| Abstract | In this study, an equiatomic FeCoNiCrMn high entropy alloy (HEA) was examined and compared to two Al-containing variants, FeCoNi₁.₅CrMnAl₀.₅ and FeCoNi₁.₅CrAl₀.₅, in terms of microstructure, phase composition and hardness. The vacuum cast, hot isostatically pressed (HIP’d) alloys were evaluated using differential scanning calorimetry (DSC), SEM, energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and Vickers microhardness testing. The DSC results indicated that the solidus and liquidus temperature of the base alloy on cooling are 1296.3 and 1314.8°C, respectively. Its microstructure exhibited a single-phase face centred cubic (FCC) structure, with a small amount of σ-phase. The two Al-containing alloys (FeCoNi₁.₅CrMnAl₀.₅ and FeCoNi₁.₅CrAl₀.₅) were observed to form a secondary phase, in a FCC matrix, along the grain boundaries and within the grains. FeCoNi₁.₅CrMnAl₀.₅ had a solidus and liquidus temperature at 1271.8°C and 1287.6°C upon cooling, while FeCoNi₁.₅CrAl₀.₅ exhibited a solidus at 1354.7°C and liquidus at 1376.1°C. The hardness of the base composition was measured at 142 HV while the addition of Al and increase of Ni content in FeCoNi₁.₅CrMnAl₀.₅ increased the hardness to 202 HV and the removal of Mn in FeCoNi₁.₅CrAl₀.₅ further enhanced the hardness to 217 HV. These results aim to form a basis for understanding the effects of HEA microstructure on the material performance in oxidising environments, such as supercritical-CO₂. |
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