Yttrium bearing silicon carbide matrices for robust ceramic composites

Application of SiC-based ceramic matrix composites (CMCs) in combustion environments demands the use of an environmental barrier coating (EBC) to prevent volatilization of the protective SiO₂ scale in flowing water vapor. The EBC only provides protection while present on the surface; cracking and spallation of the coating leaves the underlying SiC vulnerable to the oxidation-volatilization processes. A robust matrix material chemically tailored to regrow a yttrium silicate scale in the event of EBC loss has been developed by incorporating yttrium bearing species including YB₂, Y ₂O₃, and Y₅Si₃ into the SiC. During oxidation a borosilicate glass helps seal cracks while Y₂O ₃ and SiO₂ react to form Y₂Si₂O ₇ for environmental protection. Candidate compositions were oxidized for 10 min to 100 h at 1400°C and for 24 h at 1500°C to understand the scale growth. The prospects for effectively applying this approach in CMCs are discussed.