Effect Of Cobalt?Carbon And Titanium Carbide Addition On Microstructure And Properties Of Fine Grain Cemented Carbides

Cemented carbide is known as the teeth of industry and plays an important role in the national economy and social development.The use of cemented carbide is very extensive.It is mainly used for cutting tools and currently accounts for more than 90%of domestic tools.Cemented carbide has a good comprehensive properties and has been widely used in tool industry.The conflict between hardness and toughness hinders the further development of cemented carbide tools.Different compositions of fine grained cemented carbide were prepared by powder metallurgy method,the effects of cobalt content,carbon content and titanium carbide addition on microstructures and properties of fine grained cemented carbide are researched in this study.X-ray diffraction,SEM,automatic cobalt magnetometer,coercive force measuring instrument,universal testing machine and other analytical methods are used to study structure and properties of different compositions of fine grained cemented carbide.The main results are as follows: the cobalt not only fully fills the gap between the WC skeletons,but also avoids forming a cobalt pool during the sintering process.Cobalt magnetization increases as the cobalt content increases,while coercive force decreases.The microhardness and bending strength of cemented carbide have the highest values when the cobalt content is 13%.In this case,the grain size is smallest,which helps to improve the microhardness and bending strength.The fracture of cemented carbide mainly is ductile fracture,there is a large number of dimple structure in the fracture when WC particles are pulled out.The graphite phase in the microstructure increases gradually when the carbon content increases,and the WC grain grows up at the scanning electron microscope.When the addition of carbon is 0.2%,only WC and ? phases exist in the cemented carbide after sintering and the bending strength is the maximum,there is much dimple structure in the fracture.When the carbon content is 1.2%,the bending strength is the minimum and there are many graphite holes in the fracture.The hardness of the cemented carbide decreases with the increase of the carbon content.When the carbon content increases,the coercive force keeps decreasing while the content of the magnetic cobalt increases continuously,but cobalt magnetization is less than the original cobalt content.The addition of TiC can restrain W from dissolving in Co and increase the content of cobalt magnetitation in the cemented carbide.(Ti,W)C solid solution was formed by TiC and WC during the sintering process,which distributes in the corner of WC and hinders the migration of WC grains,(Ti,W)C solid solution plays a role in refining the grain.The hardness of the alloy increases with the increase of TiC content,while the bending strength decreases with the increase of TiC,because the(Ti,W)C solid solution is a hard and brittle phase.The path of crack propagation is extended with the increase of TiC content,it has an effect on improving the toughness of the cemented carbides.