Microstructure and properties of ultrafine WC-10Co composites with chemically doped VC

Vanadium carbide is the most effective grain growth inhibitor for ultrafine WC-Co composites due to its high solubility and mobility in the cobalt phase at relatively low temperatures; however, there are still some debates over the best way to introduce it into the WC-Co formulation. In this paper, the differences between admixed and chemically doped grain growth inhibitors on the microstructural development and properties of an ultrafine WC-10Co composite are discussed. The densification rate of chemically doped samples is slower in the early stage of sintering and the WC grain sizes of the sintered alloys are finer than those of admixed samples, leading to the increase of hardness and transverse rupture strength of the sintered alloys. The effectiveness of the chemically doped inhibitor is attributed to the formation of vanadium rich layers on the surfaces of tungsten carbide powders during reduction and carbonization, which alters the surface and interface energies of WC grains, impedes the contact with each other of WC grains and contributes to the resistance to W diffusion across the layer during sintering, resulting in the inhibition of nanosized particle coalescence.