Role of Co content on the gradient microstructure evolution and mechanical properties of bilayer functionally graded cemented carbides

The bilayer functionally graded WC-TiC-Co cemented carbides with different Co contents (6–14 wt%) have been successfully prepared by high pressure nitriding sintering in this study. The gradient microstructure from surface to interior was investigated to understand the microstructure evolution mechanism. The bilayer functionally graded cemented carbides are mainly characterized by outer layer and intermediate layer. The increase of Co content can promote more significant diffusion of Ti, C to form bilayer gradient microstructure and more noticeable Ti(C,N) and WC grain growth in outer layer and intermediate layer. The microhardness decreases from outer layer to intermediate layer and then increases again in the inner portion, while the fracture toughness profile shows the opposite trend. •The bilayer functionally graded carbides were successfully produced.•The increase of Co content leads to thicker outer layer.•Intermediate layer is softer but tougher than outer layer and inner portion.•The bilayer microstructure shows combination of high hardness and toughness.