This study investigates the influence of thermally grown oxide (TGO) on the lifetime of thermal barrier coatings (TBCs). In the experiments, cold sprayed NiCoCrAlY powder was deposited as the bond coat and plasma sprayed YSZ was deposited as the topcoat. The TBCs were subjected to various treatments to induce different types of TGOs at the bond coat-topcoat interface. Three types of oxide were detected, including spinel, chromium oxide, and alumina. Thermal cycling tests show how the oxides contribute to cracking and spalling in the topcoat layer and how the morphologies and constituents of the oxides can change with time and temperature.

Thermal conductivity of plasma-sprayed YSZ thermal barrier coatings depends on microstructure and significantly influences the effectiveness of the thermal barrier. In this study, YSZ coatings are deposited by plasma spraying using fused and crushed Y2O3-ZrO2 powder. Coating microstructure was modified by substrate temperature, which was varied from room temperature to 880 °C during deposition. The coating microstructure was examined from the fractured cross-section of the deposits to reveal changes in interlamellar bonding due to substrate temperature. The thermal conductivities of the YSZ coating were tested by laser flashing from room temperature to 1300 °C. The results showed that the coating deposited at room temperature exhibited a typical lamellar structure and a thermal conductivity of 1.26 W·m-1·K-1 measured at room temperature. With the increase of substrate temperature, the thermal conductivity was increased. The coating deposited at a substrate temperature of 840-880 °C consisted of trans-lamellae long columnar grains and exhibited a value of 1.95 W·m-1·K-1 at room temperature. The influence of substrate temperature on thermal conductivity is discussed based on the changes in microstructure observed.