Hetero-Deformation Induced Hardening in a CoCrFeNiMn High-Entropy Alloy

One of the most important issues in materials science is to overcome the strength-ductility trade-off in engineering alloys. The formation of heterogeneous and complex microstructures is a useful approach to achieving this purpose. In this investigation, a CoCrFeNiMn high-entropy alloy was processed via cold rolling followed by post-deformation annealing over a temperature range of 650-750 degrees C, which led to a wide range of grain sizes. Annealing at 650 degrees C led to the formation of a heterogeneous structure containing recrystallized areas with ultrafine and fine grains and non-recrystallized areas with an average size of similar to 75 mu m. The processed material showed strength-ductility synergy with very high strengths of over similar to 1 GPa and uniform elongations of over 12%. Different deformation mechanisms such as dislocation slip, deformation twinning and hetero-deformation-induced hardening were responsible for achieving this mechanical property. Increasing the annealing temperature up to 700 degrees C facilitated the acquisition of bimodal grain size distributions of similar to 1.5 and similar to 6 mu m, and the heterogeneous structure was eliminated via annealing at higher temperatures, which led to a significant decrease in strength.