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Eingeladener Vortrag
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Der Einfluss des E-Moduls und des Grundöls auf das Wälzverhalten von DLC- und Diamantbeschichtungen
(2004)
Downsizing (power-to-weight ratio) and higher speeds lead to a rise in Hertzian contact pressures in combination with an increase in surface or oil temperatures. Under such conditions, commonly used bearing steels, such as 100Cr6, reach their limits, creating a demand for alternative slip-rolling resistant steel alloys. The present work therefore compares the slip-rolling performance of various steel types with Maraging- and PM-type steel alloys such as e.g. CSS-42L™, ASP2012, BIMAX42+, in the Hertzian contact pressure range up to P0max of 4 GPa. Through-hardened 100Cr6H (AISI 52100), case-hardened 20MnCr5 (AISI 5120H) and nitrogen alloyed Croni-dur30 (AMS 5898) still compete in terms of slip-rolling and wear resistance and load carrying capacity, whereas Maraging- and PM-type steel alloys offer superior strength and toughness properties.
Das CargoLifter Ballonkransystem nutzt die Prinzipien der Leichter-als-Luft-Technologie für das Heben von Gütern. Der mit leichtem Gas gefüllte Ballon drängt in der schwereren Luft nach oben und kann somit Lasten anheben. Im Gegensatz zu erdgebundenen Kränen ist für den Luftkran die Beschaffenheit des Bodens sekundär. Der Ballonkran wird an drei Winden verankert und über die im Kranknotenpunkt zusammengeführten Seile präzise gesteuert. Beim Heben und Versetzen verbleibt die Last unter dem Ballon, der stets 100% seiner Hubkraft auch bis zu 200m Höhe und selbst weiterem Versatz behält. Reichweite bedeutet beim CargoLifter Ballonkransystem statt mehr Ausleger mehr Seil.
Das CargoLifter-Ballonkransystem nutzt die Prinzipien der Leichter-als-Luft-Technologie für das Heben von Gütern. Der mit leichtem Gas gefüllte Ballon drängt in der schwereren Luft nach oben und kann somit Lasten anheben. Im Gegensatz zu erdgebundenen Kranen ist für den Luftkran die Beschaffenheit des Bodens sekundär. Der Ballonkran wird an 3 Winden verankert und über die im Kranknotenpunkt zusammengeführten Seile präzise gesteuert. Beim Heben und Versetzen verbleibt die Last unter dem Ballon, der stets 100 % seiner Hubkraft auch bis zu 200 m Höhe und selbst weiterem Versatz behält. Reichweite bedeutet beim CargoLifter-Ballonkransystem statt mehr Ausleger mehr Seil.
In the present work an approach is presented which combines various aspects of the former models with probability considerations. It is used to simulate the impact of more than one billion Alumina particles onto a steel substrate. This approach permits the simulation of an entire erosion experiment on an average PC within about six hours.
The cause and type of solid particle erosion varies across different industries and locations in plants, for instance the particles could be volcanic ash in aero-engines, fly ash in boilers, exfoliated scale in steam turbines or mineral matter in oil excavation. In all cases the durability of materials can be improved through better surface engineering and coatings, but the development of these is restricted also due to lack of generic models. In this respect, the simulation of a single impact with finite element methods using 100.000 knots would take about 15 minutes. In order to simulate an entire particle erosion experiment, up to one billion of such impacts would have to be considered. In order to simulate an entire particle erosion experiment, the current work presents an alternative approach capable of calculating about half a billion impacts on a substrate in less than six hours on a standard PC. The predictions of the simulation will be compared to a steel sample at 600°C eroded by aluminum oxide particles with a velocity around 210 m/s.
