Effects of material creep on displacement instability in a surface groove under thermo-mechanical cycling

Displacement instability along the interface between a zirconia top coat and thermally-grown oxide (TGO) forming metal substrate is a fundamental source of failure in some thermal barrier coatings (TBCs). In this work, the effects of material creep on displacement instability near the surface groove on Fecralloy substrate subjected to thermo-mechanical cycling are investigated using finite element analysis (FEA). Assumptions and references about material properties are minimized for a more realistic analysis. Most material properties, such as TGO growth and creep parameters, are based on in-house experimental measurements. Our results show that under a small magnitude of tensile stress, cyclic history plays a major role in displacement instability, and that this role significantly fades as stress increases. We also show that creep in the substrate material predominates at the holding time of a cycle. Creep significantly enhances the deformation near the groove without mechanical load applied on the specimen, while it contributes to length change rather than deformation of the groove as the load level increases.