Effect of Ni and graphene on microstructure and toughness of titanium boride ceramic tool material prepared by spark plasma sintering

TiB2/TiC ceramic tool material toughened by Ni and graphene nanoplatelets was prepared by spark plasma sintering. Effect of Ni and graphene nanoplatelets on densification, microstructure and mechanical properties were studied. The composite containing 2 wt% Ni and 0.5 wt% graphene nanoplatelets can be fully densified at 1750 degrees C with the holding time of 5 min. Both Ni and graphene can improve densification of TiB2 ceramic. Ni also promotes more content of graphene nanoplatelets to toughening. Excess Ni leads to cracks at grain-boundaries owing to the large thermal expansion mismatch between Ni and graphene. The optimal fracture toughness is 8.3 +/- 0.43 MPa m(1/2). Crack bridging is the most effective toughening mechanism. Except the particle bridging, some blocky materials act as the bridging unit due to the anchoring effect of graphene. Bridging process by graphene failed by debonding of graphene from the matrix.