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Eingeladener Vortrag
- nein (16)
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.
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.
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.
JATROPHA - The seed of energy CO2-neutral fuels and lubricants based on sustainable non-food oils
(2009)
Costs reduction is one of the major objectives in mechanical applications with a parallel increase of the power output. Another driver represents new environmental standards and their increasing restrictions in the automotive industry leading to the question, if materials based concepts may substitute harmful EP/AW additives in lubricants. This paper presents the slip-rolling resistance of different DLC/THC coatings on steel substrates with a definite slip rate of 10%. Industrial DLC coatings of ta-C and a-C:H types from various manufacturers were deposited on steels SAE 52100 and AMS 5898 to compile the slip-rolling resistance under initial average Hertzian contact pressures between 1.5 GPa and 2 GPa. The tests were carried out on Amsler-type twin disc tribometer under the regime of mixed/boundary lubrication in unadditivated paraffinic oil (ISO VG 46) and a factory fill engine oil. The spherical steel sample was uncoated and the cylindrical coated with DLC. Some coatings achieved 10 million cycles without any damage under a maximal Hertzian contact pressure Pmax well over 2.25 GPa, thus exceeding FZG 12.
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.