Entwicklung von metallisch gebundenen Sinterbremsbelaegen fuer Hochgeschwindigkeitsschienenfahrzeug

Sintermetallic friction materials are used in frictional applications with high demands especially as brake linings in high speed trains. In order to provide an appropriate frictional behaviour these materials are porous metallic compounds including different, mainly non-metallic phases. Thus these materials are produced by means of powder metallurgy i.e. uniaxial pressing and sintering. This work deals with the influences of variable processing parameters and material components on the braking behaviour of Cu- and Fe-based-friction materials. Also the issue of different dimensioned friction and wear tests is elucidated. A swelling phenomenon usually observed during sintering of friction materials is investigated. Within the scope of this work several promising brake lining materials could be developed. (orig.)Available from TIB Hannover: RA 831(3241) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Loading characteristics of the material interface in brazed divertor joint components under fusion relevant thermal loads

The following topics were dealt with: Loading nature of the material interface in a joint component under fusion relevant loads; behavior of stress singularities in an CFC/TZM bond interface under transient high heat flux loads; plastic deformation of the ductile braze layer in a CFC/TZM bond joint under cyclic thermal loads; thermomechanical behavior of actively cooled, brazed divertor components under cyclic high heat flux loadsAvailable from TIB Hannover: RA 831(3345) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Finite Elemente Simulation gemessener Eigenspannungen in plasmagespritzten Mehrschichtsystemen

Plasma sprayed multilayer systems are used for high temperature protection. System functionality is mostly influenced by residual stresses originating in the plasma spraying process. The aim of this work was the prediction of these residual stresses. A single layer model was further developed to the analytic stress model for multilayer systems (ASM). The calculation is based on the infinite plate. Simultaneously the finite element stress model (FSM) was designed. To verify both models residual stresses in dependence on different coating parameters were measured by X-ray diffraction and compared with calculated values. The multilayer system relevant to fusion technology consists of boron carbide top coating with copper interlayer applied on substrate stainless steel 316L. The system was studied concerning the processing parameters coating temperature, top coating thickness, interlayer thickness and substrate diameter. The experimentally detected residual stress dependence on coating temperature could not be followed by the analytic stress model. It is unsuitable for describing systems with metallic interlayers. In contrast the finite element stress model showed good agreement with measured values. Accordingly all further simulations were carried out with this stress model. The model qualification was also proved by the variation of top coating thickness and interlayer thickness. All calculated results with the FSM were achieved without the explicite simulation of the coating construction. Only the residual stresses which occure during cooling of the total multilayer system from coating temperature to room temperature were calculated. This simplification could be used because the system was almost stressfree after spraying of the copper interlayer. (orig.)178 refs.Available from TIB Hannover: RA 831(3518) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Entwicklung der elektrophoretischen Beschichtung fuer die Herstellung duenner Elektrolytschichten

Die elektrophoretische Beschichtung wurde als neues Verfahren zur Herstellung von duennen, gasdichten Elektrolytschichten fuer die Feststoffelektrolyt-Brennstoffzelle (SOFC) im Rahmen des KFA-Substratkonzeptes entwickelt. Diese Entwicklung beinhaltete alle Verfahrensschritte von den Ausgangspulvern bis zum leistungsfaehigen Elektrolytschicht-Anodensubstrat-Verbund: 1. Entwicklung und Herstellung der Anodensubstrate. 2. Entwicklung und Optimierung der Elektrophoresesuspension. 3. Aufbau der Elektrophoresezellen. 4. Beschichtung der Anodensubstrate. 5. Trocknung der abgeschiedenen Schichten. 6. 'Cofiring' des Schicht-Substrat-Verbundes. (orig./MM)Electrophoretic coating was developed as a new process for producing thin, gastight electrolyte layers for the solid electrolyte fuel cell (SOFC) in the context of the KFA substrate concept. This development contains all the steps of the process from the initial powders to the capable electrolyte layer anode substrate compound: 1. Development and production of the anode substrate. 2. Development and optimisation of the electrophoresis suspension. 3. Build-up of the electrophoresis cells. 4. Coating the anode substrate. 5. Drying the separated layers. 6. Co-firing the layer/substrate compound. (orig./MM)SIGLEAvailable from TIB Hannover: RA 831(3221) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Pulvermetallurgische Entwicklung von Chrombasislegierungen und Cermets als Materialien fuer den Interkonnektor einer Festoxid-Brennstoffzelle

