Advanced Engineering Materials

Cover image for Advanced Engineering Materials

July, 2003

Volume 5, Issue 7

Pages 461–522

    1. Contents: Adv. Eng. Mater. 7/2003 (pages 461–463)

      Version of Record online: 30 JUL 2003 | DOI: 10.1002/adem.200390033

    2. Wrought Ni-Base Superalloys for Steam Turbine Applications beyond 700 °C (pages 469–483)

      J. Rösler, M. Götting, D. Del Genovese, B. Böttger, R. Kopp, M. Wolske, F. Schubert, H.-J. Penkalla, T. Seliga, A. Thoma, A. Scholz and C. Berger

      Version of Record online: 30 JUL 2003 | DOI: 10.1002/adem.200310083

      A material for the new generation of steam turbines in advanced coal-fired power plants has been found in nickel-based superalloys, yet the demands for component size and operation temperatures beyond 700 °C by far exceed the performance that such alloys undergo currently in aerospace applications. This article outlines development strategies for suitable alloys and presents two mew materials, DT 706 and DT 750. The Figure shows a microimage of DT 706 after overaging at 750 °C for 1000 hours.

    3. Friction Stir Welding – Recent Developments in Tool and Process Technologies (pages 485–490)

      W.M. Thomas, K.I. Johnson and C.S. Wiesner

      Version of Record online: 30 JUL 2003 | DOI: 10.1002/adem.200300355

      Improved weld integrity, reduced upper-plate thinning, and higher welding speeds are some striking results of progress recently made in the field of friction-stir welding through improvements of tools and processes. One technique, labelled Re-Stir™, in particular, appears promising since it generates essentially symmetrical welds (see Figure for a cross-section of the notch) and is potentially suitable for welding of dissimilar materials.

    4. High-Temperature Deformation Behavior of the Bond–Coat Alloy PWA 1370 (pages 490–493)

      J. Schwarzer and O. Vöhringer

      Version of Record online: 30 JUL 2003 | DOI: 10.1002/adem.200300354

      The high-temperature deformation behavior of the NiCoCrAlY alloy PWA 1370, which is applied as a bond-coat material in thermal barrier-coating systems, was investigated at temperatures up to 950 °C by means of constant extension rate tests (CERTs) and was described with a modified Norton creep law. Furthermore, experiments to determine Young's modulus and compressive yield strength at high temperature are reported.

    5. Preparation of the Intermediate Layers on CoNiCrMo-Alloys Using Alkaline Treatment for Improving the Bonding of Bioceramic Coating (pages 493–498)

      T. Wang, A. Dorner-Reisel and E. Müller

      Version of Record online: 30 JUL 2003 | DOI: 10.1002/adem.200300357

      Can alkaline pretreatment improve the bond between metallic implants and hydroxyapatite bioceramic coatings? Very much so, but it affords proper choice of the base. Treatment with 10 M NaOH did not result in a crystalline coating on CoNiCrMo whereas saturated Ca(OH)2 solution produces a stable, homogeneous coating of Ca2Co2O5 as a bridge compound. The Figure shows two examples of metallic knee prosthesis parts made of CoNiCrMo and CoCrMo, resp. for use in such implants.

    6. Calcium Phosphate Glass-Ceramics for Bioactive Coating on a β-Titanium Alloy (pages 498–501)

      T. Kasuga, M. Nogami and M. Niinomi

      Version of Record online: 30 JUL 2003 | DOI: 10.1002/adem.200300362

      The formation of a porous coating is the decisive feature for the bio-compatibility of silica-free calcium phosphate glass ceramics on alloy surfaces like the β-Ti structured Ti-29Nb-13Ta-4.6Zr used in this work. The ceramic composition is highly important: 50 CaO-40 P2O5-7 Na2O-3 TiO2 glass powder produces a pore-free coating unable to bind hydroxyapatite, whereas 60 CaO-30 P2O5-7 Na2O-3 TiO2 glass incorporates pores from which a crystalline hydroxyapatite phase can grow over the surface from simulated body fluid (see Figure).

    7. Hot-Pressed Glass Matrix Composites Containing Pyrochlore Phase Particles for Nuclear Waste Encapsulation (pages 501–508)

      A.R. Boccaccini, S. Atiq and R.W. Grimes

      Version of Record online: 30 JUL 2003 | DOI: 10.1002/adem.200300352

      As alternative immobilization materials for Pu-bearing nuclear waste, lead-containing glass matrix composites with homogeneously distributed lanthanum zirconate pyrochlore particles (up to 30 % by volume) have been developed. Fabrication by hot pressing at the relatively mild temperature of 610 °C leaves the pyrochlore structure of the La zirconate unchanged, which is crucial for the containment of radioactive nuclei. The Figure, an SEM image of a polished sample with 30 % La2Zr2O7, demonstrates the homogeneous particle distribution and absence of pores.

    8. Beneficial Effects of AlN as Sintering Aid on Microstructure and Mechanical Properties of Hot-pressed ZrB2 (pages 508–512)

      F. Monteverde and A. Bellosi

      Version of Record online: 30 JUL 2003 | DOI: 10.1002/adem.200300349

      Higher density of ZrB2 ceramics than with the pure material is achieved when 4.6 % of aluminum nitride are added before hot-pressing as a sintering aid. AlN supports densification and prevents grain coarsening, mainly by virtue of its ability to remove the boron oxide layer that otherwise covers ZrB2 particles. The new material (see Figure for an SEM image of a polished section) has outstanding mechanical properties, e.g. strength values of 600 and 200 MPa at 25 and 1500 °C.

    9. Unique Microcapsule Toner Synthesized by Liquid Phase Separation (pages 512–514)

      K. Teshima

      Version of Record online: 30 JUL 2003 | DOI: 10.1002/adem.200300338

      The specific design of microcapsules by liquid-phase separation on organic solvents is enabled using a method for the selection of wall materials and solvents based on solubility parameters and, finally, molecular structures of raw material candidates. The feasibility of the method is demonstrated by the fabrication of a microcapsule toner called “curlfit toner”, whose superior surface coverage properties over conventional toners are demonstrated by enlargements juxtaposed in the Figure.

    10. Carbon Nanotube Composite Deposits with High Hardness and High Wear Resistance (pages 514–518)

      X. Chen, G. Zhang, C. Chen, L. Zhou, S. Li and X. Li

      Version of Record online: 30 JUL 2003 | DOI: 10.1002/adem.200300348

      A metal–carbon nanotube (CNT) composite has been synthesized by the authors simply by dispersing CNT's in a suitable electrolyte solution and depositing the metal in an electroless manner. The thus-obtained CNT/Ni-P coatings exhibit superior mechanical properties such as high hardness and excellent wear resistance. The Figure shows the intact morphology of worn CNT/Ni-P (left) vs. the bruised surface of conventional Ni-P.

    11. Analysis of Carbon Materials by X-ray Photoelectron Spectroscopy and X-ray Absorption Spectroscopy (pages 519–522)

      I. Retzko and W.E.S. Unger

      Version of Record online: 30 JUL 2003 | DOI: 10.1002/adem.200320138

      Hard coatings such as ta:C films are of growing interest as surface protection of industrial machines and high capacity tools against wear and friction, as well as for biomedical applications, increasing the demand for information about the structure-to-property relation. Therefore, the authors applied core level X-ray photoelectron and absorption spectroscopy and spectromicroscopy in order to derive chemical information about selected carbon species.