Severe plastic deformation (SPD) is one of the methods of obtaining sub-microcrystalline structure in different crystallographic systems (e.g. aluminium, iron, magnesium). SPD causes the creation of micrometer and sub-micrometer sized subgrains in the original coarse grains of the material. The mechanism responsible for this effect is still under investigation, however, it is believed that short and long-range intersecting shear bands, produced by plastic deformation, play a major role. Sufficiently large deformation leads to a distinct structure of dislocation-free and highly misoriented fine grains.
The structural changes caused by SPD are reflected in improved mechanical properties of metals. The reported effects include increased hardness and yield stress, both featuring tendency to saturation. Other research revealed increased ductility and toughness as well as improved dumping and magnetic properties. The fine grain structure leads to superplastic behaviour of materials at lower temperatures and yet with higher deformation rates than for other superplastic materials.
Various aspects of structural changes caused by SPD have been the main research topic so far. Less attention has been paid to the mechanics of material flow and practical aspects of SPD. Anticipating commercialisation attempts, this work addresses the processing issues. First, a brief review of SPD processes will be undertaken. Next, the three most popular SPD processes of high pressure torsion (HIT), cyclic extrusion compression (CEC) and equal channel angular pressing (ECAP) will be analysed in more detail. This analysis will include strain distribution and the role of hydrostatic pressure and friction. These, in turn, will be used to address tooling concerns. Appropriate billets and feeding systems will also be considered. Survey of possible applications will show the routs of commercialisation. Finally, future developments of SPD will be suggested.