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- Kolbenring (3)
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- AlSi (2)
- Cr2O3 (2)
- Cylinder liner (2)
- Dry sliding (2)
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Organisationseinheit der BAM
Einen großen Beitrag zur Gewichtseinsparung leistet die Substitution von Grauguss-Legierungen durch moderne Aluminiumlegierungen für Pkw Kurbelgehäuse. Zur Erhöhung der tribologischen und thermomechanischen Belastungsgrenzen von Aluminiumoberflächen kommen thermisch gespritzte Schichten in Frage. Zielsetzung nachfolgender Untersuchungen ist es außermotorisch unter Misch-/Grenzreibung das tribologische Potenzial von thermisch gespritzten keramischen Schichtwerkstoffen auf Basis der Stoffsysteme Cr2O3, Cr2O3/TiO2, Cr3C2/NiCr, TiO2, TiO2/Al2O3 im Vergleich zu aktuell serienmäßig eingesetzten Graugusswerkstoffen zu ermitteln. Die Oberflächentopographien und die Schmierstoffe determinieren gegenüber GG26Cr die Verschleißsenkungspotenziale der keramischen Schichten. Eine Reduzierung der Reibungszahlen wird nicht durch keramische Oberflächenbeschichtungen, sondern durch den Einsatz von Polyglykolen als Schmiermedium erzielt.
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.
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).
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.
The effects of rapid pulse electric current sintering (PECS), substitution of WC by NbC and Co by Ni, and carbide additives (TiC and Mo2C) on the microstructure, elastic modulus, B3B transverse rupture strength (TRS) and high temperature sliding wear on WC-Co, WC-Ni, NbC-Co and NbC-Ni cermets were studied. High temperature sliding wear tests were carried out using a ball-on-disk tribometer, with a 10 N force, at a sliding speed of 1.34 m/s for 0.8 km (10 min) and 2.4 km (30 min), using 100Cr6 (AISI 52100) steel balls at 400 °C and 0% humidity. Additions of TiC and Mo2C to NbC-12Ni improved the sliding wear resistance, with TiC having the greater effect, reducing the sample wear rate by over 30% from 15.1×10−6mm3/N·m to 9.4×10−6mm3/N·m after sliding distance of 2.4 km. Generally, the LPS samples had lower wear volumes than the corresponding SPS samples, due to higher K1c and TRS.