Role of V(C, N) on gradient structure formation and mechanical properties of nanocrystalline cemented carbides

We investigated the relationship between the V(C, N) content in nanocrystalline cemented carbides and the thickness of the gradient layer, while also exploring the effects of V(C, N) content on the mechanical properties. Nanocrystalline cemented carbides featuring a cubic-phase gradient layer on their surfaces were prepared through a one-step sintering process, utilizing V(C, N) as the gradient-forming agent. The results showed that as the V(C, N) content increased, the thickness of the V(C, N) gradient layer decreased. Following the principles of the first diffusion law, we derived the kinetic equation for nanocrystalline cemented carbides with a V(C, N) gradient layer, establishing a clear connection between the gradient layer's thickness and the V(C, N) content. The thickness of the V(C, N) gradient layer exhibited a direct proportionality to the difference in V activity between the surface and the core, while displaying an inverse proportionality to the average V content of the specimen. Furthermore, the introduction of V(C, N) was found to enhance the mechanical properties of nano-crystalline cemented carbides, leading to simultaneous improvements in both hardness and fracture toughness. This enhancement underscores the significance of V(C, N) in optimizing the performance of these materials.