Industrial perspective of coating production on titanium

BioTiNet 10th January 2013
Dr James A. Curran
AN INDUSTRIAL PERSPECTIVE OF
COATING PRODUCTION ON TITANIUM
Keronite International Ltd
© Keronite 2013
“An industrial perspective of
coating production on titanium”
Talk outline
• Keronite’s coating process
Hard, wear-resistant surface oxides for Al, Mg & Ti alloys
• Typical properties and applications on Al and Mg
• Properties, applications and markets for Ti
• Bio-medical applications
© Keronite 2013
CONFIDENTIAL – Please consult [email protected] prior to onward distribution
2
Benjamin Franklin (1752)
© Keronite 2013
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Original Patent (US)
© Keronite 2013
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Origins
Applied “PEO technology” has its origins in the USSR, where it was
developed and used primarily for aerospace applications
Courtesy NASA/JPL-Caltech.
1980s – German dentistry
© Keronite 2013
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Keronite International Ltd
Keronite International specialises in the
development and worldwide commercial application of
PEO technology for surface treatment of Al, Mg and Ti
•
•
•
•
© Keronite 2013
Service provider
Equipment design & installation
Application engineering
World-leading R&D
Courtesy NASA/JPL-Caltech.
Global HQ near Cambridge (UK)
US HQ in Indianapolis
Partners and licensees worldwide
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Modern, global operations
Semi-automated Keronite production line in South Korea
© Keronite 2013
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Introduction to PEO
Plasma electrolytic oxidation
anodising
selective
conversion to
hard crystalline
ceramic oxides
© Keronite 2013
amorphous oxide film, only
a few nanometres thick
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Fir0002/Flagstaffotos
Plasma discharges
Power density similar to lightning
© Keronite 2013
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Plasma discharges
Temperature:
4,000-5,000 K
Local current (mA)
40
Duration:
10s of micro-seconds
20
Scale:
10s of microns
Interface with condensed states:
electrolyte and solid
0
0
© Keronite 2013
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Time (µs)
100
10
The process in action:
© Keronite 2013
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Process schematic
20 mm
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Structure & Composition (Al)
20 mm
20 mm
20 mm
Cross-section: dense, well-adhered layer
200 nm
Surface: features
Sub-µm
characteristic
crystallites of melt flow
X-ray diffraction
phase/crystallinity analysis
α-Al2O3 corundum
© Keronite 2013
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Hardness & wear resistance
Crystalline phases
such as α-Al2O3
1500-2000 HV0.1
250
HA
PEO
(on Al 7075)
(on Al 7075)
Keronite
Pin-on-disc (m/mm3)
200
(on AA7075)
150
100
5140 steel
50
AZ91
α-Al2O3 corundum
© Keronite 2013
Ti
Hard Anodising
AA7075
0
0
KTT
KTM
200
400
600
800
1000
Hardness (HV0.1)
1200
1400
1600
1800
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www.hennovanbergeijk.nl
Wear protection
The BMW Oracle America’s Cup Yacht
pioneered the use of Keronite™ coated winch
drums in 2007. These have since been widely
adopted in high-performance racing yachts.
Corrosion resistance
Extreme hardness
Reliability
Relative hardness (HV0.1):
Aluminium
Anodising
Hard steel
Sand
PEO
0
1000
2000
© Keronite 2009
2013
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World motorsport
Keronite coatings are widely used in motorsport.
They are in particular demand with many of the worlds’ leading
motorsport teams, including F1 teams where Keronite is the most
widely applied protective coating for magnesium.
Magnesium corrosion protection
Hardness and wear protection
Thermal protection
© Keronite 2013
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Layer structure (Al)
1 µm
Similar to anodising:
Uniform coverage of complex shapes
Well-controlled, predictable growth
Non-columnar structure: Superior edge protection
Less susceptible to corrosion, wear
Lower fatigue debit
© Keronite 2013
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Textured brake surface
High performance off-road cycle rims use Keronite to protect a machined
braking surface, delivering far greater durability than hard anodised aluminium.
+50
Relief (µm):
-25
5 mm
© Keronite 2013
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Racing yacht winch drums
Courtesy BMW Oracle
The America’s Cup Yacht BMW Oracle
pioneered the use of Keronite™ coated winch
drums in 2007. These have since been widely
adopted in high-performance racing yachts.
