Tailoring thermal and chemical properties of a multi-component environmental barrier coating candidate (Sc0.2Nd0.2Er0.2Yb0.2Lu0.2)2Si2O7

Abstract

Environmental barrier coatings, typically rare earth silicates, have been successfully employed on ceramic matrix composites in the hot zone of gas turbine engines, allowing for high fuel burn temperatures and increased flight efficiency. Yet, environmental barrier coatings face challenges as turbine temperatures continue to increase, such as increased oxidation of the underlying substrate, environmental degradation, and coating spallation. Here, we show how multi-component rare earth silicates offer a unique solution for simultaneously co-optimizing phase stability, thermo-chemical, and thermo-mechanical properties through variation of the rare earth elements implemented in the coating material. Each rare earth element added in solution was chosen to enhance specific material properties. We found that chemical stability with the turbine gaseous environment or with molten deposits could be retained, and in some cases enhanced, without detrimental effects on the phase stability or thermo-mechanical behavior. Our results demonstrate how rare earth cation mixing can lead to a 50% reduction in thermal conductivity for the given rare earth silicate mixtures. Such decreases in thermal conductivity show promise for reducing the substrate operating temperature during use, thus making multi-component rare earth silicates a novel class of dual-purpose thermal/environmental barrier coating materials.