Effect of Relative Humidity on the Tribological Performance of Pure Sliding Contacts Lubricated with Phosphorus Additive Containing Lubricants

Prior research with zinc dialkyl dithiophosphate (ZDDP) additive has shown that higher relative humidity can result in higher wear. In order to validate this phenomenon, a phosphoric additive was added to the same base oil as previous studies to explore the effect of relative humidity and water on the related tribological performances in pure sliding contacts. The post-test specimen surfaces were examined under scanning electron microscope to study the effect of relative humidity on the surface, followed by applying x-ray photoelectron spectroscopy to study the related tribochemistry behavior. It is clear that higher relative humidity results in higher wear. Oxygen concentration as oxide in the wear scar increases with the increase in relative humidity. The reaction layer thickness decreases with the increase in relative humidity, which leads to more asperity contacts and results in higher wear on the ball surface.