JATROPHA - The Seed of Energy - CO2-Neutral Fuels and Lubricants Based on Sustainable Non-Food Oils
(2009)
Paraffinöl geschmierte Wälztests wurden an extrem harten Diamantschichten auf hartem SSiC Substrat, unterschiedlichen, harten DLC-Schichten auf 100Cr6 Substraten (HRC60) sowie ausgewählten DLC-Schichten auf ungehärtetem Stahl (HRC 20) durchgeführt. Die Wälztests wurden in einem Zweischeibentribometer vom Typ Amsler bei einer anfänglichen, maximalen Flächenpressung nach Hertz von P0=2,3 GPa ausgeführt. Als Abbruchkriterium für die Tests wurde das Erreichen von n=1.000.000 Überrollungen (Langzeittests n=10.000.000 Überrollungen) oder das Auftreten einer Schädigung mit einer zusammenhängenden Fläche von A>1 mm2 festgelegt. Die Wälztests zeigten, dass das harte SSiC Substrat zwar eine stützende Wirkung auf die Diamantschicht hat, diese aber aufgrund von Rissen im Substrat versagte. Ferner gibt es wenigstens zwei DLC-Schichten, die, aufgebracht auf 100Cr6 Scheiben (HRC60), den Wälztests bis n=10.000.000 Überrollungen ohne nennenswerte Schäden widerstanden. Diese Schichten passten sich auch den Verformungen des weichen, stickstofflegierten Stahls (HRC20) an, ohne das es zu größeren Abplatzungen kam (A>1 mm2).
Renowned institutions in the field of tribology combine their testing and analytical capabilities with experts in materials/process information management technology to provide the respective Services in Europe (i-TRIBOMAT). This requires a centralized materials information management system or the standardised capture, consolidation and harmonization of tribological information.
A novel tribometer has been designed using commercially available components for sliding motion at 40kHz with amplitude between 2.5 and 5µm. The tribometer is equipped with means to measure amplitude, frequency, power required to keep the sample in motion and load applied. The effective motion between the two contacting bodies is monitored. These data are used to evaluate the coefficient of friction. The wear rate was determined after the tests. The set-up was tested using novel, non-commercial substrates such as AlFeCrTi-alloys and tungsten carbide-based coatings as well as Magnéli-type coatings (Tin-2Cr2O2n-1 and TinO2n-1). This paper presents the principle of the ultra-high frequency tribometer and first tribological quantities of materials and coatings tested.
High-power piezo-electric motors with power densities of 1.4 kW/kg display a potential for substituting hydraulic actuators. For this application, two novel tribometers of the same type have been designed using commercially available components for sliding motion at 40 kHz with amplitudes between 2.5 µm and 5 µm. The tribometers are equipped with means to measure amplitude, frequency, power required to keep the samples in motion and load applied. The effective motion between the two contacting bodies is monitored in each of the tribometers. These data are used to evaluate the coefficient of friction. The wear rate was determined after the tests. The set-ups were tested using well-known 100Cr6H (AISI 52100) samples before investigating novel, non-commercial substrates such as AlFeCrTi-alloys and tungsten carbide-based coatings as well as Magnéli-type coatings (Tin-2Cr2O2n-1 and TinO2n-1). This paper presents the principle of the ultra-high frequency tribometers and first tribological quantities of materials and coatings tested up to and above 1011 cycles. Very low wear rates in the range 10-8 mm³/Nm down to 10-10 mm³/Nm were determined under dry oscillation in air.
JATROPHA - The seed of energy CO2-neutral fuels and lubricants based on sustainable non-food oils
(2009)
In this study the so-called laser-induced periodic surface structures (LIPSS, ripples) were produced on titanium alloy (Ti6Al4V) surfaces upon scan processing in air by a Ti:sapphire femtosecond (fs) laser. The tribological performance of the resulting surfaces was qualified in linear reciprocating sliding tribological tests (RSTT) against balls made of different materials (100Cr6 steel/Al2O3/Si3N4) using different oil-based lubricants. The admixture of the additive 2-ethylhexylzinc-dithiophosphate (ZDDP) to a base oil containing only anti-oxidants and temperature stabilizers disclosed the synergy of the additive with the laser-oxidized nanostructures. This interplay between the laser-textured sample topography and the local chemistry in the tribological contact area reduces friction and wear.
