Cyclic plasticity of nickel, from single crystals to submicrocrystalline polycrystals

A survey is presented covering the results obtained by the present author and his co-workers during the last decade in studies on nickel single crystals and polycrystalline nickel cyclically deformed up to the saturation stage. Two main features of cyclic plasticity are the subject of discussion. The first part of the paper addresses the effect of the deformation temperature on the saturation stress, on the dislocation structure and on the non-uniform distribution of the shear strain in the persistent slip bands (PSBs) of nickel single crystals oriented for single slip. Besides confirming experimental findings known from previous studies on copper single crystals, new results are presented which refer above all to details of the dislocation substructure and to a quantitative evaluation of the spatiotemporal slip activity of PSBs. A second topic concerns polycrystals and focuses firstly on the influence of the grain orientation on the dislocation patterns in the individual grains, and secondly on the effect of the grain size on the dislocation substructure and on the macroscopic stress-strain response. Progress could be achieved especially by combining new imaging techniques of microscopy.