© Keronite 2011
2009
2013
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Friction & bearing surfaces
Ra = 1.61 µm
+5 µm
0 µm
-5 µm
-8 µm
Ra = 0.05 µm
20 mm
Typical friction coefficients:
µ
Keronite vs. bearing steel:
Keronite vs. Keronite:
0.6-0.7
~0.6
Lubricated Keronite:
Polished, lubricated:
~0.1
~0.03-0.04
Bearing washers
Ball valve
Knee
replacement
© Keronite 2013
(under development)
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Al MMC structures
Keronite coating
6061 AMC640xa
with 40% SiC
= 6061 with 40 Vol% SiC
1 mm
© Keronite 2013
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Image courtesy of NASA
Typical fatigue data
350
Maximum Bending Stress (MPa)
300
250
200
150
100
AMC640xa-T6 PGQ Billet (Uncoated)
50
AMC640xa-T6 PGQ Billet (Coated)
0
1,000
10,000
100,000
1,000,000
10,000,000
Number of Cylces
© Keronite 2013
Fatigue data courtesy of AMC, with permission of
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Mechanical resilience
In spite
of its hardness, the coating can be
Compliance
far more compliant than typical ceramics.
A pliable, detached coating:
30±15 GPa
This makes it very strain tolerant: for any
given strain, the coating will experience
only relatively low stresses: σ=Eε
Benefits of compliance:
Strain tolerance
Mechanical stability
Thermal stability
Wear resistance
Keronite also benefits from scale effects
such as a sub-critical crystallite scale and
crack deflection mechanisms which result
in hardness, strength, and toughness.
Sub-µm crystallites:
200 nm
© Keronite 2013
J.A. Curran, T.W. Clyne / Surf. & Coat Tech 199 (2005) p. 168
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Moulds and heat-sinks
Keronite provides a very hard-wearing surface for aluminium
tools, enabling steel replacement and improved heat transfer.
In most cases, these Keronite-coated moulds are rendered so
durable that they out-last the component production runs.
The Keronite finish is rough and stonelike, but can be polished and/or polymer
sealed for a smoother, non-stick finish
© Keronite 2013
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Structure on magnesium
20 mm
Typical surface of a thick (40 µm +) coating:
Dense, well-adhered layer
Good dimensional control
Modified by melt processes
100 mm
AZ91 Substrate
© Keronite 2013
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Phase composition
Anomag™ coatings are entirely amorphous, like most anodized coatings
MgO periclase
Mg 104
Mg 202
MgO (Periclase) 222
Mg 004
Mg 200
Mg 112
Mg 201
MgO (Periclase) 220
Mg 103
Mg 110
Mg 102
MgO (Periclase) 200
Mg 101
Mg 002
Mg 100
Keronite™ consists mainly of MgO in the cubic crystalline phase Periclase
The Keronite consists primarily of MgO Periclase
Pattern 045-0946
amorphous
© Keronite 2013
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Mg Taber abrasion
70
60
Mass loss (mg)
50
MgO periclase
Up to 815 HV
40
30
Proprietary aondising
anodising
Proprietary
20
(like Anomag™)
10
20 µm G3 Keronite
0
0
2000
4000
6000
8000
10000
12000
Revolutions of CS17 Abrader, 10N
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Mg wear protection
Cylinder configurations were tested with various alloys, counterparts and
lubricants – primarily MRI alloys under the European FP5 “NANOMAG” project
Mg
Al
Anodising
Hard steel
PEOKTM
on Mg
Sand
PEO on Al
KTA
0
500
1000
1500
2000
Hardness (HV0.1)
Keronite coated MRI201 magnesium pistons out-performed
the aluminium (AT12) reference standard and CrN coatings
© Keronite 2013
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Magnesium parts
© Keronite 2013
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Mg corrosion protection
Keronite is the only system to exceed the protection offered by Cr(VI) conversion
-Ford Motor Co. research
© Keronite 2005
© Keronite 2013
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Mg aerospace housings
Surface protection for WE43B and ZE41A cast gearbox housings:
• Cr-free corrosion protection
• Minimal fatigue debit
• Wear protection
• Paint adhesion
• DOW17 and HAE replacement
• Meets or exceeds AMS 2466 and ASTM-B-893
• Qualified pre-treatment for Rockhard Resin
© Keronite 2013
Image: Bristow Norway
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Thermal management
Coatings stable to over 900°C (1650°F)
Strain tolerant (E ~30 GPa) and resistant to thermal cycles
Thermal conductivities ranging from ~0.2 to 5 W m-1 K-1
Thermal protection
(e.g. Federal Mogul piston crowns)
Insulating heat sinks
(e.g. High power LED substrates)
The Thermal Conductivity of Plasma Electrolytic Oxide Coatings on Aluminium and Magnesium
Curran, J.A. and Clyne, T.W., Surface and Coatings Technology, v.199(2-3), pp.177-183 (2005).
