Combustion Synthesis of Si3N4-BN-SiC Composites by in-situ Introduction of BN and SiC

Si 3 N 4 -BN-SiC composites present desirable potential for engineering applications because of their improved mechanical properties and oxidation resistance.In present work, Si 3 N 4 -BN-SiC composites were successfully fabricated by combustion synthesis using Si, Si 3 N 4 diluent, B 4 C, and Y 2 O 3 as initial powders.BN and SiC were in situ introduced into Si 3 N 4 ceramics by the reaction between Si, B 4 C, and N 2 gas.The obtained Si 3 N 4 -BN-SiC composites were composed of elongated β-Si 3 N 4 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 B 4 C content on the mechanical properties of Si 3 N 4 -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, Si 3 N 4 -BN-SiC composites with bending strength of 28-144 MPa, fracture toughness of 0.6-2.3MPa•m 1/2 , Young's modulus of 17.4-54.5GPa, and porosity of 37.7%-51.8%were obtained for the samples with 0-20% (in mass) B 4 C addition.