Influence of internal oxidation of the bond-coat on the residual stress around the TGO and failure modes of the APS-TBCs: A finite element simulation study

Abstract

In this paper, the influence of internal oxidation of the bond-coat on the residual stress around the thermally grown oxide (TGO) and failure modes of the TBCs fabricated by atmospheric plasma spraying (APS) has been studied via finite element modeling. Generally, the internal oxidation will occur when the bond-coat (BC) was fabricated by APS. The produced oxide was distributed irregularly at the inner of the bond-coat, and the distribution patterns like some isolated islands, so it was called “island-like” oxide by us. As the BC layer usually consists Ni, Co, Cr, Al and Y etc., the composition of the “island-like” oxide is very complicated due to the formation Gibbs free energy are different when those metallic elements take reaction with exterior [O]. During the subsequent high temperature service conditions, a continuous thin TGO layer will be formed. In addition, the BC layer will be further endured with inner oxidation due to the [O] diffuse to the interface, the mixture oxide will appear below the TGO layer randomly, which will lead to a complicated stress distribution at the TGO/YSZ interface directly. Moreover, a small amount of Cr2O3 was formed in TGO layer, the distribution of interfacial stress was strongly influenced, resulting in complicated fluctuance of interface and unpredictable failure modes simultaneously. So, to systematically discuss the distribution of residual stress state along YSZ/TGO interface, the influence of the composition of TGO and the location of internal oxides on the distribution of interfacial stress were studied via FEM. The results show that with the increase of the percentage of Cr2O3 (wt.%) in TGO, the maximum tensile stress and compressive stress have changed evidently at the peak of TGO. Besides of considering the percentage of Cr2O3 (wt.%) in TGO, the internal oxides existed below the TGO layer have been taken into account simultaneously.