Grain-size effect on plastic flow stress of nanolaminated polycrystalline aluminum/graphene composites

XH Zhou and X Liu and JJ Shang and QS Yang, MECHANICS OF MATERIALS, 148, 103530 (2020).

DOI: 10.1016/j.mechmat.2020.103530

Nanolaminated metal/graphene composites can have many special mechanical properties, thanks to a high density of interfaces. Even though the interface effect is a key mechanism for the propagation of dislocations in nanolaminated metal/graphene composites, it is not well understood. In this paper, simulations of the molecular dynamics of nanolaminated polycrystalline aluminum/graphene (PAl/Gr) composites are performed. The results provide insight into the grain-size effect on plastic flow stress of nanolaminated PAl/Gr composites and the underlying mechanism. Extended dislocations are found to dominate the plastic deformation of the PAl/Gr composites. Both the PAl/Gr interface and the Al grain boundaries (GBs) interact with the dislocations. Three dislocation propagation forms are observed in the PAl/Gr nanolaminated composite based on the Al grain-size. By decreasing the laminate thickness, the dislocation-GB interaction can transition to a dislocation-graphene interaction. When the Al layer thickness is smaller than the in-plane grain size, the strain-hardening capability is increased due to greater ability of the dislocation/graphene-interface to store dislocations than the GBs. Besides, geometrically necessary dislocations are induced because of the deformation gradient between the graphene and Al grains, which lead to back-stress strengthening and thus strain hardening. Accordingly, a confined layer slip mechanism, which considers back- stress, is used to predict the flow stress of the PAl/Gr composites.

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