Implementing the superior hardness property of WC-Ni cemented carbide using ultrafine tungsten carbide and quaternary alloy (Ni-Co-Cu-W) system

This study presents the development of high-hardness cemented carbides for high-speed and difficult-to-machine applications through the use of a quaternary alloy binder and controlled microstructural evolution. A nanoscale quaternary alloy powder (Ni,Co,Cu,W) was synthesized via hydrogen reduction followed by mechanical milling, ensuring uniform elemental distribution in spark plasma–sintered bodies despite the short sintering duration. The incorporation of W into the binder induced carbon deficiency and promoted eta-phase formation; however, the eta phase was effectively eliminated by the addition of excess carbon, which facilitated its conversion to WC. Increasing carbon content enhanced the relative fractions of WC and metallic phases, with complete suppression of the eta phase beyond 6 % excess carbon. Optimized carbon addition yielded a hardness range of 16.1–19.6 GPa, exceeding that of conventional cemented carbides with comparable metallic phase ratios (maximum 16.6 GPa). Fracture toughness was also improved (maximum 8.6 MPa·m¹/²) due to metallic phase stabilization and solution strengthening. These results demonstrate that quaternary alloy–bonded cemented carbides, when combined with tailored carbon control, exhibit superior mechanical performance and offer strong potential as advanced tool materials in materials processing and high-speed machining.