Phase Stability of a Mechanically Alloyed CoCrCuFeNi High Entropy Alloy

Abstract

A CoCrCuFeNi high entropy alloy (HEA) is prepared from the high purity elemental Co,Cr, Cu,Fe, and Ni powders by mechanical alloying (MA) at different milling speed (200 or 350 rpm). Mechanically alloyed powder samples are subsequently annealed at different temperatures (300, 500, 700, and 800 °C). Microstructures, chemical composition, and phase stability of the powders are studied using X‐ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and energy dispersive X‐ray spectrometry (EDS). The results show that, a single phase stable FCC solid solution is formed within 5 and 50 h of milling at 350 and 200 rpm, respectively. The single FCC phase is identified to be thermally stable upto 800 °C and then it is decomposed into two FCC phases. The second FCC phase is found to be rich in Cu. The precipitation of the Cu rich phase is likely due to the positive enthalpy of mixing of Cu with other alloying elements.