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- Svahn, Fredrik, et al.
(author)
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The influence of surface roughness on friction and wear of machine element coatings
- 2003
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In: Wear. - 0043-1648 .- 1873-2577. ; 254:11, s. 1092-1098
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Journal article (peer-reviewed)abstract
- The use of low frictioncoatings like amorphous carbon or metal-doped carbon coatings on machineelements is constantly increasing. Most often, a surface treatment, e.g. grinding and polishing or honing, is required for optimal performance of the coated machineelement. This can be time consuming and costly. In this study, the effect of surfaceroughness on friction and sliding wear of two different coatings, one tungsten containing and one chromium containing coating, were examined using a ball-on-disc test. Ball bearing steel plates were grinded to different surfaceroughnesses and coated with the two different coatings. The friction was found to depend on surfaceroughness where the rougher surfaces gave higher friction coefficients. The wear rate for the a-C:W coating was found to be independent of the roughness, whereas the roughness had a strong influence on the wear rate for the a-C:Cr coating. This could partly be explained by a difference in wear mechanism, where fatigue wear was observed for the a-C:Cr coating but not for the a-C:W coating.
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- Svahn, Fredrik, 1975-
(author)
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Tribology of Carbon Based Coatings for Machine Element Applications
- 2004
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Doctoral thesis (other academic/artistic)abstract
- 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.
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