Effect of co-addition of SiC and WC on the densification behaviour and microstructural evolution of TiC-based composites

In the present study, the effect of simultaneous incorporation of SiC and WC additives on the densification behaviour and microstructural development of TiC-based composites is studied. Four different TiC-SiC-WC (TSW) composites with varying SiC and WC content were synthesized by ultrasonic wet milling followed by spark plasma sintering (SPS) at 1750 °C for 5 min under 40 MPa external pressure. The average particle size of the ultrasonic wet-milled mixture underwent an appreciable refinement from 2.48 μm (un-milled powder) to between 0.9 and 1.25 μm. The sintered compacts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and thermodynamic assessment. All TSW sintered specimens exhibited a relative density of greater than 98% with TiC +10 wt% SiC +15 wt% WC reaching the highest value of 99.2%. The XRD analysis and microstructural evaluation confirmed the in-situ formation of Ti₃SiC₂ compound for specimens TiC +15 wt% SiC +10 wt% WC and TiC +20 wt% SiC +5 wt% WC as suggested by the thermodynamic evaluation. Besides, except for specimen TiC +20 wt% SiC +5 wt% WC, some of the SiC grains with unclean grain boundaries were found to be dissolved partially within the (Ti, W) C solid solution, thereby indicating the formation of (Ti, W, Si) C solid solutions as confirmed by the SEM/EDS analysis. The optimum hardness and indentation fracture toughness of 22.43 GPa and 6.54 MPa m^½ were obtained for the samples TS10W15 and TS15W10, respectively. Crack deflection, branching, and bridging induced by the untwine SiC grains, partly un-dissolved WC particles, and (Ti, W) C solid solution phase are among the main toughening mechanisms responsible for improving the fracture toughness of the co-reinforced specimens besides the break of intertwining SiC grains.