Grain Refinement During Severe Plastic Deformation and Similitude of Subgrain Formation: A Molecular Dynamics Study

Molecular dynamics simulations of severe plastic deformation of monocrystalline and polycrystalline samples by multiaxial compression of aluminum are carried out. The structure evolution is tracked, with special attention paid to the evolution of crystal orientation, flow stress, dislocation density, and dislocation structure. The results show the formation of dislocation cells and subgrain boundaries in the early stage of deformation of the monocrystal, with a gradual increase in misorientation of the subgrain structure until grain refinement is reached. A similar stable grain size distribution is reached after severe plastic deformation of either a monocrystal or a nanocrystalline sample. The subgrains produced in the simulations have a size of approximately ∼20 nm, and this size agrees with trends observed in real experiments. This study demonstrates for the first time that the principle of similitude holds across 12 orders of magnitude of strain rate. It is necessary, though, to take into consideration that the high strain rates (10 9 s −1 ) produce higher dislocation densities ((2–4) × 10 13 cm −2 ) and higher stresses (∼1600 MPa) in the simulations compared to real experiments.