Atomistic simulation of the strain-hardening behavior of bicrystal Cu nanowires
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To determine whether plastic-hardening behavior occurs in metal nanowires, an atomistic simulation was performed to investigate the tension process in a bicrystal Cu nanowire. The results indicate that bicrystal Cu nanowires exhibit strain-hardening behavior, unlike their single-crystal counterparts. The strain-hardening behavior is related to the orientation of two crystal grains, and the number of atoms determines whether strain-hardening behavior occurs in the asymmetrically tilted bicrystal Cu nanowires. Strain hardening occurs in almost bicrystal Cu nanowires with different orientation angles. The initial yield stress is determined by the grain whose orientation angle is closer to 45° among the two crystal grains, resulting in a high value of the tilting tendency factor, and thus making it easier to generate slip.
I. INTRODUCTION
Recently, metal nanowires have received significant attention in the materials science community.1–3 From the perspective of basic theoretical research, one of the outstanding issues regarding metal nanowires is whether plastic-hardening behavior occurs in them. Strain hardening can change the strength of a ductile material by two to three orders of magnitude at low temperature. It should be noted that the strength of metals results from the interactions of dislocations, and the plastic deformation of metals results from the mutual movement of dislocations.4 This basic phenomenon about strain-hardening behavior largely determines the application prospects of metal nanowires. The application of metal nanowires will be limited if strain-hardening behavior does not occur in them. The strain-hardening behavior of metal nanowires should be very different from that in materials at the macroscale due to their small size relative to the sizes of dislocations. To fully understand the strain-hardening behavior of metal nanowires, such a behavior must be investigated on the atomic scale. Wu et al.5 used atomic force microscopy to investigate the bending process of gold nanowires. The results indicated that the load was increased during the plastic deformation of nanowires with a diameter of approximately 40 nm. This load increase indicates that dislocations still accumulate, resulting in strain-hardening behavior. However, Dou and Derby6 conducted compression experiments on gold nanowires with diameters of 30–80 nm. The level of stress was constant during plastic deformation after elastic deformation by compression, i.e., no straina)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2013.363 J. Mater. Res., Vol. 28, No. 24, Dec 28, 2013
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hardening behavior was observed. Philippe et al.7 performed bending experiments of rhodium nanowires with diameters in the range of 400–1000 nm using a scanning electron microscope; the experiments revealed that the load increased during the plastic deformation stage, and the plastic-hardening phenomenon was observed in the rhodium nanowires. In summary, the experiment
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