In-situ preparation of WC-Co composite powders

Abstract

WC-6Co and WC-10Co composite powders with uniform distribution of Co phase were successfully prepared using WO₃, Co₂O₃ and carbon black as raw materials by the process of “carbothermal pre-reduction + solid phase carbonization”. The phase evolution as well as the influences of carburizing time and temperature on the morphology and particle size of products were investigated. The results showed that there were two reduction paths for WO₃. In one case, the reduction of WO₃ was completed in the order of WO₃ → W₁₈O₄₉ → WO₂ → W and W₂C. The other was that WO₃ first reacted with Co₃O₄ to form CoWO₄, and then CoWO₄ was directly reduced to W and W₂C. Combined with the thermodynamic calculation and XRD results, W and W₂C preferentially transformed into low-carbon η phase (Co₃W₉C₄ and Co₂W₄C) rather than WC phase. Subsequently, Co₃W₉C₄ and Co₂W₄C were transformed into Co₃W₃C. Finally, the Co₃W₃C phase was further carbonized to form WC and Co phases. Moreover, the increase of Co content promoted the reduction and carbonization reactions. The morphology and particle size had little change with the extension of carburizing time. However, as the carburizing temperature rose, the particle size of WC increased obviously, and there was a serious agglomeration.