Fuel cells are electrochemical power sources, that directly convert the energy of a chemical reaction into electrical energy. By this, they have the potential for an efficient and ecologically friendly supply of energy. Fuel cells are subject to research to make the introduction of the fuel cell technology possible by improvement of processes and materials. Aim of this study was the development of materials for the interconnect of a solid oxide fuel cell. The interconnect separates the gas atmospheres and provides conduction of electrical charges to allow the use of the energy won by the fuel cell. During this study two materials were studied with respect to their suitability as interconnect materials: chromium based alloys and cermets of nickel alloy and alumina. Chromium based alloys possess a good electrical conductivity and a high oxidation resistance. By addition of yttria the oxidation resistance can be further improved. During this study the chromium based alloys were processed by mechanical alloying. The effect of the manufacturing parameters and of the composition on the microstructure and the properties of the alloys are described. It is shown, that the manufacturing parameters significantly influence the oxidation behaviour of the alloys. The microstructure has more effect on the oxidation behaviour than the exact composition of the alloy. By use of cermets of nickel alloy and alumina the thermal expansion of the interconnect can be adjusted to that of the other components of the fuel cell. Cermets were processed by pressureless sintering. Even as the melting points of the components greatly differ, relative densities of more than 95% of theoretical density were achieved by optimising the starting materials and the parameters of sintering. (orig.)142 refs.Available from TIB Hannover: RA 831(3515) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Untersuchung mesoskopischer Strukturen an der Grenzflaeche fest-fluessig

Metal clusters have been deposited on metal substrates and characterized with in-situ electrochemical Scanning Tunneling Microscopy (STM). These samples are model electrodes with defined mesoscopic structure and were used to investigate correlation between structure and electrochemical behavior of nanometer sized metal clusters. Different size distribution (1,5-9 nm), mean particle distance (0-50 nm) and chemical composition (Pt, Ru, PtSn and PtRu alloy) have been used. The model electrodes were electrochemically characterized by cyclic voltammetry and by electrooxidation of absorbed CO. Preliminary experiments have been done to use the tip of the in-situ STM as an analytical tool in order to investigate single metal clusters. Hydrogen has been electrochemically developed at Pt clusters and was detected as a current at the STM tip. A summary is given of the theoretical background concerning in-situ STM, metal clusters and their use as model electrodes. The experimental set-up and methods used are described. First the structural and electrochemical properties of the substrates are presented. Flame annealed Au surfaces, Au and Pt single crystal surfaces were used as substrates. It is demonstrated that clean electrochemical conditions can be achieved in the in-situ STM electrochemical cell by monitoring the characteristic single crystal surface voltamogram of Pt(111). Also electrooxidation of adsorbed CO is performed under in-situ STM conditions. (orig.)SIGLEAvailable from TIB Hannover: RA 831(3827) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Thermal conductivity, electrical resistivity and Lorenz function data for metallic elements in the range 273 to 1500 K

The report contains measured values of the thermal conductivity and the electrical resistivity, as well as the (total) Lorenz functions L(T) calculated from them in the temperature range 273-1500 K by two precision methods on 43 pure metals. Two precision measuring methods were brought into operation. Except for the data for six alkali and alkaline-earth metals determined by Cook et al. according to the NRCC method, all other data were determined according to the direct heating method developed from 1982 at KFA Juelich. Apart from closing various gaps in knowledge concerning thermal conductivity, for example with the noble metals, lanthanides and some other metals, including Y, Hf, Re, V, Zr and Ti, the special feature of the present report is a regular behavior found for the Lorenz functions L(T) not previously known for high temperatures. On the basis of previous conceptions, an approximation to the Sommerfeld value of L_0=2.44.10"-"8 V"2/K"2 was generally expected. However, a grouping within five approximately equidistant bands was found, covering the range from 2.15 to 3.15.10"-"8 V"2/K"2. (orig.)56 refs.Available from TIB Hannover: RA 831(3006) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Reproduzierbare Herstellung und Charakterisierung von plasmagespritzten Waermedaemmschichtsystemen auf ZrO_2-Basis

The present state-of-the-art enables the deposition of plasma-sprayed thermal barrier coating systems, especially in turbine construction, with the aim of improving the efficiency of turbines by higher inlet temperatures and thus increasing profitability and reducing pollutant emissions and (electricity generation) costs. To achieve this improvement, a two-layer system is used, consisting of a metallic, vacuum-plasma-sprayed NiCoCrAlY bond coat for oxidation protection and a ceramic 7-8wt%-Y_2O_3 ZrO_2 thermal barrier coating produced by atmospheric plasma spraying and serving as a heat shield. The studies described in this thesis concern, on the one hand, the production of coating using the F4 plasma torch with an established history in the industry as well as the new triplex torch technology. Parameter variations and parameter studies for the bond coats were carried out exclusively with the F4 torch. The top coat studies were performed with both the F4 and triplex torches. For characterization, on the other hand, extensive studies were carried out using mercury analysis, image analysis, microindenter Young's modulus and hardness measurement, thermal cycling, Raman microscopy, roughness measurements, dilatometry, SEM and optical microscopy. The factor test scheme presented here is a procedure which unambiguously defines the spraying distance as the most important factor influencing porosity and spray efficiency with the triplex torch. For both torches, increasing wear (in particular of the cathods) is detected on the basis of different layer porosities. The triplex torch was subjected to much stronger wear than the F4 torch. Wear reducing measures, such as using lower electrical power, contribute to very good reproducibilities for coating production153 refs.SIGLEAvailable from TIB Hannover: RA 831(3669) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Metall-Glas-Waermedaemmschichten fuer Turbinenschaufeln

