Driving forces in thermal barrier coatings blistering

Thermal barrier coating (TBC) systems are known to be extremely sensitive to the applied thermo-mechanical loading in terms of both microstructure evolution and of subsequent damage, leading to final failure by ceramic top-coat layer spallation. The analysis of the relationship between mechanical behavior and final failure is limited by the scatter in the experimental results. Based on a typical TBC system for columnar top-coat, this study focuses on blister evolution for pure thermal cycling. The blister is processed by LAser Shock Adhesion Test (LASAT) method. It is observed experimentally that prior to significant further interfacial debonding, the height of the blister increases with the number of applied cycles. To clarify this, a finite element analysis was developed to account for multilayer system behavior and growth strain associated to a thermal-grown oxide layer evolution. Finally, this study demonstrates that rough interfaces, elasto-viscoplastic behavior of the metallic bond-coat, and oxide growth strain are needed to model the experimentally observed evolution of the blister. Thus, the driving forces acting on bond-coat rumpling, are similar to driving forces for blister height increase and final failure of the TBC.