ABSTRACT
Nano-grained (NG) metals usually have ultra-high strength, but show reduced strain hardening rate and limited ductility compared to their coarse grained (CG) counterparts, due to the incapability of effectively accumulating dislocations inside the nano-grains. Nanocrystalline (NC) bcc metals have been found to behave very differently from NC metals with other crystal structures. With decreasing grain size, the density of mixed and edge dislocations increases while the screw dislocations become less dominated for bcc metals. Molecular dynamics (MD) simulations may be helpful and provide hints for the atomistic tensile deformation mechanisms in the GNG structure. Large-scale MD simulations have been used to elucidate the atomistic deformation mechanisms of the GNG structure of bcc Fe and the uniform NG structure of bcc Fe in the present study. The dominant deformation mechanisms are found to be closely related to the grain sizes in the GNG structure. The present findings should provide insights for developing the metals and alloys with superior mechanical properties.
