Origin of excellent strength-ductility balance unique to FCC high-entropy alloys; A Plaston-based mechanism derived from electronic structure calculations

Tsuru, Tomohito   

Some high-entropy alloys (HEAs) with the face-centered cubic (FCC) 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 has not understood what fundamental properties and features of HEAs cause such unique deformation. 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 Burger 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.