Study Of Ultra-fine Cemented Carbides Grain Growth Inhibitors Optimization And Sintering Process

In This paper, we use imported Ultra-fine WC powders producted by American OMG company and Ultra-fine cobalt powders producted by Shanghai BaiLuoDa Co.Ltd as crude materials. Alloy performance effected by grain size of grain growth inhibitors VC and Cr₃C₂, additions, different ratio of VC/Cr₃C₂ and sintering temperatures have been investigated systematically by means of scanning electron microscopy (SEM), X-RAY diffraction and differential thermal analysis (DTA). The heating effects in the course of sintering have been analyzed by DTA, and the phase structures of alloy have been researched by XRD. At the same time, inhibiting mechanics of grain growth inhibitors VC and Cr₃C₂ has been explored.The experiment results show that the pre-grinding grain growth inhibitors VC and Cr₃C₂ influence inhibiting effectiveness. As the grain sizes decreasing, the inhibiting effectiveness has changed obviously. Coercive force and hardness of alloy remarkablely raised. But VC has high oxygen content after pre-grinding, which brings disadvantages to strength and makes strength reducing.The hardness of ultra-fine WC-Co cemented carbides grows apparently as amount of grain growth inhibitors increasing, especially VC. When VC has been added in, the coercive force increases. At the same time, alloy density decreases because of augmentation of porosity. Excess grain growth inhibitors bring decline of TRS and influence densification degree. Proper amounts of grain growth inhibitors for total weight amount is 0.8wt% in the sintering schedule of 1380℃ sintering temperature and insulation for one hour.As for adding to single grain growth inhibitors, VC has the best inhibiting results, next VC/Cr3C2 and the last is O3C2. The same amounts of VC has faster increase in coercive force than Cr3C2 has. Strength reduces as VC added to, but G3C2 rises after lowering.Alloy performance is affected by variation in ratio of VC/Cr3C2 greatly. When G3C2 ratio in VC/Cr^ increases, hardness decreases and strength TRS has a maximum. Alloy in O.4G3C2-O.2VC of proportion of ingredient has best comprehensive property. Advantage sequence: VC/Cr3C2> Cr3C2>VC. As for WC-(6 1 Owt %) Co system, ratio of inhibitors comstituents of Cr3C2: VCin maximal TRS is 2—3.Through trials, we find alloy WC-8Co-0.6Cr3C2-0.2VC and WC-6Co-O.4Cr3C2-O.4TaC has better comprehensive property, and TRS separately reach 4380Mpa and 3970Mpa, hardness reach 93.0HRA and 92.8HRA.After the trial in Different sintering temperatures acting on performance of alloy WC-10Co-0.4VC-0.4Cr3C2, We find that alloy sintered in 1320°C has high porosity after alloys sintered in vacuum, and alloy sintered in 1350°C and 1380°C has little difference, alloy sintered in 1350°C has higher TRS than 1380°C, and hardness has only 1.1 HRA difference. Microscopic structure of alloy shows that sintering temperatures have apparent influence on densification and grain size. Proper sintering temperature of alloy WC-10Co-0.4VC-0.4Cr3C2 may be 1350°C 1380°CDifferential thermal analysis (DTA) shows that alloy WC-10Co-0.4VC-0.4Cr3C2 emerge liquid phase in 950°C and terminate in 1300°C.Grain growth inhibitors VC and G3C2 have different inhibiting mechanics. VC adsorbed in WC grain surface, and reduced WC surface energy. This makes WC dissolvability reduce, and segregate in WC/WC interface and stunted WC interface migration and WC grain aggregation. It is considered that G3C2 dissolve in cobalt phase and then slow up WC grain's growing.