Microstructure and formation process of gradient structure of self-diffusion composite tool materials

A self-diffusion gradient composite tool material, which was composed of Ti(C7,N3)-based cermet as the substrate and TiB2 composite as the surface layer, was fabricated by a layer-by-layer method and a vacuum hot-pressing sintering technology at 1,500°C for 30 min under 32 MPa. A new diffusion layer was formed automatically by the self-diffusion of elements. The microstructure and elements distribution of the polished cross-section and fracture surface were investigated. The results showed that the distribution of C, N, Co and Ni elements exhibited a nonlinear change in the gradient structure zone and the fracture mode of each layer was different. A process modal with three stages was set up to describe the formation process of gradient structure. The composite was composed of the surface layer, diffusion layer and substrate. The thickness of surface layer and diffusion layer was approximately 150 µm and 50 µm, respectively.