Vladimir Segal

Severe plastic deformation: simple shear versus pure shear

The paper analyzes an effect of deformation mode on structure evolution under severe plastic deformation. From a continuum standpoint, all possible strain states range from pure shear to simple shear and can be described by a single parameter. The microstructure evolution at large strains is linked with successive steps of continuous flow and flow localization. It is shown that simple shear conforms to the optimal deformation mode for development of spatial networks of high angle boundaries and fine grains during flow localization both for monotonic loading and cross loading. Using this approach, different deformation techniques for simple shear processing are considered with the emphasis on equal channel angular extrusion.

Slip line solutions, deformation mode and loading history during equal channel angular extrusion

Equal channel angular extrusion (ECAE) is analyzed by the slip line method. Full solutions are considered in function of contact friction, backpressure and tool design. It is shown that variations in boundary conditions have a moderate effect on equivalent strains but the strain distribution depends noticeably on friction uniformity and the channel geometry. The characteristic deformation mode corresponds to single shear or to sequence of shears along slip lines. The processing mechanics plays an especially important role in the loading history of material elements. During one pass, monotonic loading is realized only in the cases of zero and maximum friction. For intermediate friction, the deformation history is composed by cross loading into three divergent directions. Multi pass ECAE via different routes is linked with a grain refinement mechanism under severe plastic deformation.