Reibungs- und Verschleißminderung in Wälzkontakten durch Werkstoff- und/oder Schmierstoffkonzepte
(2018)
Leichtbaukonzepte zur Reduzierung der CO2 Emission gehen häufig mit erhöhten Anforderungen an die Belastbarkeit tribologisch beanspruchter Oberflächen einher. In Wälzkontakten jeglicher Art erhöhen reduzierte Abmessungen oder ansteigende Kräfte die Hertz'schen Kontaktspannungen, oftmals verbunden mit dem Wunsch nach einer Reduzierung der Reibung. Löschungsmöglichkeiten bieten alternative Schmierstoffe, Dünnschichten und/oder verbesserte Stahllegierungen. In mehreren Forschungsvorhaben wurden Reibverhalten und Überrollbeständigkeiten derartiger Tribosysteme in einem Zweischeiben-Wälzprüfstand (2Disk) unter Misch- bzw. Grenzreibung bei bis zu 10 Millionen Überrollungen ermittelt. Dabei betrug die Öltemperatur 120°C und die maximale Flächenpressung oberhalb von 2,25 GPa. Insgesamt wurde eine Vielzahl von Kombinationen charakterisiert. Ein Teil dieser Ergebnisse wird in dem Vortrag exemplarisch vorgestellt.
Als Ausgangspunkt für i-TRIBOMAT schließen vier renommierte Institutionen in Europa, darunter die BAM, ihre Test- und Analytik-Methoden zusammen. Es entsteht ein Testfeld aus weit über 100 Tribometern mit den entsprechenden, analytischen Kapazitäten. Alle Ergebnisse fließen in eine harmonisierte Datenbank, die tribologische Erkenntnisse mit Materialeigenschaften ebenso zugänglich macht, wie Hinweise auf ökologische und gesundheitliche Verträglichkeiten. Diese Datenbank bildet zusätzlich das Rückgrat einer Vielzahl von Modellierungsmethoden, die die Entwicklungszeiten von der Idee bis zum marktreifen Produkt deutlich verkürzen sollen. Alle diese Möglichkeiten sollen über eine europaweit agierende, zentrale Kontaktstelle zur Verfügung gestellt werden.
Erosive wear simulation
(2015)
Renowned institutions in the field of tribology combine their testing and analytical capabilities with experts in materials/process information management technology to provide the respective services in Europe (i-TRIBOMAT). This requires a centralized materials information management system or the standardised capture, consolidation and harmonization of tribological information.
In order to shorten time to market of products and to support new developments, the European Community is funding a HORIZON 2020 project called i-TRIBOMAT. In the field of tribology, renowned institutions combine their testing and analytical capabilities to provide the respective services. The later will be offered in Europe via a Single-Entry Point (SEP). Due to this combination of services, a testbed is created consisting of more than 100 tribometers. Thus, a large variety of testers exists, either commercially available or in-house built. Each tester is optimised to simulate a specific tribological contact situation. Currently, there is no standard available for the design of such testers. Especially, the way forces (normal load, friction force) and distances (e.g. stroke, linear wear) are measured, recorded and pre-processed differs from type to type. These forces and distances are essential for the determination of wear/ wear rates and coefficients of friction (COF), the core results of tribo-tests. This matter is complicated by the fact that e.g. for reciprocating motion, there are at least four different ways to determine COF. Depending on the testing conditions, these ways can lead to considerably different results. Currently, it is not obligatory to specify the method used for determining the COF.
In order to make data comparable, there is a need for measures which ensure that each tribometer is delivering similar, at best the same results under the same test conditions, irrespective of its manufacturer, design, location, determination method and even operator. The way forward are improved Round-Robin tests. First results and other challenges faced by creating comparable tribological data will be considered in the present contribution.
Aus Schmierstoffen gebildete Tribofilme bestimmen das Reibungs- und Verschleißverhalten von Tribosystemen neben der Fresslasttragefähgikeit. Die Kaltverfestigung stellt einen weiteren Mechanismus insbesondere zum Verschleißschutz dar. Unter Wälzreibung wird das funktionale Profil organischer und metallorganischer Tribofilme sowie von Kaltverfestigung verglichen, die auf verschiedenen Stahlmetallurgien innerhalb von 10.000 Überrollungen in einem 2Disk-Prüfstand erzeugt wurden. Dabei wurden Hertzsche Kontaktspannungen ober von P0max=2,14 GPa (FZG14) eingesetzt.
