Phase stability, thermo-physical properties and thermal cycling behavior of plasma-sprayed CTZ, CTZ/YSZ thermal barrier coatings

Abstract

ZrO2 co-stabilized by CeO2 and TiO2 with stable, nontransformable tetragonal phase has attracted much attention as a potential material for thermal barrier coatings (TBCs) applied at temperatures > 1200 °C. In this study, ZrO2 co-stabilized by 15 mol% CeO2 and 5 mol% TiO2 (CTZ) and CTZ/YSZ (zirconia stabilized by 7.4 wt% Y2O3) double-ceramic-layer TBCs were respectively deposited by atmospheric plasma spraying. The microstructures, phase stability and thermo-physical properties of the CTZ coating were examined using scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric-differential scanning calorimeter (TG-DSC), laser pulses and dilatometry. Results showed that the CTZ coating with single tetragonal phase was more stable than the YSZ coating during isothermal heat-treatment at 1300 °C. The CTZ coating had a lower thermal conductivity than that of YSZ coating, decreasing from 0.89 W m−1 K−1 to 0.76 W m−1 K−1 with increasing temperature from room temperature to 1000 °C. The thermal expansion coefficients were in the range of 8.98 × 10−6 K−1 – 9.88 ×10−6 K−1. Samples were also thermally cycled at 1000 °C and 1100 °C. Failure of the TBCs was mainly a result of the thermal expansion mismatch between CTZ coating and superallloy substrate, the severe coating sintering and the reduction-oxidation of cerium oxide. The thermal durability of the TBCs at 1000 °C can be effectively enhanced by using a YSZ buffer layer, while the thermal cycling life of CTZ/YSZ double-ceramic-layer TBCs at 1100 °C was still unsatisfying. The thermal shock resistance of the CTZ coating should be improved; otherwise the promising properties of CTZ could not be transferred to a well-functioning coating.