Combustion Synthesis of Si3 N4 -BN-SiC Composites by in-situ Introduction of BN and SiC

Si3N4-BN-SiC composites present desirable potential for engineering applications because of their improved mechanical properties and oxidation resistance. In present work, Si3N4-BN-SiC composites were successfully fabricated by combustion synthesis using Si, Si3N4 diluent, B4C, and Y2O3 as initial powders. BN and SiC were in situ introduced into Si3N4 ceramics by the reaction between Si, B4C, and N2 gas. The obtained Si3N4-BN-SiC composites were composed of elongated β-Si3N4 matrix and hollow spherical composites. The formation mechanism of the hollow spherical microstructure was investigated. The results show that the generated SiC and BN particles and glass phase cover on the raw materials, and hollow spherical microstructure is formed when raw particles are depleted. Furthermore, the impacts of B4C content on the mechanical properties of Si3N4-BN-SiC composites were investigated in detail. The in-situ introduction of BN and SiC is beneficial to improving mechanical properties of the composites to some extent. Finally, Si3N4-BN-SiC composites with bending strength of 28–144 MPa, fracture toughness of 0.6–2.3 MPa·m1/2, Young's modulus of 17.4–54.5 GPa, and porosity of 37.7％–51.8％ were obtained for the samples with 0–20％ (in mass) B4C addition.