Advanced Engineering Materials

Cover image for Advanced Engineering Materials

July, 2004

Volume 6, Issue 7

Pages 466–602

    1. Contents: Adv. Eng. Mater. 7/2004 (pages 466–472)

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200490005

    2. Fatigue Behaviour of Al-Matrix Composites (pages 477–485)

      O. Hartmann, K. Herrmann and H. Biermann

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400580

      The cyclic deformation behaviour and fatigue lives of different Al-matrix composites reinforced by alumina reinforcements were investigated under total strain control mode at room temperature. The composites differ in either matrix strength (peak aged vs. overaged AA6061 alloy and soft Al99.85, respectively) and/or type of reinforcement (particles, Saffil short fibres and Almax continuous fibres). The damage evolution was characterized by compliance experiments within individual stress-strain hysteresis loops. The differences of the material behaviour are discussed with respect to matrix strength and reinforcement geometry.

    3. Empirical and Data Based Modelling of Steel Technology Processes for Industrial Application (pages 486–494)

      P.R. Scheller and D. Peisker

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400579

      Process models and modelling of the fundamental relationships between the process parameters and the material properties are significant for process automation. Examples taken from the liquid steel treatment, the casting and solidification process and also from the microstructure formation and thermal influence of its properties show the practice oriented modelling of individual processing steps in the manufacturing of steel. Modelling is based both on physical and chemical fundamental principles and on data-based methods. The used data are based on own empirical investigations as well as on selected published data which are collected in the own data base.

    4. Ceramic Membranes for Filtration Applications — Preparation and Characterization (pages 495–500)

      S. Benfer, P. Árki and G. Tomandl

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400577

      This article gives an overview about the preparation and characterization of asymmetric ceramic membranes that have been developed at our institute within the last years. Depending on the required pore size of the filter active layer for filtration applications ranging from microfiltration (MF) up to nanofiltration (NF) different preparation routes have to be applied.

    5. Basic Mechanisms and Models of Multi-Wire Sawing (pages 501–513)

      H.J. Möller

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400578

      More than 80 % of the current solar cell production requires the cutting of large silicon crystals. While in the last years the cost of solar cell processing and module fabrication could be reduced considerably, the sawing costs remain high, about 30 % of the wafer production. At present the large crystals are cut using the multi-wire slicing technology [2] which has the advantage of a high throughput (several hundred wafers per day and machine), a small kerf loss of about 180 μm and almost no restrictions on the size of the ingots. Basic knowledge about the microscopic details of the sawing process is required in order to slice crystals in a controlled way. In the following the principles of the sawing process will be described in this review article as far as they are understood today.

    6. Novel Dispersion Strengthened Metals by Mechanical Alloying (pages 515–520)

      U. Martin and M. Heilmaier

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400410

      Novel oxide dispersion strengthened (ODS) metals were synthesised by mechanical alloying (MA) and subsequent consolidation via hot pressing in protective argon atmosphere. The effect of dispersoid size and volume fraction on the electrical and mechanical properties is exemplified with Cr2O3, CaO and Y2O3 as model candidates for systematically studying the principles of particle selection by Groza and Gibeling. The results for the development of the microstructure under different processing conditions show that control of the impurity level is of primary importance for achieving high-quality, fully dense material. Hence, a modified cryo-milling technique at liquid N temperature was applied. The microstructure of such ultrafine-grained (UFG) oxide dispersion strengthened silver and copper alloys was examined by means of TEM and high-resolution scanning electron microscopy (HRSEM). Data at ambient temperature are presented, revealing that the mechanical and electrical properties can be tailored within a wide range as a function of the microstructure. These results are explained by microstructural concepts for room temperature yielding and electrical conductivity.

    7. Integrated Magnesium Technology (pages 520–525)

      K. Eigenfeld, W. Tilch, S. Erchov and O. Podobed

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400414

      Recent developments in the field of green sand moulding, together with low cost of moulding materials (green sand), high degree of recyclability of moulding materials and high flexibility of green sand moulding process were the key factors, fostering Foundry Institute of Technical University of Freiberg to start an extensive study on sand casting of magnesium alloys. This study focused on two aspects: technology of green sand moulding for magnesium and mechanical properties of magnesium sand cast parts. Since aluminium-containing alloys is the most widely used group of magnesium casting alloys, we concentrated on “classic” alloy AZ91HP. Key results of this study are presented in this paper.

    8. Deformation Behaviour and Microstructure Development of Magnesium AZ 31 Alloy During Hot and Semi-hot Deformation (pages 525–529)

      R. Kawalla and A. Stolnikov

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400418

      Deformation properties and microstructure development between 20 and 450 °C were investigated for Magnesium AZ31 alloy. It was found that this alloy softens preferably by dynamic recrystallisation. This process starts at suitable deformation conditions above 150 °C. However, the temperature region above 250 °C is more interesting for the production process the semi-finished products. The recrystallised grain size depends heavily on the deformation temperature. A grain size with a mean diameter smaller than 10 μm can be created below 300 °C. For further processing of Magnesium sheets, temperatures above 100 °C are suitable, but temperatures above 300 °C are responsible for superplasticity.

