LAUSR

Abstract We report on observations of the as-cast microstructures of equiatomic quaternary and quinary multiprincipal element alloys (MPEAs) containing equiatomic ternary CoCrCu-X with X being Fe, Mn, Ni, V, FeMn, FeNi, FeV, MnNi, MnV, and NiV. Out of the 11 MPEA combinations studied, CoCrCuNi, CoCrCuFeNi, and CoCrCuMnNi displayed FCC solid solution dendritic microstructures while the remaining 8 displayed a liquid phase separation into Cu-lean and Cu-rich liquids which solidified into highly phase separated regions. Calculations for enthalpy of mixing (ΔHmix) were carried out on the possible equiatomic combinations of these alloys using Miedema's scheme for sub-regular solutions. The Calculated ΔHmix for the nominal combinations were then compared to the ΔHmix for the atomic percentages of the actual compositions determined via EDS. It was found that stable Cu-lean microstructures all have lower ΔHmix than the calculated ΔHmix for their equiatomic ratios, indicating a positive correlation between ΔHmix and stable phase formation. The FCC structures observed for CoCrCuNi, CoCrCuFeNi, and CoCrCuMnNi dendrites are in agreement with the model for valence electron concentration described in the literature.