Dynamic behaviour of mixed dislocations in FCC metals under multi-oriented loading with molecular dynamics simulations

Conventional models of plastic deformation are based on linear elastic approximations with respect to the empirical results obtained from pure screw or pure edge dislocations. In real materials, however, mixed dislocations are far more commonly observed and their motion carries the bulk of the plastic deformation. Molecular dynamics (MD) simulations are useful to 'unlock' the temperature and structure dependence of the phonon drag effect, and the phonon drag strongly influences the mobility of dislocations in FCC metals. The Burgers vector of a dislocation dictates the necessary orientation of the stress required to control the glide behaviour. Hence, the mobility of mixed dislocations can only be studied once the stress can be carefully controlled for both the τ xy and τ yz components simultaneously. It is non-trivial to accurately control the global stress components effectively under multi-orientation testing. To this end, the present study evaluates the effectiveness of utilising a well-tuned barostat to show the influence of stress loading orientation on the mobility of a mixed 30° dislocation dipole. Self-consistent results with two different EAM potentials and size-independent steady-state velocities (excluding only the lowest stress and smallest size case), suggest that this approach is valid. The glide stress, τ g , is contrasted with the shear component in a perpendicular orientation within the glide plane, referred to as the Escaig stress, τ e . When the appropriate stress control regime and cell dimensions were applied, the influence of dipole image forces were mitigated down to stresses as low as 5 MPa. The stacking fault width was influenced by τ e in an identical manner for the two different EAM potentials, once compensation was made to offset the discrepancy in the stacking fault energy.