A novel ZrB2-VB2-ZrC composite fabricated by reactive spark plasma sintering

The development of a novel ZrB2-VB2-ZrC composite using ZrB2, vanadium and graphite nano-flake powders via reactive spark plasma sintering was studied. The in-situ formation of VB2 and ZrC enhance the densification, sinterability and mechanical properties. A relative density of 99.17% was achieved for ZrB2-20 vol% VB2-20 vol% ZrC composite after RSPS at 1900 °C for 7 min under 40 MPa. The hardness and fracture toughness of the novel composite are improved by 50% and 40%, respectively, in comparison with a monolithic ZrB2 ceramic. Thermodynamic calculations and microstructural analyzes revealed that the in-situ formed VB2 and ZrC phases derived from the reaction between a transient VC phase with ZrB2 matrix. These phases were also found to be strong inhibitors of grain growth, and consequently result in improved sinterability and mechanical properties. Due discussions about the formation mechanism, characteristics and influences of such refractory reinforcement phases were investigated and schematically illustrated.