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On the effect of surface topography and humidity on lubricated running-in of a carbon based coating
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Materials Science.
2006 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 261, no 11-12, 1237-1246 p.Article in journal (Refereed) Published
Abstract [en]

The running-in behaviour of an amorphous carbon coating has been evaluated with respect to the substrate surface topography and the humidity of the surrounding environment. Four different surface treatments: polishing, grinding, wet-sandblasting and sandblasting, were employed prior to coating deposition. Sliding ball-on-disc tests were made in dry and humid air with four different oils: one PAO, one ester, one paraffinic mineral oil (all non-additivated) and one fully formulated mineral based engine oil. It was found that wet-blasted surfaces, having an Rq-value of 0.2 μm but much sharper asperities than typically ground surfaces, gave the coatings a better running-in ability compared with the other surfaces. The friction reduced rapidly from typical boundary lubricated values (0.09) to typical values of mixed boundary and EHL lubrication (0.04-0.045), without excessive wear of the steel counter body. No coating delamination was observed for coatings on this surface, and the mild wear was a fine polishing. This running-in behaviour was only observed in dry environments and only with non-additivated and non-polar oils, with PAO giving the lowest friction. In air of 50-60% relative humidity, no transition from boundary to EHL or mixed lubrication could be observed. For all oils and all surface topographies, the friction was always constant at levels typical for boundary lubrication. In dry air a thick tribo-layer composed of oxide was formed on the steel counter body but not in humid air. This oxide, along with a fine polishing of the surfaces and a macroscopic pressure reduction due to wear of the counter body, is believed to be important for the running-in ability.

Place, publisher, year, edition, pages
2006. Vol. 261, no 11-12, 1237-1246 p.
Keyword [en]
Carbon coating, Running-in, Surface roughness, Tribology
National Category
Engineering and Technology
URN: urn:nbn:se:uu:diva-92464DOI: 10.1016/j.wear.2006.03.012ISI: 000242793300008OAI: oai:DiVA.org:uu-92464DiVA: diva2:165550
Available from: 2004-11-19 Created: 2004-11-19 Last updated: 2016-06-22Bibliographically approved
In thesis
1. Tribology of Carbon Based Coatings for Machine Element Applications
Open this publication in new window or tab >>Tribology of Carbon Based Coatings for Machine Element Applications
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Demands on lower fuel consumption, reduced pollution, increased operating times, etc. force the automotive industry to constantly improve the performance of critical machine elements. In this development various carbon based coatings have proven very promising, mainly because of their low friction and high wear resistance in dry sliding contacts. The contact conditions can be very different in various machine element applications, e.g. both rolling and sliding contacts. Additionally, most contacts are usually lubricated. Hence, other properties of the coating may be required in order to obtain low friction and wear, as for instance a beneficial running-in ability.

In lubricated contacts the very high wear resistance of carbon coatings can cause fatigue damage resulting in delamination of the coating, especially when deposited on rough substrates. In rolling contacts the fatigue damage can be reduced simply by using smoother surfaces, but the thickness of both the coating and the interlayer also has a strong influence on fatigue damage.

In lubricated sliding contact tests it was found that the running-in ability could be improved by modifying the coating and/or by using an appropriate surface preparation prior to coating deposition. An increased Cr-content in the top-layer of the carbon coating reduced the friction due to the formation of a stable tribo-layer on the uncoated counter body. An even further reduced friction could be obtained by employing a fine wet-blasting of the substrate giving sharp surface asperities. The friction reduction is thought to be a result of a transition towards a higher degree of full film lubrication, due to a very fine smoothening process of both the coating and the counter body during the running-in process.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 40 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 1050
Materials science, Materialvetenskap
National Category
Materials Engineering
urn:nbn:se:uu:diva-4701 (URN)91-554-6116-6 (ISBN)
Public defence
2004-12-17, Siegbahnsalen, Ångströmlaboratoriet, Box 534, 751 21, Uppsala, 10:15
Available from: 2004-11-19 Created: 2004-11-19Bibliographically approved

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