Morphology of WC grains in WC–Co alloys

In two alloys WC–(24 wt.%) Co containing a C and W excess respectively, sintered at 1450 °C (10 h) the shape of the larger WC grains that is a prism with a truncated triangle base is studied by transmission electron microscopy. The truncation that is the ratio of the short/long triangle sides and the elongation that is the ratio of the prism/triangle heights are quantified. The grains are less truncated and flatter in the C rich alloy. In equilibrium condition the ratio of the interface energies of the prismatic facets determine the truncation. The ratio of the energies of the basal and prismatic planes determines the elongation. The measured truncation confirms the ratio of the interface energies predicted from atomistic calculation for the prismatic facets. The experimental elongation is of the same range as the ratio between the calculated energies in the W rich alloy but much smaller in the C rich alloy. The possible origins of the discrepancy – departure from the equilibrium WC grain shape, model of the WC–Co interfaces used to calculate the interface energies – are discussed.