MATERIALS TRANSACTIONS
Online ISSN : 1347-5320
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  • Kaveh Edalati, Zenji Horita
    Type: Preface
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1103
    Published: July 01, 2019
    Released: June 25, 2019
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  • Takahiro Masuda, Zenji Horita
    Type: Regular Article
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1104-1110
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: April 05, 2019
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    This study presents application of an up-scaled high-pressure torsion (HPT) process to AZ31 and AZ61 Mg alloys for ultrafine grain refinement. Disks with 30 mm diameter were processed at room temperature under 6 to 7 GPa using the up-scaled HPT facility with a maximum capacity of 5 MN (500 ton). Microstructural evolution was evaluated by hardness measurement and microscopy observations including tensile testing. The grain size was well refined to ∼150 nm and ∼100 nm at the saturated state for the AZ31 and AZ61 alloys, respectively. Superplastic elongations of ∼520% and ∼550% were then attained in the corresponding alloys when tested in tension at elevated temperatures because of the grain boundary sliding controlled by grain boundary diffusion. Upsizing of the disk sample makes for a chance to extract the tensile specimens at different radial distance within the same disk and therefore the effect of the equivalent strain on the superplastic elongations was effectively evaluated.

  • Hiromi Miura, Yu Iwama, Masakazu Kobayashi
    Type: Regular Article
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1111-1115
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: May 31, 2019
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    Microstructure and mechanical properties induced either by heavy cold rolling or multi-directional forging of Cu–Al alloy were investigated and compared. While both microstructures were developed mainly by a mechanism of mechanical twinning, the features were completely different. The former exhibited a typical heterogeneous nano-structure where “eye” shaped twin domains were surrounded by deformation bands and they were further embedded in low-angle lamellae. The latter also showed complicated feature where twin domains and ultrafine grains composed of equi-axed nano-grains were randomly distributed. Even while the latter possessed finer grain size, the former showed more superior mechanical properties, yield strength of 863 MPa and ultimate tensile strength of 1168 MPa than the latter, yield strength of 720 MPa and UTS of 870 MPa.

     

    This Paper was Originally Published in Japanese in J. Japan Inst. Copper 57 (2018) 59–64.

    Different microstructures evolved in a Cu–7 mass%Al alloy by (a) multidirectional forging to ΣΔε = 6.0 and (b) 90% cold rolling. Areas having largely different lattice lines, which suggest evolved nano-grains, were indicated by circles in (a). Lamellae were subdivided by nano-twins in (b). Fullsize Image
  • Shigeru Kuramoto, Tadahiko Furuta
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1116-1122
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: June 07, 2019
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    In the present article, recent reports on microstructure and mechanical properties in SPDed Fe–Ni–Co–Ti and Fe–Ni–Al–C alloys are overviewed. The chemical compositions in these alloys have been determined to have lattice softening where the elastic constant C′ goes to a very small value. The alloys with lattice softening were processed with severe plastic deformation, SPD, to raise the strength. Here, SPD includes severe cold working by rotary swaging, cold rolling and high-pressure torsion. These alloys have been reported to have ultrahigh strength along with good tensile ductility and the balance of strength and ductility is better than that in conventional high-strength steels. Microstructural development during the SPD process and the relation between microstructure and mechanical properties in SPDed alloys are summarized. The phase stability of γ has an important role in the microstructural development during SPD process and deformation behavior in the subsequent mechanical testing. The untransformed γ has a potent capability for plastic deformation where strain-induced transformation and deformation twinning can be expected to occur during mechanical tests after SPD processing. Simultaneous activation of these deformation mechanisms during plastic deformation would be a common feature in the lattice softened alloys, but the effects of alloying elements and phase stability on the deformation behavior have not been understood yet.

