Tensile nanomechanics and the Hall-Petch effect in nanocrystalline aluminium

This work carries out comprehensive classical molecular dynamics simulations of uniaxial tensile deformation for nanocrystalline Al samples with a broad range of different mean grain sizes. The largest nanocrystalline Al sample has a mean grain size of about 30 nm and contains over 100 millions atoms in the modeling system. The grain size dependence of yield stress and the atomic fraction of dislocations are quantified and the size dependence tensile nanomechanics are also revealed. Deformation twinning and grain boundary migration are observed as main mechanisms of tensile deformation in the nanocrystalline Al. In particular, the complete Hall-Petch relationship for the nanocrystalline Al bulk is determined for the first time in this study, from which three distinct regions are identified including the normal, inverse, and extended regions in the Hall-Petch relationship. We expect these findings will provide useful insights in the nanomechanics of nanocrystalline Al. The quantitation analyses on dislocations and mechanical properties may facilitate the design and development of high strength nanocrystalline Al and Al based alloys as well as future testing procedures for promising structural and transportation applications.