<i>In-situ</i> observation and mechanism of calcium–magnesium–alumina–silicate (CMAS) melts-induced degradation of RE ₂SiO ₅ (RE = Tb, Dy, Ho, Y, Er, Tm, and Yb) ceramics at 1500 °C

Abstract

Rare earth (RE) silicate is one of the most promising environmental barrier coatings for silicon-based ceramics in gas turbine engines. However, 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^oC 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 [0 0 1] 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.