Dislocations energetic and dynamics in FCC materials

Yue Qi, Alejandro Strachan, Tahir Cagin and William A. Goddard III

Materials and Process Simulation Center, Caltech, Pasadena, CA 91125


Using QM-Sutton-Chen many-body potential, we have studied the <110>/2 screw dislocation in nickel (Ni) via Molecular Dynamics (MD) simulations. We use a recently developed parallel MD code which allows us to study systems on the order of 105 and 106 of atoms; this program scales well until 128 processors.

We have studied different configurations, namely an isolated dislocation in a cylinder with free surfaces, as well as dipole and quadrupole systems with 3-D periodic boundary conditions. The relaxed structures show dissociation into two partials on {111} planes. (Fig [1]) The equilibrium separation distance between the two partials is 2.1 nm, which agrees well with the experimental value of 2.6+/-0.8nm for partials started as edges [Phil. Mag. 35, 1161, (1977)].

We also studied motion and annihilation process of opposite signed dislocations with different combinations of dissociation planes. When two screws dissociated on two crossing or parallel (111) planes, cross-slip has been observed. We find a barrier of 0.1eV/b for cross-slip, and the shortest distance of screw dipole is 8A at 0K.

Fig 1, Relaxed <110>/2 Screw structure, with two Shockley partials and HCP stacking between two partials on 3 layers of (111) planes.

Fig 2. Two opposite sign screws dissociated on the parallel (111) plane. The equilibrium distance of two partials, De drops and the core energy increases as the distance of two (111) planes, Do, decreases. The critical Do is 8A and the core energy barrier is 0.1eV/b, which corresponds to the cross-slip activation energy at 0K.




This research was founded by a grant from DOE-ASCI-ASAP. The facilities of the MSC are also supported by grants from NSF (MRI CHE 99), ARO (MURI), ARO (DURIP), NASA, BP Amoco, Exxon, Dow Chemical, Seiko Epson, Avery Dennision, Chevron Corp., Asahi Chemical, 3M and Beckman Institute.