Designing novel AlCoCrNi eutectic high entropy alloys

Based on pseudo-ternary phase diagram and microscopic observation, Al20.45Co10Cr10Ni59.55, Al17.5Co20Cr20Ni52.5 and Al16.3Co25Cr25Ni33.7 eutectic high entropy alloy (EHEAs) were designed. The experimental results showed that the designed EHEAs all have uniform alternating BCC/FCC lamellar microstructure. Among them, the as-cast Al17.5Co20Cr20Ni52.5 alloy exhibits better tensile property at room temperature. The ultimate tensile strength and total elongation are 1272 MPa and 14.4%, respectively. We verified that the formation of AlCoCrNi EHEAs is related to the ratio of (Co, Ni) to Al, and proposed a new method to design AlCoCrNi EHEAs by fixing the ratio of (Co, Ni) to Al in the alloy. According to the thermo-physical parameters and the ratio of (Co, Ni) to Al of the AlCoCrFeNi EHEAs (FCC/BCC) reported so far, the formation rules of this type of EHEAs were summarized. This can provide useful guidance for future design of the AlCoCrFeNi EHEAs.