Effects and correlation analysis of the sintering process on the properties of ultrafine-grained WC-Co reinforced by high-entropy alloys

Abstract

The effects and correlations of the spark plasma sintering process on the grain size, densification, and mechanical properties of ultrafine WC cemented carbides were investigated. The fine grain strengthening effect of the CrFeCoNi high-entropy alloy (HEAs) resulted in no significant change in the WC grain size, and the density, hardness, and fracture toughness of the material increased with increasing sintering temperature from 1100 to 1300 ℃. However, sintering temperatures exceeding 1300 ℃ led to binder volatilization and the cavity defects growth caused by abnormal growth of WC grains, thereby reducing the properties of the material. Extending the holding time improved material densification, but above 20 min could lead to abnormally growth of small-sized WC grains due to excessive dissolution-reprecipitation, resulting in reduced fracture toughness. Increasing sintering pressure improved grain bonding, increased interfacial volume, and reduced grain boundary porosity. However, excessively exceeding 40 MPa hinders effective discharge of gas produced by volatile binders, thus diminishing the material properties. The contradiction between alloy hardness and fracture toughness can be adjusted by utilizing HEAs and Co as binders. Optimum properties were achieved for WC-Co cemented carbides sintered at 1300 ℃ for 20 min under a pressure of 40 MPa, of with the relative density, hardness, and fracture toughness were 99.7 %, 2090.3 ± 42.2 MPa, and 12.1 ± 0.3 MPa·m^1/2, respectively.