Atomistic simulations of tensile properties and deformation mechanisms in a gradient nanostructured Al0.3CrFeCoNi high-entropy alloy

Atomistic simulations are conducted to investigate the tensile properties and deformation mechanisms of the gradient nano-grained (GNG) structure of face-centered-cubic (FCC) Al0.3CrFeCoNi HEAs, and comparisons are made with the homogeneous nano-grained (HNG) counterparts. Our computations show that the GNG Al0.3CrFeCoNi HEA primarily undergoes three typical deformation stages, i.e. linear elastic, plastic yielding and plastic flow stages, and the plastic deformation mechanism of GNG structure is dominated by the dislocation slip and stacking faults multiplication. The GNG structure possesses an obvious higher flow strength compared to the HNG counterpart, showing the extra strengthening effect. The strengthen mechanism is attributed to the tensile strain partitioning between the large grains and small grains, which causes hetero-deformation induced stress and higher dislocation density and thus strengthening the GNG structure. With the increase of temperature, the Young's modulus, yielding strength and flow strength of GNG and HNG structures all exhibit a clear decreased trend. Increasing strain rate leads to the increase of the Young's modulus and yielding strength of GNG and HNG structures. In particular, no extra strengthening effect is observed from the GNG structure at higher temperature or higher strain rate. Such a scenario can be attributed to the more dislocation slips, stacking faults and grain boundary activities in the small grains, which makes them to accommodate significant tensile strain. These findings provide deeper insights into the deformation mechanisms of GNG HEAs and offer guidance to design heterogeneous HEA structures.