Quantitative Characterization of the Interfacial Damage in EB-PVD Thermal Barrier Coating

Abstract

Considering the influence of non-equibiaxial stress state and initial residual strain on the compressive buckling of the ceramic layer, a quantitative characterization method of the damage generated at the interface between the top coat and bond coat in thermal barrier coating based on uniaxial compression was developed. It was verified by the axial compression tests of the single crystal specimens with EB-PVD thermal barrier coating after undergoing various isothermal oxidation times and thermal cycles. On this basis, the correlations between the measured interfacial damage and the thermal loads experienced as well as the thickness of thermally grown oxide (TGO) were analyzed. The results show that the critical compressive strain inducing the spallation of thermal barrier coating at room temperature can effectively characterize the accumulation of interfacial damage caused by isothermal oxidation and thermal fatigue. Under the same TGO thickness, the damage caused by thermal fatigue is greater than that caused by isothermal oxidation. The total damage generated in thermal barrier coating can be divided into three parts: oxidatively driven damage related to TGO thickness, mechanically driven damage related to stress–strain cycles in the coating, and their interaction, where the interaction term is negative.

Characterization of the Internal Stress Evolution of an EB-PVD Thermal Barrier Coating during a Long-Term Thermal Cycling

“…Existing studies have shown that the thermal mismatch stress inside the TC layer and the TGO layer is the main reason for the peeling and failure of the TBC system [ 55 ]. In addition, volume expansion induced by the phase transition of the TC layer will accelerate the initiation and propagation of cracks [ 56 ].…”