Gas phase lubrication study with an organic friction modifier

Friction modifier additives play a crucial role in controlling friction and wear of lubricated tribological systems. Model experiments in a controllable atmosphere performed by integrating a tribometer into a system of in situ surface analytical methods in vacuum can give insights into the additives functionality. In this work, thin, well-defined layers of an organic friction modifier (OFM) are adsorbed onto an iron oxide surface by means of an effusion cell immediately before measuring friction and wear. The results show that contrary to the assumption that homogeneous layers are formed, this OFM accumulates in droplets on the surface. Droplet number and radius increase with evaporation time. In friction tests, the smallest friction values are found for a low coverage of droplets. For larger droplets, friction increases due to a capillary neck of additive that forms between the sliding surfaces and is dragged along during the friction test

In Situ Studies on the Competitive Adsorption of Lubricant Additives

A key factor for improvement and innovation in lubricant development is a fundamental understanding of adsorption processes and competing adsorption mechanisms [1]. Many different base oils and additives, as well as various surfaces build a complex interaction space, which has been difficult to map with in-situ methods so far. Here we present a study on the adsorption of corrosion inhibitors, anti-wear additives and friction modifiers from a synthetic and a mineral base oil on metal (Fe2O3) surfaces. In order to obtain quantitative and spatial data during the adsorption process we set up a combined quartz crystal microbalance (QCM-D) and confocal scanning laser microscope (CLSM) [2]. In addition to QCM-D and CLSM, also a UHV-tribometer was used to study the performance of gas phase deposited additives films without environmental interferences. In combination with macroscopic performance tests using a “ball-on-three-plates-tribometer” and corrosion tests, the adsorption, the morphology and the mechanical properties of the additives were correlated with their performance. The multidisciplinary results provide exciting new insights into lubrication fundamentals and reveal so far undescribed phenomes and mechanisms of action. [1] J. Guegan et al. ,Friction Modifier Additives, Synergies and Antagonisms, Tribology Letters 67 (2019) [2] J. Honselmann et al., submitted, 201

In-situ studies of the competitive adsorption of lubricant additives

It is known that different types of surface-affine additives (i.e. antiwear/anti-corrosion/ anti-friction) can have very different adsorption behaviour on surfaces (e.g. [1–3]). The interactions can be synergistic or antagonistic in character and influences the near-surface chemistry of the sliding surfaces and therefore also the tribological performance of the system. For wear protection additives, it is for instance known that phosphor and sulfur containing layers are formed under tribological conditions (e.g. [4,5]). In this presentation we will give an overview on an ongoing study of the adsorption of selected additives using novel in-situ approaches. The found correlations are also compared to tribological experiments in order to answer the question whether synergistic effects in adsorption also lead to synergistic effects in wear reduction

Role of Nitrogen and Yttrium Contents in Manufacturing (Cr, Y)Nx Film Nanostructures

The high-power impulse magnetron sputtering (HiPIMS) technique was applied to deposit multilayer-like (Cr, Y)N(x) coatings on AISI 304L stainless steel, using pendular substrate oscillation and a Cr-Y target and varying the nitrogen flow rate from 10 to 50 sccm. The microstructure, mechanical and tribological properties were investigated by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, instrumented nano-hardness, and wear tests. The columnar grain structure became highly segmented and nanosized due to pendular substrate oscillation and the addition of yttrium. The deposition rate increased continuously with the growing nitrogen flow rate. The increase in nitrogen flow from 10 to 50 sccm increased the hardness of the coatings (Cr, Y)N(x), with a maximum hardness value of 32.7 GPa for the coating (Cr, Y)N(x) with a nitrogen flow of 50 sccm, which greatly surpasses the hardness of CrN films with multilayer-like (Cr, Y)N(x) coatings architecture. The best mechanical and tribological performance was achieved for a nitrogen flow rate of 50 sccm. This was enabled by more elevated compressive stresses and impact energies of the impinging ions during film growth, owing to an increase of HiPIMS peak voltage with a rising N2/Ar ratio

Tailoring the Hybrid Magnetron Sputtering Process (HiPIMS and dcMS) to Manufacture Ceramic Multilayers: Powering Conditions, Target Materials, and Base Layers

