO structure
4) High strength magnesium alloys containing LPSO phase
5) Kink deformation
6) Disclination
7) Application
will be discussed. Key experts in these fields have been invited to give keynote lectures on
recent advances in not only LPSO-type Mg alloys but also new related structural materials.
I am grateful to our colleagues in the world for their contributions to this symposium.
I hope you have wonderful time in this symposium.
Yoshihito Kawamura
Chairperson
LPSO2014
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Organization
Symposium Chairperson
Prof. Y. Kawamura
Kumamoto University, Japan
International Advisory Committee
Prof. A. E. Romanov
Russian Academy of Sciences, Russia
Prof. C. Wolverton
Northwestern University, USA
Prof. H. Nakajima
The Wakasa Wan Energy Research Center, Japan
Mr. H. Ohara
The Japan Magnesium Association, Japan
Mr. M. Komurasaki
The Japan Research and Development Center for
Metals, Japan
Prof. M. W. Barsoum
Drexel University, USA
Prof. O. Tsukamoto
Tokyo University of Science, Japan
Prof. R. Schmid-Fetzer
Clausthal University of Technology, Germany
Prof. S. R. Agnew
University of Virginia, USA
Prof. T. Masumoto
Research Institute for Electromagnetic Materials,
Japan
Prof. Y. Fujii
Comprehensive Research Organization for Science
and Society (CROSS), Japan
Dr. Y. Hosoya
Tokushu Kinzoku Excel Co.,Ltd., Japan
Prof. Y. Tomita
Fukui University of Technology, Japan
Steering Committee
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Prof. A. Nakatani
Osaka University, Japan
Prof. H. Inui
Kyoto University, Japan
Prof. H. Kimizuka
Prof. H. Nakashima
Kyushu University, Japan
Prof. H. Ohtani
Tohoku University, Japan
Dr. K. Aizawa
Japan Atomic Energy Agency (JAEA), Japan
Prof. K. Hagihara
Prof. K. Higashida
Prof. K. Okuda
Prof. L. Capolungo
Georgia Institute of Technology, USA
Prof. M. Yamasaki
Dr. S. Kimura
Japan Synchrotron Radiation Research Institute
(JASRI), Japan
Prof. M.T. Pérez-Prado
IMDEA Materials Institute, Spain
Prof. T. Furuhara
Prof. T. Kamiyama
High Energy Accelerator Research Organization,
KEK, Japan
Prof. T .Ohashi
Kitami Institute of Technology, Japan
Local Organizing Committee
Prof. H. Kitahara
Prof. J. Kim
Prof. K. Hokamoto
Prof. K. Ikeda
Prof. K. Takashima
Prof. L. Ruan
Prof. M. Touge
Prof. S. Ando
Prof. S. Iikubo
Kyushu Institute of Technology, Japan
Prof. T. Mayama
Prof. T. Morikawa
Prof. Y. Mine
Secretariat
Prof. J. Kim
Prof. T. Mayama
Prof. M. Yamasaki
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Symposium Information
Symposium Name
The 2nd International Symposium on Long-Period Stacking Ordered Structure and Its
Related Materials (LPSO2014)
Period
October 5(Sun.) - 8(Wed.), 2014
Venue
All technical programs and exhibition will be situated in:
Hotel Nikko Kumamoto
Address: 2-1, Kamitori-cho, chuou-ku, Kumamoto-shi, Kumamoto, 860-8536, Japan
Tel: +81-96-211-1111, Fax: +81-96-211-1175
Website: http://www.jalhotels.com/domestic/kyusyu/kumamoto/
Symposium Language
The symposium will be conducted in English
Registration Desk
The LPSO2014 Registration Desk will be open at the following place during the symposium.
The symposium secretariat will issue symposium materials to pre-registered delegates and
to those who register on-site.
Place: Serena Room, 2nd floor, Hotel Nikko Kumamoto (October 5)
Aso D Room, 5th floor, Hotel Nikko Kumamoto (October 6-8)
Operation Hours:
October 5, Sunday
15:00 - 18:30
October 6, Monday
08:00 - 17:00
October 7, Tuesday
08:00 - 13:00
October 8, Wednesday
08:00 - 11:00
Registration Fee
On-line "Early Registration"
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Regular
60,000JPY
Student
30,000JPY
On-line Regular Registration Regular
75,000JPY
Student
45,000JPY
Regular
75,000JPY (Only Cash)
Student
45,000JPY (Only Cash)
On-site Registration
Regular and student registration fee includes; admission to all technical sessions and
exhibition; Symposium kit including an abstracts books. All delegates who register as
regular and student are invited to welcome party and banquet.
Welcome Party
Welcome party will be held at Serena Room, 2nd floor of Hotel Nikko Kumamoto on 17:00 18:30 October 5, 2014. The symposium will serve light meals and drink.
Banquet
Banquet will be held at Hotel Ryugu, Amakusa on 18:00 - 20:30 October 7, 2014. Poster
Award Ceremony and some attractions will be performed in banquet.
Excursion (Option)
Excursion option paying registrants will receive an interesting overview about Mount Aso on
a sightseeing tour by bus. The tour will start from Hotel Nikko Kumamoto at 14:00, October
8. After tour the bus will bring you to the Kumamoto airport and Hotel Nikko Kumamoto.
LPSO2014 Exhibition
LPSO2014 Exhibition will take place at Higo AB Room.
Place: Higo AB Room, 5th floor, Hotel Nikko Kumamoto
Operation Hour:
October 6, Monday
08:30 - 17:30 (Installation Time: 08:30 - 10:00)
October 7, Tuesday
08:30 - 14:00
08:30 - 14:00
Symposium Secretariat
The symposium secretariat will be open during the symposium
e-mail: [email protected]
Tel: +81-96-342-3547
Fax: +81-96-342-3547
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Symposium Website
http://www.msre.kumamoto-u.ac.jp/LPSO2014/
Technical Program Information
Oral Presentation
Oral Presentation : Oral session will be held on October 6 - 8 at Aso D room, 5th floor, Hotel
Nikko Kumamoto.
Place: Aso D room, 5th floor, Hotel Nikko Kumamoto.
Operation Hours:
October 6, Monday
08:30 - 15:50
October 7, Tuesday
08:30 - 12:15
08:30 - 12:30
Oral Presentation Time
Presentation time is as follows:
Plenary Talk: 30 minutes
Invited Talk:
25 minutes
Oral Talk:
20 minutes
Poster Presentation
Poster session will be held on October 6 at Amakusa C room, 5th floor, Hotel Nikko
Kumamoto.
Place: Amakusa C room, 5th floor, Hotel Nikko Kumamoto.
Poster presentation time: October 6, Monday16:10 - 18:30 (Judging time for award)
Poster Size
Maximum space for each poster is 850 mm width and 1200 mm height. A0 size sheet
(W841 mm X H1189 mm) is available. Poster board size is 950 mm width and 1980 mm
height.
Mounting and Display
Poster should be mounted and displayed at designated time. The room attendant will
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provide the necessary material to mount the poster.
Mounting time: October 6, Monday
13:00 - 14:00
Display hours: October 6, Monday
14:00 - 18:30
Demounting time: October 6, Monday
18:30 - 19:00
Poster Award
There will be an award for the best poster. It will be selected form all poster by a jury and
the winner will be announced during symposium banquet on Tuesday evening.
Exhibition
LPSO2014 will host an exhibition of scientific instrument and industrial products. The
exhibition booths will be located close to the registration desk and poster session. Any
registered participant are welcome to visit the exhibition. Detail information can be available
at the registration desk.
Exhibitors
The East Coast Free Economic Zone (KOREA)
http://www.efez.go.kr/hb/kor
JEOL LTD.
http://www.jeol.com
FUKUDA METAL FOIL & POWDER CO., LTD.
http://www.fukuda-kyoto.co.jp/
NISSIN GIKEN Corporation
http://www.nissin-giken.co.jp/
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Program at a Glance
Oct. 6 (Mon.)
Opening
09:00-10:00
Oral
Session 1
10:00-11:00
Coffee Break
11:00-12:00
Oral
Session 2
Registration
08:00-09:00
12:00-13:00
13:00-14:00
Coffee Break
Oral
Session 5
Oral
Session 7
Lunch
Oral
Session 3
Registration
Coffee Break
Welcome
Party
Move
(Kumamoto
- Amakusa)
Poster
Session
Banquet
19:00-20:00
20:00-21:00
Move
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Coffee Break
Closing
18:00-19:00
21:00-22:00
Oral
Session 6
Group Photo
15:00-16:00
17:00-18:00
Oral
Session 4
Oct. 8 (Wed.)
Lunch
14:00-15:00
16:00-17:00
Oct. 7 (Tue.)
Registration
Oct. 5 (Sun.)
Registration
Time/Date
(AmakusaKumamoto)
Excursion
(Option)
Technical Program Information
Oral Session - 1
Oct. 06, Monday 08:30 - 10:15, Room Aso D
Chairpersons : Rainer Schmid-Fetzer and Tetsuya Ohashi
08:30 - 08:35
Welcome Address
Isao Taniguchi
08:35 - 08:40
Opening Remark
Yoshihito Kawamura
PLE - 01
08:40 - 09:10
Investigating Reversible Hysteresis in Magnesium Single Crystals Using a Spherical Tip under
Nanoindentation
Justin Griggs, Babak Anasori, Greg Vetterick, Grady Bentzel, Mitra Taheri, Roger Doherty and
Michel W. Barsoum
Drexel University, U.S.A.
INV - 01
09:10 - 09:35
Materials Science and Technology on Synchronized LPSO Structure
Yoshihito Kawamura
ORAL - 01
09:35 - 09:55
Crystal Structures of Mg-Zn-Y LPSO Phases - Compositional Dependence and Formation
Process Haruyuki Inui and Kyosuke Kishida
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ORAL - 02
09:55 - 10:15
Formation of Lamellar Long Period Stacking Ordered Structure in as-cast Mg–(0.5-5)Gd–1Zn
(at.%) Alloys
Yaxian Du, Yujuan Wu, Liming Peng, Xiaoqin Zeng and Wenjiang Ding
Shanghai Jiao Tong University, China
Coffee Break
10:15 - 10:35
Oral Session - 2
Chairpersons : Laurent Capolungo and Tadashi Furuhara
PLE - 02
10:35 - 11:05
Disclination Concept in Materials Physics and Mechanics
Alexei E. Romanov1,2,3,4, Anna L. Kolesnikova2,3,5 and Anatoly A. Vikarchuk3
1
Ioffe Physical-Technical Institute, Russia
2
ITMO University, Russia
3
Togliatti State University, Russia
4
University of Tartu, Estonia
5
Institute of Problems of Mechanical Engineering, Russia
INV - 02
11:05 - 11:30
In-situ Neutron Diffraction Study under Compressive Stress Combined with AE Measurement
of 18R LPSO Single-phase Alloy, AZ31 Alloy and Zinc
Kazuya Aizawa1, Wu Gong1, Stafanus Harjo1, Jun Abe2, Takuro Kawasaki1, Takaaki Iwahashi1 and
Takashi Kamiyama3
1
JAEA, Japan
2
CROSS-Tokai, Japan
3
Institute of Materials Structure Science, Japan
ORAL - 03
11:30 - 11:50
Structure Investigation of a Synchronized LPSO Phase in Mg–Al–Gd Alloys using Synchrotron
Radiation Microdiffraction
Shigeru Kimura1, Nobuhiro Yasuda1, Kyosuke Kishida2 and Haruyuki Inui2
1
Japan Synchrotron Radiation Research Institute, Japan
2
12
ORAL - 04
11:50 - 12:10
Microscopic Elastic Properties of Mg85Zn6Y9 Alloy with LPSO Phase by Inelastic X-ray
Scattering
S. Hosokawa1, M. Inui2, Y. Kajihara2, K. Kimura3, K. Matsuda3, A. Q. R. Baron4, M. Yamasaki1 and
Y. Kawamura1
1
2
Hiroshima University, Japan
3
4
RIKEN, Japan
ORAL - 05
12:10 - 12:30
Structure and Formation of Novel LPSO Structures in Mg-Co-Y Alloy
Mariko Egami1, Eiji Abe1, Hajime Kimizuka2, Michiaki Yamasaki3 and Yoshihito Kawamura3
1
The University of Tokyo, Japan
2
Osaka University, Japan, 3Kumamoto University, Japan
Oral Session - 3
Chairpersons : M.T. Pérez-Prado and Kazuya Aizawa
PLE - 03
13:50 - 14:20
Thermodynamic Mg Database Development and Application to Formation of LPSO Phases in
Multicomponent Magnesium Alloys
Rainer Schmid-Fetzer
Clausthal University of Technology, Germany
INV - 03
14:20 - 14:45
Effects of Pre-strain and Ageing on the LPSO Structure in Mg97Zn1Y2 Alloy
X.-F. Gu and T. Furuhara
INV - 04
14:45 - 15:10
Microgalvanic Activity and Volta Potential of LPSO Phases in Mg-Zn-Gd-Al Alloys
Michiaki Yamasaki, Manabu Ohtani and Yoshihito Kawamura
13
ORAL - 06
15:10 - 15:30
Three-dimensional Shapes and Distribution of LPSO in Mg-Zn-Gd Alloys Characterized by
Electron Tomography
K. Sato, S. Matsunaga, S. Tashiro, Y. Yamaguchi, T. Kiguchi and T. J. Konno
ORAL - 07
15:30 - 15:50
In-situ Multicolor SWAXS Approach to Examine Stability and Formation of LPSO Structures
in MgYZn alloys
Hiroshi Okuda1, Hiroto Tanaka1, Toshiki Horiuchi1, Michiaki Yamasaki2, Yoshihito Kawamura2 and
Shigeru Kimura3
1
Kyoto University, Japan, 2Kumamoto University, Japan
3
JASRI, Japan
Coffee Break
15:50 - 16:10
Poster Session
Oct. 06, Monday 16:10 - 18:30, Room Amakusa C
Chairpersons : Kenji Higashida and Koji Okuda
POS - 01
Dynamic Analysis of Kink Deformation Mechanism with High Accuracy AE Measurement
Yuki Muto, Takayuki Shiraiwa and Manabu Enoki
POS - 02
Atom-Probe-Tomographic Studies on Mg-Zn-Y Alloys with LPSO Phases
K. Inoue1, N. Ebisawa1, K. Tomura1, Y. Nagai1, H. X. Xu1,2, D. Egusa3 and E. Abe3
1
Tohoku University, Japan, 2 University of Science and Technology of China, China
3
University of Tokyo, Japan
POS - 03
First-principles Study on Stability of Mg-based LPSO Phases
Koretaka Yuge and Ryohei Tanaka
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POS - 04
Molecular Dynamics Study of Dislocation Activity during Kink Deformation of LPSO
Structure
Ryosuke Matsumoto and Masayuki Uranagase
POS - 05
Atomistic Simulation Study of the Dependence of Thermal Activation of Dislocation Nucleation
in Mg on Temperature and Applied Stresses
Masayuki Uranagase and Ryosuke Matsumoto
POS - 06
High Temperature Creep Behavior and Deformation Microstructures in a Directionally
Solidificated Long-period Stacking Ordered Mg-Zn-Y Alloy at 600 K
M. Suzuki1, S. Harada1 and K. Hagihara2
1
Toyama Prefectural University, Japan
2
POS - 07
Hydrogen Storage Property of LPSO Mg-Ni-Y Alloys
Teppei Kawasaki, Yoshinori Yamada and Kazuhiro Ishikawa
Kanazawa University, Japan
POS - 08
Hydrogenation Behavior and Structural Change of LPSO Mg-Zn-Y Alloys
Kazuhiro Ishikawa, Teppei Kawasaki and Yoshinori Yamada
Kanazawa University, Japan
POS - 09
STM Observation of Local Structures in Closed-packed Layer of LPSO
Shu Kurokawa, Hiroki Saito and Akira Sakai
Kyoto Univsersity, Japan
15
POS - 10
Kink Deformation Behavior in Long-period Stacking Ordered Structure during Uniaxial
Loading with Stress-reversal
Tsuyoshi Mayama1, Tetsuya Ohashi2, Michiaki Yamasaki1 and Yoshihito Kawamura1
1
Kumamoto University, Japan, 2Kitami Institute of Technology, Japan
POS - 11
Cyclic Hardening Behavior of Cast Mg-Zn-Y Alloys Containing Long-period Stacking Ordered
Phase
Kazuma Shiraishi, Tsuyoshi Mayama, Michiaki Yamasaki and Yoshihito Kawamura
POS - 12
Structure and Texture Variation of Mg97Al1Ca2 Alloy by High Pressure and High Temperature
Treatments
Shinsaku Yamasaki1, Masafumi Matsushita1, Ryota Inugai1, Takafumi Nagata1, Ikuya Yamada2,
Michiaki Yamasaki3, Toru Shinmei1, Tetsuo Irifune1 and Yoshihito Kawamura3
1
Ehime University, Japan, 2Osaka Prefecture University,
3
POS - 13
Structural Study for Mg97Zn1Yb2 Alloy at Ambient Pressure and after High Pressure
Treatments
Ryota Inugai1, Masafumi Matsushita1, Takafumi Nagata1, Shinsaku Yamasaki1, Ikuya Yamada2,
1
Ehime University, Japan, 2Osaka Prefecture University, Japan,
3
POS - 14
Effect of High Pressure and High Temperature Treatment on Structure and Texture of
Mg97Zn1Y2 Alloy
Takafumi Nagata1, Shinpei Yamamoto1, Masafumi Matsushita1, Tatsuya Senzaki1, Ikuya Yamada2,
1
Ehime University, Japan, 2Osaka Prefecture University, Japan
3
16
POS - 15
Structure and Stability of LPSO Phase in Mg85Zn6Y9 and Its High Pressure Phase
Tatsuya Senzaki1, Masafumi Matsushita1, Norimasa Nishiyama2, Ikuya Yamada3, Michiaki
Yamasaki4, Toru Shinmei1, Tetsuo Irifune1 and Yoshihito Kawamura4
1
Ehime University, Japan
2
Deutsches Elektronen Synchrotron DESY, Germany
3
Osaka Prefecture University, Japan
4
Kumamoto University , Japan
POS - 16
Effect of High Pressure and High Temperature Treatment on Carbon Steels
Kazuaki Onishi1, Masafumi Matsushita1, Ikuya Yamada2, Michiaki Yamasaki3, Toru Shinmei1,
Tetsuo Irifune1 and Yoshihito Kawamura3
1
2
Osaka Prefecture University, Japan
3
POS - 17
In-situ X-ray Diffraction Measurements of Collapse and Formation Process of LPSO Structure
in Mg85Zn6Y9
Masafumi Matsushita1, Jozef Bednarcik2, Norimasa Nishiyama2, Yuya Sakata1, Shutaro Akamatsu1,
Michiaki Yamasaki3 and Yoshihito Kawamura3
1
2
Deutsches Elektronen Synchrotron DESY, Germany
3
POS - 18
Deformation Twinning in a Mg-Al-Gd Ternary Alloy Containing LPSO Platelet Precipitates
Kyosuke Kishida and Haruyuki Inui
POS - 19
Development of a Gandolfi Camera Attachment for the Measurement of Single- and Polycrystalline LPSO Magnesium Alloys
Nobuhiro Yasuda and Shigeru Kimura
Japan Synchrotron Radiation Research Institute, SPring-8, Japan
17
POS - 20
Thermodynamic Properties of the Mg-Gd-Al System
S. Iikubo1 and H. Ohtani2
1
2
POS - 21
Solidification Simulation of Microsegregation Based on the Scheil-gulliver Model in
Mg97Zn1RE2 Alloys
T. Tokunaga1, H. Era1, S. Iikubo1, M. Enoki2 and H. Ohtani2
1
2
POS - 22
Cyclic Deformation Behaviors of HCP/FCC Laminated Structures
Yuichiro Koizumi, Kotaro Sano and Akihiko Chiba
POS - 23
Comparison of the Phase Equilibrium in the Vicinity of LPSO Phases in Mg-Zn-Y and Mg-AlGd Ternary Systems
Seiji Miura1, Toshiaki Horiuchi2 and Satoshi Minamoto3
1
Hokkaido University, Japan
2
Hokkaido University of Science, Japan
3
ITOCHU Techno-Solutions Corporation, Japan
POS - 24
Local Structural Relaxations and Interstitial Sites in LPSO-Mg Alloys
Kenya Yamashita, Daisuke Egusa* and Eiji Abe
* Presently at UACJ Corporation
POS - 25
Effect of Atomic Radius of Solute Elements on Local Strain Field of LPSO
S. Matsunaga, Y. Yamaguchi, S. Tashiro, T. Kiguchi, K.Sato and T.J. Konno
18
POS - 26
A First-principles Study of Interaction between Solute-enriched Layers of Mg-based LPSO
Structures
Daisuke Matsunaka and Yoji Shibutani
POS - 27
Interaction between Lattice Defects in Mg Crystal: ab Initio Local Energy Analysis
Yoshinori Shiihara1 and Masanori Kohyama2
1
2
AIST, Japan
POS - 28
Deformation and Fracture Behavior of Long Period Stacking-orderd Structure Phase in MgZn-Y Alloy
R. Maezono, Y. Mine, M. Yamasaki, Y. Kawamura and K. Takashima
POS - 29
Stress Analysis of Ridge-shaped Kink Structure in Mg Alloy with LPSO Structure Based on
Linear Elasticity
Xiao-Wen Lei and Akihiro Nakatani
POS - 30
High-temperature Creep Deformation Mechanism of Mg88-Zn5-Y7 Extruded Alloy
Hidenari Takagi and Masami Fujiwara
Nihon University, Japan
POS - 31
First Principles Calculations for LPSO Formation Scenarios
Shigeto R. Nishitani, Yosuke Yamamoto, Yuichi Sakamoto and Yoshihiro Masaki
Kwansei Gakuin University, Japan
19
POS - 32
Composition Dependence of The LPSO Poly-types Formed in Mg-Ni-Y Alloy
Takaomi Itoi, Ryosuke Masui and Shinji Arakawa
Chiba University, Japan
POS - 33
A Molecular Dynamics Study on the Structure and Formation Mechanisms of Non-basal
Dislocations in Magnesium
Hideo Kaburaki, Mitsuhiro Itakura and Masatake Yamaguchi
Japan Atomic Energy Agency, Japan
POS - 34
Description of Disclination Density in Mg-based LPSO Phase Using a Crystal Plasticity
Cosserat Model
Sotaro Tajiri and Kazuyuki Shizawa
Keio University, Japan
POS - 35
Study of Local Structures of Zn/Y Layers in LPSO Mg Alloys By X-ray Fluorescence
Holography
Kouichi Hayashi1, Koji Hagihara2, Hitoshi Izuno2, Naohisa Happo3 and Shinya Hosokawa4
1
2
3
Hiroshima City University, Japan
4
POS - 36
Phase-field Modeling for Understanding the Formation Mechanism of LPSO Phase
T.Koyama and Y.Tsukada
Nagoya Institute of Technology, Japan
POS - 37
A Dislocation-based Crystal Plasticity FE Analysis for a Single Crystal and Polycrystal of a
Mg-based LPSO Phase
Ryo Ueta, Keiko Ikeda and Kazuyuki Shizawa
Keio University, Japan
20
POS - 38
Three-dimensional Analysis of Kink Bands in LPSO Phase by using FIB-SEM
Ken-ichi Ikeda, Rie Nishio, Hongye Gao, Satoshi Hata and Hideharu Nakashima
POS - 39
Dislocations Analysis around Kink Boundaries of Mg-Zn-Y Alloy
Hongye Gao, Ken-ichi Ikeda, Tatsuya Morikawa, Kenji Higashida and Hideharu Nakashima
POS - 40
Local Structure Analysis of LPSO by XAFS
S. Yoshioka, Y. Kobayashi, K. Yasuda and S. Matsumura
POS - 41
Diffusion Coefficient of Zn and Y in Mg Investigated by Atom Probe Tomography
K. Inoue, N. Ebisawa, K. Tomura, T. Toyama and Y. Nagai
POS - 42
Dynamics and Stability of Nonlinear Vibration Modesin Layered Structure of Magnesium
Yusuke Doi and Akihiro Nakatani
Osaka University, Japan,
POS - 43
Comparison between the Microstructures with Different Heat Treatment in Mg97Zn1Y2 Alloy
POS - 44
Deformation Behavior of Mg97Zn1Y2 Alloys Studied by Neutron Diffraction
Wu Gong1, Kazuya Aizawa1, Stefanus Harjo1, Takuro Kawasaki1, Takaaki Iwahashi1 and Takashi
Kamiyama2
1
JAEA, Japan, 2High Energy Accelerator Research Organization, Japan
21
POS - 45
Reduction of Peierls Stress of LPSO Structure under Uniaxial Compression: First-principles
Calculations
Masatake Yamaguchi1, Mitsuhiro Itakura1, Motoyuki Shiga1, Hideo Kaburaki1 and Eiji Abe2
1
Japan Atomic Energy Agency, Japan
2
POS - 46
Spinodal Decomposition Behavior of the Mg-RE-TM Ternary Systems
H. Abe1, S. Iikubo2 and H. Ohtani1
1
2
POS - 47
Numerical Prediction of Solute Segregation during Rapid Solidification of Mg-Zn-Y and MgZn-Gd Alloy using Phase-field Model
Machiko Ode1, Hiroshi Ohtani2 and Masato Shimono1
1
National Institute for Materials Science, Japan
2
POS - 48
Inhomogeneous Deformation Microstructures in a Magnesium Alloy with LPSO Phase
T. Morikawa, R. Noguchi and K. Higashida
POS - 49
Creep Behavior of Extruded Mg-Zn-Gd Alloy with the LPSO Phase-stimulated Texture
Yuri Jono, Michiaki Yamasaki and Yoshihito Kawamura
POS - 50
Kink Band Propagation Behavior in Mg/LPSO Two-phase Alloy
Takeshi Minomo1, Michiaki Yamasaki1, Koji Hagihara2 and Yoshihito Kawamura1
1
2
22
POS - 51
Precipitation of LPSO Structure from Amorphous Phase in Mg85(Zn, Ni, Cu)6Y9 Ternary
Alloys
Takahiro Shiratake, Michiaki Yamasaki and Yoshihito Kawamura
POS - 52
Kink Band Formation in an 18R-LPSO Single Crystal in Bending Deformation
Tsubasa Matsumoto1, Michiaki Yamasaki1, Koji Hagihara2 and Yoshihito Kawamura1
1
Kumamoto University, Japan, 2Osaka University, Japan
Oral Session - 4
Oct. 07, Tuesday 08:30 - 10:25, Room Aso D
Chairpersons : Michel W. Barsoum and Haruyuki Inui
PLE - 04
08:30 - 09:00
Assessment of Polycrystal Plasticity Models of Deformation Twinning and Validation Using Insitu Neutron Diffraction
S.R. Agnew
University of Virginia, U.S.A.
INV - 05
09:00 - 09:25
Structure and Stability of the LPSO Phases in Several Ternary Mg Alloy
Eiji Abe
ORAL - 08
09:25 - 09:45
Atomic Resolution Analysis of LPSO Microstructure Evolution
T. Kiguchi, S. Matsunaga, Y. Yamaguchi, S. Tashiri, K. Sato and T.J. Konno
ORAL - 09
09:45 - 10:05
Kink Formation in a Compressed Mg-Zn-Y 18R-LPSO Phase
J. Wu, Y.L. Chiu and I.P. Jones
University of Birmingham, UK
23
ORAL - 10
10:05 - 10:25
Coarse-grained Modeling of In-plane Disorder-order Transformation of Solute Nanoclusters in
Mg-based LPSO Phases
Hajime Kimizuka and Shigenobu Ogata
Coffee Break
10:25 - 10:45
Oral Session - 5
Oct. 07, Tuesday 10:45 - 12:15, Room Aso D
Chairpersons : C. Wolverton and Hajime Kimizuka
INV - 06
10:45 - 11:10
Influence of Grain Boundaries on Slip Activity and Twin Propagation in Magnesium
M.T. Pérez-Prado
IMDEA Materials Institute, Spain
INV - 07
11:10 - 11:35
Multi-scale Study of Plastic Deformation in Hexagonal Metals
Laurent Capolungo
Georgia Institute of Technology, U.S.A
ORAL - 11
11:35 - 11:55
Elastic Properties of Mg-Zn-Y Alloys with a Long-period Stacking Ordered Structure
M. Tane1, Y. Nagai1, H. Kimizuka1, K. Hagihara1, Y. Kawamura2
1
2
ORAL - 12
11:55 - 12:15
Assessment of Deformation Behavior in Single Crystalline Long-period Stacking-ordered
Structure Phase of Mg85Zn6Y9 Alloy by Microtensile Tests
K. Takashima, Y. Mine, R. Maezono, K. Sakamoto, M. Yamasaki and Y. Kawamura
Group Photo
24
12:15 - 12:35
Oral Session - 6
Oct. 08, Wednesday 08:30 - 10:25, Room Aso D
Chairpersons : S.R. Agnew and Akihiro Nakatani
PLE - 05
08:30 - 09:00
First-principles Investigation of Mg-Rare Earth Precipitates and LPSO Structure
A. Issa, J. E. Saal and C. Wolverton
Northwestern University, USA
INV - 08
09:00 - 09:25
Deformation Behavior of the Synchronized LPSO Phases Accompanied by the Formation of
Deformation Bands
Koji Hagihara1, Masahito Honnami1, Takuya Okamoto1, Michiaki Yamasaki2, Hitoshi Izuno1,
Masakazu Tane1, Takayoshi Nakano1 and Yoshihito Kawamura2
1
Osaka University, Japan, 2Kumamoto University, Japan
ORAL - 13
09:25 - 09:45
Biodegradation Behavior and Cytotoxicity of Mg-Zn-Gd Alloys
Yufeng Zheng1, Dong Bian1, Nan Li1 and Liqun Ruan2
1
Peking University, China
2
ORAL - 14
09:45 - 10:05
Kink Deformation Expressed by Disclination Multipole and Dislocation Arrays
Tetsuya Ohashi, Yohei Yasuda and Keita Oikawa
Kitami Institute of Technology, Japan
ORAL - 15
10:05 - 10:25
Microstructure and Mechanical Properties of Mg96Zn2Y2 Alloy Joint Bonded by Ultrasonic
Wire Welding
Yuichi Higashi1, Chihiro Iwamoto2 and Yoshihito Kawamura1
1
2
Ibaraki University, Japan
Coffee Break
10:25 - 10:45
25
Oral Session - 7
Oct. 08, Wednesday 10:45 - 12:30, Room Aso D
Chairpersons : Alexei E. Romanov and Hiroshi Ohtani
INV - 09
10:45 - 11:10
Characteristics of Mechanical Behaviors in a Mg-based Synchronized LPSO Structure
Kenji Higashida and Tatsuya Morikawa
ORAL - 16
14H
11:10 - 11:30
Long-Period
Stacking
Order
Structures
and
the
Deformation
Behavior
of
Mg94Zn2.5Y2.5Mn1 alloy
Jinshan Zhang, Ding Li, Kaibo Nie, Chunxiang Xu, Xiaofeng Niu and Weili Chen
Taiyuan University of Technology, China
ORAL - 17
11:30 - 11:50
A Comparison of AE Behaviors Between LPSO-Mg and Al-Zn-Mg Alloys
Manabu Enoki, Yuki Muto and Takayuki Shiraiwa
ORAL - 18
11:50 - 12:10
Fabrication of Magnesium Alloy with High Strength and Heat-resistance by Hot Extrusion and
Ageing
Zijian Yu1, Yuding Huang2, Xin Qiu1, Qiang Yang1, Jian Meng1
1
Chinese Academy of Sciences, China, 2Helmholtz-Zentrum Geesthacht, Germany
ORAL - 19
12:10 - 12:30
Friction Stir Welding of the LPSO Type-magnesium Alloys
Minami Sasaki and Masashi Inoue
Fuji Light Metal Co., Ltd, Japan
12:30 - 12:40
Closing Address
Kenji Higashida
26
PLE-01
Investigating Reversible Hysteresis In Magnesium Single Crystals Using A
Spherical Tip Under Nanoindentation
Justin Griggs1, Babak Anasori2, Greg Vetterick3, Grady Bentzel4, Mitra
Taheri5, Roger Doherty6 and Michel W. Barsoum7
1
Justin Griggs, Materials Science Department, Drexel University, 3141 Chestnut Street,
Philadelphia, PA 19104, USA
2
Babak Anasori, Materials Science Department, Drexel University, 3141 Chestnut Street,
Philadelphia, PA 19104, USA
3
Michel W. Barsoum, Materials Science Department, Drexel University, 3141 Chestnut Street,
Philadelphia, PA 19104, USA, [email protected]
Some h.c.p. materials, including Mg, have been known to show a reversible hysteresis
effect during cyclic loading, the origins of which are not fully understood. In this study, the
reversible hysteresis effect of Mg single crystal was investigated using a combination of constant
cyclic and incremental loading using a spherical nanoindenter tip. The load was applied either
normal or parallel to the basal planes. Fully and spontaneously reversible loops in the stress-strain
curve were observed in both cases. (Fig. 1A). The effect of using different loads and different
number of cycles was investigated on the (0001) orientation. It was shown that the average
threshold stress was reduced from ~ 66.66 MPa by ~9.6 MPa when using an applied load of 50 mN
and 50 cycles, and reduced by ~ 21 MPa when using 150 mN and 25 cycles as compared to 50
cycles. Transmission electron microscopy (TEM) was used to study the features beneath the indent
and both <a> and <c + a> dislocations were identified. Most importantly, a low angle grain
boundary (LAGB) (Fig. 1B) was observed beneath the indents loaded normal to the basal planes.
