Experimental investigation and thermodynamic assessment of the V-W-C system

Phase equilibrium information of the V-C, W-C and V-W systems are reviewed and the V-W phase diagram was optimized by the substitutional solution model for liquid and bcc phases. A set of self-consistent thermodynamic parameters on the interaction of W and V atoms in the fcc (V,W)C and hcp (V,W)2C phases was established by CALPHAD techniques. The calculated isothermal section at 1500 °C was consistent with the available experimental literature data of the V-W-C system. To validate the thermodynamic calculations, V8C7/WC interaction couples were annealed at 1400 °C for 196 h and WC powder mixtures with 20, 40 and 70 wt.% V8C7 were sintered at 1400 °C for 15 h. The obtained materials were investigated by scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The composition of the single phase fcc (V,W)C reaction product in the interaction couple and the constituent phases of the sintered materials were consistent with the calculated phase diagram at 1400 °C.