Metallurgical alchemy by ultra-severe plastic deformation via high-pressure torsion process

Ultra-severe plastic deformation (ultra-SPD) is defined as the SPD processes in which the shear strains over 1,000 are introduced to a work piece. Despite significant activities on various SPD processes, limited studies have been conducted on the behavior of materials at shear strains over 1,000. The main reason for such limited studies is a consensus that the microstructural, mechanical and functional features usually saturate to the steady states at shear strains below 100. However, recent studies using the high-pressure torsion (HPT) method confirmed that significant changes occur at shear strains in the range of 1,000100,000. Here, some of the main findings reported recently by the application of ultra-SPD are reviewed: appearance of new levels of steady-state microhardness, atomic-scale elemental mixing in the miscible and immiscible systems, formation of new nanostructured phases/intermetallics, achievement of ultrahigh strength/high plasticity/room-temperature superplasticity, and development of advanced superconductors and hydrogen storage materials.