Microstructure and indentation of a (MoNbTaVW)C system processed by high energy ball milling followed by spark plasma sintering at 1800 °C

This work reports the development of a multi-phase (MoNbTaVW)C carbide processed using a combination of high energy ball milling and spark plasma sintering. The compact sintered at 1800 °C provided a relative density of 99.5 % and consisted of a FCC1, BCT and FCC2 phase. The microhardness and indentation fracture toughness of the sintered compact was observed to be 20.2 GPa and 4.9 MPa.m^1/2 respectively. Mechanisms of crack deflection and crack bridging were found to be operational in the sintered compact. The FCC1 phase was found to be harder and tougher than the BCT phase. Interestingly P-h curves from both FCC1 and BCT phases exhibited displacement excursions or pop-ins whose formation was attributed to nanoscale plasticity. The FCC1 phase demonstrated pop-ins of greater depth and in larger number than those observed in the BCT phase and this was attributed to its higher entropy of mixing at 1.7R vis-à-vis the BCT phase at 1.3R. The higher entropy in FCC1 phase can be correlated to higher lattice distortion which could be controlling the formation of the pop-ins in the material.