Correlation between nano-mechanical and macro-tribological properties of tribofilms derived from organic phosphoric additives

Abstract

Correlation between nano-mechanical and macro-tribological properties of the tribofilm derived from phosphoric additives was investigated. Macro friction test was performed at steel/steel contact under lubrication with poly-alpha olefin (PAO) containing these types of phosphoric additives; tricresyl phosphate (TCP), diphenyl phosphate (DPP), triphenyl phosphate (TPP). The nano-mechanical properties (viscoelasticity, adhesion, hardness, friction coefficient, and effective elastic modulus) of the tribofilms were evaluated by using atomic force microscopy (AFM) and nanoindentation tester. From the results of friction tests and surface analysis, the macro-tribological properties depended on the nano-mechanical properties of tribofilms derived from phosphoric additives under the boundary lubrication. In particular, the thick viscous tribofilm derived from the phosphoric additive exhibited the low friction phenomena. It was suggested that the nano-mechanical properties of tribofilms were the important factors governing the macro-tribological properties under the boundary lubrication.