Abradable ytterbium disilicate environmental barrier coatings: A study of steam, CMAS and combined steam-CMAS corrosion

Abradable environmental barrier coatings (EBCs) are essential for improving gas turbine efficiency with ceramic matrix composites (CMCs). This study examined ytterbium disilicate (Yb₂Si₂O₇ or YbDS) abradable EBCs with 8 %, 15 %, and 22 % porosity, deposited via atmospheric plasma spraying. Coatings were exposed to steam, CMAS, and combined steam-CMAS at 1350 °C for 100 hr. Results showed that porosity had minimal impact on corrosion resistance. Steam exposure formed a thin ytterbium monosilicate (Yb₂SiO₅ or YbMS) layer, while CMAS caused dissolution-precipitation, forming reprecipitated Yb₂Si₂O₇ and Yb-apatite (Ca₂Yb₈(SiO₄)₆O₂). Combined exposure increased CMAS penetration depth by 25 %, enhanced Yb-apatite formation, and introduced ytterbium aluminium garnet (Yb₃Al₅O₁₂, YbAG). These findings demonstrate that the interaction of CMAS and steam accelerates coating degradation, highlighting the need for optimized phase composition and microstructure to enhance abradable EBC durability under turbine-relevant conditions.