Dislocation velocities and mobilities were studied using molecular dynamics simulations for edge and screw dislocations in pure Al and Ni, and edge dislocations in Al–2.5%Mg and Al–5.0%Mg random substitutional alloys using EAM potentials. In the pure materials, the velocities of all dislocations were close to linear with the ratio of (applied stress)/(temperature) at low velocities consistent with phonon drag models, and quantitative agreement with the experiment was obtained for the mobility in Al. At higher velocities, different behaviour was observed. The edge dislocation velocity remains dependent solely on (applied stress)/(temperature) up to approximately 1.0MPa/K, and approaches a plateau velocity that was lower than the smallest 'forbidden' speed predicted by continuum models. In contrast, above a velocity around half of the smallest continuum wave speed, the screw dislocation damping has a contribution dependent solely on stress with a functional form close to that predicted by a radiation damping model of Eshelby. At the highest applied stresses, there were several regimes of nearly constant (transonic) velocity separated by velocity gaps in the vicinity of forbidden velocities; various modes of dislocation disintegration and destabilization were also encountered in this regime. In the alloy systems, there was a temperature- and concentration-dependent pinning regime where the velocity drops sharply below the pure metal velocity. Above the pinning regime but at moderate stresses, the velocity was again linear in (applied stress)/(temperature) but with a lower mobility than in the pure metal.

Atomistic Simulations of Dislocation Mobility in Al, Ni and Al/Mg Alloys. D.L.Olmsted, L.G.Hector, W.A.Curtin, R.J.Clifton: Modelling and Simulation in Materials Science and Engineering, 2005, 13[3], 371-88