Place: Materials Science and Engineering 2008, Nürnberg, Germany
Two-dimensional Dislocation Dynamics (DD) simulations are employed to study the different mechanisms of plastic deformation of ultra fine grained (ufg) metals at different temperatures. Besides conventional plastic deformation by dislocation glide within grains, we also consider grain boundary mediated plasticity by incorporating grain boundary sliding and grain boundary diffusion into the DD model. This is achieved by splitting up dislocations encountering a grain boundary into a glide and a climb part. The first one is moving conservatively along the grain boundary and thus causing grain boundary sliding; the latter moves under production or annihilation of vacancies. The motion of the climb part thus requires calculating the local concentration of vacancies within the grain boundary network. This is accomplished by solving the diffusion equation and coupling it to the dislocation motion via source and sink terms. The local vacancy concentration in turn exerts an osmotic force on the climb dislocations. The “material” is modeled as an elastic continuum that contains a defect microstructure consisting of a preexisting dislocation population, dislocation sources, and grain boundaries. The mechanical response of such a material is tested by uniaxially loading it up to a certain stress and allowing it to relax until the strain rate falls below a given threshold. The maximum plastic strain obtained for a certain stress yields the quasi-static stress-strain curve of the material. The quality of results is investigated by comparing with experimental results known from the literature.