Study On Preparation And Technology Of Ultra-Fine WC-8Co Cemented Carbides Cutting Tools Materials

Ultra-fine WC-Co cemented carbides with superior hardness and toughness are key materials of machining tools in the modem manufacturing industry. Nowadays, nanostructured WC-Co powder has been successfully synthesized. However, because of the abnormal grain growth of ultra-fine powder during the sintering processing, how to control the grain growth of WC has been the key problem of the preparation of ultra-fine hardmetals.In this study, experiment was carried out to optimize the parameters of high energy ball milling for the formation of nanostructured WC-8Co composite powder firstly. The effects of composite grain growth inhibitors (content of VC, Cr3C2, TaC, Y2O3), total carbon content of WC, sintering temperature and sintering process on properties of WC-8Co hardmetals had been studied. Finally, the types of WC-8Co cemented carbides fracture had been summarized.Study results indicated that milling time and the ratios of ball to powder were highly significant to composite powder refinement. The final milling parameters were optimized according to the experiment results and SEM micrograph. It could be obtained a kind of cemented carbides with fine and uniform grain size. The coercive force of the cemented carbides was much higher than conventional cemented carbides. During the vacuum sintering processing of WC-8Co alloys, sintering temperature and total carbon content of WC were the key factors to affect the properties of the cemented carbides. From the X-ray analysis, the .cemented carbides would have abnormal structure ofηphase if total carbon content of WC was 6.16% & 6.19%.And these cemented carbides had abnormal structure of graphite phase when total carbon content of WC was 6.24%. It can be obtained that a kind of cemented carbides with fine and uniform grain size (mean grain size was 0.45um) and favorable properties (93.8HRA,2290MPa) after vacuum sintering in Ar atmosphere at about 1390℃for 80min.The WC grain size of WC-8Co cemented carbides was much finer and the fracture types tended to WC-γphase intergranular brittle fracture after vacuum sintering in Ar atmosphere. The WC grain size of WC-8Co cemented carbides was much coarser and the fracture types tended to WC transgranular brittle fracture and WC intergranular brittle fracture.