A dislocation dynamics based higher-order crystal plasticity model and applications on confined thin-film plasticity

A higher-order crystal plasticity model based on the continuum description of dislocation dynamics is developed to investigate the confined thin-film plasticity at micro-scale. In this model the “back stress” and the “slip resistance” for each slip system are incorporated into a standard diffusion equation for crystal slip, which accounts for the motion of dislocations in a continuum level. Furthermore, a surface energy based interfacial model is introduced here to take account of the interaction between dislocations and the interface. It can provide a more comprehensive study of the interface effect on the confined crystal plastic behavior rather than the two extreme boundary models used in other higher-order crystal plasticity models in which the dislocations can freely or hardly pass through the crystal interface. Then by implementing these models into finite element code the tensions of single-crystal/polycrystal thin Al films with passivation layers are numerically investigated. Two hardening factors associated respectively with the “back stress” and “slip resistance” are qualitatively studied, and it can be concluded from present study that the “back stress” hardening may dominate the strengthening of flow stress in confined thin-film plasticity at sub-micro scale. The interfacial model is applied to successfully model the interactions of dislocation with the film-passivation interfaces.