Microstructure evolution and thermomechanical properties of plasma‐sprayed Yb ₂ SiO ₅ coating during thermal aging

Rare‐earth monosilicates (RE 2 SiO 5 , RE: rare‐earth elements), such as Yb 2 SiO 5 , have been developed for potential application as environmental barrier coating (EBC) materials. Yb 2 SiO 5 coating would experience microstructure evolution under high‐temperature environment and accordingly its thermomechanical properties would be altered. In this study, Yb 2 SiO 5 coating was fabricated by atmospheric plasma spray technique. The phase stability and microstructure change before and after thermal aging at 1300°C, 1400°C, and 1500°C were investigated. The changes in mechanical and thermal properties were characterized. The results showed that the as‐sprayed coating was mainly composed of Yb 2 SiO 5 with a small amount of Yb 2 O 3 and amorphous phase. Defects in the coating, including interfaces, pores, and microcracks, were greatly reduced with grain growth after thermal treatment. Thermal aging significantly modified the thermal and mechanical properties of the coating. The average CTE was increased by 13.1%, and the hardness and elastic modulus was increased by 42.4% and 49.4%, respectively, after thermal aging at 1500°C for 50 hour. The thermal conductivity of thermal‐aged coating was much higher than that of the as‐sprayed coating, which was still less than 2 W/(m·K). The influence of coating microstructure on the properties was analyzed and related to the failure mechanism of EBCs.