STRUCTURE AND MECHANICAL PROPERTIES OF WC-BASED HARDMETAL WITH A HIGH-ENTROPY NiFeCrWMo BINDER

Abstract

An equiatomic NiFeCrWMo high-entropy alloy (HEA) produced by mechanical alloying was used as a binder alternative to cobalt for the manufacture of WC-based hardmetals. The WC–10 HEA (wt.%) powder mixture was homogenied in a planetary-ball mill for 2 h and consolidated out by electron beam sintering (EBS) for 4 min at a temperature of 1450 °C and spark plasma sintering (SPS) for 10 min at a temperature of 1400 °C. The relative density of the sintered samples reached 99.4 %. The phase composition, microstructure, and mechanical properties of WC–10 HEA hardmetals were studied by X-ray diffraction, scanning electron microscopy, and microindentation. The effect of the NiFeCrWMo HEA binder on the microstructure and mechanical properties of WC–10 HEA hardmetals in comparison with the conventional VK8 hardmetal (WC–8 Co) was determined. The WC–10 HEA hardmetal after EBS consisted of WC grains, a NiFeCrWMo HEA binder with a bcc structure, and a small amount (3.5%) of complex carbide (Ni, Fe, Cr)_xW_yC_z, whereas after SPS the amount of the latter increased to 47% due to longer sintering time and pressure application. No noticeable growth of WC grains during the sintering of WC–10 HEA hardmetal was observed because of the multielement composition of the NiFeCrWMo HEA binder and the formation of complex carbide (Ni, Fe, Cr)_xW_yC_z layers, preventing the growth of WC grains. The hardness HV  and fracture toughness K_Iс of WC–10 HEA hardmetals after EBS were 18.9 GPa and 11.4 MPa ⋅ m^1/2 and after SPS were 19.9 GPa and 10.8 MPa ⋅ m^1/2. The hardmetals with a HEA binder exhibit an excellent combination of hardness and fracture toughness. These  values are higher than those of the conventional VK8 hardmetal (WC–8 Co) produced by EBS for 4 min at 1350 °C, whose hardness is 16.5 GPa and fracture toughness K_Iс =  9.5 MPa × m^1/2.