In situ TEM observations of reverse dislocation motion upon unloading in tensile-deformed UFG aluminium

An in situ transmission electron microscopy study has been performed on ultrafine-grained (UFG) aluminium during tensile loading and unloading in the microyield regime. The goal was to assess the reasons for the unusually large inelastic backflow that had been observed earlier during unloading on UFG material, as compared to that of conventional grain size material. It was noted that in particular edge dislocations emitted by sources within the grains during loading run back into the dislocation sources and disappear during unloading, explaining at least semi-quantitatively the rather large inelastic backflow in UFG material.