Microstructural and mechanical behavior of spark plasma sintered titanium carbide with hybrid reinforcement of tungsten carbide and carbon nanotubes

TiC, TiC-3.5 wt% WC and TiC-3.5 wt% WC-2 wt% CNT pellets were consolidated using spark plasma sintering technique at 1600 °C and 50 MPa pressure. Spray drying technique was used for the homogeneous dispersion of CNT in TiC matrix. Punch displacement data showed the relatively higher compaction of TiC on addition of 3.5 wt% of WC and 2 wt% of CNT. Raman spectra confirmed the retention of CNTs in spark plasma sintered pellet, While, HR-TEM micrographs infers the defect morphology of CNT after the sintering. Some CNTs were found to be defected with the bamboo like structure, which have ultimately provided the strong interface between TiC and CNT through mechanical interlocking mechanism. Hybrid reinforcement of WC and CNT has played a vital role in increasing the density of TiC pellet from 89% to 99% and in reducing its average grain size by ~ 31%. Further, improvement of 41% in hardness and 42% in elastic modulus were observed in sintered TiC pellet on addition of WC and CNT. Drastic improvement of 141% in fracture toughness value was found which was due to the higher critical energy release rate in TiC-3.5 wt% WC-2 wt% CNT pellet. Interfacial shear stress was evaluated using modified Cox model to investigate the higher critical energy release rate. CNT grain stitching and CNT grain gluing was found to be novel toughening mechanism apart from the conventional mechanism of CNT bridging, crack bifurcation and CNT pull out.