Effects of Different Preparation Processes on Microstructure and Properties of Cocrfeni High-Entropy Alloy

Abstract

High-entropy alloys (HEAs) have disordered solid solution structures which are stabilized by maximizing configurational entropy stability. The fabrication methods of HEAs are basically as same as that of the conventional alloys. In this work, the effects of three preparation processes of melting-casting (MC), thermo-mechanical treatment (TMT) and selective laser melting (SLM) on microstructure, mechanical, friction and corrosion properties of CoCrFeNi HEA were systematically investigated. As compared to as-MCed samples with coarse grains, the optimal combination of yield strength and ductility (yield strength ~330.05MPa, tensile strength ~661.46MPa, elongation ~55.81%) are revealed in as-MCed samples with fine grains; while as-SLMed samples exhibit the superior yield strength (494.62MPa) with the elongation more than 10%, as a result of the cellular and columnar subgrains. The friction results reveal that the wear rate of as-TMTed samples (~1.06×10 -5 mm 2 /N) is lower than that of as-MCed (~2.65×10 -5 mm 2 /N) and as-SLMed samples (~16.19×10 -5 mm 2 /N). The high-density grain boundaries of as-TMTed samples contribute to the formation of the oxide film; while the pores and cracks of as-SLMed samples as the dominant factors seriously deteriorate wear resistance. The electrochemical corrosion results indicate that the corrosion current density of as-MCed samples, as-TMTed and as-SLMed samples are 0.89μA/cm 2 , 0.53μA/cm 2 and 1.78μA/cm 2 , respectively, indicating that as-TMTed and as-SLMed samples possess the best and worst ability of corrosion, respectively. The passive film is formed in as-TMTed samples, leading to a stable and exceptional protective property by the incremental grain boundaries; while the occurrence of the local corrosion of as-SLMed samples is induced by the more exposed area of the intragranular pores and cracks in the corrosive solution.

Keywords: High-entropy alloys, Melting-casting, Thermo-mechanical treatment, Selective laser melting