SYNTHESIS AND CHARACTERIZATION OF ULTRA HIGH TEMPERATURE CERAMICS BASED COMPOSITES

Abstract

For the past decade, titanium carbide ceramics, and based composites have drawn immense attention among the scientists working in aerospace technology, defense sector, high-speed cutting tools, and corrosion-resistant coatings. 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 single mode ultrasonic wet milling followed by spark plasma sintering (SPS) at 1750 °C for 5 minutes 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 0.9-1.25 μm. All TSW sintered specimens exhibited a relative density of greater than 98%. Among all compositions, the TiC-10 wt.% SiC-15 wt.% WC specimen yielded the highest relative density 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. Moreover, the mixed mode fracture with dominant trans-granular fracture than inter-granular fracture was observed in case of TSW composites compared to dominant intergranular fracture in case of monolithic TiC. The optimum Vickers hardness and indentation fracture toughness of 22.43 GPa and 6.54 MPa.m1/2 were obtained for the TiC-10 wt.% SiC-15 wt.% WC and TiC-15 wt.% SiC-10 wt.% WC composite, which were ~ 19% and 77%, respectively higher than the monolithic TiC. 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. The TiC-5 wt.% SiC-20 wt.% WC composite exhibited the least thermal conductivity, thermal diffusivity and specific heat capacity of 19.69 W/m.K, 6.98 mm2/s and 513.86 J/Kg.K, respectively. On other side, TiC-20 wt.% SiC-5 wt.% WC composite exhibited the highest thermal conductivity, thermal diffusivity and specific heat capacity of 34.02 W/m.K, 12.89 mm2/s and 579.64 J/Kg.K respectively.