    9. On the Deformation Behaviour and Martensitic Transformations of Metastable Austenitic Steels (pages 529–535)

      M. Onyuna, H. Oettel, U. Martin and A. Weiß

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400411

      Deformation behaviour of Type AISI 304 stainless steel was evaluated by uniaxial tensile testing at different temperatures ranging from –60 °C to 200 °C. The strengthening mechanisms of strain-induced transformation of austenite to martensite and variant conversions have been discussed. Ludwigson and Berger's transformation kinetics relationship has been modified to take into consideration temperature during isothermal deformation. A plastic work interpretation of the maximum uniform elongation attained when taking into consideration the various phase transformations during deformation is presented. It has been demonstrated that finite element method (FEM) can be used with a limited number of parameters to predict the flow curves of these steels.

    10. Determination of Ductile Material Properties by Means of the Small Punch Test and Neural Networks (pages 536–540)

      M. Abendroth and M. Kuna

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400405

      This paper compares two different methods for the identification of ductile properties of materials using the small punch test to measure the material response under loading. The finite element method is used to calculate the load displacement curve of the punch depending on the parameters of a hardening law. Via systematical variation of the material parameters a data base is built up, which is used to train neural networks. The second method allows the indentification of material parameters by using a conjugate directions algorithm, which minimizes the error between an experimental load displacement curve and one calculated by the network function.

    11. Fatigue Behaviour of Cast Iron with Globular Graphite (pages 541–544)

      P. Hübner, G. Pusch and L. Krodel

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400409

      Cast iron with bainitic matrix and globular graphite, so called austempered ductile iron (ADI), allows the substitution of heat-treatable steels. The use of ADI in safety-relevant components requires knowledge of the fracture and fatigue behaviour. Cyclic stress strain behaviour and fatigue life at total strain control and random loading have been investigated at ADI (EN-GJS-1000-5) and pearlitic cast iron (EN-GJS-600-3). In addition fracture mechanic tests at cyclic loading at various stress ratios were carried out.

    12. Fatigue Strength of Heat-treatable Steel Under Static Multiaxial Compression Stresses (pages 544–550)

      H.-P. Lüpfert and H.-J. Spies

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400413

      Known conceptions of calculation for consideration of the influence of mean stresses on the fatigue strength are discussed. While previously known models do not consider the changed fracture behaviour due to acting compressive mean stresses or otherwise accept compressive mean stresses only for the same direction of action with the cyclic load, the presented new conception allows the strength assessment of arbitrary multiaxial loads.

    13. Influence of Vibration During Solidification of Molten Metals on Structure and Casting Properties (pages 550–554)

      J. Bast, J. Hübler and C. Dommaschk

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400412

      By a vibration treatment during the solidification process it is possible to change the structure. Model tests were accomplished in order to understand the procedures as deep as possible. On cylindrical samples the influence of a vibration treatment for the process of the solidification was examined. Pure aluminium and the eutectic alloy AlSi12 showed clear differences in the solidification course and in the casting structure.

    14. New Developments in Vertical Gradient Freeze Growth (pages 554–557)

      O. Pätzold, U. Wunderwald, M. Bellmann, P. Gumprich, E. Buhrig and A. Cröll

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400407

      The Vertical Gradient Freeze (VGF) technique is an important method for growing high quality compound semiconductors such as GaAs. Results obtained with a novel VGF set-up developed for the growth under influence of a rotating magnetic field (RMF) and under vapour pressure control are presented in this paper. The RMF is shown to be a powerful tool to affect the heat and mass transport within the melt in a definite way. In GaAs:Si growth, RMF induced flow results in a decreased curvature of a nominally concave-shaped interface, i.e., it contributes to an axial heat transfer at the solid-liquid interface. The axial dopant segregation of Ga in Ge is found to be improved under continuous RMF action due to better mixing of the melt. The set-up also allowed to determine the influence of carbon and the arsenic vapour pressure on the dopant incorporation and crystal quality.

    15. Process Optimization in Copper Electrorefining (pages 558–562)

      M. Stelter and H. Bombach

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400403

      Copper is one of the major metallic materials together with steel and aluminum. At present, approx. 11 Mt of copper are produced all over the world by electrorefining in sulfuric acid electrolytes. In the last years the current density could be increased to 320–340 A/m2 by simultaneous improvement of the cathode quality, although the parameters “electrolyte” and “anode quality” did not change essentially. This was possible substantially by modifying the cell design, the starter sheets and the optimization of inhibitors and flow control at the electrodes. Further possibilities to optimize this process are described in this paper.

    16. Materials and Process Development of Advanced Refractories for Innovative Metal Processing (pages 562–568)

      C.G. Aneziris, F. Homola and D. Borzov

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400417

      Improved structures of MgO carbon bonded materials due to new binder systems and due to the application of electrical currents during operation have been achieved for advanced applications in the secondary metallurgy and during near net shape metal casting.

