CMAS hot corrosion behavior of rare-earth silicates for environmental barrier coatings applications: a comprehensive review

As one of the most promising materials for environmental barrier coatings (EBCs) applications, rare-earth (RE) silicates possess good high-temperature stability, coefficients of thermal expansion (CTEs) close to those of Si-based ceramics, low thermal conductivities, and excellent hot-corrosion resistances to water vapor and calcia-magnesia-aluminosilicate (CMAS) molten salts. With the gradual understanding on thermophysical properties of rare-earth silicates, more and more researches focus on their CMAS hot-corrosion behavior, which is strongly related to the formation of corrosion products, infiltration of CMAS glass, and the final failure caused by stress-induced microcracks. In this review, the dependences of CMAS properties and sticking behavior on the composition of CMAS are introduced. Then the CMAS hot-corrosion processes of different rare-earth silicates containing rare-earth disilicates, rare-earth monosilicates, and rare-earth oxyapatites are evaluated, as well as different corrosion reactions and potential failure mechanisms during these processes. Wherein, the formation of corrosion products and the infiltration of CMAS depend on the RE: Si ratio, species of rare-earth cations, or other additives, which lead to the research prospects to modification strategies of rare-earth silicates, including the entropy-stabilized solid-solution, the composite technology and microstructure-tailored coatings. The outlook for further investigation is also highlighted.