Dislocation dynamics and multiplication via atomistic simulations

Abstract
Molecular Dynamics simulations of edge dislocation mobility under stress in ordered Ll₂ Ni₃ Al have been performed between 10K and 1000K, and at applied shear stresses ranging from 0.01 to 0.08 C₄₄. In this way it has been possible to determine the Peierls stress and mobility parameters as a function of stress and temperature. <001>{100} edge dislocations were studied, which split into closely spaced partials under stress. Under all levels of applied stress (and at lower temperatures) the initial partial dislocations would intermittently stop moving and recombine, then dissociate and move again. In all cases the dislocations exhibited a soliton-like behavior : infinite acceleration at the onset of movement, and further movement at a steady velocity (which was only weakly dependent on stress) on the order of 25% of the acoustic shear velocity . Non-classical, highly non-linear behavior was observed indicating the probability that a soliton picture of dislocation motion is more appropriate than the classical, "massive string" model that is traditionally used. Furthermore, as both the temperature and the stress were increased, dislocation multiplication became increasingly frequent, ultimately resulting in a spontaneous amorphisation transition which has signs of being a percolation process.