Semi-solid processing of the CoCrCuFeNi high entropy alloy

Abstract

High entropy alloys (HEAs) are a particularly challenging material for semi-solid processing because of the high temperatures involved. In the CoCrCuFeNi HEA examined here, the globular microstructure required for the thixoforming process was obtained by the recrystallization and partial remelting method. Based on Kazakov's criteria, a detailed characterization of the solidus-liquidus temperature range, was conducted. Semi-solid metal processing of the CoCrCuFeNi HEA was carried out at 1150°C and 1340°C, which corresponded to 15% and 35% of the liquid phase, respectively. The microstructure of the thixo-cast consisted of two face-centered cubic solid solutions: one in the form of globular grains, containing near equiatomic concentrations of Co, Cr, Fe and Ni, and the other, enriched in Cu, homogeneously distributed around grains. Depending on the process temperature, significant changes were observed in the microstructure. Compression test results of the CoCrCuFeNi HEA thixo-cast showed that yield strength was around 395MPa, while the compression strength at 40% of strain reached 1810MPa at an average hardness of 201HV. The obtained values were about 30% higher than those of the ingot material after direct casting. The melting behavior, microstructure and mechanical properties, as well as the possibility of obtaining a net-shape component in a one-step operation, make the CoCrCuFeNi HEA a promising material for thixoforming.