Advanced Engineering Materials

Cover image for Advanced Engineering Materials

April, 2007

Volume 9, Issue 4

Pages 221–327

  1. Cover Picture

    1. Top of page
    2. Cover Picture
    3. Contents
    4. Reviews
    5. Research News
    6. Communications
  2. Contents

    1. Top of page
    2. Cover Picture
    3. Contents
    4. Reviews
    5. Research News
    6. Communications
    1. Contents: Adv. Eng. Mater. 4/2007 (pages 221–226)

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200790007

  3. Reviews

    1. Top of page
    2. Cover Picture
    3. Contents
    4. Reviews
    5. Research News
    6. Communications
    1. Thixoforming of Steels – A Status Report (pages 231–245)

      W. Püttgen, W. Bleck, G. Hirt and H. Shimahara

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200700006

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      The thixoforming of metals is a new forming technology, which combines the advantages of casting and forging and focuses on the production of structural components with complex shapes. Various components made of Al and Mg are already industrially produced. However, using steels in the thixoforming processes is still a matter of research. This paper summarizes the state of the art of steel thixoforming. Besides relevant material and process parameters, different process routes, numerical modelling techniques, and tool requirements are discussed. In addition, thixoformed prototypes of different steel grades are presented and evaluated with defect index cards, which characterise occurring defects and give suggestions how to avoid them.

    2. ESR Refining Potential for Titanium Alloys using a CaF2-based Active Slag (pages 246–252)

      J.-C. Stoephasius, J. Reitz and B. Friedrich

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200700009

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      Since the end of the Cold War and due to the needs to produce titanium more cost-efficiently and thus more attractive for its civil use, the electroslag remelting (ESR) process has become an increasingly important topic of international research programs, because titanium and titanium aluminides can be chemically refined by ESR in some degree. Using ESR, titanium turnings from machining steps and scrap from foundries can be remelted, refined and provided as secondary titanium for the market at relatively favourable prices. This article investigates the removability of the main impurities out of titanium and titanium-aluminium alloys by electroslag remelting using the active slag system CaF2-Ca-(CaO). Thermochemical and kinetic aspects of the ESR process are considered.

  4. Research News

    1. Top of page
    2. Cover Picture
    3. Contents
    4. Reviews
    5. Research News
    6. Communications
    1. Semi-Solid Processing of Tailored Aluminium-Lithium Alloys for Automotive Applications (pages 253–258)

      R. Sauermann, B. Friedrich, M. Bünck, A. Bührig-Polaczek and P. J. Uggowitzer

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200700007

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      This paper describes the development and evaluation of thixoformable Al-Li-Mg-based alloys performed at the collaborative research center SFB 289, RWTH Aachen. Scandium and zirconium were added to AlLi2.1Mg5.5 (A1420) with the aid of DoE (Design of Experiments), and precursor billets were manufactured by pressure induction melting (PIM). To evaluate the thixoformability of the synthesized alloys semi-solid processed connecting rods were manufactured by the rheo container process (RCP). Subsequent heat treatment raised the mechanical properties to maximum values of tensile strength, 430 MPa, yield strength of 220 MPa, and an elongation to fracture of 13 %. The RCP process was designed for the special requirements of highly reactive alloys. The paper presents the remarkable property and process benefits of the semi-solid processing of Al-Li alloys.

    2. ADI Lost-Foam: Synergy of Process and Material (pages 259–264)

      D. dos Santos, U. Vroomen and A. Bührig-Polaczek

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200700027

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      In the Lost-Foam process foam patterns are used as models for complex and near net shape castings. These models are coated with a special refractory paint. The models are surrounded by unbonded sand and then filled with liquid metal. As the alloyed ductile iron melt decomposes the foam, the coating material is of great importance for the effective extraction of the foam decomposition products. By means of a posterior special heat treatment it is possible to achieve tensile strengths ranging from 800 to 1600 MPa with elongations ranging from 1 % to 12 %. The main achievements of the performed investigations were the development of the alloy and respective heat treatment parameters for the base ductile iron as well as a suitable coating material. Moreover, these investigations showed that it is possible to produce ADI castings capable of achieving the same mechanical properties as forged steel crankshafts with a significant weight reduction.

