Vacuum sintering of WC–8 wt.% Co hardmetals from WC powders with different dispersity

Abstract

The effect of sintering temperature and particle size of tungsten carbide WC on phase composition, density and microstructure of hardmetals WC–8 wt.% Co has been studied using X-ray diffraction, scanning electron microscopy and density measurements. The sintering temperature has been varied in the range from 800 to 1600 °C. The coarse-grained WC powder with an average particle size of 6 μm, submicrocrystalline WC powder with an average particle size of 150 nm and two nanocrystalline WC powders with average sizes of particles 60 and 20 nm produced by a plasma-chemical synthesis and high-energy ball milling, respectively, have been used for synthesis of hardmetals. It is established that ternary Co 6W 6C carbide phase is the first to form as a result of sintering of the starting powder mixture. At sintering temperature of 1100–1300 °C, this phase reacts with carbon to form Co 3W 3C phase. A cubic solid solution of tungsten carbide in cobalt, β-Co(WC), is formed along with ternary carbide phases at sintering temperature above 1000 °C. Dependences of density and microhardness of sintering hardmetals on sintering temperature are found. The use of nanocrystalline WC powders is shown to reduce the optimal sintering temperature of the WC–Co hardmetals by about 100 °C.