Physical-chemical interactions between DLC coatings and additivated lubricants

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The worldwide awareness of the threat of global warming and the demand for reduction of greenhouse gases result in continuously rising demands on energy efficiency of tribological systems. An important technology for efficiency improvement of drive systems is the deposition of diamond-like carbon coatings (DLC) on machine elements due to their favorable friction and wear behavior in tribological contacts. Therefore, the application of carbon based coatings under full lubrication is increasingly coming into focus. Regarding tribological applications under lubricated conditions, interactions between carbon based coated surface and lubricant have to be taken into consideration. This is especially an interesting research topic, as the industrially used lubricants are usually developed for the application in contact with uncoated iron based materials. In this regard, it must be noted that tribo-chemical reactions with lubricants and their additives, which leads to the formation of a tribo-chemical layer, cannot occur on diamond-like carbon coatings as on iron based surfaces. This leads directly to the need for research. The aim of this joint research proposal of IOT and FZG is to investigate physical and chemical interactions between the diamond-like carbon coating graded zirconium carbide (ZrCg) and additivated lubricants under boundary and mixed friction as well as under elastohydrodynamic lubrication (EHL) conditions. As a first step, the diamond-like coating ZrCg will be deposited by means of middle frequency magnetron sputtering (mfMS). After that tribological model tests using a pin-on-disc-tribometer, a twin-disc tribometer and gear efficiency test-rig will be carried out with different combinations of standard lubricants and additives. Basing on tribological tests, the application of comprehensive physical-chemical analytics as Focused Ion Beam/Scanning Electron Microscopy, Secondary Neutral Mass Spectroscopy and Micro Raman Spectroscopy will be used to investigate physical and chemical interactions between the carbon based coating ZrCg and lubricants/additives in tribological contacts unter lubricated conditions. Gaining valuable insights about the mechanisms govern the formation and composition of tribochemical reaction layers on DLC coating will make a valuable contribution to understanding the tribological behavior of DLC coatings unter lubrication.