  • Megumi Kawasaki, Terence G. Langdon
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1123-1130
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: May 31, 2019
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    Superplasticity refers to the ability of some metals, in special testing conditions, to exhibit high elongations of at least 400% before failure. Although this phenomenon appeared initially as a scientific curiosity, it has now become the basis for the large superplastic forming industry which makes significant contributions in many areas including the aerospace and automotive sectors. Early experiments established that superplastic flow requires a small grain size, typically below ∼10 µm, and this is generally achieved through appropriate thermomechanical processing. However, the grain sizes achieved in this way are typically of the order of a few micrometers. Recent investigations of the processing of metals through the application of severe plastic deformation (SPD) demonstrated that these techniques provide an opportunity to achieve much smaller grain sizes to the submicrometer or even the nanometer scale and this gives opportunities to develop new investigations of superplastic flow. Accordingly, this overview summarizes some of the major contributions of SPD processing to research in the area of superplasticity with an emphasis on the characteristics of the flow behavior.

  • Jae-Kyung Han, Jae-il Jang, Terence G. Langdon, Megumi Kawasaki
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1131-1138
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: May 31, 2019
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    This report presents an overview of recent studies demonstrating a bulk-state reaction involving mechanical bonding through the application of high-pressure torsion (HPT) processing on two dissimilar engineering metals. This processing approach was developed by revising the sample set-up and applying the simple procedure of alternately stacking two different metal disks using several different metal combinations. Thus, this report describes the development in microstructure after the bulk-state reactions and the mechanical properties of the HPT-induced Al–Mg, Al–Cu, Al–Fe and Al–Ti alloy systems. A microstructural evaluation confirmed the capability of the HPT procedure for the formation of heterostructures across the disk diameters in these processed alloy systems. Tribology tests and hardness values together with density measurements demonstrated an improved wear resistance and an exceptional specific strength in these alloy systems. The bulk-state reaction by HPT demonstrates a considerable potential for the bonding of dissimilar metals and the fabrication of unique metal systems.

  • Pedro Henrique R. Pereira, Roberto B. Figueiredo
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1139-1150
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: June 07, 2019
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    Finite element modelling (FEM) has been extensively performed to study the flow process, the distribution of hydrostatic stress and the temperature rise in materials processed by high-pressure torsion (HPT). This overview provides a summary and a critical assessment of the most important findings obtained by means of these FEM simulations which permitted a better understanding about the microstructural evolution during processing by HPT. For convenience, FEM investigations focused on examining the nature of the HPT facility, the plastic flow, the hydrostatic pressure and the temperature evolution in HPT processing were separated into different topics. It is shown the distributions of strain, temperature and hydrostatic pressure along the disc diameter depend upon different factors such as the configuration of the HPT facility and the dimensions of the processed sample.

    Fig. 5 Overall shape of discs processed through up to one turn of HPT processing using a nominal pressure of 1.0 GPa, a rotation rate of 1 rpm and a shear friction coefficient of 1.0 outside the depression area. Reproduced with permission.13) Copyright 2011, Elsevier. Fullsize Image
  • Xavier Sauvage, Amandine Duchaussoy, Ghenwa Zaher
    Type: Review
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1151-1158
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: May 31, 2019
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    Severely deformed materials intrinsically contain a large density of crystalline defects like dislocations or boundaries. The interactions between solute atoms or impurities with these defects play a key role in the grain refinement mechanisms as they affect dynamic recovery. This short review manuscript focusses on grain boundary segregations resulting from severe plastic deformation. The important contribution of atom probe tomography for the quantitative characterization of such segregations in various metallic alloys is at first highlighted. Then, a special emphasis is given on the physical mechanisms leading to strain induced segregations and on the connection that is sometimes observed with dynamic precipitation during severe plastic deformation. The last section is devoted to the influence of such grain boundary segregations in ultrafine grained alloys on the mechanical properties and on the thermal stability.

