Effects of WC particle size on sintering behavior and mechanical properties of coarse grained WC–8Co cemented carbides fabricated by unmilled composite powders

Three sets of coarse grained WC–8Co cemented carbides were fabricated by unmilled composite powders using three different-sized raw WC powders. Effects of WC particle sizes on shrinkage behavior and microstructure evolution of coarse grained WC–8Co cemented carbides during a sintering process were investigated by dilatometer and a scanning electron microscope. Furthermore, the mechanical properties and their wear properties were evaluated for the forthcoming potential applications. It was found that during the sintering process the densification and grain growth of the WC–8Co cemented carbides with finer carbide particles as raw materials started earlier than coarser powders regardless of the effects of lattice distortion. With increasing initial WC particle size from 2.01 μm to 4.37 μm, mean WC grain size of coarse grained WC–8Co cemented carbides rose from 3.19 μm to 6.03 μm, the Co mean free path rose from 0.67 μm to 1.24 μm. At the same time, with the increasing grain size, the transgranular fracture though the carbide phase and binder phase increased, while intergranular fracture decreased, correlating to that the transverse rupture strength and fracture toughness increased from 2264 MPa, 19.13 MPa m1/2 to 2769 MPa and 25.24 MPa m1/2, respectively. The dominant wear mechanism in sliding wear test for the WC–8Co cemented carbides transferred from extraction of small WC grains to cracking and fragmentation of the large carbide grains with the increasing grain size.