Microstructural origins for a strong and ductile Al0.1CoCrFeNi high-entropy alloy with ultrafine grains

A single-phase Al0.1CoCrFeNi high-entropy alloy (HEA) with face-centered cubic structure was subjected to cryorolling at the liquid N-2 temperature and subsequent annealing. Microstructural characterization of post-annealed samples by electron backscattered diffraction and transmission electron microscopy revealed that, the dominant grain boundaries (GBs) are of Sigma 3 type low energy twin boundaries owing to the low stacking fault energy of the HEA. The resulting ultrafine-grained single-phase HEA with abundant Sigma 3 twin boundaries shows a high strength above 1.0 GPa and a tensile strain larger than 20%. The quantitative analysis on the grain size dependence of strength suggests that a high lattice friction stress and a high GB strengthening via low energy Sigma 3 twin boundaries are two major contributions for the excellent strength-ductility balance of the ultra-fine grained HEA.