The Clarification of Friction Mechanism in Oil Lubrication for CNx Coating by In-Situ Observation of Friction Area with Reflectance Spectroscopy

Abstract

To clarify the low friction mechanism of CNx coating in PAO oil lubrication, we measured reflectance spectrum at friction area in-situ by reflectance spectroscopy during friction test against a sapphire hemisphere pin in PAO oil. We observed and estimated the thickness of PAO oil film, the surface roughness of CNx coating, thicknesses, and polarizability of the transformed layer formed on bulk CNx coating during friction test by analyzing reflectance spectrum. We proposed that the decreasing of load ratio of boundary lubrication mode to total load is the one of governing factor to reduce friction on the basis of the increasing of Λ value. Also we proposed the increasing of adsorption of PAO oil to the CNx transformed layer is the second governing factor on the basis of the increasing of polarizability of PAO oil and transformed layer, that leads to the increasing of van der Waals force between transformed layer and PAO oil as low friction mechanism of CNx in PAO oil lubrication.

Keywords

• cnx
• carbon nitride
• base oil
• oil lubrication
• reflectance spectroscopy
• in-situ observation
• friction mechanism
• lubrication mode