Tribological Behaviors of W/Mo Films under Lubrication of Zinc Dithiophosphates—Understanding Their Roles in Tribochemical Reactions

Surface treatment is an effective factor in determining tribological performance, particularly for the condition of oil lubrication. Tungsten (W), molybdenum (Mo), and tungsten-molybdenum alloy (W-Mo) films were prepared on AISI 316L steel by ion beam-assisted deposition (IBAD). Tribological tests of the three modified surfaces using zinc dithiophosphate (ZDDP) lubrication were conducted on an SRV-2 tester and the tribochemical properties of different surfaces were analyzed. Surface analysis tools such as scanning electron microscopy (SEM), X-ray diffractometry (XRD), nano-indentation, and X-ray photoelectron spectroscopy (XPS) were used to study the microstructure, hardness, and chemical characteristics of the tribofilms generated on the worn surfaces. The results showed that these three modified films had better antiwear and antifriction properties than the AISI 316L substrate using both poly-alpha-olefin (PAO) and ZDDP-containing PAO lubrication, and they had different tribochemical reactions with ZDDP that determined their tribological behaviors.