Numerical study on the competitive cracking behavior in TC and interface for thermal barrier coatings under thermal cycle fatigue loading

Abstract

Thermal barrier coatings (TBCs) have complex structures and service in the extremely high temperatures. The cracking phenomenon is usually observed at both the top coat and the interface between the bond coat and the thermally grown oxide layer under the thermal cyclic fatigue (TCF) loading. In this study, the competitive cracking behavior in top coat and interface for TBCs were numerical investigated by using a cohesive zone model (CZM) and extend finite element method (XFEM). The dominance stress controlling cracks initiation and propagation was analyzed. The initiation and propagation of TC cracks were controlled by tensile stress, while the interfacial cracking was led by tensile and shear stress commonly. Then, the results showed that the cracks in the TC layers could decrease the stress and delay the interfacial cracks propagation. In addition, this paper also analyzed the key factors affecting the cracking behaviors in TBCs. Changing of the thermal load waveform could lead different cracks propagation path in top coat and failure mode of TBCs. Moreover, the initiation location of TC cracks was independent on the interfacial roughness, but stress concentration of TBCs with the rougher interface was more evident. The thinner initial TGO layer could prolong the lifetime of TBCs. The results demonstrate that the load waveform should be designed to characterize the service environment.