Dünnschichten als Targets für den Schwerionenstrahl

Thin films targets For the understanding of the interaction between matter and matter ions are accelerated on a fixed target. The targets are self-supporting layers with a thickness between several nanometres up to centimetres. The self-supporting thin films are deposited in high-vacuum evaporation units on a soluble interlayer on a substrate, from which they can be removed. Typical materials are carbon, nearly all the metals, the transition metals and several rare earth materials. Beside the chemical purity fairly often an isotopic purity is required.     

Dünnschichtanlagen zur Herstellung von flachen Bildschirmen

The production of flat panel displays requires thin film technologies, which are also known from microelectronics. An essential difference, however, is the substrate size. The deposition of metals, dielectrics and semiconductors is carried out by sputtering and CVD processes in large area in-line systems. Dry etching for the structuring of the substrates is realized in static, single substrate machines.     

Dünne Schichten durch Deposition unter streifenden Einfall

Micro‐ and nanostructured thin films by Glancing angle deposition Physical vapour deposition under conditions of obliquely incident flux and limited adatom diffusion results in films with a columnar microstructure. These columns will be oriented toward the vapour source. An additional substrate rotation can be used to sculpt the columns into various morphologies (slanted and vertical posts, chevrons, screws or spirals). With this glancing angle deposition (GLAD) technique can prepared porous thin films with engineered structures from a variety of dielectric, semiconducting and metallic materials. The paper presents the In this paper the physical fundamentals of the GLAD technique are introduced, the production of micro‐ and nanostructures of different morphology on non‐patterned and patterned substrates is demonstrated and some possible applications of this new deposition technique are introduced.     

Neue Aspekte bei der physikalischen Abscheidung kompakter Dünnschichten aus der Gasphase am Beispiel einer praxisrelevanten Festschmierstoffschicht

New aspects regarding sputter‐depositing dense coatings, in particular a solid lubricant of practical interest Using MoS₂‐based solid lubricant films as an example, this paper focuses on approaches to preventing sputter‐deposited films from attaining columnar microstructures. This is how it becomes possible to deposit tribological coatings that are characterised by a high durability. As a result of scanning electron microscopy on microstructures, texture measurements by means of XRD, and surface analysis, focusing on sputter‐deposited MoS₂ films, a concept of how to develop thick and dense MoS₂‐based solid lubricant films was generated. At an early stage of film growth a dense and flawless microstructure forms. In order to make the favourable properties of these underlayers available for tribological applications, metallic intralayers were introduced, by means of which the MoS₂ film growth was to be repeatedly interrupted.     

Herstellung von verzahnungstragenden Werkstücken durch Kaltfließpressen

Cold Forging of Tooth-profiled Components and Bevel Gears Metal forming of complicated shaped, high loaded components is applied to increase the mechanical properties of the material. High production rates and cost saving production are the economical reasons for the growing market of cold forged accurate serial parts with ready-for-assembly shape. This report describes the production of such parts. Problems of accuracy, interchangeability and tooling are discussed therein. This report gives also important indications as to the finishing the bodies of bevel gears by machining and grinding after case hardening. Fatigue properties and impact values of cold forged parts are discussed finally.     

Die Herstellung von Sonderwerkstoffen durch isostatisches Heißpressen

Fabrication of special materials by Isostatic Hot Pressing The process of Isostatic Hot Pressing is described. The principle of compaction is explained. A review of earlier work in the literature is given. The plant in Karlsruhe — the first in the BRD — is described. The technique of right sample preparation is shown by 2 examples. One of those is the compaction of an UO₂-Mo-cermet. During Isostatic Hot Pressing a metallurgical bonding between can and fuel is observed. Some applications of the new process are: the fabrication of fuel pins for fast breeder reactors, cathodes and collectors for thermionic emitters, thermal shock resistant ceramics and metal-ceramic diffusion bonds. In the field of high speed steel and hard-metal with improved lifetime, the new process is advancing.     

Herstellung verbundverstärkter Aluminiumprofile für ultraleichte Tragwerke durch Strangpressen

Manufacture of Extruded and Continuously Reinforced Aluminum Profiles for Ultra‐Lightweight Constructions Due to similar specific properties of aluminum and steel regarding stiffness and mechanical strength only minor achievements as to their application in lightweight space‐frame structures can be attained by substituting one material for the other. Only the usage of carbon fibre materials or high performance steels promises a weight reduction as to the application of pipes and profiles in ultra‐lightweight structures. At the Chair of Forming Technology of the University of Dortmund a process has been developed which is suitable for the manufacturing of continuously reinforced profiles by means of a modified direct extrusion process. Starting from conventional aluminum billets, various continuously reinforcing elements are being embedded in the wall thickness of the profile matrix. For this process, which is being investigated in the context of the Collaborative Research Centre SFB/TR10, new extrusion dies have to be developed. During experimental studies on a 2.5 MN laboratory direct extrusion press first reinforced profiles were manufactured successfully. In order to improve the understanding of the process and to predict the efficiency of new tool concepts, FEM simulations were carried out simultaneously. Reinforced straight profiles produced with the help of this method cannot be bend due to possible damages to the microstructure. However, in combination with the process of Rounding During Extrusion, which also has been developed at the Chair of Forming Technology, these reinforced profiles will be producible with a curved contour as well.     

