Effect of the carbon content on the morphology evolution of the η phase in cemented carbides with the CoNiFeCr high entropy alloy binder

Abstract

For studying the evolution of the η phase in cemented carbides with the CoNiFeCr high entropy alloy binder, we prepared low-carbon, medium-carbon, and high-carbon cemented carbides with a 0.2 wt% difference in the C content using SHIP. The results showed that the η phase morphology was sensitive to the carbon content. When the carbon content was 4.5%, the η phase was abundant and uniformly dispersed. When the carbon content increased to 4.7%, the η phase amount decreased and became locally aggregated in large clusters, showing typical segregation. When the carbon content was further increased to 4.9%, the η phase disappeared. The η phase clusters exhibited a sharp contrast between inner and outer parts. The inner part showed the presence of the η phase, WC with small and round grains, and a small amount of binder. The outer part had only WC with large grain and sharp grains, and a large amount of binder. In addition to the inherent η phase brittleness, the η phase segregation resulted in a large hardness dispersion and a further toughness decrease.