Atomistic Analysis of Crystal Plasticity in Copper Nanowire
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0924-Z02-04
Atomistic Analysis of Crystal Plasticity in Copper Nanowire R. S. McEntire1,2, and Y.-L. Shen1 1 Dept of Mechanical Engineering, University of New Mexico, Albuquerque, NM, 87131 2 Sandia National Laboratories, Albuquerque, NM, 87185 ABSTRACT Plastic deformation in a model copper wire under tensile loading is modeled using three dimensional atomistic simulations. The primary objective is to gain fundamental insight into the nano-scale deformation features. An initial defect is utilized in the model to trigger plastic deformation in a controlled manner. A parametric study is performed by varying the atomic interaction range used in the model. When the interaction distance is small, slip is observed to be the dominant deformation mechanism. A slight increase in the interaction range results in phase transition from the FCC structure to a BCC structure. Re-orientation of the BCC lattice also occurs at later stages of the deformation. The phase transition mechanism is further enhanced if the nanowire is attached to a flat substrate. INTRODUCTION Atomistic simulation is a valuable tool for gaining fundamental understandings of material behavior. There have been extensive efforts for employing molecular dynamics simulations to study the deformation mechanisms in nano-scale metallic crystals. For instance, the strength, yield behavior, and shape memory effects of metal nanowires under uniaxial tensile loading have recently been studied [1-4]. For nano-scale specimens with large surface-to-volume ratios, the surface energy is seen to play an important role in affecting the mechanical response. However, as opposed to previous work which focused mainly on tensile loading of the specimen along high-symmetry crystallographic directions such as , and , the present study concerns tensile loading along a low-symmetry orientation. Within the framework of conventional crystal plasticity, this type of loading typically leads to “single slip” during the initial stages of deformation. Following an approach used in our previous twodimensional simulations [5,6], we utilized an embedded initial point defect for triggering plasticity events at a prescribed location in the model. Furthermore, in the present molecular statics simulations we adopted a pairwise interatomic potential and varied the cutoff distance (maximum range of atomic interaction), for the purpose of gaining fundamental insight into the influence the interaction range may have on the modeled deformation behavior. MODEL SETUP Figure 1 shows a schematic of the model setup. Atoms are packed into a FCC crystal, and the specimen takes the form of a rectangular bar to be subject to tensile stretching. (The actual atomic arrangements can be seen in Figs. 3-6 below). We consider the tensile loading orientation in [7 10 3] . This low-symmetry orientation is arbitrarily chosen to avoid multiple slips when plastic yielding is first activated. The model dimensions are characterized by the outer edges of the atomic spheres in the three directions: l = 128.0 Å, w = 24.73 Å an
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