Downsizing of combustion engines is a popular strategy to reduce fossil fuel consumption and therefore protect the environment. This approach however requires strict mechanical friction management.

Diamond-like-carbon (DLC) materials are extensively used as tribological coatings for engine parts due to their excellent combination of low friction and improved wear resistance properties. However, it is quite challenging to use DLC coatings on components which operate at high temperature and high load conditions and at high sliding velocity. Typical examples are piston-cylinder and valve-train assembly, where maximum operating temperature is in the range of 150◦C to 300◦C leading to fast DLC coating graphitisation and degradation.

To address this problem the National HIPIMS Technology Centre developed a carbon-based coating, which is simultaneously doped with Mo and W. The coating utilises tribo- chemical reactions to achieve "in-situ" formation of lubricious phases in conditions of boundary lubrication. [1,2].

State-of-the-art coatings require the use of specially formulated oils allowing formation of lubricious metal chalcogenides such as MoS₂ and WS₂ due to thermal decomposition of the various types of oil additives.

In contrast, the new coatings form these lubricious phases "in situ" via a tribo-chemical reactive process taking place at the asperity contacts. In this case the high flash temperatures in the asperity contact, (exceeding 800^oC) during sliding trigger reactions between the Mo and W dopants in the coating with Sulphur, which is a natural ingredient in the oil to form lubricious MoS₂ and WS₂ compounds. The advantage of this approach is that the solid lubricant is produced right at the tribo-contact where it is most needed and the process is effective even with non-formulated oils. Furthermore, the addition of doping elements such as Mo and W into the Carbon coating delays the graphitisation process and therefore is seen as a highly resourceful approach for preservation of coating properties at higher temperatures., (download PowerPoint slides for more information (PPTX, 4MB))

[1] P. Eh. Hovsepian, D. Doerwald, R. Tietema, A.P. Ehiasarian. "Me-doped C coating to operate in boundary lubrication conditions where the metal to C ratio does not exceed 1:4" European Patent 2 963 145. EP 14175063.8  INV. C23C14/06 C23C14/35 C23C14/02 C10M103/04 C23C1416 C23C14/34 H01J37/34 Priority claimed: EP/30.06.2014/EPA 14175063.