Study on the sintered characteristics and properties of nanostructured WC–15 wt% (Fe–Ni–Co) and WC–15 wt% Co hard metal alloys

In this work, four different vacuum sintering temperatures (1250 °C, 1300 °C, 1350 °C and 1400 °C) were studied to determine the optimal process parameters of nano WC–15 wt% (Fe–Ni–Co) and WC–15 wt% Co sintered hard metal alloys. Experimental results showed that the optimal sintering temperatures for nano WC–(Fe–Ni–Co) and WC–Co alloys were 1300 °C and 1350 °C for 1 h, respectively. The sintered nano WC–(Fe–Ni–Co) and WC–Co hard metal alloys showed a good contiguity of 0.44 and 0.42; hardness was enhanced to HRA 90.83 and 90.92; the transverse rupture strength (TRS) increased to 2567.97 and 2860.08 MPa; and K_IC was 16.23 and 12.33 MPa√m, respectively. Although the nano WC–(Fe–Ni–Co) alloys possessed a slightly lower TRS value, they exhibited superior fracture toughness (K_IC) and hardness similar to that of the nano WC–Co material. Significantly, nano WC–(Fe–Ni–Co) alloys could be sintered at a lower temperature and still retained their excellent mechanical properties. - Graphical abstract: The following figure shows the fracture morphology of the WC–(Fe–Ni–Co) and WC–Co specimens by means of high-magnification SEM after the K_IC tests. Fig. a shows that numerous binder phases (Fe–Ni–Co) existed in the crack areas, which resisted the penetration and extension of the cracks. Due to the bridging effect of the binder phase, the stress concentration of the crack tip will be resolved through plastic deformation; thus, the cracks did not continue to extend. Once the deformation reaches a critical value, the crack propagation occurs. Meanwhile, the binder phase can link together the two crack faces through the bridging process. Although parts of the cracked areas also showed the bridging effect in the WC–Co specimens, as shown by the arrows (Fig. b), the crack propagation path was not obviously affected. This result corresponds to the tortuosity phenomenon. Consequently, the bridging process suppressed the crack propagation and resulted in the increase in tortuosity. SEM observations of the bridging role of the (a) 1300 °C sintered WC–(Fe–Ni–Co), and (b) 1350 °C sintered WC–Co hard metal alloys after K_IC tests. - Highlights: • The sintered nano WC–Co alloy sintered at 1350 °C had the highest hardness (HRA 90.92). • The sintered nano WC–(Fe–Ni–Co) alloys showed a good contiguity of 0.44. • The optimal nano WC–Co sintered alloy possessed the highest TRS value (2860.08 MPa). • WC–(Fe–Ni–Co) sintered alloy possessed the highest fracture toughness of KIC (16.23 MPam1/2). • The adding of an iron–nickel instead of a cobalt binder for tungsten carbides is preferable