Calculations of Intersection Cross-Slip Activation Energies in FCC Metals Using Nudged Elastic Band Method.

摘要

The nudged elastic band (NEB) method is used to evaluate activation energies for dislocation intersection cross-slip in face-centered cubic (fcc) nickel and copper, to extend our prior work which used an approximate method. In this work we also extend the study by including Hirth locks (HL) in addition to Lomer-Cottrell locks and glide locks (GL). Using atomistic (molecular statics) simulations with embedded atom potentials we evaluated the activation barrier for a dislocation to transform from fully residing on the glide plane to fully residing on the cross-slip plane when intersecting a 120 deg. forest dislocation in both Ni and Cu. The initial separation between the screw and the intersecting dislocation on the (1 1 1) glide plane is varied to find a minimum in the activation energy. The NEB method gives energies that are approximately 10% lower than those reported in our prior work. It is estimated that the activation energies for cross-slip from the fully glide plane state to the partially cross- slipped state at the 120 deg. intersection forming GL in Ni and Cu are approximately 0.47 and approximately 0.65 eV respectively, and from the fully cross-slip plane state to the partially cross-slipped state forming LC are approximately 0.68 and approximately 0.67 eV. The activation energies for cross-slip from the fully glide plane state to the partially cross- slipped state at the 120 intersection forming HL in Ni and Cu are estimated to be approximately 0.09 and approximately 0.31 eV, respectively. These values are a factor of 3-20 lower than the activation energy for bulk cross-slip in Ni and, a factor of 2-6 lower than the activation energy for cross-slip in Cu estimated by Friedel-Escaig analysis. These results suggest that cross-slip should nucleate preferentially at selected screw dislocation intersections in fcc materials and the activation energies for such mechanisms are also a function of stacking fault energy.