Filtern
Dokumenttyp
Sprache
- Englisch (8)
- Deutsch (5)
- Mehrsprachig (1)
Schlagworte
- DLC (10)
- Slip-rolling (6)
- ZrCN (6)
- Dünnschichten (4)
- Extrembeanspruchung (4)
- High toughness steel (4)
- High pressure (3)
- Hochzähe Stähle (3)
- Additive (2)
- Additives (2)
OEMs perceive diamond-like carbon (DLC) coatings 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 gears and engines. In previous investigations it was shown, that DLC, amorphous carbon (a-C) and tetragonal amorphous carbon (ta-C) coatings can be slip-rolling resistant at least up to ten million load cycles at Hertzian contact pressures P0max of 2.9 GPa lubricated by engine oil at 120°C, Further improvements in load carrying capacity up to P0mean of 2.62 GPa (FN= 5,000 N) were achieved with alternative, available Steel metallurgies as Substrates for thin film coatings. Additional factors, such as influences of the lubrication on the surface chemistry (additives and base oils), wear and friction behavior were investigated.
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.
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.------------------------------------------------------------------------------------------------------------------------------------------------
Die Wälzbeständigkeit von harten und steifen Dünnschichten unter hohen Hertzschen Kontaktpressungen kann durch die Optimierung des 'Beschichtung/Substrat Systems' deutlich verbessert werden. Aus vorangegangenen Untersuchungen ist bekannt, dass der so genannte 'Eierschaleneffekt' kein generelles Hindernis für eine hohe Wälzbeständigkeit für harte Dünnschichten darstellen muss. Die Stabilität der Beschichtungen hängt vielmehr von dem spezifischen Prozessparametern und dem Schicht/Substrat Grenzflächendesign ab. In diesem Artikel wird experimentell nachgewiesen, dass reine amorphe Kohlenstoffdünnschichten mit Härtewerten zwischen 15 und 63 GPa für mehrere Millionen Lastzyklen unter maximalen Hertzschen Kontaktpressungen bis 3.0 GPa überrollbeständig sein können. Während alle Beschichtungen bis 10 Millionen Lastzyklen in Paraffinöl bei Raumtemperatur keine Defekte aufweisen wurde unter Verwendung eines SAE 0W-30 Motorenöls bei 120°C eine Verringerung der Überrollbeständigkeit nachgewiesen. Es wurde nachgewiesen, wie die Schichthärte und ursprüngliche Oberflächenrauheit der Beschichtung den Einlaufprozess und die Lebensdauer beeinflussen. Es konnte keine offensichtliche Korrelation zwischen Schichthärte und Lebensdauer festgestellt werden, allerdings wurde eine scheinbare Reduktion des Reibwertes mit steigender Schichthärte beobachtet werden. Dabei zeigte die härteste ta-C Schicht unter Verwendung des Motorenöls sehr geringe Reibwerte mit ~0.03.
Highly concentrated or loaded contacts in powertrain and gear applications offer significant weight savings in C02 emissions. Today, thin film coatings, alternative base oils and new additives are populär as working fields and strategies of OEMs to realize low friction tribosystems. Especially the automotive industry anticipates environmental and performance benefits in applying light-weight construction of mechanical parts, for instance in gears and engines. Light-weight strategies increase the contact stresses above 2.14 GPa (or FZG load stage 14) due to the reduction of component sizes. These demands directly raise questions about the suitability of the most promising technical solution. Alternative steels with improved mechanical properties, i.e. toughness values, which offer low coefficients of friction, optimal resistance to high contact pressure and potential to apply low friction surface coatings representing a valid alternative to conventional gear steels. Traditional bearing and gear steels, such as 100Cr6 (SAE E52100) or 16MnCr5 (1.7131) have reached their mechanical limits at contact pressures above FZG load stage 14.
Nowadays, diamond-like carbon (DLC) coatings are mainly used in many low loaded applications such as in machine tools, computer devices and many more.
Especially the automotive industry anticipates a benefit in applying such coatings in association with the lightweight construction of mechanical parts, for instance in gear components.
The ulterior motive is a global performance increase regarding environmental impact and power efficiency.
In recent years, the slip-rolling resistance of DLC, a-C and ta-C thin film coatings was improved considerably.
In view of the mechanical application of thin film coatings, there is still room for improvements.
It was experimentally shown, that a-C and ta-C coatings can be slip-rolling resistant at room temperature in unaddivated paraffin oil up to ten million cycles under Hertzian contact pressures up to P0max = 2.9 GPa.
Typically, the prime coated steel substrates were made of the hardened and tempered steels 100Cr6H and Cronidur 30.
The aim of the work this to overtake these results, i.e. at higher maximum Hertzian pressures up to P0max = 4.2 GPa.
Under such extreme conditions, it is necessary to choose special steels to avoid the failure of the substrate and to permit a higher load carrying capacity of the coating-substrate-system.
In consideration of the increased substrate properties, two high toughness spring steels and an ultra-high toughness aerospace steel were tested on a twin disc tribometer of the Amsler type as well as on an Optimol TwinDisc test rig under mixed/boundary conditions.
Different factors such as residual stresses of the substrate, influences of the lubrication, and wear behaviour were investigated.
The respective results are presented here.
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.