Compound Inhibitors Of Ultrafine Wc-8% Co Alloy And Performance

The inhibitory effect of VC/NbC on grain growth inhibitor of the Ultra-fine Cemented Carbides WC-Co is studied in this paper. The effects of properties and microstructure of WC-8% with different ratios of VC/NbC have been investigated using Mettler-Toledo, electronic testing machine, Wien hardmeter, coercive force meter, Zeiss microscope, scanning electron, and X-ray. The bset of addition of VC/NbC inhibitors were found by analysising the VC/NbC inhibition mechanism, and named it BY9. The best preparation for BY9 is got by changing the sintering temperature and the number of rubber. And the conclusions are following:1) WC-8% Co can get the best mechanical properties when the inhibitor content of VC/ NbC is 0.2% VC+NbC0.4%, and TRS and hardness is 1714MPa and 1899HV30 respectively. The density of alloy decreased, and the He of alloy increased when add compound inhibitors VC/NbC. The hardness and TRS exhibit non-monotonic variations with the concentration of NbC in the same quantity of VC, but they are higher than the ones of alloy without adding NbC. We find the concent ofα-Co in the alloy increases andηphase gradually disperses and reduces from X-ray diffraction results.2) The best sintering temperature of BY9 is 1440℃. Alloy has the best combination performance when at this temperature, the TRS is 1787MPa, and hardness is 1950HV30. With the increasing sintering temperature, porosity first decreases and then increases, WC grain size enlarges content ofηphase decreases. BY9 has the best combination performance when at 1440℃, BY9 has less porosity, and grain size is 470nm, no abnormal grain growth.3) Theηphase in BY9 gdually decreases and eventually disappears with the increase of forming agent, and graphite is observed. When the addition of rubber is 110ml/kg, the alloy has the best performance with fewηphases and no graphite phase.4) VC/NbC can effectively inhibit the WC grain growth in alloy during the sintering process, and has better effect than VC. Both porosity andηphase increase when adding VC to alloy. When the percentage of inhibitor is 0.6%, adding NbC can reduce the appearance of porosity and the content ofηphase in alloys, while can increase the content of a-Co.5) The inhibition mechanism of VC are different from NbC, both of them control grain size at different temperature ranges. At the stage of solid state sintering, VC and NbC adsorbing on the WC surface hinder the combination and growth of WC grain, at the early stage of liquid phase sintering, VC and NbC reduce the solubility of WC in the liquid phase by dissolving themselves in the liquid phase, and hinder grain enlarged, at the later of liquid phase sintering, NbC segregated to form (W,Nb)C grains and hinder the migration of WC boundaries and the grain growth.