Rebuilding the Strain Hardening at a Large Strain in Twinned Au Nanowires.

Jiapeng Sun,Zhenquan Yang,Dan Song,Liang Fang,Huan Liu,Aibin Ma,Jing Han

doi:10.3390/nano8100848

Abstract

Metallic nanowires usually exhibit ultrahigh strength but low tensile ductility, owing to their limited strain hardening capability. Here, our larger scale molecular dynamics simulations demonstrated that we could rebuild the highly desirable strain hardening behavior at a large strain (0.21 to 0.31) in twinned Au nanowires by changing twin orientation, which strongly contrasts with the strain hardening at the incipient plastic deformation in low stacking-fault energy metals nanowires. Because of this strain hardening, an improved ductility is achieved. With the change of twin orientation, a competing effect between partial dislocation propagation and twin migration is observed in nanowires with slant twin boundaries. When twin migration gains the upper hand, the strain hardening occurs. Otherwise, the strain softening occurs. As the twin orientation increases from 0° to 90°, the dominating deformation mechanism shifts from slip-twin boundary interaction to dislocation slip, twin migration, and slip transmission in sequence. Our work could not only deepen our understanding of the mechanical behavior and deformation mechanism of twinned Au nanowires, but also provide new insights into enhancing the strength and ductility of nanowires by engineering the nanoscale twins.

Highlights

Metallic nanowires have drawn a great of interest and have been extensively studied in recent years because of their unique properties and potential as a fundamental building block of nanotechnology
This strain hardening behavior occurred at incipient plastic deformation, which has been generally reported in low stacking-fault energy metals nanowires with orthogonally oriented coherent twin boundaries (CTBs) [21,22]
Larger scale molecular dynamics simulations were performed to elucidate the effect of twin orientation and spacing on mechanical behavior, especially the strain hardening and deformation mechanism at the atomic level of the cylindrical NT Au nanowires

Summary

Introduction

Metallic nanowires have drawn a great of interest and have been extensively studied in recent years because of their unique properties and potential as a fundamental building block of nanotechnology. Many nanomechanical experiments and molecular dynamics (MD) simulations have proved that metal nanowires possess extreme-high strength (Au, Ag, Cu, Ni, Al), and exhibit “smaller is stronger” trend [1,2,3,4]. Such nanowires fail at higher stresses, they may exhibit either limited or no strain hardening capability at all. This fundamental difference is attributable to the relative change between the stress required to nucleate new dislocations from free surfaces and that for the dislocation transmission at CTBs as a function of the unstable stacking-fault energy [21,22]

Methods

Results

Conclusion