Oxidation-induced microstructural evolution and failure behavior of slurry-derived YSZ thermal barrier coatings

Thermal barrier coatings (TBCs) are important surface-engineered materials for protecting high-temperature components from thermal and chemical degradation. Slurry processing provides a flexible and cost-effective route for fabricating ceramic coatings. However, the oxidation-induced evolution of their particle-sintered microstructures and associated interfacial degradation mechanisms remain insufficiently understood. In this study, 8 mol% yttria partially stabilized zirconia (YSZ) coatings were fabricated by the slurry method, and their oxidation behavior during isothermal exposure at 1100 °C was systematically investigated. The as-prepared coatings exhibited a porous particle-stacking structure with interconnected pores. During oxidation, the open pore structure initially facilitated oxygen access toward the coating/substrate interface and promoted the formation and growth of a thermally grown oxide (TGO) layer. With prolonged exposure, progressive particle sintering and microstructural densification reduced the overall pore connectivity, accompanied by a decrease in the oxidation rate. The evolution of the TGO and the redistribution of alloying elements near the interface occurred concurrently with changes in the ceramic-layer microstructure. Prolonged oxidation also reduced the strain tolerance of the ceramic layer and promoted the development of localized pores and horizontal cracks near the TC/TGO interface. After extended oxidation, the combined effects of TGO growth, thermal expansion mismatch, and oxidation-induced microstructural and phase evolution contributed to crack propagation and localized coating damage. These results clarify the coupled evolution of particle-sintered microstructures, interfacial oxidation, and damage development in slurry-derived YSZ coatings, providing insights into the microstructural design and durability optimization of slurry-derived ceramic thermal protective systems.