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      Recoverable plasticity in penta-twinned metallic nanowires governed by dislocation nucleation and retraction

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          There has been relatively little study on time-dependent mechanical properties of nanowires, in spite of their importance for the design, fabrication and operation of nanoscale devices. Here we report a dislocation-mediated, time-dependent and fully reversible plastic behaviour in penta-twinned silver nanowires. In situ tensile experiments inside scanning and transmission electron microscopes show that penta-twinned silver nanowires undergo stress relaxation on loading and complete plastic strain recovery on unloading, while the same experiments on single-crystalline silver nanowires do not exhibit such a behaviour. Molecular dynamics simulations reveal that the observed behaviour in penta-twinned nanowires originates from the surface nucleation, propagation and retraction of partial dislocations. More specifically, vacancies reduce dislocation nucleation barrier, facilitating stress relaxation, while the twin boundaries and their intrinsic stress field promote retraction of partial dislocations, resulting in full strain recovery.


          1D nanostructures are widely regarded as important building blocks for a broad range of applications. Here, the authors study dislocation-mediated plastic deformation in penta-twinned silver nanowires, finding that in situ deformation at small to moderate strains can be entirely reversible.

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          Most cited references 17

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          Stacking fault energies and slip in nanocrystalline metals.

          The search for deformation mechanisms in nanocrystalline metals has profited from the use of molecular dynamics calculations. These simulations have revealed two possible mechanisms; grain boundary accommodation, and intragranular slip involving dislocation emission and absorption at grain boundaries. But the precise nature of the slip mechanism is the subject of considerable debate, and the limitations of the simulation technique need to be taken into consideration. Here we show, using molecular dynamics simulations, that the nature of slip in nanocrystalline metals cannot be described in terms of the absolute value of the stacking fault energy-a correct interpretation requires the generalized stacking fault energy curve, involving both stable and unstable stacking fault energies. The molecular dynamics technique does not at present allow for the determination of rate-limiting processes, so the use of our calculations in the interpretation of experiments has to be undertaken with care.
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            Synthesis of silver nanostructures with controlled shapes and properties.

            Mastery over the shape of a nanostructure enables control over its properties and usefulness for a given application. By controlling the crystallinity of the seeds from which nanostructures grow and the rate of atomic addition to seeds, we selectively produced pentagonal nanowires, cuboctahedra, nanocubes, nanobars, bipyramids, and nanobeams of silver with a solution-phase polyol synthesis. The example of nanobars illustrates how the shape of a silver nanostructure affects the color of light that it scatters. We further show how silver nanowires and nanobeams can serve as conduits for both electrons and photons.
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              Dislocation processes in the deformation of nanocrystalline aluminium by molecular-dynamics simulation.

              The mechanical behaviour of nanocrystalline materials (that is, polycrystals with a grain size of less than 100 nm) remains controversial. Although it is commonly accepted that the intrinsic deformation behaviour of these materials arises from the interplay between dislocation and grain-boundary processes, little is known about the specific deformation mechanisms. Here we use large-scale molecular-dynamics simulations to elucidate this intricate interplay during room-temperature plastic deformation of model nanocrystalline Al microstructures. We demonstrate that, in contrast to coarse-grained Al, mechanical twinning may play an important role in the deformation behaviour of nanocrystalline Al. Our results illustrate that this type of simulation has now advanced to a level where it provides a powerful new tool for elucidating and quantifying--in a degree of detail not possible experimentally--the atomic-level mechanisms controlling the complex dislocation and grain-boundary processes in heavily deformed materials with a submicrometre grain size.

                Author and article information

                [1 ]Department of Mechanical and Aerospace Engineering, North Carolina State University , Raleigh, North Carolina 27695, USA
                [2 ]School of Engineering, Brown University , Providence, Rhode Island 02912, USA
                [3 ]Centre of Advanced Mechanics and Materials, Applied Mechanics Laboratory, Department of Engineering Mechanics, Tsinghua University , Beijing 100084, China
                [4 ]Max Planck Institute for Intelligent Systems , Heisenbergstrasse 3, D-70589 Stuttgart, Germany
                Author notes

                These authors contributed equally to this work

                Nat Commun
                Nat Commun
                Nature Communications
                Nature Pub. Group
                13 January 2015
                : 6
                25585295 4308715 ncomms6983 10.1038/ncomms6983
                Copyright © 2015, Nature Publishing Group, a division of Macmillan Publishers Limited. All Rights Reserved.

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