Herstellung diamanthaltiger,enkonturnaher Metallmatrix-Verbundwerkstoffe durch Laserstrahlbeschichten

Near net shape manufacturing of diamond containing metal matrix composites by Laser cladding The present paper reports about a continous near net shape process for the production of metal matrix composites (MMC). Mixed powders are in a single step process fed into a focused laser beam and clad onto a substrate making advantage of an additional sidewards arranged mould. The process allows a homogeneous distribution of thermally instable hard materials like diamonds in a liquid metal matrix and a good bonding between metal matrix and hard particles after subsequent solidification. No thermal degradation of the diamonds could be detected neither by x-ray nor by mechanical tests. Adjusting powder feed rate, feed rate of the substrate and mean power allow the production of several millimeter high finished honing tools with a pre-determined degree of intermixing between metal matrix and substrate. The overspray is considerably lower than 10 percent. By the mould arrangement (external cooling) it is possible to influence the grain size of the metal matrix. For comparable diamond concentration laser clad honing tools show equivalent roughness of the honed workpiece. Clading velocities using a l kW-Nd:YAG-laser are about 2 cm³/min. It could be demonstrated that the described technique can also be used for other coating systems.     

Herstellung neuer Hartmetalle mit Gradientenmikrostruktur durch Mikrowellensintern

Fabrication of New Cemented Carbides with Graded Microstructure by Microwave Sintering State of the art technologies for producing coated cermets and cemented carbides are in‐situ processes based on application of a reactive sintering atmosphere as well as ex‐situ processes, e. g., thermal CVD. Within the frame of the project summarised in the present paper, application of microwave radiation as heating source within both processing routes has been shown to be a viable and powerful new technology to accelerate processing rates as well as to integrate different processing steps into one process of sinter‐coating. Upon microwave sintering in reactive, e. g. nitrogen containing atmosphere, functionally graded materials are obtained from all Ti‐containing materials, with extended compositional gradients and dense Ti(C,N)‐coatings even in grades, which do not develop such coatings upon conventional vacuum sintering followed by reactive atmosphere heating. Microwave sintering offers therefore a much higher degree of variation in composition and gradient extension as compared to conventional processing routes. The acceleration of mass transport is impressive, yielding in some materials undesirably thick coatings at processing times of less than 1 h at temperature. Therefore further investigations are necessary in order to gain insight into the metallurgical processes occurring under the action of a microwave field. The thermal CVD‐process is not accelerated by the presence of the microwave field in such a significant way as the reactive atmosphere sintering is. However, using microwave heating a new reactor principle is developed, the so called “warm wall” reactor, in which only the samples are coated due to selective microwave heating, not the reactor. The coating process is performed at ambient pressure of an inert gas, immediatly after the sintering step, using precursors well known from conventional CVD. Due to microwave sintering no Co is enriched at the surface of the tool bits. Microwave sintering was expected to significantly increase the variability of processes which yield functionally graded cemented carbides and cermets and at the same time to improve the quality of the products or enable the synthesis of new materials. Based on preliminary results of cutting performance as well as process reproducibility and due the development of graded structures in materials which do not develop such microstructures under conventional processing conditions, these expectations were more than fulfilled.     

Technisch‐wirtschaftlicher Review der Herstellung tetraedrisch‐amorpher Kohlenstoffschichten durch Lichtbogenverdampfen

Technical and economical review of the production of tetrahedral‐amorphous carbon films by vacuum arc evaporation Due to the high energy of the depositing species, vacuum arc evaporation is suited for the production of tetrahedral‐amorphous carbon coatings (ta‐C). As besides, the process allows for high deposition rates, it seems to be ideal for the deposition of ta‐C in industrial mass production. However, during the evaporation process inevitably macroparticles are formed, which also deposit on the parts to be coated, degrading the coating properties considerably. Therefore, measures are necessary in order to counter the formation and/or deposition of these particles. The following article intents to give an overview of possible measures and to subject them to a technical and economical evaluation in regard to their application in industrial mass production.     

Virtuelles Werkstoff‐ und Prozessdesign funktionaler Schichten

Virtual Material‐ and Processdesign of Functional Coatings Thermally sprayed and plasma transferred arc clad coatings are often used to improve the surface properties of mechanical parts with regard to an improved wear and corrosion behavior. New coating processes and applications can be developed, if it is possible to control the coating microstructure by a defined management of the process parameters. Simulation can be used to get a detailed understanding of the process‐material interaction for a defined controlling of the process parameters with less experimental effort. This allows a systematic variation of the coating structure and to calculate the parameter set which represents the best compromise between a high deposition rate and low residual stresses in the coating. In order to model thermal spraying, the following sub‐processes are considered: gas flow, material supply, heating and accelerating of particles, particle impact on the substrate, coating formation, solidification and formation of residual stresses. The results presented in this paper will demonstrate the influence of the process parameters on particle properties and subsequently on the splat formation, the coating formation and the coating microstructure. Controlling different process parameters like material injection conditions and substrate properties, the heating, cooling and solidification behavior of the particles and the coating structure can be influenced significantly.     

