Microstructural characterization of eutectic and near-eutectic AlCoCrFeNi high-entropy alloys

The microstructure and orientation relationships in five AlCoCrFeNix alloys with eutectic (x = 2.1) and near-eutectic compositions (x = 1.9, 2.0, 2.2 and 2.3) have been characterized in this work. The eutectic and near-eutectic AlCoCrFeNix alloys have microstructures consisting of face-centered cubic (FCC) and ordered body-centered cubic (BCC) B2 phases, where the volume fraction of the FCC phase is found to increase with increasing Ni content. It is found that each eutectic colony consists of several parallel lamellae in the colony center and peripheral irregular labyrinth-like structures. The frequency of the irregular structures appears to be higher in the near-eutectic alloys than in the eutectic alloy. The ratio of the average widths of FCC and BCC lamellae is observed to be sensitive to the chemical composition and increases with the increasing Ni content. The two phases in the studied alloys display relationships close to the Kurdjumov-Sachs orientation relationship. The distribution of misorientation angles between the interphase boundaries changes as a function of the Ni content. The result of this change is a small increase in the average misorientation angle across the FCC/BCC interphase boundaries with increasing Ni content. The differences in the morphological crystallographic characteristics between the alloys are briefly discussed.