Solidification Microstructure of AlCoCrFeNi2.1 Eutectic High Entropy Alloy Ingots

AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) ingots were successfully obtained by high-frequency melting and centrifugal metal-mold casting under an Ar flow. The microstructure of the ingots was investigated by trans-scale observations using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and scanning transmission electron microscopy (STEM). The constituent phases of the ingots were identified as fcc and bcc phases by X-ray diffraction (XRD) analysis, and were not dependent on the position of the ingot. The microstructure was observed to have a primary fcc dendrite and fcc+bcc eutectic structure at the inter-dendrite region, regardless of the position of the ingots. The size of the solidification structure was affected by the cooling rate. Faster cooling rates resulted in finer solidi flcation structures. TEM observations clarified the development of L1(2) ordering structures in the primary fcc dendrite phase, while the ordering peak could not be detected by XRD analysis.