Anti-Sintering Behavior of GYYSZ, Thermophysical Properties, and Thermal Shock Behavior of Thermal Barrier Coating with YSZ/Composite/GYYSZ System by Atmospheric Plasma Spraying

In this study, Gd₂O₃ and Yb₂O₃ co-doped YSZ (GYYSZ) ceramic coatings were prepared via atmospheric plasma spraying (APS). The GYYSZ ceramic coatings were subjected to heat treatment at different temperatures for 5 h to analyze their high-temperature phase stability and sintering resistance. The thermophysical properties of GYYSZ, YSZ, and composite coatings were compared. Three types of thermal barrier coatings (TBCs) were designed: GYYSZ (TBC-1), YSZ/GYYSZ (TBC-2), and YSZ/Composite/GYYSZ (TBC-3). The failure mechanisms of these three TBCs were investigated. The results indicate that both the powder and the sprayed GYYSZ primarily maintain a homogeneous cubic phase c-ZrO₂, remaining stable at 1500 °C after annealing. The sintering and densification of the coatings are influenced by the annealing temperature; higher temperatures lead to faster sintering rates. At 1500 °C, the grain size and porosity of GYYSZ are 4.66 μm and 9.9%, respectively. At 1000 °C, the thermal conductivity of GYYSZ is 1.35 W·m^-1 K^-1, which is 44% lower than that of YSZ. The thermal conductivity of the composite material remains between 1.79 W·m^-1 K^-1 and 1.99 W·m^-1 K^-1 from room temperature to 1000 °C, positioned between GYYSZ and YSZ. In the TBC thermal shock water quenching experiment, TBC-3 demonstrated an exceptionally long thermal shock lifetime of 246.3 cycles, which is 5.8 times that of TBC-1 and 1.8 times that of TBC-2. The gradient coating structure effectively reduces the thermal mismatch stress between layers, while the dense surface microcracks provide a certain toughening effect. Failure analysis of the TBC reveals that TBC-3 exhibits a mixed failure mode characterized by both spallation and localized peeling. The ultimate failure was attributed to the propagation of transverse cracks during the final stage of water quenching, which led to the eventual spallation of the ceramic blocks.