Pramatic Atomistic Analysis of Nano-scale Metal Plasticity

Recent progresses in atomistic simulations of plastic deformation in nano-scale metallic crystals are presented. Attention is devoted to adjusting the interatomic potential parameters with the objective of gaining fundamental insight into the crystal defect processes in fcc metals. An initial defect is utilized in the molecular statics model to trigger plasticity in a controlled manner. A parametric study is performed by varying the atomic interaction range used in the copper model, such that dislocation slip behavior and/or phase transformation can first be observed without the influence of an unstable surface state of the specimen. We focus on tensile loading along a low-symmetry orientation where single slip prevails upon yielding. When the interaction distance is small, dislocation slip is seen to be the dominant deformation mechanism. A slight increase in the interaction range results in phase transition from the fcc structure to a bcc structure. Re-orientation of the bcc lattice also occurs at later stages of the deformation via a twinning operation. The phase transition mechanism is further enhanced if the nanowire is attached to a flat substrate parallel to the initial close-packed plane. When the atomic interaction range is increased further, the effect of surface stress becomes increasingly important. Plastic yielding occurs in the form of partial slip which creates a stacking fault in the slip plane. The initial point defect plays a less significant role and phase transition during deformation is suppressed. Detailed mechanisms of these atomistic features, as well as their implications to computational simulations of plastic deformation in metallic nanostructures, will be discussed.