Investigation of characteristics and properties of spark plasma sintered ultrafine WC-6.4Fe3.6Ni alloy as potential alternative WC-Co hard metals

Abstract

The present study proposed the fabrication of a WC-6.4Fe-3.6Ni hard metal alloy using spark plasma sintering (SPS) as a potential alternative to the WC-Co hard metal. Fe-36%Ni powder (mean particle size 26.9 μm) was produced from Fe and Ni commercial powders via high energy milling and the effect was analyzed. WC-6.4Fe-3.6Ni (alternative grade) and WC-Co (reference grade) were obtained from ultrafine WC powder (particle size 0.45) with 10%wt binder. SPS sintering of WC-6.4Fe3.6Ni was performed at 1100, 1200 and 1300 °C with a holding time of 5 min achieving 99.8% higher densification at 1300 °C and WC-Co was sintered at 1200 °C. The results show that increasing the sintering temperature enhanced the microstructure and hardness with a decrease in fracture toughness. The wettability of milled Fe-Ni binder during heating in the SPS process contributes to enhance densification and properties. The decrease in fracture toughness is attributed to a decrease in the binder mean free path. The XRD analysis showed that η phase was not detected for either composite grades. Studies of sintering kinetics were applied to determine the sintering mechanisms involved in the final stage of sintering, which can be elucidated by calculating the slope exponent (n) from the relationship between the shrinkage rate and sintering time. Slope exponent consistent with WC diffusion in the liquid phase was found for WC-6.4Fe-3.6Ni sintered at 1300 °C. Good properties was found for WC-6.4Fe-3.6Ni sintered at 1300 °C, showing higher hardness ~1633 HV30 and fracture toughness ~11 MPa m0.5. WC-6.4Fe-3.6Ni sintered at 1200 °C has superior hardness (1786 HV30) than WC-Co (1689 HV30). A comparison of these properties with results from similar grades in the literature shows that the WC-6.4Fe-3.6Ni alternative grade has optimal properties and can be adopted as an alternative to WC-Co grades.