Effect of Ni on the formation mechanism of TiC/Ni composites fabricated by reactive sintering

The TiC/Ni composites with 0 wt%, 55 wt% and 70 wt% Ni contents were fabricated by pressureless reactive sintering to study the effect of Ni on the formation mechanism of composites. The results show that the solid reaction between Ti and graphite is controlled by the diffusion of C through TiC layer, and the morphology of TiC layer is similar to the graphite sheet in sample without Ni. By contrast, graphite would dissolve into Ni in samples with Ni, and Ni particles would form continuous skeleton around Ti particles by solid phase sintering. Meanwhile, Ni diffuses into Ti particles to form Ni-Ti compound. Therefore, graphite and C in Ni skeleton reacts with Ti to form TiC layer on whole surface of Ni-Ti particles, resulted in the similar morphology of TiC layers to original Ti particles. Moreover, Ni plays one key role in the liquid phase sintering of TiC/Ni composites by forming Ni-Ti-C eutectic phase. The relative density of TiC/Ni composites are higher than 96%, while the samples without Ni shows no obvious shrinkage. The increase of Ni also contributes to the decrease of sintering temperature by enhancing the solution-precipitation process.