Nanostructured materials, in which the structural features (e.g., grains and/or domains separated by low-angle grain boundaries) are smaller than 100nm in at least one dimension, have attracted worldwide research interest for more than a decade because of their unique properties. For example, the combination of high strength with high ductility has been reported for some nanostructured metals and alloys: this is a rare, if not impossible, combination of mechanical properties for coarse-grained metals and alloys. Among the many techniques available for producing nanostructured materials, severe plastic deformation (SPD) is the most popular and most rapidly developing one.