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Organisationseinheit der BAM
Eingeladener Vortrag
- nein (110)
The use of alternative oils for the lubrication of automobile engines has a potential of ecological and technical advantages. It requires the detailed knowledge of several thermophysical and viscometric properties in a large temperature range (mapping). Therefore, the following properties of up to twenty-eight different oils have been measured in the temperature range from 22 °C to 150 °C: density, heat capacity, thermal conductivity, viscosity at ambient pressure, viscosity under shear rates above 10 6 s-1, and the viscosity at elevated pressures (maximum 100 MPa). The last two have been measured with a substantially improved and a newly developed apparatus, respectively. The pressure- viscosity coefficient has been measured on four hydrocarbon-based, factory-fill oils, a paraffin oil and twenty-three alternative oils. Nine of the alternative oils are based partly or completely on esters, the other fourteen on polyglycols, two of them additionally on water.
Keramische Werkstoffe haben auf Grund ihrer herausragenden tribologischen Eigenschaften in verschiedenen Bereichen der Produktion Anwendung gefunden und dadurch klassische Werkstoffe verdrängt. Gegenüber Matallen bieten sie bei Mangelschmierung sowohl unter Gleit- als auch grundsätzlich unter Wälz-beanspruchung Schutz vor adhäsivem Versagen. Hohe Herstellungskosten, bedingt bei der Endbearbeitung von Konturen mit verschiedenen und veränderlichen Radien, behindern die breite Marktdurchdringung. Mit der Modellverschleißprüfung - angelehnt an die DIN 50 324 - kann der bearbeitungsbedingte Einfluss auf das tribologische Verhalten unter Wälzreibung untersucht werden.
Englische Übersetzung von BAM Forschungsbericht 237! Keramische Werkstoffe haben auf Grund ihrer herausragenden tribologischen Eigenschaften in verschiedenen Bereichen der Produktion Anwendung gefunden und dadurch klassische Werkstoffe verdrängt. Gegenüber Metallen bieten sie bei Mangelschmierung sowohl unter Gleit- als auch grundsätzlich unter Wälzbeanspruchung Schutz vor adhäsivem Versagen. Hohe Herstellungskosten, bedingt bei der Endbearbeitung von Konturen mit verschiedenen und veränderlichen Radien, behindern die breite Marktdurchdringung. Mit der Modellverschleißprüfung - angelehnt an die DIN 50 324 - kann der bearbeitungsbedingte Einfluss auf das tribologische Verhalten unter Wälzreibung untersucht werden.
Darstellung der Anwendungen und Zukunftsperspektiven keramischer Werkstoffe zur Reibungs- und Verschleißminderung und Beschreibung der Beweggründe für den Einsatz von Keramik im High-Tech-Bereich sowie deren Wandel mit fortschreitendem Entwicklungsstand. Anschließend folgen Arbeiten, die sich mit der Reaktion keramischer Oberflächen auf statische und tribologische Gleitbeanspruchungen befassen.
Gas turbine efficiency is significantly influenced by the pressure losses caused by the inevitable gap between the rotating turbine blades and the stator parts.
Because contact between rotor and stator cannot be completely avoided with a small gap, systems are designed to allow for some rubbing. Honeycombs or abradable MCrAlY stator coatings are normally used to minimize the wear of the rotor blades when rubbing occurs. But, more efficient solutions must be developed on modern engines, because both suffer temperature limitation and standard MCrAlY have usually poor abradability. For higher temperature and closer control of the gap, a thick thermal-barrier coating must be applied on the stator, but presently with no rub-tolerance.
To increase the abradability of the stator coating, its composition and structure can be modified, but such changes must be strictly limited with respect to the loss of erosion resistance.
The solution can then lie in the hardening of the rotating blade tip to permit the use of harder ceramic or metallic coatings on the stator with greater resistance to erosion. These systems typically consist, on the blade tip, of hard particles embedded in a softer metallic matrix.
In the present programme, it is therefore intended:
- to assess the present European solutions, standard or in development, for outer air seals and blade tips.
- to develop coated grits or new grits for the hardening of the blade tips, as well as to improve the matrix and the stator coating for long life systems.
