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Eingeladener Vortrag
- nein (5)
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.
The slip-rolling resistance of DLC, a-C and ta-C thin film coatings was improved considerably in the last years, but there is still room for improvements in relation to (a) the temperature stability and (b) initial surface roughness after deposition. This paper presents a novel coating-substrate system in comparison to recently developed DLC coatings in a bench-mark test procedure exerting slip-rolling conditions in the presence of liquid lubricants. One of the Zr-based thin film coatings can withstand at least 1 million cycles under initial Hertzian contact pressures of up to P0max = 3500 MPa and oil temperatures of at least 120 °C associated with low coefficients of friction under mixed/boundary conditions or ten million of cycles under P0max = 2940 MPa. In comparison, some of the newly developed DLC coatings are slip-rolling resistant for at least up to 10 million cycles at RT (some of them also at 120 °C oil temperature) under Hertzian contact pressures of Pmax = 2600/2940 MPa. In general, Zr-based thin film coatings do not require special formulated oil formulations and Zr(C,N) bear on a straight coating architecture suited for mass production with nanosized layers.
The historical development on the discoveries of lubrication regimes for lubricated sliding contacts has been reviewed from the very beginning. It was found that the functional relationship between the coefficient of friction and the product of sliding speed and viscosity divided by the normal load well known as the Stribeck curve has been experimentally explored much earlier by Adolf Martens in 1888 long before Richard Stribeck did his pioneering measurements in 1902. However, basic work in this field of experimental hydrodynamics was done and results were published even earlier than that back in 1854 by Gustave A. Hirn, in 1879 by Robert H. Thurston and in 1883 by Beauchamp Tower.
The light-weight approach and fuel economy targets in today's automotive engineering require tribosystems, which can withstand higher contact pressures associated with low coefficients of friction. The application of high-performance coatings represents one approach among others. This paper presents some recently developed DLC coatings (a-C:H and ta-C) as well as a novel coating-substrate system (Zr(C,N)) in a benchmark test procedure under slip-rolling conditions in the presence of liquid lubricants. Various coatings with different thickness, interlayer and substrates were evaluated for their slip-rolling resistance in different lubricants at ambient temperature and at 120 °C. Results indicate that some of these coating systems can withstand at least 10 million cycles under initial Hertzian contact pressures of up to Pmax = 3.500 MPa and oil temperatures of at least 120 °C associated with low coefficients of friction under mixed/boundary conditions. Surface of the coatings and the counter bodies were analysed and compared with untreated substrates.
Hochtemperaturtribologie
(2010)
Wälzbeständigkeit von ta-C Dünnschichten unter hohen Hertzschen Beanspruchungen bis zu 3000 MPa
(2010)
Hochtemperaturtribologie
(2010)
Die Temperatur ist eine fundamentale Beanspruchungs- bzw. Einflussgröße für alle tribologischen Systeme. Für die in zahlreichen tribologischen Systemen benötigten Schmierstoffe liegen die thermischen Stabilitätsgrenzen bei etwa 400?°C. Es wird die tribologische Prüftechnik für Tribomaterialien beschrieben, die für den Einsatz in tribologischen Systemen bei hohen Betriebstemperaturen verwendbar sind. Ausgehend von metallurgischen Lösungsansätzen aus der Tribologieforschung werden Anwendungsmöglichkeiten hochtemperaturbeständiger Ingenieurwerkstoffe mit Beispielen aus der Automobiltechnik (Luftlagerung von Turboladern, Leistungssteigerung von Bremsmaterialien), der Fertigungstechnik (Standzeitverlängerung von Werkzeugen) und dem chemischen Anlagenbau (Effizienzsteigerung von Kühlkreisläufen) dargestellt.