Kohlenstoffbasierte Beschichtungen

Carbon‐based Coatings Coated components are used in many applications in motorcars. The objective of first applications was mainly wear reduction. Currently friction reduction gets more and more in the spotlight. Coatings are systematically developed and implemented as a design element. The selection of a suitable coating or a coating system should be based on an evaluation of the complete tribological system. Friction reduction is usually only possible in the boundary friction and mixed lubrication regime. The roughness of body and counterbody and their running‐in limits the possible effect. The compatibility of lubricants and coatings gets more and more important. As an example an engine oil with MoDTC additive results in increased friction of DLC coated valve‐train components in certain speed ranges. A specially for this application adjusted metal‐containing DLC (CrC/a‐C:H) avoids this effect.     

Tribologische Beschichtungen

Tribological Coatings Friction and wear limit the life of tribological systems and lead to damage valued in billion. In many cases tribologically stressed components or tools can only be economically operated with the use of lubricants. Tribologically effective films can replace lubricants or reduce the extent of their use. There are many ways to realise coatings with low friction but only carbon based coatings like DLC (diamond‐like carbon) and polycristalline diamond films combine low friction with a high wear resitant.     

Beschichtungen lassen Werkzeuge kalt

Temperature of cutting tools by thin films During the cutting process, cutting tools are exposed to complex mechanical, thermal, dynamic and tribological loads. Especially in the case of dry machining the demands on cutting tools are very high. Dry machining becomes more and more interesting because of tightened up ecolaws and increased costs for the handling of coolants. Due to a renunciation on coolants the cutting tools need to be modified to the process of dry machining. Thereby modern plasma and ion based surface technologies can be used to deposit a thin film adopting the functions of coolants, e.g. cooling and lubricating. In this research project several coating types, e.g. titanium and chromium based coatings, where developed and characterized regarding their mechanical, tribological and thermal properties. For the research, four partners collaborated permuting all steps of surface and coatings design. Materials Science Institute (WW), Aachen University of Technology, performed the development of PVD coatings and the thermophysical characterization by thermal wave analysis. Surface modifications of uncoated and coated tools by ion beam assisted deposition were carried out at Stiftung Institut für Werkstofftechnik (IWT), Bremen. To determine the cutting properties of coated tools, practical tests were performed at Laboratory for Machine Tools and Production Engineering (WZL), Aachen University of Technology.     

Hochreflektierende Beschichtungen auf Kunststoffoptiken

Metallized polymer substrates offering highest reflectance are not yet state of the art. Coating organic substrate materials is still a task that is connected with multiple problems. Insufficient adhesion of coatings on polymer substrates represents one of the main difficulties. We could show by experiment that aluminium and silver layers indicate good coating adhesion on many different polymers if they are deposited by vacuum evaporation considering certain process parameters. High reflectance values and a good climatic stability of the metal coated polymer parts are other important challenges to plastic mirrors. By performing roughness measurements on the different polymer samples and by comparing reflection values obtained after coating these samples the impact of the polymers surface quality on the reflectance after metal coating has been investigated. Particularly high reflectance above 97% was realized with a protected silver mirror as well as with dielectric enhanced aluminium. Applying these layer systems excellent reflection properties has been obtained on several plastic substrates comparable to those on glass mirrors. Furthermore the dielectric layers used for reflection enhancement showed the ability to protect the aluminium coating against climatic influences.     

Biokompatible und bioaktive polymere Beschichtungen

Biocompatible and bioactive polymer surface for most biomedical applications of polymers biocompatible surface properties are highly needed. here we present various methods to immobilize biocompatible and also bioactive hydrogels on polymer surfaces. In one approach, macroinitiator‐based reactive layers are attached to polycondensates which are able to allow the grafting‐from of various hydrogels. on the other hand, it is possible to immobilize hydrophilic polymers on various substrates by plasma and e‐beam treatment. Stability, swelling and biocompatibility of the polymer films could be verified. by incorporating ph and thermo‐responsive groups, it is possible additionally to control the swelling behaviour by external triggers.     

Beschichtungen für Life Science

Coatings for Life Science Thin film technologies being well known from semiconductor industry and corresponding technologies for microstructures are successfully used in Life Science (medical technology, pharmaceutical research or biology). These technologies are the base of the complex and miniaturized life science products. Life Science is a strongly growing part of microsystems technology enabling innovations like the cochlear implant replacing the human ear or new products like the retina implant, the latter being shortly before market entrance. Since 1960 the use of plastic material in this field grew rapidly and still today it is a growing market for plastic material manufacturers. The reasons are cheap production and easy way to sterilize plastic material disposables.Unfortunately in many cases plastic materials do not possess the desired surface properties. But an additional (functional) coating may lead to the necessary properties. Low pressure vacuum technology as a sub group of vacuum coating technology is well suited for this surface modification. Normally process temperatures are only between 20 °C – 60 °C. Ceramic and metal based products in Life Science can be modified, too. There is a wide range of coating applications e.g. diamond like coatings on stents leading to decreased thrombus formation. In this overview basics of vacuum coating technology and plasma technology are described and examplarily some aspects and applications in Life Science are shown.     

