Failure behavior of SiC/SiC composites with Si/Yb₂SiO₅ and Si/mullite/Yb₂SiO₅ EBCs in wet oxygen at 1350°C

Two structured ytterbium monosilicate environmental barrier coatings (Si/Yb₂SiO₅ and Si/mullite/Yb₂SiO₅) were prepared on SiC/SiC composites and their performance in wet oxygen at 1350°C was investigated. After 300 h of corrosion, coating peeling occurred for Si/Yb₂SiO₅–SiC/SiC, while it was intact for Si/mullite/Yb₂SiO₅–SiC/SiC system due to the mullite intermediate coating well alleviating the thermal expansion mismatched stress. During the assessment, Yb₂SiO₅ and mullite gradually densified, and a thin layer of ytterbium disilicates (Yb₂Si₂O₇) was formed at their junction as a new protective layer, which pinned into the mullite layer and significantly improved their interface bonding strength and resistance against wet oxygen. The strength retention of SiC/SiC, Si/Yb₂SiO₅–SiC/SiC, and Si/mullite/Yb₂SiO₅–SiC/SiC was 64%, 72%, and 97%, respectively, after corrosion in wet oxygen at 1350°C/300 h. Their corrosion mechanism was proposed.