The forward and backward migration of this LAGB is believed to expand and contract to yield the
reversible hysteresis effect in the (0001) orientation. Tensile twin formation plays a vital role in the
reversible hysteresis effect when loaded parallel to the basal planes. More energy is dissipated at a
given stress during the growth and shrinkage of the twins in the prismatic orientation than the
migration of the LAGB in the basal orientation.
B.
A.
250
E = 61.5 GPa
Stress (MPa)
200
E = 25.69 GPa
16 mN
32 mN
48 mN
64 mN
80 mN
10 mN
20 mN
30 mN
40 mN
50 mN
150
100
50
0
0.06
2A
0.07
0.08
0.09
0.1
Prismatic
0.11
0.12
0.13
Strain (a/R)
Figure 1. A. The indentation stress-strain curve of the nested cycles is shown on the left. Plot 2A
was loaded to 50 mN normal to the basal planes as compared to loading to 80 mN on the prismatic
face. B. TEM micrograph of a cross section of an indent showing the low angle grain boundary
(LAGB) that formed when loaded normal to the basal planes. The top portion is the parent crystal
and the bottom region is beneath the indent. The LAGB was parallel to the applied load and normal
to the basal planes.
27
INV 01
Materials Science and Technology on Synchronized LPSO Structure
Yoshihito Kawamura1
1
MRC, Kumamoto University
2-39-1 Kuro-Kami, Kumamoto 860-8555, Japan
[email protected]
Magnesium alloys are very attractive in such applications as automotive, railway and
aerospace technologies. However, their low ignition temperature and low mechanical strength have
restricted their use. New high-strength magnesium-base alloys with heat resistance and flame
resistance have been developed in Japan and are now the focus of wide attention in many parts of
1)-4)
the world . These new alloys are strengthened by a unique phase having a novel structure called
“Synchronized Long-Period Stacking Ordered (LPSO) Structure”, which features synchronization
5)
with respect to chemical and stacking modulations . These alloys are therefore called LPSO-type
Mg alloys.
The LPSO-type Mg alloys produced by extrusion of cast ingots have high yield strength
(350-520 MPa for 0.2% proof strength) and reasonable elongation (5-15 %) at room temperature,
and high elevated-temperature yield strength (250-350 MPa at 473 K). These mechanical
properties are superior to those of ordinal magnesium alloys such as AZ91, and high strength
aluminum alloys such as super duralumin and extra-super duralumin. Moreover, the LPSO-type Mg
alloys produced by rapidly solidified powder metallurgy (RS P/M) processing exhibit higher
mechanical properties and corrosion resistance than the LPSO-type Mg alloys produced by ingot
metallurgy (I/M) processing. A RS P/M Mg96.75Zn0.75Y2Al0.5 alloy has tensile yield strength of 533
7
MPa, tensile elongation of 10.6 %, and fatigue strength (10 cycles) of 325 MPa. Its specific yield
strength, specific fatigue strength and corrosion resistance are 1.6, 1.7 and 2.8 times, respectively,
as high as those of extra-super-duralumin (7075-T6). The ignition temperature of the LPSO-type
Mg alloys is ranging from 780 to 940 ℃, which is much higher than that of ordinary magnesium
alloys (470~550 ℃). The LPSO-type alloys have passed the FAA flammability test easily, with
essentially no burning at all.
Two national projects on LPSO-type Mg alloys are currently being carried out in Japan.
One is a fundamental research focusing on “Materials Science of Synchronized LPSO Structure”,
which has been started from 2011 as a research program of “Grant-in-Aide for Scientific Research
on Innovative Areas” funded by the Ministry of Education, Culture, Sports, Science & Technology in
Japan (MEXT). Three research themes, which are atomic arrangement, formation mechanisms and
mechanical characteristics, are pursued through 9 planned tasks and also 17 publicly offered
subjects by 58 researchers from 19 universities and 4 national institutes. Another one is an applied
research on the development of LPSO-type RS P/M Mg alloys for airplane applications, which has
been started from 2013 as a research program of “Advanced Materials & Process Development for
Next-generation Aircraft Structures” funded by the Ministry of Economy, Trade and Industry (METI)
of Japan. The member of this project is Mitsubishi Heavy Industries Ltd., Fuji Heavy Industries Ltd.
and Kumamoto University.
1) Y. Kawamura, K. Hayashi, A. Inoue and T. Masumoto: Mater. Trans., 42 (2001), 1172.
2) Y. Kawamura and S. Yoshimoto: Magnesium Technology 2005, p. 499, TMS (2005).
3) S. Yoshimoto, M. Yamasaki, Y. Kawamura: Mater. Trans., 47 (4) (2006), 959.
4) M. Yamasaki, M. Sasaki, M. Nishijima, K. Hiraga, Y. Kawamura: Acta Materialia, 55 (2007),
6798.
5) E. Abe, Y. Kawamura, K. Hayashi and A. Inoue : Acta Mater., 50 (2002), 3845.
28
ORAL-01
Crystal Structures of Mg-Zn-Y LPSO Phases
- Compositional Dependence and Formation Process Haruyuki Inui1,2 and Kyosuke Kishida1,2
1
Department of Materials Science and Engineering, Kyoto University,
Sakyo-ku, Kyoto 606-8501, JAPAN
2
Center for Elements Strategy Initiative for Structural Materials (ESISM), Kyoto University,
[email protected]
Recently, we have studied the crystal structures of highly-ordered LPSO phases with the 18R and
14H-type stacking in the Mg-Al-Gd system by TEM and atomic resolution high-angle annular darkfield (HAADF) STEM and have revealed the following features [1,2,3]. First, Gd and Al are enriched
in four consecutive close-packed atomic layers in each structural block, which is composed of 6
and 7 close-packed atomic layers for 18R and 14H-type LPSO phases, respectively. Second, in Gd
and Al-enriched four-consecutive atomic layer in each structural block, Gd and Al atoms form
Al6Gd8 atomic clusters with the L12-type atomic arrangement and the clusters take a long-range inplane ordered arrangement. Third, although the atomic arrangement in each structural block of the
Mg-Al-Gd LPSO phases is perfectly ordered, the Mg-Al-Gd LPSO phases generally exhibit onedimensionally disordered nature along the stacking direction of the structural blocks and
consequently, their crystal structures are found to be best described with the crystallographic
concept of the order-disordered (OD) structure [1,2].On the other hand, no apparent long-range inplane ordering has been confirmed so far for the other Mg-TM-RE LPSO phases, especially for MgZn-Y LPSO phases coexisting with hcp Mg, which have been studied most intensively. In our
previous study, we confirmed the formation of the Zn6Y8 atomic clusters with the L12-type atomic
arrangement in the structural block of the Mg-Zn-Y LPSO phase coexisted with hcp Mg. This
suggests that the difference in the in-plane ordering nature should be closely related to the
difference in the number density of the Zn6Y8 atomic clusters in the four consecutive Zn, Y-enriched
atomic layers [1] and that it would be possible to obtain the Mg-Zn-Y LPSO phases with the same
in-plane ordering as those developed in the Mg-Al-Gd LPSO phase by increasing the Zn, Y
concentration. In the present study, some Mg-Zn-Y ternary alloys containing various Mg-Zn-Y
LPSO phases with different Zn, Y-rich compositions were prepared and the crystal structure
variations of various Mg-Zn-Y LPSO phases were investigated as a function of chemical
composition as well as heat treatment conditions.
Highly ordered LPSO phases with the 14H, 18R and 10H-type stacking sequences were
successfully obtained in two types of Zn, Y-rich Mg-Zn-Y ternary ingots, namely composed of (a)
14H-LPSO, 18R-LPSO and W phases and (b) 18R-LPSO, 10H-LPSO and W phases, after
prolonged heat treatment at 500 °C. Detailed HAADF-STEM analysis revealed that the in-plane
long-range ordering of the Zn6Y8 atomic clusters in the structural block is identical to that of the
Al6Gd8 in the Mg-Al-Gd LPSO phases and the most stable polytypes for these three types of highlyordered LPSO phases were determined based on the crystallographic concept of the OD structure.
Among three types of LPSO phases, the 18R-type LPSO phase was confirmed to exhibit
compositional variation in the in-plane ordering of the Zn6Y8 atomic clusters, which can be
interpreted as the development of a highly-ordered domain structure. Details of the ordered
structure as well as crystal structure variation by the heat treatment for the three types of the MgZn-Y LPSO phases will be presented.
References
[1] M. Yokobayashi et al., Acta Mater. 59 (2011) 7287-7299.
[2] K. Kishida et al., Intermetallics 31 (2012) 55-64.
[3] K. Kishida et al., Philos. Mag. 93 (2013) 2826-2846.
29
ORAL-02
Formation of lamellar long period stacking ordered structure in as-cast
Mg–(0.5-5)Gd–1Zn (at.%) alloys
Yaxian Du, Yujuan Wu∗, Liming Peng, Xiaoqin Zeng, Wenjiang Ding
National Engineering Research Center of Light Alloys Net Forming and State Key Laboratory of
Metal Matrix Composite, Shanghai Jiao Tong University, 200240, Shanghai, P. R. China
Yaxian Du: [email protected]; Yujuan Wu∗:[email protected];
Liming Peng:[email protected]; Xiaoqin Zeng: [email protected];
Wenjiang Ding:[email protected]
Mg-(0.5-5) Gd-1Zn (at.%) alloys were prepared by induction melting process. The microstructure
and phase characterizations, especially the formation of lamellar long period stacking ordered
(LPSO) structure in as-cast alloys were analyzed by X-ray diffraction (XRD), optical microscope
(OM) and scanning electron microscope (SEM) and transmission electron microscope (TEM)
observations. It shows that a lamellar basal phase/ 14H-type long period stacking ordered (LPSO)
structure phase form within α-Mg matrix in as-cast Mg-(0.5-5) Gd-1Zn (at.%) alloys. Moreover,
interestingly, a lamellar X-phase with 14H-type LPSO structure forms at grain boundaries near
secondary eutectic β-phase [(Mg, Zn)3Gd] in as-cast Mg-(0.5-3) Gd-1Zn (at.%) alloy. Therefore,
the as-cast microstructure of Mg-(0.5-3) Gd-2Zn (at.%) alloys are composed of α-Mg solid solution,
lamellar basal phase / 14H-type LPSO structure within α-Mg matrix, X-phase with 14H-type LPSO
structure forms at grain boundaries and β-phase [(Mg, Zn)3Gd] as secondary eutectic phase. While,
the as-cast microstructure of Mg-(4-5) Gd-1Zn (at.%) alloys are composed of α-Mg solid solution,
lamellar basal phase / 14H-type LPSO structure within α-Mg matrix and β-phase [(Mg, Zn)3Gd] as
secondary eutectic phase.
Keywords: Mg-Gd-Zn alloy; Cast; Microstructure; Long period stacking ordered (LPSO); X-phase
*Corresponding author:Yujuan Wu: Tel.: +86 21-54742627; E-mail: [email protected]
30
PLE-02
Disclination Concept in Materials Physics and Mechanics
Alexei E. Romanov1,2,3,4, Anna L. Kolesnikova2,3,5 and Anatoly A. Vikarchuk3
1
Ioffe Physical-Technical Institute, 194021 St. Petersburg, Russia
2
ITMO University, 197101 St. Petersburg, Russia
3
Togliatti State University, 445667Togliatti, Russia
4
University of Tartu, 51014 Tartu, Estonia
5
Institute of Problems of Mechanical Engineering, 199178 St. Petersburg, Russia
address: Ioffe Physical-Technical Institute, Polytechnicheskaya 26, 194021 St. Petersburg, Russia
Disclinations play an important role in cases of rotation-type motions of materials constitutive parts.
Together with dislocations, they represent a class of linear defects in solids [1]. In this talk, we give
an introduction to the physics and mechanics of disclinations in solids and present an overview of
recent applications of disclination concept in materials science [2]. The following milestones of the
disclination concept are given: (i) definitions and designations [1]; (ii) geometry of disclinations[1,2];
(iii) properties of screened low-energy screened disclination configurations[1,3]; (iv) applications of
disclination approach to various materials science problems[1,2,4-6].
The mathematical definitions of Volterra and Somigliana dislocations including Frank (rotation)
vector of a disclination, types of disclinations: wedge or twist, are discussed [1,2]. The disclinations
are described for structureless and crystalline continua [1]. The properties of perfect and partial
disclinations are compared [2].
Screened disclination configurations are defined as those where the divergence of disclination
elastic strains and mechanical stresses is cancelled [3]. These screened configurations include
loops, dipoles, defects at the vicinity of a free surface and in small crystalline particles [1]. The
mathematical methods and results of calculation of disclination elastic fields and energies are given
in details [1,3].
Basing on the properties of screened disclinations a number of qualitative and quantitative models
for the structure formation and evolution in solids is considered. Disclination theory of grain
boundaries and their junctions in conventional polycrystals and graphene is presented [1]. The
bands with misorientated crystal lattice in metals and other materials are described as a result of
partial wedge disclination dipole motion [4]. In this connection, the deformation mechanisms of
long-period stacking ordered structures (LPSO) are considered. Disclination models explaining
unusual pentagonal symmetry found in nanoparticles and nanorods of materials with FCC crystal
structure are advanced [5,6]. The role of disclinations in relaxation of mechanical stresses in lattice
mismatched thin layers placed on the bulk substrate is examined and linked to the appearance of
domain configurations, which are also similar to LPSO patterns [2].
[1] A.E. Romanov and V.I. Vladimirov, Disclinations in crystalline solids, in F.R.N. Nabarro ed.
Dislocations in solids, North-Holland, Amsterdam, 1992, vol. 9,191-402.
[2] A.E. Romanov and A.L. Kolesnikova, Application of disclination concept to solid structures,
Progress in Materials Science, 2009, vol. 54, 740-769.
[3] A.E. Romanov, Mechanics and physics of disclinations in solids, European Journal of
Mechanics A/Solids, 2003, vol. 22, 727-741.
[4] V.I. Vladimirov and A.E. Romanov, Partial disclination dipole motion under plastic deformation,
Soviet Physics Solid State, 1978, vol. 20, 1795-1796.
[5] V.G. Gryaznov, J. Heydenreich, A.M. Kaprelov, S.A. Nepijko, A.E. Romanov, and J. Urban,
Pentagonal symmetry and disclinations in small particles", Crystal Research and Technology,
1999, vol. 34, 1091-1119.
[6] A.E. Romanov, A.A. Vikarchuk, A.L. Kolesnikova, L.M. Dorogin, I. Kink, and E.C. Aifantis,
Structural transformations in nano- and microobjects triggered by disclinations, Journal of
Materials Research, 2012, vol. 27, N 3, 545-551.
31
INV-02
In-situ neutron diffraction study under compressive stress combined with
AE measurement of 18R LPSO single-phase alloy, AZ31 alloy and Zinc
Kazuya AIZAWA1, Wu GONG1, Stafanus HARJO1, Jun Abe2,
Takuro KAWASAKI1, Takaaki IWAHASHI1 and Takashi KAMIYAMA3
1
J-PARC Center, JAEA, Tokai, Ibaraki 319-1195, Japan
2
CROSS-Tokai, Tokai, Ibaraki, 319-1106, Japan
3
Institute of Materials Structure Science, High Energy Accelerator Research Organization,
Tsukuba 305-0801, Japan
2-4 Shirane Shirakata, Tokai, Naka, Ibaraki, 319-1195 Japan, Email: [email protected]
Understanding of the strength mechanism of the Mg based LPSO alloys is an important issue for
not only their industrial application but also the viewpoint of metallurgical physics. The observed
deformation of the LPSO phase for uniaxial compressive stress by electron microscope technique
is the kink deformation which is usually observed in h.c.p metals such as zinc, cadmium, and it is
believed that kink deformation does not contribute to the strength mechanism. On the other hand,
the deformation twin activates in magnesium alloys for uniaxial compressive stress at room
temperature.
Therefore, we paid attention to extract the difference between the kink deformation and the
deformation twin under uniaxial compressive stress for the LPSO phase, the magnesium alloy and
zinc as a typical kink deformation material. Bulk samples were used in this study, because it is
important to evaluate average properties for deformations which may be attributed to collective
dislocation motion.
We performed in-situ neutron diffraction measurements under compressive stress combined with
AE (Acoustic Emission) measurements which is sensitive for microscopic dynamical motion, to
reveal the deformation mechanism of one-directional solidification 18R LPSO single-phase alloys
Mg85Zn6Y9, commercial extruded AZ31 alloy and polycrystal zinc, using TAKUMI, BL19 at MLF, JPARC. We evaluated AE count, AE energy distribution, AE frequency profile, correlation of AE
generation time, etc. as a function of applied stress, corresponding to evolution of neutron
diffraction profiles which detected the kink deformation for Mg85Zn6Y9 alloy and polycrystal zinc and
the deformation twin for extruded AZ31 alloy. These AE quantities showed different behavior for
applied stress (stress and strain curve) between the kink deformation and the deformation twin. For
example, in the case of the AZ31 alloy, AE energy corresponding to the deformation twin, which
activates around the yield point of the stress and strain curve, has a peak. On the other hand, there
is no characteristic AE energy peak around the yield point of the stress and strain curve for the
Mg85Zn6Y9 alloy, which activates the kink deformation. So, we conclude that microscopic
deformation mechanism of the LPSO phase, the kink deformation, is different from the deformation
twin observed h.c.p metals. Detailed discussion will be performed in the symposium.
32
ORAL-03
Structure Investigation of a Synchronized LPSO Phase in Mg–Al–Gd Alloys
using Synchrotron Radiation Microdiffraction
Shigeru Kimura1, Nobuhiro Yasuda1, Kyosuke Kishida2 and Haruyuki Inui2
1
2
Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo, Sayo, Hyogo 679-5198,
Japan
Department of Materials Science and Engineering, Kyoto University, Sakyo, Kyoto 606-8501,
Japan
New type magnesium (Mg) alloys with ternary Mg–transition metal (TM)–rare earth (RE) phases
with long period stacking-ordered (LPSO) structures are paid much attention as a lightweight
structural material because of their extra ordinary mechanical properties such as high strength and
high ductility. Even though these properties are considered to be related to the LPSO phases, the
role of the LPSO phase has not yet fully understood. This is because the precise structure
information of the LPSO phases is still unclear.
LPSO phases in Mg-Zn-RE ternary systems are reported to consist of structural blocks with 5 to 8
close-packed atomic planes, forming various poly-types with different numbers of the closepacked
atomic planes in the structural blocks and with different stackings of the structural blocks. In the
absence of the in-plane long-range ordering of the constituent atoms, polytypes expressed as 10H,
14H, 18R and 24R polytypes (according to the Ramsdell notation) are reported to form, among
which 14H- and 18R polytypes are the most dominantly observed ones [1].
Recently, two of the present authors and co-workers found a new LPSO phase of the 18R-type in
the Mg-Al-Gd system by using scanning transmission electron microscopy (STEM) and
transmission electron microscopy (TEM) [2]. The new LPSO phase shows clear in-plane longrange ordering of the constituent Mg, Al and Gd atoms, with enrichment of Gd and Al atoms
occurring in four consecutive planes of the six closepacked atomic planes. This periodically forms
Al6Gd8 clusters with the L12 type atomic arrangement. This new finding is very informative because
the local structure of the LPSO phase in the Mg-TMl-RE system, which has not fully identified yet,
is expected to be similar to that of the new LPSO phase in the Mg-Al-Gd system. Therefore, more
precise structure determination is highly desired.
Single crystal x-ray diffraction analysis is recognized as the most reliable method to obtain threedimensional atomic arrangement. Recently, synchrotron radiation (SR) focused high-flux
microbeam opened up opportunities for the application of the single-crystal diffraction technique to
micron- and submicron-sized crystals by measuring the intensities of their specific reflections [3,4].
In the present work, we therefore tried the single crystal diffraction measurement for the single
3
LPSO phase crystal with the size of about 2 × 2 × 5 μm , which was taken from a multi-phase MgAl-Gd alloys by using the focused ion beam (FIB) technique. As the result, we succeeded to obtain
good diffraction data and analyze the precise structure of the LPSO phase in the Mg-Al-Gd alloy
system.
References
[1] For example, Y. Kawamura and M. Yamasaki: Mater. Trans. 48 (2007) 2986.
[2] H. Yokobayashi, K. Kishida, H. Inui, M. Yamasaki, Y. Kawamura: Acta Mater. 59 (2011) 7287.
[3] C. Volkringer, D. Popov., T. Loiseau, N. Guillou, G. Ferey, M. Haouas, F. Taulelle, C. MellotDraznieks, M. Burghammer, and C. Riekel: Nat. Mater. 6 (2007) 760.
[4] N. Yasuda, H. Murayama, Y. Fukuyama, J.E. Kim, S. Kimura, K. Toriumi, Y. Tanaka, Y.
Moritomo, Y. Kuroiwa, K. Kato, H. Tanaka and M. Takata: J. Synchrotron Rad. 16 (2009) 352.
33
ORAL-04
Microscopic elastic properties of Mg85Zn6Y9 alloy with LPSO phase by
inelastic x-ray scattering
S. Hosokawa1, M. Inui2, Y. Kajihara2, K. Kimura3, K. Matsuda3, A. Q. R. Baron4,
M. Yamasaki1 and Y. Kawamura1
1
Graduate School of Science and Technology, Kumamoto University, Kumamoto 860-8555, Japan
Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 7398521, Japan
3
Department of Physics, Kyoto University, Kyoto 606-8502, Japan
4
RIKEN SPring-8 center, RIKEN, Sayo, Hyogo 679-5148, Japan
2
Recently, a new series of Mg alloys [1] with the microstructure containing a synchronized longperiod stacking ordered (LPSO) structure, the so-called KUMADAI Magnesium, has been attracted
considerable attention due to the excellent mechanical properties. By adding a small amount of Zn
and rare-earth metal (Y or Gd) impurities, Mg metal of soft, flammable, and light weighted becomes
much hardened and un-flammable. By taking such advantages, the new Mg alloys may be used
even for body materials of aircrafts.
Macroscopic elastic properties of these Mg alloys were intensively investigated by several
groups [2]. In particular, the temperature dependence of elastic properties is very important for the
applications as the structural materials of Mg alloys [3]. However, the microscopic information on
the dynamics of this material is still lacking. To our knowledge, only Tanaka and Ueno [4]
performed an inelastic x-ray scattering (IXS) experiment on a single crystal of the 14H phase.
We have carried out a preliminary IXS experiment on polycrystalline Mg85Zn6Y9 alloy with
~100% LPSO phase (18R) at BL35XU of the SPring-8 to examine the possibility of inelastic
experiment in the low Q region. Figure shows the inelastic scattering intensity as a function of
-1
excitation energy at 12 Q values from 1.7 to 15.9 nm ,
where whole of the first Brillouin zone is covered. As
seen in the figure, some excitation peaks are clearly
observed as indicated by the arrows, although the
data are rather scattered due to the beamtime
limitation for the IXS experiment. Even at the low Q
-1
value of 4.4 nm , a tiny peak is recognized in the
spectrum. The peaks with the highest energy would be
the longitudinal acoustic (LA) phonon excitations,
which show clear dispersion relation with Q. Beyond
the Q value of the boundary of the first and second
Brillouin zones, large peaks suddenly appear between
the LA modes and the central quasielastic peak, which
would be the transverse acoustic (TA) excitations. In
addition, another excitation appears at about 24 meV
as indicated by the down-arrows, which may be a
different branch of the LA modes.
In the presentation, we will compare the IXS results
with the macroscopic elastic constants of LA and TA
modes [2], and discuss the microscopic elastic natures
in the Mg-LPSO phase.
[1] Y. Kawamura et al., Mater. Trans. 42, 1172 (2001).
[2] M. Tane et al., Acta Mater. 61, 6338 (2013).
[3] K. Hagiwara et al., Mater. Sci. Eng. A 560, 71
(2013).
[4] K. Tanaka and A. Ueno, Abst. IMR Workshop (1819 Nov. 2013, Sendai), p.71.
34
ORAL-05
Structure and formation of novel LPSO structures in Mg-Co-Y alloy
Mariko Egami1, Eiji Abe1, Hajime Kimizuka2, Michiaki Yamasaki3 and
Yoshihito Kawamura3
1
2
Department of Materials Engineering, The University of Tokyo, Japan
Department of Mechanical Science and Bioengineering, Osaka University, Japan
3
Department of Materials Science, Kumamoto University, Japan
Faculty of Engineering Bldg. V 545, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, JAPAN
LPSO (long period stacking/order) structures formed in Mg-TM (transition metals)-RE (rare
earth elements) alloys are long period stacking derivatives of a hexagonal close-packed structure
and have a chemical order synchronized with a stacking order. The stacking structures are
systematically described by the periodic insert of stacking faults (SF) into the 2H structure of α-Mg.
So far, four types of LPSO structure, 10H, 18R, 14H and 24R have been reported for Mg-Zn-Y
alloys. All of them have AB’C’A stacking unit where B’ and C’ layers have local fcc environment,
and Zn/Y atoms are distribute at these particular four layers.
In Mg-Co-Y alloy, on the other hand, LPSO structures characterized by AB’C stacking unit
are formed [2]. We investigate the details of these novel LPSO structures in Mg-Co-Y alloys, based
on scanning electron microscopy observations and first principles calculations.
Figure 1 shows three novel LPSO structures, 15R, 12H and 21R. HAADF-STEM images
clearly show that Co/Y atoms distribute at the particular three layers AB’C. For the previous LPSO
structures, the local AB’C’A stacking is attributed to intrinsic-2 (I2)-type SF with respect to the
original 2H stacking. However, the AB’C
stacking represents intrinsic-1 (I1)-type SF;
therefore, the present LPSO structures are
systematically described as periodic
introduction of I1-type SFs into 2H stacking,
being with solute segregations at the SFs.
Hereafter, we denote these LPSO
structures as I2-LPSO and I1-LPSO
structures.
Figure 2 shows the growth
interfaces between the LPSO and 2H
crystals. Generally, I2-SF is introduced into
2H by an <a> dislocation and I1-SF is Fig. 1 Electron diffraction patterns and HAADF-STEM images of
introduced by an <a+c> dislocation. Fig. 2a a: 15R-, b: 12H- and c: 21R-LPSO structure. d: structure model
of three types of I1-LPSO structures.
shows the partial <a> dislocations at the
end of LPSO, but in fig. 2b no dislocations
with <c> component can be observed. At
the growth front, the phase-inverted
interface, represented as ACAC/ABAB
certainly occur between the local AC
stacking in the LPSO and the AB stacking
of the 2H-Mg. This is a consequence after
inverting ABAB into BABA during the
periodic introduction of the local AB’C
stacking, forming I1-LPSO without <a+c>
dislocations.
References
[1] E. Abe et al, Philos. Mag. Lett. 91 (2011)
[2] S. B. Mi and Q. Q. Jin, Scr. Mater. 68
(2013)
Fig. 2 HAADF-STEM images of the interface between 2H-Mg
and a: I2-LPSO, c: I1-LPSO and b, d: structure models of them.
35
PLE-03
Thermodynamic Mg database development and application to formation of
LPSO phases in multicomponent magnesium alloys
Rainer Schmid-Fetzer1
1
Institute of Metallurgy, Clausthal University of Technology, Robert-Koch-Str. 42,
D-38678 Clausthal-Zellerfeld, Germany
[email protected]
Integrated thermodynamic software packages are a powerful tool to analyze phase formation in
multicomponent alloys, providing key data for focused alloy and process development. The
thermodynamic database of the alloy system is the indispensable basis for this application of
Computational Thermodynamics. The database quality is crucial for the reliability of calculated
results. This quality may vary widely among available databases/datasets for the same alloy
system, and the quality is often hard to asses for the non-expert.
A concise introduction to the Calphad method, the basis for the construction of all major
thermodynamic databases for multicomponent systems, is given for the example of the Mg alloy
database. Key issues in development and extension of the large Mg database are consistency,
coherency and quality assurance. One aspect is the coherent description of large solid solution
ranges of intermetallic phases in multicomponent Mg-RE systems, in which various LPSO phases
occur. The combination of theoretical and experimental work to generate the validated database for
such Mg alloys is briefly outlined.
The phase relations of LPSO phases and quasicrystalline icosahedral phases are presented in
more detail for the Mg-Y-Zn and Mg-Gd-Zn alloy systems. In addition to calculated stable and
metastable phase diagrams, providing an overview of the system, the prediction of phase formation
in individual multicomponent magnesium alloys during solidification and heat treatment is obtained
from thermodynamic Scheil and equilibrium calculations. Such predictions are validated by
experimental observations.
36
INV-03
Effects of pre-strain and ageing on the LPSO structure in Mg97Zn1Y2 alloy
Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Japan
[email protected]
A long range periodic stacking ordered (LPSO) structure consists of regular arrangements of fourlayer high fcc structural units separated by several pure magnesium layers, commonly
synchronizing with chemical order/enrichment. The stacking order change in LPSO structure can
be realized by operating a <1-100>/3 type partial dislocations. This kind of transformation can be
treated as a diffusional-displacive transformation. Since the formation of the LPSO phase is closely
related to the partial dislocation type and their movement, external stress may alternate the
nucleation site and the structure of LPSO phase by introducing dislocations. Therefore, the effects
of aging and the small plastic deformation on the LPSO formation were investigated in a Mg97Zn1Y2
alloy. During aging at 520°C after solution-treated at 560°C, LPSO phase evenly precipitates from
the matrix, and its morphology is similar to that in the cast sample. In addition, 14H type of LPSO
phase is mainly observed even at the early aging stage. The 14H structure is kept after long time
aging. For the solution treated sample compressed at 350°C by 10% and then aged, 14H type of
LPSO phase is again observed at the early stage and remains after prolonged aging. It seems that
there is no precursor phase (such as 18R) before 14H type forms. When the pre-strain is
introduced, the LPSO phase becomes denser and finer as shown in Fig. 1(b) and 1(c). According
to Fig. 1(c), the spacing could be two times refined by pre strain. In order to differentiate the finer
spacing between LPSO plates in Fig. 1(a-b), finer scale statistic study is carried out as in Fig. 1(d)
and (e), and the spacing between the LPSO plate mainly smaller than 50 nm as shown in Fig. 1(f).
After statistical analyses, it shows that the pre-strain could reduce the plate spacing since prestrain could increase the nucleation sites. Moreover, LPSO plate with one or two structure units is
often observed in the pre-strained sample. The LPSO plate grows by the ledge mechanism in both
heat treatments. The cooperative motion of the structure units (white arrow in Fig. 1(e)) will be
discussed in terms of the possible elastic interactions between the structure units.
2 µm
2 µm
(a)
(b)
20 nm
20 nm
(d)
(c)
(e)
(f)
Fig. 1 Figure (a, d) and Figure (b, e) are the TEM image for the aged sample without pre-strain
and the sample with 10% pre strain at 350°C respectively. Both cases are aged 520°C for 1h.
Figure (c) shows the distribution of the LPSO plate spacing at the scale of Figure (a) and (b), while
Figure (f) shows the LPSO plate spacing distribution at more finer scale of Figure (d) and (e). White
arrow indicates the growth ledge.
37
INV-04
Microgalvanic activity and Volta potential of LPSO phases
in Mg-Zn-Gd-Al alloys
Michiaki Yamasaki1, Manabu Ohtani2 and Yoshihito Kawamura1
1
Magnesium Research Center, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto, 8608555, Japan
2
Department of Materials Science, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto,
860-8555, Japan
[email protected]
Magnesium alloys that stand at the top of the list of lightweight structural metals have become
attractive materials in automobile, railways, and aerospace industries where weight reduction is of
importance. Recently, ternary Mg-Zn-rare earth (RE) alloys with long period stacking ordered
(LPSO) structure phase have attracted significant attention due to their excellent mechanical
properties at room and elevated temperature. For example, rapidly solidified powder metallurgy
Mg97Zn1Y2 (at.%) alloys exhibits extremely high tensile yield strength (TYS) and reasonable
elongation. Extruded Mg97Zn1RE2 alloys also show relatively high TYS and large elongation.
These excellent mechanical properties is due to unique LPSO structure that forms coherently to the
α-Mg matrix: The LPSO phase was found to have a (0001) basal plane which is the same as that in
Mg (2H, Ramsdell notation), but its stacking periodicity was lengthened 9-fold (18R) or 7-fold (14H)
along the c-axis. The 18R- and 14H-LPSO phases have chemical modulation, in which solute
elements are enriched in four atomic layers on the closely packed plane at six and seven-period
intervals, respectively.
