Investigation of plastic deformation modes in Al0.1 CoCrFeNi high entropy alloy

Mechanisms contributing to the plastic deformation of coarse grained (CG, average grain diameter 1-2 mm), and friction-stir-processed fine grained (FG, 0.3-14 mu m) fcc Al0.1CoCrFeNi high entropy alloy was investigated. In the grain interiors of CG, deformation primarily occurred via planar slip of undissociated 1/2 < 011 > dislocations on parallel (111) planes. Stacking faults were also detected, and they appeared to have contributed to the formation of parallel (111) slip-bands. In comparison, the deformed FG microstructure was dominated by dislocation cell-like structures, which suggested that proximity to the grain-boundaries, unlike CG, have substantially influenced dislocation arrangements. Interestingly, nanoscale (similar to 2 nm thick) deformation twins were unambiguously observed in both deformed FG and CG microstructures, and that such twins did not emanate from grain boundaries. These twins invariably comprised of two variants, which lay on two different (111) habit planes oriented by similar to 70 degrees from each other. The formation of such two-variant deformation twinning provides an additional plastic deformation mode and is expected to improve the work hardening of Al0.1CoCrFeNi high entropy alloy.