  5. Communications

    1. Top of page
    2. Cover Picture
    3. Contents
    4. Reviews
    5. Research News
    6. Communications
    1. Fabrication of Micropatterned Surfaces by Improved Investment Casting (pages 265–270)

      G. J. Schmitz, M. Grohn and A. Bührig-Polaczek

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200700028

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      A defined surface texture in the sense of geometrically, relief-like functionalized surfaces of macroscopic investment castings has not been subject of research and development so far. As all materials being used in the investment casting procedure (polymers, waxes, ceramics and metals) allow duplicating structures of micron or even submicron size, investment casting of metallic components with finest surface structures should be possible and should lead to an improved functionality of the cast metallic parts. The present paper details the production of metallic parts with micropatterned surfaces and outlines actual limits as well as further developments of the investment casting process.

    2. Automation of a Vacuum Steel Centre at the Department of Ferrous Metallurgy (pages 271–273)

      U. Epple, S. Geimer, S. Schmitz and D. Senk

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200700008

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      In modern secondary metallurgy vacuum treatment plays a prominent role. For the production of current high quality steel exact alloying of all elements is necessary. Modern vacuum treatment equipment at the Department of Ferrous Metallurgy (IEHK) allows operating at regular steel plant conditions for degassing. Furthermore, a slag can remove inclusions during this process. Injection of gas by porous plugs can achieve a good mixture of the alloyed elements in the melt, and removal of inclusions is accelerated. At the IEHK a vacuum induction-melting furnace including an automation system based on open standards was installed recently. The architecture of the component-oriented process control system combines simple and customizable structures. This combination facilitates the development of new process recipes for high quality steel. Current research at the IEHK is done in the field of high-grade steel production as regards removal of undesirable elements and optimisation of production process. Additionally, new measurement equipment is tested to its suitability for vacuum steel making.

    3. Surface Conditioning of a Cold-Rolled Dual-Phase Steel by Annealing in Nitriding Atmospheres Prior to Hot-Dip Galvanizing (pages 274–279)

      F. Luther, A. Dimyati, D. Beste, W. Bleck and J. Mayer

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200700010

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      The development of steel grades for automotive applications in the recent years has been driven on by two trends: lightweight and improved crash safety. By using steels like DP (dual phase) the goals of passenger safety, fuel efficiency and environmental friendliness can be met at reasonable price. The favorite corrosion protection method for sheet steels in the car industry is the hot-dip galvanizing process. Here, an approach was made to reduce the surface enrichment of critical alloying elements of a dual phase steel grade by reactive annealing in ammonia containing atmospheres. The effects of this treatment on mechanical properties and hot-dip coating behavior are reported.

    4. Challenges in Measuring of Physical Properties of Liquid Phases for Material and Process Optimisation (pages 280–285)

      S. Akbari and B. Friedrich

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200700054

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      The exact knowledge of thermo-physical properties of molten phases is crucial to modern metallurgy. It leads to optimized process windows including better metal/slag separation, suitable slag selection or reduced slag/refractory wetting. The most important properties are melting and boiling point, electrical- and thermal conductivity, melting and transition enthalpies, wetting angle, density, viscosity and surface tension. The aim of this paper is to present opportunities, methods and uncertainties of characterization of this kind of materials. This will be examplified by measuring three physical properties (density, viscosity and surface tension).

    5. Tensile Properties of a Nanostructured Al-5083/SiCp Composite at Elevated Temperatures (pages 286–291)

      F. Tang, B. Q. Han, M. Hagiwara and J. M. Schoenung

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200600270

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      Tensile tests were conducted at temperatures of 298 to 773 K for a nanostructured composite consisting of an ultrafine-grained Al-5083 matrix reinforced with nano-scale SiC particles, which was synthesized with a powder cryomilling and consolidating technique. The nanostructured composite showed enhanced strength. Its ductility increased with increasing temperature to a maximum at 473 K, and then decreased to a minimum at 673 K. A unique work softening phenomenon was observed.

    6. The Negative Difference Effect and Unipositive Mg+ (pages 292–297)

      A. Atrens and W. Dietzel

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200600275

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      This paper evaluates current understanding of the negative difference effect (NDE) in the corrosion of magnesium. There is strong support for the existence of the unipositive magnesium ion and the unipositive Mg+ ion NDE mechanism has been shown to be useful in providing a framework within which it is possible to evaluate the expected rate of production of Mg++ and H2. However, the uncertainty concerning the existence of the unipositive Mg+ ion means that there is scope for further research.

    7. A Possible Biodegradable Magnesium Implant Material (pages 298–302)

      G. Song and S. Song

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200600252

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      The different hydrogen evolution rates for Mg immersed in simulated body fluid solutions with and without phosphates signify that the constituents of the body fluid could play different roles in the biodegradation of a magnesium implant. Currebtly, there is still a lack of fundamental understanding of the corrosion behavior of magnesium in the body fluid.

