Single and multi-component REDS systems for TEBC application: Synthesis and study of high temperature interaction with CMAS

Abstract

Multi-component rare earth disilicates RE2Si2O7 (REDS) are considered as promising materials to be used as thermal environmental barrier coatings (TEBCs) to protect ceramic matrix composites (CMCs) against environmental degradation. The combination of multiple cations in a single phase is expected to decrease the overall thermal conductivity of the material. In addition, they can also increase the phase stability at high temperatures, toughness, inertness to water vapor attack, and stability against molten deposits (CMAS) attack. In this work, single and multi-component rare earth disilicates have been successfully synthesized using a novel and quick synthesis method through solid-state reaction. The main goal of this study is to understand the thermochemical interactions of single cation (Y, Yb, Er, Ho, Lu, and Sc) disilicates and multiple cation disilicates e.g. (Y,Yb)2Si2O7, (Y,Yb,Er)2Si2O7, (Y,Yb,Er,Ho)2Si2O7 with CMAS at 1350 and 1400°C for 1h. Results have shown that the synthesized powders exhibit formation of a single monoclinic phase (β or γ types) both in single and multi-component disilicate systems. The CMAS interaction resulted in formation of REDS reprecipitates (Yb, Lu, Sc), apatite (Er, Ho, Y), and diopside (Sc) as reactive crystallization products. Finally, the multiple cation effect on the formation of the reaction products will be discussed.