PVD – Eine Erfolgsgeschichte mit Zukunft

PVD – A success story with a future PVD coatings in the range of a few nanometers up to some microns have become state of the art in engineering technology. PVD coatings can be found anywhere in our everday lives. They are used in data storage mediums such as CDs or DVDs. Car or architectural glasses are improved by thermal insulation coatings. A diffusion barrier is achieved via PVD coatings at food packaging. For decorative aspects sham jewelery and accessoires are coated as well as fittings. In the last three decades PVD coatings have been established in a variety of technical applications acquiring wear protection and/or friction reduction. First, coatings for tools have been developed, later on for components as well. So, in the past lots of experiences have been made not only in coating development, but likewise in methodical product design. By contrast, the surface has not yet been regarded as construction element. Here the knowledge is just at the beginning. The achieved performance of coated components can be improved drastically if the tribological system consisting of coating, substrate and intermediate material is designed for one single application with regard to the macro‐ and micro geometry. An exemplary application derived from the collaborative research center (SFB 442) “Environmentally friendly tribosystems” at the RWTH Aachen university is discussed. Results of fundamental research and their way into industrial applications are presented. The research development is reflected with regard to the development of the industrial PVD market. Regarding a process chain for the exemplary application the development method of surface technology is explained beginning with the production up to field testing of a new product.     

nanoHVOF – Prozesstechnik und Schichteigenschaften einer neuen,hochdichten Spritzschicht

Thermal spray layers are used as protective coatings against wear and corrosion. A vast range of metallic and non metallic materials can be utilized in tailor made surfaces for engines, turbines or agricultural equipment. Conventional thermal spray coatings often show imperfections. Melting or infiltrations of porous layers are methods to improve coating quality even though they are expensive. Special thermal spray processes like HVOF are more advantageous in these cases. The nanoHVOF produces high density coatings with a high hardness. It includes powder, torch and nozzle techniques. The new developed nanoHVOF‐process is described, wear properties are evaluated and nanoHVOF‐coatings metallographically examined. The comparison between nanoHVOF and conventional HVOF coatings is presented.     

SiNx-Submikrometerschichten – Parameteroptimierung –

SiN_x-submicrometer coatings – Optimization of the film properties – The influence of the deposition conditions on the properties of SiN_x-coatings was investigated. The characterized SiN_x-coatings were deposited by the help of reactive magnetron sputtering. Gas pressure and film thickness were varied. Scanning electron microscopic views of the cross sections show a columnar structure varying with the deposition parameters. The different structures are comparable to the known structure zone models. There is a transition from dense structures to open columnar structures with increasing gas pressure. The Microstructure of coatings also changes with increasing film thickness. Especially deposition conditions promoting shadowing effects lead to a large growth of the column diameter with increasing thickness. The intrinsic stresses and the ultramicrohardness of the coatings change with changing gas pressure, too. Dense structures have high intrinsic stresses and a high hardness while coarse columnar structures have low intrinsic stresses and a low hardness. The influence of the deposition parameters on wear behaviour and adhesion of the SiN_x-coatings was investigated by cavitation tests. Dense coatings with high intrinsic stresses show adhesion failures, and coatings with lower stresses and coarse columnar structures fail because of their lower intrinsic stability. Thus, there is an optimum gas pressure, at which the best properties are reached. It can be shown that with decreasing film thickness adhesion increases.     

Slip‐rolling resistance of ta‐C and a‐C coatings up to 3,000 MPa of maximum Hertzian contact pressure

The slip‐rolling resistances of hard and stiff thin films under high Hertzian contact pressures can be improved by optimizing the “coating/substrate systems”. It is known from former investigations that the so‐called “egg‐shell” effect is no general hindrance for high slip‐rolling resistance of thin hard coatings. The coating stability depends more on specific deposition process and coating/substrate interface design. In this article it is experimentally shown, that pure amorphous carbon thin films with hardness between 15 and 63 GPa can be slip‐rolling resistant several million load cycles under a maximum Hertzian contact pressures of up to 3.0 GPa. Whereas all coatings were stable up to 10 million load cycles in paraffin oil at room temperature, reduced coating lifetime was found in SAE 0W‐30 engine oil at 120°C. It was shown how the coating hardness and the initial coating surface roughness influence the running‐in process and coating lifetime. No clear correlation between coating hardness and coating lifetime could be observed, but friction coefficients seem to be reduced with higher coating hardness. Very low friction down to ?0.03 in unmodified engine oils was found for the hardest ta‐C film.     

