Phase stability of an high-entropy Al-Cr-Fe-Ni-V alloy with exceptional mechanical properties: First-principles and APT investigations

Al_0.5Cr_0.9FeNi_2.5V_0.2 (GS2.5) high-entropy alloys (HEAs) have been demonstrated to display an ultrahigh strength and can accommodate large plastic strains owing to their unique nanostructures with a low-misfit coherent nanostructure combining a near-equiatomic disordered face-centered-cubic (FCC) structured matrix with high-content ductile L1₂-structured nanoprecipitates. To comprehend the stability of unique nanostructure of GS2.5 HEA, the role of the principal elements in phase stability and mechanical properties were investigated by the first-principles calculations and virtual crystal approximation (VCA) methods. The stability of L1₂-structured nanophase and FCC-structured matrix were evaluated by calculating the elastic constants, Debye temperature and melting temperature. The results show that Cr is the dominate element among the principal elements that affects the stability and ductility of the L1₂-structured and FCC-structured phases. We predicted that decreasing Cr concentration could lead to a stable isotropic spinodal order-disorder nanostructure, and the prediction was validated by follow-up experiment. This work provides a method to optimize the phase structure of HEAs with near- spinodal nanostructure.