Another eutectic point of Co–Cr–Fe–Ni-M (Hf, Ta, Nb) high-entropy system determined using a simple mixture method correlated with mixing enthalpy

In order to improve mechanical properties and particularly poor ductility of eutectic high-entropy alloys (EHEAs) consisting of ductile face-centered cubic (FCC) and brittle Laves phases, this study proposed a strategy to vary the eutectic compositions and, in turn, microstructures and mechanical properties. Apart from the only one eutectic point already reported for Co–Cr–Fe–Ni-M systems, another eutectic point was successfully determined in the present study, when considering mixing enthalpies between Co, Cr, Fe, Ni and M (M = Hf, Ta, Nb) together with the simple mixture method. The microstructures, characterized using X-ray diffraction and scanning and transmission electron microscopes correlated with energy dispersive spectroscopy, consisted of alternatively eutectic FCC and Laves phases. Only one melting endothermic peak was observed by differential scanning calorimetry, which additionally supported the formation of fully eutectic microstructures. Compared to the reported eutectic CoCrFeNiHf_0.4, the developed eutectic (CoCrFeNi)_0·6(Co_0·26Cr_0·06Fe_0·15Ni_0.31Hf_0.4) had different area fractions and widths of FCC and Laves phases, leading to different compressive mechanical behaviors. This study proves that the proposed method is an easy and feasible way to adjust the eutectic compositions of EHEAs consisting of FCC and Laves phases, promoting the further development of this group EHEAs.