Atomic-scale analysis of deformation mechanisms of nanotwinned polycrystalline Ni nanowires during tension

Large-scale molecular dynamics simulations have been performed to investigate deformation mechanisms in nanotwinned polycrystalline Ni nanowires (NWs). Atomic-scale dislocation nucleation and propagation activities were captured during tension. Yield stresses were found to decrease with the reduction of twin boundary spacing (TBS) below 3.66 nm, exhibiting an inverse Hall-Petch (HP) relation. Atomic-scale analysis shown that the transition in intra-granular deformation mechanism from partial dislocations nucleation and gliding inclined to the twin boundaries (TBs) to partial dislocations nucleation and gliding parallel to the TBs appeared to be the direct cause of the inverse HP relation. In addition to this, full dislocation and grain boundary migration were also captured. The strain localization during tension was highlighted to understand the atomic mechanisms leading to the catastrophic failure of the nanotwinned polycrystalline NWs. These findings should contribute to the understanding the deformation mechanisms of nanotwinned polycrystalline NWs and provide insights into the possibility of tuning the microstructure to elicit desired mechanical properties.