High resolution transmission electron microscopy study in VC-doped WC–Co compound

Microstructure evolution in VC-doped WC–Co was investigated using high-resolution transmission electron microscopy (HRTEM) associated with X-ray energy dispersive spectroscopy (EDS) with a special interest in WC/Co and WC/WC boundaries. It was found that the morphology of carbide grains changed largely by the addition of VC. The WC/Co interfaces tend to form facetting with fine multi-steps of (0001) and {} habits by VC-doping. In addition, the facetting morphology of WC/Co interfaces was confirmed to be already formed in solid state from an examination with a quenched compound from 1200˚C, which is below the eutectic temperature of 1320˚C between WC and Co system. EDS analysis with the sub-nano scale probe revealed that the doped V was strongly concentrated to the two habits. However, the amount of concentrated V was different among them, i.e. more at (0001) habit than at { } habits. V is considered to be concentrate at the boundary during grain growth to accompany the migration of the two habits because most of the doped V solves into the Co-phase and not into WC grains. Thus it can be supposed that the retardation of the grain growth of WC grains is due to the concentration of V at the migration front of the two habits.Meanwhile, WC/WC boundaries were found to be directly in contact each other and free from the second phase such as the amorphous phase whereas the segregation of Co and also V could be detected by EDS analysis. This fact suggests that the grain boundary migration between the adjacent WC grains may be mainly controlled by the solid–solid diffusion.