The Preparation Of Nanocrystalline WC And Its Influence On The Properties Of YG8 Hardmetals

WC-Co hardmetals is a kind of important cutting tool material and die material, which has the pivotal function to the industry development and society's progress. Recently,researchers have found that ultra-fine or nanostructured WC-Co hardmetals was of superior hardness,superior toughness,superior wearing strength and fatigue strength. In this work,the experiment have been done to study the preparation of nanocrystalline WC-Co powder through high energy ball milling method,the molding of the powder and the binders'influence on it,the vacuum sintering process of the WC-8Co flan and the nanocrystalline WC's influence on YG8 hardmetals were also studied.The preparation of ultra-fine WC-Co raw powder through high energy ball milling was studied at first. This research showed that the powder got smaller and smaller as the milling time went by. By means of the particle size test equipment and scanning electron microscope (SEM),the results showed that the average size of the particle had reached 0.37μm and 0.29μm when the raw powders were milled for 48 hours and 60 hours. The carbon-lack cemented carbide phase andε-Co phase were both found in the produced powders using X-ray diffraction (XRD). It can be concluded that some of the carbon had been lost from WC-base and someα-Co had changed intoε-Co during the high energy ball milling process.At the same time two different binders were studied to invest their influence on the moulding of the composite powders. By means of thermal gravity analysis(TGA) and differential scanning calorimeter (DSC),we found that SBS was the best binder for the moulding of hardmetals. The further experiment also proved this conclusion.The dependence of microstructure and mechanical property on the technical parameters of vacuum sintering was also investigated in this paper; the density,hardness and microstructure of the sintered nanostructured WC-Co hardmetals was measured and analyzed to have determined the optimal vacuum sintering parameters. It can be concluded that the sintering temperature at 1380℃,the sintering time lasting for 60 minutes was the optimal parameters of vacuum sintering.At last the nanocrystalline WC's influence on the properties of YG8 hardmetals was studied. The parameters of microstructure and mechanical property reveled that the best amount of the nano-sized WC addition was 12wt%. When addition was at that level,the sintering sample's grain size would reach 500nm,with the hardness 93HRA.