Advanced Engineering Materials

Cover image for Vol. 7 Issue 9

September, 2005

Volume 7, Issue 9

Pages 779–861

    1. Cover Picture: Laser Surface Modification of a Crystalline Al-Co-Ce Alloy for Enhanced Corrosion Resistance (Adv. Eng. Mater. 9/2005)

      J. G. Hoekstra, S. B. Qadri, J. R. Scully and J. M. Fitz-Gerald

      Version of Record online: 22 SEP 2005 | DOI: 10.1002/adem.200590017

      The surfaces of Al-Co-Ce bulk crystalline alloys have been successfully laser processed resulting in amorphous-like surface layer formation with enhanced corrosion characteristics (see Figure). The material system, Al84Co7.5Ce8.5, is one of several next generation alloy compositions scientifically designed to form a metallic glass under the proper processing conditions. This material system exhibits both local composition changes and enhanced corrosion resistance (left to right) in comparison to their native counterparts.

    2. Breakthroughs in Optimization of Mechanical Properties of Nanostructured Metals and Alloys (pages 787–794)

      C. C. Koch, K. M. Youssef, R. O. Scattergood and K. L. Murty

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500094

      While nanocrystalline metals can have strength and hardness values factors of 10 or more greater than their conventional grain size counterparts, ductility in tension has been disappointing, typically less than 2% elongation. This paper reviews the limitations to ductility in nanocrystalline materials and presents the results of recent breakthroughs wherein both high strength and good ductility are observed.

    3. Current Transport at the Atomic Scale (pages 795–803)

      U. Schröter, E. Scheer, R. Arnold, C. Bacca, T. Böhler, J. Grebing, P. Konrad, V. Kunej, N. Kang, H.-F. Pernau and C. Schirm

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500101

      Electrical contacts of the width of only one atom can be realized by the break-junction technique. The conductance decreases stepwise due to structural reconfigurations when tearing a nano-bridge in the few-atom range. Transport is described by an ensemble of channels with possibly quite high transmission probabilities. For a single break-junction the last one-atom contact consists of a material-specific channel ensemble, determined by the chemical valence as verified for quite a number of metals. d-electrons in half-metals and spin-effects in magnetic materials will complicate this simple model. Break-junctions also provide ideal contacts to investigate transport through freely suspended clusters or molecules like DNA.

    4. Laser Surface Modification of a Crystalline Al-Co-Ce Alloy for Enhanced Corrosion Resistance (pages 805–809)

      J. G. Hoekstra, S. B. Qadri, J. R. Scully and J. M. Fitz-Gerald

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500103

      The surfaces of Al-Co-Ce bulk crystalline alloys have been successfully laser processed resulting in amorphous-like surface layer formation with enhanced corrosion characteristics (see Figure). The material system, Al84Co7.5Ce8.5, is one of several next generation alloy compositions scientifically designed to form a metallic glass under the proper processing conditions. This material system exhibits both local composition changes and enhanced corrosion resistance (left to right) in comparison to their native counterparts.

    5. Scanned Probe Microscopy-Mediated Patterning of Metallic Nanostructures (pages 811–814)

      L. C. Teague and J. D. Batteas

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500085

      Various direct-write and mulit-step chemical patterning approaches, utilizing scanned probe microscopy techniques as a key design tool are being explored for the creation of nanoscale metallic features. Using these methods, an assortment of feature shapes and sizes have been created on metallic and semiconducting surfaces.

    6. Boundary Strengthening over Five Length Scales (pages 815–821)

      N. Hansen

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500102

      At present there is a strong scientific and industrial interest in strong metals where the strength can be obtained by introduction of grain boundaries and dislocation boundaries by a variety of processes. The structural dimension of these materials covers a scale from the nanometre range to the micrometre/submicrometre level i.e. five length scales, and a multiscale analysis has been applied to the relationship between strength and the boundary parameters.