- to optimize the most promising of these systems, that will be tested on development rigs and on engine.
The consortium includes several engine manufacturers, which are the potential users of the innovating solutions to be developed, companies having a large experience in the field of abradables and tip coatings
and non industrial partners involved in tribology and materials science.
Tribologisches Hochtemperaturverhalten keramischer Werkstoffe unter Festkörperreibungsbedingungen
(1988)
This paper presents the friction and wear behaviour of monolithic titanium-molybdenum carbonitride and tungsten carbide. These materials have been tested sliding against themselves, carbons, fibre reinforced glasses and molybdenum coatings and compared to other ceramics and ceramics composites under unlubricated condition up to 800 °C and 6 m/s.
Self-mated sliding couples of titanium-molybdenum carbonitride display, especially under high-temperature friction, a pronounced wear resistance compared to ceramics and ceramicceramic composites. This very good property is due to the tribo-oxidative formation of so-called lubricious oxides, e.g. Magnéli phases of rutile. They exhibit sliding wear rates under unlubricated friction up to 800 °C as known from mixed/boundary lubrication.
Within the different test conditions, the wear rates of a variety of stationary monolithic materials samples sliding against rotating specimen of (Ti, Mo)(C, N) are always in the group with the lowest wear rates.
The association of the wear resistance, mechanical strength, fracture toughness and low density makes the (Ti, Mo)(C, N) material a complete solution for complex customer demands.
The results presented in this paper have clarified experimentally, that titania-based Magnéli-phases (Ti4O7/Ti5O9 and Ti6O11) with (121)-shear planes exhibit more anti-wear properties than lubricious (low-frictional) properties. The results for dry sliding indicate that the coefficients of friction lie in the range of 0.10.6 depending on sliding speed and ambient temperature. The COF decreased with increasing temperature (T= 22800°C) and increasing sliding speed (?= 1-6 m/s). The dry sliding wear rate was lowest for the Al2O3 at 1 m/s at 800°C with values of 1.7 × 10-8 and 6.4 × 10-8 mm3/N m, comparable to boundary/mixed lubrication, associated with a high dry frictional power loss of 30 W/mm2. The running-in wear length and, more important, the wear rate decreased under oscillating sliding tests with increasing relative humidity. The contact pressure for high-/low-wear transition increased under oscillating sliding tests with increasing relative humidity. At room temperature and a relative humidity of 100% the steady-state wear rate under dry oscillating sliding for the couple Al2O3/Ti4O7Ti5O9 was lower than 2 × 10-7 mm3/N m and therefore inferior to the resolution of the continuous wear measurement sensor. TEM of wear tracks from oscillating sliding revealed at room temperature a work-hardening as mechanism to explain the running-in behavior and the high wear resistance. The hydroxylation of titania surfaces favours the high-/low-wear transition.
Der Einfluss des E-Moduls und des Grundöls auf das Wälzverhalten von DLC- und Diamantbeschichtungen
(2004)
Dry friction and wear rates as under liquid lubrication of ceramic/carbon couples up to 450°C
(2004)
In a high temperature tribometer, stationary carbon has been tested against different rotating ceramics (SiC, Si3N4, Al2O3, WC-6Ni, MgO-ZrO2, (Ti, Mo)(C, N)) and stainless steel (DIN 1.4876). The rotating discs were grinded, polished and/or lapped. For most material combinations, the wear morphology is known from available literature. A transfer film with a typical wear pattern was found on the rotating disc. The combination of antimony graphite EK3245 against MgO-ZrO2 did not form carbonaceous transfer layer. Through advanced variation of the roughness up to Rpk=0.011?µm, the wear rate has been reduced to Kv 3.5×10-8?mm3/N?m at a stable coefficient of friction in a millirange of µ~0.008 for a sliding distance of 20.000?m.
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.