Flächeneinfluss bei der PACVD‐Beschichtung

Impact of the active surface on properties of DLC films in the PACVD coating chamber. In the automotive industry, economic and stable industrial processes to apply hard coatings for tribological applications are required. Hence detailed knowledge about the influence of coating parameters on the film characteristics is essential. the following paper deals with the process of plasma activated chemical vapor deposition with focus on the effect of the parameter “active area in the coating chamber“ on the properties of diamond‐like‐carbons (DLC). the coatings are deposited in an industrial coating chamber using reactive magnetron sputtering with a pulsed bias voltage (40 kHz) and at constant pressure. During the investigation of the influence of active area and current density on the mechanical and tribological properties of the DLC films, the expected correlation between active area and current density could be confirmed. By regulating the current density, consistent film properties could be achieved, independently of the active area in the chamber. Furthermore improved wear characteristics of the film – crucial for the endurance of heavily loaded automotive components – were achieved by adapting the load pattern of the chamber.     

Cumulative author index for volumes 99–110

The problems facing the engineering designer in the selection and specification of surface coatings are outlined. In particular the benefits and difficulties of the systems concept in coating selection are discussed. A computer-based technique utilizing artificial intelligence principles has been developed to assist the designer in this area. Two programs POLYCOAT and TRIBCOAT are under development which can be interrogated in an interactive response-oriented mode by the non-expert designer. Knowledge is encoded in a series of rules of the situation→action form which can represent the scientifically inexact factors in coating selection. In effect these “expert systems” emulate the performance of a human consultant in the field, having a capability for decision making in open-ended domains.     

Deposition of PVD Coatings on different geometries and local characterization for reliable properties

Although the characteristics of PVD coatings in research and development papers are very promising, in the field of tribology the industrial application of these coating types is restricted to special market segments up to now: the deposition of hard coatings is state of the art on tools, whereas PVD coated machine components are quite rare. This is caused by the coatings profile of properties, the various surroundings and the demands for application reliability. The last aspect is the main topic of this contribution. Reliability is especially important for machine components, because tools may fail after relative short life time compared to machine parts. Besides this tools and the corresponding production equipment are designed for fast tool replacement in contrast to other machines, which should work without standstill and with a minimum of maintenance. Characteristics of coated systems must be guaranteed in practice theory and laboratory experiments have to show what is possible. On the one hand reproduction of the deposition process must be guaranteed to enter application fields with high demands for reliability, on the other hand characterization of coated systems must be standardized with admissible deviations for communication between coaters and users. These aspects are important for decisions concerning the use of coating substrate systems in tribology besides the topics of technical function. The present investigation shows main reasons for deviations in results of PVD coatings.     

Zur Ermittlung der Abscheidungseigenspannungen und verbleibenden Eigenspannungen in galvanisch hergestellten Nickelschichten nach der Spiralkontraktometer- und Streifendehnungs-Methode

Concerning Investigation of Internal Electrodeposition Stress and Residual Internal Stress in Electrodeposited Nickel Coatings by Spiral Contractometer and “Strip Dilatometer” Methods . For assessing the affect of material and plating conditions on internal stress in electrodeposited coatings and its influence on material strength of plated parts it is better knowing internal stress in thin, just deposited layers (while plating process continuous) and also the course of internal stress in the coating (after plating has been finished) instead of investigating an average stress in the coating. In order to get this more substantial information on internal stresses in electrodeposited coatings a deposition model – gradual composition of the coating – and stress calculation methods were developed for Spiral Contractometer and “Strip Dilatometer”. Both methods were applied on measurements in a Watts-Nickel electrolyte.     

Abscheidung superharter Kohlenstoffschichten mittels Laser‐Arco® auf dem Weg vom Labor in die industrielle Serienfertigung

Superhard carbon film deposition by means of Laser‐Arco® on the way from the Laboratory into the industrial series coating Diamond‐like carbon films (DLC) are more and more applied as wear protection coatings for components and tools due to their unique combination of high hardness, low friction and sticking tendency to metallic counter bodies. Up to now applied DLC films are hydrogen containing (a‐C:H) or metal carbon films (Me‐C:H) deposited by a plasma assisted CVD process from carbon‐hydrogen gas mixtures. Their wide industrial effort results from that the can be deposited with slowly modified coating machines for classical hard coating (e.g. TiN or CrN). A new generation DLC films are the hydrogen‐free ta‐C films (ta‐C = tetrahedral bounded amorphous carbon) with a between two and three‐times higher hardness and with a resulting higher wear resistance under extreme condition than classical DLC films. They have excellent emergency running properties at lubrication break down. Their industrial application is more difficult due to that they cannot deposited with modified coating machines for classical hard and DLC coating and a new technology with corresponding equipment was not available up to now. The laser controlled, pulsed arc deposition technology (Laser‐Arco®) of the Fraunhofer IWS Dresden has this potential. In kind of a Laser‐Arc‐Module‐source the ta‐C film deposition can be integrated in every industrial used deposition machine.     

