YPO₄: A promising environmental barrier coating candidate against corrosion of molten CMAS

Calcium-magnesium-alumina-silicate (CMAS) attack is one of the major challenges for environmental barrier coatings (EBCs) applied on the hot-sections of silicon carbide based ceramic matrix composites (CMCs) in aero-engines. YPO₄ is a promising EBC candidate owing to its coefficient of thermal expansion (CTE) compatibility with CMC_S and superior corrosion resistance to water vapor. In this work, single phase YPO₄ ceramic was successfully fabricated and its corrosion-resistance to synthesized CMAS and natural volcanic ash at 1300–1400 °C was investigated. At 1300 °C, the chemical reaction between YPO₄ ceramics and molten CMAS accelerated, forming a continuous and dense reaction layer composed of Ca₈MgY(PO₄)₇ and Ca₆MgY₃(SiO₄)₂(PO₄)₅ phases, thereby effectively inhibiting CMAS infiltration. With the increase in corrosion time, the reaction layer thickness follows a near-parabolic trend. At temperatures above 1300 °C, the formation of the reaction layer was constrained due to the extremely low viscosity of CMAS and its fast infiltration rate. In contrast to CMAS, volcanic ash did not react with YPO₄ ceramic at high temperature due to its relatively low CaO content. These findings are expected to provide comprehensive understanding on the corrosion performance and mechanism of REPO₄ coating materials.