The LPSO phase acts as alloy-strengthening component because of their unique plastic
deformation behavior. From the viewpoint of corrosion science, however, the LPSO phase may be
considered as a secondary phase causing potential difference from the α-Mg matrix phase [1,2].
When we discuss the electrochemical homogeneity, it is important to clarify the Volta potential
difference between α-Mg matrix and LPSO phases in Mg-Zn-RE alloys. Recently, higher resolution
in Scanning Kelvin probe (SKP) measurement is obtained using an atomic force microscope
(AFM); scanning Kelvin probe force microscopy (SKPFM) has been established as a powerful
technique to characterize the corrosion process associated with locally electrochemical
heterogeneities on the surface of alloys. So, in this study, SKPFM was used to investigate the
surface potential distribution of the cast Mg-Zn-Gd-Al alloys with different concentration of Al
element. Addition of Al to the Mg-Zn-Gd alloys affects Volta potential of the LPSO phase because
Zn elements would be replaced with Al elements in the LPSO structure. We discuss influence of
change in the Volta potential difference between alpha-Mg and LPSO phases on corrosion
properties of the alloys.
[1] M. Yamasaki, S. Izumi, Y. Kawamura, H. Habazaki: Appl. Surf. Sci. 257 (2011) 8258.
[2] S. Izumi, M. Yamasaki, Y. Kawamura: Corros. Sci. 51 (2009) 395.
38
ORAL-06
Three-Dimensional Shapes and Distribution of LPSO in Mg-Zn-Gd Alloys
Characterized by Electron Tomography
K. Sato1, S. Matsunaga2, S. Tashiro2, Y. Yamaguchi2,
T. Kiguchi1 and T. J. Konno1
1
Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Sendai 980-8577, Japan
Depertment of Materials Science, Tohoku University, 6-6 Aoba, Aramaki, Sendai 980-8579, Japan
[email protected]
2
Magnesium alloys containing a transition metal together with a rare earth element such as Mg-Zn-Y
have been attracting much interest as next generation lightweight structural materials due to their
properties such as low density, high specific strength, damping capacity, recycling efficiency, and
so on. The strength of the materials can be attributed to the unique long-period stacking ordered
(LPSO) structure (synchronized LPSO) formed in α-Mg matrix [1]. In spite of the technical
importance, the formation mechanism of the synchronized LPSO has not been clarified yet. Recent
structural characterization of the LPSO relies on scanning transmission electron microscopy
(STEM) with the improved resolution and chemical sensitivity. The state-of-the-art electron imaging
enables atomic scale characterization of structural and chemical irregularity in the LPSO [2].
However, the images obtained by this technique are projections of three-dimensional (3D) objects;
and in order to better understand the nature of formation behavior of the LPSO, a direct 3D
visualization is greatly desired. In this respect, electron tomography has opened a new prospect;
the technique can retrieve 3D structural information usually missing in (S)TEM. In this study we
hence intend to characterize 3D structures of the LPSO formed in Mg97Zn1Gd2 cast alloys (a type II
alloy [3]) at an early stage of precipitation. A tilt series of Z-contrast STEM images were obtained
3
using an FEI TITAN 60-300 STEM operating at 300 kV with a CEOS probe corrector.
Figure 1(a) shows a HAADF-STEM image of a Mg97Zn1Gd2 alloy after aging at 773 K for 9
ks. The beam incidence is close to [11-20]Mg. Distribution of LPSO is clearly seen as straight lines
by Z-contrast. The rectangular area surrounded by broken lines were then selected and
reconstructed by simultaneous iterative reconstruction technique (SIRT) after tilt-axis correction.
Figure 1(b) shows a snapshot of the reconstructed volume corresponding to the 2D image shown
in Fig.1(a). As seen, shapes and distribution of the LPSO are reproduced. Another snapshot shown
in Fig.1(c), viewing from an oblique direction, revealed an existence of a “dent-shaped” area of the
LPSO as marked by an arrowhead, which has not been reported so far. It is presumed that such an
irregular shape is related to the in-plane growth mechanism of the LPSO [4].
Figure 1 An original
HAADF-STEM image
(a), and corresponding
reconstructed images
processed by SIRT (b,
c). The reconstructed
volume is 3618nm ×
4504nm × 1360nm with
a pixel size of 6nm. The
tilt axis is parallel to the
arrow shown in Fig.1(a).
References
[1] Y. Kawamura, K. Hayashi, A. Inoue, T. Msumoto, Mater. Trans. 42, 1172 (2001).
[2] T. Kiguchi, Y. Ninomiya, K. Shimmi, K. Sato, T.J. Konno, Mater. Trans. 54, 668 (2013).
[3] M. Yamasaki, M. Sasaki, M. Nishijima, K. Hiraga, Y. Kawamura, Acta Mater. 55, 6798 (2007).
[4] This work is supported by the Grant-in-Aid for Scientific Research on Innovative Areas
“Synchronized Long-Period Stacking Ordered Structure” (Grant Nos.26109702 and 23109006)
from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
39
ORAL-07
In-situ Multicolor SWAXS Approach to Examine
Stability and Formation of LPSO structures in MgYZn alloys
Hiroshi Okuda1, Hiroto Tanaka1, Toshiki Horiuchi1, Michiaki Yamasaki2,
Yoshihito Kawamura2 and Shigeru Kimura3
1
Kyoto University, Sakyoku, Kyoto 606-8501 Japan
Kumamoto University, Kurokami,Kumamoto 860-8555 Japan
3
JASRI Spring8, Sayo Hyogo 679-5198 Japan
[email protected]
2
The stability of synchronized LPSO structure during isothermal annealing and also under heating
/cooling at a constant rate has been examined by small-angle scattering/diffraction measurements
To examine the relative stability of several periodicity and their relationship with the microstructures,
simultaneous measurements of several peaks originating from LPSO, in-plane order, and the
fundamental diffraction peaks are important. To realize such simultaneous measurements with a
limited area of detectors, we worked on the use of higher harmonics, i.e., multicolor SWAXS for insitu measurements. Single wavelength measurements were made for ex-situ measurements to
obtain detailed scattering profiles.
The in-situ measurements have been performed at beam-line 04B2 of Spring8, Japan, with
fundamental wavelength of 37.8 keV and third/fourth harmonics of 113 keV/151keV with a use of a
Si 111 crystal. Figure 1 shows the photograph of measurement system, with two II-CCD area
detectors. The system detects diffractions from periodicity of 14H, 18R and 10H, and the in-plane
diffraction peaks overlapped by Bragg peaks given by higher harmonics in the SAXS detector,
while the additional detector mainly picks up diffraction by fundamental wave, aiming at having a
better resolution when the sample shows several phases. In the present work, we demonstrate the
microstructure change during heating/cooling the MgYZn alloys with the composition of
Mg85Y9Zn6, a nominally 18R single phase composition, and Mg97Y2Zn1, an α-Mg and 14H LPSO
two-phase composition.
During heating, Development of LPSO phase was observed in both composition. For both
compositions, LPSO structures having one shorter periodicity, i.e., 10H for 18R and 18R for 14H
were clearly observed in the as-cast samples. During heating, competition between the two
structures occurs, as was also observed for isothermal annealing of the alloys[2][3]. In the
intermediate temperatures, the diffraction from LPSO increased and that for in-plane order
sharpened, and the peak position for in-plane order
moved towards larger q. At higher temperatures, both of
the LPSO peaks decreased with temperatures, and
eventually diminished while the Bragg peak turned into
halo pattern representing liquid phase.
On the other hand, the in-plane order appeared at a
temperatures much lower than the temperature where
the LPSO/ in-plane peak disappear upon melting. It
suggested direct formation of LPSO phase from
supercooled liquid for Mg85Y9Zn6 samples. Although
the in-plane order develops in a very short time/
temperature during cooling, the peak position did not
move significantly with temperatures.
Fig.1 In-situ SWAXS setup at Spring8
References.
[1] H.Okuda et al., Scr. Mater. 2013, 68. 575,
[2] H.Okuda et al. Scr. Mater. 2014, 75, 66
[3] H.Okuda et al.,Metall.Mater.Trans. A 2014 accepted.
40
POS-01
Dynamic analysis of kink deformation mechanism
with high accuracy AE measurement
Yuki Muto1*, Takayuki Shiraiwa1 and Manabu Enoki1
1
Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo
113-8656, Japan
*Corresponding author’s e-mail: [email protected]
In recent years, it has been reported that Mg alloys with long-period stacking ordered (LPSO)
structure have very high yield strength. This will be attributed to kink bands in LPSO phase, and it
is important for improvement of the mechanical properties of LPSO Mg alloys to understand the
dynamic behavior of kink bands. However, dynamic motions of kink bands have not been
investigated in detail due to the difficulties in measurement. In this study, acoustic emission (AE)
measurement was conducted during tensile tests and four-point-bending tests with LPSO alloy to
detect in-situ signals generated by the deformation process. According to AE analysis, the effect of
kink bands on the mechanical properties of LPSO Mg alloys will be discussed.
41
POS-02
Atom-Probe-Tomographic Studies on Mg-Zn-Y alloys with LPSO phases
K. Inoue1, N. Ebisawa1, K. Tomura1, Y. Nagai1, H. X. Xu1,2, D. Egusa3,
and E. Abe3
1
The Oarai Center, Institute for Materials Research, Tohoku University
2145-2 Narita, Oarai, Ibaraki 311-1313, Japan, [email protected]
2
Department of Modern Physics, University of Science and Technology of China, Hefei, 230026,
China
3
Department of Materials Science and Engineering, University of Tokyo, Tokyo 113-8656, Japan
Atom probe tomography (APT) is a unique method for elemental mapping in 3D real space by
detecting atoms one by one, which is field-evaporated from the apex of needle-shaped specimen.
APT characteristics include nearly atomic-scale spatial resolution and elementally independent
detection efficiency. We apply this method to analyze elemental distribution in Mg-Zn-Y alloys with
long period stacking ordered (LPSO) structures. Figure 1 (a) and (b) show atom maps and
concentration profiles of Zn and Y in 14H and 18R structures in Mg97Zn1Y2 alloys. Periodical
enriched layers of Zn and Y with interval distance of 1.8 nm in 14H and 1.6nm in 18R are clearly
observed, which is consistent with the results of the STEM observation. The ratios of Y to Zn within
the enriched layers observed by APT are different between 14H and 18R. In the case of 18R, the
ratio of Y to Zn is 1.3, which is in good agreement with that value for Zn6Y8 clusters (1.33)
proposed by the first principles calculations. In the case of 14H, the ratio is 1.1, i.e., the
concentration of Y is almost same as that in 18R while the concentration of Zn is higher than that in
18R. In the presentation modulation of the concentration in transformation from 18R to 14H will be
presented. In addition, determination of diffusion coefficient of Zn and Y in Mg by using APT, now
in progress, will be introduced.
Fig. 1 (a) atom maps and (b) concentration profiles of Zn and Y in 14H and 18R structures of
Mg97Zn1Y2 alloys.
42
POS-03
First-principles study on stability of Mg-based LPSO phases
Koretaka Yuge1 and Ryohei Tanaka1
1
Department of Materials Science and Engineering, Graduate School of Engineering,
Kyoto University, Yoshida Honmachi, Sakyo-ku, Kyoto 606-8501, Japan
Mg-based ternary alloys with long-period stacking ordered (LPSO) phases is one of the promising
candidate for light-weight structural materials with high yield strength and ductility for next
generation, while mechanism of its formation and stable structures in atomic scale are still under
discussion. Theoretically, first-principles-based investigations have been amply employed to
address free energy surface, effects of lattice vibration on phase stability, effective interactions
between solute clusters and formation energies for different stacking type of such as 14H and
1)-4)
Since LPSO phases are composed of ternary elements, number of possible atomic
18R.
arrangements considered should become far beyond practical limitation of first-principles
calculations. This severely prevents from comprehensive understandings of how microscopic
states in LPSO phases distributed in phase space, making it difficult to quantitatively discuss phase
stability of the phases at finite temperatures. In the present work, we combined first-principles
calculation and cluster expansion (CE) technique to effectively address energetic stability in terms
of the possible microscopic states.
The CE is used to express any scalar observables (here, we consider internal energy) by using
complete and orthonormal basis functions in terms of ternary atomic arrangements. CE interactions
are optimized based on genetic algorism and “maximum weighted validation” developed by our
group, enabling to predict energy for any given microscopic state without loss of accuracy in firstprinciples calculations. In the present study, Mg-based alloys including Mg-Y-Zn are chosen, where
their energetic stability is quantitatively discussed based on the above approach: For structures
with small number of atoms, formation energy for ALL possible microscopic states is estimated,
and for those with larger number of atoms, Monte Carlo statistical simulation is performed to
effectively sample stable as well as metastable states based on the optimized CE interactions.
Composition dependence of stable states at T=0 K will also be discussed.
References
1) S. Iikubo et al., Phys. Rev. B 86, 054105 (2012).
2) H. Kimizuka et al., Scripta Mater. 69, 594 (2013).
3) S. Iikubo et al., Mater. Trans. 54, 636 (2013).
4) J.E. Saal et al., Scripta Mater. 67, 798 (2012).
43
POS-04
Molecular Dynamics Study of Dislocation Activity
during Kink Deformation of LPSO Structure
Ryosuke Matsumoto1 and Masayuki Uranagase2
1
Department of Mechanical Engineering and Science, Graduate School of Engineering, Kyoto
University, Building C3, Kyoto-Daigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan
Email address: [email protected]
2
Department of Mechanical Engineering and Science, Graduate School of Engineering, Kyoto
University, Building C3, Kyoto-Daigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan
Recently developed Mg alloys that contain long period-stacking-ordered (LPSO) phases have
attracted considerable attention because they have been reported to exhibit excellent mechanical
properties, including high yield stress and reasonable ductility [1]. Although some literatures show
that the LPSO phases yield by kink deformation under compression [2], the microscopic process is
unclear. This study aims to reveal the dislocation activity, such as corrective motion of dislocations
to form kink boundaries, during kink deformation using MD (molecular dynamics) simulations.
The model material employed in this study is LPSO phase with 10H stacking which is composed by
single element whose interatomic interaction is described by the Lennard-Jones potential [3]. Here,
we performed two kinds of MD simulations; (1) bending deformation of beams under compressive
load parallel to the basal plane, and (2) compressive deformation of square columns including
initial dislocations which constitute TB (tilt boundary). All simulations were performed at 300 K.
Figure 1 shows a representative structure change during bending deformation. The simulation
model is composed by about 1.5 million atoms and the pictures show only defects. It is confirmed
that, initially, (a) non-basal slips occur, and (b) low angle boundaries are formed through cross-slip
mechanism described in Ref. 3. When the misorientation angle reaches about 20°, (c) the
boundaries become dislocation source, and (d) the dislocation emission drastically increases the
misorientation angle. Figure 2 shows typical deformation modes observed compression of square
columns with initial TB. The result indicates that once tilt boundary is formed in LPSO through
some process, such boundary emits a lot of dislocations under compressive load and cause kink
deformation.
References
[1] Kawamura Y., Hayashi K., Inoue A. and Masumoto T., Mater. Trans., 42, (2001), 1172–1176.
[2] Hagihara K., Yokotani N. and Umakoshi Y., Intermetallics, 18, (2010), 267-276.
[3] Matsumoto R., Uranagase M. and Miyazaki N., Mater. Trans., 54, (2013), 686-692.
Fig. 1 Structure change during bending
deformation of a beam under compressive load
of 0.75 GPa along [1120]
44
Fig. 2 Typical deformation modes observed
by compressive deformation simulation of
square columns: θ0 indicates initial TB angle
POS-05
Atomistic Simulation Study of the Dependence of Thermal Activation of
Dislocation Nucleation in Mg on Temperature and Applied Stresses
Masayuki Uranagase1 and Ryosuke Matsumoto1
1
Department of Mechanical Engineering and Science, Graduate School of Engineering,
Kyoto University, Kyoto 615-8540, Japan
[email protected]
KUMADAI magnesium [1], which is an alloy consisting of magnesium (Mg), zinc, and yttrium, has
overwhelming strength in comparison with conventional Mg alloys. Many experimental results
suggest that characteristic deformation mode of long-period stacking ordered (LPSO) phase
crystallized on the cell boundary of α-Mg phase affects this strength. This deformation mode, which
accompanies formation of kink band [2], cannot be observed in conventional Mg alloys.
In 1949, Hess and Barrett [3] proposed the mechanism of kink deformation. In their mechanism, it
is necessary to nucleate edge dislocation pairs in different slip planes to form kink bands. If this
mechanism is true, then we may have a question how these dislocations nucleate within the crystal.
To solve this question, it will be essential to quantitatively evaluate nucleation of dislocations.
In this talk, we pay attention to dislocation nucleation in Mg under the
shear stress τ applied in the slip direction. Atomistic simulations are
performed for evaluation of the activation free energy Gac of dislocation
nucleation. However, conventional molecular dynamics simulations have
limitations of applicable time scale. In the present work, metadynamics
method [4] is applied to overcome this problem. In addition, this method
enables easy evaluation of the activation free energy.
In Fig. 1, we show the snapshot of the atomic plane just above the
Fig. 1 Snapshot of the
slip plane to confirm nucleation of an extended dislocation loop in the
atomic plane during the
process of a basal slip. Atoms which locally consist of hexagonal
dislocation nucleation.
close-packed structure, face centered cubic structure, and other
structure are colored by light gray, dark gray, and black, respectively.
In Fig. 2, we show temperature T dependence of the activation free
energy of nucleation of a dislocation loop for τ = 0.5, 0.6, 0.7, 0.8,
and 0.9 GPa from the top. For each τ, the activation free energy
decreases almost linearly as temperature increases. The activation
free energy is generally expressed as Gac = Hac - TSac, where Hac and
Sac represent enthalpic and entropic contributions, respectively. We
also found the linear relation between Hac and Sac, which is often called
enthalpy-entropy compensation [5].
In Fig. 3, the dependence of the activation free energy of nucleation Fig. 2 Dependence of the
activation free energy on
of a dislocation loop on the normal stress in the [11 2 0] direction is
temperature.
shown. This figure clearly shows the tendency that the activation free
energy increases as the normal stress increases. Increase in the
normal stress in the [11 2 0] direction leads to compression of the
crystal in the [11 2 0] direction and tension of it in [ 1 100] and
[0001] directions. This elastic deformation decreases the magnitude
b of Burgers vector and increases the distance d between the adjacent
planes parallel to the slip plane. Our result indicates that the activation
free energy decreases as b decreases and/or d increases. This is
similar to behavior of Peierls potential. The same tendency is also
found when the normal stress is applied in the [0001] direction.
[1] Y. Kawamura et al., Mater. Trans. 42, 1172 (2001).
[2] K. Hagihara et al., Intermetallics 18, 267 (2010).
Fig. 3 Normal stress
[3] J. B. Hess and C. S. Barrett, Trans AIME 185, 599 (1949).
dependence
of
the
activation free energy.
[4] A. Laio and F. L. Gervasio, Rep. Prog. Phys. 71, 126601 (2008).
[5] A. Yelon et al., Rep. Prog. Phys. 69, 1145 (2006).
45
POS-06
High Temperature Creep Behavior and Deformation Microstructures
in a Directionally Solidificated Long-Period Stacking Ordered
Mg-Zn-Y Alloy at 600 K
M. Suzuki1, S. Harada2 and K. Hagihara3
1
Department of Mechanical Systems Engineering, Faculty of Engineering,
Toyama Prefectural University, 5180 Kurokawa, Imizu, Toyama, 939-0398, Japan
([email protected])
2
Undergraduate student in Faculty of Engineering, Toyama Prefectural University,
5180 Kurokawa, Imizu, Toyama, 939-0398, Japan
(Now with in Central Japan Railway Company, Japan)
3
Department of Adaptive Machine Systems, Graduate School of Engineering, Osaka University,
2-1, Yamadaoka, Suita, Osaka 565-0871, Japan ([email protected])
Long period stacking ordered (LPSO) type Mg-RE-TM (RE: rare earth elements, TM: transition
metal elements) ternary alloys have been focused because of their excellent mechanical properties.
In the present investigation, high temperature creep strength and the activated deformation modes
in LPSO phase have been studied.
The material used in the investigation is a directionally
solidificated (DS) LPSO type Mg-9%Y-6%Zn (at %) alloy. Compressive creep tests have been
carried out under constant stresses in air and around 600 K.
Compressive creep specimens (2
mm x 2 mm x 3 mm, parallelepipeds) were machined and were held at the test temperature for 3 h
before creep test to stabilize temperature of the testing system. Loading direction is parallel to the
growth direction.
Deformation microstructures were observed by using transmission electron
microscope (TEM) operated at 200kV and analyzed by electron backscatter diffraction pattern
(EBSD) measurements in a field-emission type scanning electron microscope (FE-SEM).
The threshold behavior is observed in the DS Mg-9%Y-6%Zn alloy. Stress exponent of this alloy
is significantly changed around 100 MPa, which is the corresponding stress of the compression
yielding of a DS-LPSO alloy (Mg-7%Y-5%Zn) to the growth direction at 600 K [1]. The value of the
stress exponent in high stress region is around 8. This value is similar to the cast LPSO type MgNi-Y based cast alloy. High density of kink boundaries are formed in this stress region at the
beginning of the creep. On the other hand, the stress exponent of low stress region (below 100
MPa) is more than 50. Kink boundaries are hardly observed in this stress region after 3% creep
deformation. Therefore, the clear transition of the stress exponent of this alloy is caused by the
yielding (buckling) of LPSO grains under loading. The features of kink formed at high stress
region is similar to that at room temperature compression, but their density is obviously changed.
The kink density of crept specimen (ε~0.3) is significantly lower than that of the specimen deformed
at room temperature.
TEM observation revealed that a-dislocations are observed not only on the basal planes, but also
on the non-basal planes in crept specimens under low stresses. Few dislocations having Burgers
Vector with c-components are observed after creep. Many long straight dislocation segments
parallel to their Burgers Vectors are observed from the TEM observation with [0001] indicant beam
condition. Therefore, these dislocation segments are slip on the basal and/or the prismatic planes.
The high activation energy for creep was reported in several kinds of LPSO-type Mg-RE-TM alloys.
Therefore, the activation of non-basal a-dislocations are significantly important during creep in
LPSO type magnesium alloys.
Reference
[1] K. Hagihara et al: Intermetallics 18(2010), 267
46
POS-07
Hydrogen storage property of LPSO Mg-Ni-Y Alloys
Teppei Kawasaki1, Yoshinori Yamada2 and Kazuhiro Ishikawa2
1
Graduate Student of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa,
Ishikawa 920-1192, Japan
2
Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa,
Corresponding author: [email protected]
Recently, the LPSO structure was found in the Mg-TM-RE (TM: transition metal, RE: rare earth
metal) alloys. The LPSO structure is consisted of periodical stacking of Mg layers and TM-RE
condensed layers. The Mg-based alloys show poor hydrogen storage property, because they have
a low catalytic effect for dissociation of hydrogen molecules and low hydrogen diffusivity. It is
expected that the TM-RE condensed layers activate the dissociation of hydrogen and act as a
diffusion path for hydrogen, which improves the hydrogen storage property of Mg based alloys. The
aim of this study is to investigate the hydrogen storage capacity and structural change in a
hydrogen atmosphere of the LPSO Mg-Ni-Y alloy, and to obtain a basic knowledge of its
hydrogenation property.
The Mg85Ni6Y9 alloy, LPSO single phase, was pulverized and activated in a vacuum at 673 K. After
activation, hydrogen storage rate and PCT (Pressure-Composition-Temperature) property were
measured at 573~673 K in 0~4 MPa H2. Before and after measurements, morphological and
structural changes of the LPSO alloys were observed using an SEM and XRD, respectively.
When 4 MPa hydrogen gas was introduced into the sample container, pressure drop was observed
immediately at each temperature. However, it takes 20 hours to reach the equilibrium condition at
678 K. The XRD pattern of the sample, which was cooled down to RT, indicates that the LPSO
phase decomposes to the YH2, YH3, MgH2 and Mg2NiH4 hydrides. Resulting from the PCT
measurements, the LPSO phase absorbs 4.8 wt % (1.6 H/M) hydrogen at 665 K. In the PCT
diagram, two plateau pressures are observed, which means that two hydrogenation reactions exist.
The first plateau pressure is observed at around 1.4 MPa at 665 K and reduced with decreasing
temperature. By Van' t Hoff analysis, the enthalpy change of this hydrogenation is estimated to be
about -74 kJ/mol H2, which is close to that of the formation of the MgH2 hydride. Similarly, the
second plateau pressure corresponds the formation of the Mg2NiH4 hydride.
47
POS-08
Hydrogenation Behavior and Structural Change of LPSO Mg-Zn-Y Alloys
Kazuhiro Ishikawa1, Teppei Kawasaki2 and Yoshinori Yamada1
1
2
Graduate School of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa,
Graduate Student of Natural Science and Technology, Kanazawa University, Kakuma, Kanazawa,
Corresponding author: [email protected]
Mg based alloys have been expected as a hydrogen storage alloys with a large capacity. However,
they show low activity for dissociation of hydrogen molecule to atoms and low hydrogen diffusivity,
which makes difficult to use them practically such as on-board hydrogen storage alloys. Some of
the Mg-Tm-Re (Tm: transition metal, Re: rare earth metal) alloys show the LPSO structure, that is,
periodical stacking of Mg layer and Tm-Re condensed layer. The condensed layer has similar
composition to Tm-Re based hydrogen storage alloys. If the Tm-Re layer acts as a dissociation site
and a diffusion path for hydrogen, Mg-based high performance hydrogen storage alloys can be
obtained. The aim of this study is to obtain a basic knowledge of hydrogenation behavior and
structural change during hydrogenation of the LPSO alloys and to discuss a possibility for hydrogen
storage or permeation alloys.
The Mg85Zn6Y9 alloy, LPSO single phase, was pulverized and hydrogenated at 673 K. During
hydrogenation, YH2 and YH3 hydrides are formed below 0.1 MPa hydrogen atmosphere. Then, Mg
transforms to MgH2 at 1.7 MPa H2. Resulting from XRD analysis, the LPSO phase decomposes to
YH2, YH3, MgH2 and Mg2Zn after hydrogenation.
-10
0.5
Hydrogen permeability Φ of this alloy is in the order of 10 (molH2/m/s/Pa ) at 623 K, which is a
fraction of that of pure Pd. Using the hydrogen solubility coefficient K, which is obtained by PCT
measurement, the hydrogen diffusion coefficient D in this alloy is estimated to be in the order of 10
2
9
(m /s).
Disproportionation reaction is occurred in the LPSO Mg-Zn-Y alloy during hydrogenation, so that
reversible hydrogen absorption-desorption is impossible. Hydrogenation rate and hydrogen
diffusivity of the LPSO alloy are lower than those of the LaNi5 hydrogen storage alloy.
48
POS-09
STM Observation of Local Structures in Closed-Packed Layer of LPSO
Shu Kurokawa, Hiroki Saito and Akira Sakai
Department of Materials Science and Engineering, Kyoto Univsersity. Kyoto 606-8501, Japan
[email protected]
Introduction
Scanning Tunneling Microscopy (STM) is one of the most powerful surface microscopy techniques
for investigation of atomic and electronic structures of surfaces. However, the application of STM to
the bulk materials has been very limited because STM needs very, almost atomically, flat surface
for successful observations. However, the ability of STM to image only atoms in the surface layer
with very high spatial resolution makes it a unique tool to analyze the materials with very fine and
disordered structures. In this study, we have prepared atomically flat surfaces that retain the atomic
arrangements found inside the material by cleaving Mg-Zn-Y LPSO samples and observed local
arrangements and electronic properties of Y-Zn clusters in closed-packed layer of LPSO.
Experimental
18R type Mg85Zn6Y9 and 14H type Mg84Zn7Y9 have been investigated. To prevent oxidation,
-8
cleavage of the sample was carried out in ultra-high vacuum (better than 1x 10 Pa) condition.
Samples were cooled down to Liq. N2 temperature during cleavage and STM observation since our
SEM observation shows that cleavage in Liq. N2 makes more flat surfaces. Also, low temperature
is advantageous to stable and accurate STM imaging.
Results
Figure 1 shows typical STM image of cleaved LPSO structures. Ab-inito simulations show the dark
spots in these images correspond to Zn-Y clusters. From the STM images, histogram of clustercluster distance was constructed and shown in fig.2. Obviously, the feature of the histogram in 18R
is different from that in 14H: the first peak in the histogram is located at the distance of 6nn
(nearest neighbor) in 18R while 8nn in 14H.
To clarify the structure of clusters and interaction between them, we have carried out STS
(scanning tunneling spectroscopy). Our preliminary results on 14H show that there is no difference
in density of states between the Zn-Y clusters, which may indicate the uniformity in the atomic
structures of Zn-Y clusters in 14H type LPSO. On the other hand, STS mapping shows that there
are non-uniformity in density of states in the areas distant from clusters. At present, we are
studying the origin of observed non-uniformity in density of states.
Fig.1. Typical STM images of cleaved LPSO. (a) 18R
LPSO made by Directional solidification (DS) method. (b)
DS 14H LPSO.
Fig.2. Histogram of cluster-cluster distance.
49
POS-10
Kink deformation behavior in long-period stacking ordered structure
during uniaxial loading with stress-reversal
Tsuyoshi Mayama1, Tetsuya Ohashi2,
Michiaki Yamasaki1 and Yoshihito Kawamura1
1
Kumamoto University; Kurokami 2-39-1, Chuo-ku, Kumamoto, JAPAN
[email protected]
2
Kitami Institute of Technology; Koen-cho 165, Kitami, JAPAN
In magnesium based long-period stacking ordered (LPSO) structure, kink bands are frequently
observed after plastic deformation [1-5]. The formation of kink bands induces plastic strain in caxis direction. For LPSO structure in which plastic anisotropy is significant [3], the additional
deformation mode due to kink bands formation could increase the formability during metal forming
processes such as rolling and extrusion. Furthermore, the strain hardening due to kink band
formation has been also suggested in LPSO structure [4]. Therefore, kink deformation behavior in
LPSO structure should be made clear with the aim of understanding of mechanical properties of
LPSO structure.
In this study, kink deformation behavior in long-period stacking ordered (LPSO) structure during
uniaxial loadings with stress-reversal is investigated. Experimentally, uniaxial tensile loading after
compressive loading of as-cast polycrystalline Mg85Zn6Y9 alloy (approximately 100% volume
fraction of LPSO phase) was performed at room temperature. To study the development of kink
bands, surfaces morphology and crystal orientations of undeformed, compressed and elongated
specimens were compared by SEM/EBSD analysis. To clarify the mechanism of formation and
development of kink bands in LPSO structure, numerical analysis by a crystal plasticity finite
element analysis was also performed.
References
[1] Yoshimoto, S. et al., Materials Transactions 47 (2006) 959-965.
[2] Noda, M. et al., Materials Transactions 50 (2009) 2526-2531.
[3] Hagihara, K. et al., Intermetallics 18 (2010) 267-276.
[4] Shao, X. H. et al., Acta Materialia 58 (2010) 4760-4771.
[5] Yamasaki, M. et al., Acta Materialia 61 (2013) 2065-2076.
50
POS-11
Cyclic hardening behavior of cast Mg-Zn-Y alloys
containing long-period stacking ordered phase
Kazuma Shiraishi, Tsuyoshi Mayama,
Michiaki Yamasaki and Yoshihito Kawamura
1
Kumamoto University, Kurokami 2-39-1, Chuo-ku, Kumamoto, 860-8555, Japan
[email protected]
Magnesium alloys with based long-period stacking ordered (LPSO) phase shows excellent
mechanical properties compared with conventional magnesium alloys [1, 2]. Although several
strengthening mechanisms were reported for the LPSO structure [3-6], the contributions of each
mechanisms to strain hardening behavior have not been fully clarified. Whereas strain hardening
behavior of directionally solidified (DS) Mg-Zn-Y alloy has been reported [7], the details of strain
hardening behavior of polycrystalline Mg-Zn-Y alloy have not been studied so far except for high
temperature behavior [8].
In this study, strain hardening behavior of polycrystalline as-cast Mg-Zn-Y alloy was studied.
Influences of LPSO phase on strain hardening behavior of cast Mg-Zn-Y alloys were investigated
from the tension-compression cyclic loading with a constant strain amplitude under a constant
strain rate at room temperature for as-cast Mg-Zn-Y alloys with four volume fractions of LPSO
phase. The results showed that the stress amplitude of the alloy with high volume fraction of LPSO
phase continuously increased up to 100th cycle. With increase in volume fraction of LPSO phase,
the increase in the stress amplitude became significant. The evaluation of the contributions of
isotropic hardening and kinematic hardening to cyclic hardening indicated that the amount of
kinematic hardening significantly increased during cyclic loading in Mg-Zn-Y with high volume
fraction of LPSO phase.