    8. Consolidating and Deforming SiC Nanoceramics Via Dynamic Grain Sliding (pages 303–306)

      H. Peng, D. Salamon, J. Bill, G. Rixecker, Z. Burghard, F. Aldinger and Z. Shen

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200600243

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      β-SiC nano-powder (30 nm) was densified and thereafter deformed in a Spark Plasma Sintering apparatus. High strain rates, ∼ 1x \. 10–3 /s, were achieved during densification and deformation of the SiC nanoceramics. It was found that dynamic grain sliding, a rapid process that stimulates grain sliding lubricated by a liquid phase but does not activate grain-boundary migration, is a common mechanism responsible for both processes.

    9. Synthesis of Nd-YAG material by citrate-nitrate sol-gel combustion route (pages 307–312)

      A. L. Costa, L. Esposito, V. Medri and A. Bellosi

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200600264

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      Polycrystalline, Neodymium doped, yttrium aluminum garnet Nd:YAG is a functional materials for solid-state lasers. The synthesis of Nd:YAG powders requires a strict control of the precursor reactivity and composition. Sol-gel citrate-based methods increase the chemical homogeneity and reactivity of the precursor powder. Calcination performed around 900 °C leads to the formation of pure YAG phase at temperatures much lower than the temperature required for the solid-state reaction (1600 °C).

    10. A Novel Cemented Hard Alloy Prepared by Mechanical Alloying and Hot-Pressing Sintering (pages 313–315)

      Z. Qiao, X. F. Ma, W. Zhao, H. Tang, S. Cai and B. Zhao

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200600245

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      Owing to its exceptional hardness and superior wear resistance, tungsten carbide (WC) has a wide range of industrial applications. In recent years, many studies have been focused on how to improve the physical and chemical properties of WC, as well as to reduce its high operating cost. One aim of this work was to fabricate the (W0.5Al0.5)C0.5-Co alloy bulk bodies. Hot-pressing (HP) as a common technique is a suitable and economical method to facilitate the sintering of (W0.5Al0.5)C0.5-Co hard alloy. Additionally, the mechanical properties and the microstructures of (W0.5Al0.5)C0.5-Co bulk bodies were tested.

    11. A Novel Approach to the Robust Ti6Al4V-Based Superhydrophobic Surface with Crater-like Structure (pages 316–321)

      Z. Guo, J. Liang, J. Fang, B. Guo and W. Liu

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200600259

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      In this paper, the authors describe a simple and inexpensive method for fabricating a superhydrophobic surface on Ti6Al4V alloy substrate without any chemical modification by means of constructing an appropriate surface roughness. Most interestingly, we found that the as-prepared surface has good mechanical properties, compared to the other superhydrophobic surfaces disclosed to date. Such a surface might be used as friction-reduction and anti-wear material, as well as a self-cleansing material.

    12. High Performance Si-SiC Composite Coating for C/C Composites Prepared by a Two-Step Pack Cementation Process (pages 322–324)

      J.-F. Huang, F. Deng, X.-B. Xiong, H.-J. Li, K.-Z. Li, L.-Y. Cao and J.-P. Wu

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200600235

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      High performance oxidation resistant Si-SiC coating for C/C composites was prepared by a two-step pack cementation method using silicon, graphite powders as source materials and Al2O3, MgO, B2O3 as additives. XRD analyses revealed that the obtained coating was composed by β-SiC, Si and α-SiC; SEM analyses displayed that the as-prepared coating exhibited dense surface and cross-section microstructures. Isothermal oxidation test in air at 1773 K showed that the weight loss of the as-obtained Si-SiC coating coated sample after 200h was only 4.42 × 10–4 g.cm–2. The main cause of the weight loss of the coated sample after long time oxidation is due to the vaporization and exhausting of SiO2 glass film which could not provide sufficient glass phase to seal the holes.

    13. An Organic-Inorganic Nanohybrid Based on Lunar Soil Simulant (pages 325–327)

      Y. Qiao, J. Chen and A. Han

      Article first published online: 2 APR 2007 | DOI: 10.1002/adem.200600212

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      Using a polymer-silicate nanointerphase, lunar soil simulant grains can be strongly bonded together, forming a load-carrying organic-inorganic nanohybrid. The tensile strength is orders-of-magnitude higher than that of ordinary portland cements. This technique, when being extended to real lunar soils, is of great potential in developing high-performance space infrastructure materials based on locally harvestable resources.

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