© Keronite 2013
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Thermal properties
Keronite has a wide range of applications in
wear-resistant, “high”-temperature applications
The Thermal Conductivity of Plasma Electrolytic Oxide Coatings on Aluminium and Magnesium
Curran, J.A. and Clyne, T.W., Surface and Coatings Technology, v.199(2-3), pp.177-183 (2005).
© Keronite 2013
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High-power substrates
Developed for high dielectric strength (>2kVAC,DC) insulation
Resistant to thermal shock & thermal cycles of over 500°C (900°F)
Coating stable to over 900°C (1650°F)
Minimal thermal barrier (λ >2 W m-1 K-1)
Patent WO2006075176:
“Electrical power substrate”
• High-power electronics
• LED lighting systems
• Plasma processing
© Keronite 2013
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Electrical substrate
Patent WO2006075176: “Electrical power substrate”
WO2006075176 Electrical Power Substrate
Renovalia® concentrated solar photovoltaic systems
© Keronite 2013
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Dielectric strength
26 kV breakdown strength
(in proprietary hybrid system)
© Keronite 2013
Fir0002/Flagstaffotos
2-3 kV dielectric (GΩ at 600 °F)
with minimal thermal resistance
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“An industrial perspective of
coating production on titanium”
Talk outline
• Keronite’s coating process
Hard, wear-resistant surface oxides for Al, Mg & Ti alloys
• Typical properties and applications on Al and Mg
• Properties, applications and markets for Ti
• Bio-medical applications
© Keronite 2013
37
Hardness & wear resistance
Wear protection presents a challenge for us on titanium
because the oxides are not very much harder than Ti
250
Pin-on-disc (m/mm3)
200
Keronite on
Al 7075
150
100
5140 steel
KTT
50
AZ91
0
0
200
Ti
KTM
Hard Anodising
AA7075
400
600
800
1000
1200
1400
1600
1800
Hardness (HV0.1)
© Keronite 2013
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Ti6Al4V bearing carriers
Ti6Al4V landing gear bearing carriers for Boeing 737NG MROs
737-SL-32-172
BAC 5696
Keronite provides an improved bearing refurbishment service:
• Improved wear performance
• Improved anti-galling protection
© Keronite 2013
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Ti6Al4V wear protection
Ti6Al4V against SAE52100 steel, block-on-ring dry sliding wear test
8
Wear volume (mm3)
7
6
5
4
3
2
1
0
0
20
40
60
80
100
120
Applied Load (N)
C. Martini, J.A. Curran et al., Wear 269 (2010) pp. 747–756
© Keronite 2013
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Ti6Al4V coating variants
Coating phase composition (weight %):
20±3 % Rutile TiO2
100%
Amorphous
TiO2
1200
Hardness (HV0.1)
1000
800
600
30±4% AnataseTiO2
Anodised
Ti6Al4V
Standard
Keronite on Ti
Tialite
Keronite
Silicate
Keronite
New 2012
Keronite
Keronite is hardened
by generating
crystalline phases
Amorphous
a-Al
2O3 TiO2
Amorphous
TiO
2
Al2TiO5
Tialite
Al TiO5
Tialite
g-Al
2O3 2
Anatase
TiO2
Anatase
TiO
 Rutile TiO2 2
Amorphous
SiO2
Amorphous
SiO2
Rutile
Amorphous
SiO
2
Rutile
TiO2
TiO2
g-Al2O3 TiO2
c-Al2O3
Anatase
a-Al2O3
a-Al2O3
Tialite
Al2TiO5
 Amorphous TiO2
400
Ti6Al4V substrate
200
0
© Keronite 2013
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Ti6Al4V coating variants
