Hot corrosion of RE2SiO5 with different cation substitution under calcium-magnesium-aluminosilicate attack

Rare earth (RE) silicates have been applied as advanced environmental barrier coatings (EBCs) to protect silicon carbide fibers reinforced silicon carbide ceramic matrix from water vapor and molten salt corrosion in engines. This process, however, is limited by volcanic ash corrosion as assessment of ash-induced corrosion is anecdotal and quantitative data are insufficient. In this account, the corrosion behavior of RE monosilicates (RE2SiO5, RE = Y, Lu, Yb, Eu, Gd, and La) by calcium-magnesium-aluminosilicate (CMAS), with similar composition as volcanic ash, was comprehensively investigated. Results indicated that RE2SiO5 could react with CMAS at 1200 °C at the interface, where the products crystallized in CMAS glass. RE2Si2O7 was formed by the reaction between RE2SiO5 and silica (SiO2) in CMAS, which was followed by corrosion of RE2Si2O7 by CMAS. RE2SiO5 with Type B structure showed better resistance toward CMAS than RE2SiO5 with Type A structure. Moreover, RE2SiO5 with larger radii of RE3+ cations led to easy formation of oxyapatite phase; however, RE2SiO5 with smaller radii of RE3+ cations easily formed garnet phase. Besides, smaller radii RE3+ cations induced slower reactions. These findings can contribute to identifying, preventing, and minimizing the damage to matrix components with EBCs caused by volcanic ash.