Papers by Keyword: Severe Plastic Deformation (SPD)

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Authors: Xiao Lin Wu, Wei Xu, Masahiro Kubota, Kenong Xia
Abstract: Bulk magnesium was consolidated from pure Mg particles with an average size of ~59 µm by back pressure equal channel angular pressing. The Mg powder was processed at 200°C for 4 and 8 passes, respectively, using route C. The consolidated materials displayed density of 1.78 g/cm3, compared to the theoretical value of 1.74 g/cm3 for pure Mg. Vickers microhardness (HV) values were measured to be about 54. Compressive tests at room temperature revealed yield strengths of 100-110 MPa and ultimate strengths of up to 142 MPa with strains to fracture of ~9%, comparable to those for extruded pure Mg. Microstructures were examined using optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM).
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Authors: Kenong Xia, Wei Xu, Xiao Lin Wu, S. Goussous
Abstract: Severe plastic deformation (SPD) has received considerable attention for its capability to produce ultrafine and nano structured materials. On the one hand, SPD, especially in the forms of equal channel angular pressing (ECAP) and high pressure torsion (HPT) is able to refine bulk materials with coarse grain structures. On the other hand, SPD has been used to synthesise 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 the conventional sintering processing. It is particularly relevant to consolidating particles with non-equilibrium microstructures and to producing complex multiphase alloys. In this summary, ECAP as an effective process to synthesise a range of light metal based materials from particles with various sizes and structures, including aluminium and aluminium composites, titanium and magnesium, will be demonstrated. Full density and good bonding are achieved easily with the application of a back pressure. Microstructures from nano to ultrafine scales have been produced, resulting in significantly enhanced strength. Simultaneous increase in ductility has also been achieved in some alloys by virtue of multi-scale structures.
119
Authors: Kenong Xia
Abstract: The progress in bulk ultrafine and nanostructured materials through consolidation of particles by severe plastic deformation (SPD) is reviewed. The focus is on the processes of high pressure torsion (HPT) and equal channel angular pressing (ECAP) with or without the application of a back pressure. Various materials consolidated are described in terms of their densities, microstructures and mechanical properties. The important processing parameters and their effects on the resulting materials are discussed. It is shown that SPD consolidation of particles is an effective way of producing bulk nanostructured materials although much work is needed to understand the consolidation behaviour and to design the optimum compositions and microstructures.
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Authors: Konstantin Ivanov
Abstract: Characteristic features and thermal stability of the structure of molybdenum processed by high pressure torsion, equal-channel angular pressing or multy-step forging have been investigated using transmission electron microscopy, X-ray diffraction analysis and orientation imaging microscopy. The structural factors responsible for the strengthening and thermal stability of molybdenum processed have been obtained. It has been demonstrated that only high pressure torsion is an effective method to refine molybdenum structure (down to 0.2 µm). Recrystallization occurs during the others investigated processing disabling significant grain size reduction.
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Authors: T. Akaki, H. Morimoto, Hiroshi Numakura, Daisuke Terada, Nobuhiro Tsuji
Abstract: We have studied the crystal defects in severely deformed pure iron, by combining mechanical spectroscopy with measurements of Vickers hardness and electrical resistivity. Iron of 99.99% purity and a material in which the C content is further reduced to below 1 at. ppm were deformed to strains up to 5.6 by accumulated roll-bonding. Mechanical loss and dynamic shear modulus of as-deformed samples were measured over the temperature range from –195°C to 800°C. Effects due to dislocations and grain boundaries have been identified. Thermal stabilities of the defects have been examined through variations in the mechanical loss during heating-run and cooling-run measurements. It is found that the small difference in the carbon content influences the densities of defects and microstructure, as well as the thermal stability. They are consistent with the recovery behaviour observed through hardness and resistivity in isochronal annealing experiments.
233
Authors: Wolfgang Lechner, Werner Puff, Gerhard Wilde, R. Würschum
Abstract: A positron annihilation study of free volumes was performed on Cu-Zr and Al-Sm alloys in the course of repeated cold rolling (RCR) in order to contribute to the microscopic understanding of the complex processes of solid-state amorphization and nanocrystallization. In addition to positron lifetime spectroscopy, which yields information on the size of free volumes, twodimensional Doppler broadening technique was applied in order to study the local chemical environment of free volumes on an atomistic scale. Both in Cu60Zr40 and Al92Sm8 a characteristic variation of the chemical environment of free volumes with the number of folding and rolling (F&R) cycles could be observed. In the first (Al-Sm) and intermediate state (Cu-Zr) of F&R, free volumes with an enhanced amount of Sm or Zr content in the local environment occur, indicating interfacial segregation or the formation of solute-vacancy complexes. Upon further F&R cycling, a complete (Cu-Zr) or partially amorphous structure (Al-Sm) is obtained with the free volumes exhibiting a chemical environment characteristic of the average chemical composition. In contrast to melt-spun or ball-milled amorphous alloys, free volumes of the size of a few missing atoms are found in amorphous alloys prepared by RCR presumably due to strong athermal conditions of F&R cycling.
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Authors: Kyung Tae Park, Eui Gil Lee, Won Jong Nam, Yong Sin Lee
Abstract: Two commercial Al alloys having different second phase particle distributions were subjected to severe plastic deformation (SPD) via equal channel angular pressing with or without subsequent cold rolling, and the effect of such SPD on the particle size distribution of the alloys was investigated. The particles larger than ∼ 3 μm were fragmented into several smaller ones by SPD. Contrarily, those smaller than ∼ 3 μm were hardly broken up by SPD but their distribution became more uniform. Along with these findings and the theoretical models for cavity nucleation at second phase particles, the cavitation behavior of ultrafine grained Al alloys during low temperature or high strain rate superplastic deformation was discussed.
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