Orientation- and microstructure-dependent deformation in metal nanowires under bending

Device miniaturization requires the bending of nanowires (NWs) on the nanoscale. To explore the mechanical behavior the mechanisms of plastic deformation of nickel nanowires of different orientations, sizes and twin structures under bending were investigated by means of molecular dynamics simulation. We show that plastic deformation can be either homogeneous or heterogeneous, depending on the NW orientation. Bending 〈1 2 1〉 oriented NW leads to homogeneous plastic flow, attributed to the large capacity for storage of axial extended dislocations (AEDs). AEDs are formed by constriction and cross-slip of inclined extended dislocations to the neutral (1 1 1) planes. The stacking of AEDs forms new defect structures, such as micro-twins and small hcp embryos. More localized deformation appears in NWs with 〈1 1 1〉 and 〈0 1 0〉 orientations at large bending angles, which is mainly caused by the pile-up and escape of inclined dislocations. The mechanical behavior of NWs is altered by introducing preset nano-twins,. The strength increases monotonically as the twin boundary spacing decreases. Among the three orientations the 〈1 2 1〉 oriented NWs with twin structure have been demonstrated to possess both high strength and ductility. A theoretical model based on geometrically necessary dislocations is proposed to quantify the contribution of various defects to the plastic deformation under bending, which links the continuum theory and atomistic simulations.

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