The sintering and creep and cracking of thermal barrier coatings under thermal cycling

During service, thermal barrier coating will generally go through a series of complicated nonlinear phenomena. In this work, a constitutive framework is provided for the sintering and creep of ceramic top-coat under thermal cycling. The influence of the top-coat sintering and creep was investigated using a three-dimensional thermal barrier system model. It is found that the top-coat sintering gives rise to an obvious reduction in the low-temperature out-of-plane stress within the top-coat but hardly has an effect on the high-temperature out-of-plane stress. The bond-coat/TGO interface is subjected to significant normal stresses upon cooling to ambient temperature, which have greater magnitudes because of the top-coat sintering. Nonetheless, the top-coat creep has very limited effects on the out-of-plane stress within the top-coat and the normal stress across the bond-coat/TGO interface. The cohesive damage model was used to evaluate the delamination of bond-coat/TGO interface under thermal cycling. It is found that the interface delamination could promote the out-of-plane tension of the top-coat and then accelerate the cracking of the top-coat. A static crack is preset in the top-coat to analyze the influence of top-coat crack on the interface delamination. It is found that the top-coat crack hardly affects the normal stresses across the bond-coat/TGO interface and therefore is less likely to facilitate the interface delamination.