The grain size of WC-20%Co alloy affected by the addition carbides such as TiC, VC, Cr₃C₂, ZrC, NbC, Mo₂C, HfC and TaC was in detail investigated. Specimens were sintered mainly at 1400°C for 1 hr. The mean grain size of starting WC powder was about 0.6μ.
Results obtained were as follows: (1) When the liquid phase was saturated by the addition carbides at sintering temperatures, the restriction effect of VC on the grain growth of WC was the largest, followed by Mo₂C, Cr₃C₂, NbC, TaC, TiC, ZrC(≅HfC). In this case, there existed a strong correlation. between the restriction effect of addition carbides and the solubility limit in the liquid phase (or the formation free energy). (2) On the other hand, when the liquid phase contained a certain amount of dissolved metals of addition carbides, i.e., about 1.5at% for the starting Co, the effectiveness was in the following order; VC>NbC>TaC>TiC>Mo₂C>Cr₃C₂>ZrC≅HfC. (3) Considering the restriction effect and the shape of carbides precipitated, VC addition was considered to be the most suitable for the grain growth inhibitation of WC, followed by Cr₃C₂, NbC and TaC.