Dünnschichtsolarzellen

Thin Film Solar Cells The direct conversion of sunlight into electricity — photovoltaics (PV) — has emerged as a strongly growing market during the past years. Today, more than 80 % of the world market is supplied by solar modules based on mono‐ or polycrystalline silicon wafers. Thin‐film solar cells promise significantly lower costs for photovoltaic energy conversion, and thus will probably dominate the PV‐market in the future. Consequently, the production of thin film solar cells will lead to key technologies of the 21^st century. This article addresses the three most advanced types of thin‐film cells describing the status of these technologies at the laboratory level, in pilot production, and in first production lines. The challenges along the way from laboratory developments towards mass production are discussed, fo cusing on the central role of the vacuum‐based technologies applied for thin film deposition.     

Herstellung von Hartstoffschichten durch nachträgliche Erwärmung von ionenimplantiertem Titan

Generation of hard coatings by post‐implantation heat treatment of ion implanted titanium Nitrogen and carbon ions were implanted into titanium and Ti‐6Al‐4V at substrate temperatures below 50°C. Due to the low temperature, no formation of titanium nitride or titanium carbide was observed. After a post‐implantation heat treatment X‐ray diffraction patterns showed interference lines of titanium nitride and titanium carbide, respectively. Differences in the diffusion coefficients of nitrogen and carbon in α‐ and β‐titanium lead to different crystallite sizes of the hard phases. An expansion of the substrate lattice and the formation of the hard phases caused an increase in hardness and an enhanced wear resistance of titanium alloys.     

Herstellung massiver metallischer Gläser aus kristallinen Gefügen durch lokales kleinvolumiges Umschmelzen

Metallic glasses, or the so‐called bulk metallic glasses (BMGs), have peculiar properties such as extreme strengths and hardness while their specific ferromagnetic properties can be controlled accurately by the alloy content which is due to their amorphous structure. This special properties combination makes them interesting for research and technology. In the current research work, the development of a novel method for the creation of amorphous structure via locally limited re‐melting of the crystalline Fe‐based pre‐alloys is presented. Two alloys, namely Fe₇₆Si₉B₁₀P₅ and Fe₄₃Co₇Cr₁₅Mo₁₄C₁₅B₆ (at.‐%), are produced by melting and slow solidification. The solidified dendritic, crystallographic bulk afterwards is locally heat treated by electron beam welding. Here, a high‐energy electron beam is focused onto the crystalline surface of the pre‐alloy, so that the material is melted rapidly at the surface for a short time and then re‐solidified very fast by self‐quenching. By this process technique both the surface and a relative big volume of the material is glazed. For the evaluation of the amorphous phase scanning electron microscopy coupled with energy dispersive X‐ray analysis (SEM/EDX) and high‐resolution electron diffraction based on transmission electron microscopy (HRTEM) were used. These methods are able to show the lack of structural order of the atoms and by that amorphous structures were evaluated [1].     

Herstellung von verschleißfesten WC-Co Schichten durch Hypersonic Flammspritzen

Preparation of Wear Resistant WC-Co Coatings by Hypersonic Flame Spraying The basic principle of hypersonic flame spraying is shortly described. With this process WC-Co coatings are produced, using two powders of the same chemical composition and same range of grain size, but different in their morphology. The investigation of the coatings leads to the result that sound coatings of high density, high hardness and high bond strength can be produced within a wide range of process parameters. Significant differences in the microstructure of such coatings can be achieved through the difference in powder morphology rather than through a variation of process parameters.     

Untersuchungen zur Herstellung flächig gekrümmter Bauteile durch den Einsatz der Robotertechnik beim Freiformschmieden

Analyses for the production of plane‐curved work pieces by the assist of a robot in open‐die forging The forging process is characterised by its high level of flexibility of the applicable materials and the semifinished part‐geometry which is achieved by simple tools. A 6‐axis hydraulic forging robot was installed as a manipulator (adequate carrying capacity: 300kg) to complete a hydraulic open‐die‐forging press (max. force: 6,3 MN) at the Institute of Metal Forming (IBF) of the RWTH Aachen University some years ago. The goal was to get a higher complexity and a higher reproducibility of forged workpieces compared to today´s forging plants. This equipment offers the possibility of manufacturing plane‐curved workpieces in an industrial scale by hotforming. The parts can be used for the following closed‐die‐forging operations by material pre‐distribution. An industrial application is an aluminium‐bulkhead applied in aviation, which is subjected to severe material demands.