Processing,microstructure and properties of in-situ reinforced SiC matrix composites

SiC matrix composites were fabricated by in-situ formation of transition metal boride and carbide particles from oxide powders by carbothermal reactions. Dense composites with various microstructures were produced by pressureless sintering and additional hot-isostatic pressing. The microstructures and mechanical properties of the composites were dependent upon the pressureless-sintering temperature. The use of submicron-sized TiO₂ lead to fine and equiaxial TiB₂ particulates. The composites exhibited high flexural strengths (>700 MPa). At higher sintering temperatures, the grain growth of SiC swept the boride into clusters with larger sizes and anisotropic shapes, which improved the fracture toughness of the composite at the expense of strength.