Investigating phase formations in cast AlFeCoNiCu high entropy alloys by combination of computational modeling and experiments

Abstract

Selection and thermal stability of phases are important in design of high entropy alloys (HEA). In this study, phase formations in cast AlFeCoNiCu HEA were investigated. Ab-initio molecular dynamics (AIMD) simulations were used to determine crystal structures of phases at different temperatures in equiatomic composition of AlFeCoNiCu. The AIMD results showed a possible coexistence of a face-centered cubic (fcc) phase and a body-centered cubic (bcc) phase at the room temperature and indicated stabilization of a single fcc phase above 1070K at the equiatomic composition of AlFeCoNiCu. The phase diagrams of AlFeCoNiCu system were calculated using a modified thermodynamic approach based on CALPHAD and Muggianu's methods. The calculated phase diagrams showed formation of the same two phases at the room temperature, and a phase transformation at about 1010K to form a single fcc phase. The characterization experiments utilizing scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) confirmed the crystal structures and composition of phases determined by AIMD simulations and phase diagram calculations. High temperature XRD (HTXRD) analysis showed a significant increase in weight fraction of the fcc phase at high temperatures confirming the predicted phase transformation.