Advanced Engineering Materials

Cover image for Vol. 8 Issue 8

August, 2006

Volume 8, Issue 8

Pages 687–759

  1. Cover Picture

    1. Top of page
    2. Cover Picture
    3. Contents
    4. Review
    5. Communications
    1. Cover Picture: Three Dimensional Characterization of Unmodified and Sr-Modified Al-Si Eutectics by FIB and FIB EDX Tomography (Adv. Eng. Mater. 8/2006)

      F. Lasagni, A. Lasagni, C. Holzapfel, F. Mücklich and H. P. Degischer

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200690016

      This article provides a study of the three-dimensional morphology of different eutectic architectures of unmodified and Sr-modified AlSi-alloys. These 3D-structures were reconstructed by means of a new Focused Ion Beam – Energy Dispersive Spectroscopy (FIB-EDX) method, consisting in 2D sectioning and subsequent computer imaging. The Si-structure and its interconnectivity are investigated, as well as the morphological changes induced by the addition of Sr.

  2. Contents

    1. Top of page
    2. Cover Picture
    3. Contents
    4. Review
    5. Communications
  3. Review

    1. Top of page
    2. Cover Picture
    3. Contents
    4. Review
    5. Communications
    1. Advanced Ceramic Materials for High Temperature Applications (pages 693–703)

      M. Belmonte

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200500269

      The need to achieve higher efficiencies of energy production are one of the driving forces that justify the current development of advanced ceramic materials for high temperature applications, namely those associated to energy and transportation industries. Ceramic matrix composites (CMCs), thermal barrier coatings (TBCs), environmental barrier coatings (EBCs) and solid oxide fuel cells (SOFCs) are increasingly used to work under the new demanding conditions. In this review, the recent progress and trends in the research and development of CMCs, TBCs, EBCs and SOFCs based on ceramic materials for high temperature applications are highlighted.

  4. Communications

    1. Top of page
    2. Cover Picture
    3. Contents
    4. Review
    5. Communications
    1. Ceramic Foams for Al-Recycling (pages 705–707)

      J. Luyten, W. Vandermeulen, F. De Schutter, C. Simensen and M. Ryckeboer

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200600085

      The recycling of Al scrap requires an efficient purification step. In this investigation a filter technique is used to remove intermetallic compounds containing Fe, Mn and Si out of the molten Al. The paper describes the synthesis of the filters, the construction of the filter installation, and the results of the different filter tests.

    2. The Exploitation of Superplasticity in the Successful Foaming of Ceramics after Sintering (pages 708–711)

      A. Kishimoto, T. Higashiwada, H. Asaoka and H. Hayashi

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200600070

      A model ceramic foam was produced by expanding the sintered dense shell of refractory 3 mol% yttria-stabilized zirconia, utilizing its superplastic deformation. The conventional production of porous ceramics by the sintering of a foamed precursor results in either insufficient sintering if porosity is to be maintained, or sacrifices porosity in order to improve inter-grain bonding. In the new model ceramics, the foaming procedure is carried out following sintering and there is no reduction in inter-grain bonding; instead, a high level of porosity is attained along with high structural reliability.

    3. Generation Mechanism and in situ Growth Behavior of α-Iron Nanocrystals by Electron Beam Induced Deposition (pages 711–714)

      W. Zhang, M. Shimojo, M. Takeguchi, R.-C. Che and K. Furuya

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200600026

      Amorphous iron-containing deposits were formed on carbon films by electron beam induced deposition with a precursor of iron pentacarbonyl and alpha-Fe nanocrystals were grown around the target tip deposits when the electron beam irradiation time was longer than 1000 s.

    4. Crystallization Kinetics of the (Zr58Ni13.6Cu18Al10.4)Nb1 Bulk Metallic Glass (pages 714–719)

      D. Qiao, C. Fan, P. K. Liaw and H. Choo

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200500282

      The differential thermal analysis (DTA) curve of the (Zr58Ni13.6Cu18Al10.4)Nb1 bulk metallic glass (BMG) shows that there are two exothermic crystallization peaks and two endothermic melting peaks. The BMG has been completely crystallized in the first crystallization peak. X-ray shows that the quenched BMG only includes the glass single phase. The BMG heated to 823 K (between the first and the second crystallization peak) has the precipitation of the cubic NiZr2. The BMG heated to 1003 K (after the second crystallization peak) has the cubic NiZr2, bct NiZr2, and bct CuZr2. HRTEM shows that there are some nano-crystalline phases for the quenched BMG.

    5. Three Dimensional Characterization of Unmodified and Sr-Modified Al-Si Eutectics by FIB and FIB EDX Tomography (pages 719–723)

      F. Lasagni, A. Lasagni, C. Holzapfel, F. Mücklich and H. P. Degischer

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200500276

      This article provides a study of the three-dimensional morphology of different eutectic architectures of unmodified and Sr-modified AlSi-alloys. These 3D-structures were reconstructed by means of a new Focused Ion Beam – Energy Dispersive Spectroscopy (FIB-EDX) method, consisting in 2D sectioning and subsequent computer imaging. The Si-structure and its interconnectivity are investigated, as well as the morphological changes induced by the addition of Sr.