Coating phase composition (weight %):
1200
Hardness (HV0.1)
1000
800
600
Anodised
Ti6Al4V
Standard
Keronite on Ti
Tialite
Keronite
Silicate
Keronite
2012
Amorphous
a-Al2O3 TiO2TiO
2
Development Amorphous
Al2TiO5
Tialite
Al TiO5
Tialite
g-Al
2O3 2
Anatase
TiO2
Anatase
TiO
 Rutile TiO2 2
Amorphous
SiO2
Amorphous
SiO2
Rutile
Amorphous
SiO
2
Rutile
TiO2
TiO2
g-Al2O3 TiO2
c-Al2O3
Anatase
a-Al2O3
a-Al2O3
Tialite
Al2TiO5
 Amorphous TiO2
400
Ti6Al4V substrate
200
0
© Keronite 2013
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Hardness distribution
40
15
14
13
30
11
10
9
8
Occurrence
Hardness (GPa)
12
20
7
6
10
5
4
3
0
10 20 30 40 50 60 70
Distance from substrate-coating interface (µm)
© Keronite 2013
0
5
6
7
8
9 10 11 12 13 14 15
Hardness (GPa)
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Non-stick surfaces
Keronite won DuPont’s Plunkett award in 2002
for innovation with Teflon®:
PEO is the best way to stick PTFE
(or many other “non-stick” materials)
to Al, Mg or Ti
A very hard-wearing, non-stick surface is achieved
PEO+PTFE to prevent phalangeal tendon adhesion
© Keronite 2013
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PEO TiO2 coatings
A wide range of phase compositions and surface structures is achievable
a-TiO2
r-TiO2
Ti6Al4V
“Doping” is possible: Ca, P…
even 10-30% HA is allegedly achievable
© Keronite 2013
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Surface structure
Range of pore structures and sizes from nm to 10s of µm
Surface area enhancements by a factor of 100x
© Keronite 2013
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Porous scaffolds
10 µm
1 mm
Continuum of fine-scale porosity:
µm to nm scale
High surface area:
~10 m2 per g
Photocatalytic surfaces on Ti:
Anatase TiO2
Microbial Fuel Cell
© Keronite 2013
100 nm
1 µm
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Photoactivity
High proportions (~90 Wt %) of anatase TiO2 have been achieved, and the coatings
enhance the rate of Methylene Blue dye degradation by factors of 2-5 on flat plate
0
100
90
80
70
60
50
40
30
20
10
0
Phase proportion (wt %)
-0.01
y = -0.00016x
-0.02
y = -0.00030x
ln (C/Co)
Anatase
Rutile
Amorphous
Other Crystalline
-0.03
-0.04
y = -0.00042x
-0.05
-0.06
y = -0.00047x
y = -0.0010x
-0.07
0
10
20
Process time (minutes)
© Keronite 2013
0
40
80
120
Exposure time (minutes)
160
48
photocatalyst
30 µm
Surface area >6 m2 g-1
~90% anatase TiO2
Water purification
© Keronite 201
2013
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Dental implant surfaces
There are various suppliers of PEO-coated titanium dental implants.
These include market-leader Nobel Biocare’s TiUnite technology
www.nobelbiocare.com
www.nobelbiocare.com
© Keronite 2013
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TiUnite™
www.nobelbiocare.com
“Nobel Biocare has received FDA clearance to claim a more rapid bone
formation and greater amount of bone in contact with the TiUnite™
surface during healing.
The enhanced bone response to TiUnite™ results in faster and
stronger osseointegration and, thereby, better maintenance of the
implant stability compared to machined titanium implants. When placed
in soft bone and immediately loaded, the enhanced osseointegration of
Nobel Biocare TiUnite™ implants results in higher success rates
compared to machined implants.