Beanspruchungsverhalten von PVD-CrN Beschichtungen auf Leichtmetallwerkstoffen

Behaviour of light metals with PVD-CrN coatings using different test methods The application of thin hard coatings on machining tools, e.g. drilling tools is state of the art. The increase of lifetime of coated Tools compared to uncoated tools is well known. [1]. In this context ?separation of functions”? is an often used phrase, by meaning the separation of functions of the volume and the surface of materials. Going one step forward, from the point of view of tribology or corrosion this means, you have ?only”? to protect the surface by using a ?good”? coating without looking at the material underneath. In the past the influence of substrate materials or the optimization of the system (substrate-coating) was not the main aim of PVD development. Looking at substrate and coating as a system is especially necessary, if the differences of the properties of substrate and coating are large (e.g. hard coating – light metals). This paper shows different aspect of the tribological and electrochemical characterization of PVD coated light metals (CrN coating).     

Funktionelle Beschichtungen auf Basis anorganischer Nanosole

Functional coatings on basis of inorganic nanosols The controlled hydrolysis of silicon or metal alkoxides produces nanoparticulate oxide sols which condense to thin transparent gel films on any substrates after coating and drying (so‐called “sol‐gel process”). The co‐hydrolysis and co‐condensation of different alkoxides (chemical modification) as well as the embedding of different additives (physical modification) offers almost unlimited possibilities to vary the properties of nanosols and, therefore, also of the resulting coatings, and to adapt them to the purpose intended. By coating of flexible substrates like textiles, papers or polymer foils it is possible to combine the material protecting functions of the inorganic oxide layer with new functional qualities, e. g. modification of surface energy and charge, alteration of the optical properties, realization of biocompatible and bioactive properties.     

Potentiale moderner PVD‐Beschichtungen

Potentials of Innovative PVD Coatings Hard PVD‐Coatings for wear protection of tools are commonly used in many production purposes for about 20 years. Based on the experiences made with PVD‐processes for deposition of hard coatings “tribological coatings” with optimized friction properties have been developed. These friction optimized coatings can take over some of the lubricants functions in unlubricated processes. Today in many operations the use of additional lubricants can be avoided or at least minimized using innovative tool coatings. As a consequence expensive cleaning processes of the parts can be omitted and environmental pollution is reduced.     

Entwicklungstendenzen auf dem Gebiet der organischen Beschichtungen

Development trends in the field of organic coatings . Modern materials for organic coatings are supposed to permit economic processing and should be unobjectionable in environmental terms. These requirements can only incompletely be satisfied by modification of conventional products. Thus the aspects are good for water-soluble binders as well as for solvent-less materials curing by chemical reaction only. However, developments in the processing field are becoming even more important than those of materials. Electrostatic spraying procedures and dipping techniques with trichlorethylene as solvent demonstrate the progress made in generally approved methods. The use of powder as coating material, the method of film-curing by electron beams, and the electro-coating process, however, are novel procedures based on appropriate physical effects.     

Beschichtungen für Zahnräder

Coatings for gear wheels In order to optimize the goal, steel gear wheels regarding load‐carrying capacity and wear, thin film coatings were tested. Different coating systems were examined numerically with the software ELASTICA® for their suitability. The characteristics of the coating systems were determined dependent on the material, its surface treatment as well as the diameters of relevant rolling partners. Differences were made between macroscopic rolling contacts between the teeth profiles and microscopic contacts with surface roughness and abrasion particles. First the four best suitable coating systems were deposited on simplified rollers and examined under different conditions. Two coating systems were determined, which show special suitability for the coating of the gear wheels. The first system is an a:C‐H coating with an CrN interlayer. The second system is an a:C‐H coating wtih an CrN interlayer on a plasma‐nitrided substrat (Duplex‐process). In order to protect the coatings on the teeth, their involute profile was provided with a tip relief. As gear wheel materials 16MnCr5, 42CrMo4 as well as the special steel ETG®88 were used. Two kinds of flow fats were used as lubricants and additional the unlubricated operation was examined. The gear wheels were tested at three different speeds on a test machine especially built for it. The testing routine was carried out in so‐called power‐stages. Each stage means a defined number of contacts and a certain Hertzian stress on the teeth profiles. With each stage the Hertzian stress was increased. The end of operation time is the beginning of cavitation pitting. The test results showed that in particular with the steel 16MnCr5 and 42CrMo4 the used Duplex‐systems leads to considerable increases of the load‐carrying capacity of the tooth flanks and the wear resistance. This increase was observed both with fat‐lubricated and with unlubricated gear wheels. The results for the special steel ETG®88 were less promising. An unlubricated operation could be made possible by the described coatings, which would not have been possible without the coatings. However the results are not as good as the results of uncoated gear wheels wih use of minimum fat lubrication. The reason could be an insufficient nitriding‐depth. For the selected steel the plasma‐nitriding parameters were investigated with the goal of optimized nitriding‐depth. Unfortunately up to the end of this project the gear wheels could not be treated with the optimized Duplex‐Process. At present the attempts with optimally plasma‐nitrided gear wheels are carried out. After that it would be possible to give recommendations for the plasma‐nitriding process and the necessary coating as well as the selection of the fat.     

