Microstructure Evolution and Hardness Improvement of WC-Co Composites Sintered with Fe Substituting Part of Co Binder

WC-13Co (wt.%) composite with Fe added was prepared by pressureless sintering, and its microstructure and mechanical properties were analyzed by X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) and Vickers hardness tester. The effect of Fe and C content on the microstructure of the eta phase, binder phase, grain size and porosity, as well as mechanical properties in the W-Co-Fe-C system, was discussed quantitatively. The position of added Fe in the lattice of the composites is clarified. When 2%-4% Fe was added, Fe existes in both the binder phase and the low-carbon eta phase. In the lattice of the eta phase, Fe occupies the position of Co and Fe uniformly existes in the binder with the structure of simple cubic when the composites is in the eutectic phase region. Differently from the previous report that the growth of WC in liquid Fe was severely limited, the size of WC in the W-Co-Fe-C system increases from 1.14 mu m to 1.21 mu m when the content of Fe increases from 0 to 4%, which indicates that the growth behavior of WC in liquid CoFe was different from that in liquid Fe, but closer to that in liquid Co. The sample added both 2% Fe and 1% C has the optimum matching of hardness and toughness. Compared with the hardness of 979 HV30 in the sample without adding Fe and C, the hardness of the sample with both 2% Fe and 1% C added achieved 1071 HV30, which is increased by 9.4% under the conditions of a slight increase in fracture toughness.