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- Dry sliding (2)
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Organisationseinheit der BAM
Thermally sprayed TiO2-x coatings under mixed lubrication and unlubricated sliding conditions
(2004)
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.
Wear tests are often used in engine development in order to characterize the functional profile of surfaces interacting with lubricants. This paper proposes a new test procedure to determine Stribeck-type curves for the tribosystem piston ring/cylinder liner involving test pieces prepared from engine components. The Variation of the friction coefficient with sliding speed depends on the structure and Constitution of the base oil, the viscosity index, the surface topography of the liner and ring, and the friction modifiers used. Novel organic friction modifiers of low molecular mass not only reduce the friction coefficients under mixed / boundary lubrication, but also in the fluid film regime. In addition, the influence of surface roughness on the wettability of surfaces can be significant for both static and dynamic wetting. For this reason, the interaction of the lubricant with the surfaces was also investigated to enable a correlation between the surface properties of the liquid and solid phases and the tribological behavior.
Wear tests are often used in engine development in order to characterize the functional profile of surfaces interacting with lubricants. This paper proposes a new test procedure to determine Stribeck-type curves for the tribosystem piston ring/cylinder liner involving test pieces prepared from engine components. The variation of the friction coefficient with sliding speed depends on the structure and constitution of the base oil, the viscosity index, the surface topography of the liner and ring, and the friction modifiers used. Novel organic friction modifiers of low molecular mass not only reduce the friction coefficients under mixed / boundary lubrication, but also in the fluid film regime. In addition, the influence of surface roughness on the wettability of surfaces can be significant for both static and dynamic wetting. For this reason, the interaction of the lubricant with the surfaces was also investigated to enable a correlation between the surface properties of the liquid and solid phases and the tribological behavior.