8 wt% Y2O3-ZrO2 spray powder and thermally sprayed as thermal barrier coatings on outer air seals were characterized by Raman microprobe spectroscopy (RMS) and transmission electron microscopy to investigate the lateral distribution, composition, structure and grain size of ZrO2 phases and to separate ZrO2 and Y2O3. RMS of transfer layers on ZrO2-coated shrouds after rub tests against SiC laser-tipped metallic blades showed the formation of metallic oxides MeIMeII2O4 of spinel type. Wear tracks were partly covered by graphite and spinel-type oxides. In some cases, the latter were better detectable after laser enhanced cleaning by burning off the covering carbon layer.
Plusieurs essais coopératifs multilaboratoires ont été effectués en 1997, 1998, 1999, 2000 et 2001 par le groupe de travail DIN 51834 Essais tribologiques dans l'appareil translation-oscillation. Il s'agit d'essais effectués sur des machines différentes et dans différents lieux. Pour simplifier, on les dénomme essais circulaires. L'analyse statistique des résultats a examiné l'influence du choix du solvant, du modèle de l'appareil et des paramètres sur les caractéristiques tribologiques des différentes huiles. Le coefficient de frottement et les taux d'usure peuvent être classés selon les dix différents solvants utilisés: l'isopropanol donne des coefficients de frottement plutôt bas et l'isoparaffine des coefficients plutôt élevés. La variation du coefficient de frottement selon le modèle de machine se situe entre 0,2 % et 0,9 % et les taux d'usure ne sont pas non plus affectés par les solvants. Le diamètre de l'empreinte est insuffisant pour caractériser la résistance à l'usure d'une huile. Le critère pour l'adhésion a du être redéfini. La répétabilité et la reproductibilité ont été améliorées.
Raman spectroscopic investigations in tribologically stressed contacts of (Ti,Mo)(C,N) ceramics
(1997)
In the current study, the tribological properties of TiC-based coatings paired with polycrystalline alumina under unlubricated sliding conditions were investigated in order to demonstrate the technological and engineering potential of such coatings. (Ti,Mo)(C,N)-Co coatings were prepared from an agglomerated and sintered spray powder by HVOF spraying using JP-5000 equipment. Cr3C2-NiCr coatings were studied for comparison. Sliding wear tests were performed over the temperature range from 23°C to 800°C with sliding speeds in the range 0.3-3 m/s, a wear distance of 5000 m and a normal force of 10 N. Wear rates of coatings and sintered alumina counterparts were measured separately. Compared with Cr3C2-NiCr coatings, (Ti,Mo)(C,N)-Co coatings showed significantly lower total wear rates, corresponding to those found in the region of mixed/boundary lubrication. With few exceptions, the coefficients of friction were found to be lower for (Ti,Mo)(C,N)-Co coatings than for Cr3C2-NiCr coatings. After tests were performed, the coating microstructures were studied by optical microscopy and SEM. The oxide scales formed on the coating surfaces were investigated by SEM and X-ray diffraction. Comparison of the total wear rates of the couples consisting of sintered alumina and a (Ti,Mo)(C,N)-Co coating with those of other alumina-ceramic and hardmetal-hard metal tribological systems demonstrates the immense potential of TiC-based coatings for sliding wear applications.
In situ Acoustic Emission for wear life detection of DLC coatings during slip-rolling friction
(2006)
Different diamond-like carbon (DLC) coatings on a steel substrate (100Cr6) were tested under slip-rolling friction conditions against uncoated counter bodies of the same steel. The initial maximum Hertzian pressure was varied in a range of P0 = 1.52.3 GPa. The friction tests were carried out under dry conditions and with an unadditivated paraffin oil as lubricant. It could be shown that the thickness of the coatings affects the respective wear life. Further, a very important factor for the wear life of a coating under lubricated slip-rolling conditions is the roughness of the surface of the respective counterbody. The wear life tests were monitored by recording in situ the Acoustic Emission (AE) signals. Some causes for a high AE activity could be identified.
Thermally sprayed TiO2-x coatings under mixed lubrication and unlubricated sliding conditions
(2004)
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).
