Sintering and failure behaviour of EB-PVD thermal barrier coating after isothermal treatment

Electron beam-physical vapour deposition (EB-PVD) yttria-stabilised zirconia (YSZ) thermal barrier coatings (TBCs) were exposed to isothermal treatments at 1050, 1150 and 1200 °C. The as-deposited EB-PVD TBCs have typical columnar microstructure with larger columns near the top surface than that near the TBC/substrate interface. The difference in microstructure of TBCs across its thickness leads to difference in degree of sintering. Meanwhile, the sintering of TBC at high temperature is constrained by metal substrate and the coating surface is less constrained than the TBC/substrate interface. After isothermal treatment at 1050, 1150 and 1200 °C, microstructural evolution, Young's modulus and micro-stress were determined to characterize local sintering across thickness of TBCs. In addition, failure phenomena of TBCs have been examined in relation to Young's modulus of the coating and thermally grown oxide (TGO) thickness. A model developed based on calculation of strain energy release rate is applied here to predict lifetime of the TBCs, and an agreeable result was obtained after consideration of stress gradient in the coating.