Liquid Phase Migration and Shape Distortion of WC-Co Cemented Carbides during Sintering -The Effect of Temperature Gradient in Sintered Compacts during Cooling-

WC-Co cemented carbides (alloys) sometimes exhibit shape distortion during sintering which cannot be explained by the inhomogeneity of the green density or the effect of self-weight. We investigated the shape distortion of WC-Co alloys during sintering focusing on the liquid phase migration (LPM) and the temperature gradients that arise within the sintered compact. In order to accurately capture the phenomenon, ground round bars were reheated under various conditions, and the distribution of Co content and diameter along the longitudinal direction was investigated in detail. As a result, we found that during cooling after sintering, an inevitable temperature gradient is generated in the round bars, and the LPM occurs from the high temperature region to the low temperature region, resulting in the shape distortion. The faster the cooling rate, the larger the distortion. It was also found that the liquid phase migrates from the Co liquid phase region toward the Co solid-liquid coexistence region. We have concluded that the LPM towards the solid-liquid coexistence region is caused by the migration pressure occurring in the region, which we have named ΠSL. ΠSL should be generated because FWC/Co(S) derived from γWC/Co(S) and γCo(L)/Co(S) is higher than FWC/Co(L) derived from γWC/Co(L).