Effect of submicron silicon carbide powder addition on the processing and strength of reaction-sintered mullite-silicon carbide composites

Abstract

Mullite-silicon carbide composites were fabricated via a reaction sintering using SiC and alumina (Al₂O₃) powders. The mullite phase was in situ synthesized from the reaction between the oxidation-derived SiO₂ and alumina. The effects of incorporating submicron (∼0.5 μm) SiC powder (in addition to the coarser (∼65 μm) SiC powder) on the microstructures, densities, and flexural strengths of the composites were investigated. The addition of submicron SiC powder was found to increase the mullite content, relative density, and flexural strength of the composite. The 6-h-sintered composite containing 40 mass% submicron SiC powder had the highest flexural strength. A slightly lower strength was observed for the composite containing 50 mass% submicron SiC powder. This was attributed to there being insufficient alumina in the starting powder for synthesizing the mullite. The composites sintered for 6 h typically had flexural strengths of ∼90 MPa at 25% porosity.