Materialien für die Brillenbeschichtung in Aufdampfanlagen

Materials for ophthalmic coatings in PVD – coating equipments In our days we cannot have an isolated view only at the coatings for organic lenses. We need to analyse the interaction of substrates, hardcoats and layerdesigns to deliver a longlife – quality of the complete complex “eyeglases”. Special in the field of organic substrates we could observe in the last years an enormous change. The push to deliver more and more thinner and lighter lenses, produces materials with higher indices. The result from this problem is not the adaptation of the antireflection desin at the substrate index but the adaption at the mechanical and thermal properties of these substrates. The caoting labs influence at the complete system is more or less reduced only by the antireflection system. The substrate‐ and hardcoat material could be influenced only by the “world player” for ophthalmic systems. All the small and middle size coating labs worldwide must buy the substrates‐ and the hardcoat materials and have to accept the quality. The only exertion of influence is in the selection of film materials for the AR‐coating and the process technology. The right choise of coating material in quality, form and costs is crucial for a high quality AR‐ coating. A multitude of factors must be considered for the selection of the adequate material.     

A perspective on the optimisation of hard carbon and related coatings for engineering applications

Hard carbon coatings hold the key to improved performance for many types of products. However the achievement of these improvements requires the selection of the appropriate type of carbon coating and therefore the correct process and appropriate deposition parameters. The huge range of properties achievable in carbon coatings is mainly due to the ability of carbon to form different types of interatomic bonds, to take up different sites, and to adopt different structures. In addition to intrinsic material properties, other factors must also be considered for each application, such as the adhesion level achievable and coating cost. This complex situation explains why the number of applications for hard carbon films is still more limited than originally expected. Despite the considerable progress achieved during the last decade in hard coating technologies, practical results often appear conflicting, with differences in properties occurring even within the same types of coatings. Furthermore, the many different deposition systems and processes which have been developed introduce further complications in regard to (for example) achievable coating uniformity and deposition rates. Thus, there is often confusion in the use of certain fundamental principles, especially regarding the growth mechanisms and the effects which produce more dense homogeneous and stable coating materials. This is especially true for the improved properties of tetrahedral amorphous carbon films, which are different from previously reported diamond-like carbon materials, and can be created by adapting and improving existing industrial processes, to offer advantages compared to earlier coatings, and hence possibilities for important new applications. This paper discusses issues relating to intrinsic material properties, and practical aspects such as adhesion, to provide a framework for the development, selection and use of hard carbon coatings in practical situations.     

EURAXLES – A global approach for design,production and maintenance of railway axles: WP4 – “Tools,technologies and surface protection systems minimizing the negative influence of corrosion or surface damage on the free axle surface“

Work Package 4 “Tools, technologies and surface protection systems minimizing the negative influence of corrosion or surface damage on the axle surface” of the EURAXLES project aimed on development of practical solutions for wheelset protection systems to avoid corrosion and damages at the axles and thus minimizing the risk of axle failures. The work included investigations for improving the paint adhesion by grit‐blasting of the axle surface, alternative and innovative coating systems, recommendations for quality tests of painting and coatings and also investigation of unpainted axles.     

Elektronen–Spin–Resonanz – Eine Methode zur Bewertung der Radikalaktivität auf photokatalytischen Implantatoberflächen

Electron Spin Resonance – A Method for Testing the Radical Activity of Photocatalytic Implant Surfaces In a project funded by the Landesstiftung Baden–Wuerttemberg in the research program “biological materials / biocompatibility” is the applicability of electron spin resonance (ESR) for the proof of photocatalytically produced radicals among other things reviewed. The light–triggered generation of radicals on a photo catalyst can be analyzed in–situ under UV–A–irradiation in the ESR spectrometer. Thereby radicals are quantified by their quantum–mechanical spin by absorption measurements in a magnetic field. In the context of the project photo–catalytic TiO2 coatings of the anatas crystal modification are examined on implants for their suitability as antimicrobial surface coatings. The produced radicals can decompose surface contaminations. In order to get a deeper understanding of the generation process of radicals for the production of antimicrobial surfaces, it is of interest to determine radical species and radical quantities. Both can be examined with the ESR on photo–catalytic TiO₂ coatings, dependently of the irradiation dose. In the following article it is shown that the ESR can contribute to demonstrate the effectiveness of the photo–catalytic coatings. Time–dependent contact angle measurements and electron spectroscopy for chemical analysis (ESCA) complete the ESR results. The results lead also to an extended understanding of the photo–catalytic generation of radicals on anatas TiO     