    7. Bio-mimetic scaling of mechanical behavior of thin films, coatings, and surfaces by Laser Interference Metallurgy (pages 823–826)

      C. Daniel, T. John Balk, T. Wübben and F. Mücklich

      Version of Record online: 22 SEP 2005 | DOI: 10.1002/adem.200500110

      Biological solutions to enhance strength and stability often use hierarchical composite structures. The effect is not based on large chemical variations, but instead is realized by structural composites with long-range order. Laser Interference Metallurgy is a newly developed technique that utilizes this biological approach to optimize the mechanical properties of surfaces and thin films. The possibility of scaling mechanical properties is quantitatively analyzed and compared with the biological approach.

    8. Formation of Dendritic Nanotubes under an Electric Field (pages 827–829)

      Y. Cui, C. L. Xu, Q. Y. Han, H. Choo and P. K. Liaw

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500106

      The formation of dendritic nanaotube structures was observed when an electric field was implemented in the nanotube-containing solution. This phenomenon can be attributed to the movements of the charged carbon nanotubes and ions attached on the nanotube surface under the condition of the force of attraction or repulsion from the electric field.

    9. Temperature-Dependent Microstructures in Fatigued Ultrafine-Grained Copper Produced by Equal Channel Angular Pressing (pages 829–833)

      X. W. Li, S. D. Wu, Y. Wu, H. Y. Yasuda and Y. Umakoshi

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500108

      Ultrafine-grained copper samples produced by equal channel angular pressing were cyclically deformed at different temperatures under a constant stress amplitude of 200 MPa, and the corresponding microstructures were investigated by transmission electron microscope. The increase in temperature during cycling facilitated the grain coarsening and led further to the general change of microstructures from dislocation walls to well-defined cells as well as to the occurrence of a few annealing twins in final microstructures of fatigued UFG copper at the temperature above recrystallization.

    10. Elevated Temperature Deformation Behavior of Zr-Based Bulk Metallic Glasses (pages 833–841)

      M. Heilmaier and J. Eckert

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500080

      The elevated deformation behaviour of Zr-based metallic bulk metallic glasses is reviewed in a wide temperature and strain rate range within the supercooled liquid region. Newtonian viscous flow and homogeneous deformation at constant viscosity is observed. In accord with Spaepen's free volume theory it is experimentally verified that the extraordinarily high plastic deformability in BMGs is controlled by the competing effects of free volume generation and annihilation.

    11. Electromagnetic Detection and Characterization of Tungsten Carbide Inclusions in Non-Ferromagnetic Alloys (pages 841–846)

      W. D. Feist, G. Mook, J. H. Hinken, J. Simonin and H. Wrobel

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500081

      Manufacturing anomalies introduced during machining of critical parts, although rare in occurrence, have become a significant cause of gas turbine disk cracking events in the aero-engine. One kind of these anomalies is inclusion of foreign material. Breakage of the machine tool cutting edge can lead to residual tool particles being impacted in the surface of the component. These particles may initiate fatigue crack growth significantly reducing fatigue life. The paper presents electromagnetic methods for their detection and characterization based on eddy currents and residual magnetic fields.

    12. On the Impact of Macroscopic Phase Separation on Solidification Microstructures (pages 846–851)

      M. H. Wu, A. Ludwig, M. Pelzer and U. Postl

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500098

      A term “macroscopic phase separation” is used to describe the relative motion between different phases during solidification. This paper reports three of the latest multiphase modelling results to demonstrate the role of the phase separation in solidification and the formation of the microstructure and macrosegregation.

    13. Simple Flow Rules for Modeling the Behaviour of Inhomogeneous Viscoplastic Materials (pages 852–858)

      F. Montheillet and G. Damamme

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500100

      The “Iso-W” approach recently proposed to generate simple flow rules for two phase materials is extended to nonlinear viscoplastic constituents and generalized, which produces three families of models. Comparison with the Hashin-Shtrikman bounds leads to select the variant assuming strain rate compatibility and stress equilibrium. The “Iso-W” assumption is in fairly well agreement with the Mori-Tanaka and self-consistent models for mixtures of both linear and nonlinear materials.

    14. A Novel Method to Prepare Zeolites with Hierarchical Porosity (pages 858–861)

      I. Santacruz, M. I. Nieto, R. Moreno, M. Faraldos and E. Sastre

      Version of Record online: 21 SEP 2005 | DOI: 10.1002/adem.200500091

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