Understanding the Atomic-Scale Deformation in CoNiCrFeMn Nanocrystalline High Entropy Alloy with Gradient Structure

Gradient high entropy alloys have attained great attention due to their exceptional mechanical properties. Here, molecular dynamic simulations are reported to introduce CoNiCrFeMn high entropy alloy with gradient structure and understand the relation between structural gradient and mechanical performance. The effect of gradient structure on the mechanical properties was studied by characterizing the structural evolution and dislocation substructures during tension loading. The gradient distributions of deformation faults and dislocations from the surface to the center of samples were explored in detail. Quantitative analysis shows that simultaneous improvement of ductility and strength is afford by high densities of dislocations in the grain interior. Moreover, the results revealed that the energy barrier for nucleation of deformation faults in the deformed layer of gradient high entropy alloy is higher than in uniform sample. The high strength and work hardening of gradient high entropy alloy attributed to the geometrically necessary dislocations distributed in grain interiors and having a form of bundles of concentrated dislocations. Based on the simulation results, the synergy between high strength and high ductility in high entropy alloys can be achieved through the gradient structure. The present study gives a method to better understanding the deformation mechanisms and mechanical properties of high entropy alloys with gradient structure.