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Superplastic Deformation of Defect-Free Au Nanowires via Coherent Twin Propagation

Harold S. Park's picture

Since 2005, researchers have known via molecular dynamics simulations that ultra-small (i.e. < 5 nm diameter) FCC metal nanowires can exhibit unique shape memory and pseudoelastic behavior driven by surface stress effects resulting from their very small cross sectional dimensions - see ( and (  The process involves tensile loading of a rhombic <110> nanowire with {111} transverse surfaces that, after about 40% tensile strain, can reorient to a <100> nanowire with {100} transverse surfaces, and a square cross section.  The shape memory effect or pseudoelasticity is determined by whether the nanowire is stable in the new <100> orientation, or whether additional thermal energy is required to cause the surface-stress-driven reorientation back to <110>/{111}.  

Experimental studies of these deformation paths have not existed until recently, when in the attached paper recently published in Nano Letters (, we found that <110> gold nanowires with {111} transverse surfaces can indeed reorient under tensile loading to <100> wires with {100} surfaces.  The reorientation occurs through ~40% tensile strain, is driven by coherent and long range (micrometer scale) propagation of twin boundaries, and occurs for the range of nanowire diameters tested (40-150 nm).  The results are novel and demonstrate the gold nanowires to uniquely be both superstrong and superplastic.  



PDF icon seoNL2011.pdf3.11 MB


Dear Prof Park,

Nice to see your work on Nano Letter on Super plastic Deformation in Au nanowire. I am having few observations:

1. It is well known that <110> orientaion is energetically more stable as compared to <100> oriented FCC metallic nanowire, based on first principle and MD simulations. A large no. of shape memory and pseudoelasticity is reported in the literature. It was nice to see those behaviors via experimentally.

As we know that the stress-strain behavior reported in region II is basically the phase transformation/reorientaion of an initial <110> oriented phase to <100> phase, which is recoverable. How this region could be considered as plastic deformation?


2. As literature says, for ceramics, failure strain of ~100% and for metals ~400-500% are considered as superplasticity. The failure strain reported in the paper is order of ~50% in metallic nanowire, should be considered as superplastic.

Or, it should have been superelastic behavior, as that region II is recoverable (as per atomistic simulations results)?

Anyway I have not gone through the paper in details. I ll read this intersting article. Thanx for sharing the manuscript.


Vijay Kumar Sutrakar 


Harold S. Park's picture

Dear Vijay:

Thanks for your comments and for your interest.  To answer your questions:

1.  The region II is considered "plastic" in this case because there is no recovery back to the initial <110> orientation.  For these wires, they are actually synthesized chemically as the lower energy <110>/{111} wire with rhombic cross section - there is no surface-stress-induced reorientation from <100> to <110>.

2.  Again, for the sizes considered experimentally (50-150 nm), there is no recovery due to surface stress since the cross section is too large.  I suspect that as the synthesis approach improves and smaller cross section nanowires can be made, then the surface-stress-induced reorientation may occur, but we will have to wait to test that.  

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