Wasserstofffreie amorphe Kohlenstoffschichten ‐ abgeschieden durch plasmaaktivierte Hochratebedampfung

Hydrogen free amorphous carbon coatings ‐ deposited with plasma‐activated high‐rate evaporation By using the technology of the plasmaactivated electron beam evaporation we deposited hydrogen free amorphous carbon coatings with deposition rates of up to 100 μm/h. The results of the mechanical and tribological investigations show the potential of these layers for the use in case of wear resistance. Hardnesses of up to 16GPa were proved. The actual state of the characterisation of the coatings is described and the outlook onto possibilities of further optimisation is given.     

Diamantartige Kohlenstoffschichten steigern die Effizienz

Diamond‐like carbon thin films enhance efficiency — laser arc deposition of ta‐C Rising prices for fossil fuels as well as the increasing effects of the climate change due to the emission of greenhouse gases reveal the necessity of saving energy. Low friction coatings have an enormous potential in saving energy. Carbon based coatings — named as DLC coatings — are especially well suited for low friction coatings. In particular hydrogen‐free tetrahedral amorphous carbon (ta‐C) coatings are of great interest due to their extraordinary low wear properties. In addition they show excellent low friction properties and especially in combination with specific lubricants the so‐called super low friction effect. For the deposition of ta‐C coatings PVD methods have to be applied instead of CVD methods as it is the case for conventional DLC coatings. We have developed a deposition method which is based on a pulsed arc steered by a laser (Laser‐Arc). This allows us to use large cathodes resulting in a high long‐term stability. Furthermore, the carbon plasma source can be combined with a filtering unit removing almost all droplets and particles, which usually are characteristic for an arc process. The resulting Laser‐Arc source allows for the deposition of smooth and virtually defect‐free ta‐C coatings with a competitive deposition rate.     

Hochleistungsplasmen zur Synthese diamantähnlicher Kohlenstoffschichten

HPPMS high‐performance plasmas for the deposition of diamond‐like carbon coatings Diamond‐like carbon (DLC) coatings Diamond‐like carbon (DLC) coatings can be used in many different applications, due to their adjustable properties like hardness as wear reduction. Regarding to the synthesis of these coatings, research is upon the High Power Pulsed/Impulse Magnetron Sputtering (HPPMS/HiPIMS), which in contrast to conventional processes like the Pulsed Laser Deposition (PLD) provides smooth coatings and therefore less postprocessing. Previous to the coating deposition in‐situ plasma analysis can be utilized to identify the process parameters. The aim relevantof this work was to identify process parameters which enable to generate a high amount and energy of carbon ions, which are required to synthesize hard DLC coatings. Regarding to the carbon ionization the promising process parameters mixture and pressure of the process gas as well as the HPPMS pulse parameters were varied. Finally, process parameters for the DLC coating deposition could be derived from these investigations.     

Tribologisches Verhalten von harten und superharten Kohlenstoffschichten

Tribological behavior of superhard amorphous carbon films The tribological behaviour of amorphous carbon films is determined by monomolecular covering layers strongly attached to the surface. They cause the very low friction in normal humid air, their absence in dry air or vacuum leads to high friction. Any lubricants usually do not improve the tribological behaviour in comparison to air. However for non‐hydrogenated ta‐C films by attachment of specially adapted lubricants an additionally marked reduction of friction is possible.     

L'oxyde de vanadium amorphe hydrate

Hydrated amorphous vanadium pentoxide obtained by quenching of molten V₂O₅ in water is compared to amorphous V₂O₅ previously obtained by splat cooling. The first one contains some strongly bonded water which prevents crystallisation up to 300°C. Short range order around V⁴⁺ ions seems to be the same in both samples and in orthorhombic V₂O₅. Disorder in the amorphous phases leads to a localization of the charge carriers, the electron mobility being about ten times smaller than in the crystalline oxide.     

Verschleissfeste Antihaftschichten auf Basis modifizierter diamantähnlicher Kohlenstoffschichten

In this article technological developments in the field of modified diamond‐like‐carbon (DLC) coatings are described. The most well‐known properties of such DLC‐coatings are high hardness, high wear resistance, a very low friction coefficient (e.g. vs. Steel) and a very good chemical inertness. By doping the amorphous network with non‐metallic elements it is possible to influence the wettability of the DLC coatings over a wide range. This possibility to prepare a wear resistant sticking or non‐sticking DLC‐film opens a wide field of very different technical applications.     

