Twisting of a Pristine α-Fe Nanowire: From Wild Dislocation Avalanches to Mild Local Amorphization.

Yang Yang,Jun Sun,Ekhard K H Salje,Xiangdong Ding

doi:10.3390/nano11061602

Yang Yang, Jun Sun + Show 2 more

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https://doi.org/10.3390/nano11061602

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Abstract

The torsion of pristine α-Fe nanowires was studied by molecular dynamics simulations. Torsion-induced plastic deformation in pristine nanowires is divided into two regimes. Under weak torsion, plastic deformation leads to dislocation nucleation and propagation. Twisting-induced dislocations are mainly <111> screw dislocations in a <112>-oriented nanowire. The nucleation and propagation of these dislocations were found to form avalanches which generate the emission of energy jerks. Their probability distribution function (PDF) showed power laws with mixing between different energy exponents. The mixing stemmed from simultaneous axial and radial dislocation movements. The power-law distribution indicated strongly correlated ‘wild’ dislocation dynamics. At the end of this regime, the dislocation pattern was frozen, and further twisting of the nanowire did not change the dislocation pattern. Instead, it induced local amorphization at the grip points at the ends of the sample. This “melting” generated highly dampened, mild avalanches. We compared the deformation mechanisms of twinned and pristine α-Fe nanowires under torsion.

Highlights

IntroductionThe nucleation and propagation of these dislocations were found to form avalanches which generate the emission of energy jerks
State Key Laboratory for Mechanical Behaviour of Materials, School of Materials Science and Engineering, Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK
Metallic nanowires show high pseudoelasticity with full shape recovery from a uniaxial tensile strain larger than 40% [1,2,3,4]. Such an excellent shape recoverability in metallic nanowires defines their potential for applications as sensors, actuators, energy storage and transfer devices etc. in micro-electrical-mechanical systems (MEMS or NEMS)

Summary

Introduction

The nucleation and propagation of these dislocations were found to form avalanches which generate the emission of energy jerks. Their probability distribution function (PDF) showed power laws with mixing between different energy exponents. At the end of this regime, the dislocation pattern was frozen, and further twisting of the nanowire did not change the dislocation pattern Instead, it induced local amorphization at the grip points at the ends of the sample. Metallic nanowires show high pseudoelasticity with full shape recovery from a uniaxial tensile strain larger than 40% [1,2,3,4]. The applications of gradient stress fields such as bending and torsion are more common [6,7,8]

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