Phase Transformation in EB-PVD Yttria Partially Stabilized Zirconia Thermal Barrier Coatings during Annealing

Electron‐beam physical‐vapor‐deposited thermal barrier coatings consisting of ZrO2 stabilized by 7 wt% Y2O3 were investigated in regard to phase transformation after annealing. Free‐standing ceramic layers were heat‐treated in air, for up to 200 h, in the temperature range 1200°—1400°C and then analyzed by X‐ray diffractometry. Based on information obtained from the {111} and {400} peaks, the phase composition and the Y2O3 content in the phases were calculated. At the start of transformation, small grains of a low‐Y2O3t phase and a c phase formed. After >30 h at 1300°C and at 1400°C, a mixture of a t phase deficient in Y2O3, an m phase, and a c phase formed after cooling, with the Y2O3 contents in the phases roughly predicted by the phase diagrams. The results of the present study are discussed here in detail and compared with data for plasma‐sprayed coatings.