Phase and properties evolution of plasma sprayed rare earth silicate coatings

Abstract

Rare-earth silicates have been pursued for many years as candidates for Environmental Barrier Coatings for the protection of silicon carbide (SiC) based components in the new generation of aero and power production turbine engines. The properties and behavior of these materials are usually reported based on theoretical studies or measurements done on bulk specimens, but their prospective use is in the form of coatings. One of the most extended ways of depositing these coatings is plasma spray which produces partially or totally amorphous deposit and changes towards SiO2 lean chemical composition. In this work is comparatively discussed the effect of plasma spray deposition on Yb2Si2O7, Y2Si2O7 and the mixed cation silicate (Y0.5Yb0.5)2Si2O7 coatings. The phase evolution with temperature and its impact on the coefficient of thermal expansion, microstructure and thermal conductivity are described. The stability of crystalline phases, properties and absence of cracks in its microstructure makes (Y0.5Yb0.5)2Si2O7 a more optimum candidate among the studied rare-earth silicates for environmental barrier applications.