Rare earth (RE) silicate is one of the most promising environmental barrier coatings for silicon-based ceramics in gas turbine engines. However, calcium–magnesium–alumina–silicate (CMAS) corrosion becomes much more serious and is the critical challenge for RE silicate with the increasing operating temperature. Therefore, it is quite urgent to clarify the mechanism of high-temperature CMAS-induced degradation of RE silicate at relatively high temperatures. Herein, the interaction between RE₂SiO₅ and CMAS up to 1500 ℃ was investigated by a novel high-temperature in-situ observation method. High temperature promotes the growth of the main reaction product (Ca₂RE₈(SiO₄)₆O₂) fast along the [001] direction, and the precipitation of short and horizontally distributed Ca₂RE₈(SiO₄)₆O₂ grains was accelerated during the cooling process. The increased temperature increases the solubility of RE elements, decreases the viscosity of CMAS, and thus elevates the corrosion reaction rate, making RE₂SiO₅ fast interaction with CMAS and less affected by RE element species.

Model composites consisting of SiC fiber and Yb₂SiO₅ were processed by the spark plasma sintering (SPS) method. The mechanical compatibility and chemical stability between Yb₂SiO₅ and SiC fiber were studied to evaluate the potential application of Yb monosilicate as the interphase of silicon carbide fiber reinforced silicon carbide ceramic matrix composite (SiC_f/SiC CMC). Two kinds of interfaces, namely mechanical and chemical bonding interfaces, were achieved by adjusting sintering temperature. SiC_f/Yb₂SiO₅ interfaces prepared at 1450 and 1500 ℃ exhibit high interface strength and debond energy, which do not satisfy the crack deflection criteria based on He–Hutchison diagram. Raman spectrum analyzation indicates that the thermal expansion mismatch between Yb₂SiO₅ and SiC contributes to high compressive thermal stress at interface, and leads to high interfacial parameters. Amorphous layer at interface in model composite sintered at 1550 ℃ is related to the diffusion promoted by high temperature and DC electric filed during SPS. It is inspired that the interfacial parameters could be adjusted by introducing Yb₂Si₂O₇–Yb₂SiO₅ interphase with controlled composition to optimize the mechanical fuse mechanism in SiC_f/SiC CMC.