Galvanisches Verzinken von Magnesiumlegierungen

Zinc‐Plating of Magnesium Alloys Magnesium alloys are highly susceptible to corrosion that limits their application when exposure to corrosive service conditions is needed. One of the ways to prevent corrosion is to coat the magnesium‐based substrate to avoid a contact with an aggressive environment. Results concerning corrosion behaviour of wrought AZ31 magnesium alloy with electrolytic zinc coatings deposited from different electrolyte solutions are described. Evaluation of corrosion processes in chlorides containing solutions was performed by electrochemical measurements. It was found that thick and dense electrolytic zinc coatings formed on AZ31 significantly improve the corrosion behaviour of magnesium alloy after one hour immersion of zinc coated magnesium alloys in corrosive media. Further increase of immersion time leads to relatively fast decrease of corrosion properties. Electrolytic zinc coatings obtained in consecutive alkaline / acidic process demonstrate an improvement of corrosion resistance of coated AZ31. The time to coating degradation strongly increases.     

Superplastizität von Magnesiumlegierungen

Superplasticity of Magnesium Based Alloys In despite of the increasing interest of the industry in extremely lightweight materials during the last years an intensive industrial use of those materials due to the their restricted cold-workabilit caused by the hexagonal lattice is still very limited. Considering this limitation a solution is provided by the superplastic forming of magnesium based alloys which in contrast to other types of materials is neither metallurgically developed nor process optimized. A very promissing step is the cost-saving and recycling-favorable production of a very fine grained microstructure through the use of extruded magnesium alloy chips. After a short introduction of the theoretical basics and methods to quantify the superplastic behavior the results of velocity change test with different magnesium alloys will be shown.     

Erschließung von Magnesiumlegierungen für tribologisch‐korrosive Komplexbeanspruchung mittels durch Plasmaanodisation erzeugter Korrosionsschutzschichten

Development of Plasma Anodised Magnesium Alloys for Tribological and Corrosive Complex Applications Sufficient corrosion resistance of technical magnesium alloys is generally ensured by anodising the components in aqueous electrolytes. In the majority of cases these processes bear environmental risks due to the highly toxically electrolytes and are subjected to substantial legal regulations. Considering these facts the plasma anodisation seems to be a prospective method to obtain good corrosion resistance without using toxic substances. The main goal of the plasma anodisation is the substitution of the aqueous electrolyte by an oxygen plasma. The plasma anodised surfaces were well characterized and the corrosion resistance was proved in the salt spray test according to DIN 50021 SS. For the tests the magnesium die cast alloy AZ91 hp was used. The tests included plasma anodised, plasma anodised and PVD coated and only PVD coated specimens. After the salt spray test the surface of plasma anodised specimens showed sporadic filliform corrosion. The plasma anodised specimens showed superior corrosion behaviour in comparison to the only PVD‐ coated ones. The polished magnesium as well as the as casted samples showed more corrosion attack than the anodised specimens.     

Fügen von Magnesium und Magnesiumlegierungen

Welding of Magnesium and Magnesium alloys Magnesium is mainly connected by screws. In this paper the results of experiments with different welding processes will be presented. The following methods have been applied: TIG, MIG, Nd: YAG‐Laser and CO₂‐Laser welding, electron beam welding and High Power Diode Laser welding.     

Laserstrahl‐ und Reibschweißen von Magnesiumlegierungen

Laser Beam and Friction Welding of Magnesium Alloys The need for weight and cost reduction forces the engineer to develop new alloys with good options for design as well as to constantly optimize the industrial processes with regards to their utilizability and efficiency. With regards to these aspects it is of great interest to investigate the weldability of these newly developed alloys. The focus is put on both a high performance process and a special prosess for low heat influence. Furthermore, new methods will be presented which will make it possible to reduce the number of test runs as well as to identify influences and interactions between main process parameters and marks of quality.     

