Atomistic simulations on the dissociation of a screw dislocation in BCC-Fe

Abstract

Dislocations play a crucial role in plastic deformation. The behavior of the dislocations can vary with size. In the present investigation, we studied the characteristics of the three-fold dissociation of a screw dislocation in BCC-Fe using molecular dynamics simulations. A screw dislocation with different lengths (L) and diameters (D) ranging from 2 nm to 80 nm was created in a cylindrical nanowire oriented along X = [1¯ 01], Y = [121] and Z = [1 1¯ 1] directions. The tensile load was applied along the Z-direction with a strain rate of 108 /s or 107 /s. Three-fold dissociation was noticed on three co-zonal {110} planes with trailing stacking faults. The screw dislocation was not stable in the model system if the value of D ≤ 2 nm due to the image forces arising from the surfaces. The stress required for the three-fold dissociation was independent of the size of the nanowires. However, the screw dislocation was deformed by forming a dislocation loop instead of a three-fold dissociation when L ≥ 40 nm. Further, the three-fold dissociation mechanism was limited to lower temperatures below 20 K. These results were further cross-checked with the other interatomic potentials.