B4C ceramics toughened by TiB2–graphite-agglomerated inclusions

Abstract

In this study, B₄C–TiB₂–graphite ceramic composites were prepared via reactive hot-pressing sintering using B₄C and TiC as the raw materials. The reaction process, microstructure, and mechanical properties were investigated. The solid-phase reaction is a diffusion-controlled process, wherein the B atoms diffuse into TiC and react to form TiB. Thereafter, TiB₂ is generated with the entry of subsequent B atoms. A core–shell structure is formed, wherein TiB₂ particles are wrapped by layered graphite. The products TiB₂ and graphite inhibit the growth of B₄C matrix grains, which are instrumental in fine grain strengthening. In addition, the novel TiB₂–graphite-agglomerated structure significantly improves the fracture toughness of the ceramic composites through crack deflection, bridging, and branching toughening mechanisms. Therefore, the comprehensive properties of B₄C–TiB₂–graphite ceramic composites are better than those of pure B₄C ceramics. Specifically, the fracture toughness is approximately 6.77 MPa m^1/2, which is considerably higher than that of pure B₄C ceramics (2.47 MPa m^1/2).