Großflächige Beschichtungen mit der mikrowellenangeregten Plasmapolymerisation

Plasma enhanced chemical vapour deposition is a common known technology for coating plastics with a wide variety of coating properties. In comparison to lower frequencies microwave enhanced plasmas shown a comparatively high deposition rate which is of decisive importance for industrial use. But for many of these microwave plasma sources the coated are is quite small or the coating homogeneity is unsufficient. IKV developed a microwave plasma source for coating substrates up to 450 × 140 mm². Coating rate is up to 0.1 μm/min and layer thickness inhomogeneities are less than 1%. Difference concepts for energy input like the “Gigatron” or ?Duo-Plasmaline”? concept will be presented.     

Optische in‐situ Prozessverfolgung und ‐steuerung

In situ optical monitoring and process control: Measuring transmittance and reflectance of optical coatings during deposition Optical monitoring techniques havebecome indispensable parts of deterministic preparation strategies for sophisticated optical coatings. Traditional versions of optical broadband monitoring are based on measurements of the transmission spectrum or alternatively the reflection spectrum of the growing film. In the case of practically loss‐free samples, both approaches principally deliver equivalent information. In the case of absorbing coatings, the information gained from the different spectra may be no more equivalent. Instead, it may be reasonable to record both spectra simultaneously, in order to get a more complete picture of the status of the growing film. We present a corresponding measurement setup designed for use in typical coating evaporation processes and demonstrate its application to the deposition of alumina coatings as well as aluminum mirrors.     

Oxidation protective coatings for γ‐TiAl – recent trends

Engine designers show continued interest in γ‐TiAl based titanium aluminides as light–weight structural materials to be used at moderately elevated temperatures. Although alloy development has made significant progress in terms of mechanical properties and environmental resistance, protective coatings have been developed that help to extend the lifetime of these alloys significantly. The major challenge of coating development is to prevent the formation of fast growing titania. Furthermore, changes of coating chemistries at high temperatures have to be considered in order to avoid rapid degradation of the coatings due to interdiffusion between substrate and coating. The paper describes recent work of the authors on different coatings produced by means of magnetron sputter technique. Thin ceramic Ti‐Al‐Cr‐Y‐N layers tested at 900 °C exhibited poor oxidation resistance. In contrast, intermetallic Ti‐Al‐Cr, Si‐based and aluminum rich Ti‐Al coatings were tested at exposure temperatures up to 950 °C for 1000h resulting in reasonable and partially excellent oxidation behaviour.     

Exploring the Nickel–Graphene Nanocomposite Coatings for Superior Corrosion Resistance: Manipulating the Effect of Deposition Current Density on its Morphology,Mechanical Properties,and Erosion‐Corrosion Performance

The use of graphene‐based composite as anti‐corrosion and protective coatings for metallic materials is still a provocative topic worthy of debate. Nickel–graphene nanocomposite coatings have been successfully fabricated onto the mild steel by electrochemical co‐deposition technique. This research demonstrates the properties of nickel–graphene composite coatings influenced by different electrodeposition current densities. The effect of deposition current density on the; surface morphologies, composition, microstructures, grain sizes, mechanical, and electrochemical properties of the composite coatings are executed. The coarseness of deposited coatings increases with the increasing of deposition current density. The carbon content in the composite coatings increases first and then decreases by further increasing of current density. The improved mechanical properties and superior anti‐corrosion performance of composite coatings are obtained at the peak value of current density of 9 A dm^?2. The incorporation of graphene sheets into nickel metal matrix lead to enhance the micro hardness, surface roughness, and adhesion strength of produced composite coatings. Furthermore, the presence of graphene in composite coating exhibits the reduced grain sizes and the enhanced erosion–corrosion resistance properties.

     

High performance hard carbon coatings (diamond‐like coatings)

Different dLc coating types are applied at an industrial scale by sulzer Metco thin Film. The coatings are generated with different coating architecture. Deposition methods are: magnetron sputtering, electron beam evaporation and PA‐cVd. Reactive magnetron sputtering is used to deposit metal containing a‐c:h coatings (a‐c:h:Me), e.g. MAXit W‐ch. Pure a‐c:h coatings as functional top coatings are used for cavidur®, MAXit® AhdLc and special versions of dylyn® coatings. In addition to the pure a‐c:h coatings, doped a‐c:h coatings are also used. The dylyn® family of coatings is comprised of at least one layer a‐c:h:si:O. The dylyn® coatings may be doped with metal (a‐c:h:ti:si:O) to adapt selected properties like electrical conductivity.