Effects of structure of zinc dialkyldithiophosphates on tribological properties of tetrahedral amorphous carbon f ilm under boundary lubrication

Effects of the structure of zinc dialkyldithiophosphates (ZDDPs) on the tribological properties of a tetrahedral amorphous carbon (ta-C) film were investigated. Friction tests were performed at diamond-like carbon (DLC)/DLC and steel/steel contacts under lubrication with poly-alpha olefin (PAO) and PAO containing six types of ZDDPs with different alkyl groups. The tribological properties of the ta-C film depended on the chemical composition of ZDDP-derived tribofilms on the outermost surface, which depended on the abundance ratio of neutral-ZDDP and basic-ZDDP in the ZDDP solution. Thus, the ZDDP forms play important roles in the tribological properties of the ta-C film. All these results suggest that the ZDDP forms can determine the tribological properties of the ta-C film lubricated with the ZDDP solution.