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L I t E r A t U r s E r v I c E Warmfestigkeit der hochfesten Aluminium-Legierungen. Es ist somit zu erwarten, dass die Anwendung von rasch erstarrten AlTi2-, AlZrl,3-Vorlegierungen zur Entwicklung von neuen Legierungsvarianten mit spezifisch optimierten Eigenschaften führen kann, die eine günstige Alternative zu Al-Cu-Sandgusslegierungen mit Zugaben an teueren Elementen wie Silber, Cer oder Scandium darstellen. 5 Abb., 2 Tab., 33 Qu. ALUMINIUM 11 (2008) Kokillenguss L. Curkovic, M. Fuduric, St. Kurajica Chemical Stability of Alumina Ceramics in Sulphuric Acid MP Materials Testing 50 (2008) 6, S. 336-340 The study of chemical stability of ceramics in acid and alkalis makes it possible to predict their service properties in these media. For this reason, the chemical resistance of cold isostatically pressed (CIP) high-purity alumina ceramics (99.8% Al 2 O 3 ) was studied in different concentration of sulphuric acid (2 wt.%, 10 wt.% and 20 wt.%) at room temperature. Chemical stability was monitored by the determination of the amount of Al3+, Mg2+, Ca2+, Na+ Si4+, and Fe3+ ions eluted in different concentrations of sulphuric acid by means of atomic absorption spectrophotometry (AAS). The corrosion rate constants for ClP-alumina specimens after immersion in H 2 SO 4 solution using different concentrations were determined. Increasing the concentration from 2 to 20 wt.% it was notified that the corrosion susceptibility in H 2 SO 4 Solutions for the CIP-alumina specimens at room temperature decreases. 3 Figs., 3 tables, 9 sources. ALUMINIUM 11 (2008) F. Habashi The periodic table and the metallurgist Metall 7-8/2008, S. 454-460 Andere Werkstoffe As science advances, its laws become fewer but of greater scope. In this respect the periodic law, which is the basis of the periodic table, represents a major step in the progress of chemistry – it affords the natural classification of the elements. The periodic table was developed by chemists more than one hundred years ago as a correlation for the properties of the elements. With the discovery of the infernal structure of the atom, it became recognised by physicists as a natural law. When the crystalline structure of solids was studied, the nature of the chemical bonds was understood, and the theory of metals was put forward, it became an essential tool not only for chemists and physicists, but for metallurgists as well. Of the 87 naturally occurring elements, 63 are described as metals, 16 as non-metals, and 9 as metalloids. It is suggested that chemists abandon the old tradition of numbering the groups in the periodic table, and to give descriptive names instead. 6 Figs., 5 tables, 6 sources. ALUMINIUM 11 (2008) Allgemeine Wissenschaften J. Rögner, E. Kerscher, V. Schulze, D. Löhe Mechanical Properties of Primary Shaped Notched Micro Specimens Made of Aluminum Bronze Advanced Engineering Materials 2008, 10, No. 6, S. 529-533 During the last decades a trend toward miniaturisation in each area of technology led to advances in each technical area. As a result of this, micro mechanical and micro electro mechanical systems became more and more important parts of technology. For the development and dimensioning as well as for increasing the reliability of microcomponents it is necessary to know the differences between micro and macro scale regarding the mechanical behaviour of the components, which are influenced by the production process as well as by geometric boundary conditions, such as notches. This is one aim of the Collaborative Research Centre 499 (SFB 499): “Design, Production and Quality Assurance of Molded Microcomponents made of Metallic and Ceramic Materials”. Within this paper investigations and evaluation methods are presented that show the influence of notches on the mechanical properties of microcomponents made of aluminium bronze. The specimens were produced by micro casting at the Institut für Materialforschung III of the Forschungszentrum Karlsruhe. In section 2 it is described how the characterisation of specimens was carried out. The results of the tensile tests as well as the evaluation methods are presented and discussed in section 3. 6 Figs., 4 tables, 12 sources. ALUMINIUM 11 (2008) W. Fragner, K. Papis, P. Uggowitzer, J. Wosik Herausforderungen und Lösungsmöglichkeiten bei der Herstellung von Verbundgussbauteilen Giesserei-Praxis 7-8/2008, S. 243-248 Andere Werkstoffe Aktueller Leichtbau, vor allem in der Automobilindustrie, setzt besonders auf Mischbauweise, in der verschiedene Materialien eingesetzt werden, um eine Lösung zu erzielen, die eine optimale Kombination aus niedrigem Gewicht, Funktionalität und Preis ist. Daher werden immer öfter Komponenten in Hybridbauweise in Erwägung gezogen. Eine Möglichkeit der Verbindung unterschiedlicher, vornehmlich metallischer Komponenten ist der Verbundguss. Beim Verbundguss wird ein Gussteil bereits durch den Gießprozess mit einem oder mehreren anderen Bauteilen verbunden. Fügeschritte wie Schweißen, Kleben oder Nieten können dadurch eingespart werden. Das Verfahren eignet sich für verschiedene Werkstoffkombinationen, wobei in dem Beitrag auf drei Kombinationen eingegangen wird. Dabei wird ein Einlegeteil in fester Form, meist ein Halbzeug mit einem Bindungspartner in flüssiger Form umgossen. Die Verbindung kann beim Verbundguss grundsätzlich durch Kraft-, Form- und Stoffschluss zustande kommen. 