Designing High Entropy Alloys with Dual fcc and bcc Solid-Solution Phases: Structures and Mechanical Properties

Abstract

High entropy alloys (HEAs) with a single fcc phase are usually ductile but not strong, while HEAs with a single bcc phase have high strength but low ductility. Therefore, the combination of fcc and bcc phases was adopted to optimize the mechanical properties. Based on a latest data collection of reported HEAs with a single fcc phase, with dual fcc and bcc phases, and with a single bcc phase, the current work shows that the average valence electron concentration (VEC) and its standard deviation (δVEC) can describe quantitatively phase selection between the fcc and bcc phases in HEAs. Highest (lowest) hardness, highest (lowest) strength, and lowest (highest) ductility were found at the same critical value of VEC* ≈ 6.13 (δVEC* ≈ 0.207), which corresponds to the HEA with a single bcc (fcc) phase. The current work provides some quantitative rules for designing HEAs with dual fcc and bcc phases as well as modulating strength and ductility.