(0119) Oxidation-Diffusion Model: Simulation of oxidation-nitridation-induced microstructural degradation in a cracked Ni-based superalloy at high temperature

Kang Yuan, Ru Lin Peng, Xin-Hai Li, Sten Johansson, Yan-Dong Wang

Contact: Kang Yuan (kang.yuan@liu.se). Linköping University, Sweden

Introduction

Results - Modelling

Conclusions

Superalloys may be cracked due to mechanical loading, and

gaseous atoms or moleculars (e.g. O, N), would diffuse

inwards along the cracks to cause microstructural

degradation of the superalloys by oxidation and nitridation.

A oxidation-diffusion model, by combining DICTRA and

Matlab, has been built in this study to simulate the

microstructural evolution and the diffusion of alloying

elements in a superalloy IN-792 at high temperature due to

external and internal oxidation and nitridation.

Acknowledgements

1. Internal oxidation and nitridation of Al and Ti occurred under

a porous Cr2O3 layer formed along the cracking surfaces;

2. The formation of the internal oxides and/or nitrides of Al and

Ti resulted in the depletion of Ni3(Al,Ti)-γ’ phases in the

superalloy;

3. An oxidation-diffusion model captured the main features of

the microstructural evolution and the diffusion behavior of

alloying elements in the superalloy.

Fig. 2. (a) A SEM image showing a crack in the superalloy (“1” for Cr-rich oxides along the crack, “2” for Al2O3 and AlN, “3” for TiN, and “4” for γ+γ’). (b) The EDS composition profiles of elements in the red square in figure (a).

Fig. 1. (left image) a failed blade made of superalloy from gas turbine engine;

(right image) the creep testing (950 °C, 680 h) on IN-792.

Materials

Results - Microstructures

IN792:Ni-12.5Cr-9Co-4.175W-4.175Ta-3.975Ti-3.375Al-1.9Mo-0.1others, wt.%;

Turbine

blade

attack

F F

Fig. 3. EDS maps of elements for the red square in Fig. 2a.

Fig. 4. SEM image in the blue square in Fig. 2a. “1” for Ti-rich nano precipitates tracking the previous γ’ phase, and “2” for TiN with a triangular-kind shape.

Fig. 5. SEM image showing the internal nitridation of Ti and the degradation of γ’ phases in the superalloy (the arrow shows the diffusing direction of N). “1” for γ matrix phase, “2” for γ’ phase, “3” for decomposing Al-rich, Ti-lack γ’ phase, “4” for nano Ti-rich precipitate in “3”, and “5” for TiN.

𝑋 =2𝑐𝑂

𝑠𝐷𝑂

𝜈𝑐𝐴𝑙0 𝑡

1/2

Future work:

Penetration depth of internal

oxides or nitrides (Wagner’s

law):

XTiN>XAlN>XAl2O3

Fig. 6. The fitted parabolic curves for the depletion of Cr, Ti and Al due to oxidation and nitridation.

Fig. 7. The oxidation-diffusion model. X denotes the penetration depth of the internal oxidation and nitridation.

Fig. 8. Modelling results of (a) the alloying composition profiles (by atomic%) and (b) the γ’ profile (by volume%, with balance of γ) for the cracking oxidation in the superalloy IN-792 after the oxidation and nitridation at 900 °C for 680 h.

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