    17. Studies on a Novel Route to C/SiC (pages 568–572)

      E. Müller, R. Dittrich and K. Moritz

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400404

      Electrophoresis was used for infiltration of two-dimensional woven carbon fibre fabrics with ethanolic SiC powder suspension for producing fibre reinforced ceramic-matrix composites. In these experiments, due to the electrical conductivity of the carbon fibers, the fabrics were used as deposition electrode. In an applied electric DC field the powder particles move into the fabric where they were deposited also within the spaces between single filaments of fiber rovings. By using SiC slurries containing additional sintering aids a high degree of infiltration was obtained within processing times of only a few seconds for a single fabric. Laminated green bodies consisting of stacked single fabrics were slowly dried to avoid crack formation. Pressureless sintering and hot pressing were compared as sintering methods.

    18. Short Fiber Reinforced Hydroxyapatite-based Bioceramics (pages 572–577)

      A. Dorner-Reisel, E. Müller and G. Tomandl

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400401

      If hydroxyapatite-based bioceramics should be exploited under load bearing conditions, mechanical properties, for instance fracture toughness and reliability, need to be improved. The following contribution relates own research results about short fiber reinforced hydroxyapatite for hard tissue engineering to actual developments in this field. In addition to mechanical properties, attention is given to methods of tailoring the fiber-matrix interface, promoted decomposition of hydroxyapatite due to the fiber reinforcement, the presence of amorphous calcium phosphate and the biological behaviour.

    19. Functional Cubic Thin Films — A Structure View (pages 577–581)

      D. Rafaja

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400402

      Real structure of materials influences their physical properties. Thus, the understanding of the relationship between the structure parameters and the materials properties is a necessary basis for materials design. X-ray diffraction is a powerful experimental technique, which yields the required information about the microscopic and mesoscopic structure expressed in terms of lattice parameters, residual stress, microstrain, crystallite size, texture and crystal anisotropy. Application of advanced X-ray methods and related computational procedures is illustrated on a detailed structure study of cubic uranium nitride thin films that shows the connection between the microscopic and the mesoscopic structure parameters.

    20. Structure and Properties as a Result of Electron Beam Surface Treatment (pages 581–588)

      R. Zenker

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400416

      A new generation of high frequency 3D deflection technique opens up manifold possibilities for a wider application of electron beam (EB) technologies for surface treatment. A high flexibility of process parameters connected with high productivity is obtained from the simultaneous interaction of the EB in several processing areas or by carrying out several processes simultaneously. The change of material and component-specific surface properties can be adapted as required. An outstanding improvement of properties can be reached. Typical technological characteristics are explained and the influence of EB parameters on microstructure and properties is discussed. It has been shown that the EB is becoming more and more attractive and important for industrial applications of thermal surface technologies such as hardening, combined thermochemical treatment/hardening, remelting, surface alloying and dispersing

    21. Czochralski-grown Single Crystals with Acentric Symmetry Group 32 (pages 588–594)

      R.B. Heimann and M. Hengst

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400400

      Single crystals with calcium gallium germanate (Ca3Ga2Ge4O14, CGG) structure such as langasite La3Ga5SiO14 (LGS), its niobium (‘langanite’, La3Ga5.5Nb0.5O14, LGN) and tantalum (‘langataite’, La3Ga5.5Ta0.5O14, LGT) analogs as well as strontium niobium gallium silicate (Sr3NbGa3Si2O14, SNGS) and strontium tantalum gallium silicate (Sr3TaGa3Si2O14, STGS) were grown with high perfection by the Czochralski pulling technique. Specific electric conductivity, optical activity, and dielectric, piezoelectric, bulk and surface acoustic, elastic, and electro-optic properties were measured.

    22. Biaxial Fracture Test of Silicon Wafers (pages 594–598)

      C. Funke, E. Kullig, M. Kuna and H.J. Möller

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400406

      The statistical fracture stress distribution of silicon wafers was obtained by biaxial plate bending tests in combination with finite element calculations. For the correct interpretation of these tests it is important that the finite element calculations imply wafer thickness and elastic properties of the multicrystalline silicon wafer, otherwise the resulting stresses will be estimated to high. The Weibull distribution of fracture stresses yields different parameters for each test series of silicon, depending on the surface preparation and wafer manufacturing condition.

    23. Topography of Defect Parameters on Si and GaAs Wafers (pages 598–602)

      K. Dornich, B. Gründig-Wendrock, T. Hahn and J.R. Niklas

      Article first published online: 4 AUG 2004 | DOI: 10.1002/adem.200400415

      A new measurement technique is presented which is able to analyse defects in semiconductor wafers with pieces of information like DLTS. However, in contrast to DLTS the technique is non-destructive, contact- free and highly spatially resolving. Shallow and deep levels can be investigated in un-doped or doped semiconductors. In addition, photoconductivity and carrier lifetime topograms of wafers are possible with extremely low injection levels.