Einfluss der Oberflächenbehandlung auf das Korrosionsverhalten von Magnesiumlegierungen

For the coating of magnesium alloys, especially those that should be used in medical technologies, fluoride coatings are tested and used. These coatings should enable a predictable degradation behavior for future implant materials. Presently the pre‐ and post‐treatment processes vary, so an optimum to achieve defined thicknesses of the fluoride layers is still not established. The present investigations are based on the process parameters known from the literature, they are discussed and compared. Different pre‐treating times of the base material (pure magnesium and a magnesium‐aluminum‐calcium alloy as a comparison) in 200 g/l sodium hydroxide combined with 96 hours of immersion in 40 % fluoride acid are examined.     

Charakterisierung von Plasmapolymeren mittels Thermolumineszenzmessungen

Characterization of Plasmapolymers by Thermoluminescence Thin plasma polymer films were deposited using the pulsed plasma (pp) mode. These plasma polymers should possess a more chemically regular structure because of the lower monomer fragmentation during the short plasma pulses and the chemical chain propagation during the plasma‐less periods than those produced by the conventional continuous‐wave (cw) mode. In addition to the use of the classic thin film characterization method XPS the method of thermoluminescence was applied to characterize defects and structural specifics in the polymer films produced by pp or cw‐plasma mode. The thermoluminescence method was applied to functional groups‐carrying plasma polymer layers, which are used in medical technology for forming biocompatible and bioactive coatings or in metal‐polymer composites as adhesion‐promoting interlayers.     

Die Bewertung von Kreditgarantien mittels Hyperoptionen

Zusammenfassung. Aus finanzwirtschaftlicher Sicht k?nnen Kreditgarantien als Verkaufsoptionen auf das anteilige Gesamtverm?gen einer Unternehmung interpretiert werden. Die Bewertung von Kreditgarantien erfolgt üblicherweise mit dem Ansatz von Merton. Bei diesem Modell wird jedoch unterstellt, da? sowohl für den garantierten Kredit als auch für das nicht garantierte Fremdkapital vor Ablauf der Laufzeit keinerlei Zins– und Tilgungszahlungen geleistet werden. Unsere Arbeit pr?sentiert ein Modell zur Bewertung von Garantien auf Kredite mit beliebigen Zins– und Tilgungsmodalit?ten. Das vorgeschlagene Bewertungsmodell wird auf Kredite mit unterschiedlichen Tilgungsformen angewendet. Darüber hinaus werden Sensitivit?tsanalysen bezüglich der Einflu?faktoren auf die aus dem Modell resultierenden Pr?miens?tze durchgeführt. Eingegangen: 2. Februar 1999 / Angenommen: 9. Dezember 1999     

Untersuchung von IBBD-Aluminium-Schichten mittels elektrochemischer Rauschanalyse

Examination of IBDA-aluminum-layers by electrochemical noise analysis The quality of extremely thin surface coatings for wear and corrosion protection is significantly influenced by pores and film defects (voids, micro cracks, coated impurities), which can occure in the processing stage. These sites are substantially responsible for a mechanical or chemical degradation of the coating at contact with respective surrounding conditions. To meet the requirements of protection the processing stage is optimized by minimizing pores and flaws. Therefore a suitable testing method is necessary to detect the dissolution of the substrate at voids in the earliest stage and to examine large series with acceptable time expenditure for a statistical accuracy. Investigations for the optimization of coating parameters were carried out by means of Electrochemical noise analysis (ENA) on IBAD-aluminum-layers (ion beam assisted deposition) at mild steel(Ck45).     

Bestimmung von Ausgas- und Desorptionsraten mittels Restgasanalysator

Determination of Outgassing and Desorption Rates by Means of Residual Gas Analysis Especially when using plastic materials in vacuum chambers it is essential to know the amount of gases outgassing from the surface of those materials. Depending on the so-called outgassing or desorption rate one can decide if the proposed plastic material is suited for the desired application and how the vacuum system has to be configured, so that the use of the particular material makes sense. The article will demonstrate by means of 2 examples that there exist temperature-dependent outgassing behaviors of different materials. It also gives an overview of the measuring equipment set up to determine the outgassing rates.     

