Evaluation of Bonding Strength between WC Grains in WC-Co and WC-VC-Co Cemented Carbides

Cemented carbides of fine-grained WC-Co combined with VC has high hardness and strength for cutting tool. VC is known as a grain growth inhibitor; however, its effect on the microscopic mechanical properties, especially the WC-WC bonding strength, remains unclear. In this study, we investigated the WC-WC interfacial structure and the strength of WC-Co, WC-Ni and WC-VC-Co. Microcantilevers, including the WC-WC interface, were fabricated using mechanical polishing and focused ion beam (FIB) methods. Bending tests were performed using the nanoindentation technique to determine the WC-WC interfacial bonding strength. The results showed that the WC-VC-Co have lower strength than WC-Co. Transmission electron microscopy (TEM) observations indicated the segregation of V on the WC surface. The V-based thin layer reduces the strength between the WC grains, resulting in poor mechanical properties that induce WC-particle dropout. Hence, appropriately controlling the amount and size of VC is crucial for achieving good mechanical properties.