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, Y2O3, and Y5Si3 into the SiC. During oxidation a borosilicate glass helps seal cracks while Y2O3 and SiO2 react to form Y2Si2O7 for environmental protection. Candidate compositions were oxidized for 10 min to 100 h at 1400 degrees C and for 24 h at 1500 degrees C to understand the scale growth. The prospects for effectively applying this approach in CMCs are discussed.