Nanocrystalline W, Co, C, Transition Phase Powders Carbide

Nano-grained cemented carbides possess a series of excellent mechanical performances such as high transverse rupture strength and high hardness, which can meet the urgent demands in aerospace, information technology, mould and cutting application. However, the rapid intrinsic growth characteristic of nanometer WC grain during sintering process lead nano-grained cemented carbides with excellent mechanical performances is not acquired.Therefore, the purpose of this dissertation was explored the preparation of superfine grain or nano-grained cemented carbide, which used nano-grained W, Co, C transitional phase powders as raw materials through high energy ball milling W-Co-C mixed powders.In this paper, phase transformation, WC grain growth characteristic and WC grain growth inhibiting during sintering of W, Co, C transitional phase powders were studied by X-ray and SEM. Carbon content control, performances of sintered alloys was also studied.During sintering process, nano-grained W, Co, C transitional phase powders transformed into transitional phases such as W₂C, Co₆W₆C and Co₃W₃C. These transitional phases would be completely transformed into WC and Co by the diffusion of carbon when sintering temperature increased or sintering time prolonged. So, YG10 cemented carbides with sintering density 14.46g/cm³ and shrinkage rate 27.2% were obtained when W, Co, C transitional phase powders compacts sintering at 1375℃ for 30min.Research showed that modified nanometer ZrO₂ could effectively decrease the size of WC grain, promote sintering densification and remarkable improve the hardness of cemented carbides, which was a kind of effective WC grain growth inhibitor. And introduction of 0.3-0.42wt% carbon black excess effectively balanced the carbon loss due to the absorption of O₂. And cemented carbides with carbon content 5.37-5.53wt%composed of WC and β-Co phase, which strength and hardness were 2763MPa and 91.1HRA respectively, were acquired.Rod-like WC grains with 100nm in radial dimension and 1.2 am in length were formed as sintering at 1375℃ for 30min. In-situ formation ofnanometer rod-like WC reinforced cemented carbide is hopeful being obtained using nano-grained W> Co> C transitional phase powders as raw materials, and which is a feasible new method of fabrication high performance hardmetal alloy.