Failure characteristics and life prediction for thermally cycled thermal barrier coatings

The effect of high temperature hold time at 1050 °C on thermal fatigue properties and failure characteristics of electron beam-physical vapor deposited (EB-PVD) thermal barrier coated samples (TBCs) was investigated in this work. To clarify this effect, the microstructure, especially that near the interface after certain thermal cycles was characterized by scanning electron microscopy (SEM). Results revealed that with increasing hold time at high temperature, fatigue life first increased then decreased and the failure mode diverted from the interfacial failure mode to one that consisted of both the interfacial failure mode and failure within the TBC. Failure was determined by strain energy density in the ceramic coating and the TGO, the fracture toughness of the ceramic coating, the TGO and the interface, and their correlations with microstructure defects near the interface. Based on analysis of the failure mechanism and the microstructure evolution near the interface, and by combining the simulation modeling of the thermal cycling response, a damage accumulation life prediction model was developed in terms of the TGO thickness. This model, which considered the evolution of the fatigue stress due to the increase in TGO thickness, was able to predict thermal fatigue life of the TBCs/nickel based superalloy system under different thermal cycling histories.