Effect of microstructure evolution on thermal properties for plasma-sprayed Lu2Si2O7 environmental barrier coatings

In this study, the microstructure and thermal properties of the plasma-sprayed free-standing Lu₂Si₂O₇ coating before and after thermal aging at 1350 °C were investigated. The tri-layer Yb₂SiO₅/Lu₂Si₂O₇/Si EBCs were designed and prepared onto SiC_f/SiC substrates, and its thermal shocking behaviors were also explored. Results showed that the as-sprayed coating was mainly composed of Lu₂Si₂O₇ and amorphous phase, and significant microstructural evolution, such as grain growth and defects reduction, was observed after thermal aging. Plastic deformation and well damage tolerance including twinning and dislocation were confirmed by TEM analysis. The CTE of the coating before and after heat treatment were similar, while the thermal conductivity increased after thermal aging. After 100 thermal cycles, penetrating microcracks in the Yb₂SiO₅ top layer were mostly stopped at the Yb₂SiO₅-Lu₂Si₂O₇ interface, implying the excellent crack propagation resistance of the tri-layer EBCs. The thermal shock behaviors were clarified based on microstructure combined with thermal stresses analysis.