Theoretical and experimental investigation of Xenotime-type rare earth phosphate REPO4, (RE = Lu, Yb, Er, Y and Sc) for potential environmental barrier coating applications

The mechanical and thermophysical properties of Xenotime-type REPO 4 (RE = Lu, Yb, Er, Y and Sc) have been theoretically and experimentally investigated for a potential environmental barrier coating (EBC) topcoat application. The results show that the current studied REPO 4 exhibits a quasi-ductile property, suggesting a potential long life expectancy of its made coatings. Further, from the study of underlying parameters governing thermophysical properties of a ceramic, low thermal expansion coefficients (TECs) and low thermal conductivities cannot be achieved simultaneously, due to mutual exclusive nature of above two parameters. REPO 4 has been unveiled to have rather small TECs, attributing partly to its weak lattice anharmonicity, and is thus well-matched with silicon carbide based ceramic matrix composites. Last, the current investigated REPO 4 exhibits very good high-temperature water vapor corrosion resistance, excellent calcium-magnesium aluminosilicates (CMAS) resistance as well as excellent chemical compatibility with silicon bond coats at elevated temperatures. Therefore, the Xenotime-type rare earth phosphates are a promising EBC topcoat material.