Investigation Of Fabrication, Microstructures And Mechanical Properties Of Ultra-fine Grained WC-Co Alloys

Ultra-fine or nanostructured WC-Co cemented carbides with enhanced strength and toughness are key engineering materials for machining tools and moulds in modern manufacturing industries. WC/Co composite powders were prepared through planetary ball milling method and sol-gel method, respectively. The ultra-fine WC-10wt.%Co cemented carbides were obtained through low-pressure sintering. The effects of raw cobalt powder, milling speed, sintering temperature and doping amounts of rare earth La on the microstructures and mechanical properties of the hard alloys were investigated using X-Ray diffraction, scanning electron microscope and mechanical properties testings, with the following conclusions can be drawn:(1) A decrease in the cobalt particle size from17to1.4μm can obtain a uniform and dense microstructure and high mechanical properties for WC-10Co-0.25VC-0.45Cr3C2alloys. Hardness and fracture toughness of the alloys are also increased. The alloy fabricated by a milling speed of200rpm as well as a sintering temperature of1400℃exhibits the highest hardness plus considerable fracture toughness.(2) Homogeneously distributed ultra-fine WC-Co composite powders could be obtained through the sol-gel method and the addition of trace La element can decrease the quantity of Co3W3C phase in the WC-Co composite powders and prohibit the martensite transformation from fcc structured Co to hcp structured Co. Addition of trace La element can decrease the quantity of Co3W3C phase in the sintered WC-Co alloys so as to promote the hardness, fracture toughness and strength.This research systematically studied the effect of preparation parameters of ball milling on the microstructures and mechanical properties of the sintered WC-Co alloys and developed a new method to fabricate WC/Co composite powders. It can effectively shorten the production process and provide a reference for fabricating high-performanced cemented carbides.