Numerical analysis of CMAS penetration induced interfacial delamination of transversely isotropic ceramic coat in thermal barrier coating system

During the high-temperature operation of the electron beam physical vapor deposited (EB-PVD) thermal barrier coating system (TBCs), the environmental calcium-magnesium-alumina-silicate (CMAS) deposition would penetrate into the gaps between the columnar microstructure of top-coat. This penetration affects the mechanical behavior of coating and then induces the interfacial delamination of the coating from the substrate. In this paper, a physical model incorporating the CMAS penetration and the columnar microstructure of EB-PVD ceramic top-coat (Y2O3-Stabilized ZrO2, YSZ) is developed. Firstly, continuum analysis is carried out to investigate CMAS induced interfacial delamination in TBCs, in which the ceramic top-coat is simplified as a transversely isotropic material. Theoretical analysis indicates that CMAS penetration primarily affects the overall in-plane modulus of the top-coat. It is also shown that the in-plane modulus of the top-coat is the most critical parameter determining the energy release rate and mode mixity. Moreover, the effect of columnar microstructure of top-coat on the interfacial delamination is analyzed. The results demonstrate that the increase of both CMAS modulus and penetration thickness can greatly promote the energy release rate for driving the interfacial delamination. The mechanism of CMAS induced interfacial delamination is that the infiltration of CMAS into columnar gaps increases the overall effective in-plane modulus of the top-coat, thereby facilitating delamination of the coat.