    Fig. 9 3D reconstruction of a volume (88 × 88 × 110 nm3) analyzed by APT in a 2024 Aluminum alloy processed by HPT at RT (shear strain ∼ 300) and aged at 150°C. Al atoms are displayed in blue, Mg atoms in green and Cu atoms in red. It clearly exhibit intensive GB segregation and stabilization of the UFG structure resulting from SPD. Fullsize Image
  • M. Demirtas, G. Purcek
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1159-1167
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: May 31, 2019
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    Achieving superplasticity at high temperatures and at very low strain rates is considered to be the most important disadvange of superplastic forming processes. Therefore, it is crucial to achieve superplastic behavior at low temperatures and high strain rates. To do so, it is well known that, high amount of grain refinement in the superplastic material is required. Very recent advances in severe plastic deformation (SPD) techniques based on imposing very high strains to the material provide abnormal grain refinement, and ultrafine-grained (UFG) microstructures can be achived in metallic materials by this manner. Formation of UFG microstructures via SPD methods like equal channel angular pressing (ECAP), high pressure torsion (HPT) and friction stir processing (FSP) bring about superplastic behavior in some classes of alloys even at room temperature (RT) as an extreme example of low temperature superplasticity. This paper overviews the studies aiming to investigate the RT superplasticity in some specific metals and alloys after UFG formation by SPD methods. UFG formation or nanostructuring of the materials by SPD to attain RT superplasticity were analyzed in detail. Also, the parameters affecting the RT superplasticity in different classes of materials and superplastic deformation mechanisms operated at RT superplasticity were explained.

  • Yoshifumi Ikoma
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1168-1176
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: June 07, 2019
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    Severe plastic deformation (SPD) has been widely studied in order to enhance the strength and ductility of metallic materials. Among various SPD processing techniques, high-pressure torsion (HPT) can be applied to various brittle materials including semiconductors. In this overview, we report on the HPT processing of Si, Ge, and compound semiconductor GaAs. When crystalline Si was subjected to HPT, metastable body-centered-cubic (bcc) Si-III and rhombohedral Si-XII as well as amorphous regions were formed. After annealing, Si-III and Si-XII reversely transformed to diamond-cubic Si-I. No appreciable photoluminescence (PL) peak was observed from the as-HPT processed samples while a broad PL peak originating from Si-I nanograins appeared after annealing. The electrical resistivity was increased just after compression without anvil rotation, but it decreased after HPT-processing because of the formation of semimetallic Si-III. In the case of Ge, metastable tetragonal Ge-III was formed by room-temperature HPT processing. A broad PL peak originating from diamond-cubic Ge-I nanograins was observed after annealing. The metastable bcc Ge-IV was observed in the cryogenic-HPT-processed samples. In the case of GaAs, no metastable phase was observed in the HPT-processed samples. A strong PL peak associated with the bandgap disappeared after HPT processing. An additional PL peak in the visible light region appeared after annealing. These results suggested that noble properties such as optical and electrical properties can be obtained by applying HPT processing to semiconductor materials.

    Fig. 20 Schematic diagram of phase transformation and grain refinement mechanism of semiconductor materials by HPT processing. Fullsize Image
  • Laszlo S. Toth, Cai Chen, Arnaud Pougis, Mandana Arzaghi, Jean-Jacques ...
    Type: Review
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1177-1191
    Published: July 01, 2019
    Released: June 25, 2019
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    The High Pressure Tube Twisting (HPTT) process was first proposed in 2009 as an efficient new Severe Plastic Deformation (SPD) process. Since then it has been successfully applied on many different materials and the results have been reported in several publications and thesis works. The purpose of this overview is to present and evaluate the main results of the published papers and thesis works and also to present new contributions. Special attention is given to the strain gradient which appears in the tube wall for which a new empirical formula is presented.

  • V. Beloshenko, Iu. Vozniak, Y. Beygelzimer, Y. Estrin, R. Kulagin
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1192-1202
    Published: July 01, 2019
    Released: June 25, 2019
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    Severe plastic deformation (SPD) has come to the fore over the last decades as a potent way to improve the mechanical and physical properties of metallic materials. The use of such techniques for polymers has a long history and can be proud of its significant achievements, but they are less familiar to the metal research community. This review provides insights in the use of SPD techniques to modify the microstructure and properties of polymers and summarizes the salient results obtained in this area. It is hoped that this exposé will be of interest to the broader materials community, beyond the borders of polymer research.

