Microstructure and mechanical properties of self-diffusion gradient cermet composite tool materials with different characteristics of surface layer

Abstract Self-diffusion gradient cermet composite tool materials with different characteristics of surface layer were prepared by a vacuum hot-pressing sintering technology at 1475 °C for 30 min under 32 MPa. A subsurface layer was formed automatically by a self-diffusion driving force during sintering. The evolutions of microstructure and elements distribution were investigated, and the effects of vanadium carbide (VC) content and surface layer thickness on microstructure and mechanical properties were discussed. The results showed that the Co, Ni and N elements were redistributed and formed a subsurface layer gradient zone. N element diffused toward the surface layer, while Co and Ni metal binder were abundant in the subsurface layer. The density and mechanical properties were improved by the addition of VC in the surface layer. The flexural strength, substrate hardness and surface hardness of the self-diffusion gradient composite with a surface layer thickness of 230 µm were 1198±135 MPa, 23.68±0.68 GPa and 28.22±0.87 GPa, respectively, when 4 mass% VC was used.