Non-monotonic variation of structural and tensile properties with Cr content in AlCoCrxFeNi2 high entropy alloys

Abstract

A series of AlCoCrxFeNi2 (x = 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4) high entropy alloys (HEAs) were designed to investigate the structural evolution and tensile properties variation with Cr content. It was found that all the alloys were composed of face-centered cubic (FCC) phase and disordered body-centered cubic (BCC) plus ordered body-centered cubic (B2) region. However, the volume fraction of FCC phase first increased and then decreased with increasing Cr content, while the valence electron concentration (VEC) values kept decreasing, which contradicts with the universal VEC criterion. Here, the partition ratio of Cr element in FCC/(BCC + B2) region was introduced to describe the structural evolution and phase stability. Our work reveals that Cr is FCC stabilizer at low concentration, and promotes the formation of BCC phase at high concentration. Similarly, the strength and ductility exhibit a non-monotonic variation with increasing Cr content.