On the effect of surface topography and humidity on lubricated running-in of a carbon based coating
2006 (English)In: Wear, ISSN 0043-1648, E-ISSN 1873-2577, Vol. 261, no 11-12, 1237-1246 p.Article in journal (Refereed) Published
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.
Carbon coating, Running-in, Surface roughness, Tribology
Engineering and Technology
IdentifiersURN: urn:nbn:se:uu:diva-92464DOI: 10.1016/j.wear.2006.03.012ISI: 000242793300008OAI: oai:DiVA.org:uu-92464DiVA: diva2:165550