Fatigue life of cast Inconel 713LC with/without

protective diffusion coating under bending,

torsion and their combination

ESIS TC2 (Micromechanisms) Oxford, 2.4.-3.4. 2012

Jaroslav Pokluda1,2), Karel Obrtlík3), Karel Slámečka1,2),

Jana Horníková1,2), Marta Kianicová4)

1) Faculty of Mechanical Engineering, Brno University of Technology, Brno, Czech Republic

2) Central European Institute of Technology, Brno University of Technology, Brno, Czech Republic

3) Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno, Czech Republic

4) Faculty of Industrial Technologies of Púchov, Alexander Dubček University of Trenčín, Púchov, Slovakia

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

Nominal chemical composition of nickel-based superalloy IN 713LC.

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).

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

EDS analysis – outer layer.

substrate

diffusion zone

outer layer pores

cracks

Location Al-C Cr-C Ni-C Nb-S Mo-S

#1 50.9 4.1 45.0

#2 31.7 56.8 3.0 8.5

#3 18.6 16.6 64.8

Out-of-pack coating (1050 C, 5h), heat-treatment (950 C, 5h) at the Politechnika Śląska, Katowice.

The specimen geometry.

Experimental details

Experiments - overview.

Testing machine MZGS-200

operating in the load-control

regime.

Symmetric (R=-1) bending and

torsion with a sinusoidal cycle of

frequency f 30 Hz.

Room temperature, laboratory

ambient air environment.

a

a a

z

Loading ratio:

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

2 2

ekv 3a a

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

2 2

1a a

c c

Gough-Pollard (empirical)

max, ,max

21c

a n c

c

Mataka (critical plane)

2, ,max

33c

a h c

c

J

Crossland (stress invariants)

n

2J

max

h…second invariant of stress deviator tensor; …hydrostatic stress

…maximal shear stress; …normal stress on critical plane

Multiaxial Fatigue Life Criteria

Gough-Pollard Mataka Crossland

Log (

Nf,

exp)

Log (Nf,calc) Log (Nf,calc) Log (Nf,calc)

conservative

non-conservative

conservative conservative

non-conservative non-conservative

Multiaxial Fatigue Life Criteria

( ) ( )

,exp ,calc

log ( )

,exp

log log

log

i i

f fi

i

f

N NE

N

Logarithmic relative error index:

Nf = (103,105) cycles All specimens

conservative

non-conservative non-conservative

conservative

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 high-

temperature 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

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.

Acknowledgements

Ladislav Čelko

Simona Pospíšilová

Petr Řehák