References
[1] Kawamura, Y. et al., Materials Transactions 42 (2001) 1172-1176.
[2] Yoshimoto, S. et al., Materials Transactions 47 (2006) 959-965.
[3] Hagihara, K. et al., Acta Materialia 58 (2010) 6282-6293.
[5] Shao, X. H. et al., Acta Materialia 58 (2010) 4760-4771.
[6] Yamasaki, M. et al., Acta Materialia 59 (2011) 3646-3658.
[8] Matsumoto, R. et al., Materials Science and Engineering A 548 (2012) 75-82.
51
POS-12
Structure and texture variation of Mg97Al1Ca2 alloy by high pressure and high
temperature treatments
Shinsaku Yamasaki1, Masafumi Matsushita1, Ryota Inugai1, Takafumi Nagata1,
Ikuya Yamada2, Michiaki Yamasaki3, Toru Shinmei4, Tetsuo Irifune4, Yoshihito
Kawamura3
1
Department of Mechanical Engineering, Ehime University, Matsuyama 790-8577, Japan
Nanoscience and Nanotechnology Research Center, Osaka Prefecture University, Sakai
599-8570, Japan
3
Magnesium Research Center, Kumamoto University, Kumamoto 860-8555, Japan
4
Geodynamics Research Center, Ehime University, Matsuyama 790-8577, Japan
Corresponding author address: Department of Mechanical Engineering, Ehime University, 3
Bunkyo-cho, Matsuyama 790-8577, Japan, [email protected]
2
Mg-TM-RE ternary alloy systems show long period stacking ordered structure (LPSO)
synchronized with chemical concentration. In particular, Mg-Zn-Y system shows 4 kinds
synchro-LPSO in Mg rich corner of ternary phase diagram. To organize the previous research for
Mg-TM-RE system, atomic radius and mixing entropy are important factor [1]. Further it is unclear
that the effect of electronic configuration for formation of LPSO structure.
As far as we know, non-RE element synchro-LPSO has not been discovered yet. Then, we have
attempted to make it using high pressure synthesize technique.
Calcium (Ca) has approximately 10 % larger atomic radius and 41 % smaller bulk modulus than
those of Y. Taking into the consideration that the atomic volume and bulk modulus of each element,
the ratio of atomic volume of Mg: Al: Ca under high pressure becomes similar to Mg: TM: RE system,
which LPSO phase have been already discovered. If Ca can take the place of RE, it is benefit from
the view of elements strategy.
Then, we have performed high pressure and high temperature (HPHT) treatment to Mg97Al1Ca2 at
3 and 7 GPa and at various temperatures using Kawai-type multi anvil high pressure apparatus.
After that structure and texture of recovered samples after HPHT treatment have been investigated.
As the result, we confirmed some changes of texture and structure of Mg97Al1Ca2.
(a)
(b)
SEM images of as casted Mg97Al1Ca2 (a) and Mg97Al1Ca2 recovered from 3 GPa, 700 ℃ (b).
Reference
[1] Y, Kawamura, M. Yamasaki, Materials Transactions, 48 (2007) 2986
52
POS-13
Structural study for Mg97Zn1Yb2 alloy at ambient pressure and after high
pressure treatments
Ryota Inugai1, Masafumi Matsushita1, Takafumi Nagata1, Shinsaku Yamasaki1,
Ikuya Yamada2, Michiaki Yamasaki3, Toru Shinmei4, Tetsuo Irifune4,
Yoshihito Kawamura3
1
2
Nanoscience and Nanotechnology Research Center, Osaka Prefecture University, Sakai 5998570, Japan
3
4
Long period stacking ordered structures (LPSO) synchronized with chemical concentration have
been discovered in some Mg-TM-RE ternary alloys. However in case of RE = Yb, the LPSO have
not been discovered yet.
Yb has characteristic properties, which are different from other lanthanides that take a LPSO
structure in Mg-TM-RE ternary alloy system. In regular trivalent RE metals, which take a LPSO
structure in Mg-TM-RE, pressure induced crystal structure transition sequence at room
temperature is hcp → α-Sm → dhcp → FCC. In contrast, at room temperature, Yb shows structural
transition in sequence FCC → BCC → HCP with increasing pressure. Further metallic radius of Yb
is larger than other lanthanides. At ambient pressure and room temperature, electronic
14
0
2
configuration of Yb is considered to 4f 5d 6s . The 4f and 6s levels are filled and 5d level is empty.
According to previous studies at ambient pressure, valence of Yb metal is +2. However, with
increasing pressure, the volume of Yb metal shows significant decrease, and then above 4.0 GPa,
mean valence of Yb metal is changed from +2 to +3 accompanying with FCC to BCC pressure
induced crystal structural transition [1, 2]. This change is considered to be caused by the promotion
of 4f level electron to 5d level. Further after this transition, Yb has similar metallic radius and
valence to regular trivalent RE metals lanthanides, which take a LPSO structure in Mg-TM-RE
ternary system. If atomic radius could be most important to form a LPSO, the Mg97Zn1Yb2 alloy
would take a LPSO under high pressure. Further if the mean valence could be important to form
LPSO, the Mg97Zn1Yb2 alloy would take a LPSO above 4 GPa.
Then in this research, we report the result of high pressure and high temperature (HPHT)
treatment effects on Mg97Zn1Yb2 alloy. HPHT treatments have been performed at 3 and 5 GPa at
various temperatures. After this treatment, we have investigated the crystal structure and texture.
As the result, we confirmed clear changes both in crystal structure and texture.
(a)
(b)
SEM images of recovered Mg97Zn1Yb2 alloys from 3 GPa, 700 ℃ (a) and 5 GPa, 700 ℃(b).
Reference
[1] H. T. Hall, J. D. Barnett, L. Merrill, Science 139(1963)111.
[2] A. Fuse, G. Nakamoto, M. Kurisu, N. Ishimatsu, H. Tanida, J. alloys. Compd. 376 (2004) 34.
53
POS-14
Effect of high pressure and high temperature treatment on structure and
texture of Mg97Zn1Y2 alloy
Takafumi Nagata1, Shinpei Yamamoto1, Masafumi Matsushita1, Tatsuya
Senzaki1, Ikuya Yamada2, Michiaki Yamasaki3, Toru Shinmei4, Tetsuo Irifune4,
Yoshihito Kawamura3
1
2
3
4
As casted Mg97Zn1Y2 alloy consisted of hexagonal closed packed structure (hcp) and 18R type
long period stacking ordered structure (LPSO) synchronized with chemical concentration. The 18R
LPSO in Mg97Zn1Y2 is transformed to 14 H LPSO by annealing at 500 ℃. It means that 18R and
14H LPSO structure exist with between small energy barriers in casted Mg97Zn1Y2 alloy. The
formation mechanism of LPSO phases is unclear, further the relationships of energetic stability
have not been explained by the computer simulated experiment yet.
The phase behaviors of alloys at extreme condition, such as high temperature, high pressure, are
complex problem, but the information required from these experiments bring us many implications
for stability of crystal structure.
According to the previous our study for the effect of high pressure and high temperature (HPHT)
treatments on Mg85Zn6Y9 alloy, which consists of 18R and 10H type LPSO structures at ambient
pressure, these LPSO phases vanished after HPHT treatments at 7 GPa above 600 ℃ and the
phase divided to body centered cubic based super lattice structure, which include Y and Zn, and
Mg rich hcp phase. These two phases show very thin lamella structure.
In case of Mg97Zn1Y2, concentration of Zn and Y is lesser than that of Mg85Zn6Y9. Further 18R
and 14H LPSO is compensating in Mg97Zn1Y2 at ambient pressure. In this presentation, we report
HPHT treatments effect on the Mg97Zn1Y2 alloy and then compare with the result of Mg97Zn1Y2 with
Mg85Zn6Y9. HPHT treatment at 3 and 7 GPa and various temperatures have been performed using
Kawai-type and Cubic anvil type high pressure apparatus. After that, the structure and texture of
recovered samples after HPHT treatments were investigated. LPSO structure in Mg97Zn1Y2 is
remained after HPHT treatment even at 7GPa above 600 ℃ and new phase appears as shown in
figure 1, which is quite different from that of Mg85Zn6Y9.
Intensity (arb.unit)
7 GPa 700 ℃
7 GPa 600 ℃
as cast
0
20
40
2theta (degree)
60
80
Fig. 1 X-ray diffraction patterns of Mg97Zn1Y2 of as cast and recovered from 7 GPa at each
temperature.
54
POS-15
Structure and stability of LPSO phase in Mg85Zn6Y9 and its high pressure
phase
Tatsuya Senzaki1, Masafumi Matsushita1, Norimasa Nishiyama2, Ikuya
Yamada3, Michiaki Yamasaki4, Toru Shinmei5, Tetsuo Irifune5, Yoshihito
Kawamura4
1
2
Deutsches Elektronen Synchrotron DESY, 22607 Hamburg, Germany
3
Nanoscience and Nanotechnology Research Center, Osaka Prefecture University, Sakai
599-8570, Japan
4
5
Studies at high pressure bring us helpful information to understand the properties of materials.
Long period stacking order structure (LPSO) synchronized with chemical concentration in Mg-Zn-Y
ternary alloy is very interesting from the view of structural science in condensed matter, but the
formation and stability mechanism of this structure is still unclear. Therefore our group have been
investigated the effect of high pressure and high temperature (HPHT) treatment on the Mg85Zn6Y9
alloy, which include 18R and 10H LPSO at various temperatures and pressures.
The LPSO phase of Mg85Zn6Y9 is stable at room temperature up to 15 GPa. In contrast, at high
temperature, LPSO phases become unstable under high pressure. The pressure-temperature
phase diagram of Mg85Zn6Y9 is shown in Figure 1. Considering from powder X-ray diffraction, the
BCC based super lattice structure (L21 type) appear at 3 GPa above 600℃. Further increase in the
pressure, LPSO phase disappears and LPSO phase cannot be formed above 600℃. The X-ray
diffraction pattern of recovered sample from 7 GPa, 700℃ is shown in Figure 2. The duplex phase
consisted of L21 type and hcp structures are formed. With increasing pressure, the grain becomes
smaller. Further according to in- situ X-ray diffraction measurements under 3GPa at various
temperature. LPSO collapse with increasing temperature and L21 type and hcp structure phase
formed. Further increase of temperature, the alloy was melted and the LPSO phase can be formed
by the quench above melting temperature. Moreover, the stability of L21 type and hcp duplex phase
obtained HPHT treatment has been investigated using DSC measurements.
14H+18R
+L21+?
Temperature (℃)
800
700
Red line: Peak positions simulated from L21 type structure
Blue line: Peak positions simulated from hcp structure
hcp + L21 type phase
600
18R+10H LPSO+L21 type
500
18R+10H LPSO
400
300
0
2
4
6 8 10 12 14 16
Pressure (GPa)
Fig.1 Pressure-temperature phase diagram
of Mg85Zn6Y9
Intensity (arb. unit)
900
0
10 20 30 40 50 60 70 80
2 theta (degree)
Fig.2 X-ray diffraction pattern of recovered
Mg85Zn6Y9 from 7 GPa, 700 ℃.
55
POS-16
Effect of high pressure and high temperature treatment on carbon steels
Kazuaki Onishi1, Masafumi Matsushita1, Ikuya Yamada2, Michiaki Yamasaki3,
Toru Shinmei4, Tetsuo Irifune4, Yoshihito Kawamura3
1
2
3
4
Long period stacking ordered structures (LPSO) synchronized with chemical concentration existed
in Mg-TM-RE system are consisted of both ABAB… stacking of hcp and ABCABC… stacking of
FCC structures. These LPSOs improve of mechanical properties through the characteristic
deformation process of the phase. Kawamura and Yamasaki have been organized the criteria of
LPSO of Mg ternary alloy system and their group has been discovered many Mg based LPSO
alloys [1]. However as far as we know, the LPSOs synchronized with chemical order have been not
discovered in other element based alloy. Then our group has been searching for the LPSOs in the
non-Mg alloy using high pressure synthesized method.
To attempt searching for non-Mg LPSO, it is considered that the hcp structure element should be
selected as base element. Then, we have selected ɛ-Fe as the base element. It is well known that
hcp structure of Fe is stable at the pressure above 10 GPa at room temperature, however the hcp
structure cannot be recovered at room temperature after released pressure. If ɛ-Fe could be
recovered from high pressure, it would use as the base element. Then we add carbon into Fe and
high pressure and high temperature (HPHT) treatments have been performed to obtain ɛ phase.
Many studies have been performed for Fe-C system at ambient and high pressures both
experiments and computer simulations [2]. According to the previous reports at ambient pressure,
Fe-C compounds take many kind structures, such as cubic, orthorhombic, hexagonal and so on.
However the experiment research for recovered sample for HPHT treatments is no so many [3]. In
particular, the research above 10 GPa is few [4].
Then we have attempted HPHT treatments on various chemical concentrations Fe-C at 13 GPa at
various temperatures using Kawai-type multi anvil apparatus. In this presentation, we mentioned
the crystal structures and texture of recovered samples of Fe-C after HPHT treatments.
References
[1] Y, Kawamura, M. Yamasaki, Materials Transactions, 48 (2007) 2986
[2] O. A. Bannykh, K. Enami, S. Nagasaki and A. Nishiwaki. (2001). Tetsugoukinjyoutaizusyu (Fe
alloy constitution diagram). 14-16. Tokyo : AGUNE SCIENCE CENTER PUBLISHING CO., LTD.
[3] L. E. Shterenberg, V. N. Sleaev, I. A. Korsunskaya and D. S. Kamenetskaya, high temp. high
pressures 7 (1975)517-522.
[4] V.K.Grigorovich. (1969). Izvest. Akad. Nauk SSSR, Metally No.1. 53-68
56
POS-17
In-situ X-ray diffraction measurements of collapse and formation process of
LPSO structure in Mg85Zn6Y9
Masafumi Matsushita1, Jozef Bednarcik2, Norimasa Nishiyama2, Yuya
Sakata1, Shutaro Akamatsu1, Michiaki Yamasaki3, Yoshihito Kawamura3
1
2
Deutsches Elektronen Synchrotron DESY, 22607 Hamburg, Germany
3
840.7 K
837.2 K
823.4 K
10H (002)
847.1 K
10H (002)
18R (003)
18R (003)
As casted Mg85Zn6Y9 have two type long period stacking ordered structure synchronized with
chemical concentration (LPSO), one 18R and another is 10H LPSO [1]. To consider collapse and
creation process of these states, we have performed in-situ X-ray diffraction (XRD) measurements
for Mg85Zn6Y9 using synchrotron radiation in P02.1 beam line in DESY. The sample cut and put in
the quarts capillary, and then the sample was furnace filled Ar. The temperature was increased in
10 K/min, from 323 to 863 K and then decreased down to 323 K. The wave length of X-ray was
2
0.20715 Ǻ in size 0.6 × 0.6 mm . The distance between sample to the 2D-detector (Perkin Elmer
2
PE1621: 2048 × 2048 pixels, 1pixel = 0.2 × 0.2 mm ) is 2 m. In the measurements, we collected 1
XRD pattern in 20 s, and then crystal information for 3 K is included in each XRD pattern. This
system can be measured for the diffraction peaks with d value between 2 and 25 Ǻ, thus the long
distance peaks which is caused chemical modulation and peaks from structural modulation of 2 Ǻ
order can be collected in same time. Therefore through the XRD measurements, variation of
chemical and structural modulation can be defined. The space group using analysis for 18R and
10H LPSOs are P3212 and P63/mcm, respectively [2, 3].
The length of a and c axis of 18R LPSO obtained XRD pattern at 323 K are 11.200 and 47.101 Ǻ,
respectively. The peak from (100) is broad even at 323 K, which is corresponding to the small
angle X-ray diffusion [1]. Further (013) peaks 18 R becomes vanished at 778 K. present result
means the instability of d100. Intensities of peaks from 10H LPSO structure decrease faster than
18R LPSO with increasing temperature as shown in Figure 1 (a). With decreasing temperature
path, 18R LPSO formed higher temperature than 10H LPSO as shown in Figure 1 (b). Thermal
-5
-1
-5
-1
expansion coefficients (α =dl/ldT) of a and c axis of 18R LPSO is 2.5 × 10 K and 2.6 × 10 K ,
respectively.
(b)
(a)
850.5 K
826.8 K
2
3
817.0 K
809.5 K
823.7 K
1
819.6K
4
2 theta (degree)
5
1
2
3
4
5
2 theta (degree)
Fig.1 XRD pattern of Mg85Zn6Y9 near melting (a) and solidification temperature (b).
References
[1] H. Okuda, T. Horiuchi, T. Tsukamoto, S. Ochiai, M. Yamasaki, Y. Kawamura, Scrip. Mater., 68
(2013), 575.
[2] D. Egusa, E. Abe, Acta Materialia, 60 (2012) 166.
[3] M. Yamasaki, M. Matsushita, K. Hagiwara, H. Izuno, E. Abe, Y. Kawamura, Scrip. Materi., 78-79
(2014) 13.
57
POS-18
Deformation twinning in a Mg-Al-Gd ternary alloy containing LPSO platelet
precipitates
Kyosuke Kishida1,2 and Haruyuki Inui1,2
1
Department of Materials Science and Engineering, Kyoto University,
2
Center for Elements Strategy Initiative for Structural Materials (ESISM), Kyoto University,
[email protected]
Magnesium alloys containing Mg–TM (transition-metal)–RE (rare-earth) ternary precipitates with
long-period stacking-ordered (LPSO) structures have attracted considerable attention as promising
light-weight structural materials because of the simultaneous achievement of high strength (~600
MPa) and good ductility (~5 %), which has been achieved by extrusion at high temperatures above
350°C [1,2]. Such attractive properties has been considered to be achieved by grain refinement of
the Mg matrix in the vicinity of bent LPSO platelet precipitates as a result of recrystallization [3,4].
However, the detailed mechanisms behind this have largely remained unsolved. The lack of
knowledge on fundamental properties of the LPSO phases such as crystal structure, thermal
stability and deformation mechanisms is largely responsible for this. Previous studies by Hagihara
et al. [5,6] on plastic deformation of the LPSO phases using directionally-solidified ingots revealed
that the basal slip is the easiest deformation mode operative in most crystal orientations, while
deformation bands are formed when the grains of the LPSO phases are compressed nearly along
the basal plane. They concluded that the deformation bands are kink bands, the boundary of which
are formed by accumulated numerous basal dislocations perpendicular to the basal plane, based
on the classical model proposed by Hess and Barrett [7]. However, considering relatively large
rotation (or bending) angles about 30~60 degree between the matrix and deformation bands raise
a serious question as to whether or not all these deformation bands are formed actually by the
numerous activation of basal dislocations, which have to glide on basal planes nearly parallel to the
loading axis. In the present study, deformation microstructures of a Mg-Al-Gd alloy containing
ternary LPSO precipitates after plane-strain compression at room temperature in order to elucidate
mechanisms for the formation of the deformation bands in the Mg-LPSO precipitates.
A magnesium alloy containing the 18R-type Mg-Al-Gd LPSO platelet precipitates parallel to the
basal plane was found to deform by the c-axis tension twinning on {11 2̄1}, whose passage causes
the bending of the LPSO platelets, when Mg grains are oriented favourable for the extension along
the c-axis during the plane-strain compression at room temperature. The bending of the LPSO
platelets was found to be caused by the deformation twinning equivalent to the {11 2̄1} twinning in
the Mg matrix [8].
References
[1] Y. Kawamura, K. Hayashi, A. Inoue, T. Masumoto, Mater. Trans. 42 (2001) 1172.
[2] Y. Kawamura, M. Yamasaki, Mater. Trans. 48 (2007) 2986.
[3] K. Hagihara, A. Kinoshita, Y. Sugino, M. Yamasaki, Y. Kawamura, H.Y. Yasuda, Y. Umakoshi,
Acta Mater. 58 (2010) 6282.
[4] M. Yamasaki, K. Hashimoto, K. Hagihara, Y. Kawamura, Acta Mater. 59 (2011) 3646.
[5] K. Hagihara, N. Yokotani, Y. Umakoshi, Intermetallics 18 (2010) 267.
[6] K. Hagihara, Y. Sugino, Y. Fukusumi, Y. Umakoshi, T. Nakano, Mater. Trans. 52 (2011) 1096.
[7] J.B. Hess, C.S. Barrett, Trans. Am. Inst. Min. Met. Eng. 185 (1949) 599.
[8] K. Kishida, A. Inoue, H. Yokobayashi, H. Inui. Scripta Mater. (2014) in press.
58
POS-19
Development of a Gandolfi Camera Attachment for the Measurement of
Single- and Poly-crystalline LPSO Magnesium Alloys
Nobuhiro Yasuda and Shigeru Kimura
Research and Utilization Division, Japan Synchrotron Radiation Research Institute, SPring-8
1-1-1 Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan
E-mail : [email protected]
The magnesium (Mg) alloys with synchronized long-period stacking ordered (LPSO) phases are
paid attention to high strength, light-weight and nonflammable properties. The nature of these
properties is intensively studied by both experimental and theoretical approaches in the world.
However, the determination of precise atomic arrangement of the LPSO-phase was difficult
3
because the area of single LPSO phase is too small (less than 10 μm ).
To investigate the properties of functional materials such as LPSO Mg alloys, we have
developed a Gandolfi camera attachment which can be attached on high precision diffractometer at
SPring-8 BL40XU beamline [1, 2]. Using this attachment, powder diffraction pattern data can be
obtained even from a highly oriented crystal (Fig. 1).
To demonstrate the validity of this attachment, thermal expansion coefficients of an 18R-LPSO
Mg alloy (Mg85Zn6Y9) and α-phase Mg (α-Mg) were determined. Diffraction images of Mg85Zn6Y9
3
3
and α-Mg with size of 0.3 x 0.3 x 1.0 mm and 0.2 x 0.2 x 0.6 mm , respectively, were obtained at
temperature from 90 to 450K. Figure 2 is measured diffraction images of Mg85Zn6Y9 and α-Mg.
Because the lattice of Mg85Zn6Y9 is larger, many peaks were observed. As temperature increases,
2θ angle of diffraction peaks shifted to lower angle side because of thermal expansion (Fig. 3). In
the preliminary analysis using a few diffraction peaks, thermal expansion coefficient of Mg85Zn6Y9 is
smaller than that of α-Mg. The precise analysis using Rietveld analysis are now in progress. The
comparison of thermal expansion coefficient between Mg85Zn6Y9 and α-Mg and the details of the
Gandolfi attachment will be presented.
(a)
(b)
Figure 1 (a)Photograph of
measured Mg85Zn6Y9 alloy.
(b) Diffraction images using ωrotation and Gandolfi methods.
Figure 2 The diffraction images
of Mg85Zn6Y9 and α-Mg.
Figure 3 Diffraction peak profiles of
Mg85Zn6Y9 at temperature of 90, 200,
300 and 400K.
References
[1] N. Yasuda et al., J. Synchrotron Rad., 16, 352-357 (2009).
[2] N. Yasuda et al., AIP Conference Proceedings, 1234, 147-150 (2010).
59
POS-20
Thermodynamic properties of the Mg-Gd-Al system
S. Iikubo1, and H. Ohtani2
1
Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology,
Kitakyushu 808-0196, Japan
2
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University,
Sendai 980-8577, Japan
The long period stacking ordered (LPSO) Mg-based alloys are characterized by the periodical
arrangement of a stacking fault (SF) introduced on the hcp lattice. In addition, rare earth and
transition metal atoms added to alloys form a chemically ordered structure in the SF layers. The
origins of the formation of the compositional and structural modulations attract enormous interest in
the field of materials science. Our group has pointed out that the hcp solid solution of the Mg-Y-Zn
system shows a strong tendency to phase separation between the Mg-rich region and the Y- and
Zn-rich region [1,2]. This system has a typical LPSO structure. On the other hand, the Mg-Gd-Al
system shows the feature of so-called Order-Disorder (OD) structure; in which highly ordered Gd-Al
clusters appear in the stacking fault planes [3]. Thus in the present study, to investigate the
difference in the microstructures between these two alloys from the thermodynamic point of view,
the free energies of the hcp and fcc solid solutions in the Mg-Gd-Al system were calculated by
means of the cluster variation method, taking account of the accurate finite temperature effect of
atomic configuration.
Figure 1 (a) shows the contour lines for the spinodal decomposition temperatures of the hcp
phase in the Mg-Gd-Al system, being calculated from the second derivative of the free energies.
The spinodal decomposition region is limited in the vicinity of Mg-rich region, and maximum
temperature is around 800 K. Compared with the Mg-Y-Zn system, the temperature is slightly lower.
Furthermore phase separation behavior in this system seems rather week. On the contrary, the
spinodal decomposition temperatures of fcc phase are much higher than those of hcp phase, as
shown in Fig. 1 (b), and a clear phase separation behavior in the fcc phase is observed. On the
basis of the knowledge on the thermodynamic properties, we will discuss a difference in the
formation mechanism of the LPSO structures between the Mg-Y-Zn and Mg-Gd-Al systems.
[1] R. Masumoto, H. Ohtani, and M. Hasebe, J. Japan Inst. Metals, 73(2009) 683–690.
[2] S. Iikubo, S. Hamamoto, and H. Ohtani, Mater.Trans. 54(2013) 636-640.
[3] H. Yokobayashi et al., Acta Mater., 59 (2011) 7287-7299.
(a)
(b)
Figure 1 Spinodal temperature contours for (a) Mg-Gd-Al hcp phase, (b) Mg-Gd-Al fcc phase.
60
POS-21
Solidification Simulation of Microsegregation Based on the Scheil-Gulliver
Model in Mg97Zn1RE2 Alloys
T. Tokunaga1, H. Era1, S. Iikubo2, M. Enoki3 and H. Ohtani3
1
Department of Materials Science and Engineering, Kyushu Institute of Technology
1-1, Sensui-cho, Tobata-ku, Kitakyushu 804-8550, Japan
E-mail: [email protected]
2
Department of Biological Functions Engineering, Kyushu Institute of Technology
2-4, Hibikino, Wakamatsu-ku, Kitakyushu 808-0196, Japan
3
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University
2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan
The Mg97Zn1Y2 (at.%) alloy, developed by Kawamura et al.,[1] exhibits high strength and good
ductility at both room and high temperatures. These superior mechanical properties arise
principally from the formation of a new 18R-type long period stacking ordered (LPSO) structure
during solidification. The formation of LPSO structures in Mg97Zn1RE2 (RE: rare-earth metals) has
been comprehensively investigated and the criteria for REs for formation of LPSO structures were
proposed based on mixing enthalpy of the Mg-RE and Zn-RE binary systems, solid solubility of RE
in Mg, and the difference in atomic radius between Mg and RE.[2] Furthermore, Mg97Zn1RE2 alloys
are classified into two types according to if LPSO structure is formed in the as-cast state. For type I
alloys, the LPSO structure is formed during solidification, whereas for type II alloys, there is no
LPSO structure in the as-cast state, but the LPSO structure precipitates after annealing at high
temperatures.[2] The LPSO structures are observed mainly at the final solidification region, and
therefore, it is useful to obtain knowledge on the solute segregation behavior in Mg97Zn1RE2 alloys
to provide basic information for understanding of the formation mechanism of the LPSO structure.
In this study, the microsegregation behavior during solidification of various Mg97Zn1RE2 alloys has
been evaluated using the solidification simulation based on the Scheil-Gulliver model.
The solidification simulation was conducted using the Scheil module implemented in ThermoCalc software, and the thermodynamic parameters for Mg-Zn-RE ternary systems were taken from
literatures. It should be noted that the ternary thermodynamic parameters were not taken into
account in this simulation.
The simulations indicated that the enrichment of RE rather than Zn in the liquid phase was
predicted for the Mg97Zn1Y2 (type I) and Mg97Zn1Gd2 (type II) alloys, whereas the enrichment of Zn
rather than RE in the liquid phase took place for Mg97Zn1Nd2 alloy, which is classified as non-LPSO
alloys. From this result, it seems likely that the enrichment of RE whose radius is larger than that of
Mg in the final solidification region is a key role for the formation of the LPSO structures in
Mg97Zn1RE2 alloys.
References
[1] Y. Kawamura, K. Hayashi, A. Inoue and T. Masumoto: Mater. Trans. 42 (2001), 1172-1176.
[2] Y. Kawamura and M. Yamasaki: Mater. Trans. 48 (2007), 2986-2992.
61
POS-22
Cyclic Deformation Behaviors of HCP/FCC Laminated Structures
Yuichiro Koizumi1, Kotaro Sano1 and Akihiko Chiba1
1
Institute for Materials Research, Tohoku University,
2-1-1 Katahira, Sendai, Miyagi 980-8577, Japan
Fatigue is one of the most common fracture mechanisms of structural materials subjected to loads
repeatedly. It is of great importance to clarify the fatigue mechanism of Mg-based alloys with long
period stacking-ordered (LPSO) structures in order to avoid the unexpected failures of the alloys.
On the other hand, the fatigue mechanism of LPSO structure is of great scientific interest because
of the unique characteristics of plastic deformation mechanisms, which are arising mainly from the
dislocation slip strongly constrained to the basal plane on which the stacking of HCP-Mg layers and
FCC layers enriched with transition metal (TM) and rare-earth (RE) elements are formed. In this
presentation, the characteristics of cyclic deformation behaviors of alloys with HCP/ FCC laminated
structures are discussed as the basis for understanding the fatigue behavior of LPSO-Mg alloys.
In Co-Cr-Mo alloys, which are widely used for orthopedic implants, lamellar structure consisting
of FCC-metastable phase and HCP-stable phase stacked parallel to their {1 1 1} planes and (0 0 0
1) plane respectively are formed by strain induced martensitic transformation (Fig. 1) during cyclic
deformation [1]. Plastic strain under cyclic loading is localized into the HCP layer, and very steep
extrusions and intrusions which readily act as notches, are formed at the surface (Fig.2). Similar
localization of slip to the HCP layers may take place in LPSO Mg alloys deformed by shear
parallels to basal plane. However, quite different fatigue mechanism is also expected to operate
because the distance between HCP layers (i.e. thickness of FCC layer) is approximately 1 nm,
which allows dislocations in different HCP layers interact elastically, whereas the distance between
HCP-layers in Co-Cr-Mo alloy is larger than several nm (too large for dislocations to interact with
other dislocations across FCC-layers. Such dislocation-dislocation interaction may result in the
formation of fatigue dislocation structure unique to LPSO Mg alloy.
In Ti-Al alloy, which are used for jet engines, lamellar structure consisting of γ-TiAl phase with
L10-type FCC-based ordered structure and α2-Ti3Al phase with D019-type HCP-based structure is
formed. During cyclic deformation of lamellar Ti-Al alloy sheared parallel to the lamellar interfaces,
plastic strain is localize to the γ-TiAl FCC-based layer, and steep extrusions are formed in contrast
to the case of Co-Cr-Mo alloy. Cyclic loading parallel to lamellar interfaces results in slips not
parallel to the lamellar interface, deformation twinning in γ-TiAl phase, and prism slip in α2-Ti3Al
phase depending of the thickness of the lamellae which ranges from 10 nm to 1 μm. The thickness
of FCC-layers and HCP-layers in synchronized LPSO-Mg alloy are thinner than the lamellae
thickness of Ti-Al alloys by more than one order of magnitude, and quite different deformation
mechanism, i.e. kink deformation [3], operate.
Thus, it is suggested that unique fatigue mechanisms, crack initiation at surface relief formed by
kink deformation and/or strain localization in kinked area are expected to occur in LPSO-Mg alloy.
Fig.1 Schematic illustration of formation of HCP lamella
from metastable FCC matrix by strain induced
martensitic transformation (SIMT) in Co-Cr-Mo alloy.
Fig.2 Cross sectional TEM images
of HCP/FCC lamellae and surface
relief formed by cyclic deformation
of Co-Cr-Mo alloy.
References
[1] Mitsunobu T, Koizumi Y, Lee BS, Chiba A. Scripta Materialia 2014;74:52-55.
[2] Yasuda HY, Nakano T, Umakoshi Y. Philos Mag 1995;71:127-138.
[3] Hagihara K, Yokotani N, Umakoshi Y. Intermetallics 2010;18:267-276.
62
POS-23
Comparison of the phase equilibrium in the vicinity of LPSO phases
in Mg-Zn-Y and Mg-Al-Gd ternary systems
Seiji Miura1, Toshiaki Horiuchi2 and Satoshi Minamoto3
1
Faculty of Engineering, Hokkaido University, Kita-13, Nishi-8, Nishi-ku, Sapporo 060-8628, Japan,
[email protected]
2
Hokkaido University of Science, Sapporo, Japan
3
Science & Engineering Systems Division, ITOCHU Techno-Solutions Corporation, Tokyo, Japan,
It is widely accepted that the LPSO alloys can be classified into two types. Type I is an LPSO
phase formed during solidification, and type II is an LPSO phase formed by heat-treatment. Such
difference may affect not only on the degree of the order of the crystal structure but also on the
microstructure which has significant effect on the mechanical properties. Mg-Zn-Y alloy is former
one, while Mg-Al-Gd seems to be latter one. In this study the difference in the phase equilibrium
including LPSO phases in the Mg-Zn-Y and Mg-Al-Gd ternary systems is investigated. Several
LPSO phases in Mg-Zn-Y system equilibrate each other and also with alpha-Mg, Mg24Y5, Mg2Y, Iphase and a ternary Mg-Zn-Y phase. On the other hand, Al2Gd-related phase is the primary phase
during solidification in Mg-Al-Gd ternary system in a wide composition area. LPSO phase appears
after a heat treatment by the reaction between alpha-Mg and Mg3Gd phase.
