Abstract
A new model of creep at intermediate temperatures in Al is presented, based on a set of previous results of in situ experiments. This model explains the origin of the high forward stresses necessary to extract dislocations from sub-boundaries, and the strong correlation between the speed of sub-boundary migration and the creep rate, asevidenced at different temperatures and by means of in situ strain-rate jumps. High stresses originate from incompatibilities of glide which occur during migration. Under such conditions, it is shown that the creep rate is controlled by a geometrically necessary glide of screw dislocation segments in {100} planes, i.e. by nucleation and propagation of kinks in these non-compact. As the kink energy is estimated from an experimental determination of the ‘dissociation’ energy in Al, all the parameters of the creep law are in good agreement with experimental values.