Microstructure and Thermal Property Evolution of Plasma-Sprayed Lu2SiO5 EBCs Under High Temperature Environments

Lutetium monosilicate (Lu₂SiO₅) has been considered as environmental barrier coatings (EBCs) materials for SiC_f/SiC. Microstructural evolution and thermal properties changes of the Lu₂SiO₅ coating would occur in high temperature environment. In this study, Lu₂SiO₅ coating was fabricated by vacuum plasma spray technique. The microstructure, thermal stability, thermal conductivity, as well as thermal expansion behavior of the coating before and after thermal aging at 1350 °C were investigated. The tri-layer EBCs of Lu₂SiO₅/Yb₂Si₂O₇/Si 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 Lu₂SiO₅, Lu₂O₃ and amorphous phases, and significant microstructural evolution, such as grain growth and defects reduction, was observed after thermal aging. The coating exhibited linear expansion, and the CTE of the coating before and after heat treatment were similar, while the thermal conductivity increased after thermal aging. Thermal shock results showed that the coating remained intact after 100 cycles, and penetrating microcracks in the Lu₂SiO₅ top layer were mostly stopped at the Lu₂SiO₅-Yb₂Si₂O₇ interface, indicating that the tri-layer EBCs on the SiC_f/SiC substrate had good thermal shock resistance. The thermal shock behaviors were explained based on microstructure combined with thermal stresses analysis.