Large scale atomistic simulations of screw dislocation structure, annihilation and cross-slip in FCC Ni

Using QM-Sutton-Chen many-body potential, we have studied the 1/2a<1 1 0> screw dislocation in nickel (Ni) via molecular dynamics (MD) simulations. We have studied core energy and structure using a quadrupolar dislocation system with 3D periodic boundary conditions. The relaxed structures show dissociation into two partials on (1 1 1) planes. The equilibrium separation distance between the two partials is 2.5 nm, which is larger than the derived value according to experimental data, due to low stacking fault energy given by the QM-Sutton-Chen force field. From our calculations, the core energy for the 1/2a<1 1 0> screw dislocation is 0.5 eV/b. We also studied motion and annihilation process of opposite signed dislocations. We build the dipole system with two combinations of dissociation planes: (a) two dislocations dissociated on intersecting slip planes and (b) two on parallel planes. The process of cross-slip and associated energy barriers are also calculated from these simulations.