Microstructure and mechanical properties of ultra-fine WC/Co cemented carbides and binderless tungsten carbides

Abstract

Cemented carbides, consisting of WC grains bound by the Co phase, have been used as cutting tools, rock drill tips and other wear resistant components during the last several decades. The effects of the variations of Co composition and the addition of other types of cubic carbides have been investigated to improve the properties of WC-Co cemented carbides. In recent days, nanocrystalline WC-Co cemented carbides have been developed by thermochemical and thermomechanical process named as spray conversion process. The WC particle sizes in powders fabricated by spray conversion process can be reduced to about 100nm. If the grain growth behavior is properly controlled during the sintering process, the WC grain size in sintered cemented carbides can be reduced below 400nm. Recent studies of mechanical properties of nanocrystalline WC-Co cemented carbides proposed different mechanisms for fracture and deformation of nanocrystalline WC-Co cemented carbides according to the microstructure and chemical composition. However, the deformation mechanisms of either nanocrystalline or even conventional WC-Co cemented carbides have not been clearly understood yet. In this study, the mechanical properties and microstructures of nanocrystalline and conventional WC-Co cemented carbides were investigated. The nanocrystalline WC-10Co cemented carbides powders were manufactured by reduction and carbonization of the nanocrystalline precursor powders which were prepared by spray drying process of solution containing ammonia meta-tungstate(AMT) and cobalt nitrate. The WC powders with average size of about 100nm in diameter were mixed homogeneously with Co binder phase and were sintered at 1375℃ under a pressure of 1mtorr. In order to compare the microstructures and mechanical properties with the nanocrystalline WC-10Co, commercial WC powders in a diameter ranged 0.57-4㎛ were mixed with Co powders, and were sintered at the same condition with that of nanocrystalline powders. TaC, $Cr_3C...