Entwicklung von Diffusionsschichten auf Nickelbasiswerkstoffen für den Einsatz in chlorhaltigen Hochtemperaturprozessen

Development of diffusion coatings on nickel base alloys for the use in chlorine‐containing high temperature processes To open up the possibility of using sewage sludge ashes as fertilizers the removal of their heavy metal contents is obligatory. A process newly developed at the BAM Berlin executes this separation in highly chlorine‐containing atmospheres at temperatures of up to 1000 °C [1]. Unfortunately there are no materials available which can withstand such conditions over longer periods of time. This project deals with the development of materials that allow the operation in highly corrosive environments. The corrosion resistance of nickel base alloys against chlorine‐induced high‐temperature corrosion will be optimized by application of aluminum‐ and/or silicon‐containing diffusion coatings. As coating method the pack cementation process was selected. In this process, the metal to be coated is embedded in a powder, consisting of the coating metal, a halogen‐distributor (e.g. ammonium chloride) and aluminum oxide as filler material. During an annealing process of several hours at temperatures of 800 to 1000 °C, gaseous metal halides form. They diffuse through the powder pack and decompose at the substrate surface, thereby depositing the coating metal. Subsequent solid phase diffusion results in the formation of a protective diffusion layer. From the thermodynamic point of view, materials with a high content of aluminum and silicon show best prerequisites to build up slow‐growing, stable oxide layers with a high potential to protect the material against corrosive attacks. The actual performance of the materials will be examined in long‐time tests under simulated field conditions (high temperatures and chlorine‐containing atmospheres).     

Neue Kunststoffe für den Einsatz in der Technik

New engineering plastics. Plastics are increasingly materials for all fields of industrial, commercial and personal life. This results in numerous specific requirements with respect to their properties which cannot be fulfilled by conventional plastics. The way to improved materials is characterized by several features:

• — development of new polymers,
• — improvement of raw material production and technology,
• — copolymerization,
• — usage of all possibilities as given by multiphase systems.

     

Schweißen von Hohlstrukturen und offenporösen Metallschäumen für den Einsatz in Kombi‐Kraftwerken

Welding of Hollow Structures and Open‐Porous Metal Foams for Application in Combined Cycle Power Plants For applications within the scope of novel cooling concepts joining technologies for sandwich composites and open‐porous metal foams are researched in the context of the Collaborative Research Centre 561 “Thermally highly loaded, porous and cooled multi‐layer systems for combined cycle power plants”. The research motivation and application fields of the different structures are defined. Welding processes and strategies for manufacturing these structures are specified as well as the joining technologies’ characteristics. Planned future works for enhancements of the processes and structures are listed.     

Nitridische und oxinitridische HPPMS‐Beschichtungen für den Einsatz in der Kunststoffverarbeitung (Teil 1)

Nitride and oxy‐nitride HPPMS coatings for the application in the plastics processing (Part 1) In plastics processing adhesive and abrasive wear are some of the main damage mechanisms. For the wear protection and in order to increase the tool life time as well as to improve the quality of the plastic products, binary or ternary chrome‐based coatings like CrN and (Cr,Al)N deposited by physical vapor deposition (PVD) are used. As the chemical composition of the coating has a significant impact on the surface oxide layer formed after deposition and therefore on the wetting behavior of the plastic melt on the tool surface, the aim on this work was to synthesize different coatings from the system Cr‐Al‐O‐N. Therefore, a nitride coating (Cr,Al)N and two quaternary oxy‐nitride coatings (Cr,Al)ON were deposited by using a dcMS/HPPMS (direct current magnetron sputtering/high power pulse magnetron sputtering) hybrid process by varying the oxygen flux. This articles emphasis is on explaining the influence of varying the oxygen flux during the coating process on the coating properties as well as the composite properties towards the plastic mould steel. On this basis a follow up article in the next issue will concentrated on the more application oriented system properties of the three coating systems towards a polycarbonate melt.     

Oberflächenspannungsmesstechnik für den Prozesseinsatz

Using Surface Tension Measurement in Applications When cleaning surfaces it is crucial for the process stability that the optimum surfactant concentration is maintained. The concentration of free surfactants can be measured by determining the surface tension. SITA Messtechnik has developed an innovative sensor based on the bubble pressure method. This sensor makes it possible to continuously measure surface tension with a high reliability. With this application for monitoring cleaning baths the potential to save money arises in regard to the use of raw materials, waste disposal and the costs resulting from undiscovered production failures.     

Nitridische und oxinitridische HPPMS‐Beschichtungen für den Einsatz in der Kunststoffverarbeitung (Teil 2)

Nitride and oxy‐nitride HPPMS coatings for the application in the plastics processing (Part 2) In the previous issue three oxy‐nitridic hard coatings on CrAl‐basis were investigated. These coatings were deposited by physical vapour deposition (PVD) as protective coatings against adhesive and abrasive wear in polymer extrusion. The coatings were developed using a variation of the oxygen content to investigate the influence of the chemical composition on the coating properties as well as composite properties between the coating and the coated tool. Following up on these findings this article will focus on the application oriented system properties of the three investigated coating systems towards the polycarbonate melt.     

