The tribological behaviour of ta-C and a-C:H carbon films was analysed by pin-disc tests under ultra high vacuum (<10^-5 mbar). The tests were executed on a commercial High Vacuum Tribometer (CSM-Instruments) and compared with results obtained under controlled atmospheric pressure conditions.

In this work, we present the comparison of the friction coefficients under high vacuum and under controlled atmosphere conditions of two sets of carbon films, one prepared by FCVA (giving rise to hydrogen free carbon), the other by PECVD (leading to hydrogenated carbon). The structure of these films was analysed by Raman and RBS-ERD spectroscopy as well as by XR reflectometry.

We will demonstrate that under vacuum, FCVA carbon layers do not slide ( µ = 0,5-0,7) but PECVD carbon films have a good sliding behaviour (µ = 0,1-0,3). An inverse behaviour was observed under controlled atmospheric conditions.

These first results indicate a predominant role of the structure of the films, as analysed by Raman and RBS-ERD spectroscopy as well as by XR reflectometry, on the tribological characteristics of the carbon films. In particular the influence of hydrogen concentration seems to be directly linked to the Vacuum tribological behaviour of the coatings.

In the past, the development of modern engines and transmissions would have been impossible without advanced lubricant additive chemistry and proper lubricant formulation. In order to meet demanding durability and performance requirements engine and transmission oils contain a wide range of additives. Especially anti-wear (AW) and extreme-pressure (EP) additives are crucial in minimizing friction and wear and protecting contact surfaces under severe contact conditions. It is described in detail that the mechanism by which AW and EP additives reduce friction and wear of metallic surfaces under boundary lubrication is due to formation of tribofilms, activated by tribochemical reaction between additive molecules and metallic surface. Introduction of DLC coatings opens further possibilities in improving performance of automotive components, which can not longer be achieved only by lubricant design. Although DLC coatings show low friction and wear under dry sliding conditions the majority of automotive components will remain lubricated, at least for the near future. Therefore, for successful application of coated components aimed for further performance enhancement in automotive industry (lower friction and fuel consumption, higher load bearing capacity,...) coatings will have to perform adequately also under oil-lubricated conditions. Investigations so far indicate that in certain cases DLC coated surfaces may show improved tribological properties when lubricated by additivated oil. However, the mechanism responsible is not yet fully understood.

With the aim to add some further understanding to this important area and to be able to fulfill future automotive requirements, the paper will focus on describing reactions of EP and AW additives with DLC coatings aimed for automotive components. Results from investigations on doped and un-doped DLC coatings tested under boundary lubricated conditions will be presented and compared to uncoated steel surfaces.

New advanced thermal spray technology allows providing wear resistant coatings on the cylinder surface on Aluminum or Magnesium engines. The obtained special surface topography after the finishing allows to decrease significantly the coefficient of friction and to decrease the fuel consumption of an amount of 2 to 4 percents.

Engine tests on diesel and gasoline engines have confirmed the value of this technology regarding the aspect of energy saving.

This coating technology is introduced since four years in Europe by the manufacturing of high power diesel respectively gasoline engines. The combination of different MMC coating materials allows the development of new specific solutions for each types of engine. Coatings with improved corrosion resistance and abrasion resistance were also developed and are available now. A brief overview on other applications of thermal spraying in the automotive industry will be given also.