Beschichtungen und Evakuierung von Vakuum‐Solarkollektoren

Coating and Evacuation of Solar Collector Tubes The company NARVA, a traditional German producer of fluorescent lamps, has started in 2005 the development of a new vacuum absorber tube for collecting of solar energy for warmth of buildings or for process heat. By adapting the experience of lamp making NARVA is using their self produced soda lime glass, coated with Siliciumdioxide nano particles for the collector tubes. This coating gives better transmission, less corrosion and a behaviour like safety glass in case of destruction. A other interesting item in the development of the vacuum process is the „light oven”︁. By use the light oven it was possible to reach the necessary temperature on the absorber fin for an effective desorption of the water molecules from the surface of the fins and to reach the target vacuum.     

Erweiterter Einsatz von Turbomolekular Vakuumpumpen durch Beschichtungen

Turbomolecular‐pumps (TMP) can be used for suction of gas in a wide range of pressure. Limitations are primarily due to thermal and chemical capacity especially of the highly loaded pumping rotor. Prospects and limits to extend application fields by use of adequate functional coatings are reported.     

Nanocomposite‐Beschichtungen auf CBN‐Werkzeugen

Nanocomposite coatings on CBN‐tools CBN (cubic boron nitride) cutting materials are often used to improve the properties of cutting tools. This allows new applications and processes, which are not possible with common cutting materials (e.g. hard metals). Today CBN cutting materials are mostly coated to estimate the wear by an optical evaluation. Coatings on CBN cutting materials for enhancement of the tribological properties are normally not used. For improvement of the properties of used CBN tools during the cutting process a coating technology was developed. This technology combines the advantages of CBN cutting materials with the excellent properties (e.g. hardness, temperature stability) of nanostructured materials. Investigations with different coating systems and pre‐treatment processes were done to test the CBN cutting tools. These investigations have been shown, that nanocomposite coatings can be used to enhance the tool life of CBN cutting tools. Important for an increase in the tool life is a very good coating adhesion, which can be reached by special adhesion layers and an optimized coating structure.     

Maßgeschneiderte Beschichtungen für moderne Isolierglasanwendungen

Customized coatings for high performanceglazing The article considers the state of art in Low‐E Glazing Technology. Technological circumstances are discussed as well as the practical use of modern insulating glass products. Some trends in the development of coated products are mentioned in an overview.     

Kohlenstoffbasierte Beschichtungen für automotive‐Komponenten

Carbon‐based coatings for automotive components The outstanding properties of carbon‐based coatings are the low friction against steel and the wear resistance, interconnected with the high hardness. In lubricated systems coatings only work in the mixed and boundary friction regime; this means as long as primary body and counter body are still in contact. The properties of coatings can be adjusted in wide ranges. A purposeful adaptation requires that the tribological system is sufficiently well understood. It has been shown that solutions based on coatings are only sub‐optimal if the coating is only introduced at the end of the designphase. A greater benefit is obtained, when the scope for development as given by a coating is utilized already in the early design phase. The coating is accepted as a design element. To test the suitability of the selected coating quickly and inexpensively in advance, the usual standard laboratory tests are not always appropriate. A test set‐up has to be close enough to the application to generate useful results. These considerations are illustrated using the example of a piston pin coating. The roughness of the primary body and of the counter body is of particular importance for the adjustment of the coating system, when high loads are applied. The example presented here shows that the usual indicators for surface roughness like R_a and R_z are not always sufficient.     

Untersuchungen zum Erosionsverschleiß an schweißtechnisch hergestellten Beschichtungen

Erosion resistance of hard‐facing deposits Erosive wear is inflicted by flying, bumping and furrowing particles inside the gaseous medium. Especially air vents – fan blades are the principal victims ‐ and conveying systems are attacked by solid particle impingement if fly ash, raw‐meal, cement or clinker are involved. High load of particles in combination with high circular velocities cause enormous loss of material on exposed components. Hard‐facing deposits as produced by flux‐cored arc and plasma trans‐arc welding in form of wear plates or local overlays at pertinent places are able to diminish this effect. Secure dimensioning of above mentioned systems during project engineering status only is hardly possible. So far solutions for wear protection are mainly based on time‐ and cost‐intensive field tests on the part of the manufacturer or user of affected plants and equipment. Within the framework of presented investigations experiences in laboratory testing of hard‐facing materials for attacked components are discussed. Wear tests on platings by practically relevant media give information about influencing factors as well as wear‐ and damage‐mechanism.