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The microstructure, phase behavior, mechanical properties, and corrosion properties of a series of Al10Cr15(Fe3Mn)75−x(Ni)x medium-entropy alloys (MEAs) spanning 0–20 at% Ni were studied to elucidate the chemistry-structure-property relationship of this system as a function of Ni content. This work demonstrates that from an initial BCC phase Al10Cr15(Fe3Mn)75 MEA, Ni additions of 5 and 10 at% result in the formation of ordered B2-phase precipitates due to interaction of Ni with Al, resulting in high hardness (∼475 HV). Further Ni addition to 15 at% leads to a dual-phase FCC+BCC structure, with B2 phase precipitates distributed in the BCC matrix relatively rich in Al and Ni but depleted in Cr. This dual-phase structure has a high yield strength (YS) of 600 MPa with a total elongation of 15%. Additionally, the B2 precipitates in BCC phase serve as preferential sites for corrosion in 0.6 M NaCl. Increasing Ni content to 20 at% results in lower YS of 300 MPa, but a significant improvement in ductility and corrosion resistance due to the increased FCC phase fraction. 

Electrochemical behavior of Ni alloys (Ni, β-NiAl, β-NiAl/Cr) was investigated in LiCl-KCl-Na2SO4 electrolyte at 700 °C under three gaseous atmospheres (Ar, O2, O2-0.1%SO2). In oxidizing atmospheres, Ni rapidly degraded due to instability of NiO, and alumina-rich scale on β-NiAl provided limited protection against hot corrosion (e.g., cracks in the scale under O2-0.1%SO2); however, the addition of both Al and Cr resulted in enhanced corrosion resistance by forming a mixed-oxide (Al2O3-Cr2O3) scale in oxidizing atmospheres. In hot corrosion processes of Ni alloys, the formation and stability of oxide scales in the molten salt were influenced by gaseous atmosphere and alloying elements.