Synthesis of TiB2/Ti(C,N) cermet by RSPS: formation mechanism, shrinkage behavior, and mechanical properties

TiB2/Ti(C,N) cermet was prepared by reactive spark plasma sintering from the Co-Ti-BN-C-carbide powder compact. The formation mechanism and shrinkage behavior were studied. Results showed that Ti(C,N) was produced by the diffusion of C atoms into a preformed TiN. TiN-forming reaction was exothermic, which would lead to the occurrence of deep macropores and an abnormal expansion phenomenon. With increasing temperature, the macropores became increasingly shallow. Eventually, they disappeared through the viscous flow and dissolution-reaction-precipitation mechanisms. This behavior was primarily responsible for sintering densification. Among various carbide additives, TaC displayed the optimal effect. The hardness and fracture toughness of cermet reached 1917.4 HV and 8.81 MPa.m-1/2. The reason was the formation of a black core/gray rim structure by the diffusion of heavy elements in liquid into the Ti(C,N). Results from the present work could offer a deep understanding of reactive spark plasma sintering, and would be beneficial for the development of Ti(C,N)-based cermet.