Powder consolidation by severe plastic deformation and its applications in processing ultrafine and nanostructured aluminium and composites

Severe plastic deformation (SPD) based processes have shown great potential in producing bulk ultrafine and nanostructured materials. In addition to refining grains, SPD processes such as equal channel angular pressing (ECAP) and high pressure torsion (HPT) can be used to fabricate bulk materials from particles. It enables particles from nano to micro scales to be consolidated into fully dense materials at much lower temperatures and shorter times, compared to conventional sintering. It is especially suitable for producing complex multiphase alloys and nanocomposites. In this paper, the mechanism of SPD consolidation is illustrated using the example of equal channel angular pressing (ECAP) of micro- and nano-scaled pure Al particles. It is shown that consolidation and good bonding require the particles to undergo plastic deformation rather than sliding over each other. In addition to monolithic materials, Al-C composites have been produced in combination with mechanical milling. In another example, Al and Ti particles have been mixed and consolidated using a combination of mechanical alloying and ECAP to obtain ultrafine and nanostructured alloys. In all cases, the mechanical behaviour is dependent on the scale and distribution of the phases, and both strength and ductility can be significantly improved by finer sizes and more uniform distribution, which are achievable through SPD processing.