The cause and type of solid particle erosion varies across different industries and locations in plants, for instance the particles could be volcanic ash in aero-engines, fly ash in boilers, exfoliated scale in steam turbines or mineral matter in oil excavation. In all cases the durability of materials can be improved through better surface engineering and coatings, but the development of these is restricted also due to lack of generic models. In this respect, the simulation of a single impact with finite element methods using 100.000 knots would take about 15 minutes. In order to simulate an entire particle erosion experiment, up to one billion of such impacts would have to be considered. In order to simulate an entire particle erosion experiment, the current work presents an alternative approach capable of calculating about half a billion impacts on a substrate in less than six hours on a standard PC. The predictions of the simulation will be compared to a steel sample at 600°C eroded by aluminum oxide particles with a velocity around 210 m/s.
The performance of titanium alloy (Ti6Al4V) surfaces was investigated in lubricated reciprocating sliding tribological tests (RSTT). Special emphasis was laid on the effect of surface nanostructures in area of contact on the respective friction and wear behaviour. These so-called laser-induced periodic surface structures (LIPSS, ripples) were produced on the titanium alloy surface upon scan processing in air by an ultrashort pulsed femtosecond (fs) laser. As lubricant served two types of base oils, a pure polyalcylene-glycol, and an SAE 0W30 oil containing only antioxidants and temperature stabilizers. Tribological tests were carried out on polished as well as LIPSS covered areas using both types of base oil. A test metrics was established, combining the additive 2-ethylhexyl-zincdithiophosphate (ZDDP) or the ionic liquid [P6,6,6,14] [DEHP] (98% purity) with the respective base oils. The test metrics also considered the orientation of motion with respect to the orientation of the structures formed on the surface. Results are presented which show that the interplay between LIPSS and the local chemistry formed by the respective additives is beneficial for the tribological behaviour of the titanium alloy. Certain combinations of base oil, additive and LIPSS reduced friction and wear significantly in the tribological contact.
Leichtbaustrategien im Antriebsstrang erhöhen durch Downsizing die Hertz’schen Kontaktpressungen und die mechanischen Lasten. Dadurch müssen neben wälzbeständigen Stählen auch dazu passende reibungsmindernde Konzepte gefunden werden, in der vorliegenden Arbeit wurden alternative, hoch zähe Stähle mit einer Wälzbeständigkeit bis Pomax = 4,2 GPa untersucht, welche mit geeigneten Grundöl- und Additivkombinationen die Reibungszahlen herunter auf 0,025 reduzieren konnten. Diese alternativen Stahllegierungen erlauben nicht nur an der Zahnflanke sehr hohe Kontaktpressungen, sie bieten außerdem entsprechende Zähigkeits- und Festigkeitseigenschaften für den Zahnfuß. In vorangegangenen Untersuchungen wurde eine Vielzahl verschiedener Dünnschichten auf ihre Überrollbeständigkeit unter Extrembeanspruchungen validiert. Allerdings zeigte sich bei den meisten Dünnschichten ein Qualitätsunterschied von Charge zu Charge. Unter Verwendung verschiedener organischer, metallorganischer und anorganischer Additive konnten, sich daran anschließende Versuche, vielversprechende Ergebnisse erzielt werden. Sämtliche Versuche unter extremen Beanspruchungen wurden bei +120°C Öltemperatur auf Zwei-Scheiben-Tribometern vom Typ AMSLER und 2Disk von Optimol Instruments unter Misch-/Grenzreibungsbedingungen durchgeführt und die tribologischen Eigenschaften der neuartigen, unbeschichteten Stähle und in Relation zu leistungsstarken DLC-/ZrCN Dünnschichten gesetzt.
