Microstructure and mechanical properties of ultrafine-grained WC-CoNiFe-Cr3C2-VC cemented carbides with a multi-principal-element alloy binder

Ultrafine-grained WC-Co cemented carbides with low binder content are promising for precision machining but are constrained by a narrow sintering window and a hardness–strength trade-off. Here, we combine a CoNiFe multi-principal-element alloy (MPEA) binder with a composite Cr3C2-VC grain growth inhibitor (GGI) to produce an ultrafine-grained WC-6MPEA-Cr3C2-VC cemented carbide with enhanced stability and mechanical performance. The combination of a Cr3C2-VC composite GGI and an MPEA binder significantly improves grain refinement, reducing the average WC grain size to 0.28 μm (down from 0.32-0.37 μm observed with a single GGI or a conventional Co binder). Additionally, the MPEA binder effectively suppresses the FCC-to-HCP transformation, lowering the HCP-structured binder content from 0.5% to 0.1%. The refined WC grains and stable two-phase microstructure promote crack deflection and localized transgranular fracture. As a result, the WC-6MPEA-Cr3C2-VC sample achieves a superior comprehensive mechanical performance, including a Rockwell hardness of 93.7 HRA, a Vickers hardness of 1974 HV30, and a transverse rupture strength of 3016 MPa. These findings demonstrate that combining MPEA binder design with Cr3C2-VC composite inhibition provides an effective route for improving the overall mechanical performance of low-binder ultrafine-grained WC-based cemented carbides.