Excellent combination of compressive strength and ductility of (CoCrFeNi)x(Co0.26Cr0.07Fe0.16Ni0.31Hf0.4) 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 0.8). 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 ~0.39 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. [Display omitted] •(CoCrFeNi)x(Co0.26Cr0.07Fe0.16Ni0.31Hf0.4) microstructure changes from hyper-eutectic to hypo-eutectic with x increase.•Eutectic point is simultaneously obtained when x = 0.7 and x = 0.8 of (CoCrFeNi)x(Co0.26Cr0.07Fe0.16Ni0.31Hf0.4).•The eutectic microstructure changes from irregular lamella to regular lamella when increasing x value.•(CoCrFeNi)x(Co0.26Cr0.07Fe0.16Ni0.31Hf0.4) have a better combination of compressive strength and ductility than CoCrFeNiHfx.