Advanced Engineering Materials

Cover image for Advanced Engineering Materials

May, 2003

Volume 5, Issue 5

Pages 267–378

    1. Details to the cover pictures (page 272)

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200390031

    2. Unique Features and Properties of Nanostructured Materials (pages 277–284)

      H. Hahn

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310091

      An overview of nanostructured materials, irrespective of their synthesis process, is attempted in this review article. Various microstructural features such as clusters or isolated nanoparticles, agglomerated nanopowders, consolidated nanomaterials and nanocomposites of all material classes are considered. A section surveys the characterization tools available; another one summarizes property-microstructure relationships. Finally, a brief outlook on applications and initial industrial use of nanomaterials is presented.

    3. Properties, Benefits, and Application of Nanocrystalline Structures in Magnetic Materials (pages 285–290)

      R. Grössinger, R. Sato, D. Holzer and M. Dahlgren

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310081

      The magnetic properties of nanocrystalline hard and soft magnetic materials are summarized. When the grain size becomes of the order f (the magnetic exchange length), exchange coupling occurs and triggers material-dependent effects: In isotropic hard magnetic materials, exchange coupling causes enhanced remanence, while in soft magnetic materials it decreases coercivity and losses, leading to improved properties.

    4. Equivalent Strains in Severe Plastic Deformation (pages 291–295)

      H.P. Stüwe

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310085

      A concept that allows to compare strains achieved by different SPD methods, designated “equivalent strain”, is introduced and discussed by the author. Their definition may be based on the shape of the specimen, or on the plastic work spent. Complications arise when strain is accumulated in increments with variable strain path. In this case, it may be helpful to introduce efficiency factors which depend on the material property under discussion.

    5. Paradoxes of Severe Plastic Deformation (pages 296–300)

      R.Z. Valiev

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310089

      Severe plastic deformation (SPD) can induce microstructural features and properties in materials that differ from those known for conventional cold deformation. In particular, unusual phase transformations leading to highly metastable states associated with formation of supersaturated solid solutions, disordering or amorphization and further decomposition during heating, high thermal stability of SPD-produced nanostructures, and the paradox of strength and ductility in some SPD-processed metals and alloys are discussed.

    6. Importance of Disclinations in Severe Plastically Deformed Materials (pages 301–307)

      A.E. Romanov

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310087

      Disclination models for the processes in plastically deformed materials are reviewed here. After a definition of key parameters, the properties of screened disclination configurations with small energies are considered, and bands with misoriented crystal lattice described as a result of partial wedge disclination dipole motion. Finally, the disclination approach is used to describe work hardening at large strains and to analyze grain boundaries in conventional poly- and nanocrystals.

    7. Texture Evolution in Severe Plastic Deformation by Equal Channel Angular Extrusion (pages 308–316)

      L.S. Tóth

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310084

      Most techniques of severe plastic deformation are based on simple shear deformation. Hence, textures that evolve in simple shear or in Equal Channel Angular Extrusion (ECAE) are discussed in detail here. The classical “simple shear model” of ECAE is juxtaposed with a new, more precise flow field which uses an analytical flow function adapted from finite element calculations.

    8. Boundary characteristics in Heavily Deformed Metals (pages 317–322)

      G. Winther and X. Huang

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310088

      The fabrication of nanostructured metals by plastic deformation to very high strains is currently the subject of intensive research. An important topic is the evolution of the characteristics of deformation induced boundaries, in particular their spacing and misorientation. This paper reviews the present understanding of the relations between these characteristics, and the microscopic mechanisms and macroscopic mode of deformation.

    9. The Meaning of Size Obtained from Broadened X-ray Diffraction Peaks (pages 323–329)

      T. Ungár

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310086

      X-ray diffraction peak profile analysis (DPPA) is a powerful tool for the characterization of microstructures either in bulk or in loose powder. While the dislocation density and structure obtained from DPPA correlate generally well with TEM observations, for crystallite size definite discrepancies are observed at times. The author critically reviews literature data where crystallite or grain size were determined by both methods in parallel, and discusses the deviating results in terms of the microstructures in different types of specimens.

