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Reversible cyclic deformation mechanism of gold nanowires by twinning–detwinning transition evidenced from in situ TEM
Reversible deformation of metal nanowires accommodating large strains by twinning-detwinning
In situ studies of deformation in metal nanowires have yielded interesting results, as recently published in Nature Communications. An international research team performed cyclic loading on gold nanowires and observed twinning and detwinning phenomena, respectively caused by tensile and compressive loading, and elucidate the underpinning mechanism by molecular dynamics simulations.
Small-scale mechanics has been spurred by two groundbreaking discoveries, namely that shrinking the size leads to an increase in strength (that is, the ‘smaller is stronger' size effect ), and also to a change of deformation mechanism from dislocation slip to deformation twinning  or vice versa . When it comes to deep sub-micrometer or to nanometer scale single crystals, the crystallographic orientation is yet another important parameter determining the deformation mechanism . Knowing the experimental conditions under which a particular mechanism dominates the deformation of nanowires is of prime importance, since it determines the strength as well as the ductility of nanowires. Recently, an international team including researchers from Korea, Germany and Austria showed that dislocation-free gold nanowires deform by twinning and detwinning upon tensile and compressive loading, respectively. The underpinning mechanisms were elucidated by molecular dynamics simulations as just published in Nature Communications .
Twinning is classically considered a directional deformation mode, in other words the plastic deformation occurred once is permanent. In this work, employing quantitative nanoscale deformation experiments in situ in a transmission electron microscope, Lee et al.  observed for the first time that nanoscale twins that formed during tensile loading of a gold nanowire are repeatedly erased upon subsequent compressive loading. This new deformation mechanisms termed detwinning allows for reversible plastic deformation by growth and shrinkage of nanotwins. This reversible twinning-detwinning process accommodates large tensile/compressive strains of more than 30% in a pseudo-elastic manner, which can be beneficially utilized in applications requiring high ductility in addition to ultra-high strength, for example, to minimize damage for cyclically loaded nano-objects used in integrated circuits or for mechanical energy storage in nanoelectromechanical systems.
`This is another piece added to our understanding of the sometimes puzzling world of small scale deformation, which had not been possible without basic research funding offered by the Austrian Science Fund FWF´ says Prof. Kiener, who has been successfully collaborating with Prof. Oh for several years in the field. The current work was supported by a bilateral research project funded by NRF (NRF-2012K2A1A9054818) and FWF (I-1020), which is gratefully acknowledged.
Further details can be found in:
"Reversible cyclic deformation mechanism of Au nanowires by twinning-detwinning transition as evidenced from in-situ TEM" by Subin Lee, Jiseong Im, Youngdong Yoo, Erik Bitzek, Daniel Kiener, Gunther Richter, Bongsoo Kim, and Sang Ho Oh, Nature Communications, 10.1038/ncomms4033 .
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