Microstructure and mechanical properties of as-cast CoCrFeMnNi high entropy alloy

Abstract

In this study, we made large-scale ingots of CoCrFeMnNi high entropy alloy by vacuum induction melting. The as-cast CoCrFeMnNi high entropy alloy contained a high proportion of columnar structures with a few equiaxed grains, and showed single phase fee solid solutions without macro segregation and low interstitial levels. The tensile properties along the three different loading directions were investigated at low-temperature and room temperature. A decrease in temperature led to an increase in yield and tensile strengths. The increase in anisotropy due to the columnar structure was negligible. Unlike wrought CoCrFeMnNi high entropy alloys, twins were actively formed in the specimen deformed at room temperature. Mechanical twinning was found to be a result of the coarse grain size, over 500 um, of the as-cast CoCrFeMnNi high entropy alloy, which effectively reduced the critical stress for twinning. Charpy impact tests were also conducted, and the absorbed energy of the CoCrFeMnNi high entropy alloy showed no dependence on the temperature or loading directions. The results of this study provide an understanding of pilot-scale high entropy alloy castings, and are expected to be utilized as basic properties for manufacturing large-scale high entropy alloy castings, which are effective in severe environments.