In addition to the publications supporting the FDA-cleared claims for the
TiUnite™ implant surface, more than twenty references are
available, which cover the use of TiUnite™ implants in various clinical
and preclinical situations, using different types of protocols, and with
various follow-up times…”
http://www.nobelbiocare.com/en/about-nobel-biocare/research-development/tiunite
© Keronite 2013
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In-vivo tests
Y.-T. Sul / Biomaterials 24 (2003) 3893–3907
Eighty implants were inserted in the femora and tibiae
of ten mature New Zealand white rabbits for 6 weeks.
Hitsomorphometrical tests
(Toluidine blue stain)
BMC %
Removal torque (Ncm)
Removal torque
(after 6 weeks healing)
Control
© Keronite 2013
PEO
Control
PEO
Control PEO
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PEO TiO2 coatings
“Standard PEO”
The wider range of PEO coatings
that have evolved more recently
have not been explored.
a-TiO2
r-TiO2
Ti6Al4V
© Keronite 2013
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In-vitro tests of wider PEO
In-vitro tests such as studies of chondrocyte and osteoblast proliferation and
differentiation have been conducted on a wider range of PEO coating types
Cell adhesion to plasma electrolytic oxidation (PEO) titania coatings,
H.J. Robinson, A.E. Markaki, C.A. Collier and T.W. Clyne
J. Mech. Behav. Biomed. Mater. 2011 Nov;4(8):2103-12
Bovine chondcrocyte proliferation on Keronite coatings after 3 and 6 days
© Keronite 2013
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Surface structure
Hope is to distinguish between roles of surface chemistry and morphology
© Keronite 2013
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Cell and tissue adhesion
FEGSEM micrograph of a Keronite-treated Cp-Ti surface, with an adherent bovine
chondrocyte (critical point dried), showing intimate contact between the cell and Keronite
© Keronite 2013
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Adhesion testing
Enzymatic removal
Stress fibres
Observation
Cell spreading
Focal Adhesions
Global Population
Individual cells
Mechanical forces
Normal forces
© Keronite 2013
Shear forces
“Cell Adhesion to Plasma Electrolytic Oxidation (PEO) Titania Coatings, Assessed using a Centrifuging
Technique”, Robinson, H.J., et al., Journal of the Mechanical Behaviour of Biomedical Materials, 408 (2011)
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Systematic study
Trypsin enzyme
Ti6Al4V substrate
Ra 0.2 ± 0.1 µm
Ti6Al4V
PEO “phosphate”
Ra 4.3 ± 0.1 µm
Normal force
TiO2
Ti6Al4V
PEO “mixed”
Ra 7.5 ± 0.3 µm
Al2TiO5
Shear force
Ti6Al4V
© Keronite 2013
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Resistance to enzyme
Bovine chondrocytes, exposed to trypsin protease
enhancement
Both PEO coatings show better
performance than Ti6Al4V and the
best performance is from the
roughest surface…
…this may be a geometrical effect.
Al2TiO5
Ti6Al4V
© Keronite 2013
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Measuring cell adhesion
Direct measurements of cell adhesion:
2) By mechanical force
Empty tube
Substrate
Cell culture medium
Cells adhered
to this surface
“Cell Adhesion to Plasma Electrolytic Oxidation (PEO) Titania Coatings, Assessed using a Centrifuging
Technique”, Robinson, H.J., et al., Journal of the Mechanical Behaviour of Biomedical Materials, 408 (2011)
© Keronite 2013
60
“An industrial perspective of
coating production on titanium”
Talk outline
• Keronite’s coating process
Hard, wear-resistant surface oxides for Al, Mg & Ti alloys
• Typical properties and applications on Al and Mg
• Properties, applications and markets for Ti
• Bio-medical applications
© Keronite 2013
61
Summary
Plasma electrolytic oxidation can form a wide range of oxide
structures on the surfaces of Al, Mg and Ti alloys.
On Ti, the traditional markets of wear-protection may be of little
interest (even with non-stick surfaces for implants), but PEOTiO2 is a well-established surface treatment to improve the
adhesion of dental implants.
The wider variety of phase structures achievable
(such as anatase TiO2, and Ca/P-enriched oxides)
and the wider range of surface structures
offers scope for further improvements
but remains to be evaluated systematically.
© Keronite 2013
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Contact information
Dr James A. Curran
Royal Society Industry Fellow
[email protected]
Keronite International Ltd
53 Hollands Road
Haverhill
CB9 8PJ
© Keronite 2013
63