Thermally sprayed TiO2-x coatings under mixed lubrication and unlubricated sliding conditions
(2004)
Tribologie des céramiques
(2013)
Les ceramiques modernes sont differentes des ceramiques traditionnelles (carrelage, materiaux de construction, porcelaine); on les distingue par des adjectifs tels que « techniques », « industrielles » ou « thermomecaniques ». Les ceramiques industrielles sont caracterisees par leur caractere refractaire marque et de grandes duretes. Leur mediocre tenacite explique leur sensibilite ä la presence de defauts, d'oü leur reputation d'etre peu resistantes et cassantes.
Les ceramiques techniques sont utilisees pour:
• leurs proprietes electriques ou dielectriques;
• leurs proprietes magnetiques et de supraconducteurs ;
• leurs proprietes optiques;
• leurs proprietes chimiques;
• leurs proprietes biologiques;
• leurs proprietes nucleaires.
En outre, eiles sont employees pour leurs proprietes mecaniques, thermomecaniques et tribologiques, ainsi que pour leur tenue face ä la corrosion. Nous allons nous concentrer sur leur comportement tribologique.
Nullverschleiß
(2012)
Biolubrifiants
(2011)
Un point de départ pour la mise en route des lubrifiants « neutre à l'environnement » ont été les huiles perdues et les fuites accidentelles, les lubrifiants perdus rejoignant les sols et les eaux (voir lac de Constance).
Même en prenant en compte les voies du recyclage, la combustion dans les moteurs et les fuites connues, environ 30 % (entre 20 % et 40 %, selon les études) du volume de lubrifiants entre dans l'environnement par des voies non attribuables ou est probablement mis en décharge de manière illégale.
Avec de tels chiffres publics, les arguments des lobbyistes de l'industrie pétrochimique, affirmant que, dans la plupart des applications, les fluides sont enfermés dans des réservoirs clos et étanches, ne convainquent pas les politiques. C'est aussi peut-être parce que, en Allemagne, environ 60 % des particuliers changent leur huile eux-mêmes.
OEMs perceive diamond-like carbon (DLC) coatings 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 gears and engines. In previous investigations it was shown, that DLC, amorphous carbon (a-C) and tetragonal amorphous carbon (ta-C) coatings can be slip-rolling resistant at least up to ten million load cycles at Hertzian contact pressures P0max of 2.9 GPa lubricated by engine oil at 120°C, Further improvements in load carrying capacity up to P0mean of 2.62 GPa (FN= 5,000 N) were achieved with alternative, available Steel metallurgies as Substrates for thin film coatings. Additional factors, such as influences of the lubrication on the surface chemistry (additives and base oils), wear and friction behavior were investigated.
Leichtbaustrategien im Antriebsstrang erhöhen durch Downsizing die Hertz’schen Kontaktpressungen und die mechanischen Lasten. Dadurch müssen neben wälzbeständigen Stählen auch dazu passende reibungsmindernde Konzepte gefunden werden, in der vorliegenden Arbeit wurden alternative, hoch zähe Stähle mit einer Wälzbeständigkeit bis Pomax = 4,2 GPa untersucht, welche mit geeigneten Grundöl- und Additivkombinationen die Reibungszahlen herunter auf 0,025 reduzieren konnten. Diese alternativen Stahllegierungen erlauben nicht nur an der Zahnflanke sehr hohe Kontaktpressungen, sie bieten außerdem entsprechende Zähigkeits- und Festigkeitseigenschaften für den Zahnfuß. In vorangegangenen Untersuchungen wurde eine Vielzahl verschiedener Dünnschichten auf ihre Überrollbeständigkeit unter Extrembeanspruchungen validiert. Allerdings zeigte sich bei den meisten Dünnschichten ein Qualitätsunterschied von Charge zu Charge. Unter Verwendung verschiedener organischer, metallorganischer und anorganischer Additive konnten, sich daran anschließende Versuche, vielversprechende Ergebnisse erzielt werden. Sämtliche Versuche unter extremen Beanspruchungen wurden bei +120°C Öltemperatur auf Zwei-Scheiben-Tribometern vom Typ AMSLER und 2Disk von Optimol Instruments unter Misch-/Grenzreibungsbedingungen durchgeführt und die tribologischen Eigenschaften der neuartigen, unbeschichteten Stähle und in Relation zu leistungsstarken DLC-/ZrCN Dünnschichten gesetzt.
