The Effect of Orienting Carbon Coatings Alloyed with Carbide-Forming Elements on the Antifriction Properties of Lubricants

The effect of the alloying of diamond-like orienting carbon coatings by carbide-forming elements (tungsten, molybdenum, and silicon) exerted on the antifriction properties of lubricant PAO-4 with a surfactant additive such as oleic acid and two chemically active additives (zinc dithiophosphate and molybdenum dithiocarbamate) is studied. The antifriction properties of the compared environments containing sulfur abruptly increase upon the friction of steel against coatings alloyed with tungsten or molybdenum (the friction coefficients decrease to 0.02–0.05), whereas in the case of environments containing no sulfur, the friction coefficients are about 0.15. This phenomenon can be explained by the formation of molybdenum and tungsten dichalcogenides as a result of the tribochemical interaction of these metals with the sulfur contained in the lubricating lubricant.