Rapid solidification of AlCoCrFeNi2.1 High-entropy Alloy

In this work the effect of cooling rate on the dual-phase (L12/B2) AlCoCrFeNi2.1 Eutectic High-Entropy Alloy was investigated. AlCoCrFeNi2.1 powders were made using a drop-tube facility, achieving powders of sizes ranging from 850 µm ≤ d < 1000–38 µm ≤ d < 53 µm with corresponding estimated cooling rates of 114 Ks−1 to  K s−1 respectively. Average interlamellar spacing decreases from 2.10 µm in the as-cast alloy to 348 nm in the powders of the 38 µm < d < 53 µm size fraction. Although decreased interlamellar spacing is expected to enhance microhardness, such a relation was not as strong as expected, with microhardness of the powders found to vary only slightly from an average value of 340 Hv0.03. This unexpected result is explained via the observation of increased FCC volume fraction. With increasing cooling rate, the microstructure of AlCoCrFeNi2.1 was found to evolve gradually from regular eutectic to colony eutectic, followed by dendritic with eutectic the interdendritic regions. In particles of size d < 212 µm BCC dendrites were observed, either dominating the structure or coexisting with FCC dendrites.