Untersuchung des tribologisch‐mechanischen Verhaltens amorpher Kohlenstoffschichten mittels Load Scanner

Amorphous carbon coatings have a beneficial tribological behaviour since they provide low friction even under dry sliding conditions and at the same time they offer a good wear protection. Under high loads, the applicability of state‐of‐the‐art amorphous carbon coatings is limited by mechanical failure. However, there is still little knowledge concerning the precise failure mechanisms under application‐oriented conditions. In the present study, cylindrical specimens of a cold work tool steel were coated with two commercial amorphous carbon coating systems: a WCC coating with an a‐C:H:W top layer and a DLC coating which architecture is based on that of the WCC coating, but contains an additional a‐C:H top layer. The coated specimens were tested on a load‐scanning test rig in dry sliding contact against uncoated specimens of the same steel substrate. In the tests, the specimens were loaded with a normal force in the range of 13 and 350 N, corresponding to a maximum contact pressure of 1 to 3 GPa. The number of load cycles was varied between 1 and 60. Firstly, the load‐dependent friction behaviour was monitored. Secondly, the tests were stopped at different total cycle numbers allowing for an evaluation of the progress of wear and damage by scanning electron microscopy. For both coating systems, adhesive pick‐up of counter body steel was observed prior to mechanical failure. Whilst the WCC coating system showed first indications of local failure after several load cycles and at contact pressures exceeding 2 GPa, the DLC coating system showed catastrophic failure on a global scale only after few load cycles and over the whole investigated load range.     

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.     

Propriétés électriques des couches minces de GaSb amorphe

The electrical conductivity of sputtered amorphous GaSb films has been investigated as a function of the annealing conditions. The variation of the electrical conductivity with temperature may be explained in terms of a reduction of imperfections in the GaSb films. Following the model of Mott and Davis we calculate a conductivity gap of 0.76 eV for a stable amorphous state obtained by annealing at 210 °C.     

Hydratation et texture fibreuse de V2O5 amorphe

Reversible hydration of amorphous V₂O₅ has been performed in order to study the effect of water upon the properties of the oxide. A drastic change of the ESR spectrum is observed, which turns from anisotropic to isotropic upon hydration. This has been interpreted in terms of a brownian motion which, by analogy with the V₂O₅ gels, is supposed to be due to the fibrous texture of the amorphous oxide.     

Minderung von Reibung und Verschleiß von Bauteilen aus Aluminium mit diamantähnlichen Kohlenstoffschichten (DLC)

Reduction of friction and wear for parts made of aluminium by diamond-like carbon coatings Reduction of friction and wear of machine parts and tools is usually achieved by separating the participating surfaces. This is predominantly done by liquid lubricants. Solid lubricant coatings replace them where hydrodynamic lubrication is not possible or not active. Among the hard and friction reducing layers diamond-like carbon films (DLC) have distinguished themselves as the most interesting representatives. They are deposited on metallic and ceramic parts in a glow discharge of a hydrocarbon gas at temperatures between 150 and 200 °C. Those low deposition temperatures, their very low dry sliding friction coefficient of 0.05 to 0.1, and an elastic recovery of 90 % differentiate them from PVD coatings to a high degree. DLC can also be deposited on light metals with thicknesses of more than 30 μm. For closed films an outstanding protection against corrosion is established. Machining and forming of light metals can be done without cooling lubricants.     

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.     

Indice de réfraction du silicium amorphe hydrogéné préparé par glow discharge entre 95 et 723 K

Optical properties of hydrogenated amorphous silicon films prepared by glow discharge on fused quartz substrates held at temperatures T_s of between 50 and 350°C were determined from near-normal specular reflectance and transmittance measurements in the energy range 0.5–2.5 eV. The measurements were made at various temperatures T_m in the range 95–723 K. The refractive index dispersion data below the interband absorption edge were analysed using the Wemple and Didomenico model. The dispersion energy E_d of samples deposited at 280 and 350°C was found to be independent of T_m but a function of the hydrogen content for T_m < 573 K; the variation in the average gap E_m with temperature T_m was compared with the theoretical models of Varshni and Ravindra. For T_m > 573 K reversible or irreversible variations in the static refractive index n₀ lead to an increase in the dispersion energy owing to a rearrangement of the matrix with or without alteration of the hydrogen content. An interpretation in terms of rearrangement of the matrix under annealing without a decrease in the hydrogen content is proposed for the observed irreversible variations in the static refractive index n₀ of the film deposited at 50°C.     

Obtention de films étain-azote par pulvérisation cathodique réactive-identification de la phase amorphe Sn3N4

The conditions for obtaining tin-nitrogen films by reactive cathodic sputtering in a d.c. system have been determined. The influence of the sputtering parameters on the deposition rate and the density of the films was studied. The amorphous nature of the films was demonstrated by electron diffraction. The different components were identified by microanalysis and infrared spectroscopy. The study shows that the films consist of an amorphous tin nitride matrix Sn₃N₄ containing molecular nitrogen and traces of free tin.     

Characterisation of amorphous carbon coatings for magnetic storage devices via AFM‐Nanoscratching devices. AFM‐Nanoscratching an amorphen Kohlenstoffschichten für die Speichertechnologie

The mechanical properties of ultra‐thin amorphous carbon films used as protective coatings for magnetic storage devices were investigated by means of atomic force microscopy (AFM). Diamond‐tipped cantilevers were used in order to generate scratches with residual scratch depths of only a few Angstroms and even below. The presented method simulates mechanical strains at the head‐disk interface. A driftcompensating image subtracting technique allows the visualisation of these ultra‐shallow scratches and enables the mechanical characterisation of only few Nanometer films widely independent from the hardness of the substrate. The scratch resistance as it is defined here correlates well with the mass density and the sp³ content of the investigated films.