Origin of Excellent Strength-Ductility Balance Unique to FCC High-Entropy Alloys: A Plaston-Based Mechanism Derived from Electronic Structure Calculations

Abstract

Some high-entropy alloys (HEAs) with the face-centered cubic structure have an excellent strength-ductility balance. While unique deformation modes such as fine twinning patterns other than dislocation glide contribute to the mechanical properties, it is still unclear what properties and features of HEAs cause such unique deformation process. In the present study, fundamental properties responsible for the excellent mechanical properties of CoCrFeNiMn and its subsystems were explored comprehensively by the first-principles calculations. The local lattice distortion reaches almost 2% of the Burgers vector, which contributes to improving strength in HEAs. Furthermore, the stacking fault energy (SFE) was significantly low in random solid solution, while it increases around some domains where the short-range order (SRO) is formed. The increase in the SFE is caused by the disturbance of the chemical SRO and the spin order due to the SF formation. Our calculations suggest that low and high SFE domains distributed in a solid solution region unique to HEAs lead to successive activation of various deformation modes (Plaston), which achieves excellent strength-ductility balance.

Fundamental properties responsible for the mechanical properties in equiatomic CoCrFeNiMn, CrFeNiMn and CoCrNi. Large lattice distortion and low and high SF domains associated with the degree of SRO formation contribute to the excellent strength-ductility balance in FCC-HEAs.