Effect of SiC Content on B4C-SiC Composites Fabricated by Mechanical Alloying-hot Pressing

Dense B4C-SiC composite ceramics were fabricated through mechanical alloying using coarser B4C and SiC powders as starting powders, and subsequent hot pressing sintering at 1950 degrees C without any sintering aid. The influences of the content of SiC on mechanical properties of the composite ceramics were studied through determining relative density of composite ceramics, Vickers hardness, flexure strength and fracture toughness. Combined with the microstructure and component analysis technologies of XRD, SEM and TEM, the relationship between microstructure and mechanical properties of the composite ceramics was investigated. The results indicate that the relative density and fracture toughness of the composite ceramics are improved with increase of SiC content, and reach the maximum value at 96.1% and 4.6 MPa.m(1/2), respectively, with SiC content of 50wt%. However, with the increase of SiC, the Vickers hardness and flexure strength are enhanced firstly and then decreased. The maximum values are 25.5 GPa and 480 MPa, respectively, with SiC content of 20wt%. Homogeneous dispersion of SiC phase in B4C matrix is one of the reasons why the composite ceramics possess higher flexure strength. Fracture toughness of the composite ceramics is significantly higher than that of monomeric B4C. The main reasons are attributed to powerful interfacial bonding between B4C and SiC as well as the higher fracture toughness of SiC.