Preparation Of WC Base Cemented Carbides With New Binder Phase And Plate-like WC Grains

WC-Co base cemented carbides with plate-like WC grains possess higher hardness and toughness than normal WC-based hardmetals. Meanwhile, the cemented carbides with new binder phase have lower costs. Thus, WC base cemented carbides with new binder phase and plate-like grains is a promising candidate for conventional WC-based cemented carbides. In the present paper, series of WC-Co base cemented carbides with plate-like WC grains were produced by vacuum sintering. The mechanical properties of the cemented carbides were improved by changing the composition of the binder phase and the effects of preparing the WC powder by mechanical alloying were also be studied.The relationship among composition, manufacturing process, microstructure and mechanical properties of WC base cemented carbides with new binder phase and plate-like WC grains have been investigated by differential scanning calorimetry(DSC), X-ray diffraction(XRD), energy dispersive spectrdmeter(EDS) and scanning electron microscopy(SEM).In the first part of the dissertation, the phase and microstructure transformation during sintering and the influnces of the sintering technology on the cemented carbides have been studied. The results were obtained as follows: with the sitering temperature rising or sintering time extending, the hard phase particles were growing gradually and the length-thickness ratio of the particles possess the trend of improving at first then reducing. With the declining of the heating rate, the length-thickness ratio of the particles were improved constantly. The cemented carbides have the excellent mechanical properties when sintered at 1400? for 60 min and the heating rate in 800-1200? was 2?/min with hardness of 91.3HRA, TRS of 2676 MPa and KIC of 31.4MPa?m1/2The effects of the composition of the binder phase such as Ni/Co ratio, the addition of Fe and the addition of Cr have been studied. Some conclusions were drawn as follows: when the Ni/Co ratio was 3/7 or 5/5, the cemented carbides exhibit a better mechanical properties due to the grain size of WC phase were smaller and the length-thickness ratio of the hard phase were higher. But when the Ni/Co ratio reached to 7/3 or 10/0, the grains grew up owned to the obviously agglomeration of the hard phase and the decreasing of the length-thickness ratio, the cenmented carbides exhibit a lower mechanical properties. The cemented carbides showed the best mechanical properties with the TRS of 2448 MPa, hardness of 90.0HRA, KIC of 21.2 MPa?m1/2. With the addition of Fe in binder phase, the grain size increased continuously, the length-thickness ratio of the hard phase were higher when Fe/(Fe+Co+Ni) ratio were less than 0.2 then droped obviously when the Fe/(Fe+Co+Ni) ratio up to 0.5. The hardness, transverse rupture strength and fracture toughness improved gradually and then reduced. The cemented carbides exhibit the best mechanical properties when Fe/(Fe+Co+Ni) were 0.05 with the hardness of 90.6HRA, TRS of 2497 MPa, KIC of 26.7 MPa?m1/2. When Cr/(Cr+Co+Ni) were 0.05, the mechanical properties remain unchanged. While Cr/(Cr+Co+Ni) up to 0.1, the mechanical properties reduced seriously.Finally, the effect of ball-milling time at the processing of W-C system mechanical alloying on mixed powder have been studied. WC compound evenly distributed was obtained successfully when the ball-milling time up to 96 h. At the middle(12~24h) and the second half(48~96h) of the ball-milling processing, the particle size of the WC phase decreased significantly. And the effects of the material which was prepared by mechanical alloying after compressing molding and sintering have also been pointed out, the result were obtained as follows: the microstructure of the WC phase refining to some extend but distribute unhomogeneous. The hardness of the material keep unchanged basically, transverse rupture strength decreased and fracture toughness improved.