Atomistic simulations of cross-slip nucleation at screw dislocation intersections in face-centered cubic nickel

Abstract

The Escaig model for thermally activated cross-slip in face-centered cubic (fcc) materials assumes that cross-slip preferentially occurs at obstacles that produce large stress gradients on the Shockley partials of the screw dislocations. However, it is unclear as to the source, identity and concentration of such obstacles in single-phase fcc materials. Embedded atom potential, molecular-statics simulations of screw character dislocation intersections with 120° forest dislocations in fcc Ni are described that illustrate a mechanism for cross-slip nucleation. The simulations show how such intersections readily produce cross-slip nuclei and thus may be preferential sites for cross-slip. The energies of the dislocation intersection cores are estimated and it is shown that a partially cross-slipped configuration for the intersection is the most stable. In addition, simple three-dimensional dislocation dynamics simulations accounting for Shockley partials are shown to qualitatively reproduce the atomistically determined core structures for the same dislocation intersections.

Keywords:

• cross-slip
• dislocation intersections
• atomistic simulations
• embedded atom potentials
• dislocation dynamics simulations

Acknowledgements

The authors acknowledge use of the 3D molecular dynamics code, LAAMPS, which was developed at Sandia National Laboratory by Dr. Steve Plimpton and co-workers. The authors also acknowledge use of the ‘Matlab’ version of 3D dislocation dynamics code, ParaDiS, which was developed at Lawrence Livermore National Laboratory by the ParaDiS team. This work was supported by the AFOSR, and by a grant of computer time from the DOD High Performance Computing Modernization Program, at the Aeronautical Systems Center/Major Shared Resource Center. The work was performed at the U.S. Air Force Research Laboratory, Materials and Manufacturing Directorate, Wright-Patterson AFB.