The mechanical and wear behavior of CrN/CrAlN multilayers were improved by tailoring the experimental conditions of a hybrid magnetron sputtering process based on a high-power impulse (HiPIMS) and two direct current magnetron sputtering (dcMS) power supplies. To this end, the influence of the base layer and of the combination of Cr and CrAl targets, which were switched to the dcMS and HiPIMS power supplies in different configurations, were investigated with respect to the growth of ceramic CrN/CrAlN multilayers onto commercial gas-nitrided diesel piston rings. The microstructure, grain morphology, and mechanical properties were evaluated by field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and instrumented nanoindentation. Bench wear tests simulating the operation of a combustion engine were conducted against a gray cast iron cylinder liner under reciprocating conditions using 0W20 oil as a lubricating agent enriched with Al$_{2}$O$_{3}$ particles. The results revealed a significant increase in hardness, resistance to plastic strain, and wear resistance when two CrAl targets were switched to a HiPIMS and a dcMS power supply, and a Cr target was powered by another dcMS power supply. The compressive coating stresses were slightly reduced due to the soft Cr base layer that enabled stress relief within the multilayer. The proposed concept of hybrid magnetron sputtering outperformed the commercial PVD coatings of CrN for diesel piston rings manufactured by cathodic arc evaporation

Lock-in thermography as a rapid and reproducible thermal characterization method for magnetic nanoparticles

Lock-in thermography (LIT) is a sensitive imaging technique generally used in engineering and materials science (e.g. detecting defects in composite materials). However, it has recently been expanded for investigating the heating power of nanomaterials, such as superparamagnetic iron oxide nanoparticles (SPIONs). Here we implement LIT as a rapid and reproducible method that can evaluate the heating potential of various sizes of SPIONs under an alternating magnetic field (AMF), as well as the limits of detection for each particle size. SPIONs were synthesized via thermal decomposition and stabilized in water via a ligand transfer process. Thermographic measurements of SPIONs were made by stimulating particles of varying sizes and increasing concentrations under an AMF. Furthermore, a commercially available SPION sample was included as an external reference. While the size dependent heating efficiency of SPIONs has been previously described, our objective was to probe the sensitivity limits of LIT. For certain size regimes it was possible to detect signals at concentrations as low as 0.1 mg Fe/mL. Measuring at different concentrations enabled a linear regression analysis and extrapolation of the limit of detection for different size nanoparticles

Raw Data: Gas phase lubrication study with an organic friction modifier

XPS / tribometer / mass spectrometer raw data supporting the publication "Gas phase lubrication study with an organic friction modifier

Strengthening subject-related learning. The use of video clips at schools in a socially challenging situation

Die Herstellung von Bildungsgerechtigkeit und die Ermöglichung gesellschaftlicher Teilhabe in einer digitalen Welt sind zentrale Fragestellungen für die Zukunftsfähigkeit unseres Bildungssystems und der Gesellschaft. Wie digitales Lernen im Verbund mit fachlichem Lernen gelingen kann, zeigt das hier vorgestellte schulstufen- und schulformübergreifende Projekt zur Erstellung und Nutzung von Erklärvideos. Schüler*innen einer 6. Klasse erstellen Erklärvideos für Grundschüler*innen in sozial benachteiligter Lage, um sie beim fachlichen (hier: mathematischen) Lernen zu unterstützen. Eine der zentralen Erfahrungen der Schüler*innen sowie der begleitenden Lehrkräfte ist dabei, dass nicht allein Ausstattungsfragen und finanzielle Mittel für den Erfolg wichtig sind, sondern die Vernetzung von Medieneinsatz und fachlichem Lernen. So gelingt die Produktion und Rezeption von Erklärvideos für das fachliche Lernen nur, wenn dies kriteriengeleitet und adressatengerecht geschieht. Dann kann das fachliche Lernen mit Blick auf die einzelnen Lernenden gut gelingen, z. B. hinsichtlich metakognitiver Strategien, sprachbezogener Herausforderungen oder verschiedener Zugänge und Darstellungen. (DIPF/Orig.)Improving educational equity and promoting the ability to participate in society are key questions in the digital world - for the sustainability of our educational system as well as our society in general. How fostering digital along with mathematical skills can be achieved is exemplarily shown by our project, which focusses on the conception and us age of learning videos and crosses boundaries between school types and years: Students of German secondary schools create such videos for elementary school students enrolled at schools which are socially disadvantaged to foster their mathematical skills. The key experience of the students and their teachers is that neither equipment issues nor financial resources alone lead to educational achievement. Instead, the production of effective learning videos requires the criteria-led and appropriate preparation for the specific addressees, e. g. regarding meta-cognitive strategies, language-related challenges or various approaches to and varying representations of the mathematical content. (DIPF/Orig.