Filtern
Dokumenttyp
Sprache
- Englisch (5)
- Deutsch (2)
- Französisch (1)
Schlagworte
- Slip-rolling (8) (entfernen)
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).
Diamond like carbon (DLC)-coatings are applied very successfully on computer discs. Sliding friction tests confirm their high performance as dry lubricants with friction coefficients (COFs) below 0.1. In contrast to sliding tests, until very recently most of the DLC-coatings failed in slip-rolling test after fewer cycles than uncoated samples. However, present tests with DLC-coatings of seven different suppliers show a more promising tribological behaviour under slip-rolling conditions. The DLC-coatings were deposited onto steel 100Cr6, HRC 60, with a thickness of 23 ?m. The counter bodies were uncoated, grinded or polished 100Cr6 discs with 30 mm radius of curvature. The tests were performed on a twin disc testing rig (Amsler type) with paraffin oil under boundary/mixed lubrication and rolling with 10% slip. The initial, average Hertzian contact pressure was adjusted to Pm = 1.0, 1.25, and 1.5 GPa. The failure criterion was defined as the occurrence of a single damaged area larger than 1 mm2, which was controlled by optical microscopy (OM). An acoustic emission (AE) measurement system was installed as an additional online control for coating failure. The stressed coatings and the chipping areas were analyzed by OM, SEM, EDX, AFM and Raman spectroscopy.
Until now, the results reveal that a large scatter in lifetime of coatings occurs not only between samples of different coaters but also between the samples of one single batch. The highest lifetime reached by a DLC-coating under these testing conditions is 10 × 106 cycles. That is the highest life time for a coating tested under the testing conditions above in our laboratory so far. The following factors were identified to influence the life time of the coatings: coating thickness, interlayer type, topography of the coatings, counter body roughness and mechanical properties. But the most important factor determining the life time of the coatings is that the coating process does produce homogenous layers free of faults.
Le secteur automobile doit faire face actuellement à de nouveaux challenges au niveau de la construction allégée, des économies de carburant et des coûts. Ces exigences motivent la mise au point de tribosystèmes pouvant résister à des pressions de contact de plus en plus élevées avec de faibles coefficients de frottement. L'optimisation de systèmes existants par l'application de revêtements de surface performants représente une alternative intéressante. Ce texte présente les performances de couches minces dans des conditions d'essais de slip-rolling (roulement à composante de glissement) en présence de lubrifiants liquides. Après une première sélection à température ambiante, les revêtements les plus performants ont été testés à 120 °C. Il s'agit de revêtements DLC en carbone hydrogéné (a-C:H) et en carbone tétraédrique (ta-C) de dernières générations ainsi qu'un nouveau système « revêtement/substrat ». Certains des revêtements DLC développés récemment sont résistants en slip-rolling au moins jusq'à 10 millions de cycles à 120 °C dans l'huile moteur sous des pressions hertziennes de contact de P0max = 2600 / 2940 MPa. De plus, le nouveau système revêtement Zr(C,N)x/substrat peut résister au moins à 1 million de cycles sous des pressions hertziennes initiales de contact allant jusqu'à P0max = 3500 MPa et à des températures de lubrifiant d'au moins 120 °C. -----------------------------------------------------------------------------------------------------------------------------------------------
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 surface coatings represents one approach among others. This paper presents thin film coatings performances in a bench mark test procedure exerting slip-rolling conditions in the presence of liquid lubricants. After a first selection at room temperature, the most resistant coatings were evaluated at 120 °C. These are newly developed DLC coatings (a-C:H & ta-C) as well as a novel coating-substrate system. Some of the newly developed DLC-coatings are slip-rolling resistant for at least up to 10 million cycles at 120 °C oil temperature) under Hertzian contact pressures of P0max = 2600 / 2940 MPa. Furthermore, this novel Zr-based thin film coating 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.
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.
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.
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.