Numerical analyses of the residual stress and top coat cracking behavior in thermal barrier coatings under cyclic thermal loading

Acting as one of the original cracks for interfacial delamination, the horizontal roughness-induced top coat crack plays an important role in the premature failure of the air plasma sprayed thermal barrier coating system. Thus, the residual stress and top coat cracking behavior in thermal barrier coatings under cyclic thermal loading were numerically investigated. The effects of thermally grown oxide swelling, creep, and interfacial roughness were taken into account. The arbitrary top coat cracking was modeled using the extended finite element method. In addition, the effect of the interfacial cracking on top coat cracking and their mutual interaction were investigated using the cohesive zone model. The results showed that the top coat crack initiated before thermal cycling due to large residual stress, the combination of the thermally grown oxide swelling and creep relaxation promoted crack propagation during the early periods, and the crack continued to grow with the thermally grown oxide thickening during the later periods. The initiation and propagation of the interfacial crack between the thermally grown oxide and bond coat accelerated the top coat cracking, and their mutual interaction led to premature interfacial delamination.