Microstructure and Thermal Cycling Behavior of Ta2O5 and Y2O3 Co-doped ZrO2 Coatings

Ta2O5-Y2O3 co-doped ZrO2 (TYSZ) powders were prepared by high-temperature solid-phase synthesis, and a TYSZ coating was prepared by atmospheric plasma spraying (APS). The phase structures, coefficient of thermal expansion (CTE), and thermal conductivity of the TYSZ and YSZ coating were studied. Thermal cycling was performed at 1400 °C to evaluate the feasibility of TYSZ as an optimal ceramic material for next-generation gas-turbine thermal barrier coatings. The results indicate that the sintered agglomerated TYSZ powders are regular solid spheres with uniform particle size and good flow performance, which meet the requirements of the APS. The TYSZ coating had a typical layered structure, and the coating bond strength was 27.5 MPa. In contrast to the stable t phase of the powder, the TYSZ coating has a cubic phase due to oxygen defects caused by oxygen escaping during spraying. After high-temperature heat treatment (>1300 °C), the cubic phase of the TYSZ coating reverted to the t phase. Due to the specially designed substitution defects, the coefficient of thermal expansion of TYSZ is slightly lower than that of YSZ, and the thermal conductivity is much lower than that of the YSZ coating. After 84 cycles, spalling and cracking occurred in the TYSZ coating near the bond coat and ceramic interface. The mismatch in the coefficient of thermal expansion between the TYSZ coating and the substrate appears to be the primary reason for the coating failure.