Formation mechanisms of zinc, molybdenum, sulfur and phosphorus containing reaction layers on a diamond‐like carbon (DLC) coating

Abstract Diamond‐like carbon (DLC) coatings are nowadays successfully applied on industrial components like pistons, piston rings and bearings in lubricated tribological contacts due to friction and wear reducing effects. In contradiction thereto, todays lubricants and additives are designed for tribological steel/steel contacts, whereby the knowledge on tribochemical layer formation on steel surfaces is comprehensive in contrast to the physical‐chemical interactions between diamond‐like carbon coatings, lubricants and additives. Therefore the formation mechanisms of zinc, molybdenum, sulfur and phosphorus containing reaction layers on a zirconium modified diamond‐like carbon coating a‐C : H : Zr (ZrC g ) in lubricated tribological contacts were analyzed by means of pin‐on‐disc (PoD) tribometer by varying the distances from s = 200 m–3,000 m under boundary and mixed friction conditions at T = 90 °C and a contact pressure p = 1,300 MPa regarding the application of diamond‐like carbon coatings on gears. The base lubricant poly‐alpha‐olefin (PAO) was formulated using the anti‐wear (AW) and extreme pressure (EP) additive zinc dialkyldithiophosphate (ZnDTP) and the friction modifier (FM) additive molybdenum dialkyldithiophosphate (MoDTP). The chemical composition of the tribochemical reaction layers by means of and Raman spectroscopy and x‐ray photoelectron spectroscopy (XPS) as well as for the thickness differ significantly by varying the additivation.