Künstliche und natürliche Verbundwerkstoffe für den Einsatz bei hohen Temperaturen

Artificial and Natural Composites for High Temperature Application. Artificial composites are made by embedding reinforcing fibers into a metallic matrix f. i. by means of powder metallurgy. Natural composites are defined by the thermodynamic equilibrium: directional solidified eutectics as natural composites of high stability at high temperatures. Composites will probably replace conventional superalloys as turbine blades in jet engines allowing higher temperatures of combustion and therefore resulting in higher efficiency. Examples of such composites as materials for engine design are discussed. New processing methods (high energy rate forming and directional casting) and some recent results are described. Practical examples are mentioned and an outlook given for use in the near future.     

Zum Einfluss des Schweißens auf das Kriechverhalten moderner Stähle für die thermische Energieerzeugung

The influence of welding on creep behaviour of modern steels for thermal power generation Un‐ and low alloyed ferritic/bainitic Chromium steels as well as high alloyed ferritic/martensitic 9–12 % Chromium steels are widely used for high temperature components in thermal power generation. Welding in all its variety is the major repair and joining technology for such components. The weld thermal cycle has significant influence on the base material microstructure and its properties. The Heat Affected Zone is often regarded as the weakest link during high temperature service. While weldments of un‐ and low alloyed ferritic Chromium steels can show significant susceptibility to Reheat Cracking in the coarse grained heat affected zone, weldments of high alloyed ferritic Chromium steels generally fail by Type IV Cracking in the fine grained heat affected zone during long term service. In this paper the influence of the weld thermal cycle on the base material microstructure is described. Long‐term creep behaviour of weldments is directly related to the main failure mechanisms in creep exposed ferritic weldments and implications for industries using heat resistant ferritic steels are shown.     

Einsatz von Mikroplasmen für die Herstellung von Silizium‐Mehrlagenaufbauten

Micro Plasma Processes for MEMS Packaging The encapsulation of MEMS devices can be difficult, since released micromechanical parts (e.g. membranes, valves, and cantilevers) tend to stick to the surrounding surfaces. Area‐selective surface modification is a new approach, developed by the Fraunhofer‐Institute for Surface Engineering and Thin Films (IST), to overcome these problems. From a more general point of view, area‐selective surface tailoring with microplasmas is an attractive topic for micro systems production. The business transfer of the technique by implementation into the SU SS mask is currently being evaluated.     

In‐situ‐Sauerstoffmesszellen für den Einsatz im Vakuum. In‐situ oxygen sensors for the use in vacuum

The use of galvanic cells with oxide‐ion‐conducting solid electrolytes as sensors in vacuum allows to measure directly the oxygen partial pressure deciding for redox processes at the surface of workpieces during heat treatments. The oxygen exists either as a free molecular gaseous component or in the thermodynamic equilibrium with other gases. The bases of the known gas potentiometry are valid also in vacuum. Reducing gases are indicated in redoxquotients as Q_H = p(H₂O)/p(H₂). For the technique of measurements with solid electrolytes in vacuum special requirements arise. Probes with air reference electrode are already offered commercially. A solid reference electrode formed with Cu and Cu₂O was tested now in the range of pressure from 1 to 10^‐7 bar. It is usable at sensor temperatures between 400 and 650 centigrades. Important disturbances by oxygen permeability of the solid electrolyte were not observed in this temperature range. Changes of the composition of rest gases in vacuum, often arising as a result of wall reactions are indicated by alterations of p(O₂) or Q_H respectively. The accuracy of measurements is improved by consideration of temperature differences between the electrodes.     

Vakuumsystem für den Hochenthalpie-Windkanal

The Institute for Experimental Fluid Mechanics of the DLR in Göttingen has been charged with the task of manufacturing a wind tunnel (unique in Europe) for the investigation of Re-entry Aerodynamics with High Enthalpy Streaming for the simulation of real gas effects.     

Bestimmung der Gasabgabe von nichtmetallischen Werkstoffen für den Einsatz im Ultrahochvakuum (UHV)

When a solid is brought into an evacuated room, it gives off more or less gas of different composition. Literature data on gas release rates are available for established materials, but they are only comparable with each other to a limited extent due to the different measuring techniques and setups used. A qualitative study of the desorbed substances in addition to quantitative data is rarely found. For new products, these data are not yet available in many cases. For this reason, a computer-controlled experimental and measuring facility was set up at the Research Centre Jülich to study the outgassing behaviour of non-metallic materials and special components under ultrahigh vacuum conditions. The mode of operation and setup of this apparatus will be briefly presented in the following. The results obtained will be discussed with the aid of an example, which is representative of the measurements performed to date.     

Aktivlöten von keramischen Segmenten für den Einsatz in verschleißkritischen Bereichen von Schmiedegesenken

Active brazing of ceramic inlays for the application in wear critical areas of forging dies The use of reinforcing ceramic segments in forging tools is investigated and has been successfully tested with model of dies recently. With reinforcing ceramic segments, however, the thermal widening of the steel tool is a major problem for forging dies. Further, only rotationally symmetrical ceramic inserts can be used as reinforcements which restricts the shape capabilities in tool design significantly. A considerably greater design flexibility is possible if the ceramic segments are brazed into the die body material. To this end, reactively brazed ceramic‐metal composites are to be developed and tested for feasibility in the forging process.     

Anforderungen an Beschichtungen für den optischen Gerätebau

Demands on Coatings for Optical Devices Growth in optical technologies requires reliable optical equipment composed in important parts by high quality optical thin film components. Outstanding performance in coatings is an essential demand for optimum functionality and overall stability of the optical apparatus. Developmen of new / hybrid film deposition techniques for industrial use and search for new materials and improved film system design are strictly required.