Advanced Engineering Materials

Cover image for Advanced Engineering Materials

October, 2003

Volume 5, Issue 10

Pages 693–752

    1. Contents: Adv. Eng. Mater. 10/2003 (pages 693–696)

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200390036

    2. Physical Aspects of Process Control in Selective Laser Sintering of Metals (pages 701–711)

      S. Das

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200310099

      Direct selective laser sintering (SLS) is a layered manufacturing technique that can produce fully dense, functional components in high performance metals. In this review, a first step is taken towards identifying and understanding some important physical mechanisms in direct SLS, and helps in selecting materials most amenable to SLS, and in designing machinery and processes. The Figure shows a solidified droplet in a “powder-on-plate” experiment.

    3. Voltage Breakdown in Random Composites (pages 713–715)

      A.A. Gusev and O.A. Guseva

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200300380

      Voltage breakdown is a strongly localized phenomenon in random-microstructure composites because the different dielectric constants of metal and polymer matrix turn a uniform external field across the structure into spatially non-uniform local fields. The authors show that rather small computer models are sufficient to extract reliable estimates for the breakdown fields in lab-scale samples. The Figure shows a cut through a periodic unstructured mesh of a Monte Carlo model with 27 spheres.

    4. New Processing Techniques of Ceramic Foams (pages 715–718)

      J. Luyten, S. Mullens, J. Cooymans, A.-M. De Wilde and I. Thijs

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200300381

      Three alternative manufacturing techniques for ceramic foams are compared in this article: a reaction bonded-modified (RB) polyurethane replica technique, gel casting, and a method of hollow building blocks (see Figure for a sample built up by different hollow spheres). The strength of the ceramic foams was tested by 3p-bending and compression. Also, structural parameters were characterized by image analysis and computer-assisted x-ray tomography.

    5. Deformation of PZT Under Tension, Compression, Bending, and Torsion Loading (pages 718–722)

      T. Fett and D. Munz

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200300385

      The behavior of PZT under various external influences at a range of electric fields has been investigated in the present study. Poled and unpoled PIC 151, a commercial soft PZT, was subjected to strain measurements in pure tension and compression tests, thin-walled tubes of the unpoled material also to torsion tests to study the deformation under biaxial loading. These tests allow to determine the non-symmetric yield condition for the plastic deformations and to describe it with the Drucker-Prager criterion.

    6. Effect of the Temperature of Molten Magnsium on the Thermal Explosion Synthesis Reaction of Al–Ti–C System for Fabricating TiC/Mg Composite (pages 722–725)

      Q.C. Jiang, H.-Y. Wang, Q.-F. Guan and X.-L. Li

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200300364

      Detailed insight into the thermal explosion synthesis (TES) of a TiC/Mg composite has been gained by the authors. SEM microstructures and XRD patterns of TiC/AZ91D obtained by TES synthesis from Mg and Al-Ti-C preforms reveal that the temperature of the molten Mg greatly influences the incubation time for the TES reaction and the reaction product. Thus, TiAl3 clusters present at a reaction temperature of 700 °C (see Figure) disappear when the reaction is performed at 900 °C.

    7. Fabrication, Microstructure, and Mechanical Properties of Tip/Al Composite (pages 725–729)

      C. Cui, Y. Shen, Y. Li, J. Sun and S.-B. Kang

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200300378

      The fabrication and properties of Tip/Al (i.e. aluminum in-situ reinforced with titanium particles, see Figure for its microstructure), a metal-matrix composite with excellent mechanical features, are described. In their plasma jet synthesis of Tip/Al, the Ti wire feed rate, spray optimization, and electromagnetic stirring are identified as crucial for the quality of the material. Due to the different melting points of Ti and Al, the Ti droplets are instantly quenched in the liquid Al.

    8. Ex-situ Formation Periodic Interlayer Structure to Improve Significantly the Impact Damage Resistance of Carbon Laminates (pages 729–732)

      X.-S. Yi, X. An, B. Tang and Y. Pan

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200300360

      A periodically interleaved carbon laminate system, wherein solid thermoplastic thin layers are interleaved into each carbon ply, has been fabricated by means of an “ex-situ” type synthesis in which the thermoset and thermoplastic components are separated and interact only at elevated temperature. The Figure shows the boundary area between the two-phase granular and a pure epoxy-resin structure within a single carbon ply.

    9. Two-Directional TiNi Shape Memory Alloy Film (pages 732–735)

      H. Takagi, K. Okano, S. Juodkazis, S. Matsuo and H. Misawa

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200300347

      A change from a memorized convex to a concave curvature between 10 °C for the martensitic and 50 °C for the austenitic transition is the important feature of a novel two-directional shape TiNi memory alloy film fabricated by sputtering. The key to two-directional actuation is Ti3Ni4 precipitate formation attained by an Ni enrichment (55.6 %) in the alloy. The Figure shows the bending of a strip placed over a steaming cup of tea after 0.1 to 0.4 seconds.

    10. Damage Behavior of Air-Plasma-Sprayed Thermal Barrier Coatings under Foreign Object Impact (pages 735–737)

      A.F. Dericioglu, S. Zhu, Y. Kagawa and H. Kasano

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200300386

      How do thermal barrier coatings react to the impact of a foreign object? The authors examined the damage done by a projectile to an air-plasma-sprayed coating system. Apart from permanent deformation, chipping of the ceramic top coat around the impression sites occurs at impact velocities above 150 m s–1. At increasing impact speed, the cracks in the top coat tend to elongate and result in coating removal (see Figure for a cross-section).

    11. Deformation-induced Structural Changes in Bulk Metallic Glass at Room Temperature (pages 738–741)

      Y.F. Deng, L.L. He, Q.S. Zhang, H.F. Zhang and H.Q. Ye

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200300383

      Room-temperature local structure changes in a bulk metallic glass, namely crystallization and void formation, occur after uniaxial compressive plastic deformation; probably this is due to the creation of free volume. Deformation-induced nanocrystallization may provide a synthesis of bulk amorphous-nanocrystalline alloys. The Figure shows a TEM image of voids in a bulk Zr55Al10Ni5Cu30 specimen prepared by standard twin-jet electrolytic thinning followed by low-angle ion milling.

    12. In-Situ Reaction Synthesis of Oxide-Boron Nitride Composites (pages 741–744)

      G.-J. Zhang, J.-F. Yang, M. Ando, T. Ohji and S. Kanzaki

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200300363

      Oxide-Boron Nitride Composites with high strain tolerance and good mechanical/thermal shock resistance were prepared by reactive hot pressing taking advantage of in-situ reactions between aluminium borates, AlN and Si3N4. The in-situ formed BN phase is in agglomerate shape, as shown by an SEM fractograph of mullite/BN (see Figure): the fine particles located at the junctions of the matrix particles consist of BN.

    13. Investigation of the Correlation between Texture and Microstrucure on a Submicrometer Scale in the TEM (pages 745–752)

      S. Zaefferer

      Article first published online: 27 OCT 2003 | DOI: 10.1002/adem.200320382

      TEM is preferable to SEM for Local Texture Analysis when high spatial resolution and accurate orientation determination are targeted, for 3D and quantitative determination of lattice defects, and in investigating materials with high lattice defect densities. The author depicts some successful case studies in which the results justify the often painful sample preparation for TEM. The Figure illustrates the determination of dislocation line direction in a Ti sample.