Influences of the preparation methods of WC–Co powders on the sintering and microstructure of coarse grained WC–8Co hardmetals

Abstract

WC–8Co slurry powder, ball milling powder and composite powder were prepared and WC–8Co hardmetals were produced via vacuum sintering at 1450°C. The morphologies, the lattice distortion and the thermal expansion test of WC–8Co powders were investigated using scanning electron microscope, X-ray diffraction and dilatometer, respectively. The results show that the lattice distortion can decrease the liquid phase formation temperature and influence the shrinkage of WC–8Co. The strains of ball milling powder, slurry powder, composite powder (4.09μm) and composite powder (2.08μm) are 0.185%, 0.029%, 0.028% and 0.05%, whose corresponding liquid phase formation temperatures are 1356°C, 1331°C, 1350°C, and 1345°C respectively. The solid phase shrinkage proportions of slurry powder, composite powder (4.09μm) and composite powder (2.08μm) are 45.50%, 45.73% and 53.00%, respectively. However, the solid phase shrinkage proportion of WC–8Co ball milling powder is up to 75.23% due to the highest strain. Furthermore, the comparison of microstructures between WC–8Co alloy (from ball milling powder) and WC–8Co alloy (from 4.09μm composite powder) confirms that decreasing the degree of lattice distortion can increase the liquid phase formation temperature and inhibit the growth of WC grain.