Nucleation of Plasticity in Alpha-Iron Nanowires
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NUCLEATION OF PLASTICITY IN ALPHA-IRON NANOWIRES K. P. Zolnikov, D. S. Kryzhevich, and A. V. Korchuganov
UDC 548.4; 539.4
The paper presents research results of the defect nucleation and propagation in the structure of nanosized iron samples with a perfect body-centered cubic lattice under a uniaxial tension along different crystallographic directions. The molecular dynamics method is used in these investigations. It is found that the mechanisms of plasticity nucleation considerably depend on the sample orientation relative to the load direction. The yield point exceedance along the [112] crystallographic direction leads to the twin nucleation on one of the sample edges. In this twin, the formation of dislocations occurs. Localized face-centered cubic arrangements can appear at the front of twinning dislocations. A large number of twins having the high growth velocity and low thickness generate in the crystal during tension along the [110] crystallographic direction. During tension, the twins tend to transform to dislocations. If tension occurs along the [111] crystallographic direction, the plastic strain generation has a well-defined dislocation nature. An avalanche of dislocations proceeding from tension causes the dislocation piercing of the free surface, leaving vacancies in the bulk material at their intersections. Keywords: nanowires, anisotropy, defective structure, plastic strain, mechanical load, atomic mechanisms, molecular dynamics.
INTRODUCTION Nanomaterials are widely used for fabrication of electronic and mechanical components of various devices [1]. The importance of nanomaterials in practical use is stipulated by their unique physical and mechanical properties. The size reduction of a single crystal to a nanoscale level significantly affects its strength and ductility that are determined by the nature of formation and development of the defective structure of the material [2, 3]. The size reduction results in a stronger effect of free surfaces on the nanomaterial behavior and properties. Moreover, nanosized crystalline samples have no defects in the material structure. In polycrystalline materials, the grain size plays a significant role in the plastic behavior of the material. The grain size reduction to a nanoscale level provides the transition from plastic to brittle deformation due to a lower contribution of the strain hardening [4–6]. The size of single-crystal materials as well as the grain size in polycrystals largely determine the deformation mechanisms and, as a consequence, mechanical properties of single crystals. The local structural rearrangements induced by thermal vibrations of the crystal lattice and the stress redistribution caused by external influences lead to the nucleation of different structural defects [7–9]. Experimental research into the nanocrystal behavior under mechanical loading faces difficulties associated with the small space-time scale processes that occur during structural rearrangements in the crystal lattice. A more effective approach to studying the atomic me
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