Excellent combination of compressive strength and ductility of (CoCrFeNi)_x(Co_0.26Cr_0.07Fe_{0 .16}Ni_0.31Hf_0.4) high-entropy alloys

Instead of conventional CoCrFeNiHfx high-entropy alloys (HEAs), we investigated the evolution of microstructure and compressive mechanical properties of (CoCrFeNi)(x)(Co0.26Cr0.07Fe0.16Ni0.31Hf0.4) HEAs with varying x. Increasing x from 0.5 to 1.0, the microstructure changes from hyper-eutectic ones consisting of primary Laves phase and eutectic structure (x < 0.7), firstly to eutectic ones consisting of alternative FCC and Laves phase (x = 0.7 and 0.8), and finally to hypo-eutectic ones consisting of primary FCC phase and eutectic structure (x > 0.8). Interestingly, two different morphologies of eutectic microstructures are observed when x = 0.7 and 0.8 probably due to different fusion entropies of each phase. Increasing x from 0.5 to 1.0 reduces the yield strength from 1661 +/- 64 to 688 +/- 17 MPa but enhances the compressive ductility due to an increased fraction of soft FCC phase from similar to 0.39 to similar to 0.74. The second phase strengthening is the main strengthening mechanism. Importantly, when x = 0.9 and 1.0, these two alloys are not fractured when the strain reaches 0.5, one of which shows a large yield strength of 1028 +/- 45 MPa (x = 0.9). Compared with conventional CoCrFeNiHfx, the studied HEAs exhibit a much better combination of compressive strength and ductility. (c) 2021 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).