Competitive reaction behavior and formation mechanism of reactively spark plasma sintered TiB2-TiC composite ceramics with tunable compositions

Abstract

TiB₂-TiC composite ceramics with tunable compositions (70 wt% < TiB₂ < 100 wt%) were fabricated by the reactive spark plasma sintering (SPS) technique using Ti, B₄C, and TiB₂ as raw materials. The effects of sintering temperature and holding time on the densification, electrical, and mechanical properties of composite ceramics were investigated. Additionally, the competitive reaction behavior of the Ti-B₄C-TiB₂ ternary system and the formation mechanism of TiB₂-TiC composite ceramics were systematically highlighted, respectively. The TiB₂-TiC composite ceramics successfully obtained 98.9 % relative density, 8.0 ± 0.3 μΩ∙cm electrical resistivity, and 6.8 ± 0.2 MPa∙m^1/2 fracture toughness at the sintering temperature of 1800 °C, pressure of 35 MPa, and holding time of 5 min. As the sintering temperature was increased in the Ti-B₄C-TiB₂ ternary system, competitive reactions occurred not only between Ti and B₄C as well as between Ti and TiB₂ reactants, but also between B₄C and in-situ generated TiC, accompanied by the formation of TiB and free carbon in the system. The enhancement of fracture toughness could be attributed to the generation of TiB. Meanwhile, the establishment of a conductive network, which was promoted by the presence of free carbon, resulting in significant reduction in electrical resistivity. However, as a consequence of the deformation and dissociation of the free carbon, a reduction in the load-bearing cross-section resulted in a corresponding reduction in the flexural strength of the composite ceramic.