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- Engine oil (2)
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- Triboaktive Werkstoffe (2)
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- (Ti,Mo)(C,N) (1)
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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.
The use of alternative base oils, like esters or polyglycols, with more intrinsic properties for the lubrication of automobile engines has a potential for ecological and technical advantages. Being in competition with hydrocarbon-based formulations, detailed knowledge of several thermophysical and viscometric properties as well as tribological properties over a large temperature range are required (mapping). The tested polymer-free polyglycols and ester-based formulations displayed no visible tribological weaknesses regarding wear resistance and EP-behavior as well as offering significant advantages in order to meet metal- and ash-free and bio-no-tox criteria. Especially the formulated polyglycols without friction modifiers also showed an intrinsic retention of low coefficients of friction and a hydrodynamic film forming behavior comparable to hydrocarbon-based factory-fill oils. The wear resistance and EP-behavior of low-additivated polyglycols, but also of esters, can be enhanced by means of triboactive materials. Lubricious oxides or triboactive materials and polar base oils, or a combination thereof, may substitute the EP and AW properties realized by the additives, thus enabling long drains and responding to eco-tox or bio-no-tox requirements as well as restrictions from the chemical box.
Oxidation resistance is one of the limiting factors for long drains, bionotox, LowSAP or NoSAP engine oils. The French iron catalyzed oxidation test (ICOT) uses 60 ppm iron acetylacetonate as diluted catalyst under an aeration of 10 L/h at 170°C. The ICOT ranks the oxidation stability of oils according to three properties: a. the viscosity increase (e.g., max. Δη40°C<100 % or Δη100°<100 %), b. the increase to an individual TAN (e.g., max. 7.5 mgKOH/g) and c. the oxidative evaporation losses of max. 10 % at Δη=100 % due to oxidation. This paper describes the ICOT method standardized as GFC Lu 36T 03 and the obtainable accuracy. Also, results are compiled achieved with this test for factory fill engine oils as well as alternative prototype engine oils based on esters, blends of esters with hydrocarbons, and polyglycols.
Two new substoichiometric titania (TiOx) coatings designated for cylinder liner application were deposited on specimen of grey cast iron GG20HCN with high carbon content by plasma spraying. First, a TinO2n-1 coating was prepared by atmospheric plasma spraying (APS) using a sintered and agglomerated Magnéli-type spray powder. Second a TiO1.95-x coating was deposited with a vacuum plasma spray (VPS) process using a commercial, fused and crushed TiO1.95 powder. The tribological behaviour of these coatings under lubricated conditions was compared with uncoated specimen of this grey cast iron. As counter bodies a widespread used APS-sprayed Mo-NiCrBSi piston ring coating (MKP81A®), an advanced HVOF-sprayed WC/Cr3C2-based (MKJet502®) ring coating as well as non-commercial prototype APS-sprayed TinO2n-1 and APS-sprayed (Ti,Mo)(C,N) + 23NiMo (TM23-1) coatings were tribotested.
The interaction of the pairs with prototype engine oils based on esters and polyglycols were studied under mixed/boundary lubrication using the BAM test method. Lubricants were factory fill engine oils, ester-containing lubricants with low-SAP (sulphurashphosphor) and/or bio-no-tox properties as well as polyglycole-based lubricants. The ester and polyglycole-based engine oils respond both to bio-no-tox criteria and are polymer-free. They follow different strategies to reduce zinc, phosphorus and sulphur to assure a low ash content.
Both TiOx coatings designated for cylinder liners meet or exceed the wear resistance of the grey cast iron with high carbon content when paired with APS-sprayed TinO2n-1 or Mo-NiCrBSi piston ring coatings. Overall, in nearly all pairs the wear rates of the APS TinO2n-1 coating were lower than those of the VPS TiO1.95-x coating.
In order to characterize the tribological behaviour under oil-off, dry-running conditions, additional tests were performed under unlubricated unidirectional sliding conditions at 22 and 400 °C for a sliding speed of 1 m/s against sintered polycrystalline Al2O3 as stationary specimen.