    6. Investigation on Forming Defects During Thixo-forging of Aluminum Alloy AlSi7Mg (pages 724–730)

      K. K. Wang, R. Kopp and G. Hirt

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200500210

      The appearance of pores and segregation between solid/liquid phases during semi-solid forming has been a long-term challenge for the large scale utilization of semi-solid forming in industry. Both phenomena can be influenced by velocity, temperature and pressure. In this study a flat flange and an angled flange were used in investigating the metal flow behavior during thixo-forging of aluminum parts. Evaluations of the thixo-forged parts were performed with x-ray inspection, microstructure and segregation analysis. The experimental results show significant tendencies between the types of the flange and the forming defects of pores and segregationThe results of numerical simulations showed that the hydrostatic stress was the main reason for the appearance of pores. The x-ray inspections revealed that the appearance of pores and segregation during thixo-forging could be avoided or alleviated by optimized die design.

    7. Long Fibre Reinforced NiAl: High Temperature Material for Turbine Blades (pages 730–735)

      M. Rosefort, C. Dahmen, A. Bührig-Polaczek, W. Hu, H. C. Y. Zhong, G. Gottstein, D. Hajas and J. M. Schneider

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200600004

      For environmental reasons an increase of the efficiencies of power stations is needed and further improvements of materials are essential. Today combined gas and steam turbine power stations obtain overall efficiencies of 58 %. Temperatures of approximately 1230 °C in gas turbines exceed the load limits of the commonly used materials. For efficiency increase turbine inlet temperatures must be increased up to 1350 °C (ISO) in the gas turbine.

    8. Simultaneously Improving Strength and Ductility of Magnesium using Nano-size SiC Particulates and Microwaves (pages 735–740)

      W. L. E Wong and M. Gupta

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200500209

      Magnesium composites containing nano-size SiC particulates were synthesized using powder metallurgy technique incorporating microwave assisted rapid sintering. Microstructural characterization revealed minimal porosity and the presence of a continuous network of nano-size SiC particulates decorating the particle boundaries of the metal matrix. Mechanical characterization revealed that the addition of nano-size SiC particulates lead to a simultaneous increase in microhardness, 0.2% yield strength, ultimate tensile strength and ductility of the matrix.

    9. Processing, Microstructure and Mechanical Properties of in Situ Al-based Metal Matrix Composite Reinforced with 22 wt%WAl12 Particles (pages 740–743)

      S. G. Cai, X. F. Ma, H. G. Tang, W. Zhao, C. J. Zhu, J. M. Yan, Z. H. Qiao and B. Zhao

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200600008

      The MAed Al-15wt%W14Al86 sintered at 650 °C for 30min. In situ formed WAl12 intermetallic reinforcements with size μm were dispersed continuously in the Al matrix. Its fracture surface was of the cleavage type. The observation demonstrated the effectiveness of the WAl12 intermetallic phase reinforcement in this MMC.

    10. The Influence of Magnetic Fields on the Mechanical Behaviour of Granular Materials Used for Foundry Moulding: Numerical and Experimental Analysis (pages 743–749)

      P.-M. Geffroy, J. Goni, X. Pena, D. Bernard and J.-F. Silvain

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200600007

      Understanding the mechanical behaviour of granular materials is of financial importance in many industries, including the geotechnical [1], pharmaceutical and foundry sectors. In the latter, granular materials are used as mould elements for lost foam (sand) and magnetic moulding (steel shot) processes. This study focuses on optimising mould geometry and magnetic field characteristics (intensity and orientation) to obtain the desired dimensions of the final product.

    11. Stress Corrosion Cracking and Hydrogen Diffusion in Magnesium (pages 749–751)

      A. Atrens, N. Winzer, G. Song, W. Dietzel and C. Blawert

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200600050

      Evaluation of recent data for hydrogen (H) diffusion in magnesium (Mg) yielded a new equation for the diffusion coefficient of H in Mg. This indicates that there can be significant H transport ahead of a stress corrosion crack in Mg at ambient temperature and that H may be involved in the mechanism of stress corrosion cracking in Mg.

    12. Feasibility Study of Brazing Aluminium Alloys Through Pre-Deposition of a Braze Alloy by Cold Spray Process (pages 751–753)

      L. Zhao, K. Bobzin, F. Ernst, J. Zwick, J. Roesing and E. Lugscheider

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200600001

      Cold spray process is a relatively new coating process with several special properties which are interesting for brazing technology. In the study, a braze alloy Al12Si was deposited onto aluminium alloy 6063 by cold spray process. The deposited samples were heat-treated at 500 and 615 °C. Due to the rupture of oxide scale on braze alloy particles and substrates, a diffusion process occurred between the particles and between the particles and substrates during heat-treatments. The deposited samples could be well brazed with uncoated counter parts both under argon atmosphere as well as in air with fluxes. The results show that pre-deposition of braze alloys by cold spray process can be a very useful tool for brazing aluminium alloys.

    13. Microstructure of Porous TiO2 Coating on Pure Ti by Micro-arc Oxidation (pages 754–759)

      C. Chen, Q. Dong, H. Yu, X. Wang and D. Wang

      Version of Record online: 23 AUG 2006 | DOI: 10.1002/adem.200500274

      Oxide coatings were deposited on the substrate of pure titanium by a technology called micro-arc oxidation. The phase content, surface and cross-section micrographs, element distributions of the coating were observed and analyzed by XRD, SEM and EDS, respectively. A transitional zone with a thickness of 3–4 μm was observed on the interface between the coating and substrate, and the coating has an high hardness of 567 HV0.025. It is believed that the micro-arc oxidation technique will have a great potential for the surface activation for Ti-implants.

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