Amorphous, hydrogenated carbon films (a-C:H) have been prepared in a PECVD device from methane and ethine as the source gases.The aim was to deposit films at high growth rates while keeping high hardness (25 ± 3 GPa). Hardness, hydrogen content and surface roughness were investigated dependent on the process conditions. Further investigation showed, that the mechanical properties of the a-C:H films are determined by the energy of the ions and the ratio between the film forming ion and the film forming neutral fluxes. On the basis of the collected data the optimal deposition conditions were determined and suggestions for further improvement of the deposition were made. / Amorphe, wasserstoffhaltige Kohlenstoffschichten (a-C:H) wurden mittels PECVD-Verfahren abgeschieden, wobei Methan und Ethin als Quellgase verwendet wurde. Ziel war dabei die Abscheidung der Schichten mit hohen Aufwachsraten unter Beibehaltung hoher Härten (25 ± 3 GPa). Härte, Wasserstoffgehalt und Oberflächenrauhigkeit der Schichten wurden in Abhängigkeit von den Prozeßbedingungen untersucht. Weitere Untersuchungen zeigten, daß die mechanischen Eigenschaften der a-C:H Schichten von der Energie der Ionen und dem Verhältnis der schichtbildenden Ionen- und Neutralteilchenflüsse bestimmt werden. Auf der Grundlage der gewonnenen Daten können die optimalen Abscheidebedingungen festgelegt, und Vorschläge zur weiteren Verbesserung der Schichtabscheidung gemacht werden.

Amorphous, hydrogenated carbon films (a-C:H) have been prepared in a PECVD device from methane and ethine as the source gases.The aim was to deposit films at high growth rates while keeping high hardness (25 ± 3 GPa). Hardness, hydrogen content and surface roughness were investigated dependent on the process conditions. Further investigation showed, that the mechanical properties of the a-C:H films are determined by the energy of the ions and the ratio between the film forming ion and the film forming neutral fluxes. On the basis of the collected data the optimal deposition conditions were determined and suggestions for further improvement of the deposition were made. / Amorphe, wasserstoffhaltige Kohlenstoffschichten (a-C:H) wurden mittels PECVD-Verfahren abgeschieden, wobei Methan und Ethin als Quellgase verwendet wurde. Ziel war dabei die Abscheidung der Schichten mit hohen Aufwachsraten unter Beibehaltung hoher Härten (25 ± 3 GPa). Härte, Wasserstoffgehalt und Oberflächenrauhigkeit der Schichten wurden in Abhängigkeit von den Prozeßbedingungen untersucht. Weitere Untersuchungen zeigten, daß die mechanischen Eigenschaften der a-C:H Schichten von der Energie der Ionen und dem Verhältnis der schichtbildenden Ionen- und Neutralteilchenflüsse bestimmt werden. Auf der Grundlage der gewonnenen Daten können die optimalen Abscheidebedingungen festgelegt, und Vorschläge zur weiteren Verbesserung der Schichtabscheidung gemacht werden.

This article describes the compositional depth profiling (CDP) of diamond-like carbon (DLC) layers by Glow Discharge-Optical Emission Spectrometry (GD-OES). The DLC layers were deposited on flat steel samples. Analysis by using a Charge Coupled Device (CCD) GD-OES instrument revealed saturation effects of the carbon lines at 156 nm and 165 nm. Therefore, the application of these lines for CDP of DLC layers is not possible. A third line at 193 nm was not affected by this saturation effect and is therefore a good choice for calibration. A second effect was observed as a non-flat crater in combination with large differences of the sputtering rate factor of the substrate (1.1) and the DLC (0.032) led to an unusual behaviour at the interface between the DLC layer and substrate. Both measurements of the crater shape and of the sputtered coating weight up to the interface and just behind it showed clearly that about 30% of the DLC layer remains at the crater edge, once the crater centre reaches the interface. This was found to be the main reason for the incorrect DLC-layer thickness, if the intersection between the carbon and iron concentration was used as a measure for the end of the DLC layer.

Achieving sustainable lubrication by using environmentally friendly formulated lubricants has became an essential component of the transition process from fossil-powered vehicles to electrified transportation. Mixtures, or aqueous solutions of molecules such as polyhydroxy alcohols, and glycols usually known as green lubricants make it possible to achieve low friction coefficients under different lubrication conditions, which constitutes a potential alternative to improve the tribological performance of moving parts in automotive systems, at the same time that the environmental requirements are satisfied. There is a need to improve the protection against mild-wear and micropitting offered by green-lubricants before consider using them in the transmission gear box of battery electric vehicles BEVs, where their low shear-stress resistance can potentially help to improve the vehicle efficiency. Therefore, this research work aims to gain understanding of the tribological behaviour of rolling-sliding elements under glycerol-based lubrication, with focus on assessing the influence of different glycerol-based lubricant formulations on the wear modes associated to rolling contact fatigue such as micropitting, and macropitting.  Micropitting tests were carried out by using a micropitting rig, with a roller on ring planetary configuration. The evolution of microcracks, and micropitting was studied for several glycerol-based lubricants at different slide-to-roll ratios (SRRs) 5-30%, and different load contact conditions 1.5-2.5 GPa. A comparison against a fully formulated transmission oil has been performed. A relationship between the surface damage morphology and the operating conditions has been established. The lubrication regimes of DLC coated contacts and uncoated contacts in presence of glycerol-based lubricants were investigated through the construction of 3D friction maps, and Stribeck curves in a wide range of rolling speeds, and SRR testing conditions. The capability of two different DLC coating systems to prevent micropitting onset due to rolling contact fatigue in presence of glycerol-based lubricants was studied: Cr/a-WC:H/a-C:H and a-C:Cr.  Under mixed-lubrication regime it was found that a reduction up to 51% of friction can be achieved by using glycerol-based lubricants compared to a commercial transmission oil. The initial low friction coefficients at low contact cycles was attributed to the low pressure-viscosity coefficient of the glycerol-based lubricants. Friction was even further reduced with the increasing contact cycles since glycerol aqueous solutions were found to promote mild-wear, causing a smoothing of the surface asperities and therefore an enhancement of the hydrodynamic effect due a higher lambda ratio (Λ), making possible to trigger superlubricity in the contact. Surface micro-cracking was found to decrease at low SRR values under glycerol-based lubrication contrasted to the contacts lubricated with a fully formulated transmission oil. Once microcracks were nucleated, micropitting progressed faster in the contacts lubricated with glycerol-based lubricants, while micropitting was null or significantly delayed in presence of transmission oil. With the increasing SRR surface microcracks density and micropitting was found to became higher. The reduction of microcracks density with a glycerol-glycol based lubricant was attributed to the adsorption of long glycol molecules on the steel surface that avoid the direct interaction between asperities. The faster micropitting progression was attributed to the presence of dissolved water in the contact. Thin DLC a-C:Cr coatings were shown to significantly mitigate the penetration of surface initiated pits into the steel substrate, which was translated in a lower volume loss. Local micro-delamination was found to be the main reason behind coating failure in presence of glycerol-based lubricants, as a result, pitting took place on the steel exposed areas.

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