Metallurgical Alchemy by Ultra-Severe Plastic Deformation via High-Pressure Torsion Process

Abstract

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. [

Synthesis of Nanostructured TiFe Hydrogen Storage Material by Mechanical Alloying via High‐Pressure Torsion

“…In summary, this study together with earlier studies on the application of HPT for synthesis or processing of hydrogen storage materials confirm the potential of method for future developments in this field. As the addition of a third element to TiFe, such as Pd, Ni, Mn, and Zr, can facilitate the activation, synthesis of such ternary intermetallics by HPT can be considered as a potential future application.…”

“…[24] However, the concentration of oxygen contamination and/or the level of oxidation is always more significant, when powders are processed by the HPT method. [32,68,69] In summary, this study together with earlier studies on the application of HPT for synthesis [54][55][56][57][58] or processing [49][50][51][52][53] of hydrogen storage materials confirm the potential of method for future developments in this field. As the addition of a third element to TiFe, such as Pd, [11] Ni, [12] Mn, [13][14][15][16] and Zr, [17][18][19] can facilitate the activation, synthesis of such ternary intermetallics by HPT can be considered as a potential future application.…”

“…To have a complete and uniform phase transformation, larger shear strains should be applied, as attempted earlier for other materials. [36][37][38][39][40][41][42][43][44][45][46][47][48][54][55][56][57][58] However, the main reason that larger shear strains were not applied in this study was due to the extremely high hardness of TiFe at large number of turns, which could make significant damage to the HPT anvils.…”

“…Automatic phase mapping using the ASTAR device in Figure e shows the presence of some amount of HCP phase even at 3–5 mm away from the disc center, suggesting that the mechanical alloying is not completed. To have a complete and uniform phase transformation, larger shear strains should be applied, as attempted earlier for other materials . However, the main reason that larger shear strains were not applied in this study was due to the extremely high hardness of TiFe at large number of turns, which could make significant damage to the HPT anvils.…”

“…[34,35] The method was used successfully by the group of authors to synthesize various kinds of nanostructured intermetallics in different systems, such as Al-Ni, [36] Al-Ti, [37] Al-Cu, [38] Al-Ti-Ni, [39] Fe-Ni, [40] Mg-Ti, [41,42] Mg-Zr, [43] Mg-Hf, [44] Mg-Ni-Pd, [45] and Mg-V-Cr. [46] It is worth mentioning that, following publication of two articles in 2004 [47] and 2007, [48] the HPT process became popular not only for processing [49][50][51][52][53] but also for synthesizing [54][55][56][57][58] various kinds of hydrogen storage materials.…”