Nanomaterials by Severe Plastic Deformation: NanoSPD5

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Authors: Ruslan Valiev
Abstract: Nanjing University is hosting the 5-th in a row of NanoSPD conferences, which continues a series of the preceding conferences: in Moscow (1999), Vienna (2002), Fukuoka (2005) and Goslar (2008). This paper highlights the major landmarks of NanoSPD activity for the past years from the standpoint of the International NanoSPD Steering Committee. Special attention is given to topics relating to nanostructuring of metals by SPD processing for advanced properties as well as new trends in developing SPD techniques for practical application. Another concern of the committee is in introduction and discussion of the terminology applied in this new field of science and engineering.
Authors: Terence G. Langdon
Abstract: It is well established that processing through the application of severe plastic deformation (SPD) provides opportunities for achieving exceptional grain refinement to the submicrometer or even the nanometer level. This paper provides a brief summary of the developments in SPD processing from the earliest days in ancient China to research at the present time. It is shown that SPD research and bulk nanostructured materials have had a significant impact on the field of Materials Science. Using citation data and examining the publication records for five major journals, the analysis shows research in these areas accounts for a large fraction of the top ten all-time most cited papers in these journals.
Authors: Koichi Tsuchiya, Octav Ciuca
Abstract: Process of nanostructure formation and amorphization by high pressure torsion (HPT) were studied for various intermetallic compounds. In ZrCu after HPT deformation, optical microscopy revealed that numerous shear bands formed running nearly parallel to the shear direction. Partial amorphization was confirmed by X-ray diffraction and TEM observations. Detailed TEM observations revealed localized amorphization within the nano-scale shear bands. For HPT deformation of zone-melted Zr50Cu40Al10 the preferential amorphization of ZrCu phase was observed. On the contrary, amorphization was not observed for Ni3Al even after HPT deformation of 100 turns; the sample remained to be disordered nanocrystalline of about 50 nm. The process and mechanism of the grain refinement and amorphization will be compared and discussed for these intermetallic compounds.
Authors: Rimma Lapovok, Yuri Estrin, Richard Djugum, Andre Lerk
Abstract: Among the known severe plastic deformation (SPD) techniques, there is a special group of processes involving friction-induced shear. One of the sample or work-piece dimensions used in such processes, namely the thickness, is much smaller than the other two dimensions. The well-known process of High Pressure Torsion (HPT) and the relatively new Cone-Cone (CC) method applied to thin conical samples fall into this category of SPD techniques. Wrought aluminium alloy 2124 was used to study the effect of CC processing on microstructure and mechanical properties. The influence of the processing parameters, including the rotation speed and thickness of the conical strip specimens on the microstructure and the mechanical properties of the CC-processed material was investigated.
Authors: Viktor Varyukhin, Yan Beygelzimer, R. Kulagin, O. Prokof'eva, Alexey Reshetov
Abstract: We present a study of the kinematics of Twist Extrusion (TE) and show that the mode of deformation in ТЕ is a simple shear. Unlike in Equal-Channel Angular Pressing (ECAP), there are two main shear layers perpendicular to the specimen axis. TE has a significant commercial potential due to the following physical effects: intensive grain refinement; homogenization and mixing; intensive powder consolidation. Donetsk Institute for Physics and Engineering created a TE Center to showcase the process and educate investors. Our experience with the center has shown that the most prospective directions are producing ultrafine-grained (UFG) alloys for medical and aircraft applications.
Authors: Werner Skrotzki, Robert Chulist, Benoît Beausir, Matthias Hockauf
Abstract: Equal-channel angular pressing (ECAP) was applied to polycrystalline NiAl at temperatures around the brittle-to-ductile transition temperature (BDTT). NiAl rods encapsulated in a steel jacket were ECAP-processed in a die with a channel angle of 120°. The microstructure and texture were characterized by electron backscatter diffraction with a scanning electron microscope. The volume fraction of the texture components typical for simple shear in the intersection plane of the channels changes in the range of the BDTT.
Authors: Farid Z. Utyashev
Abstract: Nanostructured (NS) metallic materials can exhibit high strength at room temperature and superplastic properties at elevated temperatures. This enables to enhance their technological and structural properties, when producing various parts from them. For producing NS materials by severe plastic deformation (SPD), the development of effective SPD techniques for practical use is an urgent task. It is shown that solution of such a task should take into account strain compatibility on the macro-, meso- and micro-levels. Not only shear but also rotational deformation mode should be considered. Properties of NS materials and possibilities of their structural applications are considered from this point of view.
Authors: Hideaki Iwaoka, Yosuke Harai, Z. Horita
Abstract: High-pressure torsion (HPT) was conducted with ring samples of pure Al (99.99%) having different thicknesses. They were cut from an Al plate with 10 mm thickness to dimensions having inner and outer diameters of 23 and 30 mm with thicknesses of 2 mm or 4 mm. HPT was conducted at room temperature under a pressure of 1 GPa at a rotation speed of 1 rpm. It is shown that the strain was introduced more intensely in the mid part on the cross section. This strained region extended with increasing number of revolution and covered throughout the cross section in the 2 mm thickness ring after 30 revolutions. The intense-strained region extended to ~3 mm in the 4 mm thickness ring after 30 revolutions but remains almost the same even after 100 revolutions. The thickness of ~3 mm may be an upper limit to achieve homogeneous introduction of the strained region throughout the cross section.
Authors: Andrey Molotnikov, Rimma Lapovok, Tao Peng, Yuri Estrin
Abstract: Densification of metallic powders by means of extrusion is regarded as a very attractive processing technique that allows obtaining a high level of relative density of the compact. However, the uniformity of the relative density depends on that of strain distribution and on the processing parameters. Several variants of extrusion can be used for compaction of metal particulates, including the conventional extrusion (CE) and equal channel angular pressing (ECAP), often referred to as equal-channel angular extrusion. Each of these processes has certain advantages and drawbacks with respect to compaction. A comparative study of these two extrusion processes influencing the relative density of compacts has been conducted by numerical simulation using commercial finite element software DEFORM2D. The results have been validated by experiments with titanium and magnesium powders and chips.

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