Coatings for slip-rolling
(2014)
Diamond-like carbon (DLC) coatings are perceived as part of a strategy for low frictional tribosystems. Especially the automotive industry anticipates a benefit in applying such coatings in association with the lightweight construction of mechanical parts, for instance in gear and engine components. Therefore, in previous investigations amorphous carbon (a-C) and tetragonal amorphous carbon (ta-C) coatings were inspected. For up to ten million cycles at Hertzian contact pressures P0max of 2.9 GPa it was shown that these coatings are slip-rolling resistant not only at room temperature in the presence of unaddivated paraffin oil, but also up to 120 °C oil temperature. The steel substrates in this investigation were made of the hardened and tempered steels 100Cr6H and Cronidur 30. The aim of the current work is manifold. The Hertzian contact pressures should be increased up to P0max of 4.2 GPa by using new steel metallurgies as substrates for thin film coatings. These steel metallurgies are also assessed, if they can compete as uncoated couples. Two high toughness spring steels and an ultra-high toughness aerospace steel were tested in a twin disc tribometer of the Amsler type as well as in an Optimol 2Disk test rig under mixed/boundary conditions in a factory fill SAE 0W-30 engine oil. Different factors such as influences of the lubrication, surface chemistry and wear behaviour were investigated.
Contact formation and development are the basis of friction and wear modelling and understanding. Unanimously topography formation and development in friction contacts are regarded of highest importance for understanding and modelling friction processes. The frequently found running in behaviour of sliding contacts is—aside from the build up of reaction and transfer layers-at least partly caused by the topography development due to friction processes until a stable equilibrium state is reached.
Experimental results of friction and topography measurements are presented which demonstrate the mutual modification of friction and contact topography.
A special experimental set up with an AFM allowed to correlate the measured friction forces with the contact position and the topography at this point. In this way, friction force transitions and changes can be assigned to topography changes due to abrasion, adhesion and wear particle agglomeration.
Contact surfaces with artificial regular structures have been prepared to avoid problems with topography and friction correlation due to the statistical nature of roughness on technical contact surfaces. The friction effects of roughness were simulated by etched ditches of defined width, depth and distance on silicon or metal surfaces. This allowed to explain the mutual influences of topography and friction. The effect of a single asperity and of the 'roughness structures' could be demonstrated.
Topography measurements with an AFM correlated with the friction force could help to understand friction changes without changing any parameter.
The prediction of the properties of the materials used in the operation of components is of enormous importance, in order to accelerate the development process of new components. To evaluate new materials in terms of their performance (in a component), the development of new innovative methods is necessary. These methods can also be summarized under the term lab-to-field or materials – upscaling, meaning materials being characterised in a laboratory and their properties being upscaled to the component performance by means of e.g. simulation. i-TRIBOMAT is a EU funded project (H2020, GA Nr. 814494) aiming at building an Open Innovation Test Bed for tribological material characterization and offering corresponding services from tribological characterization of new materials to simulation models for predicting the performance of industrial components. By bundling the infrastructure, know-how for characterization and building a digital platform, i-TRIBOMAT becomes the world’s largest open innovation test bed for tribological material characterization.
We review contact mechanics with emphasis on the rheological (time dependent) properties of polymers and their relations to surface roughness, material properties, and friction as well as wear behavior of rubbing polymer surfaces. The main concept of polymer mechanics related to tribology consists of three basic elements involved in friction: deformation resulting in the real area of contact of rough surfaces, contact adhesion, and shear and rupture of materials in the contact during the sliding friction. The results of classical work are included, which addresses the real contact area calculation and the description of adhesion interaction between rough surfaces. A brief review of experimental investigations concerning the surface characterization by means of bearing curves, the intermolecular force interaction using the adhesion parameter, the effect of temperature on the real contact area, the formation of transferred polymer film during friction, and tribological behavior of ultrathin polymer layers are presented and their implications discussed.
Adhesion measurements are presented which were carried out with an atomic force microscope between polymer balls attached to a cantilever and a silicon wafer under ultra high vacuum conditions. In using a silicon surface with a defined structure a correlation between adhesion force and contact area was found. This correlation could partly be explained by the Johnson-Kendall-Roberts model, if a change of the surface energy is assumed as a result of the structuring. For a constant geometric contact area an additional structuring leads to a decrease of the adhesion force.