  • Hadi Razavi-Khosroshahi, Masayoshi Fuji
    Type: Review
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1203-1208
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: May 31, 2019
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    Photocatalytic activity of most metal oxides is restricted to the ultraviolet (UV) range of solar spectrum due to their large band gap. Since UV accounts for only 5% of the solar spectrum, designing metal oxide semiconductors with capability of absorbing visible light has been widely attempted. The large band gap of metal oxides can be reduced by various methods like doping with metallic or non-metallic ions, however a better photocatalytic activity can not be achieved necessarily by these methods due to fast recombinations of electron and hole. In recent years, authors have paid attention to the high pressure phases of metal oxides, which theoretically possess narrow band gaps, being able to absorb visible light. In this review, high pressure phases of well-known metal oxides like titania (TiO2), zirconia (ZnO), and yttria (Y2O3) have been stabilized by applying a severe plastic deformation method, and photocatalytic properties of them have been evaluated.

  • V.V. Popov, E.N. Popova
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1209-1220
    Published: July 01, 2019
    Released: June 25, 2019
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    Nowadays potentialities of obtaining bulk nanostructured materials with unique properties by various techniques of severe plastic deformation (SPD) are comprehensively studied, and niobium, being a refractory, but plastic enough metal, is an ideal object for such studies. Besides, niobium is a metal of special interest as an advanced functional material, being one of the main constituents of such important electro-technical materials as high-strength Cu–Nb composites and multifilamentary Nb3Sn-based and NbTi superconductors. The present paper is an overview on evolution of Nb microstructure under SPD via different routes and under large plastic deformation by cold drawing of composite wires (in a Cu matrix). The main attention in this paper is paid to the original studies of the authors (with their coauthors), but the available publications on the topics considered are involved and reviewed as well.

  • Kaveh Edalati
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1221-1229
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: May 31, 2019
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    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 1,000–100,000. 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.

  • Jenő Gubicza
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1230-1242
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: June 07, 2019
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    Processing of metallic materials by Severe Plastic Deformation (SPD) leads to the formation of many lattice defects (e.g., vacancies, dislocations, twin faults and grain boundaries). In this paper, the characteristic features of the defect structure in SPD-processed bulk metallic materials are overviewed. The influence of the material properties, such as the melting point, stacking fault energy and solute content, as well as the SPD-processing conditions (e.g., SPD route and applied hydrostatic pressure) on the type and densities of defects is discussed in detail. In addition, the effect of lattice defects on the mechanical strength of SPD-processed materials is oveviewed.

    Fig. 2 The maximum dislocation density as a function of the melting point (Tm) and SFE for pure fcc metals processed by ECAP at RT. The solid and dashed arrows indicate that the higher the melting point and the lower the SFE, respectively, the larger the saturation dislocation density. Fullsize Image
  • Hiroyuki Miyamoto, Motohiro Yuasa, Muhammad Rifai, Hiroshi Fujiwara
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1243-1255
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: June 07, 2019
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    The significant and complex effect of plastic deformation on corrosion behavior involves changes in not only dislocation density but also other metallurgical factors such as grain size, texture, chemical inhomogeneity, phase transformation and residual stress. With the advent of severe plastic deformation (SPD), the effect of plastic deformation on corrosion in the ultrahigh strain range is becoming an important issue. However, our understanding of corrosion properties of SPD materials lags far behind than that of their other properties, e.g. their mechanical properties. In this review, the role of dislocations and grain boundaries generated by SPD was highlighted in pure metals and single-phase materials, where plastic deformation and grain refinement proceed mainly by dislocation activity. Accordingly, the complicated effect of chemical inhomogeneity arising from impurity segregation and precipitation was excluded from discussion, while other implicit effects were included. It is essential to elucidate the effect of so-called ultrafine-grained (UFG) structures which develop progressively to a saturation over a very wide strain range. Unfortunately, the literature mainly compares the corrosion behavior of UFG and coarse-grained (CG) materials, and the degree of perfection of UFG formation and the resultant effects on corrosion vary between studies. The limited number of studies that examines corrosion behavior systematically over a wide strain range suggests that, in most cases, the effect of plastic deformation on corrosion extends into the SPD region gradually, with no anomalous change. That is, SPD improves the corrosion resistance to further degree in a passive environment, whereas it increases the dissolution rate in a non-passive environment. However, several works reported an abrupt change in corrosion resistance, which could be attributed to UFG formation. A marked improvement is observed in Fe–Cr alloys, where passivation becomes more protective owing to UFG formation induced by SPD. In severely deformed materials, structural alterations in dislocations and grain boundaries have a very high impact on the corrosion kinetics because of their closely spaced configuration.

