Formation of Grain Boundaries in Liquid-Phase-Sintered WC–Co Alloys

The origin of WC/WC grain boundaries in liquid-phase-sintered WC–Co alloys has been investigated in a WC–Mo₂C–Co model system using coarse WC polygrain powder. The evolution of grain shape during liquid phase sintering was able to be identified by observing a growth layer that contained Mo. During liquid phase sintering, most of the grain boundaries in the powder were penetrated by a Co liquid but some of them were not. Electron backscattered diffraction analysis confirmed that some boundaries in the powder, in particular, Σ2 twist boundaries and Σ97 special boundaries, remained intact during liquid phase sintering. These experimental results confirm that the grain boundaries of WC grains in liquid-phase-sintered WC–Co alloys originated from those present in the starting powder.