Competing deformation mechanisms in nanocrystalline metals and alloys: Coupled motion versus grain boundary sliding

Plastic deformation of nanocrystalline Pd and Cu as well as the demixing systems Cu–Nb and Cu–Fe is studied by means of atomic-scale computer simulations. The microstructures are specifically chosen to facilitate mesoscopic grain boundary sliding. The influence of segregating solutes on the deformation mechanisms is studied and different cases of solute distributions are compared. We find that the competition between mesoscopic grain boundary sliding and coupled grain boundary motion is controlled by the concentration and distribution of segregating solutes. By analyzing the microstructural evolution and dislocation activity we make a connection between the atomistic solute distribution and the mechanisms of deformation, explaining the observed stress–strain behavior. The detailed analysis of the normal grain boundary motion reveals a stick–slip behavior and a coupling factor which is consistent with results from bicrystal simulations.