    Fig. 5 Dynamic polarization curves of (a) CG, and (b) UFG Fe–8%, 10%, 12%Cr alloys in 3.5%NaCl solution.35) Fullsize Image
  • Andrea Bachmaier, Reinhard Pippan
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1256-1269
    Published: July 01, 2019
    Released: June 25, 2019
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    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.

  • O. Renk, R. Pippan
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1270-1282
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: June 07, 2019
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    Grain refinement of materials by severe plastic deformation, investigation and understanding of their properties and phenomena has been a subject of intensive research over the last three decades. Along with the invention and development of these processes it has been recognized, that grain refinement is not indefinite but stagnates for single phase materials. Accordingly, the minimum grain sizes achievable are in the range between 50 and 500 nm. Motivated to find ways to overcome these limitations, effort has been made to understand the reasons behind. Various processes were suggested to cause saturation of grain fragmentation. While all of these assumptions and models were not based on direct observations, recently in-situ approaches allowed significant progress in understanding microstructural evolution and the principle restoration processes during severe straining. It is the aim of this work to recap important earlier findings, reconsider proposed models and to present our current understanding of the processes limiting grain refinement upon severe straining. Further it will be discussed, that similar processes generally occur during deformation of such fine scaled materials. They do not only govern saturation of grain refinement during severe deformation but more important also the mechanical response and performance of these materials. This motivates an in-depth understanding and therefore open questions as well as discrepancies between various experiments will be deliberately highlighted to stimulate further research and thus progress within this area.

  • Ádám Révész, Zsolt Kovács
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1283-1293
    Published: July 01, 2019
    Released: June 25, 2019
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    Bulk metallic glasses having a disordered amorphous structure have been in the focus of recent intensive materials research due to their special mechanical properties, however, these materials exhibit brittleness in conventional unconstrained deformation modes. High-pressure torsion as a special severe plastic deformation method, which applies constraints on the material, can induce significant plasticity in metallic glasses. Apart, the deformation can promote structural changes in the glass, such as anisotropy and nanocrystallization. The inhomogeneity generated by torsional shear deformation in bulk metallic glasses can be detected in internal surfaces. The final structure and morphology of the deformed material depend on the processing parameters (deformation rate, shear strain, temperature and pressure) of the high-pressure torsion apparatus.

