Grain boundary sliding in irradiated stressed Fe-Ni bicrystals: a molecular dynamics study

Molecular dynamics simulations were used to model grain boundary sliding in stressed Fe-Ni bicrystals exposed to low energy neutron irradiation. We studied how sliding stress thresholds and sliding mechanisms changed with variations in the Ni boundary morphology and boundary geometry. Simulations corresponding to ordered boundary Ni distributions and coincident-site lattice (CSL) geometries relaxed stress through a dislocation-mediated sliding mechanism. Such a mechanism was found to follow Orowan's law, in which the stress relaxation rate is proportional to the dislocation velocity. Alternatively, simulations of disordered Ni distributions and non-CSL boundary geometries were described by a random shuffling process with time-dependent stress relaxation rate. Nevertheless, irrespective of the stress relaxation process followed by the bicrystals, after reaching equilibrium, the amounts of boundary displacement and stress relaxation were always found to be proportionally related. These observations might prove useful to groups working on building continuum (macroscopic) models of deformations in irradiated materials.