63
POS-24
Local structural relaxations and interstitial sites in LPSO-Mg alloys
Kenya Yamashita, Daisuke Egusa* and Eiji Abe
Department of Materials Engineering, The University of Tokyo, Japan
*
Presently at UACJ Corporation
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan
LPSO(long period stacking/order) structures formed in Mg-TM(transition metal)-RE(rare earth
elements) alloys are long-period stacking derivatives of the hexagonal-close-packed Mg structure.
They have long-period chemical-ordered
structures along the stacking direction as well as
stacking order. The chemical order synchronizes with the stacking faults (SF) represented as a
AB’C’A stacking unit. TM/RE atoms distributes at these particular four layers and form local L12-type
clusters in the units [1]. In Mg-Zn-Y alloys, L12-type clusters relax significantly [1] and form a large
space at the center of the clusters. The occurrence of large space suggests the interstitial sites at
the center of the clusters.
In Mg-10 at. %Zn- 15 at. %Y alloys, highly
ordered 10H-type LPSO phase are discovered [2].
We investigate the details of the interstitial sites in
the L12-type clusters in the 10H-type LPSO
structures based on scanning electron microscopy
observations and first principles calculations.
Figure 1a shows 10H-type LPSO structure
formed in Mg-Zn-Y alloy. The clusters are shown
clearly and arranged at a high degree of order.
Figure 1b shows the averaged image of the
clusters. A dark spot is clearly seen in the averaged
image, indicating the existence of the interstitial site.
The intensity analysis with the aid of STEM image
Fig1 ABF-STEM image of a:10H-LPSO structure
simulations shows that the interstitial sites are
and b: averaged L12-type cluster
almost fully occupied by Mg atoms.
References
[1] D. Egusa and E. Abe, Acta Materialia 60 (2012) 166–178
[2] M.Yamasaki et al. Scr. Mater. 78-79(2014) 13-16
64
POS-25
Effect of Atomic Radius of Solute Elements on Local Strain Field of LPSO
S. Matsunaga1, Y. Yamaguchi1, S. Tashiro1, T. Kiguchi2, K.Sato2
and T.J. Konno2
1
Depertment of Materials Science, Tohoku University
6-6, Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan
2
Institute for Materials Research (IMR), Tohoku University
2-1-1, Katahira, Aoba-ku, Sendai, 980-8577, Japan e-mail: [email protected]
Synchronized long-period stacking ordered structure (LPSO) in Mg-TM-RE alloys (where “TM”
and “RE” denote transition metal and rare earth elements, respectively) is well known for giving
high mechanical properties [1]. As for the formation mechanism of LPSO, many researchers have
examined the atomic-level structural characterization, however, unresolved issues still remains. We
focused on local strain field accompanied with LPSO, and previously revealed that normal strain
field is formed in c-axial direction in LPSO [2]. On the other hand, Egusa et al. revealed that
distorted L12 type Zn6Y8 clusters shrink in enriched layer using a first-principle calculation [3],
however, the relationship between normal strain and cluster formation is not clarified. Then, we
have elucidated the relationship between normal strain and the cluster formation in the light of the
species of enriched elements.
Fig.1 (a) shows a Bragg-filtered HAADF-STEM image taken in an LPSO region of Mg-TM-RE
(left) and an analyzed normal strain map obtained from the image using Peak Pairs Analysis (PPA)
(right) [4]. Fig.1 (b) shows the normal strain, i.e. contraction of the spacing of basal planes of the
enriched layers in Mg-Zn-Y compared with that of the non-enriched layers. The normal strains in
the normal direction of the basal plane of the enriched layers in Mg-Zn-Y and Mg-Zn-Gd are almost
same. On the other hand, the strain in Mg-Zn-Er and Mg-Ni-Y are 3% and 5% are larger than those
of Mg-Zn-Y and Mg-Zn-Y, respectively. This result indicates that differences of atomic sizes affect
the normal strain through the shrinks of the L12 cluster.
Fig.1 (c) shows a structural model of L12-type clusters in Mg matrix after a structural relaxation.
As a result of the relaxation using VASP code, there were differences of c-axis direction shrinkage
depending on solute element pairs. There was little difference of shrinkage between Zn-Y and ZnGd, however, there were much larger shrinkages in Zn-Er or Ni-Y pairs. Fig.1 (d) shows the
correlation between normal strain or structural relaxation and average atomic sizes of solute
element pairs. The values of the strain analysis and relaxation are coincident owing to the rough
approximation; however, the tendency is consistent: small average atomic sizes cause large strain
and relaxation. In other words, atomic size differences between Mg and enriched elements affect
the shrinkages of TM6RE8 clusters, and consequently, it causes each of normal strain which
depends on the species of TM-RE pairs.
References
[1] Y. Kawamura, K. Hayashi, A. Inoue and T. Masumoto: Mater. Trans, 42, 1172 (2001).
[2] T. Kiguchi, Y. Ninomiya, K. Shimmi, K. Sato and T.J. Konno: Mater. Trans. 54, 668 (2013).
[3] D. Egusa and E. Abe: Acta Mater. 60, 166 (2012).
[4] P. Galindo, S. Kret, A.M. Sanchez, J-Y. Laval, A. Yanez, J. Pizzaro, E. Guerrero, T. Ben and S.I.
Molina: Ultramicroscopy 107, 1186 (2007).
Fig.1 (a) HAADF-STEM image of a part of LPSO and
normal strain map (b) Profile of normal strain map
(c) Structural model of L12 clusters in Mg after relaxation
(d) Relation between strain and average atomic sizes.
65
POS-26
A First-principles Study of Interaction between Solute-enriched Layers of
Mg-based LPSO Structures
Daisuke MATSUNAKA1,2, and Yoji SHIBUTANI1,2
1
Department of Mechanical Engineering, Osaka University, JAPAN
Center for Atomic and Molecular Technologies, Osaka University, JAPAN
2-1 Yamadaoka, Suita, Osaka 565-0871, JAPAN [email protected]
2
Recently, Mg alloys have been attracting attention because of its light weight. In particular, MgM-RE alloys (M: main group or transition metal, RE: rare earth) with long-period stacking ordered
(LPSO) phases show excellent mechanical performances such as high yield strength and ductility,
which are considered to be caused by the LPSO structures. The LPSO structures consist of the
periodical arrangement of basal stacking faults (SFs) and the enrichment of solute atoms in the
vicinity of SFs. HAADF-STEM measurements observed that the L12-type clusters of solute atoms
are formed and aligned at each SF [1]. A recent theoretical study evaluated the binding energy of
solute atoms to SF and the solute-solute pair interaction in Mg based on first-principles calculations
and showed that these potentials for solute atoms can describe the formation of the L12 clusters [2].
However, the physical origin of the periodical arrangement of the solute-enriched layers with the
L12 clusters still remains controversial.
To investigate interaction between the neighboring solute-enriched layers, we evaluate the
formation energies of the L12 cluster in the LPSO structures with the various periods and positions
of stacking of the solute-enriched layers, using first-principles calculations. The formation energy
per L12 cluster in the LPSO structures is defined as
TOT
f
𝐸𝐸L1
= �𝐸𝐸LPSO
− 𝑁𝑁Mg 𝜇𝜇Mg − 𝑁𝑁M 𝜖𝜖M − 𝑁𝑁RE 𝜖𝜖RE �/𝑁𝑁L12
2
Formation energy (eV)
where 𝑁𝑁(Mg,M,RE) and 𝑁𝑁L12 are the numbers of Mg, solute atoms, and the L12 cluster in the cell,
respectively. 𝜇𝜇Mg is the energy per atom for hcp Mg, and ϵ(M,RE) is the energy per each solute atom
in Mg matrix, which was obtained by subtracting 35𝜇𝜇Mg from the total energy for the model of one
substituted atom (M, RE) and 35 Mg atoms. The models used in this study adopt the in-plane
arrangement of the L12 clusters in the 2√3 × 2√3 hexagonal supercell. Fig. 1(a) shows the
formation energies of the L12 cluster in the 10H, 18R, 14H and 24R LPSO structures of the Mg-AlGd system. Figure 1(b) represents the stacking positions of the L12 clusters between the
neighboring solute-enriched layers. The obtained formation energy tends to increase as the
distance of the solute-enriched layers decreases. On the other hand, for 10H, the formation energy
is lowest at the A0 stacking position where the clusters of the neighboring solute-enriched layers
are close to each other. The dependence of the formation energy on the stacking position is less
for the other structures with the larger distance of the solute-enriched layers.
-4
-4.1
-4.2
-4.3
-4.4
-4.5
-4.6
-4.7
-4.8
10H
18R
14H
24R
A3
A2
A1
A0
C0 C2
C1
A1
A0 A2
A3
C0C1C2
(a)
(b)
Figure 1 (a) The formation energy of the L12 cluster in various structures of the Mg-Al-Gd system
and (b) the stacking positions between the neighboring solute-enriched layers.
[1] H. Yokobayashi et al., Acta Mater. 59, 7287 (2011).
[2] H. Kimizuka and S. Ogata，Mater. Res. Lett. 1, 213 (2013).
66
POS-27
Interaction between lattice defects in Mg crystal:
ab initio local energy analysis
Yoshinori Shiihara1, and Masanori Kohyama2
1
Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba,
Meguro-ku, Tokyo 153-8505, JAPAN.
2
Research Institute for Ubiquitous Energy Devices (UBIQEN),
AIST, 1-8-31, Midorigaoka, Ikeda, Osaka 563-8577, JAPAN.
Long-Period-Stacking-Order (LPSO) structure observed in Mg alloys such as a Mg-Y-Zn alloy has
been considered to give prominent mechanical properties, e.g. high ductility, to those alloys. The
unique microstructural feature of the Mg alloys is that solute rare-earth and transition-metal atoms
are segregated into the stacking faults of their LPSO structure. Since the stability of the
microstructure stems from the atomic-scale interactions between the stacking faults and the solute
atoms, understanding how these lattice defects interact each other should be useful to deeply
investigate the stability and the origin of the LPSO structure.
Ab initio calculations based on the density functional theory has been often utilized to discuss the
stability of an atomic configuration with lattice defects through its defect energetics, e.g., stacking
fault energy, defect formation energy, segregation energy, etc. Ab initio local energy analysis
recently developed [1-3] allows one to reveal the distribution of the defect energies localized in the
vicinity of lattice defects. The analysis can provide a deep insight into the defect energetics through
a direct comparison of the local energy distribution and another local quantity given by the ab initio
method such as electron density or partial density of states. The aim of this study is to examine the
availability of the local energy analysis for the interaction of the lattice defects inside the LPSO
structures in order to reveal the interaction between the lattice defects inside the Mg matrix. As the
simplest fundamental case of such simulations, we performed the local energy analysis on several
Mg polytypes. The obtained results show that the energetic interaction between two stacking faults
is negligible small and that the distribution of the fault energies can be expressed by the
superposition of the fault energy distributions of I1. In the poster presentation, we will show the
local energy distribution in the Mg polytypes with a solute atom and discuss the interaction between
a stacking fault and solute atoms.
Reference
[1]
M. Yu, D.R. Trinkle, R.M. Martin, Phys. Rev. B 83 (2011) 115113.
[2]
S.K. Bhattacharya, S. Tanaka, Y. Shiihara, M. Kohyama, J. Phys. Condens. Matter 25
(2013) 135004.
[2]
H. Wang, M. Kohyama, S. Tanaka, Y. Shiihara, J. Phys. Condens. Matter 25 (2013)
305006.
67
POS-28
Deformation and fracture behavior of long period stacking-orderd structure
phase in Mg-Zn-Y alloy
R. Maezono1, Y. Mine1, M. Yamasaki2, Y. Kawamura2, K. Takashima1
1
Department of Materials Science and Engineering, Kumamoto University Kurokami, Chuo-ku,
Kumamoto 860-8555, Japan
2
Magnesium Reserch Center, Kumamoto University Kurokami, Chuo-ku, Kumamoto 860-8555,
Japan
[email protected]
Mg-Zn-Y alloys exhibit superior mechanical properties as compared to conventional Mg alloys.
These excellent properties are attributed to the existence of a long period stacking ordered (LPSO)
structure phase in Mg-Zn-Y alloys. For practical application of these alloys, it is important to
examine the deformation and fracture mechanisms of the LPSO phase. In this study, the
deformation and fracture behavior of LPSO single crystals were investigated at room temperature
using microscale testing techniques.
The material used was a directionally solidified (DS) Mg85Zn6Y9 alloy with an LPSO single phase.
The grain size of the LPSO phase was approximately 200 µm. The orientation of the LPSO grains
was determined by electron backscatter diffraction (EBSD) analysis, and microsized cantilever
beam specimens [50 µm (L) × 10 µm (W) × 20 µm (B)] were fabricated by focused ion beam (FIB)
machining from a single LPSO grain. Two types of specimens with different beam orientations were
prepared. In the <a> specimen, the beam direction was close to [11-20] and the side surface was
close to (0001), whereas in the <c> specimen, the beam direction was parallel to [0001] and the
side surface was (10-10). Notched specimens were also prepared for each specimen in order to
investigate the fracture behavior. The notch plane was close to (10-10) and the notch direction was
cloce to [11-20] for the <a> specimen. For the <c> specimen, the notch plane was (0001) and the
notch direction was [11-20]. The notches were also introduced by FIB machining and the notch
depth to width ratio (a/W) was set to be ~0.5 for each specimen. Microbending tests were carried
out using a mechanical testing machine for microsized specimens, which was developed in our
laboratory.
The <a> specimen exhibited ductile deformation behavior. Many traces were found on the tensile
part of the fixed end of the specimen, and these traces were confirmed to be prismatic slips from
SEM and EBSD observations. The critical resolved shear stress (CRSS) for prismatic slip was
calculated to be 443 MPa. In the load-displacement curve of the <c> specimen, several load drops
were observed repeatedly. SEM and EBSD observations revealed the activation of basal slip on
the tensile part of the fixed end of the specimen. The CRSS of basal slip was calculated to be 18
MPa, and this value is close to those obtained from previous research. In addition, the activation of
a {11-29} twin was also suggested near the fixed end.
The fracture behavior was examined using notched specimens. In the notched <a> specimen, the
1/2
fracture occurred in a brittle manner, and the fracture toughness (KQ) value was 2.2 MPa m . A
step-like fracture surface was observed, and these steps were deduced to be related to the
separation of prismatic planes. On the other hand, plastic deformation occurred at around the notch
tip for the notched <c> specimen. SEM and EBSD observation suggest that (0001) basal slips were
activated at the notch tip. The above results suggest that the LPSO phase exhibits large anisotropy
both for deformation and fracture behavior.
68
POS-29
Stress Analysis of Ridge-Shaped Kink Structure in Mg Alloy with LPSO
Structure based on Linear Elasticity
Xiao-Wen LEI1, Akihiro NAKATANI2
1
Department of Adaptive Machine systems, Osaka University, 2-1 Yamadaoka, Suita, Osaka
565-0871, Japan
2
Department of Adaptive Machine systems, Osaka University, 2-1 Yamadaoka, Suita, Osaka
565-0871, Japan. [email protected]
Key words: Ridge-Shaped Kink Structure, Dislocation, Dislocation, Configurational Force
1. Introduction
Kink deformation bands appearing in compressed specimens of Mg alloy with long-period
stacking ordered structure (LPSO) are thought to contribute to improving their mechanical
properties. Ridge-shaped kink structure is a kind of kink deformation bands that have been
(1, 2)
. Both nucleation and growth of the structure, however,
observed commonly in the LPSO alloy
have not sufficiently clarified yet. In this paper, the stress field of ridge-shaped kink structure is
analyzed by using a lattice defect theory based on linear elasticity to obtain some important
knowledge from a viewpoint of mechanics. The singular field of stress components in the vicinity of
the tip of the ridge, the relationship between strain energy and ridge angle, and the stress
distribution around the ridge-shaped kink structure are discussed in detail.
2. Properties of ridge-shaped kink structure on linear elasticity
The ridge-shaped kink structure can be modelled as a set of continuously distributed dislocations
(3)
on the basal planes . We can prove that this structure is mechanically equivalent to the
combination of dipoles of disclinations and Somigliana dislocations. Figure 1 shows the analytical
solutions of the singular field of the stress components near the tip of ridge structure in infinite body.
According to an asymptotic analysis, logarithmic singularity appears in the vicinity of the tip. The
normal components, σxx (σ11) and σyy (σ22), changes gradually, while the shear component, τxy (σ12),
converges to a constant. Figure 2 shows the distribution of stress components in a simply-supported
rectangular specimen, in which the solution is obtained by the superposition of both an analytical
solution of infinite body and the finite element solution of the supplementary problem with the
appropriate boundary conditions. Figure 3 shows the variety of strain energy as a function of the
ridge angle. The function is a quadratic function that monotonically increases. We can estimate the
configurational force for the growth of ridge-shaped kink structure as the differential of the function.
Fig.1 Singular field of stress near
Fig.2 Stress distribution around
the tip of ridge-shaped kink structure the ridge-shaped kink structure
Fig.3 Strain energy as a
function of ridge angle
Acknowledgment
This work was supported by a Grant-in-Aid for Scientific Research on Innovative Areas,
"Synchronized Long-Period Stacking Ordered Structure", from the Ministry of Education, Science,
Sport and Culture, Japan.
References
[1] Y. Kawamura, K. Hayashi, A. Inoue, T. Masumoto. Materials Transactions, 42 (2001) 1172.
[2] K. Hagihara, N. Yokotani, Y. Umakoshi. Intermetallics. 18 (2010) 267–276
[2] A. E. Romanov, V. I. Vladimirov. Disclinations in Crystalline Solids, in F. R. N. Nabarro (eds.).
Dislocation in Solids. 9 (1992) 191-402.
69
POS-30
High-temperature creep deformation mechanism of Mg88-Zn5-Y7 extruded alloy
Hidenari Takagi1 and Masami Fujiwara1, 2
1
Division of Applied Physics, College of Engineering, Nihon University, Fukushima 963-8642, Japan
2
[email protected]
70
Indenter Displacement
p 2 / p1
Pressure Ratio, r = ( p2 / p1 ) t 0 → 0
Introduction: An extruded magnesium alloy composed of an α-Mg matrix phase and a long-period
stacking-ordered (LPSO) phase has recently attracted significant interest because of its mechanical
properties that are superior to those of commercial wrought magnesium alloys, such as excellent
strength and ductility. The LPSO phase indisputably plays a key role in determining the
high-temperature deformation of this dual-phase alloy. In the present study, the creep characteristics
of an LPSO single-phase alloy were investigated using the instrumented indentation testing
technique, and the creep mechanism of this alloy is discussed on the basis of experimental results.
Experimental procedures: A Mg88-Zn5-Y7 (mol%) ingot, which was composed almost only of the
LPSO phase, was extruded at a temperature of 723 K with an extrusion ratio of 10. After annealing
at 373 K for 21.6 ks in an argon atmosphere, indentation creep tests were carried out at
temperatures of 573–673 K (0.70Tm - 0.82Tm, Tm: absolute melting point).
Results and discussion: (1) The relationship between the indentation creep rate and indentation
pressure can be expressed by a constitutive equation for power-law creep. Here, the stress
exponent is 5.1, and the activation energy for creep is Qc = 314 kJ/mol. Referring to the literature,
the activation energy for the self-diffusion of Mg is 135 kJ/mol, while the corresponding value for Zn
solute atoms in the Mg matrix phase is 120 kJ/mol. Further, the energy required to fully constrict an
a-type screw dislocation extended on the basal plane of Mg can be estimated to be 570 kJ/mol.
Clearly, the above-mentioned Qc value lies between these values. (2) TEM observation results for
the deformed LPSO phase show that numerous a-type dislocations glide on the basal planes and
often cross-slip onto the non-basal planes. In fact, other researchers have reported that the a-type
dislocations extend on the basal plane of the LPSO phase. (3) Deformation behaviors right after
rapid load reduction during indentation creep tests were investigated at temperatures of 573–673 K.
It was found that when the indentation pressure is reduced from p1 to p2, as shown in the inset of
Figure 1, creep continues again after a stopping time t0 (corresponding to the recovery period) that
follows the instantaneous specimen spring-back. The ratio p2/p1 for t0 → 0 can be derived by
extrapolating these experimental data. The obtained p2 value is known to be proportional to the
average internal stress that opposes the dislocation movement prior to the sudden change in load.
Figure 1 shows that the ratio of the internal
1.00
stress σi and applied stress σa is
maintained at an almost constant value of
0.85 at temperatures of 623–673 K. This
0.95
finding indicates that effective stress (σe =
σa - σi) corresponding to 15% σa exists,
0.90 1.0
which causes dislocation cross-slip during
Indentation Time
high-temperature creep. (4) All the
above-mentioned experimental results
0.85
suggest that extended dislocations glide on
the basal planes in free-flight motion.
0.6
20
0
t0
0.80
Further, they are stopped by some obstacle
550
600
650
700
and are then constricted temporarily by a
Test Temperature, T / K
mechanically and thermally activated
Fig. 1 Temperature dependence of the ratio of
process, thereby leading to cross-slipping
internal stress and applied stress
onto the non-basal planes.
POS-31
First Principles Calculations for LPSO formation scenarios
Shigeto R. Nishitani, Yosuke Yamamoto, Yuichi Sakamoto, and Yoshihiro
Masaki
Department of Informatics, Kwansei Gakuin University, Gakuen 2-1, Sanda, 669-1337, Japan,
[email protected]
The formation mechanism of the long period stacking ordered (LPSO) structure is still under
discussion. The players on the stage are two: the stacking faults (SF) and the solute atoms. Two
simple scenarios are immediately derived: 1) periodic stacking faults are first induced and then the
solute atoms are concentrated around each SF layer, or 2) middle range solute ordering is first
occurred and then the stacking faults are induced. The aim of this research is checking the
scenario by the energy assessments using the first principles calculations.
The first principles calculations have been
performed with VASP(Vienna Ab initio
Simulation package) for the Mg-Zn-Y
system.
For investigating the solute
orderings, many configurations have been
checked. For the interactions of solutesolute atoms, pair-pair solutes, or SFsolute atoms, the energy changes are very
small or attracting the solute atoms each
other. The large energy contribution is
only observed in the model for the
interaction between clusters and solute
atoms. When we changed the distance
between the L12 cluster and the Zn atoms,
the energy decreased monotonously in Fig.1 Energy changes on the inter-distance between
the range of 0.2 eV as shown in Fig.1.
L12 cluster and Zn atom. Schematic configuration of
them is shown in the inset. Note that four lines
The other critical change is observed in
represent the different equivalent sites but deviations
the solute atoms effect on the SF
are small.
energies. Two blocks below and above
the SF were sliding each other as
schematically drawn in the inset of Fig.2.
The energy changes during the sliding
with and without Zn and Y atom pair are
compared. The activation energy of the
stacking fault formation with Zn and Y
added model shows the one third of that
without Zn and Y as shown in Fig.2.
After the first principles energy
assessment, we have a new scenario
for the LPSO formation: 1) a SF attract
the solute atoms and make L12 clusters,
2) additional solute atoms are swept out
and condensing at a few layers off from
the SF, and 3) this condensation makes
other SFs induced easily.
Fig.2 Energy changes on the displacement along [1
-1 0 0], where solid and dotted lines represent with
and without solute pair respectively. Note that the
energies at x=1.0 mean the SF energy, and at
around x=0.5 mean the activation energy of SF.
71
POS-32
Composition dependence of the LPSO poly-types formed in Mg-Ni-Y alloy
Takaomi Itoi1*, Ryosuke Masui1 and Shinji Arakawa1
1
Department of Mechanical engineering, Chiba University, Chiba 263-8522, Chiba.
*Corresponding e-mail address: [email protected].
Mg alloy is expected as a structural material for excellent lightness. In particular, Mg alloy
with long period stacking ordered phase can be expected as excellent mechanical property. It is
known that the LPSO phase is forms in Mg-TM (transition metals) -RE (Rare earth metals) systems
as stable phase. [1-3]
Therefore, Mg alloy with LPSO phase was developed using a conventional method, cast,
extrude, or rolling and they showed excellent mechanical properties. During a development of high
strength Mg alloy, the LPSO structure with several poly-types (10H, 18R, 14H and 24R) were
observed in these alloy systems.[4,5] Because the LPSO poly-type are constructed by periodical
Mg atomic layers between TM6RE8 clusters, we suggested that composition dependence of these
poly-types brings significant knowledge for structural origin of the LPSO structure. [6,7]
Furthermore, LPSO single phase could be expected excellent mechanical properties at high
temperature range. However, the composition range is not clear at present.
In present study, we have prepared LPSO poly-types in the Mg-Ni-Y alloy. The Mg-Ni-Y
alloy ingots were prepared by electric furnace in Co2 atmosphere. Microstructure was investigated
by SEM and TEM.
The LPSO phase was observed in the Mg97Ni1Y2 (at.%) alloy. The Mg97Ni1Y2 alloy was
consisted of Mg and LPSO phase, and estimated area-fraction of the LPSO phase was about 24 %.
From electron diffraction pattern of the LPSO phase showed 18R-type LPSO structure. Areafraction of LPSO phase was increased with increasing of solute elements content. The Mg85Ni6Y9
(at.%) alloy consisted of 18R- and 10H- type LPSO structures in as-cast state.
A 12R-type LPSO structure was observed in the Mg79Ni9Y12 (at.%) alloy which was
increasing solute concentration. Thus, composition dependence of LPSO poly-types was
recognized in the Mg-Ni-Y alloy system.
[1] Y. Kawamura, K. Hayashi, A. Inoue, T. Masumoto, Material Trans., JIM 42 (2001) 1172.
[2] Y. Kawamura, T. Kasahara, S. Izumi, M. Yamasaki, Scripta Materialia 55 (2006) 453.
[3] T.itoi,
[4] T. Itoi, T. Seimiya, Y. Kawamura, M. Hirohashi, Scripta Materialia 51 (2004) 107.
[5] M. Matsuda, S. Ii, Y. Kawamura, Y. Ikuhara, M. Nishida, Mater. Sci. and Eng 386 (2004) 447.
[6] H. Yokobayashi, K. Kishida, H. Inui, Y. Yamasaki, Y. Kawamura, Acta Materialia 59 (2011) 7287.
[7] D. Egusa, E. Abe, Acta Materialia 60 (2012) 166.
72
POS-33
A molecular dynamics study on the structure and formation mechanisms
of non-basal dislocations in magnesium
Hideo Kaburaki1, Mitsuhiro Itakura2 and Masatake Yamaguchi3
1
CCSE,Japan Atomic Energy Agency, 2-4 Shirakta-Shirane, Tokai, Ibaraki, Japan
[email protected]
2
CCSE,Japan Atomic Energy Agency, 5-1-5 Kashiwanoha, Kashiwa, Chiba, Japan
3
CCSE,Japan Atomic Energy Agency, 2-4 Shirakta-Shirane, Tokai, Ibaraki, Japan
The generation of non-basal dislocations, such as c+a dislocations, near the c-axis direction is the
key to inducing the widespread plasticity in highly anisotropic hcp magnesium. In particular,
dislocation structures near the deformed kink bands have been in attention in the deformation
processes of LPSO-Mg alloys. Using the molecular dynamics method, we have studied the
formation process of c+a screw and edge dislocations from the perfect dislocation state, in
particular, focusing on the temperature dependent properties of the splitting process. We also
studied interaction processes of the a screw dislocation and the c dislocation for the formation of a
c+a dislocation. Here, we employed various forms of c dislocations, such as straight and loop
dislocations. In the case of the c edge dislocation loops, we confirmed that various forms of
polyhedra appeared due to the splitting process. In this process, we applied the shear stress for the
a screw dislocation to cross-slip in the c-direction to interact with the c dislocation. The effects of
temperatures up to 500K and the strain rates have been assessed in relation to the final structure
of the formed dislocation. Behavior of dislocations near the kink will also be discussed in the
presentation.
73
POS-34
Description of Disclination Density in Mg-based LPSO Phase
Using a Crystal Plasticity Cosserat Model
Sotaro Tajiri1 and Kazuyuki Shizawa2
1
Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku,
Yokohama -shi, Kanagawa-ken, 223-8522, Japan, [email protected]
2
Department of Mechanical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku-ku,
Yokohama-shi, Kanagawa-ken, 223-8522, Japan, [email protected]
In this study, a new model which can describe a kinking in LPSO phase due to disclination is
developed. A disclination model is known as a useful tool to show the kink bands with the
misorientation in the crystal lattice. The mathematical model of disclination density has been
proposed by deWit[1], and a work by Fressengeas[2] is often cited as an example of applying
disclination density to the numerical simulation of the continua. Since information of the curvature is
required for material points in disclination theory, the model should be constructed on the basis of
the concept of Cosserat continua. We adopt a model called the couple stress theory among the
Cosserat models. In addition, since the crystal plasticity theory which can handle information of
crystal orientations is a useful method in the computational simulation for meso-scale deformations
of the metallic materials, the Cosserat model is newly developed in the present study to be
consistent with the crystal plasticity theory.
Assuming that a quantity characterizing the elementary process of rotational plastic deformation is
the disclination angle, the kinematics for crystal plasticity Cosserat model is described. The
disclination density tensor is also defined in this kinematics. The elasto-viscoplastic constitutive
equation for couple stress is derived by a thermodynamic approach and the argument used in the
hardening rule of couple stress is examined. However, it is unknown how the disclination density
contributes to the material hardening. Therefore, we adopt a linear hardening rule for simplicity in
the present analysis.
Using this model, a two-dimensional FE analysis for a single crystal plate of Mg based LPSO
phase is performed. In the framework of Cosserat theory, an intrinsic length is introduced as the
length scale, and the size is set to 1/10 of the element size in this analysis. The disclination density
distribution obtained by the present computations is shown in Fig.1. It can be seen from Fig.1 that
areas with high disclination density appear within or in vicinity of the kink band. Thus, it can be
considered that the kink band formation is explained by disclination density approach.
5000 µm −2
d(α )
θ wedge
−5000 µm −2
Fig.1 Wedge disclination density on basal slip system (U/L = 1.00%)
References
[1] R. deWit, J. Res. Nat. Bur. Stand., 77A - 1, 49(1973).
[2] C. Fressengeas, V. Taupin and L. Capolungo, Int. J. Sol. Struc., 48, 3499(2011).
74
POS-35
Study of local structures of Zn/Y layers in LPSO Mg alloys
by X-ray fluorescence holography
Kouichi Hayashi1, Koji Hagihara2, Hitoshi Izuno2, Naohisa Happo3,
and Shinya Hosokawa4
1
Institute of Materials Research, Tohoku University, Sendai 980-8577, Japan
[email protected]
2
School/Graduate School of Engineering Osaka University, Osaka 565-0871, Japan
3
Graduate School of Information Sciences, Hiroshima City University, Hiroshima 731-3194, Japan
4
Graduate School of Science and Technology, Kumamoto University, Kumamoto 860-8555, Japan
Zn/Y layer
X-ray fluorescence holography (XFH)1) is a relatively new local structural analysis method,
which can determine atomic arrangements around a specific element without any prior knowledge
of structures. It can directly reconstruct 3D atomic images using Fourier transformation. We
consider that XFH is a third method of structural analysis at the atomic level after X-ray diffraction
(XRD) and X-ray absorption fine structure (XAFS). As known by many researchers, XRD and
XAFS are established methods that are widespread use in various fields. XRD and XAFS provide
information on long-range translational periodicities and very local environments, respectively,
whereas XFH gives 3D information on the local order and can visualize surrounding atoms with a
large range of coordination shells.
Finding novel nanometer clusters is one of the major advantages of XFH. For example, in
2009, we studied the phase transition behavior of Ti50Ni44Fe6 single crystal, a shape-memory-alloy
related material. This material exhibits parent (P), incommensurate (IC), and commensurate (C)
phases when the temperature is decreased to below room temperature. While the atoms in
Ti50Ni44Fe6 are distributed homogeneously in the P-phase, they formed cluster-like structures with a
radius of 8 Å in the C-phase, where the motion of the atoms inside the clusters is frozen. This is
valuable information for understanding the phonon softening at the phase transition.2)
In addition to the feature of “3D medium-range local structure observation”, XFH is very
sensitive to the displacement of atoms from their ideal positions, and one can obtain quantitative
information about local lattice distortions by analyzing reconstructed atomic images.3) When
dopants with different atomic radii from the matrix elements are present, the lattices around the
dopants are distorted. However, using the conventional methods of structural analysis, one cannot
determine the extent to which the local lattice
Zn hologram
distortions are preserved from the dopants. XFH is
Ｙ hologram
a good tool for solving this problem.