11 Bild., 2 Tab., 17 Qu. ALUMINIUM 11 (2008) Verbundguss C. op’t Hoog, N. Birbilis, Y. Estrin Corrosion of Pure Mg as a Function of Grain Size and Processing Route Advanced Engineering Materials 2008, 10, No. 6, S. 579-582 The precise effect of grain size on corrosion at a fundamental level is not widely understood. In this work we will focus solely on the corrosion of magnesium of 99.9% purity, in order to address a critical fundamental knowledge gap in the assessment of Mg corrosion as a function of grain size. This is of a critical importance as corrosion susceptibility for a given environment is commonly interpreted in terms of Pourbaix diagrams, which do not account for the effect of any micro-structure parameters, such as grain size. Furthermore they tell us nothing about the rate at which Mg may corrode in the active region. With regards to Mg, the oxide layer is not stable in aqueous solutions owing to high compression stresses within the oxide layer (geometrical mismatch with respect to the hexagonal Mg lattice), which Für Schrifttum zum Thema „Aluminium“ ist der Gesamtverband der Aluminiumindustrie e.V. (GDA) der kompetente Ansprechpartner. Die hier referierten Beiträge repräsentieren lediglich einen Ausschnitt aus dem umfassenden aktuellen Bestand der GDA-Bibliothek. Die von der Aluminium-Zentrale seit den dreißiger Jahren kontinuierlich aufgebaute Fach-Bibliothek wird duch den GDA weitergeführt, ausgebaut und auf die neuen Medien umgestellt. Sie steht allen Interessenten offen. Ansprechpartner ist Dr. Karsten Hein, E-Mail: karsten.hein@aluinfo.de 92 ALUMINIUM · 11/2008
L I t E r A t U r E s E r v I c E cause cracks. One possible way of compensating for this effect is by deliberately introducing a large volume fraction of grain boundaries in the bulk material and diminishing the mismatch. However, it is unknown if the oxide that forms on such boundary regions in Mg will have better coherency and if this will be manifest in the corrosion response. Also, the development of advanced casting methods for Mg alloys leading to thin sections below 1 mm translates to an urgent need to study the effect of grain size on corrosion to ensure the integrity of such components or at least understand the factors which control it. We would like to emphasise that there is a lack of literature on purely microstructural effects on corrosion, particularly in the absence of alloying elements. If the effects of chemistry could be isolated and the grain structure varied, then potentially the effect of grain size on corrosion could be determined. Some relevant prior works however have indicated that a decrease in the grain size improves corrosion resistance for γ-stainless steel, and was found to reduce the localized effects of corrosion such that both intergranular corrosion rate and pitting were reduced. Corrosion resistance also increased with decreasing grain size in zirconium at high temperature when nanocrystalline grains were compared to coarse grains. It was further found that corrosion morphology was altered as polycrystalline Cu was grain refined by equal channel angular pressing, whilst corrosion reduction was also demonstrated for IF steel. 4 Figs., 12 sources. ALUMINIUM 11 (2008) Magnesium E. Ebach-Stahl, M. Fröhlich, R. Braun, Chr. Leyens Improvement of the High-Temperature Oxidation Resistance of γ-TiAl by Selectively Pre-treated Si-based Coatings Advanced Engineering Materials 2008, 10, No. 7, S. 675-677 Light weight materials are interesting for high temperature applications in the aerospace as well as automotive industries. Especially for highly stressed components, where materials with low density are requested, γ-TiAl based alloys are attractive to replace the heavy steels and nickel-based alloys because of their good mechanical properties including high specific stiffness, high tensile strength and good creep resistance in a temperature range from 700°C up to 900°C. Titanium aluminides based on γ-TiAl were tested success-fully as parts of automotive engines as well as components in aeroengines, such as low pressure turbine blades. However, application of titanium aluminides is limited to service temperatures below about 750°C due to insufficient oxidation resistance at higher temperatures caused by the formation of fast growing and porous titania. To improve the oxidation behaviour of TiAl the formation of non protective TiO 2 has to be prevented. A method to increase the oxidation resistance of γ-TiAl is the use of coatings. As reported in the literature, Si-based coatings can form stable titanium silicide phases with good oxidation resistance. In this work Ti-Si coatings were deposited on γ-TiAl based material, and their protection capability was evaluated. 