Nucleation of Plasticity in Alpha-Iron Nanowires

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 [11$\overline{2}$] 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 [1$\overline{1}$0] 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.