In our study of LPSO Mg alloys, we will
investigate the environmental structures around Zn
and Y in LPSO Mg alloys by measuring Zn K and Y
K XFH holograms. (Fig.1) Maximum sizes of LPSO
3
domains are limited to ~2000 x 500 x 100 µm .
However, our current XFH setup cannot measure
such small samples. To realize the XFH
experiments of the LPSO Mg alloys, we must
improve our apparatus by installing an X-ray
Mg
Zn
Y
focusing optics and fine stage. First experiment will
be carried out in early July. We will present some
Fig.1 Concept of measurements of Zn K and
data of this experiment in the conference.
Y K XFH holograms.
1) K. Hayashi, et al. J. Phys.: Condens. Matter 24,
093201 (2012).
2) W. Hu, et al. Phys. Rev. B 80, 060202(R) (2009)
3) S. Hosokawa, et al. Phys. Rev. B 87, 094104 (2013).
75
POS-36
Phase-field modeling for understanding
the formation mechanism of LPSO phase
T.Koyama and Y.Tsukada
Department of Materials Science and Engineering, Nagoya Institute of Technology,
Gokiso-cho, Showa-ku, Nagoya 466-8555, JAPAN
e-mail address: [email protected]
It is known that the long-period stacking ordered (LPSO) structure in Mg-Y-Re (Re the rare-earth
elements) alloys establishes the excellent mechanical properties among Mg-based light metals.
The LPSO phase has unique phase formation process, i.e. the displacive structural phase
transition accompanies the diffusional phase transformation, where the solute rich nano-cluster is
formed inside the LPSO structure. Although the structural details of LPSO phase have recently
been made clear through several advanced experimental methods, the formation mechanism of
LPSO structure has not been explained sufficiently. In this study, two types of the models: (1)
mesoscopic model and (2) nano-cluster model, which explain the formation process of LPSO
structure, are demonstrated based on the framework of phase-field method.
Both the stacking fault formation by dislocation movement and the diffusion-controlled phase
decomposition are simultaneously considered in the "mesoscopic model" on the ternary alloy
systems Mg-X1-X2 (X1=Gd,Ho; X2=Zn,Al). On the other hand, in the "nano-cluster model", we
assumed the formation process of LPSO phase to be a uniform nano-structure formation
constructed by the strongly-interacting fcc-type nano-clusters.
Due to limitations of space, henceforth we explain the result of nano-cluster model only. Figure 1
shows the two-dimensional model simulation of LPSO phase formation calculated on the side
plane of hcp structure (c-axis is vertical direction). Blue, black and red parts indicate hcp region,
solute-rich hcp cluster and solute-rich fcc cluster, respectively. The repulsive chemical interaction
and the long-range elastic interaction are considered among nano-clusters. Figure (a) is an initial
setting of microstructure, i.e. the nano-cluster nucleus array is located at the center part. Note that
the nano-cluster microstructure gradually expands vertically because we don't introduce the
composition fluctuation in the initial microstructure (a). It is interesting that nano-clusters align
automatically because of the strong interaction among nano-clusters. Since the Gibbs energy of fcc
nano-cluster is lower than that of hcp one, the structural phase transition of nano-cluster from hcp
(black part) to fcc (red part) is reasonable. However, the hcp region between nano-clusters also
transforms to fcc, which is difficult to explain from the consideration of Gibbs energy. It should be
emphasized that the mathematical
model of this simulation is quite similar
to the model which has been developed
in the field of microstructure formation of
block-copolymer. According to the
category of phase transformations, the
microstructure formation on blockcopolymer is classified into an orderdisorder phase transition. As the
molecule size of polymer is large, the
phase formation process on blockcopolymer has usually been modeled by
the microstructure simulation technique.
Since LPSO structure has large unit cell,
it may be reasonable that the formation
Fig.1 Two-dimensional model simulation of LPSO phase
mechanism of LPSO phase is described
formation at 573K. (a) t’=0, (b) t’=3, (c) t’=5, (d) t’=7,
by using the model of polymer science.
(e) t’=10, (f) t’=12, (g) t’=14 and (h) t’=17.
Acknowledgment: This work was supported by a Grant-in-Aid for Scientific Research on Innovative
Areas: “Materials science on synchronized LPSO structure (Grant Number 23109001)”.
76
POS-37
A Dislocation-based Crystal Plasticity FE Analysis
for a Single Crystal and Polycrystal of a Mg-based LPSO Phase
Ryo UETA1, Keiko IKEDA2 and Kazuyuki SHIZAWA3
1
Graduate School of Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohoku-ku,
2
3
In this study, a finite element analysis based on a dislocation-based crystal plasticity model is
performed to investigate deformation and hardening mechanisms of a Mg-based LPSO phase. A
crystalline structure of the LPSO phase is regarded as that of a HCP crystal for simplicity and we
do not consider any activities of deformation twins because it is unclear whether they occur in the
LPSO phase. Critical resolved shear stresses of the active slip systems in the LPSO phase are set
to be consistent with experimental results.
We carry out FE analyses for a single crystal of the LPSO phase with various initial crystal
orientations. Figure 1 (a) and (b) show the distribution of a geometrically necessary (GN)
dislocation density on a predominant basal slip system which is tilted initially at the angle of 3° with
respect to the compression axis and the distribution of rotation angle due to the basal slip after 5%
compression, respectively. A kink band is formed at the lower part of the specimen and the
negative and positive signs of the GN dislocations are accumulated mostly on the upper and lower
boundaries of the kink band, respectively. In addition, the crystal lattice in the kink band is
considerably rotated. We compare these results with the experimental data for a micro-pillar
specimen and validity of the numerical model is discussed.
Polycrystalline analyses of the LPSO phase are performed using a simple specimen which is
composed of three LPSO strips. The basal plane is inclined 10° to the compression axis in the
middle strip of the specimen, while basal planes in the two strips of specimen on both sides are
arranged parallel to the compression axis. Figure 2 shows the distribution of the GN dislocation
density on the basal slip system after 1% compression. Deformation localization occurs around the
center of the specimen and a kink band is formed across three strips. The distribution of the GN
dislocation density in the center strip is similar to that of the single crystal analysis and ridges in the
wedge-like deformation areas on both free surfaces have high GN dislocation densities.
(a) GN dislocation density
(b) Rotation angle
Fig. 1 Distributions of dislocation and orientation in
single crystal after 5% compression.
Fig. 2 Distribution of GN dislocation density
on basal slip system in strip-shaped
polycrystal after 1% compression.
77
POS-38
Three-dimensional analysis of kink bands in LPSO phase by using FIB-SEM
Ken-ichi Ikeda1, Rie Nishio2, Hongye Gao3, Satoshi Hata1 and
Hideharu Nakashima1
1
Faculty of Engineering Sciences, Kyushu University,
6-1, Kasuga-koen, Kasuga-city, Fukuoka 816-8580, Japan
2
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University,
6-1, Kasuga-koen, Kasuga-city, Fukuoka 816-8580, Japan
3
Faculty of Engineering, Kyushu University, 744, Motooka, Nishi-ku, Fukuoka 819-0395, Japan
For environmental and energy saving problem, many industries tend to use light materials to
replace heavy materials. In recent years, magnesium alloys have used a lot of applications in
automobiles, electronic equipment and aerospace applications due to their good mechanical
properties, low density and ease of recycling. The hot-extruded Mg-Zn-Y alloys are composed of
an α-Mg matrix and a long-period stacking ordered (LPSO) phase and show superior mechanical
properties. The 0.2% proof strength of Mg97Zn1Y2 alloy can exceed 600 MPa with an elongation of
5% at room temperature [1]. In Mg-Zn-Y alloys, LPSO phases have an important role to improve
the mechanical properties, where kink bands formation is an essential mechanism to obtain such
the strength and the elongation [2]. However, the details of the formation process and mechanism
of kink bands have not been clarified yet.
In this study, the morphology of kink bands in LPSO phase is investigated by using FIB-SEM. We
use FEI Scios and Versa FIB-SEM equipped with high contrast back scattered image detector and
electron back scattered diffraction detector. The three dimensional morphology and crystal
orientation distribution of kink bands are discussed from these experimental data.
[1] Y. Kawamura, K. Hayashi, A. Inoue and T. Masumoto: Mater. Trans., 42 (2001) 1172-1176.
[2] K. Hagihara, N. Yokotani and Y. Umakoshi: Intermetallics, 18 (2010) 267276.
78
POS-39
1
Dislocations analysis around kink boundaries of Mg-Zn-Y alloy
Hongye Gao1, Ken-ichi Ikeda2, Tatsuya Morikawa1, Kenji Higashida1 and
Hideharu Nakashima2
Faculty of Material Science and Engineering, Kyushu University, 744, motooka, nishi-ku, Fukuokacity 819-0395, Japan
2
Faculty of Engineering Sciences, Kyushu University, 6-1 Kasuga-koen, Kasuga, Fukuoka
816-8580, Japan. [email protected]
Mg alloys, as lightweight structural materials, have been considered for automotive structural
components for improving fuel efficiency. However, in contrast to their advantages, low density,
and specific elastic modulus, the lower strength as compared to aluminum alloys is their great
weakness. The main challenge in developing Mg alloys is to increase the strength as well as the
ductility. It was reported that, in a long-period stacking ordered (LPSO) phase, deformation twins
were suppressed, and instead, kink bands were observed within the LPSO structure in Mg-Zn-RE
alloys [1]. Kink formation is an important deformation mechanism of LPSO phases when basal slip
is inhibited. However, no previous study has clarified the fundamental mechanism why mechanical
properties are improved by the formation of kink bands. Therefore, it is important to observe
dislocation distributions of kink boundaries in LPSO phases.
Figure 1 (a) shows a TEM bright-field image of the kink boundary in a Mg88Zn5Y7 (at%) alloy.
There are bending LPSO planes with a strain concentrate line in dark contrast corresponding to
stacking faults and many extended a-dislocations. Here, the kink boundary is a low angle kink
boundary, and gradual and continual deformations of LPSO phases are caused by the random
formation of a-dislocations. Fig. 1 (b) shows the corresponding HAADF-STEM image of the position
within the dotted rectangle in Fig. 1 (a). In LPSO phases, one can see many long dark lines of
stacking faults often appearing in Mg-Y-Zn alloys due to introduced extended dislocations. Fig. 1
(c) is a high-magnification TEM bright-field image of lattice fringes taken around the tip of the kink
boundary, as plotted in Fig. 1 (a). The tip of the low angle kink boundary shows a complicated
microstructure, which is a triangle area occupied by deformed LPSO phases due to high strain
concentration. Fig. 1(d) shows the corresponding bright-field image around the kink boundary,
taken at the position within the solid rectangle in Fig. 1 (a). Even there is no obvious linear
boundary observed during kinking, dislocations already formed around the kink of LPSO phases. In
Fig. 1 (d), there are a lot of dislocations due to smoothly kinking, and these dislocations exhibit a
regular and proper arrangement.
In summary, complex dislocation distributions around kink boundaries have far exceeded our
imagination. Dislocations with Burgers vectors along c-axis were found close to kink boundaries,
and they are thought to play an important role to affect bending angles of kink boundaries.
Fig. 1 (a) TEM bright-field image of the kink boundary in a Mg88Zn5Y7 (at%) alloy, and (b) the
corresponding HAADF image of the position within the dotted rectangle in Fig. 1 (a). (c) A highmagnification TEM bright-field image of lattice fringes taken around the tip of the kink boundary, as
plotted in Fig. 1 (a). (d) The corresponding bright-field image around the kink boundary, taken at the
position within the rectangle in Fig. 1 (a).
[1] K. Amiya, T. Ohsuna, and A. Inoue: Mater. Trans. 44 (2003) 2151-2156.
79
POS-40
Local structure analysis of LPSO by XAFS
S. Yoshioka1, 2, Y. Kobayashi1, K. Yasuda1, S. Matsumura1, 2
1
Faculty of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka-shi 819-0395, JAPAN
Reseach Center for Synchrotron Light Applications, Kyushu University, 6-1 Kasuga-koen, Kasugashi 816-8580, JAPAN
2
Magnesium based alloys in Mg-Zn-Gd need the aging procedure for the formation of 14H-type
LPSO structure at high temperature (623 K <) [1, 2]. Additionally, this system has many crystal
structures and morphologies depending on the aging temperature and holding time; the aging at
lower temperature (< 573 K) produces β’ (Mg7Gd), β1 (Mg5Gd) and β (Mg5Gd) -phases and
enormous number of stacking faults. Therefore structural transition on annealing procedure is
complicated. The crystal structure determinations have been performed by diffraction methods with
electron, synchrotron x-ray and neutron beams. However, the local structures of Zn and Gd in each
phase have not fully discussed. In this study, our final goal is to determine the local structure
behaviors around Zn and Gd on precipitation process of LPSO phase from Mg97Zn1Gd2 cast alloy.
We adopt x-ray absorption fine structure (XAFS) method.
The Mg97Zn1Gd2 cast alloy and aged for 24 hour at 480 ˚C were investigated, as the first step.
The Gd L3-edge and Zn K-edge XAFS measurement were carried out at Kyushu University
beamline (BL-06) of Kyushu synchrotron light source (SAGA-LS) in Japan using with Si(111)
double crystal monochromator. All of the spectra were recorded in transmission mode at room
temperature. Sample thicknesses were prepared for optimal absorption signal.
Figure 1 shows x-ray absorption near edge structure (XANES) spectra for as-casted and aged
Mg97Zn1Gd2. The peak top position of white line Gd L3-edge for annealed sample located at higher
energy than that of as-cast sample by 0.5 eV. The shape of Zn K-edge spectrum is also changed
by aging. These XAFS spectrum differences between as-cast and annealed samples suggest for
the local structure changes of each Gd and Zn from the as-casted sample, which consists of α-Mg
and Mg3Gd-type intermetallic compound, to the 14H-type LPSO structure.
Fig. 1. (a) Gd L3-edge and (b) Zn K-edge XANES spectra for Mg97Zn1Gd2 as
casted (solid blue) and aged for 24 hour at 480 ˚C (dashed red).
[1] M. Yamasaki, T. Anan, S. Yoshimoto, Y. Kawamura, Scr. Mater. 53 (2005) 799-803
[2] M. Yamasaki, M. Sasaki, M. Nishijima, K. Hiraga, Y. Kawamura, Acta Mater. 55 (2007) 67986805
80
POS-41
Diffusion Coefficient of Zn and Y in Mg investigated by Atom Probe
Tomography
K. Inoue, N. Ebisawa, K. Tomura, T. Toyama, Y. Nagai
The Oarai Center, Institute for Materials Research, Tohoku University
2145-2 Narita, Oarai, Ibaraki 311-1313, Japan, [email protected]
Diffusion coefficient is one of the most important physical parameter to understand the
microstructural evolution during thermal aging and gives a useful information on the material design.
In the past, the diffusion coefficients have been determined by electron probe microanalysis,
activity measurement, and so on. Determination of diffusion coefficient in these techniques requires
long-range diffusion at distances of at least several microns due to the spatial resolution limit.
Atom probe tomography (APT) is a unique method for elemental mapping in 3D real space with
nearly atomic-scale spatial resolution. APT has many advantages on diffusion research, compared
with conventional methods. By using APT, very short-range diffusion (tens of nanometers) is
enough for the determination of the diffusion coefficient because of high spatial resolution. Thus,
lower temperature diffusion process could be observed. Furthermore owing to 3D mapping, not
only bulk diffusion but also grain boundary diffusion can be determined by APT.
In this research, sample preparation for APT measurements is one of the key issues. As shown
in Fig. 1, in the case of bulk diffusion, needle specimen is fabricated from diffusion couple by
selecting matrix region sufficiently far from grain boundary (GB) using focused-ion beam (FIB)
apparatus. Whereas in the case of GB diffusion, needle specimen is fabricated in order to include
the GB in the apex of the needle specimen.
In the plan, diffusion coefficient of Zn and Y in Mg will be determined at several annealing
temperatures. From the temperature dependence, activation energy will be deduced. In the
presentation, the research in progress will be introduced.
Fig. 1. Schematic figure of sample preparation for determination of diffusion coefficient of Zn
in Mg.
81
POS-42
Dynamics and Stability of Nonlinear Vibration Modes
in Layered Structure of Magnesium
Yusuke Doi1 and Akihiro Nakatani2
1
Department of Adaptive Machine Systems, Graduate School of Engineering, Osaka University
2-1 Yamadaoka, Suita, 565-0871 Osaka, Japan
[email protected]
2
Department of Adaptive Machine Systems, Graduate School of Engineering, Osaka University
2-1 Yamadaoka, Suita, 565-0871 Osaka, Japan
In this study, we investigate dynamics of large amplitude vibration that is continued from phonon
modes of small amplitude approximation in a layered structure of magnesium. Using a numerical
method coupling molecular dynamics method and newton method, we obtain periodic solutions
with finite amplitudes from the initial solution that is obtained from the first-principle molecular
dynamics simulation. Moreover unstable dynamics and resultant post process after unstabilization
are investigated by molecular dynamics simulation. We observe energy localization and
delocalization during the process.
82
POS-43
Comparison between the microstructures with different heat treatment in
Mg97Zn1Y2 alloy
Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai, Japan
[email protected]
In recent years, one kind of magnesium alloys consisting of rare earth elements (RE) and transition
elements (TM), containing a long range periodic stacking ordered (LPSO) structures, are found to
be with good mechanical properties at both room and elevated temperatures. The LPSO structure
consists of regular arrangements of four-layer high fcc structural units separated by several pure
magnesium layers. According to recent investigation of the elastic strain energy between structure
units, the neighbour structure units with opposite shear directions are most preferred, when it
precipitate from the matrix. However, as for the Mg97Zn1Y2 alloy, the LPSO structure usually forms
during the casting process, and the high temperature (above 537°C) stable LPSO phase 18R is
kept. Further ageing can make 18R transform to 14H LPSO phase with help of the faulted 18R.
The precipitation of the LPSO phase from the solution treated matrix is rarely reported. Present
work will compare different microstructures in Mg97Zn1Y2 with different heat treatments, i.e. (1)
direct ageing of cast sample, (2) direct ageing of extruded sample, and (3) ageing of a solution
treatment sample. The morphology of the first and third heat treatment is similar, as shown in Fig. 1,
but with different LPSO structure. The LPSO in the first process is 18R, while that is 14H in the
third process at the early ageing stage. The hardness of the latter case is higher than the former
case during the ageing process due to more even distributed LPSO plate. The LPSO phase in the
second process is 18R at early stage, Fig. 2. The formation of 14H in the third process involves no
precursor phase, such as 18R. 14H LPSO is stable after long time ageing while 18R structure in
other processes will transform to 14H. The LPSO phase grows by the ledge mechanism.
(b)
(a)
50µm
(c)
50µm
50µm
Fig. 1 Microstructure for samples aged at 520°C (a) cast sample, (b) extruded sample, and (c)
solution treated sample
Fig. 2 TEM images of (a-c) the extruded and aged sample with 18R and (d-f) the solution treated
and aged sample with 14H
83
POS-44
Deformation Behavior of Mg97Zn1Y2 Alloys Studied by Neutron Diffraction
Wu GONG1, Kazuya AIZAWA1, Stefanus HARJO1,
Takuro KAWASAKI1, Takaaki IWAHASHI1 and Takashi KAMIYAMA2
1
J-PARC Center, JAEA, Tokai, Ibaraki 319-1195, Japan
Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba
305-0801, Japan
2-4 Shirane Shirakata, Tokai, Naka, Ibaraki, 319-1195 Japan, Email: [email protected]
2
Ternary Mg–Zn–RE (rare earth) alloys consisting of a long period stacking ordered (LPSO) phase
and an α-Mg phase have attracted high attention due to its excellent mechanical properties [1]. In
the previous work, it was found that the LPSO phase was the harder component during tensile
deformation by using in-situ neutron diffraction [2]. The compression deformation mechanisms of
these alloys, which possibly include basal slip, twinning and kink deformation, are still unclear. In
the present study, in-situ neutron diffraction was employed to investigate the anisotropic
deformation behavior of the LPSO and α-Mg phases during compression.
Two Mg97Zn1Y2 alloys for as-cast and as-extruded conditions consisting of approximately 20%
volume fraction of the LPSO phase, which have different initial textures, were studied. In-situ
neutron diffraction experiments were conducted on the beamline 19 ‘TAKUMI’ at Japan Proton
Accelerator Research Complex (J-PARC). The lattice strains combined with the texture evolution
obtained from the diffraction profiles were used to estimate deformation mechanisms.
Fig.1a shows the evolution of the lattice strains as
a function of the applied stress for each {hk.l}
diffraction reflections along axial direction in the
as-cast alloy. The α-Mg phase exhibits strong
anisotropic deformation behavior: (1) the basal slip
occurred in (10.1), (10.2) and (10.3) oriented
grains after -50MPa due to their higher Schmid
factors for the basal slip system; (2) when applied
stress exceed -111 MPa, {10.2}<10.1> tensile
twinning was activated in (10.0) and (11.0)
oriented grains, which was determined by
combining with the texture evolution results. The
LPSO phase grains yielded corresponding to the
generation of basal slip in α-Mg phase. It should
be caused by the plastic accommodation during
the surrounding basal slip of α-Mg, because their
basal planes were parallel with each other. In asextruded alloy (Fig.1b), it is obvious that the {hk.l}
diffraction reflections of the LPSO phase share
more lattice strain than basal slip α-Mg grains,
which implies that the LPSO phase plays a role of
harder component in this alloy. The kink bands in
the LPSO grains introduced by hot working were
considered to suppress the basal slip and increase
the strength.
Fig.1 Evolution of the axial lattice strains as a
function of applied stress: (a) as-cast
Mg97Zn1Y2, and (b) as-extruded Mg97Zn1Y2.
Stress-strain curve was added as a reference.
References
[1] Y. Kawamura, K. Hayashi, A. Inoue and T. Matsumoto: Mater. Trans. 42 (2001) 1172-1176.
[2] K. Aizawa, W. Gong, S. Harjo, J. Abe, T. Iwahashi and T. Kamiyama: Mater. Trans. 54 (2013)
1083-1086.
84
POS-45
Reduction of Peierls stress of LPSO structure under uniaxial compression:
First-principles calculations
Masatake Yamaguchi1, Mitsuhiro Itakura1, Motoyuki Shiga1, Hideo Kaburaki1,
and Eiji Abe2
1
Center for Computational Science and e-systems, Japan Atomic Energy Agency, Tokai-mura,
Ibaraki 319-1195 (or 5-1-5, Kashiwanoha, Kashiwa, Chiba 277-8587), Japan
2
Department of Materials Science and Engineering, University of Tokyo, Tokyo 113-8685, Japan
Email: [email protected]
We have conducted first-principles calculations for the
generalized stacking fault (GSF) energy in LPSO structure of
10H Y-Ni-Mg system under uniaxial compression. The
electronic structure calculations were performed using VASP
code in non-magnetic state. The compression is applied by
5% in lattice constant in each direction as shown in Fig. 1.
From the calculated GSF energy surface, maximum restoring
force (τmax) is calculated. Then, Peierls stress (σP) is
estimated from the theoretical equation suggested by Joos
and Duesbery [1].
The calculated GSF energy, τmax, and σP are shown in Fig.2.
For the case of no compression (Fig.2a), τmax, and σP are the
same between two slip directions ([11-20] and [1-210]). For
the cases of [11-20] compression, on the other hand, τmax, and
σP are greatly reduced in the [11-20] direction, and are
increased in the [1-210] direction (Fig.2bc). These results
indicate that the dislocation slip becomes easy in the parallel
direction of uniaxial compression, but becomes difficult in the
perpendicular direction.
[1] B. Joos, M. S. Duesbery: Phys. Rev. Lett. 78(1997)266.
Fig.2: (a) No compression
(b)(c) 5% compression for
<11-20>.
Fig.1:
10H
Y-Ni-Mg
LPSO
structures. (a) Side view and three
slip planes (1.,2.,3.) (b) Top view
of basal plane and two directions
of compression (<11-20> and <1100>).
85
POS-46
Spinodal decomposition behavior of the Mg-RE-TM ternary systems
H. Abe1, S. Iikubo2, and H. Ohtani1
1
Institute of Multidisciplinary Research for Advanced Materials, Tohoku University,
Sendai 980-8577, Japan
2
Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology,
Kitakyushu 808-0196, Japan
An LPSO structure is characterized by the periodical arrangement of a stacking fault (SF)
introduced on the hcp lattice. In addition, rare earth (RE) and transition metal (TM) atoms added to
alloys form a chemically ordered structure in the SF layers. These Mg alloys are in general classed
as the Type-I alloys in which LPSO structure forms during solidification, as well as the Type-II
alloys for the LPSO structures appeared during hot working after solidification. There might be a
difference in the spinodal decomposition temperatures between the Type-I alloys and Type-II alloys
in the vicinity of the solidification compositions. This difference possibly influences the formation
mechanism of the LPSO structures in each type of alloys. Thus in the present study, the spinodal
temperatures in the Mg-Y-Zn alloys and Mg-Gd-Co alloys belonging to the Type-I alloys as well as
the Mg-Gd-Zn and Mg-Y-Al systems classified to the Type-II alloys were calculated, and the
difference of the spinodal decomposition behavior between the Type-I and Type-II alloys was
investigated.
The calculation procedures are summarized as follows. The total energies of various ordered
structures composed of hcp space lattice are computed by means of the first-principles method.
Then, the total energies are used to extract the chemical interaction energies, i.e., the effective
interaction energies, between component atoms in various crystalline environments. The Gibbs
free energy of the hcp phase was evaluated using the cluster variation method, and the spinodal
points were calculated from the second derivative of the free energies.
Figure 1 shows the contour lines of the spinodal decomposition temperatures for the four ternary
systems. Assuming 90-95 at. % Mg and the RE/TM ratio to be 0.7-1.3 for the final solidification part,
the spinodal temperatures of
Mg-Y-Zn system show in
between 750 and 950 K, and
the Mg-Gd-Co ternary system
has the temperatures between
700 and 1000 K. On the other
hand, the spinodal temperatures for the Mg-Gd-Zn system
and the Mg-Y-Al system of the
Type-II alloys are in the range of
600 and 850 K, and are lower
than those of Type-I alloys.
According to these calculated
results, it might be suggested
that the spinodal decomposition
will not occur during solidification because diffusivity of the
atoms is not high enough in the
Type-II alloys compared with the
Type-I alloys. In this type of
alloys, spinodal decomposition
occurs during the subsequent
annealing treatment and will
form LPSO structure.
Figure 1 Spinodal temperature contours for (a) Mg-Y-Zn, (b) MgGd-Co, (c) Mg-Gd-Zn and (d) Mg-Y-Al ternary hcp phases.
86
POS-47
Numerical prediction of solute segregation during rapid solidification
of Mg-Zn-Y and Mg-Zn-Gd alloy using phase-field model
Machiko Ode1*, Hiroshi Ohtani2 and Masato Shimono1
1
Computational Materials Science Unit, National Institute for Materials Science, 1-1 Namiki
Tsukuba Ibaraki 305-0044, Japan
2
Institute of Multidisciplinary research for Advanced Materials, Tohoku University, 1-2-1 Aoba
Sendai, Miyagi 980-8577, Japan
* [email protected]
The synchronized Long-Period Stacking Order (LPSO) phase was first observed as a secondary
solidified phase in the Mg97Zn1Y2 alloy [1]. The LPSO-Mg alloy exhibits strength and ductility
equivalent to those of practical Al-based alloys and has garnered special interest as a lightweight
structural material. The LPSO structure is observed various Mg-based alloys containing transition
metal (TM) and a rare earth (RE) metal (TM: Al,Co,Cu,Ni,Zn, RE: Gd,Tb,Dy,Ho,Er,Tm) [2] and
they are classified into two types depending on when LPSO structure forms. The Mg-Zn-Y alloy
belongs to Type I, where the LPSO phase is formed during solidification, while the Mg-Zn-Gd alloy
is Type II, in which the LPSO phase precipitates during heat treatment. Although considerable
experimental work on the LPSO phase has been done, the difference between the two types is not
well understood.
In the present study, the phase-field model is applied to study the difference between two gropes.
The CALculated PHAse Diagram (CALPHAD) based thermodynamic functions for Mg-Zn-Y system
[3] and Mg-Zn-Gd system [4] are incorporated into the calculation. The solidification process of the
primary phase, a-Mg phase, is numerically simulated and from the obtained solute field, the driving
force for the nucleation of secondary phase, LPSO phase, is estimated. In the case of Mg-Y-Zn
alloy, the driving force becomes negative, in other words thermodynamically stable, when the
residual liquid fraction is 25 vol.%. The experimental research reports that the ratio of LPSO phase
is also 25% in the same cooling condition as the present calculation [5]. This agreement suggest
that the driving force criteria can predict the fraction of LPSO phase and when the LPSO phase
precipitates. It is also shown that the LPSO phase in the Mg-Y-Zn alloy is more thermodynamically
stable comparing to Mg-Gd-Zn alloy since the driving force of the Mg-Gd-Zn alloy is always larger
than that of Mg-Y-Zn alloy. This stability difference of the LPSO phase is caused by the solute
segregation in the liquid phase.
[1] Y. Kawamura, K. Hayashi and A. Inoue: Mater. Trans. 42 (2001) 1171–1174.
[2] M. Yamasaki, T. Anan, S. Yoshimoto and Y. Kawamura: Scr. Mater.53 (2005) 799–803.
[3] R.Masumoto, H.Ohtani and M.Hasebe, J. Japan Inst. Metals, 73( 2009) 683-690.
[4] TTMG-4, www.thermocalc.com
[5] T. Itoi, T. Seimiya, Y. Kawamura, M. Hirohashi, Scr. Mater. 51 (2004) 107–111.
87
POS-48
Inhomogeneous Deformation Microstructures in a Magnesium Alloy with
LPSO Phase
T.Morikawa1, R.Noguchi2 and K.Higashida1
1
Department of Materials Science and Engineering, Kyushu University,
Motooka 744, Fukuoka 819-0395, Japan
2
Graduate School of Engineering, Kyushu University, Japan
[email protected]
Inhomogeneous deformation behavior in a magnesium alloy which is almost occupied by longperiod stacking order (LPSO) phase has been investigated by using high-precision marker method
and SEM observation. Particular emphasis is laid on the aspect of kinks, which is one of the
characteristic microstructures generated in the LPSO phase.
Mg alloys containing some transition metals such as Zn and rare earth elements such as Y or Gd
have a characteristic microstructure including the LPSO phase and the usual hcp matrix phase.
The superior mechanical properties of the Mg alloy should be closely related not only to the
microstructural inhomogeneity induced by the difference in the deformability of the dual phases but
also to the characteristic deformation microstructures of LPSO phase. The kinks were generated by
working such as extrusion in the LPSO phase, which raises the strength of LPSO phase. Then,
such hard LPSO phase should contribute to the increase of yield and tensile strength of the alloy.
SEM-EBSD analysis revealed the many wedge-shape microstructures with high angle boundaries,
which indicates that the kinking occurred by the compression test. In order to clarify the details of
such kinking behavior, high-precision marking method using electron beam lithography has been
employed. Large distortion of markers and migration of kink wall were observed on the specimen
surface. The formation mechanism of such microstructural inhomogeneity in the LPSO phase is
discussed.
88
POS-49
Creep Behavior of Extruded Mg-Zn-Gd Alloy
with the LPSO Phase-Stimulated Texture
Yuri Jono1, Michiaki Yamasaki2 and Yoshihito Kawamura2
1
Graduate Student, Department of Materials Science, Kumamoto University, 2-39-1 Kurokami,
Chuo-ku, Kumamoto 860-8555, Japan, [email protected]
2
Magnesium Research Center, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto 8608555, Japan, [email protected]
Mg-Zn-rare earth (RE) alloys with a long period stacking ordered (LPSO) phase have attracted
much attention because of their excellent mechanical properties [1] and high creep resistance [2].
The microstructural feature of LPSO phase is formation of long-period stacking-ordered variants of
an hcp-Mg structure with chemical modulation, in which both RE and Zn are enriched in four atomic
layers at regular period intervals [3]. Mg-Zn-Gd alloy is one of the LPSO-typed Mg alloys. This alloy
indicates the precipitation of 14H-LPSO phase in α-Mg matrix coherently at high temperature aging
treatment at more than 623 K [4]. The precipitation morphology of the LPSO phase can be
controlled to be a block-shape or a plate-shape by changing aging temperature and duration. The
mechanical properties of Mg-Zn-Gd alloys with those LPSO phase are drastically improved by
plastic deformation owing to formation of multimodal microstructure that consists of fiber-shaped
LPSO phase grains, hot-worked α-Mg grains, and dynamically recrystallized (DRXed) α-Mg grains
[5]. As features of each region, the worked αgrain region and LPSO phase grain region have
coarse grains of 10 µm or greater and a strong basal texture. The DRXed αgrain region has
fine grains of approximately 1 µm and a random orientation. In the mechanical properties at room
temperature, the textured grains take strength and the DRXed α grains improve ductility.
