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A new eutectic high-entropy alloy (EHEA) of Cr 41 CoFeNi was prepared by arc melting technique. The microstructure and corrosion resistance of the Cr 41 CoFeNi EHEA were systematically investigated by EBSD, TEM, EIS and XPS analyses. The results revealed that the Cr 41 CoFeNi EHEA showed a dual-phase structure consisting of BCC phase and FCC phase, and the morphologies displayed the lamellar eutectic and network-shaped eutectic. Compared with 316 L stainless steel, the Cr 41 CoFeNi EHEA exhibited a better anti-corrosion property in 0.5 M H 2 SO 4 solution. This was mainly attributed to the formation of a dense and stable Cr-oxide layer on the surface of Cr 41 CoFeNi EHEA, which retarded further dissolution of the matrix. Moreover, bound water could adsorb metal ions to form a new protective film, which played an important role in improving the corrosion resistance of the Cr 41 CoFeNi EHEA. However, the elemental segregation and chemical potential difference between phases increased the defects in the passive film and accelerated its pitting corrosion of low potential phase. Moreover, the (Co, Fe, and Ni)-enriched FCC structured phase was preferentially eroded. • A novel eutectic high-entropy alloy of Cr 41 CoFeNi(EHEA) was designed and fabricated • The corrosion mechanisms of EHEA and 316 L stainless steel(316 L SS) were clarified • The passive film thickness of EHEA was about 5.3 times greater than that of 316 L SS • The main constituents of passive film on EHEA were Cr-oxide and bound water [ABSTRACT FROM AUTHOR]

The CoNiCr x (x = 1, 1.4, 1.8, and 2) medium-entropy alloys were synthesized by vacuum arc-melting method to systematically investigate the roles of Cr on microstructures and mechanical properties. The results of microstructural characteristics indicated that both CoNiCr and CoNiCr 1.4 alloys have a single face-centered cubic (FCC) structure, while CoNiCr 1.8 and CoNiCr 2 alloys consist of FCC plus body-centered cubic (BCC) hypoeutectic and eutectic. The formation of FCC and BCC phases could be probably evaluated using the VEC criteria. The tested mechanical properties demonstrated that CoNiCr 1.8 alloy exhibited the best comprehensive properties at room and liquid nitrogen temperatures (RT and LNT), whereas the yield strength and hardness of CoNiCr 2 alloy were higher than those of other alloys, which may be mainly attributed to the second-phase strengthening and the fine and lamellar microstructure. The yield strength of CoNiCr 2 alloy at RT and LNT was 3.8 and 1.9 times (514 MPa and 825 MPa) that of CoNiCr alloy. In addition, the precipitation of dense and ordered FCC (L1 2) phase could primarily contribute to the enhance of yield strength of CoNiCr 1.4 alloy. • Cr addition facilitates the formation of L1 2 nano-particles and BCC/B2 phase. • The CoNiCr 1.8 hypoeutectic medium-entropy demonstrates an excellent strength and ductility synergy at liquid nitrogen temperature. • A CoNiCr 2 lamellar eutectic medium-entropy with FCC/L1 2 and BCC/B2 is designed. • L-C lockers dominate the deformation of lamellar eutectic MEAs under cryogenic condition. [ABSTRACT FROM AUTHOR]