The dilution of biogenic fuels into lubricating engine oils often leads to a shortening of the recommended oil drains (between 30% and 60%) and an increase in wear. The large number of overlapping and influencing factors, of which dilution and polymerization of fuel components in the engine oil are emphasised, makes it difficult to find a uniform solution to prevent failures in the various applications.
Insofar single solutions for the different types of biofuels are needed. The contribution of base oil chemistry and additives as well as triboactive materials is featured to deal with the adverse effects of biofuels. In the frame of the European Commission (EC)-funded project 'cleanengine', tentative engine oils based on esters with a content of renewables and polyglycols are formulated to increase the lubricant's tolerance in engines fuelled with biofuel-based blends, with the aim of ensuring required lubricating and wear protection performance while keeping oil drain intervals unchanged.
The present paper focuses on four-stroke diesel applications, fuelled by biodiesel (fatty acid methyl ester — FAME) as well as by rapeseed oil and Jatropha oil (pure vegetable oils, triglycerides), together with relevant blends of those biofuels and conventional diesel fuel.
This paper screens the functional profile (in particular rheological, toxicological, bio-compatibility, tribological and biofuels affinity) of lube families with respect to biofuel contamination. Moreover, this is followed by the contributions of piston ring and liner materials as well as thin film coatings.
The slip-rolling resistances of hard and stiff thin films under high Hertzian contact pressures can be improved by optimizing the 'coating/substrate systems'. It is known from former investigations that the so-called 'egg-shell' effect is no general hindrance for high slip-rolling resistance of thin hard coatings. The coating stability depends more on specific deposition process and coating/substrate interface design. In this article it is experimentally shown, that pure amorphous carbon thin films with hardness between 15 and 63 GPa can be slip-rolling resistant several million load cycles under a maximum Hertzian contact pressures of up to 3.0 GPa. Whereas all coatings were stable up to 10 million load cycles in paraffin oil at room temperature, reduced coating lifetime was found in SAE 0W-30 engine oil at 120°C. It was shown how the coating hardness and the initial coating surface roughness influence the running-in process and coating lifetime. No clear correlation between coating hardness and coating lifetime could be observed, but friction coefficients seem to be reduced with higher coating hardness. Very low friction down to ~0.03 in unmodified engine oils was found for the hardest ta-C film.------------------------------------------------------------------------------------------------------------------------------------------------
Die Wälzbeständigkeit von harten und steifen Dünnschichten unter hohen Hertzschen Kontaktpressungen kann durch die Optimierung des 'Beschichtung/Substrat Systems' deutlich verbessert werden. Aus vorangegangenen Untersuchungen ist bekannt, dass der so genannte 'Eierschaleneffekt' kein generelles Hindernis für eine hohe Wälzbeständigkeit für harte Dünnschichten darstellen muss. Die Stabilität der Beschichtungen hängt vielmehr von dem spezifischen Prozessparametern und dem Schicht/Substrat Grenzflächendesign ab. In diesem Artikel wird experimentell nachgewiesen, dass reine amorphe Kohlenstoffdünnschichten mit Härtewerten zwischen 15 und 63 GPa für mehrere Millionen Lastzyklen unter maximalen Hertzschen Kontaktpressungen bis 3.0 GPa überrollbeständig sein können. Während alle Beschichtungen bis 10 Millionen Lastzyklen in Paraffinöl bei Raumtemperatur keine Defekte aufweisen wurde unter Verwendung eines SAE 0W-30 Motorenöls bei 120°C eine Verringerung der Überrollbeständigkeit nachgewiesen. Es wurde nachgewiesen, wie die Schichthärte und ursprüngliche Oberflächenrauheit der Beschichtung den Einlaufprozess und die Lebensdauer beeinflussen. Es konnte keine offensichtliche Korrelation zwischen Schichthärte und Lebensdauer festgestellt werden, allerdings wurde eine scheinbare Reduktion des Reibwertes mit steigender Schichthärte beobachtet werden. Dabei zeigte die härteste ta-C Schicht unter Verwendung des Motorenöls sehr geringe Reibwerte mit ~0.03.
Biolubrifiants
(2013)