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 (Yb 2 Si 2 O 7 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 (Yb 2 SiO 5 or YbMS) layer, while CMAS caused dissolution-precipitation, forming reprecipitated Yb 2 Si 2 O 7 and Yb-apatite (Ca 2 Yb 8 (SiO 4 ) 6 O 2 ). Combined exposure increased CMAS penetration depth by 25 %, enhanced Yb-apatite formation, and introduced ytterbium aluminium garnet (Yb 3 Al 5 O 12 , 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.