    Severe plastic deformation of bulk metallic glasses by high pressure torsion results in a dense and complex shear band structure (a, b). On contrary, glassy samples exhibit well-separated parallel shear bands developed after torsion at ambient pressure with the same shear strain (c). The complex shear band structure can form only at much higher ultimate strains at low pressure (d). Fullsize Image
  • Valery I. Levitas
    Type: Review
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1294-1301
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: June 07, 2019
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    Numerous experiments have documented that combination of severe plastic deformation and high mean pressure during high-pressure torsion in rotational metallic, ceramic, or diamond anvils produces various important mechanochemical effects. We will focus here on four of these: plastic deformation (a) significantly reduces pressure for initiation and completion of phase transformations (PTs), (b) leads to discovery of hidden metastable phases and compounds, (c) reduces PT pressure hysteresis, and (d) substitutes a reversible PT with irreversible PT. The goal of this review is to summarize our current understanding of the underlying phenomena based on multiscale atomistic and continuum theories and computational modeling. Recent atomistic simulations provide conditions for initiation of PTs in a defect-free lattice as a function of the general stress tensor. These conditions (a) allow one to determine stress states that significantly decrease the transformation pressure and (b) determine whether the given phase can, in principle, be preserved at ambient pressure. Nanoscale mechanisms of phase nucleation at plastic-strain-induced defects are studied analytically and by utilizing advanced phase field theory and simulations. It is demonstrated that the concentration of all components of the stress tensor near the tip of the dislocation pileup may decrease nucleation pressure by a factor of ten or more. These results are incorporated into the microscale analytical kinetic equation for strain-induced PTs. The kinetic equation is part of a macroscale geometrically-nonlinear model for combined plastic flow and PT. This model is used for finite-element simulations of plastic deformations and PT in a sample under torsion in a rotational anvil device. Numerous experimentally-observed phenomena are reproduced, and new effects are predicted and then confirmed experimentally. Combination of the results on all four scales suggests novel synthetic routes for new or known high-pressure phases (HPPs), experimental characterization of strain-induced PTs under high-pressure during torsion under elevated pressure.

    Fig. 3 Stationary solutions for interaction of the phase transformation to a HPP (red color) and dislocations in a bicrystalline sample subjected to normal stress and shear strain, without (a) and with (b) plasticity in the right grain. Dislocation pileup causes PT at pressure (averaged over the grain) significantly smaller than under hydrostatic loading with a single dislocation. Dislocations promote PT by producing stress-tensor concentrators (a) but also suppress PT through relaxation of stresses near the tip of the dislocation pileup (b). The contour lines of the equilibrium PT work are presented in black and, in most cases, coincide with the stationary phase interfaces. This figure is reproduced with permission from Ref. 39). Fullsize Image
  • Gerhard Wilde, Sergiy Divinski
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1302-1315
    Published: July 01, 2019
    Released: June 25, 2019
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    The present knowledge on grain boundary-related phenomena specific for severely plastically deformed materials is reviewed and critically analyzed in detail. Severe plastic deformation is shown to introduce specific metastable states of the grain boundaries which are characterized by enhanced diffusion rates, high-density of specific structure elements and large (still localized) elastic strains. An intrinsic heterogeneity of the deformation-induced modifications is revealed and examined on different scales. Relations between the existence of deformation-modified grain boundaries, specific microstructure features and resulting properties are highlighted.

  • Ghader Faraji, Hesam Torabzadeh
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1316-1330
    Published: July 01, 2019
    Released: June 25, 2019
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    Severe Plastic Deformation (SPD) processes have been extensively investigated in the last 30 years to facilitate the production processes of nanostructured (NS) or ultrafine-grained (UFG) materials with unique properties. However, the majority of the efforts were limited on the laboratory-scale investigations not to be able to overcome the demands for industrial scale applications. Researchers have tried to introduce effective industrial methods for processing large and long UFG/NG materials. In this review, all industrial processes especially continuous SPD methods which are more suitable for mass production are categorized and explained. Furthermore, the factors influencing the process efficiency were presented to give a vision to the researchers who want to step in this scientific field. Finally, the industrial processes were compared regarding final microstructure and properties.

  • Werner Skrotzki
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1331-1343
    Published: July 01, 2019
    Released: June 25, 2019
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    Equal channel angular pressing (ECAP) is a severe plastic deformation (SPD) technique leading to refinement of the grain size of materials to submicron or even nano-size length scales. As a result SPD processed materials simultaneously possess high strength and moderate ductility and therefore have a high potential for technical applications. Because of this, much work has been devoted to the evolution of microstructure and texture and their relation to the mechanical properties. However, pressing materials through an angled channel is a complicated deformation process leading to deformation heterogeneities across the billet cross section manifested in gradients of microstructure and texture. Therefore, it is the aim of the present paper to give an overview focusing on the ECAP specific deformation heterogeneities and their related strength gradient in the billets produced. Based on the results reported, which are gained from experiment and simulation, some general conclusions on minimizing the deformation heterogeneities in ECAP are drawn.

