Dynamics of sliding metal surfaces as case study for complex systems
Herstellung und Eigenschaften von Funktionsmaterialien
Zusammenfassung der Projektergebnisse
When the surfaces of two machine components are in sliding contact, the direct view at the sliding interface where friction is generated is blocked. Therefore the sliding contact is often called a “buried interface”. This hindrance makes it notoriously difficult to study and predict tribological behavior. To make it worse, physical and chemical effects on many length scales affect friction and wear properties. An analysis of the problem after an experiment has finished is often not very meaningful because tribological processes like wear are strongly non-linear and do not reflect the dynamics that occur within the tribocontact. For a better understanding of those processes it is needed to obtain time-resolved data of friction forces, wear, topography and other important quantities. The number of in-situ experiments in modern Tribology is thus constantly rising and includes the measurement of lubricant film thickness, transfer film formation, chemistry and wear. Combining a submicrometer-precise positioning system and a novel digital holographic microscope for fast measurement of topography we were able to develop an experimental platform which allows for the first time to acquire the three dimensional topography of the sliding track of a metal surface under lubrication with up to 15 frames per second. The topopgraphical resolution of this method is in the order of several nanometers while the lateral resolution is comparable to an optical microscope. Therefore we are using atomic force microscopy in addition for the measurement of topography with even higher lateral resolution. The time-resolved topography measurements allowed a view at the formation of wear particles in a lubricated metallic sliding contact. We found different mechanisms that are working in parallel within the copper/steel tribosystem. We observed that some ten to hundreds of nanometers deep voids constantly appear and vanish on the copper surface. This happens when due to the strong shear gradient within the nearsurface zone becomes nanocrystalline. At the same time crack-like features grow within the nanocrystalline zone that extend parallel to the surface and finally leave the material as wear particles. The resulting crack edges rapidly heal by plastic processes. Therefore the location where single wear particles originated from cannot be seen anymore after a few cycles of continuing sliding. The experiments that were carried out on copper also help to understand the evolution of the friction. Plowing copper out of the sliding track causes a large fraction of the initial friction. But the plowing contribution is not constant and therefore the coefficient of friction decreases quickly. The in-situ observation of the sliding track allowed us to discriminate plowing friction from sliding friction as a function of time. With adding just a few percent of zinc the behavior of the friction coefficient becomes more complicated. We found that besides the formation of a grain-refined zone underneath the sliding surfaces, also the composition of the material changes significantly. In the early stage of sliding the near surface becomes enriched with zinc oxide. Zinc oxide however is well known for its friction reducing effect. Therefore we believe that alloys can provide low friction if they contain a low friction phase that is able to segregate to the surface.
Projektbezogene Publikationen (Auswahl)
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Message from the Scientific Organizers, Tribol. Lett. 39, 1
M. Dienwiebel, M. Scherge and P. Gumbsch
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„Meet important foreign tribologists“, The Tribology special edition WTC Nr. 264, Shinjusha (in japanischer Sprache)
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Thermolubricity in atomic-scale friction, Physical Review B 78, 15440 (2008)
K.B. Jinesh, S. Yu. Krylov, H. Valk, M. Dienwiebel and J.W.M. Frenken
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Torque and Twist against Superlubricity, Physical Review Letters 100, 046102 (2008)
A. E. Filippov, M. Dienwiebel, J. W.M. Frenken, J. Klafter and M. Urbakh
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Verfahren zur Fertigbearbeitung einer Oberfläche eines Werkstückes unter Ausbildung eines Dritten Körpers, DE 2008-102008034447 A: 20080724
M. Dienwiebel, M. Weber, M. Scherge, P. Gumbsch
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Design and construction of a novel tribometer with online topography and wear measurement, Rev. Sci. Instrum. 81, 063904 (2010)
S. Korres and M. Dienwiebel
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Friction and Wear Behavior of Fe-DLC Coatings, Reports of C.I.T. 57 (2010) (In japanischer Sprache)
Ken'ichi Hiratsuka, M. Dienwiebel and Jean-Michel Martin
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On the Tribochemical Action of Engine Soot, Wear 269, 1 (2010)
S. Antusch, M. Dienwiebel, E. Nold, P. Albers, U. Spicher and M. Scherge
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The effect of sample finishing on the tribology of metal/metal lubricated contacts, Wear 268, 1518 (2010)
P. Berlet, M. Dienwiebel, and M. Scherge
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Experimental and numerical atomistic investigation of the third body formation process in dry tungsten/tungsten-carbide tribo couples Tribol. Lett. 50, 67-80 (2012)
P. Stoyanov, P.A. Romero, T.T. Järvi, L. Pastewka, M. Scherge, P. Stemmer, A. Fischer, M. Dienwiebel, M. Moseler
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In-situ observation of delamination on lubricated sliding surfaces Acta. mater. 60, 420-429 (2012)
S. Korres, T. Feser and M. Dienwiebel
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A New Approach to Link the Friction Coefficient with Topography Measurements during Plowing, Wear 303, 202-210 (2013)
S. Korres, T. Feser, and M. Dienwiebel
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Friction and Wear Mechanisms of Tungsten-Carbon Systems: A Comparison of Dry and Lubricated Conditions ACS Applied Materials and Interfaces 5, 6123-6135 (2013)
P. Stoyanov, P. Stemmer, T.T. Järvi, R. Merz, P.A. Romero, M. Scherge, M. Kopnarski, M. Moseler, A. Fischer and M. Dienwiebel
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The running-in mechanisms of binary brass studied by in-situ topography measurements Wear 303, 465-472 (2013)
T. Feser, P. Stoyanov, F. Mohr and M. Dienwiebel
