Fabrication of graphite reinforced TiCxNy by spark plasma sintering technique: A comparative assessment of microstructural integrity and nanoindentation properties

This study investigated the fabrication of three different binderless TiC_xN_y (where the values of x and y are 0.5, 0.7, 0.9 and 0.5, 0.3, 0.1 respectively) reinforced with 0.5 wt%, 1.0 wt%, and 1.5 wt% graphites. The reinforcement particles were dispersed in TiCN matrix using the high energy ball milling technique, and the admixed powders were sintered using the novel spark plasma sintering method. The phase analysis and the structural morphologies of the starting powders and sintered specimens were analyzed using field emission scanning electron microscope (FE-SEM), Transmission electron microscope (TEM), and X-ray diffractometer (XRD), respectively. The milling process outcomes showed that the composite powders contain some isolated graphite powders distributed around the matrix as titanium carbonitride. The stoichiometry of the processed powders gave some consistency in the carbon-rich phase. The significant improvement in the properties of as-sintered composites, including microstructure, elastic modulus, fracture toughness, and hardness, was due to the presence of graphite in the ceramic composite. The graphite were also observed to improve the relative densities of specimens as the optimum relative density was achieved at 99.56% when 1.5 wt% of graphite was dispersed in TiC_0.9N_0.1. The nanohardness and elastic modulus values of the most improved composites are as follow; From the nanohardness test, the composites with 0.5 wt% graphite + TiC_0.5N_0.5, 1.5 wt% graphite + TiC_0.7N_0.3 and 1.0 wt% graphite + TiC_0.9N_0.1 had their nanohardness values recorded as 34.5 GPa, 33.3, and 35.1 GPa, respectively, while the highest elastic modulus of 350 GPa was recorded in TiC_0.5N_0.5 and TiC_0.7N_0.3 with respective reinforcement addition of 0.5 and 1.5 wt% graphite respectively. There is a clear increase in grain growth and graphite segregation when 1.5 wt% of graphite was dispersed in TiC_0.9N_0.1. However, the uniform distribution of grains was observed when the same (1.5 wt% graphite) proportion of nanoparticle was dispersed in TiC_0.5N_0.5 and TiC_0.7N_0.3 composites.