Numerical Study on Effect of Non-uniform CMAS Penetration on TGO Growth and Interface Stress Behavior of APS TBCs

The penetration of CaO–MgO–Al2O3–SiO2(CMAS) is one of the most significant factors that induce the failure of air-plasma-sprayed thermal barrier coatings (APS TBCs). The direct penetration of CMAS changes the thermal/mechanical properties of the top coat (TC) layer, which affects the thermal mismatch stress behavior and the growth of thermally grown oxide (TGO) at the TC/bond coat (BC) interface, thereby resulting in a more complicated interface stress state. In the present study, a two-dimensional global model of APS TBCs with half of the TC layer penetrated by CMAS is established to investigate the effect of non-uniform CMAS penetration on the interface stress behavior. Subsequently, a local model extracted from the global model is established to investigate the effects of interface morphologies and CMAS penetration depth. The results show that non-uniform CMAS penetration causes non-uniform TGO growth in APS TBCs, which consequently causes the stress behavior to vary along the interface. Furthermore, the CMAS penetration depth imposes a significant effect on the TC/TGO interface stress behavior, whereas the interface roughness exerts a prominent effect on the stress level at the BC/TGO interface under CMAS penetration. This study reveals the mechanism associated with the effect of non-uniform CMAS penetration on the interface stress behavior in APS TBCSs.