Effects of geometrical and material parameters of top and bond coats on the interfacial fracture in thermal barrier coating system

Under extreme thermal cycling delamination initiates and propagates on the interface between top coating and bond coating in thermal barrier coating (TBC) system. The objective of this work is to study the effects of geometrical and material parameters, such as the thicknesses and moduli of top and bond coats, on the interfacial delamination behavior of TBC. The interfacial crack driving force is obtained as functions of the Young's moduli of top and bond coats, the thicknesses of top coat and bond coat, etc. It is shown that in case of a stiffer top coat deposited on a relatively compliant bond coat the interfacial delamination can emerge more easily since the driving force approaches to an enormous value while emanating from the root of a channel surface crack. It is concluded that interfacial delamination can easily be initiated for a thick, stiff top coat. Considering the thermal barrier and mechanical loading carrying capabilities of coatings, optimal top coat thickness exists for the optimization design of TBC structure.