Growth mechanisms of WC in WC–5.75 wt% Co

Abstract

The grain growth mechanisms of WC in WC–5.75 wt% Co are studied in this work. The two well known growth modes of WC in cemented carbides (coalescence process and solution/reprecipitation process) are both observed and show temperature dependence. At low temperatures (1100 and 1200 °C), the growth of WC grains is mainly through coalescence. At intermediate temperatures (1300 °C), coarsening of most WC grains takes place via isotropic growth, accompanied by the shape relaxation leading to the faceting of round grains. At high temperatures (1400 °C), layer-by-layer structures, resulting from anisotropic growth, are observed. Both isotropic growth at 1300 °C and anisotropic growth at 1400 °C are assisted by the solution/reprecipitation process. This is the first time that layer-by-layer structures are observed for WC crystals in WC–Co. The formation mechanism of layer-by-layer structures has been discussed based on the 2D nucleation and growth mechanism and the diffusion rates of W and C atoms within the Co binder at different temperatures.