Interfacial failure behavior of Thermal Barrier Coatings (TBCs) at high temperatures: An in-situ indentation study based on X-ray imaging

Interfacial failure behavior is a major concern during the service of thermal barrier coatings (TBCs). Quantitative study on interfacial failure behavior of TBCs at high temperatures remains a great challenge. In this study, an in-situ high-temperature cross-sectional indentation (HCSI) method based on X-ray imaging was developed. The out-of-plane displacement of TBCs was measured by in-situ digital radiography (DR) technology. The morphology of the interfacial crack was characterized by an in-situ computer tomography technology. It was found that the interfacial fracture region tended to be semi-elliptical shaped. The strain energy during HCSI was quantified and analyzed by finite element analysis (FEA). The composite stress intensity factor (SIF) and the mixed modal angles at high temperatures were obtained by analyzing the stress field at the crack tip. Interfacial toughness of TBCs at RT, 400 °C, and 800 °C were obtained. The interfacial toughness changes little ranging from RT to 400 °C, while it sharply decreases ranging from 400 °C to 800 °C. A prediction model for the evolution of interfacial toughness with temperature was obtained. The competition mechanism of interfacial cracks at different temperatures was discovered. The relationship between the change in interfacial toughness and the failure mode evolution was discussed.