    Equal channel angular pressing of colored plasticine visualizing the inhomogeneous straining taking place in this severe plastic deformation process due to friction of the billet at the die walls. With increasing friction an open corner gap is closed and a dead metal zone (DMZ) forms. The inhomogeneous deformation leads to heterogeneities in microstructure, texture and mechanical properties across the billet. Fullsize Image
  • Thierry Grosdidier, Marc Novelli
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1344-1355
    Published: July 01, 2019
    Released: June 25, 2019
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    After a short recall of various techniques that use shots to induce surface severe plastic deformation and a brief survey of the advantages of having a gradient structure for mechanical properties, this manuscript presents recent developments taking advantages of the “reactivity” of these modified surfaces in the fields of corrosion, “duplex” surface treatments as well as potential applications for an easier activation of H-storage materials. The importance of controlling the processing parameters (including temperature) to get the optimum gradient structure depending on the desired applications as well as the necessary requirements for a high quality microstructure and chemical characterizations are also highlighted.

  • Ruslan Z. Valiev, Evgeny V. Parfenov, Lyudmila V. Parfenova
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1356-1366
    Published: July 01, 2019
    Released: June 25, 2019
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    Recent years have witnessed a series of numerous investigative activities to improve existing metallic biomaterials (Ti and Ti alloys, stainless steels, Mg and Fe alloys) by their nanostructuring for advanced medical applications using severe plastic deformation (SPD) processing. Nanostructured metals are peculiar for their enhanced strength and fatigue life, which makes them an excellent choice for fabrication of implants with improved design for dentistry and orthopedics. Moreover, surface modification of nanometals by chemical etching and bioactive coatings show a significant improvement of biomedical properties. Various studies conducted in this field make it possible to fabricate miniaturized dental implants and nanoTi plates with enhanced osseointegration.

    R&D approach for manufacturing of medical implants with improved design and biofunctionality using nanostructured metals and their surface modifications Fullsize Image
  • Terukazu Nishizaki, Kaveh Edalati, Seungwon Lee, Zenji Horita, Tadahir ...
    Type: Overview
    Subject area: Special Issue on Severe Plastic Deformation for Nanomaterials with Advanced Functionality
    2019 Volume 60 Issue 7 Pages 1367-1376
    Published: July 01, 2019
    Released: June 25, 2019
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    This overview describes the progressive results of the superconducting critical temperature in bulk nanostructured metals (niobium, vanadium and tantalum) processed by high-pressure torsion (HPT). Bulk nanostructured superconductors provide a new route to control superconducting property, because ultrafine-grain structures with a high density of grain boundaries, dislocations, and other crystalline defects modify the superconducting order parameter. The critical temperature Tc in Nb increases with the evolution of grain refinement owing to the quantum confinement of electrons in ultrafine grains. In V and Ta, however, Tc decreases at a certain HPT revolution number (i.e. at certain strain levels). The different behaviour of Tc in the three materials is explained by the competition effect between the quantum size effect and disorder effect; these effects are characterized by the parameters of grain size, electron mean free path, and superconducting coherence length.

    Fig. 3 Critical temperature Tc as a function of HPT revolution numbers N for HPT-Nb. Three samples were measured for each N. The broken line indicates Tc for N = 0 and for a single crystal of Nb.32) Fullsize Image
  • Taufiq Hidayat, Peter C. Hayes, Evgueni Jak
    Type: Regular Article
    2019 Volume 60 Issue 7 Pages 1377-1383
    Published: July 01, 2019
    Released: June 25, 2019
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    Most metallurgical smelting processes operate over a limited range of compositions and temperatures but generally, even with complex slag systems, within a given primary phase field. Knowledge of the sensitivity of the liquidus to changes in composition enables improved temperature control and stability of operation. The paper describes a general approach that was used to characterize the liquidus temperatures of the “Cu2O”–“FeO”–SiO2–Al2O3 slags in an electric slag cleaning furnace operation as function of the principal chemical components using a combination of available computer based thermodynamic database descriptions of complex slags and targeted series of laboratory experiments. An approximate mathematical relationship, valid for a limited range of compositions and temperatures, has been developed describing the liquidus temperature of the slags as a function Fe/SiO2 ratio, Cu, and Al2O3 concentrations in slag.