4 Figs., 1 tables, 19 sources. ALUMINIUM 11 (2008) Metallkunde F. Klocke, K. Gerschwiler, S. E. Cordes, R. Fritsch Analyses of the Performance Potential of Oxidic PVD Wear-Protection Coatings on Cutting Tools Using the Example of Crystalline γ-Al 2 O 3 Advanced Engineering Materials 2008, 10, No. 7, S. 622-627 Oxidic coating systems are characterised by a multitude of outstanding properties when it comes to cutting technology. These properties include a high resistance to oxidation, chemical stability, low heat conductivity, high resistance to abrasive wear and a low proneness towards adhesion. For this reason, indexable inserts have been coated for many years now with coating systems based on aluminium oxide (Al 2 O 3 ) for turning and milling operations. Due to its high level of brittleness, Al 2 O 3 is not usually applied as a single coating, but only in combination with other hard materials in multi-layer coatings. The deposition of the thermodynamically stable high-temperature modification of the aluminium oxide – the α-Al 2 O 3 – is achieved via a CVD process. This process has been established in an industrial context for more than two decades. Due to process restrictions, it has not been possible up to now to produce the dielectric oxide layers using a PVD operation. Due to the outstanding wear protection and high performance potential of these layers, intensive research has been undertaken over the past few years to achieve this. An initial approach was to deposit amorphous aluminium oxide (α-Al 2 O 3 ) using a high-frequency sputter technique. However, due to the low coating rate and the associated lengthy process times, this operation proved inefficient for coating cutting tools. With the aid of pulse technology it is possible to coat cutting tools for turning, milling and drilling with crystalline oxidic PVD coatings at substrate temperatures of between 500 to 650°C. The oxide coatings may be applied as a mono- or multi-layer coating in combination with nitridic intermediate layers. As shown in the example of the TiAlN/γ-Al 2 O 3 coating system during drilling and milling operations on the nickel-based alloy, Inconel 718, and the quenched and tempered steel, SAE4140+QT, crystalline oxidic PVD coatings represent a new coating generation with enormous performance potential. Al 2 O 3 has a range of properties which predestine its use as a coating material in cutting technology. The combination with other elements to form binary or ternary oxidic coating systems and the deposition of these as multi- or nano-layers provide a multitude of new possibilities for developing PVD coatings that are adapted in a targeted way to meeting particular requirements. Enormous potential is thus available for increasing the performance of cutting tools. 8 Figs., 7 sources. ALUMINIUM 11 (2008) Zerspanen S. Bender, J. Goellner, A. Atrens Corrosion of AZ91 in 1N NaCl and the Mechanism of Magnesium Corrosion Advanced Engineering Materials 2008, 10, No. 6, S. 583-587 The light-weight of magnesium alloys means that they are of considerable interest in transport applications such as automobile construction where it is important to minimise weight. However, their corrosion properties cause concern so much research has been carried out recently on mechanistic aspects of magnesium corrosion. Under conditions of applied current or external polarisation, magnesium alloys exhibit a strange hydrogen evolution behaviour because more hydrogen is evolved at a more positive potential or at a higher anodic current density. This phenomenon is of considerable continuing interest. It is called the negative difference effect (NDE). The experiments were made difficult by the gaseous hydrogen produced shielded the electrode from the solution and precipitation of Mg(OH)2. These experimental difficulties can be overcome by (a) choice of a horizontal specimen orientation and solution stirring and (b) use of a large volume of acid solution, i. e. pH 2. The study would be more convincing test of the standard model of Mg corrosion if it was carried out over a larger range of current density values and for greater time period (i. e. larger amounts of corrosion). Both however increase the experimental issue of Mg(OH)2 precipitation. It is indeed possible that the overall rate of corrosion is related to the hydrogen evolution reaction. Indeed this speculation could be tested if it is possible to develop a mathematical prediction between the applied current density and the amount of magnesium going into solution, amount of hydrogen evolved or functions of these. For AZ91 corroding in 1N NaCl, the volume of evolved hydrogen, the weight loss and the mass of Mg2+ ions was measured for applied current densities from 0 to 6 mA/cm 2 . The measured weight loss was corrected for Mg(OH)2 precipitated on the specimen. The experimental results agreed with the Standard excepted model of Mg corrosion involving the unipositive Mg+ ion. 1 Fig., 3 tables, 47 sources. ALUMINIUM 11 (2008) Metallkunde ➝ ALUMINIUM · 11/2008 93
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