Rare-earth disilicate systems for T/EBC application: Synthesis and high temperature interaction with CMAS

Abstract

Thermal and environmental barrier coatings (TEBCs) that are intended to be used on top of ceramic matrix composites (CMCs) require complex properties such as high temperature phase stability, toughness, inertness to water vapor attack, and protection against silica deposit (CMAS) attack. Multi component rare earth disilicates RE2Si2O7 (REDS) such as mixtures of Y, Yb, Er, Ho, Lu, and Sc have been identified as promising TEBC materials due to their high-temperature phase stability, low thermal conductivity, and coefficients of thermal expansion similar to SiC-CMCs (4.5x10-6). A novel synthesis method using high-energy milling and solid-state reaction has been successfully developed for producing multi-component REDS powders rapidly. The current work also focuses on understanding the thermochemical reactions between single-component Y, Yb, Er, Ho, Lu, and Sc disilicates as well as multi-component REDS with different CMAS sources at 1350 and 1400 °C for 1h using REDS+CMAS powder mixtures (), respectively. Results showed the successful synthesis of monoclinic RE disilicatephases (β and γ types). Structural and chemical analysis confirmed the formation of REDS (Yb, Lu, Sc) reprecipitates, reactive crystallization products as apatite (Er), and intrinsic crystallization products such as diopside. Additionally, Y and Ho thermochemical reactions will be discussed.