    Fig. 9 Effect of Al2O3 in bulk on the mass%solid as function of Cu in bulk at fixed temperature = 1200°C and Fe/SiO2 ratio in the bulk = 1.5 mass/mass as predicted by the polynomial equation obtained in the present study. Fullsize Image
  • Tetsuji Saito, Toru Horita, Daisuke Nishio-Hamane
    Type: Regular Article
    2019 Volume 60 Issue 7 Pages 1384-1389
    Published: July 01, 2019
    Released: June 25, 2019
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    The magnetic properties and structures of (Sm,Zr)5(Fe,Co)17−xTix (x = 0–2.0) melt-spun ribbons were investigated in the as-quenched condition and after annealing. The as-quenched (Sm,Zr)5(Fe,Co)17−xTix (x = 0–0.5) specimens consisted of the Sm5Fe17-type and SmFe3-type phases, while the as-quenched (Sm,Zr)5(Fe,Co)17−xTix (x = 1.0–2.0) specimens contained the SmFe3-type phase. These specimens showed low coercivity regardless of the Ti content. Heat treatment of the melt-spun ribbons resulted in a drastic increase in coercivity. The maximum coercivity of 1.11 MAm−1 was achieved in the (Sm,Zr)5(Fe,Co)15.5Ti1.5 specimen annealed at 1073 K. Microstructural studies revealed that the annealed specimen consisted mainly of the SmFe3-type phase. The achieved high coercivity of the annealed specimen was therefore attributed to the existence of the SmFe3-type phase.

  • Shoji Ueda, Shinji Sannakanishi
    Type: Technical Article
    2019 Volume 60 Issue 7 Pages 1390-1397
    Published: July 01, 2019
    Released: June 25, 2019
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    In die casting design, residual stress and thermal deformation based FEM analysis are gaining enormous importance.

    Shiga et al. have reported that the thermal and residual stress of the I-shaped model could be more accurately predicted by using the elasto-plastic-creep model than by using the conventional elasto-plastic model.

    In this study, factors affecting the contact forces between the die and the casting were analyzed by using a little more complicated model than the I-shaped model. The results clearly indicate that, irrespective of shapes, the plastic strain term affects the contact forces the most, and that the creep term further reduces the contact forces. Furthermore, a comparison between the simulated and measured values of the residual stress of an aluminum die-cast product confirms the superiority of the elasto-plastic-creep model than the elasto-plastic model in predicting the residual stress, which could also be used instead of the contact forces.

     

    This Paper was Originally Published in Japanese in J. JFS 90 (2018) 386–392. The title of this paper was slightly modified to match the content of the paper. The references from 3) to 6) were added.

  • Fei Xing, Xiaoming Qiu, Cui Luo, Ye Ruan, Dengfeng Wang
    Type: Rapid Publication
    2019 Volume 60 Issue 7 Pages 1398-1401
    Published: July 01, 2019
    Released: June 25, 2019
    [Advance publication] Released: May 31, 2019
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    This paper investigated phase transformation and fracture modes in formability test of dissimilar ultra high strength DP1180-DP590 tailor welded blanks. The welded joints with full penetration were obtained by increasing input power.

    The fusion zone was mainly consisted of lath martensite (LM), bainite (B) and retained austenite (γ). With the increase of input power, microstructure evolution in fusion zone is: finer LM + B → coarse LM + B + Baxial (Baxial represents bainite formed in axial zone). And with finner martensite and bainite dispersed, interfacial cohesion and plasticity was improved and phases were elongated and extensively deformed, which resulted in the transition of fracture modes in formability test. Furthermore, the formability of TWBs achieved superior cupping height, and increased by 20.4% compared with the specimen cracked in fusion zone.

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