A nanostructural approach to the interfacial phenomena in spark plasma sintered TiB₂ ceramics with vanadium and graphite additives

A novel TiB₂-based composite, with metallic vanadium and nano-graphite additives, was fabricated by spark plasma sintering. A comprehensive investigation was carried out to clarify the sintering behavior and interfacial phenomena. The in-situ synthesis of crystalline V₃B₄, V₆C₅, and TiC phases was proved. The formation of V₆C₅ was attributed to the ordering phase transformation promoted by carbon vacancies in the initially-synthesized VC. TiC was formed due to the reduction of TiO₂ impurity with graphite additive. Simultaneous addition of vanadium and graphite not only resulted in the reduction of B₂O₃ impurity, but also the synthesis of V₃B₄ nano-crystals, which shows the critical role of oxide impurities on the final phase arrangement. The liquid state of B₂O₃ at high temperatures promoted the possibility of such reactions. The in-situ formation of such phases led to significant improvements in the mechanical properties. Compared to the monolithic TiB₂ consolidated through similar conditions, 50% increase in fracture toughness and 27% enhancement in elastic modulus were observed.