Thermal cycling failure mechanism and damage quantification of PS-PVD sprayed Yb₂Si₂O₇ environmental barrier coating

The thermal cycling behavior and failure mechanism of Yb₂Si₂O₇ environmental barrier coatings (EBCs) deposited by plasma spray-physical vapor deposition were investigated after 1000 cycles of exposure in dry air at 1350 °C and 1250 °C. A damage quantification method based on interfacial damage was developed to characterize the degradation of EBCs. The results revealed that thermal cycling induced the formation of pores in the top coat (TC) and bond coat (BC) layers as well as in the interface regions. The thermally grown oxide (TGO) layer at the interface progressively thickened, leading to the initiation of vertical cracks, followed by delamination at the TGO/BC interface. The damage caused by thermal cycling was significantly more severe than that induced by isothermal oxidation, with localized delamination observed after only 800 cycles. Interfacial delamination was the primary mode of thermal cycling damage. Frequent temperature fluctuations resulted in oxidation instability, manifested by the formation of TGO layers with distinct color contrasts. Furthermore, a damage constitutive model was established based on the degradation of critical spallation resistance and thermoelastic theory. The damage quantification theory was validated, as evidenced by the prediction of damage evolution and the corresponding delamination failure in room-temperature compression tests after thermal cycling. The damage evolution followed a power-law function of the number of cycles, providing a valuable reference for the quantitative assessment of EBCs damage.