▎ 摘　　要

Reducing grain size into nanoscale could effectively enhance the strength of crystalline metals, while there is a critical grain size below which softening occurs as grain size further decreases. This strengthening-to-softening changeover accompanies simultaneous deformation mechanism transition from dislocation mediated to grain boundary (GB) mediated processes. To improve the strengthening effects, dislike the conventional nanosheets and laminated graphene embedded in graphene reinforced metal-matrix composites (GRMMCs), here a strategy is presented, via molecular dynamics simulations, to derive a new GRMMC in the form of nanoscale Cu grains fully enclosed by graphene-boundary (GrB). It is demonstrated that the strong dislocation storage and lacking conventional GB-mediated mechanisms in the designed GRMMC could result in extremely high strength of 8.77 GPa and pronounced strain hardening rate compared with nanocrystalline Cu. The design of GB engineering through replacing metallic GBs via GrBs may pave a new way to tailoring GRMMCs without anisotropic limitations, realizing excellent strength and strain hardening capacity. (C) 2020 The Authors. Published by Elsevier Ltd.