Effects of Nickel and Iron Content on the Microstructures and Mechanical Properties of Cemented Carbide with Coarse and Fine-Grained Heterostructures

Cemented carbides are composite materials that combine both structural and functional properties. However, the inherent trade-off between strength and toughness presents a significant challenge in fully leveraging the synergistic potential of these dual-phase materials. In this study, cemented carbides with coarse and fine-grained heterogeneous structure were fabricated. The effects of nickel (Ni) and iron (Fe) content on the microstructures and mechanical properties of these heterogeneously structured cemented carbides were systematically investigated. Microstructural analysis revealed that the fine-grained granules are uniformly embedded in the coarse-grained region, forming a typical network-like mixed-grain structure. The introduction of the heterogeneous structure enables cemented carbides to achieve a remarkable balance of high strength and toughness. Specifically, the materials exhibit optimal strength-toughness matching with a transverse rupture strength of 2949 MPa, a fracture toughness of 23.65 MPa·m^-1/2, and a hardness of 1430 HV when the proportion of Ni and Fe content reaches 4.2 wt.%. The toughening mechanism is primarily attributed to the increased volume fraction and stabilized dimensions of CoNiFe binder phases, which promote interfacial decohesion at WC/WC and WC/binder boundaries while suppressing transgranular fracture. These mechanisms collectively contribute to enhanced toughening and crack propagation resistance. This study establishes foundational insights into achieving a synergistic combination of strength and toughness in cemented carbides.