Effect of additive-Si3N4 on mechanical properties of Ti–B–C composites

Rod-like phase TiB2, formed by reaction of B4C and Ti, in situ toughened Ti–B–C composites, and improved the mechanical properties of composites. But additives as added to system of B4C–Ti damaged the mechanical properties of Ti–B–C composites and restrained the formation of rod-like TiB2. The particles of TiB2, β-SiC and Ti(C, N) were produced by addition of 20 vol.% Si3N4 that reacted with B4C and Ti. The thermodynamic processing of the reaction of B4C, Ti, and Si3N4 was studied. Each of grain size is about 2 μm and distributes uniformly in composites. TiB2 did not develop into rod-like microstructure, but equiaxial crystal owing to restraint of interrelated unfavorable factors. The crystalline phases were determined by X-ray diffractometry (XRD) and the microstructure of composite was observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite possesses high density (>99%) and the fracture toughness of composites by addition of 20% Si3N4 is 7.11 MPa √m. We discussed the effect of Si3N4 on the mechanical properties of composites and analyzed the mechanisms of toughening.