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 SiCf/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 SiCf/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 SiCf/SiC substrate had good thermal shock resistance. The thermal shock behaviors were explained based on microstructure combined with thermal stresses analysis.