Die Oxidation an Bondcoats in Waermedaemmschichtsystemen waehrend des Betriebes ist eines der zentralen Probleme des Einsatzes von Waermedaemmschichten (WDS) auf Gasturbinenschaufeln. Diese Oxidation ruft die Abplatzungen der oxidkeramischen WDS hervor und begrenzt damit die moeglichen Einsaetze der WDS im Turbinenbau. In dieser Arbeit wird ein neuer Werkstoff fuer WDS hergestellt und untersucht, dessen Hauptaufgabe es ist, neben der Waermedaemmfunktion einen verbesserten Oxidationsschutz zu leisten. Als neuer Werkstoff wird Metall-Glas eingesetzt; im Unterschied zu oxidkeramischen Schichten besitzt eine Metall-Glas-WDS keine Rissstruktur und kann deswegen gasdicht hergestellt werden. Eine hohe Thermoschockbestaendigkeit des neues WDS-Systems wird mittels einer genauen Anpassung der Waermeausdehnungskoeffizienten von Schicht und Substrat erreicht. Ausserdem koennen die Metall-Glas-Schichten bei Temperaturen hoeher als 500-600 C die thermischen Spannungen durch plastische Verformung abbauen. Die Metall-Glas-Verbundwerkstoffe besitzen die thermischen, physikalischen und mechanischen Eigenschaften, die weder fuer Metalle noch fuer Glaeser typisch sind: sie bilden also eine neue Werkstoffart, die besonders fuer Schichten neue Perspektiven oeffnet. Im Vergleich zu WDS-Systemen aus YSZ sind die Metall-Glas-Systeme fast gar nicht erforscht. Diese Systeme koennen aus mehreren unterschiedlichen Legierungen und Glaesern bestehen und dabei ganz unterschiedliche Eigenschaften besitzen. Die Metall-Glas-WDS, die in dieser Arbeit untersucht wurden, wurden fuer den Einsatz in Gasturbinen entwickelt und muessen den harten Betriebsbedingungen entsprechen: Temperatur auf der WDS-Oberflaeche ca. 1200 C, starker Thermoschock, Betriebsdauer mehr als 10000h. Es gibt natuerlich andere Einsatzmoeglichkeiten fuer diese neue Schichtart. In Frage kommen die Faelle, in denen es um Gaskorrosionsschutz und eine Waermedaemmung geht. Die Metall-Glas-WDS koennten z.B. fuer Dieselmotoren (Waermedaemmung der Kolben) sehr interessant sein. (orig.)Oxidation on bondcoats in thermal insulation systems during operation is one of the central problems of thermal insulation layers on gas turbine blades. The author presents a new material with improved oxidation protection characteristics. It is based on metal/glass; in contrast to oxide ceramics, metal/glass systems have no crack structure and can be made gastight. High thermoshock resistance can be achieved by matching the thermal extension coefficients of the insulating layer and substrate. At temperatures beyond 500-600 C, thermal stresses are removed by plastic deformation. The systems described here are suited for difficult operating conditions. They are an interesting option also for diesel engines (thermal insulation of pistons).Available from TIB Hannover: RA 831(3818) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Optimierung von Anoden der Hochtemperatur-Brennstoffzelle durch Korrelation von Herstellungsverfahren, Gefuege und Eigenschaften

Solid oxide fuel cells (SOFCs) are electrochemical devices which directly convert the chemical energy of a fuel into electricity. At the Research Centre Juelich, the planar substrate concept has been developed, in which the anode, which is a cermet of nickel and yttria-stabilized zirconia, consists of a supporting, porous anode substrate and a thin finely structured coating. The anode substrate currently used has been studied in detail using various methods of characterization, and its properties and microstructural features were determined for further optimization experiments. Various low-cost starting materials and different processing techniques were used for substrate production. These substrates were evaluated on the basis of their properties and microstructure with a view to application in solid oxide fuel cells. A series of microstructural tests have been carried out on anode substrates and anode layers with respect to their long-term stability. Ageing of the anodes due to Ni agglomeration was described quantitatively and in terms of a model. Low Ni agglomeration was observed whenever both Ni as well as YSZ and pores were as finely distributed as possible. (orig.)23 refs.Available from TIB Hannover: RA 831(3678) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman