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- Friction (153) (entfernen)
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Eingeladener Vortrag
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The influence of temperature and counterbody material on the tribological properties of a-C:H coatings deposited on Cronidur 30 steel has been investigated in a lubricated ball on disk contact situation. The results show, that the wear volumes of the system increase exponentially with increasing temperature. Two different wear mechanisms seem to have a major influence: First, the abrasive action due to materials hardness and second, the tribooxidation when silicon nitride is counter material.
The influence of temperature and counterbody material on the tribological properties of a-C:H
coatings deposited on Cronidur 30 steel has been investigated in a lubricated ball on disk
contact situation with alpha-alumina and silicon nitride as counterbodies. The results show, that the wear volumes of the systems increase exponentially with increasing temperature, for alpha-alumina more than for silicon nitride. Two different wear mechanisms seem to have a
major influence: First, the abrasive action due to materials hardness and second, the tribo-oxidation when silicon nitride is counter material.
The process window and range of functional properties of NbC is wide, because micro-hardness, hot hardness, sliding wear resistance, elastic modulus and toughness can be tailored by the C/Nb ratio, because Nb4C3, Nb6C5 and other short and long range ordered phases occur in the region of homogeneity of NbCx (0,75≤ x ≤1.0) in the binary Phase diagram, and by the type of binder. Further improvements enable the addition of secondary carbides. Supporting results from literature and different grades with varying C/Nb ratio or binder types were illuminated. Thus, the NbC system offers to producers a wider process window, than WC. The impact of these tailored properties on sliding wear and cutting performance was illuminated by tribological and machining results. NbC can be synthesized by carbothermal conversion of Nb2O5 or be metallurgically grown in melts and leached out as coarse NbC cubes. NbC provides comparably lower friction in many relevant tribo-contacts and displays low wear. NbC and Nb2O5 have so far no REACH classification related to human toxicology and are not listed as substances of very high concern contrary to WO3 and Co3O4.
Tribofilms formed during dry sliding usually exhibit a nanocrystalline structure and complicated composition. In the present study, tribofilms consisting mainly of a solid lubricant, namely graphite nanoparticles, are considered. Systems providing such tribofilms are candidates for anti-friction applications. Since sliding action always leads to mixing of the materials at both sides of the tribological interface, it was of major interest to study the impact of different amounts of a hard constituent, SiC in the considered case, within the soft matrix systematically. Furthermore, the impact of normal pressure was considered. A mechanically mixed layer was observed for the whole range of normal pressures and SiC volume fractions. The calculated coefficient of friction decreased significantly with increasing thickness of this layer but was only marginally affected by SiC volume fraction, which is good news for anti-friction applications.
Friction at the microscale during reciprocal sliding tribotests was studied for the first time with self-mated steel (100Cr6/AISI 52100) taking advantage of an atomic force microscope (AFM). To this aim, microsized steel particles were glued to the AFM-cantilever and employed as colloidal tips to perform tribotests on a steel disc. The torsion of the cantilever, which correlates with the friction force, was measured during the tests. Few tests with the same load did not yield any wear and show that the load and adhesion contributions to friction stay constant when the shape of the test particle does not change. Most of the presented tribotests engendered wear. For those tests, the increase of friction during the tribotests was attributed to the emerging plowing contribution. Furthermore, analysis of both torsion and local slope gives information on the creation of wear particles and their influence on friction.
The focus of this study is to evaluate of hydrogen on the friction and wear behavior of a wide range of polymer materials. Thereby, the tribological performance of filled and unfilled polymers from different suppliers were compared at room temperature in air and hydrogen gas (H2) as well as in liquid hydrogen at -253°C (LH2).
The focus of this study is to evaluate the influence of hydrogen on the friction and wear behavior of a wide range of polymer materials. Thereby, the tribological performance of filled und unfilled polymers from different suppliers were compared at room temperature in air and hydrogen gas (H2) as well as in liquid hydrogen at -235°C (LH2).
The research institution TEKNIKER has coordinated the EUROPEAN Project EREBIO, were different biodegradable lubricants have been formulated by FUCHS and BAM for heavy duty engines (GUASCOR), and passenger cars (RENAULT). In the frame of this article, it has been summarised the results obtained when developing biodegradable passenger car lubricants in combination with triboreactive materials.
Replacing hydrocarbon-based oils with biodegradable products is one of the ways to reduce adverse effects on the ecosystem caused by the use of lubricants. The application of low or no sulphur, ash and phosphorous (lowSAP) ester- or polyglycol-based oils, intended for passenger car engine lubricants as substitutes for hydrocarbon-based oils, required the preparation of a composition of lubricants with comparable tribological and functional properties.
The study is focussed on passenger car motor oils (PCMO) with reduced metal-organic additives. This is necessary in order to reduce the ash build-up in the after treatment system and therefore improve its efficiency and lifetime. High fuel efficiency and long drain intervals are requested, as well. To follow a line in a consequent way, these oils have to be biodegradable and non-toxic to the aqueous environment according to the directive EC/1999/45, coherent with other international standard. In a modern diesel or gasoline engine, the engine oils has to fulfil quite a number of different functions, such as lubricating and cooling the system, wear protection, soot and particle handling with less deposit tendency and so on.
In the paper a study of the biodegradability, toxicity and the tribological properties has been carried out for new developed prototype engine bio-oils. Also, some different plasma sprayed triboreactive coatings have been deposited on cast iron piston rings, being studied also their tribological properties. Finally, the behaviour of the new bio-oils selected and plasma sprayed triboreactive coatings on piston rings have been screened in a real engine.
The frictional response of molybdenum bis(C11-14 branched and linear alkyl) carbamodithioate oxo thioxo complex (Mo-dttc) versus bismuth dimethyldithiocarbamate (Bi-dtc) and bismuth dodecylbenzene Sulfonate (Bi-ddbsa) slip-rolling under mixed/boundary lubrication (T=120°C, n=10 millions of cycles, P0max=2.25 GPa) in PAO-based formulation against three different steel alloys were compared.
Ceramic particulate composites in the system SiC-TiC-TiB2 sliding against SiC and Al2O3 under water
(1999)
The tribological behaviour of SiC, SiC-TiC and SiC-TiC-TiB2 was determined in oscillating sliding against SiC and -Al2O3 in water at room temperature. The tribo-systems with the composite materials containing TiC and TiB2 differ significantly from the systems with the single phase SiC: The wear is reduced and the friction is increased. The wear reduction up to a factor of 10 is mainly due to the formation of an oxide film containing titanium oxides which is soft, stable in water and well adhering to the bulk material. This oxide film is transferred to the alumina ball but not to the silicon carbide ball.
This chapter deals with the development of polyetheretherketone (PEEK) and polytetrafluoroethylene (PTFE)-based composites, optimized for low friction and low wear performance under extreme environments. It is demonstrated that the incorporation of a harder polymer component into PTFE (such as PEEK particles), a short fiber reinforcement (e.g. carbon fibers (CFs)) and internal lubricants (e.g. PTFE particles) helps to reduce the friction and to improve the wear resistance over a very wide temperature range.
The automotive industry places significant importance on downsizing components to achieve greater efficiency. The goal of reducing CO2 emissions has led to the development of lightweight materials that are also able to enhance performance. In light of these aspirations, the aim of this study is to characterize two novel, high-performance steels, as well as a 'classical' gear steel for comparison with each other and currently applied materials. The gear steel underwent carburization and subsequent deep freezing treatments in an attempt to yield discrete sample groups with respect to residual austenite. The high-performance steels were heat treated as recommended by their respective manufacturers, and were not carburized. Elemental analyses were conducted by multiple methods to ensure accurate results. Residual austenite contents of the steels and the depth profiles of residual stresses were determined by X-ray diffraction (XRD). Hardness profiles were taken from the testing surfaces into the material core. The carburization of 20MnCr5 led to higher hardness and the greater concentration of carbon in the carburization zone more representative of a hardened SAE E52100, or 100Cr6/102Cr6, than of a non-carburized 20MnCr5. Residual austenite contents ranging from approximately 6–14 vol% were generated, though effectively providing only two, rather than the desired four discrete sample groups. Residual stresses from machining and carburization were measured directly at the sample surface, and from carburization alone below the surface. The high-performance steels fulfilled manufacturer expectations in terms of elemental content, hardness between 50 and 55 HRC and strongly martensitic microstructure character. Finally, slip-rolling endurance testing (T=+120 °C, 10,000,000 cycles, approximately 19 days in a factory fill engine oil) was carried out on all materials, whereby coefficient of friction distributions during testing and wear coefficients after testing were calculated. Testing was performed up to and including P0Mean=1.94 GPa (P0Max=2.91 GPa, FN=2000 N). Ultimately, the non-carburized high-performance steels showed competitive wear performance and better friction behaviour than the carburized 20MnCr5, which has been attributed to their work hardening capability.
We review contact mechanics with emphasis on the rheological (time dependent) properties of polymers and their relations to surface roughness, material properties, and friction as well as wear behavior of rubbing polymer surfaces. The main concept of polymer mechanics related to tribology consists of three basic elements involved in friction: deformation resulting in the real area of contact of rough surfaces, contact adhesion, and shear and rupture of materials in the contact during the sliding friction. The results of classical work are included, which addresses the real contact area calculation and the description of adhesion interaction between rough surfaces. A brief review of experimental investigations concerning the surface characterization by means of bearing curves, the intermolecular force interaction using the adhesion parameter, the effect of temperature on the real contact area, the formation of transferred polymer film during friction, and tribological behavior of ultrathin polymer layers are presented and their implications discussed.
Contact formation and development are the basis of friction and wear modelling and understanding. Unanimously topography formation and development in friction contacts are regarded of highest importance for understanding and modelling friction processes. The frequently found running in behaviour of sliding contacts is—aside from the build up of reaction and transfer layers-at least partly caused by the topography development due to friction processes until a stable equilibrium state is reached.
Experimental results of friction and topography measurements are presented which demonstrate the mutual modification of friction and contact topography.
A special experimental set up with an AFM allowed to correlate the measured friction forces with the contact position and the topography at this point. In this way, friction force transitions and changes can be assigned to topography changes due to abrasion, adhesion and wear particle agglomeration.
Contact surfaces with artificial regular structures have been prepared to avoid problems with topography and friction correlation due to the statistical nature of roughness on technical contact surfaces. The friction effects of roughness were simulated by etched ditches of defined width, depth and distance on silicon or metal surfaces. This allowed to explain the mutual influences of topography and friction. The effect of a single asperity and of the 'roughness structures' could be demonstrated.
Topography measurements with an AFM correlated with the friction force could help to understand friction changes without changing any parameter.