High-Pressure Torsion Deformation Induced Phase Transformations and Formations: New Material Combinations and Advanced Properties

Abstract

Heavy plastic shear deformation at relatively low homologous temperatures is called high-pressure torsion (HPT) deformation, which is one method of severe plastic deformation (SPD). The aim of the paper is to give an overview of a new processing approach which permits the generation of innovative metastable materials and novel nanocomposites by HPT deformation. Starting materials can be either coarse-grained multi-phase alloys, a mixture of different elemental powders or any other combination of multiphase solid starting materials. After HPT processing, the achievable microstructures are similar to the ones generated by mechanical alloying. Nevertheless, one advantage of the HPT process is that bulk samples of the different types of metastable materials and nanocomposites are obtained directly during HPT deformation. It will be shown that different material combinations can be selected and materials with tailored properties, or in other words, materials designed for specific applications and the thus required properties, can be synthesized. Areas of application for these new materials range from hydrogen storage to materials resistant to harsh radiation environments.

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

“…[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.…”

“…The elemental mixing improves with increasing the distance from disc center, indicating the importance of shear strain on mechanical alloying and controlling the phase transformation, in good agreement with earlier publications. [32][33][34][35] The microstructure of sample processed by HPT for ten turns was examined in detail using transmission electron microscopy (TEM), as shown in Figure 4, in different modes, such as bright-field imaging (Figure 4a), selected area electron diffraction (SAED) analysis (Figure 4b), dark-field imaging (Figure 4c), automatic orientation mapping (Figure 4d), and phase mapping ( Figure 4e) using an automatic crystal orientation and phase mappings (ASTAR device). Note that the phase map was overlaid with the reliability map in Figure 4e, and thus, the black regions in the image correspond to the phases that could not be identified with high reliability.…”

“…Motivated by earlier studies on the application of the HPT method to as-cast TiFe, [23][24][25] in this study and for the first time, we synthesize the TiFe hydrogen storage materials from the Ti and Fe powders by the HPT method and examine its activation (see the principles of HPT in the previous studies [28,29] ). It should be noted that HPT as a severe plastic deformation (SPD) method shows high potential to produce nanostructures, [30,31] control phase transformations, [32,33] and achieve solid-state reactions. [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.…”

High‐pressure torsion of SiO2 quartz sand: Phase transformation, optical properties, and significance in geology

“…However, the grain size is drastically reduced after HPT processing and the number of diffracted points in the SAED analysis are increased to form a ring pattern in Figure 4D (this pattern was taken from the d area in Figure 4B). Grain refinement by HPT processing is a result of plastic strain effect, which was reported in various metallic 53–55 and nonmetallic 56–58 materials. On the contrary, in Figure 4E, the diffraction points in SAED disappear and a hollow pattern corresponding to amorphous SiO 2 appears (this pattern was taken from the e area of Figure 4B).…”

Formation and Thermal Stability of ω-Ti(Fe) in α-Phase-Based Ti(Fe) Alloys

“…Originally, the SPD methods were utilized to generate bulk nanocrystalline materials that show, in many cases, better physical and mechanical properties than their microcrystalline counterparts [9,10]. Later, it turned out that the unique properties are also facilitated by diffusive and displacive (martensitic) phase transformations, which occur in the material during the HPT process [11][12][13]. However, the mechanism of the phase transformations and the influence of the initial microstructure on the phases formed after HPT are not fully understood yet.In the unary Ti system, titanium exists in three modifications: as hexagonal α-Ti (space group (SG) P6 3 /mmc) that is stable at low temperatures, as cubic β-Ti (SG: Im3m), which is stable at high temperatures, and as hexagonal ω-Ti (SG: P6/mmm), which is stable at high pressures.…”