Effect of the multimodal microstructure on creep resistance of the extruded Mg-Zn-Gd alloys has
been investigated [2]. As a result, the textured grains improved the creep resistance and the
DRXed α grains decreased the creep resistance. However the creep behavior of the extruded MgZn-Gd alloys have not yet been elucidated in detail. Therefore, in this study, creep strain
distribution of the extruded Mg-Zn-Gd alloys with the multimodal microstructure was investigated by
a micro-grid marking method.
An extruded specimen was prepared from 673 K-aged ingot by direct extrusion at 623 K and
extrusion ratio of 10. The specimen contains the fiber-shaped LPSO phase grains, the worked
coarse α-Mg grains, and the DRXed fine α-Mg grains. Those area fractions were 7%, 65%, and
28%, respectively. Tensile creep test using the flat plate-shaped specimen with micro-grids was
also carried out at 473 K under 210 MPa. Total 50 microgrids were drawn on center region of the
flat plate-shaped specimen. A size of micro square was 0.5 μm × 0.5 μm. A total size of a microgrid was 10 μm × 13 μm. An equivalent strain of each deformed micro-square was calculated after
secondary creep. The average equivalent strains with and without grain boundaries (GB) were
~0.088 and ~0.047, respectively. This large strain at the micro-squares containing GB would be
due to grain boundary sliding (GBS). However, the contribution of the GBS to total equivalent strain
was only 20%. Most of the creep deformation of the extruded Mg-Zn-Gd alloy was intra-grain glide,
especially in the worked grains. The GBS tends to occur at the GB next to the coarse worked
grains with high Schmid factor, therefore this GBS would be the slip-induced GBS; in other words,
this GBS is one of accommodation of large strain in the worked grain region.
References
[1] Y. Kawamura, K. Hayashi, A. Inoue and T. Masumoto: Mater. Trans. 42 (2001) 1172-1176.
[2] Y. Jono, M. Yamasaki, Y. Kawamura: Mater. Trans. 54 (2013) 703-712.
[3] E. Abe, A. Ono, T. Itoi, M. Yamasaki, Y. Kawamura: Philos. Mag. Lett. 91 (2011) 690-696.
[4] M. Yamasaki, M. Sasaki, M. Nishijima, K. Hiraga, Y. Kawamura: Acta Mater. 55 (2007)
6798-6805.
[5] M. Yamasaki, K. Hashimoto, K. Hagihara and Y. Kawamura: Acta Mater. 59 (2011) 3646-3658.
89
POS-50
Kink band propagation behavior in Mg/LPSO two-phase alloy
Takeshi Minomo1, Michiaki Yamasaki2, Koji Hagihara3, Yoshihito Kawamura2
1
Graduate Student Department of Materials science, Kumamoto University, 2-39-1 Kurokami,
Chuo-ku, Kumamoto 860-8555, Japan
2
Magnesium Research Center, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto
860-8555, Japan
3
Department of Adaptive Systems, Graduate School of Engineering, Osaka University, 2-1
Yamadaoka, Suita, Osaka 565-0871, Japan
[email protected], [email protected]
Recently Mg-Zn-Y alloys containing a long period stacking ordered (LPSO) phase have been
attract great attention because of their excellent mechanical properties [1]. The LPSO structures in
the Mg-Zn-Y alloys show a periodic chemical modulation as well as LPSO. Since the apparent
chemical modulation occurs with confined Zn/Y distributions around stacking faults and
synchronizes with the relevant stacking order, these structures are referred to as “synchronized
LPSO structures” [2]. Previous research suggests that the change in the atomic arrangement and
characteristic segregation of Y and Zn atoms to specific layers strongly hinder the formation of
twins in the LPSO phase. Instead, kinks appear as an accommodation mechanism for plastic strain
[3]. Since kink-deformation bands are macroscopically formed perpendicularly to the primary slip
direction, they effectively counteract basal slipping, resulting in alloy strengthening. Therefore, it is
very important to clarify the formation mechanism of kink bands in the Mg alloys during plastic
deformation. In this study, we have investigated formation and growth behavior of kink bands in
Mg/LPSO two-phase Mg-Zn-Y alloys under compressive loading. Particular attention has been paid
to kink band propagation behavior through a Mg/LPSO phase interface/boundary.
The Mg89Zn4Y7 (at.%) ingots were produced by high frequency induction melting of pure Mg
(99.99 wt.%), Zn (99.9 wt.%), and Y (99.9 wt.%) metals. Direction solidification (DS) was conducted
with the master ingots using the Bridgman technique at a growth rate of 0.5 mm/min under an Ar
atmosphere. The LPSO (18R, after Ramsdell) and α-Mg (2H) phases possess coherent phaseinterface; (0001)18R//(0001)2H, <11-20>18R//<11-20>2H. Here, Miller-Bravais Indices for 18R structure
is based on the Mg-rich hcp structure layers in the 18R-LPSO phase. The rectangular specimens
that are approximately 1 x 1 x 1.5 mm in size were fabricated from the central part of as-grown DS
crystals by mechanical polishing. The compression tests were performed using an Instron testing
-4
-1
machine at a strain rate of 5.0 x 10 s . Loading direction is parallel to the [11-20]18R.
Microstructures of the specimen before and after compression were observed using a scanning
electron microscope. Distribution of intra-grain lattice rotation axis in a compressed DS micro
crystal specimen was investigated by using intra-granular misorientation axis analysis (IGMA)
using electron back-scattered diffraction [4].
In the <11-20>-compressed specimen, wedge-shaped and ridge-shaped kink bands form within
both LPSO and α-Mg phases and they propagate along <0001> of 18R and 2H crystals. IGMA
analysis revealed that almost all kink bands that observed in this study possess <1-100> lattice
rotation axis. A few <1-100>-typed kink bands that form in the LPSO phase region penetrate the αMg phase region without varying of the lattice rotation axis. This result suggests that if deformation
twinning is restricted in the α-Mg grain that is surrounded by LPSO phase grain, deformation kink
plays an important role for accommodation mechanism in the hcp-Mg phase, instead of twinning.
[1] Y. Kawamura et al. Mater. Trans. 42 (2001) 1172; Mater. Trans. 48 (2007) 2986.
[2] E. Abe et al. Phil. Mag. Lett. 91 (2011) 690.
[3] K. Hagihara et al. Intermet. 18 (2010) 267.
[4] M. Yamasaki et al. Acta Mater. 61 (2013) 2065.
90
POS-51
Precipitation of LPSO Structure from Amorphous Phase
in Mg85(Zn, Ni, Cu)6Y9 Ternary Alloys
Takahiro Shiratake1, Michiaki Yamasaki2 and Yoshihito Kawamura2
1
Graduate Student Department of Materials science, Kumamoto University,
2-39-1 Kurokami Chuo-ku, Kumamoto
860-8555, Japan
2
Magnesium Research Center, Kumamoto University, 2-39-1 Kurokami Chuo-ku, Kumamoto
860-8655, Japan
[email protected], [email protected]
Long period stacking ordered (LPSO) structures in Mg-Zn-rare earth (RE) ternary system having
periodic chemical modulation as well as long period stacking have drawn attention due to their
mechanical performance as new lightweight metallic structural materials [1]. Their unique structure
and mechanical properties, in particular, their characteristic deformation mechanism, have been
investigated in last decade. Although the details of LPSO structure having several polytypes,
namely, 10H, 14H, 18R, and 24R, were examined by electron microscopy [2], there are many
aspects yet to be examined from the viewpoints of formation kinetics and phase stability. One of
unsolved issues is "Which forms dominantly, periodic stacking fault or chemical modulation?" In our
previous studies, formation behavior of LPSO phase in the Mg-Zn-RE alloys has been investigated:
An LPSO phase was formed in Mg97Zn1RE2 alloys with RE = Y, Gd, Dy, Ho, Er, Tb and Tm. Mg-ZnY, Mg-Zn-Dy, Mg-Zn-Er, Mg-Zn-Ho and Mg-Zn-Tm alloys were classified as type-I, in which the
LPSO phase is formed during solidification. Mg-Zn-Gd and Mg-Zn-Tb alloys belong to type-II, in
which the LPSO phase precipitates with soaking at more than 623 K [3]. Some Mg-Zn-RE alloys
that belong to type-I can form single phase with 18R-type LPSO structure. In the case of Mg-Zn-Y
alloy system, Mg85Zn6Y9 (at%) composition forms 18R-type LPSO single phase. So, in this study,
the crystallization of a melt-spun Mg85(Zn, Ni, Cu)6Y9 (at%) alloys was studied in order to
understand the LPSO phase formation on the crystallization kinetics and mechanism.
The Mg85M6Y9 (at. %, M = Zn, Ni, Cu) ingots were produced by high frequency induction melting.
Melt-spun ribbon specimens were prepared from Mg85M6Y9 ingots by single roller-melt spinner in Ar
atmosphere. Copper wheel circumferential speed was 50 m/s and the argon gas pressure was 6070 kPa. Thermal stability and crystallization of the as-quenched alloys were studied by means of
–1
DSC at scanning condition with heating rate of 5, 10, 20, 40 K min , as samples were heated in Pt
pans under pure Ar atmosphere. The structure of these samples was investigated by X-ray
diffractometory (XRD) and transmission electron microscopy (TEM).
The DSC curve of rapidly solidified Mg85Zn6Y9 alloy ribbons showed sharp first exothermic peak in
the 450 K-500 K, and the weak second exothermic peak in the 550 K-600 K. Two exothermic
peaks were also observed at same temperature ranges in the DSC curve of Mg85Ni6Y9 and
Mg85Cu6Y9. The structure of these samples was investigated by TEM. As-quenchd Mg85Zn6Y9 alloy
ribbon specimen has amorphous matrix phase with small amount of nano-crystals. In the
Mg85Zn6Y9 RS ribbon that was heat-treated at 473 K, small amount of nano-crystallized grains were
observed. On the other hand, In the Mg85Zn6Y9 RS ribbon that was heat-treated at 673 K, not a
few submicron-sized crystals with 18R-typed LPSO structure were obsereved. From the results of
DSC measurement and TEM observation, the 18R-type LPSO phase is not formed directly from
the Mg85Zn6Y9 amorphous phase.
[1] Y. Kawamura et al. Mater. Trans. 42 (2001) 1172.
[2] E. Abe et al. Philos. Mag. Lett. 91 (2011) 690.
[3] Y. Kawamura et al. Mater. Trans. 48 (2007) 2986.
91
POS-52
Kink Band Formation in an 18R-LPSO Single Crystal in Bending Deformation
Tsubasa Matsumoto1, Michiaki Yamasaki2, Koji Hagihara3,
and Yoshihito Kawamura2
1
Graduate Student Department of Materials science, Kumamoto University, 2-39-1 Kurokami,
Chuo-ku, Kumamoto 860-8555, Japan, e-mail: [email protected]
2
Magnesium Research Center, Kumamoto University, 2-39-1 Kurokami, Chuo-ku, Kumamoto
860-8555, Japan
3
Department of Adaptive Systems, Graduate School of Engineering, Osaka University, 2-1
Yamadaoka, Suita, Osaka 565-0871, Japan
Mg-based long period stacking ordered (LPSO) structure has been attracted considerable
attention due to its unique plastic deformation as well as its novel microstructure [1, 2]. In the
LPSO phase in the Mg-Zn-Y alloys, the apparent chemical modulation occurs with confined Zn/Y
distributions around stacking faults and synchronizes with the relevant stacking order, these
structures are referred to as “synchronized LPSO structures”. The characteristic segregation of Y
and Zn atoms to specific layers strongly hinder the formation of twins in the LPSO phase. Instead,
kinks appear frequently as an accommodation mechanism for plastic strain. Furthermore, kink
band boundaries that are macroscopically formed perpendicularly to the primary slip direction
prevent basal<a> slip, so if quite a few kink band boundaries are formed in Mg-Zn-Y alloys, they
effectively counteract basal slipping, resulting in alloy strengthening. However the formation
mechanism of kink bands has not been clarified yet in detail. Therefore, in this study, we have
investigated the formation and propagation behavior of kink bands in an 18R-LPSO structure in
Mg-Zn-Y alloys that experienced bend deformation. Crystallographic feature of the kink bands is
unveiled by intra-grain misorientation axis (IGMA) analysis using electron back-scattered diffraction
(EBSD) [3].
Mg85Zn6Y9 (at%) master ingot was produced by high frequency induction melting of pure Mg
(99.99 wt.%) and Zn (99.9 wt.%) metals and Mg-20 wt.%Y master alloy in a cylindrical carbon
crucible. Direction solidification (DS) was performed with Mg85Zn6Y9 master ingot using the
Bridgman technique at a growth rate of 0.5 mm/min under Ar atmosphere. The sheet-shaped 18RLPSO single crystal small specimens that are approximately 1.8 x 1.8 x 0.09 mm in size were
fabricated from the DS bulk specimen by mechanical polishing. The specimen experienced
bending deformation with maximum plastic strain of ~0.083 by hydrostatic pressing against a thinwire of φ1 mm using pure Indium as pressure medium. The specimen was placed on the top of
thin-wire with a crystallographic orientation <10-10>18R was parallel to the longitudinal direction of
the wire. So, the direction of tension/compression in bending deformation was parallel to <1210>18R. Here, Miller-Bravais Indices for 18R structure is based on the Mg-rich hcp structure layers
in the 18R-LPSO phase. Microstructures of the specimen before and after bending were observed
using a SEM. Distribution of intra-grain lattice rotation axis in a compressed DS micro crystal
specimen was investigated by using IGMA in EBSD technique.
In the bent 18R-LPSO crystal, many ridge-shaped kink bands were observed in the (10-10)18R
cross-section. Kink bands propagate along <0001>18R from inner wall side of specimen to outer
wall side, but tips of ridge-shaped kink bands stop around middle position that corresponds to
stress neutral plane in the bent specimen. IGMA analysis revealed that kink bands observed in this
study possessed various lattice rotation axes, but kink bands produced an IGMA distribution
concentrated on the <uvt0> arc of the inverse pole figure irreducible triangle. This IGMA distribution
suggests that kink deformation occurs through a combination of basal <a> slip modes.
[1] E. Abe et al. Phil. Mag. Lett. 91 (2011) 690.
[2] K. Hagihara et al. Intermet. 18 (2010) 267.
[3] M. Yamasaki et al. Acta Mater. 61 (2013) 2065.
92
PLE-04
Assessment of Polycrystal Plasticity Models of Deformation Twinning and
Validation Using In-situ Neutron Diffraction
S.R. Agnew1*
1
Materials Science and Engineering, University of Virginia, Charlottesville, Virginia, U.S.A.
E-mail: agnew@ virginia.edu
The effect of deformation twinning has been incorporated within polycrystal plasticity models for
over three decades. Initially, the interest was in explaining the different texture evolution within pure
face centered cubic metals (e.g. copper) and their alloys (e.g. brass). A noteworthy demonstration
was made by Van Houtte [1], who incorporated the ideas of prior authors into a generalized Taylor
model and sought to minimize the number of new grain orientations, which were introduced into the
polycrystal plasticity calculation over the course of incremental, large strain deformation. Tomé,
Lebensohn, and Kocks [2] introduced two more strategies to overcome the problem of grain
proliferation. One was termed the volume fraction transfer scheme and the other was termed the
predominant twin reorientation (PTR) scheme. The former eliminates the proliferation of grain
orientations by simply populating orientation space at the beginning of the calculation and then
transforming volume fraction among the available orientations which describe the polycrystal. The
latter involves reorienting entire grains when a threshold amount of twinning has occurred. Kalidindi
[3] proposed quite a different scheme, which has been popular within finite element
implementations of crystal plasticity. In this approach, the grains (nodal descriptions) are
subdivided into matrix and twin domains with Most recently, Wang et al. [4] introduced a strategy to
account not only for twinning during monotonic deformation but also detwinning which occurs
during strain path changes. They dubbed their model the twinning-detwinning (TDT) model. The
later developments (PTR, Kalidindi, and TDT) have been employed to simulate the mechanical
response of hexagonal close packed (hcp) metals and alloys, as well as their texture evolution.
Throughout the lecture, specific attention will be drawn to the most common deformation twinning
mode in hcp metals, including Mg, the {10.2} twinning mode. Although twinning is blocked by the
long period stacking order (LPSO) phase [e.g. 5], many of the most exciting materials based on this
phase also contain significant volume fractions of Mg solid solution phase, which does undergo
deformation twinning. The twinning models will be evaluated relative to their ability to describe
certain features of the mechanical response which are common to textured Mg alloys: 1)
tension/compression yield strength asymmetry, 2) strain hardening plateau or yield point elongation
[e.g. 6], and finally, 3) rapid strain hardening [e.g. 7].
In-situ neutron diffraction data will be used to validate the modeling, especially as pertains to
characterizing the twin volume fraction evolution and the internal strains within twins, as originally
demonstrated by Brown et al. [8] and Clausen et al. [9]. Particular attention will be paid to the
notion of a “relaxation” or “back-stress” within the twins upon their formation and growth. Recently
obtained data from conventional Mg alloy, ZK60A, will be used for many of these comparisons.
[1] P. Van Houtte, Acta Metall., 26, 591 (1978).
[2] C.N. Tomé et al., Acta Metall. Mater, 39, 2667 (1991).
[3] S.R. Kalidindi, J. Mech. Phys. Solids, 46, 267 (1998).
[4] H. Wang et al., Mater. Sci. Eng. A, 555, 93 (2012).
[5]
M. Matsuda et al., Mater. Sci. Eng. A, 386, 447 (2004).
[6] O. Muránsky et al Mater. Sci. Eng. A 527, 1383 (2010).
[7] A. Oppedal et al., Phil. Mag. A, 93, 4311 (2013).
[8] D.W. Brown et al., Mater. Sci. Eng. A. 399, 1 (2005).
[9] B. Clausen et al., Acta Mater. 56, 2456 (2008).
93
INV-05
Structure and stability of the LPSO phases in several ternary Mg alloy
Eiji Abe
Department of Materials Science & Engineering, University of Tokyo, Japan
7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, JAPAN
LPSO (long period stacking/order) structures in several ternary Mg alloys are
fundamentally long period stacking derivatives of a hexagonal close-packed structure, and the
resultant stacking polytypes accompany a unique chemical order that occurs to synchronize with
the corresponding stacking order [1]. We have successfully constructed model structures of the
LPSO crystals based on STEM atomic imaging and first-principles calculations [2], demonstrating
that the state-of-the-art microscopy is now able to provide a precise structure model with the aid of
energy-based computer optimizations. We further attempt to tune the LPSO structures including a
unique annular bright-field (ABF) imaging [3], finding intriguing insights that the significant local
relaxations would generate interstitial atomic sites even in the close-packed LPSO structures.
Ordered characteristics of the LPSO structures in Mg-X-R alloys are well represented by
the X6R8 clusters with a L12-type configuration (ordered version of face-centered-cubic, fcc). It is
found that atomic relaxation behaviors significantly differ depending the alloy systems, as being
significant at the X6R8 clusters; large distortions from the ideal L12 configuration take place for the
Zn6Y8 and Zn6Gd8 clusters, while do not for the Ni6Y8 and Al6Gd8 clusters. Interestingly, such large
displacements of Zn/R (R =Y, Gd) atoms cause generations of internal ‘voids’ at the Zn6R8 cluster
centers (Fig.1), which are sufficiently capable for incorporating an extra atom as interstitials. Indeed,
introduction of the interstitials (I) into the previous LPSO structure models turns out to increase
remarkably a thermodynamic stability for all the possible candidate atoms, I = Mg, Zn and Y, the
validity of which is further confirmed by an energy-convex-full criterion according to the
energetically-tuned Mg-Zn-Y phase diagram. These theoretical predictions are experimentally
verified with the aid of a novel ultrahigh-sensitive scanning transmission electron microscopy
imaging [3], leading to a conclusion that Mg atoms convincingly exist at the relaxation-induced Isites in the Mg-Zn-Y LPSO phase (Fig. 2).
Fig.1 Local Zn-Y configurations before (left)
and after (right) the energetic relaxations [2].
References
[1] E. Abe et al, Philos. Mag. Lett. 91 (2011)
[2] D. Egusa and E. Abe, Acta Mater., 60 (2012) 166.
[3] R. Ishikawa et al., Nature materials, 10 (2011) 278.
94
Fig.2
Ultrahigh-resolution
STEM
imaging of HAADF (left) and ABF (right)
of the highly-ordered Mg-Zn-Y LPSO
phase (10H-type).
ORAL-08
Atomic Resolution Analysis of LPSO Microstructure Evolution
T. Kiguchi1, S. Matsunaga2, Y. Yamaguchi2, S. Tashiro2, K. Sato1
, and T.J. Konno1
1
Institute for Materials Research, Tohoku University
2-1-1, Katahira, Aoba-ku, Sendai, 980-8577, Japan
2
Depertment of Materials Science, Tohoku University
6-6, Aoba, Aramaki, Aoba-ku, Sendai, 980-8579, Japan
A novel “synchronized long-period stacking ordered structure (LPSO)” was discovered recently
in Mg-TM-RE alloy systems (TM and RE respectively denote transition and rare earth metals). It
shows better mechanical properties than those of conventional Mg and Al alloys [1]. Mg-Zn-Y
alloys show four polytypes depending on the thermal history and the solute concentration: 10H,
14H, 18R, and 24R type LPSOs [2,3]. Although the formation and growth mechanisms of the LPSO
have not been elucidated, Zhu et al. recently reported experimental results for the transformation
mechanism between 18R-type and the 24R-type LPSO in Mg96.7Zn0.8Y2.4Zr0.2 alloys [4]. They
showed that the transformation is a diffusional-displacive type accompanying the ledge mechanism
with atomic shuffle, and that 24R-type irregular stacking plays a role in the transformation.
We have also quantitatively elucidated elementary steps of the transformation between the
18R-type and the 24R-type LPSO in aged Mg97Zn1Y2 alloys on an atomic scale using aberrationcorrected high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM)
and Peak Pair Analysis (PPA) [5]. The transformation proceeds with a nano-size transition region
[4]. Our previous result shows only an exchange between 18R-type and the 24R-type stacking
sequence, by which the transformation is not understood.
In the HAADF-STEM image in Figure 1, the as-cast Mg85Zn6Y9 alloys include two types of
transition regions. Reportedly, as-cast Mg85Zn6Y9 alloys including 10H-type and 18R-type polytypes,
were transformed into an 18R-type. The transformation is expected to proceed from right to left as
10H+10H+14H→18R+18R+10H. No 14-H type LPSO has been reported in Mg85Zn6Y9 alloys, but it
is expected to have irregular stacking like the 24R-type in Mg97Zn1Y2 alloys. The transformation
starts from the Irregular stacking sequence corresponding to minor polytypes in a given nominal
composition. Figure 1 shows that a pair of transition regions mutually collaborates in the
transformation of “10H+10H+14H→18R+18R+10H”. One leads to a one-layer shift. The other twolayer shift is in the [0001]α direction. The stacking exchange from H-type to R-type needs not a
two-layer shift but a one-layer shift stated
above. However, the net effect of the twolayer shift is the same as the one-layer shift
because the upper transition region is
inflated by the one-layer shift of the lower
transition region. A pair of transition regions
with one-layer and two-layer shifts is
equivalent to two one-layer shifts. A 10Htype LPSO therefore transforms into an
18R-type LPSO. Stacking irregularity joins
the flats and localizes the disordered region
Figure 1 HAADF-STEM image of transformation
in the two enriched layers.
polytypes
from
10H-type
to
18R-type
Acknowledgment
accompanied with 14H-type irregular stacking
This work is partially supported by MEXT
sequence in Mg85Zn6Y9 alloy.
KAKENHI (23109006).
References
[1] Y. Kawamura, K. Hayashi, A. Inoue, and T. Masumoto, Mater. Trans. 42, 1172 (2001).
[2] M. Matsuda, S. Ii, Y. Kawamura, Y. Ikuhara, and M. Nishida, Mater. Sci. Eng. A, 393, 269
(2005).
[3] D. Egusa, and E. Abe, Acta Mater. 60, 166 (2012).
[4] Y.M. Zhu, A.J. Morton, and J.F. Nie, Acta Mater. 60, 6562 (2012).
[5] T. Kiguchi, Y. Ninomiya, K. Shimmi, K. Sato, and T.J. Konno, Mater. Trans. 54, 668 (2013).
95
ORAL-09
Kink formation in a compressed Mg-Zn-Y 18R-LPSO phase
J. Wu1, Y.L. Chiu1 and I.P. Jones1
1
University of Birmingham, Edgbaston, Birmingham, B15 2TT, UK
Corresponding author: Department of Metallurgy and Materials, University of Birmingham, Edgbaston,
Birmingham, B15 2TT, UK, [email protected]
Dislocation organisation in a Mg94Zn2Y4 alloy has been studied using TEM, focusing on the kink
boundaries within the long period stacking ordered (LPSO) phase. The as-cast Mg94Zn2Y4 alloy was
compressed at room temperature to 2%, and kinks have been observed. In the compressed samples,
𝑎𝑎
dislocations with Burgers vector of 〈2� 110〉 have been found to pile up on the basal plane and form
3
dislocation walls in the LPSO phase. These dislocation walls caused crystal lattice rotation along the
[15� 40] zone axis but in two opposite directions with a resulting total kink angle of about zero. The kink
boundaries act as obstacles to hinder further dislocation movement. The formation of the kinking may
be explained by the generation of dipole-pair dislocations as proposed by Hess and Barrett. Although
𝑎𝑎
basal slip is the dominant slip system in the LPSO phase, non-basal dislocations of 〈2� 110〉{01� 12}
3
were also observed at room temperature, which would affect the mechanical properties.
[1]
96
J. Hess and C. Barrett: Transactions of the American Institute of Mining and Metallurgical
Engineers 185 (1949) 599-606
ORAL-10
Coarse-Grained Modeling of In-Plane Disorder-Order Transformation of
Solute Nanoclusters in Mg-based LPSO Phases
Hajime Kimizuka1 and Shigenobu Ogata2
1
Department of Mechanical Science and Bioengineering, Osaka University,
1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan,
2
Department of Mechanical Science and Bioengineering, Osaka University,
1-3 Machikaneyama-cho, Toyonaka, Osaka 560-8531, Japan,
To understand the fundamental mechanism of the formation of Mg-based long-period stacking
ordered (LPSO) phases, it is important to elucidate the essential natures of heterogeneities and
medium-range orders in two-dimensional solute-cluster packing at stacking-fault-type interfaces,
which are an inherent part of the crystal lattice of the LPSO structures. In this study, we proposed
and established a coarse-grained (CG) modeling approach based on ab initio calculations for
predicting the equilibrium superlattice structures of solute nanoclusters confined in an atomically
close-packed stacking fault [1-3]. The approach was used to exploit the intriguing solute-enriched
layers observed in Mg-M-Y (M = Al or Zn) LPSO phases as examples of multicomponent stackingfault complexions (i.e., interfacial phases). We investigated the energetic stability and twodimensional ordering with varying packing density of L12- and E21-type core-shell-like M-Y clusters
in the stacking fault, depending on the temperature and composition, by considering effective
intercluster interactions derived from first-principles calculations based on the density functional
theory. Using the results of the ab-initio CG Monte Carlo calculations, we characterized the
positional and orientational orders of the attractively or repulsively interacting solute clusters in two
dimensions, in particular the transformation of the possible local ordering patterns of clusters,
considering them analogous to two-dimensional colloidal hard-sphere system. The CG model
indicated that the Zn-Y clusters are arranged in multiple (i.e., at least two) kinds of six-fold domain
structures with intercluster distances of 2√3aMg and √19~√21aMg, respectively, in a manner
consistent with recent scanning tunneling microscopy (STM) measurements [4]. The increase in
volume fraction of solute clusters results in close packing transition of solute clusters, which
explains the steady reduction of radial correlation length between clusters that was observed in
small-angle X-ray scattering measurements for Mg85Zn6Y9 LPSO alloys during the annealing at
high temperature [5].
This study was supported by Grant-in-Aid for Scientific Research on Innovative Area,
“Synchronized LPSO Structure,” No. 23109004.
References:
[1] H. Kimizuka, S. Kurokawa, A. Yamaguchi, A. Sakai, and S. Ogata, submitted (2014).
[2] H. Kimizuka and S. Ogata, Mater. Res. Lett. 1, 213 (2013).
[3] H. Kimizuka, M. Fronzi, and S. Ogata, Scr. Mater. 69, 594 (2013).
[4] S. Kurokawa, A. Yamaguchi, and A. Sakai, Mater. Trans. 54, 1073 (2013).
[5] H. Okuda et al., Scr. Mater. 68, 575 (2013).
97
INV-06
Influence of grain boundaries on slip activity
and twin propagation in magnesium
M.T. Pérez-Prado
1
IMDEA Materials Institute, C/ Eric Kandel, 2, 28906 Getafe, Madrid, Spain
Grain boundaries (GBs) constitute potent obstacles to dislocation motion and twin propagation and
the average grain size (d) is strongly linked in a vast number of materials to the macroscopic yield
strength (σy) by the well-known Hall-Petch law. However, the influence of GBs on individual slip
systems and on twin selection remains, to date, an open question. This presentation will review,
first, recent observations by electron backscatter diffraction (EBSD) assisted slip trace analysis of a
clear transition from non-basal to basal slip-dominated flow in pure magnesium polycrystals when d
decreases below 36 µm, i.e., at grain size ranges that are very relevant for most structural
applications. This change in slip activity is related to an increase in the CRSSnon-basal/CRSSbasal ratio
with decreasing d, consistent with a more potent GB strengthening of non-basal than basal
systems. This research highlights the urge to revise the dominant deformation mechanisms in
microcrystalline metals in order to define effective strengthening strategies. Second, the strong
effect of grain boundary misorientation (θ) on twin selection during twin propagation, recently
revealed by 3D-EBSD measurements and continuum modeling, will be discussed. It will be shown
that non-Schmid effects, such as the activation of low Schmid factor (SF) variants or of double
tensile twins, are absent in the vicinity of low misorientation boundaries and that they become more
abundant as θ increases. These findings underline the complexity of twin-grain boundary
interactions and emphasize the need to incorporate heterogeneities in the intragranular stress
fields into numerical models
98
INV-07
Multi-scale study of plastic deformation in hexagonal metals
Laurent capolungo
Collaborators: D. Rodney, S.Berbenni, L.Leclercq, P.A. Juan, N. Bertin, C. Pradalier, C.N. Tome.
Abstract: Current multi-scale strategies aiming at linking atomistic events leading to plasticity to
both the microstructure evolutions and mechanical response of metals raise several fundamental
problems. The author will provide a personal perspective on the matter. Emphasis will be brought
onto the problem of validation of multi-scale studies dedicated to complex loading of polycrystalline
aggregates. These approaches essentially revolve around baton passes of limited information from
one scale to another. One such critical variable passed along different scales is the defect content
in the material. In the present case, the defects of interests are twins and dislocations. Regarding
dislocations, the author will present recent studies showing how these can be quantified reliably
and how fine scale discrete defect based modeling can be used to assess the role of different
defects interaction in the response of polycrystalline materials. To that end both discrete dislocation
dynamics and Eshelbian micromechanics polycrystal models will be used. In addition, a second
aspect of work will be dedicated to the case of twinning. Here too, the combined use of atomistic
simulations, experimental characterization via EBSD and TEM and the use of continuum based
mechanics approach will be made to provide preliminary understanding of the processes of twin
nucleation, propagation and growth and of their contribution to work hardening. Emphasis will be
made here on the identification of the mechanism responsible for twin thickening and on the latent
interactions between twin domains. The work will consider Mg as model hexagonal materials.
99
ORAL-11
Elastic properties of Mg-Zn-Y alloys with a long-period stacking ordered
structure
M. Tane1*, Y. Nagai1, H. Kimizuka2, K. Hagihara3, Y. Kawamura4
1
The Institute of Scientific and Industrial Research, Osaka University,
8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
2
Graduate School of Engineering Science, Osaka University, 1-3 Machikaneyama, Toyonaka,
Osaka 560-8531, Japan
1
Department of Adaptive Machine Systems, Graduate School of Engineering,
Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan
4
Magnesium Research Center, and Department of Materials Science, Kumamoto University,
2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan
* email: [email protected]
The elastic properties of Mg-Zn-Y alloys with a long-period stacking ordered (LPSO) structure
were investigated, focusing on the elastic properties of LPSO phase single crystal. Directionally
solidified (DS) Mg85Zn6Y9 (at.%) alloy polycrystals consisting of a single phase of the 18R-type
LPSO structure were prepared using the Bridgman technique; it should be noted that the growth of
a large single crystal which was suitable for the measurement of elastic constants was quite difficult.