Barriereausrüstung von Kunststoffen mittels PECVD

Effect Mechanisms in PECVD Barrier Coating of Plastics Especially optical transparency as well as very high barrier functionality, preventing the transmission of gas and aroma, qualifies silicon‐oxide as material of choice for thin PECVD‐coatings on plastics. Whereas permeation through plastics can be described by the Arrhenius‐model, there is no universal model for transport mechanisms through single or multilayer PECVD‐coatings. Models that do exist describe diffusion through defects. These models presume that no permeation besides transmission through these defects occurs. Topic of this research is to determine which model fits the experimental data of oxygen‐ and water vapour‐transmission of experimental data. In order to investigate the applicability of different models, single‐ and both‐sided are compared using different layer architectures.     

Die Integration von Multikriteria-Verfahren insbesondere mittels neuronaler Netze

Zusammenfassung In diesem Beitrag werden verschiedene Konzepte zur Integration von Verfahren zur Entscheidungsfindung bei mehrfacher Zielsetzung in ein entscheidungsunterstützendes System untersucht. Zunächst wird dazu auf verschiedene Ziele eines solchen entscheidungsunterstützenden Systems, insbesondere Interaktivität und Lernverhalten, eingegangen. Danach werden verschiedene Integrationsansätze vorgestellt. An einem Beispiel wird die kombinierte Verwendung mehrerer Methoden demonstriert. Als besonderes interessanter Integrationsansatz erscheint die Nutzung neuronaler Netze. Schließlich wird der Ansatz einer objektorientierten Implementierung dargestellt.This article was processed using Springer-Verlag T_EX OR Spektrum macro package 1.0 and the AMS fonts, developed by the American Mathematical Society.     

Herstellung von Präzisionsschichten mittels Ionenstrahlsputtern

Precise thin film synthesis by ion beam sputter deposition Ion beam sputter deposition (IBSD) is a promising technique for the fabrication of high performance thin films because of the well defined and adjustable particle energies, which are rather high in comparison to other PVD techniques. Recent developments concerning long‐term stability and lateral uniformity of the ion beam sources strengthen the position of the IBSD technique in the field of precise thin film synthesis. Furthermore, IBSD offers a more independent choice of relevant deposition parameters like particle energy and flux, process gas pressure and deposition rate. In this paper we present our currently installed large area IBSD facility “IonSys 1600”, which was developed by Fraunhofer IWS Dresden and Roth & Rau company (Hohenstein‐Ernstthal). Substrate sizes of up to 200 mm (circular) or up to 500 mm length (rectangular) can be coated and multilayer stacks with up to six different materials are possible. Tailored 1‐ or 2‐dimensional film thickness distributions with deviations of < 0.1 % can be fabricated by a relative linear motion of the substrate holder above an aperture. In order to demonstrate the advantages of the IBSD technique especially for sophisticated materials and films with high requirements concerning purity, chemical composition or growth structure, several examples of deposited multilayers for various applications are presented.     

Beschichtung von metallischen Membranen mittels Pulsed Laser Deposition

Coating of metallic membranes by pulsed laser deposition There is increasing demand to functionalize meso‐ and nano‐porous materials by coating and make the porous substrate biocompatible or environment friendly. However, coating on a meso‐porous substrate poses great challenges, especially if the pore aspect ratio is high. In the current work the pulsed laser deposition (PLD) method is used for coating Ni₃Al‐based meso‐porous membranes with diamond‐like carbon (DLC) layers of high thickness homogeneity and adhesion.     

Mikrostrukturierung von fotoschablonen mittels nichtreaktiver hochfrequenzionenätzung

An estimate is made of the effective thickness of the resist mask for delineating a pattern into a processed film with minimum dimensional changes during non-reactive ion etching. The selectivity of the etching process, the thickness of the processed film, the evolution of the mask edge profile and the redeposition of the sputtered material are taken into account. In accordance with this estimate, the technological processes of the non-reactive r.f. ion etching of photmasks of Fe₂O₃, chromium and CrO_x/Cr/CrO_x were investigated using a contact-printed AZ 1350 resist mask. The experimental results thus obtained are interpreted by a model representation of the etching profile and are illustrated by scanning electron microscopy photographs. The conclusion drawn is that non-reactive r.f. ion etching in argon (sputter etching) is a suitable method for the microstructuring of photomasks with micron and submicron dimensions.