    10. The Role of Hydrostatic Pressure in Severe Plastic Deformation (pages 330–337)

      M.J. Zehetbauer, H.P. Stüwe, A. Vorhauer, E. Schafler and J. Kohout

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310090

      The presence of an enhanced hydrostatic pressure is one of the main features of severe plastic deformation. High pressure torsion experiments with Cu at room temperature show that, while onset strains of deformation stages III to V are unaffected by pressure, flow stresses do increase significantly. A comparison of theory and experiments reveals that flow stress depends not only on the elastic moduli and formation energy of lattice defects, but also on lattice diffusion, which presumed to control the pressure-specific evolution of the structure.

    11. ARB (Accumulative Roll-Bonding) and other new Techniques to Produce Bulk Ultrafine Grained Materials (pages 338–344)

      N. Tsuji, Y. Saito, S.-H. Lee and Y. Minamino

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310077

      A comparison of accumulative roll bonding (ARB) and other severe plastic deformation processes for the formation of ultrafine-grain (UFG) structures is the focus of this contribution; special stress is put on the role of shear deformation. The ARB process, the only SPD technology that uses rolling deformation itself, is suitable for producing the bulk UFG material continuously, and allows a closer insight into the formation mechanism and properties of such materials.

    12. Atomistic Modeling of Strength of Nanocrystalline Metals (pages 345–350)

      H. Van Swygenhoven, P.M. Derlet and A. Hasnaoui

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310080

      Large scale atomistic simulations of model nanocrystalline materials are used to investigate the plastic deformation mechanisms active in interface dominated materials, with the view to understanding the origin of the related high strength seen in the experiment. Results are presented detailing both inter- and intra-granular deformation processes under uniaxial tensile and nano-indentation loading conditions.

    13. Fatigue of Severely Deformed Metals (pages 351–358)

      A. Vinogradov and S. Hashimoto

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310078

      The current knowledge of fatigue phenomena of ultra-fine grain materials made by SPD is summarized in this article, and possible mechanisms of their plastic degradation and deformation evaluated in the light of available experimental data. The discussion was confined to the influences exerted by the two most prominent effects of Severe Plastic Deformation, i.e. grain refinement down to the nanoscopic scale, and the dislocation accumulation up to limiting densities of 1016 m–2.

    14. Achieving a Superplastic Forming Capability through Severe Plastic Deformation (pages 359–364)

      C. Xu, M. Furukawa, Z. Horita and T.G. Langdon

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310075

      SPD processing leads to very significant grain refinement in metallic alloys. If these ultrafine grains are reasonably stable at elevated temperatures, high tensile ductilities and superplastic elongations in alloys that are generally not superplastic can be achieved. Also, the production of ultrafine grains affords superplastic flow at strain rates significantly faster than in conventional alloys, enabling the rapid fabrication of complex parts by superplastic forming. This paper examines superplasticity in Al alloys processed by equal-channel angular pressing.

    15. Diffusion in Nanocrystalline Metals and Alloys—A Status Report (pages 365–372)

      R. Würschum, S. Herth and U. Brossmann

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310079

      Diffusion is a determining property for the extent to which the interfaces in nanocrystalline samples differ from conventional grain boundaries. The present article offers an overview of diffusion in monocrystalline metals and alloys with emphasis on crucial parameters such as structural relaxation, grain growth, porosity, and the specific type of interface. On the basis of the available diffusion data, the diffusion-mediated processes of deformation and induced magnetic anisotropy are discussed.

    16. Commercialization of Nanostructured Metals Produced by Severe Plastic Deformation Processing (pages 373–378)

      T.C. Lowe and Y.T. Zhu

      Version of Record online: 13 JUN 2003 | DOI: 10.1002/adem.200310076

      The first SPD-processed metals are commercially available now in a few market sectors. Although SPD technology is still at an early stage of development, the pace of work in this field has grown dramatically, and busy patent activity foreshadows that additional products and markets, encompassing a larger array of metals, are imminent. Large volume production of SPD metals is, however, not likely to emerge before the economics of continuous processing methods are established and greater penetration of key markets is secured.