Effects of heating rate and metal binder on the microstructure and mechanical properties of self-diffusion gradient cermet composite tool materials

Abstract

Self-diffusion gradient cermet composite tool materials with different metal binder contents and Ni/(Co + Ni) mass ratios were fabricated to improve the mechanical properties. The effects of heating rate and metal binder on the microstructure and mechanical properties of self-diffusion gradient composite were investigated. For the heating rates considered, it was revealed that the heating rate of 30 °C/min was in the vicinity of optimum to yield the desired mechanical properties and fine microstructure. It was found that the flexural strength increased and the hardness decreased with increasing Ni binder content, while the addition of Co binder led to an excessively thick rim phase which was detrimental to the flexural strength. Applying a proper amount of Ni binder appeared to be beneficial for fabricating gradient composites with desired self-diffusion process during sintering. For the experimental conditions considered in this study, the best mechanical properties can be obtained when 6 mass% Ni in the surface and 12 mass% Ni in the substrate were used, which gave flexural strength, substrate hardness and surface hardness at 1488 ± 190 MPa, 20.96 ± 0.30 GPa and 25.12 ± 0.48 GPa, respectively.

Keywords: Gradient composite - Heating rate - Mechanical properties - Metal binder - Microstructure