<i>In-situ</i> observation and mechanism of calcium–magnesium–alumina–silicate (CMAS) melts-induced degradation of RE <sub>2</sub>SiO <sub>5</sub> (RE = Tb, Dy, Ho, Y, Er, Tm, and Yb) ceramics at 1500 °C
Zhilin Tian, Keyu Ming, Liya Zheng, Zhilin Chen, Fan Zhou, Peng Fei Liu, Zihao Qiu, Donghui Wei, Bin Li, Jingyang Wang
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 RE<sub>2</sub>SiO<sub>5</sub> and CMAS up to 1500<sup>o</sup>C was investigated by a novel high-temperature in-situ observation method. High temperature promotes the growth of the main reaction product (Ca<sub>2</sub>RE<sub>8</sub>(SiO<sub>4</sub>)<sub>6</sub>O<sub>2</sub>) fast along [0 0 1] direction, and the precipitation of short and horizontally distributed Ca<sub>2</sub>RE<sub>8</sub>(SiO<sub>4</sub>)<sub>6</sub>O<sub>2</sub> 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 RE<sub>2</sub>SiO<sub>5</sub> fast interaction with CMAS and less affected by RE element species.