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Study of thickness dependence of sputtered-carbon coating for low friction valve lifters
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 3-4, 241-250 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents test and stress calculation results of two thicknesses (0.7 and 1.7 mu m) of amorphous a-C:Cr-coated standard rollers for a cam roller follower valve train mechanism in a diesel truck engine. The coated rollers were tested for 100 h on equipment simulating near-normal engine running conditions. For the thicker coating, the results show mainly polishing wear and low wear on the cam surface. The thinner coating delaminates and the cam shows higher wear. The delamination may be the product of high tensional stresses in the thinner coating, as determined by finite element calculations. These tensions allow surface cracks to propagate down to the chromium interlayer and vice versa.

Place, publisher, year, edition, pages
2006. Vol. 261, no 3-4, 241-250 p.
Keyword [en]
camshaft, roller, carbon coating, tensional stress
National Category
Engineering and Technology
URN: urn:nbn:se:uu:diva-92461DOI: 10.1016/j.wear.2005.10.002ISI: 000239678300002OAI: oai:DiVA.org:uu-92461DiVA: diva2:165547
Available from: 2004-11-19 Created: 2004-11-19 Last updated: 2011-06-23Bibliographically 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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