Synergistic Enhancement of Hardness and Toughness in WC-Co Cemented Carbides Reinforced with (TiZrHfNbTa) (C, N) High-Entropy Carbonitride

The simultaneous enhancement of hardness and toughness in WC-Co cemented carbides remains a critical and persistent challenge for advanced cutting-tool applications, where conventional materials often suffer from inherent property trade-offs. In this study, a novel composite ceramic material-WC-(TiZrHfNbTa) (C, N) high-entropy carbonitride (HECN)-Co composite-was successfully fabricated via dry ball milling and spark plasma sintering (SPS) at 1300 °C following 90 h of ball milling. By incorporating varying amounts of HECN (0-15%, mass fraction, same below), the microstructure and mechanical properties of the composites were systematically tailored. The results demonstrate that the addition of HECN effectively refines the WC grains and increases the material density, leading to a pronounced improvement in hardness. Notably, the composite with 10% HECN (WC-10%HECN-9Co) exhibits an optimal balance of hardness and fracture toughness, achieving a Vickers hardness of 2375 ± 25 HV30 and a fracture toughness of 12.9 ± 1.1 MPa·m^1/2. In contrast, excessive HECN addition (15 wt.%) induces excessive grain refinement, which significantly impairs toughness. Our study demonstrates that the introduction of (TiZrHfNbTa) (C, N) HECN as a reinforcing phase offers a viable and effective strategy for designing cemented carbides with an exceptional hardness-toughness synergy, showing great promise for demanding cutting applications such as high-speed machining and the processing of hard-to-cut materials.