The X-ray pole figure analysis revealed that in the DS polycrystals the < 1120 > direction in the
hexagonal expression was oriented along the solidification direction. For the DS polycrystals with
the strong crystallographic texture, a complete set of elastic stiffness components was measured
with resonant ultrasound spectroscopy combined with electromagnetic acoustic resonance. To
deduce the elastic properties of LPSO phase single crystal from the elastic properties of polycrystal,
an inverse Voigt-Reuss-Hill approximation was developed. By analyzing the elastic stiffness of DS
polycrystals on the basis of the inverse Voigt–Reuss–Hill approximation, the elastic stiffness
components of the single-crystalline LPSO phase were determined. It was revealed that the
Young’s modulus of the LPSO phase along < 0001> was higher than that along < 1120 > , and the
Young’s modulus and shear modulus were clearly higher than those of pure magnesium with
hexagonal close-packed structure. The elastic properties of LPSO phase single crystal were
analyzed by first-principles calculations based on density functional theory and micromechanics
modeling based on Eshelby’s inclusion theory and Mori-Tanaka’s mean-field theory. The analyses
indicated that the long periodicity of the 18R-type stacking structure hardly enhanced the elastic
modulus, whereas the Zn/Y-enriched atomic layers, containing stable short-range ordered clusters,
exhibited high elastic modulus, which contributed to the enhancement of the elastic modulus of the
LPSO phase in the Mg–Zn–Y alloy [1].
[1] M. Tane, Y. Nagai, H. Kimizuka, K. Hagihara, Y. Kawamura, Acta Mater. Vol. 61 (2013), pp.
6338-6351.
100
ORAL-12
Assessment of Deformation Behavior in Single Crystalline Long-Period
Stacking-Ordered Structure Phase of Mg85Zn6Y9 Alloy by Microtensile Tests
K. Takashima1, Y. Mine1, R. Maezono2, K. Sakamoto2,
M. Yamasaki3, Y. Kawamura3
1
Department of Materials Science and Engineering, Kumamoto University,
Kurokami, Kumamoto 860-8555, Japan
2
Graduate School of Science and Technology, Kumamoto University,
Kurokami, Kumamoto 860-8555, Japan
3
Magnesium Research Center, Kumamoto University, Kurokami, Kumamoto 860-8555, Japan
The long-period stacking-ordered (LPSO) structure phase in Mg-Zn-Y alloys is considered to play
an important role in strengthening of the alloys. However, the effect of the LPSO phase on the
mechanical properties has not yet been fully identified as the size of the LPSO phase is usually in
the range of micrometers. Thus it is rather difficult to measure the mechanical properties of just the
LPSO phase by using a conventional mechanical testing technique. In this study, microsized
single-crystalline tensile specimens were prepared from one LPSO grain, and the deformation
behavior of the single-crystalline LPSO phase was investigated using microtensile tests.
A directionally solidified Mg85Zn6Y9 alloy with a LPSO phase was fabricated by the Bridgman
method. The crystallographic orientation of each grain was determined by electron back-scatter
diffraction analysis, and microsized tensile specimens with a gauge section size of 20 × 20 × 50
3
μm were prepared from one grain of the LPSO phase by focused ion beam machining.
Microtensile tests were carried out using a mechanical testing machine for microsized specimens.
Basal slip ({0001} <11-20>) was activated in the specimen with the loading direction at an angle of
approximately 45 deg relative to [0001], and the corresponding critical resolved shear stress
(CRSS) was determined to be 13 MPa. The elongation was over 50% and the sample fractured in
a ductile manner. The specimen with the loading direction perpendicular to [0001] exhibited brittle
fracture, and its tensile strength was 280 MPa. The fracture surface consisted of facets and the
facets appeared to be associated with {10-10} planes. The specimen with a loading direction
parallel to [0001] exhibited anomalous deformation behavior, and the {11-29} twin was deduced to
occur. The CRSS for the {11-29} twin was determined to be approximately 75 MPa, which was
more than five times higher than that corresponding to the basal slip. The mechanical properties of
the LPSO structure phase showed large crystallographic anisotropy.
101
PLE-05
First-Principles Investigation of Mg-Rare Earth Precipitates and LPSO
Structures
A. Issa, J. E. Saal, and C. Wolverton
Northwestern University, Dept. of Materials Science and Eng., Evanston, IL 60202
[email protected]
To help understand the large strengthening response of RE additions to Mg, we describe several
recent uses of density functional theory (DFT) calculations to study the energetic stability and
morphology of LPSO phases and β’’ and β’ precipitates.
LPSO Structures
Mg alloys containing long-period stacking ordered (LPSO) structures exhibit remarkably high
tensile yield strength and ductility. They have been found in a variety of ternary Mg systems of the
general form Mg–XL–XS, where XL and XS are elements larger and smaller than Mg, respectively. In
this work, we examine the thermodynamic stability of these LPSO precipitates with density
functional theory, using a newly proposed structure model based on the inclusion of a Mg interstitial
atom. We predict the stabilities for 14H and 18R LPSO structures for many Mg–XL–XS ternary
systems: 85 systems consisting of XL = rare earths (RE) Sc, Y, La–Lu and XS = Zn, Al, Cu, Co, Ni.
We predict thermodynamically stable LPSO phases in all systems where LPSO structures are
observed. In addition, we predict several stable LPSO structures in new, as-yet unobserved Mg–
RE–XS systems. Many non-RE XL elements are also explored on the basis of size mismatch
between Mg and XL, including Tl, Sb, Pb, Na, Te, Bi, Pa, Ca, Th, K, Sr—an additional 55 ternary
systems. XL = Ca, Sr and Th are predicted to be most promising in terms of forming stable LPSO
phases, particularly with XS = Zn. Lastly, several previously observed trends amongst known XL
elements are examined. We find that favorable mixing energy between Mg and XL on the facecentered cubic lattice and the size mismatch together serve as excellent criteria determining XL
LPSO formation.
β’’ and β’ precipitates
In an effort to understand the exceptional precipitation strength in Mg–RE (RE = rare earth) alloys,
we use first-principles density functional theory calculations to study the energetic stability, elastic
constants and coherency strain energy of Mg3RE-D019 precipitate phases in a Mg matrix.
Coherency strain energies of Mg–Mg3RE binary systems provides an explanation for the observed
prismatic plate-shaped morphology of many Mg–RE precipitates. We further use first-principles
calculations to uncover an unexpected instability of Mg/β’’ interfaces, and we link this instability
directly to the formation of the β’ precipitates. We show that β’ forms due to the energetic
preference for alternating planes of Mg and β’’. Our work here reconciles the seeming discrepancy
of experimental observations, and elucidates the role of interfacial energy in dictating the sequence
of the Mg-RE alloy aging reaction. Finally, we predict the precipitate morphology in Mg-rare earth
(RE) element binary alloys using a multi-scale modeling approach by combining a threedimensional (3D) phase-field model and first-principles density functional theory (DFT) calculations.
The predicted morphologies of β’ precipitates are in excellent agreement with existing experimental
observations.
References
• J. E. Saal and C. Wolverton, "Thermodynamic Stability of Mg-based Ternary Long-Period
Stacking Ordered Structures" Acta Mater. 68, 325 (2014).
• Issa, J. E. Saal, C. Wolverton, "Physical factors controlling the observed high-strength
precipitate morphology in Mg–rare earth alloys", Acta Mater. 65, 240 (2014).
• Y.Z. Ji, A. Issa, T.W. Heo, J.E. Saal, C. Wolverton and L.-Q. Chen, “Predicting β’ Precipitate
Morphology and Evolution in Mg-RE Alloys Using a Combination of First-Principles
Calculations and Phase-field Modeling”, Acta Mater. (in press, 2014).
• Issa, J. E. Saal, C. Wolverton, " Formation of High-Strength β’ Precipitates in Mg-RE Alloys:
The Role the of Mg/β’’ Interfacial Instability", submitted, 2014.
102
INV-08
Deformation behavior of the synchronized LPSO phases accompanied by
the formation of deformation bands
Koji Hagihara1*, Masahito Honnami1, Takuya Okamoto1,
Michiaki Yamasaki2 , Hitoshi Izuno1, Masakazu Tane3,
Takayoshi Nakano4, and Yoshihito Kawamura2
1
Department of Adaptive Machine Systems, Graduate School of Engineering,
Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
2
Magnesium Research Center, and Department of Materials Science, Kumamoto University,
2-39-1 Kurokami, Chuo-ku, Kumamoto 860-8555, Japan
3
The Institute of Scientific and Industrial Research, Osaka University,
8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan
4
Division of Materials and Manufacturing Science, Graduate School of Engineering,
Osaka University, 2-1, Yamadaoka, Suita, Osaka 565-0871, Japan
* email: [email protected]
The long-period stacking ordered phase (LPSO-phase) has recently been the focus of much
attention as an attractive strengthening phase for Mg alloys [for example 1-3]. In order to clarify the
strengthening mechanism of Mg/LPSO two-phase alloys, it is first necessary to clarify the
mechanical properties and plastic deformation behavior of the LPSO-phase itself. We achieved this
by using the crystals dominantly composed of the aligned LPSO phase grains, prepared by a
directional solidification (DS) process [4] and an extrusion process [5]. It was elucidated that the
LPSO phase is deformed mainly by the operation of (0001) basal slip as similarly to the Mg, but in
addition the formation of "deformation bands" was found to effectively accommodate the plastic
strain in case that the operation of the basal slip was macroscopically hindered. However, the
details on the nature of the deformation bands in the LPSO phase have not been sufficiently
clarified yet. The origin of the deformation band is still unknown, and the possibility of the
deformation kink band and/or the deformation twin has been discussed. To clarify this, in this study
the crystallographic nature of the deformation bands formed in the LPSO phase was examined by
scanning electron microscope-electron backscatter diffraction (SEM-EBSD) pattern analysis. As a
result, the deformation band in the LPSO phase was found to show three arbitrariness on its
crystallographic nature: an ambiguous crystal rotation axis that varied on the [0001] zone axis from
band to band; an arbitral crystal rotation angle that was not fixed and showed relatively wide
distributions; and a variation in crystal rotation angle depending on the position even within a
deformation band boundary itself. These features were coincident with those observed in the
deformation bands formed in Zn polycrystals, suggesting that the formed deformation bands in
LPSO phase crystals are mainly deformation kink bands.
The formed deformation bands are considered to affect the mechanical properties of the alloy. In
particular, in the extruded alloy many deformation bands are introduced during the extrusion
process for the accommodation of stress concentration. The introduced deformation bands are
supposed to act as obstacles to the motion of basal dislocation. However, this effect has not been
quantitatively estimated yet. In this presentation, the influence of the introduced deformation bands
on the further deformation behavior of the LPSO phase crystal will be also discussed based on the
results of the compression tests using the DS and extruded LPSO phase crystals.
References
[1] Kawamura Y, Hayashi K, Inoue A, Masumoto T. Mater Trans 2001;42:1172-1176.
[2] Hagihara K, Kinoshita A, Sugino Y, Yamasaki M, Kawamura Y, Yasuda HY, Umakohsi Y.
Acta Mater 2010;58:6282-6293.
[3] Oñorbe E, Garcés G, Pérez P, Adeva P. J Mater Sci 2012;47:1085-1093.
[4] Hagihara K, Yokotani N, Umakoshi Y. Intermetallics 2010;18:267-276.
[5] Hagihara K, Kinoshita A, Sugino Y, Yamasaki M, Kawamura Y, Yasuda HY, Umakoshi Y.
Intermetallics 2010;18:1079-1085.
103
ORAL-13
Biodegradation behavior and cytotoxicity of Mg-Zn-Gd alloys
Yufeng Zheng1, Dong Bian1, Nan Li1 and Liqun Ruan2
1
Department of Materials Science and Engineering, College of Engineering, Peking University,
Beijing 100871, CHINA [email protected]
2
Magnesium Research Center, Kumamoto University, Kurokami 2-39-1, Kumamoto-shi 860-8555,
JAPAN
Instead of using metallic biomaterials as bio-inert materials, biomaterials scientists and engineers
have been trying to take advantage of the biocorrosion(biodegradable) properties of magnesium
and its alloys to develop various biodegradable implants. The desirable magnesium implants
should stimulate disease tissues to recover while gradually degrade within time at a reliable rate
and finally disappear.
In this present work, three different as-rolled Mg-Zn-Gd alloys were manufactured. Effects of the
addition of Zn and Gd on the microstructure and mechanical properties have been studied. The
degradable behaviors in Hank’s solution have also been investigated. The indirect cell assay and
hemocompatibility experiment were taken to evaluate the cytotoxicity and hemocompatibility.
Overall, we comprehensively evaluated the feasibility of the Mg-Zn-Gd alloys to be biodegradable
materials.
The results showed that the addition of Zn and Gd elements improves the strength and elongation
of magnesium. Electrochemical results implied that Mg-1.7Zn-0.2Gd alloy has the lowest corrosion
rate among all the materials in our study. In cell assay, Mg-1.7Zn-0.2Gd extract promoted the
growth of MG63 cell line and showed less cytotoxicity of L929 and VSMC cell lines, while was
inversely detrimental to the growth of ECV304 cells. Besides, the cytotoxicity of the alloys
decreased while the concentration of extract descended, as for L929, VSMC and ECV304 cells.
Results from hemolysis experiment showed that the hemolysis rate of Mg-1.7Zn-0.2Gd alloy was
so close to 5%.
From all the comprehensive and systematic investigations, we can conclude, Mg-1.7Zn-0.2Gd alloy
has a favorable combination of strength and ductility, a low corrosion rate, acceptable
hemocompatibility without obvious cytotoxicity. It’s one kind of promising biodegradable
magnesium alloy.
104
ORAL-14
Kink deformation expressed by disclination multipole and dislocation arrays
Tetsuya Ohashi1, Yohei Yasuda1,
and Keita Oikawa1
1
Kitami Institute of Technology; Koencho 165, Kitami, JAPAN
[email protected]
The physical picture for kink deformation given by Hess and Barrett [1] shows that plastic
deformation takes place in a band shaped region where plastic slip direction is perpendicular to the
direction of the band and two parallel arrays of edge dislocations are formed at the boundaries
between slipped and not-slipped regions. Burgers vector of the edge dislocations is perpendicular
to the direction of the array and the stress field formed by the arrays can be given by the stress
field associated with two dipoles of wedge type disclinations [2,3]. However in the microstructure of
LPSO type magnesium alloys compressed in the direction parallel to the c-direction, shape of the
kinked region often shows birds-beak appearance and the plastic slip in one-half of the structure
looks to be reversed to the one in the other-half of the structure [4]. Experimental observation
shows that the rotation of crystal lattice is θ/-2θ/θ type and this again shows that the birds-beak
type kink deformation has a compound structure of two slipped regions where positive and
negative shear slip deformations take place in each region. Another point to be discussed is that
the boundaries between slipped and not-slipped regions are not perpendicular to the slip direction.
In this case, Burgers vector of the dislocations along the boundaries is no longer perpendicular to
the boundary and the simple model of disclination dipoles is not sufficient to evaluate the stress
field around the birds-beak type kink deformation but additional arrays of dislocations along the
boundaries are needed, as already suggested by Nakatani and Lei [5].
In this communication, we try to understand such deformation field by multiplying some theoretical
solutions for wedge type disclinations and continuously distributed edge dislocations. Results
show that the total of the Frank vector of the wedge disclinations at the tip of the birds-beak does
not disappear and some relations between the magnitudes of Frank vectors are obtained, as well
as the line density of edge dislocations on the kink-boundaries. Theoretical results are compared
to some numerical results and discussions are made on the elastic strain energy associated to
such structures.
References
[1] Hess, J.B. and Barrett, C.S., Trans. AIME, 185(1949), 599-606.
[2] Li, J.C.M., Surf. Sci., 31(1972), 12.-26.
[3] Pertsev, N.A. et al., J. Mater. Sci., 16(1981), 2084-2090.
[4] Hagihara, K. et al., Intermetallics, 18(2010), 267-276.
[5] Nakatani, A., Lei, X.W., Japan Inst. Met. Mat., Spring meeting, (2014).
105
ORAL-15
Microstructure and mechanical properties of Mg96Zn2Y2 alloy joint
bonded by ultrasonic wire welding
Yuichi Higashi1＊, Chihiro Iwamoto2, Yoshihito Kawamura1
1
Graduate School of Science and Technology, Kumamoto University,
2-39-1 Kurokami, Kumamoto 860-8555, Japan
2
Department of Materials Science and Engineering, Ibaraki University,
4-12-1 Nakanarusawa, Hitachi, Ibaraki 316-8511, Japan
*Corresponding author. E-mail address: [email protected]
Ultrasonic welding is an attractive method because bonding is quickly obtained without extra heat
in the air. In this report, this technology was applied to join Mg96Zn2Y2 two-phase alloy plates which
contain a-Mg matrix and a long-period stacking ordered (LPSO) phase [1], [2]. The yield stress and
the elongation of this Mg alloy reach approximately 420 MPa and 10%, respectively [1]. The
excellent mechanical properties seem to originate both the refined grains of a-Mg matrix and the
LPSO phase [1]. This study investigated microstructure and mechanical properties of the Mg96Zn2Y2
alloy joint.
Samples we used were an extruded Mg96Zn2Y2 alloy. The Mg alloy plates were machined in the
strip from the as-received cylindrical base alloy. Commercial Mg alloy plates AZ31B were also used
to compare the weldability. These Mg plates were welded using an ultrasonic welding machine
(Toshiba Mitsubishi-Electric Industrial System-Corporation and Sonomac Japan INC.). The joints
were cut perpendicular to the weld interface and the microstructure was observed by SEM and TEM.
A shear tensile test was performed to examine the strength of the joints.
After welding, a wide band with fine Mg grains and Mg compounds was produced around the weld
interface. Outside the interfacial band, grain growth occurred. The Mg96Zn2Y2 alloy joints exhibited
an interface fracture mode or a partial plug fracture mode. The crack passed inside the interfacial
band and seemed to have passed between the grains and the compounds. It was considered that
the compounds contributed to the development of cracks during shear tensile test. The strength of
the Mg96Zn2Y2 alloy joints was higher than that of the AZ31B joints despite small the welded
diameter.
References
[1] S. Yoshimoto, M. Yamasaki, Y. Kawamura: Mater. Trans., Vol.47, No.4 (2006), 959-965.
[2] E. Abe, Y. Kawamura, K. Hayashi and A. Inoue: Acta Mater., 50 (2002), 3845-3857.
106
INV-09
Characteristics of mechanical behaviors in a Mg-based synchronized LPSO
structure
K. Higashida and T. Morikawa
1
Department of Materials Science and Engineering, Kyushu University,
Motooka 744, Fukuoka 819-0395, Japan
[email protected]
Inhomogeneous deformation behavior in a magnesium alloy which is almost occupied by longperiod stacking order (LPSO) phase has been investigated by using high-precision marker method,
SEM -EBSD technique and TEM. Particular emphasis is laid on the formation of kink bands which
is one of the most characteristic behaviors observed in this alloy.
Mg alloys containing Zn and rare earth elements such as Y or Gd have a characteristic
microstructure including the LPSO phase and the usual hcp matrix phase. The strengths of the
Mg. It is due to the following two factors. First, the CRSS of
LPSO phase are larger than that of α-Mg.
basal slip of the LPSO phase is about 10 times larger than that of pure Mg. Second,
twinning system, which is easily operated in pure Mg, does not appear in deformed LPSO phase.
Therefore, the hard LPSO phase should contribute to the increase of yield and tensile strength of
the alloy including the LPSO phase.
When the LPSO phase is subject to compressive stress along the direction nearly parallel to the
basal plane, a characteristic microstructure called "kink bands" is generated in the LPSO phase.
TEM observations reveal the occurrence of abrupt bending of the basal planes with large
misorientations at the kink bands.
The kink formation is thought be an effective plastic deformation mechanism as a kind of
buckling when the basal slip deformation is geometrically inhibited, but it should be noted that it is
not only a deformation mechanism but also an important mechanisms for strengthening the LPSO
phase, although the strengthening mechanism has not been necessarily clarified yet. Therefore,
the investigation of the details of morphology and formation behavior of the kink bands is important
to understand those mechanisms.
In the present study, to clarify the details of kinking behavior, high-precision marker method
using electron beam lithography has been employed. Figures 1(a)(b) show an example which
indicates the motion of a kink wall in a Mg LPSO phase. The dotted line labeled BC (kink band
wall) in Fig.1(a) moves to that labeled DE in Fig.1(b). It was also observed that the angle of kinking
at the kink bands increased with increasing compressive strain. Thus kink band walls are mobile
and the kinking angle increases with plastic strain. However, kink bands once stabilized contribute
to the effective resistance against the basal slip. Those formation process and strengthening
behaviors are discussed.
Fig.1 Motion of a kink band wall revealed by lithograph marker: (a) =6%, (b) =9%. The
arrows labeled A indicate the same position common to the both figures.
107
ORAL-16
14H long-period stacking order structures and the deformation behavior of
Mg94Zn2.5Y2.5Mn1 alloy
Jinshan Zhang*,Ding Li, Kaibo Nie, Chunxiang Xu, Xiaofeng Niu,Weili Chen
College of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024,
PR China
*Corresponding author:Tel./fax: +86 351 601 8208;
E-mail address: [email protected] (J. Zhang).
Abstract: Since the low solid solubility Zn , Y during conventional casting , the segregation of the
Mg94Zn2.5Y2.5Mn1 alloy is serious. Most of Zn, Y element are segregated at grain boundaries to form
W-phase and X-phase. In this study, the effects of solidification rate and heat-treatment on the
microstructure of Mg94Zn2.5Y2.5Mn1 alloys were investigated. The results showed that the faster
solidification rate could refine the microstructure while the slower solidification rate as well as the T4
heat-treatment(The air cooling after solid solution treatment) could promote the diffusion of Zn, Y
element, reduce the non-equilibrium crystallization and the the solute segregation and ultimately
lead to the generation of lamellar 14H phases with long-period stacking order (LPSO) structure in
α-Mg matrix. After direct extrusion, the X-phases and 14H-LPSO phases were bended with small
kinking angles. The ultimate tensile strength and elongation of the direct extrusion processed alloy
at room temperature are 386.9 Mpa and 13.5% respectively.
Keywords: Mg-Zn-Y-Mn alloys; Long period stacking ordered (LPSO); solidification rate;
heat-treatment; direct extrusion
108
ORAL-17
A comparison of AE behaviors between LPSO-Mg and Al-Zn-Mg alloys
Manabu Enoki1, Yuki Muto1 and Takayuki Shiraiwa1
1
Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku,
Tokyo 113-8656, Japan
*Corresponding author’s e-mail: [email protected]
Acoustic emission (AE) is well known as an elastic wave in materials due to deformation, fracture
and so on. Macroscopic mechanical properties of materials such as strength, elongation, fracture
toughness, fatigue strength and corrosion characteristics are related to dynamic microscopic
behaviors in materials which are mostly sources of AE. One of the advantages of using AE method
is to globally monitor the deformation and fracture behaviors in samples with high sensitivity. Many
researches have been done to understand the deformation or fracture behaviors in various
materials including metals, ceramics, polymers and composites by analysis of AE behaviors.
However, electrical or mechanical noises sometime interfere in the effective AE signals related
fracture behaviors. Recently our research group has developed a novel AE analysis system with
continuous recording function of AE waveforms in order to avoid noises and extract useful
information related to deformation behaviors in materials. Our system also includes advanced
waveform analysis methods such as wavelet transform with high frequency resolution and accurate
location algorithm by Akaike information criteria (AIC) picker.
This AE method has been applied various mechanical tests of Al-Zn-Mg alloys. For example,
twinning and dewtinning behaviors of Mg-3%Al-1%Zn alloy were investigated. Detwinning occurs in
the twinned areas during tensile loading in the opposite direction. Different AE features depending
on the strain level were observed and detwinning behavior was divided into three stages. In the first
stage, many AE signals with higher peak frequency were generated, then very few AE signals were
observed in the second stage, and finally again some AE signals with lower peak frequency were
observed in the third stage. The results suggested that twin boundary starts to move in the first
stage, then twin area shrinks in the second stage, and twin area disappears in the third stage.
Deference of AE characteristics in each stage seems to be caused by these phenomena. It can be
concluded that AE is an effective method for evaluation of detwinning behavior.
Deformation anisotropy of extruded Mg-3%Al-1%Zn alloy was also investigated on specimens with
different tilt angles from extrusion direction. Mean Schmid factor for main deformation mechanisms
were calculated to explain anisotropy of the extruded magnesium alloy and deformation behavior
investigated by tensile test and texture observation was well explained by calculated Schmid factor.
By analyzing AE during deformation, it was found that the future of AE from twinning varies
according to its behavior and texture condition on which that occurs. Twin growth contributed to AE
energy much less than nucleation. Therefore, AE energy was much more sensitive to twin
nucleation than to twin growth. In addition, AE energy from twin nucleation was also affected by the
size of twins, and large twins generates relatively high AE energy.
In this paper, AE behavior in Mg alloys with long-period stacking ordered (LPSO) structure is
compared with that in Al-Zn-Mg alloys to discuss the difference in dynamic microscopic fracture
phenomena. Kink bands in LPSO phase are characteristic phenomena and these contributions to
mechanical properties are considered by the analysis of AE behaviors during tensile and fracture
toughness tests. The effect of LPSO amount on fracture mechanism was clearly observed as the
differences in AE behaviors.
109
ORAL-18
Fabrication of magnesium alloy with high strength and heat-resistance
by hot extrusion and ageing
1
Zijian YU , Yuding HUANG2, Xin QIU1, Qiang YANG1, Jian MENG1*
1
State Key Laboratory of Rare Earth Resources Utilization, Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences, Changchun 130022,PR China
2
MagIC—Magnesium Innovation Centre, Helmholtz-Zentrum Geesthacht, Max-Planck-Str. 1, D21502 Geesthacht, Germany
*corresponding author, 5625 Renmin Street, Changchun 130022,PR China, [email protected]
Hagihara et al. suggested that the plastic anisotropy of the LPSO phase could be used to
strengthen the mechanical properties of Mg alloys according to the positional relationship between
the LPSO phase and the load direction. Up to now, much attentions have been paid to the
strengthening mechanism of LPSO phase at room temperature and its structural features. However,
its influences on the thermal stability of microstructure are rarely reported.
o
The alloy was prepared by melting pure Mg and Zn at 750 C in an electric furnace under a mixed
atmosphere of carbon dioxide and sulfur hexafluoride. The additions of other elements were carried
out using Mg–20Gd (wt%), Mg–20Y (wt%), Mg–20Nd (wt%) and Mg–30Zr (wt%) master alloys.
After melting and stirring, the melt was poured into a water-cooled cylindrical iron mold with a
o
diameter of 90 mm at 720 C. The homogenization annealing of this cylindrical billet was performed
o
at 535 C for 24 h followed by T4 treatment. Their microstructures were observed using OM, XRD,
SEM, EDS and TEM.
The selected-area diffraction (SAD) patterns indicate the existence of another phase. In this pattern,
extra diffraction spots are evenly arranged between directed spot and (0002)α fundamental spot
along the [0001]α. This indicates that the rod-like shaped precipitate is the 14H-type LPSO phase.
The XRD results demonstrated that some 14H-type LPSO precipitates formed during annealing at
o
o
400 C and 450 C. The formation of 14H-LPSO phase during high temperature annealing may
contribute to a good stability of grain size. In addition to the β(Mg5RE) and 14H-type LPSO phases,
a fine lamellar precipitate is observed in the extruded samples with and without T5 treatment.
These fine lamellar precipitates are of over 500 nm in length and less than 2 nm in thickness. SAD
patterns show that streaks are visible along the [0001]α direction at the (0000)α and the {1010}α
positions. These diffraction patterns indicate that the habit plane of the fine lamellar precipitate is
parallel to the basal plane of Mg matrix. The TEM micrographies observed along the [1120]α show
that β′phase precipitates uniformly distribute in the matrix. The corresponding diffraction spots
located at 1/4(1010)α, 1/2(1010)α, 3/4(1010)α are indicated by white arrowheads in Fig.7d.
Table 1The mechanical properties of as-extruded and T5 samples
o
Alloys
Temperature( C)
Elongation (%)
σ0.2 (MPa)
σb (MPa)
25
327
377
3.8
200
290
357
5.0
Extruded (F)
250
268
286
10.5
300
172
193
54.4
25
373
473
4.1
200
343
405
4.2
Extruded+T5
250
316
369
6.3
300
212
232
35.7
Note: F—as-extruded; extruded+T5—peak-aged at 200oC.
Compared with the β phase, the finely dispersed LPSO phase has a better thermal stability, since
it remains stable after annealing at high temperatures. After annealing, the peaks of LPSO phase
still exist while the peaks of Mg5RE disappear. The intensity of LPSO peaks is also stronger,
o
indicating that the annealing treatment at 450 C may result in the formation of more LPSO phases.
o
Most Mg5RE phases dissolves at temperatures above 400 C, the content of alloying elements in
the Mg matrix increases; and new LPSO structures form during the annealing process. The existing
LPSO phase remains stable during annealing treatment. Thus, the volume fraction of LPSO
phases probably increases. LPSO phase normally possesses a relative large aspect ratio and
distributes along grain boundaries. They act as the main strengthening phase instead of Mg5RE in
o
this alloy when the temperature exceeds 400 C.
110
ORAL-19
Friction Stir Welding of the LPSO type-magnesium alloys
Minami Sasaki1 and Masashi Inoue3
1, 2
Fuji Light Metal Co., Ltd. 2168 Nagasu Nagasu-mati Tamana-gun Kumamoto Japan
Minami Sasaki: [email protected]
Fuji Light Metal co., ltd has been producing the extrusion of aluminum alloy since 1969. And in
late years, as new business, we began sale of the wrought magnesium alloys, and we’ve been
pushing forward the production technology development until now.
The joining technology is elemental technology to make the versatility of the alloy, and the high
strength wrought magnesium alloys such as the LPSO type alloy need the appropriate joining in
consideration of their characteristic.
[1, 2, 3]
Which
Friction stir welding (FSW) is a joining process that was developed by TWI in 1991.
[4, 5, 6]
Furthermore, FSW often exhibit better joint
can reduce the joining defects than fusion welds.
efficiency than fusion welding or friction welding. From such advantages, this process is used for
[7, 8]
The schematic illustration of FSW is shown in
the joining of the large structure of aluminum.
the figure1. A turning tool is pushed into the interface to weld. The materials are softened by the
frictional heat from tool, and then material flow occurs. By material flow during welding, the stir
zone shows a characteristic microstructure, that usually consisting of fine uniaxial recrystallized
[1, 2, 4, 9, 10]
grains. And this fine structure often causes superior mechanical properties than matrix.
We’ve welded the various magnesium alloys by FSW, and investigated their properties. In present
study, we welded the extruded plate of the LPSO type-Mg alloy and investigated the influence that
welding condition gave to microstructure and mechanical properties. The welded plate of LPSO
type-Mg alloy showed the welding efficiency of more than 95 %, that was superior efficiency in
comparison with that of general wrought Mg alloys. The weld zone that a cross section
[1, 2, 4]
and there were
perpendicular to the welding direction had a typical nugget-shaped stir zone,
no defects. Figure 2 shows the SEM image of the stir zone. By frictional heat and the plastic flow,
the stir zone had the very fine recrystallized grains and LPSO structures less than 1 µm.
For more information about these, I report it on that day.
Figure 1. Schematic illustration of the frictionstir-welding process.
Figure 2. SEM image of the stir zone.
[1] C. J. Dawes and W. M. Thomas: Welding J., 1996, vol. 75 (3), pp. 41-45.
[2] C. J. Dawes: Proc. 6th Int. Symp. of JWS, JWS, Nagoya, Japan, 1996, pp. 711-718.
[3] W. M. Thomas and E. D. Nicholas: Mater. Design, 1997, vol. 18 (4-6), pp. 269-273.
[4] C. G. Rhodes, M. W. Mahoney, W. H. Bingel, R. A. Spurling, and C. C. Bampton: Scr. Mater., 1997, vol. 37, pp. 355-361.
[5] Y. S. Sato, H. Kokawa, M. Enomoto, and S. Jogan: Metall. Mater. Trans. A, 1999, vol. 30A, pp. 2429-37.
[6] Y. S. Sato, H. Kokawa, M. Enomoto, S. Jogan, and T. Hashimoto: Metall. Mater. Trans. A, 1999, 30A, pp. 3125-3130.
[7] M. R. Johnsen: Welding J., 1999, vol. 78 (2), pp. 35-39.
[8] J. G. Wylde: J. Jpn. Inst. Light Met., 2000, vol. 50, pp. 189-197.
[9] R. S. Mishra, M. W. Mahoney, S. X. Mcfadden, N. A. Mara, and A. K. Mukherjee: Scr. Mater., 2000, vol. 42, pp. 163-168.
[10] Y. S. Sato, H. Kokawa, K. Ikeda, M. Enomoto, S. Jogan and T. Hashimoto: Metall. Mater. Trans. A, 2001, vol. 32A, pp.
941-948.
111

Technical program

Transcription

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