Fatigue life of cast Inconel 713LC with/without

Fatigue life of cast Inconel 713LC with/without
protective diffusion coating under bending,
torsion and their combination
Jaroslav Pokluda1,2), Karel Obrtlík3), Karel Slámečka1,2),
Jana Horníková1,2), Marta Kianicová4)
1)
2)
3)
4)
Faculty of Mechanical Engineering, Brno University of Technology, Brno, Czech Republic
Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic
Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno, Czech Republic
Faculty of Industrial Technologies of Púchov, Alexander Dubček University of Trenčín, Púchov, Slovakia
ESIS TC2 (Micromechanisms)
Oxford, 2.4.-3.4. 2012
Introduction
Motivation
Project MPO FR-TI1/099 (2009-2012) financed by the Ministry of Industry and Trade
of the Czech Republic – Research and Development Leading to Innovation of Small
Turbine Engines (Brno University of Technology, Faculty of Mechanical Engineering,
PBS Velká Bíteš, a.s, Czech Republic).
Nickel-based superalloy Inconel 713LC
 low-costs material produced mainly for the aircraft gas turbines market
 harsh operating conditions (high temperatures, temperature gradients, abrupt thermal
changes, oxidizing and corroding atmosphere, high pressures, multiaxial stresses)
Protective coatings
 bond coatings (diffusion and overlay coatings), thermal barrier coatings
 diffusion coatings (Al, Cr, Si or Pt), TGO supplies oxidation and hot-corrosion
resistance
Biaxial bending-torsion fatigue
 very little information on the fatigue behaviour under
complex loading modes
 goal: to evaluate the fatigue behaviour of
specimens made of Inconel 713LC furnished with
aluminium and aluminium-chromium protective
diffusion coatings under bending, torsion and
combined bending-torsion loading
Ni-based superalloy Inconel 713 LC
Microstructure: solid solution g + harden phase g‘ + primary complex carbides of MC
type (on Ta, Ti, Nb, Mo, Cr, Zr base) + secondary complex carbides of M23C6 type (on
W, Ti, Cr, Nb base).
Nominal chemical composition of nickel-based superalloy IN 713LC.
C
Mn
Si
Cr
Ti
Al
Fe
B
Zr
Nb
Ta
Mo
Cu
Co
0.05
0.05
0.05
12.08
0.75
5.91
0.10
0.01
0.1
2.02
0.05
4.58
0.05
0.05
Monotonic properties of INC 713LC at room temperature: yield strength σy ≥ 677 MPa,
ultimate tensile strength σu ≥ 745 MPa, ductilityA5 ≥ 3 %.
Protective diffusion Al-Cr coating
cracks
pores
outer layer
diffusion zone
substrate
Out-of-pack coating (1050 C, 5h), heat-treatment (950 C, 5h)
at the Politechnika Śląska, Katowice.
EDS analysis – outer layer.
Location
Al-C
Cr-C
Ni-C
#1
50.9
4.1
45.0
#2
31.7
56.8
3.0
#3
18.6
16.6
Nb-S
Mo-S
8.5
64.8
Experimental details
 Testing
operating
regime.
machine MZGS-200
in the load-control
 Symmetric (R=-1) bending and
torsion with a sinusoidal cycle of
frequency f  30 Hz.
 Room temperature, laboratory
ambient air environment.
Loading ratio: z 
a
The specimen geometry.
 a   a 
Experiments - overview.
Material
bending
b-t (z ≈ 0.5)
torsion
total
Inconel 713LC
8
6
7
21
Inconel 713LC + Al coating
10
8
9
27
Inconel 713LC + AlCr coating
9
5
8
22
S-N curves – bending
S-N curves – bending + torsion
 ekv   a2  3 a2
High temperature push-pull tests
*
*
*
S-N curves – torsion
SEM – bending
*
B38 38-2: Inconel 713LC+AlCr coating, bending, Nf = 1.5 104 cycles.
SEM – bending + torsion
*
B38 17-10: Inconel 713LC+Al coating, bending + torsion, Nf = 6.0 104 cycles.
SEM – push-pull, 800 °C
*
B38 P1: Inconel 713LC+Al coating, push-pull, 800 C, Nf = 397 cycles.
SEM – torsion
*
B38 37-2: Inconel 713LC+Al coating, torsion, Nf = 8.5 104 cycles.
Multiaxial Fatigue Life Criteria
Gough-Pollard (empirical)
2
2
 a  a 
    1
 c   c 
Mataka (critical plane)
 2 c

 1  n,max   c
 c

 max,a  
Crossland (stress invariants)
 3

J 2,a   c  3   h,max   c
 c

 max …maximal shear stress;
J2
 n …normal stress on critical plane
…second invariant of stress deviator tensor;
 h …hydrostatic stress
Multiaxial Fatigue Life Criteria
Gough-Pollard
conservative
Crossland
conservative
Log (Nf,exp)
conservative
Mataka
non-conservative
Log (Nf,calc)
non-conservative
Log (Nf,calc)
non-conservative
Log (Nf,calc)
Multiaxial Fatigue Life Criteria
Nf = (103,105) cycles
All specimens
conservative
conservative
non-conservative
Logarithmic relative error index:
non-conservative
i
log
E

)
)
log N (fi,exp
 log N (fi,calc
)
log N (fi,exp
Conclusions
In the LCF domain, the presence of coating slightly reduces the fatigue
resistance to room-temperature bending, combined bending-torsion as
well as to high-temperature push-pull loading. Conversely, it slightly
increases the torsion resistance at room temperature.
The different response seems to be caused by the different nucleation
efficiency of secondary-phase particles within the diffusion zone.
The observed differences between the fatigue life of coated and
uncoated specimens are rather minor. Consequently, one can assume that
the deposition of the coating on turbine blades will lead to a longer service
life of these components since the coating substantially improves the hightemperature oxidation and corrosion resistance of blades.
Concerning the multiaxial fatigue life prediction methodologies,
the Matake criterion shows good prediction capability for combined
bending-torsion data, especially in the LCF region.
Thank you for your
attention
Acknowledgements
Ladislav Čelko
Simona Pospíšilová
Petr Řehák
The authors greatly acknowledge the financial support provided by the Ministry
of Industry and Trade of the Czech Republic (Project MPO FR-TI1/099)
and by the Czech Science Foundation (Project P108/12/0144). K.S. wishes to thank
for the bursary provided by ESIS.