Biaxial stress in La2Ce2O7/YSZ thermal barrier coatings for oxidation evolution

Abstract

High temperature oxidation could cause the spalling and failure of thermal barrier coatings (TBCs). La2Ce2O7(LCO)/YSZ double-layer TBCs were investigated with high temperature oxidation at 1100 °C, 1150 °C and 1200 °C, respectively. Interfacial crack propagation and TGO growth behavior were comparatively investigated, and the failure of double-layer TBCs is the result of the joint action of interface transverse crack propagation and TGO growth. Due to the difference in thermal expansion coefficients, the YSZ layer is subjected to biaxial stress, which contains the TGO growth stress and the thermal mismatch stress during the oxidation process. The transverse crack propagation was developed at the LCO/YSZ interface and the YSZ/BC interface, eventually. The thermal barrier coatings TGO thickened abnormally at 1000 °C and 1150 °C, while delamination at the LCO/YSZ interface resulted in coating failure at 1200°C. The thermal mismatch stress at the LCO/YSZ interface increased mainly due to the thermal expansion coefficient between LCO and YSZ. Transverse microcracks at the LCO/YSZ interface gradually propagated, resulting in delamination failure to LCO/YSZ. Therefore, the failure mechanism of biaxial internal stress has important guiding significance for the application of double-layer TBCs.