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Performance of DLC coatings in heated commercial engine oil
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Tribomaterial)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Ångströms Tribomaterialgrupp)
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences. (Ångströms Tribomaterialgrupp)
(Ionbond Netherlands)
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2013 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 304, no 1-2, 211-222 p.Article in journal (Refereed) Published
Abstract [en]

Multilayer Diamond Like Coatings (DLC) are widely used to protect highly loaded components from wear and/or to reduce the friction losses in combustion engines. The uppermost layer of the coating controls the chemical situation in the contact and is therefore a very important part of modern multilayer coatings. To examine the individual performances and assess differences and potentials of modern DLC coatings, four commercially available DLCs designed for automotive components with different doping elements together with an uncoated reference were tested in high performance engine oils heated to 90 °C at two different initial contact pressures. The coefficient of friction generally was higher in the tests with the lower initial contact pressure (approximately 20% for all combinations) and the specific wear rate was also up to 100% higher for some combinations. It was also found that a used motor oil showed up to 30% higher friction than when fresh and at the same time reduced the wear in most cases. The tungsten doped coating showed the highest wear, but also the lowest coefficient of friction. The Si doped coating showed the best wear results, most probably due to the ability to make use of the additives in the oil to form a protecting tribofilm.

Place, publisher, year, edition, pages
2013. Vol. 304, no 1-2, 211-222 p.
National Category
Nano Technology Tribology
Research subject
Engineering Science with specialization in Materials Science
Identifiers
URN: urn:nbn:se:uu:diva-192720DOI: 10.1016/j.wear.2013.04.036ISI: 000322611800026OAI: oai:DiVA.org:uu-192720DiVA: diva2:600644
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research
Available from: 2013-01-25 Created: 2013-01-25 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Triboactive Component Coatings: Tribological Testing and Microanalysis of Low-Friction Tribofilms
Open this publication in new window or tab >>Triboactive Component Coatings: Tribological Testing and Microanalysis of Low-Friction Tribofilms
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Coatings are often used on critical components in machines and engines to reduce wear and to provide low friction in order to reduce energy losses and the environmental impact.

A triboactive coating not only provides this desired performance, it also actively maintains the low friction by a structural or chemical change in a very thin top layer of these already micrometer thin coatings. This so-called tribofilm is often 5-50 nm thick and can be formed either from the coating itself or by a reaction with the counter surface or the surrounding atmosphere, i.e. gas, fuel, oil, etc. The tribofilm will maintain the wanted performance for as long as the system is not chemically disturbed.

This thesis provides a detailed overview of the functionality of triboactive low-friction coatings, in many different systems. The majority of the tribofilms discussed, formed in very different environments, are built up by tungsten disulfide (WS2), which is a material similar to graphite, with a lamellar structure where strongly bonded atomic planes may slip over each other almost without resistance. The major difference is that WS2 is an intrinsically triboactive material, while graphite is not. However, graphite and other carbon-based materials can be made triboactive in certain atmospheres or by addition of other elements, such as hydrogen.

The remarkable affinity and driving force to form such WS2 low-friction tribofilms, regardless of the initial states of the sulfur and tungsten, and even when the forming elements are present only at ppm levels, is a recurrent observation in the thesis.

Addition of an alloying element to sputtered coatings of WS2 can improve its mechanical and frictional properties significantly. Several promising attempts have been made to find good candidates, out of which a few important ones are investigated in this thesis. Their achievable potential in friction reductions is demonstrated.

By reducing friction, energy losses can be avoided, which also results in lower particle and exhaust emissions, which directly reduces the environmental impact. Triboactive coatings are shown to be a promising route to significantly improve tribological applications and allow more environmental friendly and energy efficient vehicles.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 98 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1011
Keyword
tribofilms, low-friction coatings, tungsten disulfide, TEM
National Category
Materials Engineering Nano Technology
Research subject
Materials Science
Identifiers
urn:nbn:se:uu:diva-191223 (URN)978-91-554-8576-4 (ISBN)
Public defence
2013-02-22, Siegbahnsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 10:15 (English)
Opponent
Supervisors
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research
Available from: 2013-02-01 Created: 2013-01-09 Last updated: 2013-02-11Bibliographically approved

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Forsberg, PeterGustavsson, FredrikRenman, ViktorJacobson, Staffan

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