Solidification Microstructure of AlCoCrFeNi_2.1 Eutectic High Entropy Alloy Ingots

Abstract

  AlCoCrFeNi_2.1 eutectic high entropy alloy (HEA) ingots were successfully obtained by high-frequency melting and centrifugal metallic mold casting under 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 ingots. In particular, dendrite fcc and inter-dendrite fcc and bcc eutectic structures were observed, regardless the position of the ingots. The solidification structure was affected by cooling. Faster cooling rates resulted in finer solidification structures. TEM observations clarified the development of L1₂ ordering structures in the dendrite fcc phase, while the ordering peak could not be detected by XRD analysis.