Friction reduction effect of sulfur-containing
environment acceptable lubricants and
interpretation of the mechanism by wetting parameters


Takuya Nakase1, Shinji Kato2, Mathias Woydt3 and Shinya Sasaki4

1KYB Corporation, Materials Engineering Sect., Basic Technology R&D Center, Kanagawa-ken, Japan

2KYB Corporation, Engineering Headquarters, Automotive Components Operations, Gifu-ken, Japan

3BAM (Federal Institute for Material Research and Testing), Division 6.3 Tribology and Wear Protection, Berlin, Germany

4Tokyo University of Science, Department of Mechanical Engineering, Tokyo, Japan

It is expected that the wettability would be a parameter describing lubrication property which shows good correlation with the friction coefficient under mixed/boundary lubrication. To determine wettability a contact angle measurement was employed. In this study, the surface free energy σs of plasma electrolytic oxidation (PEO) coating on A6061 alloy and the surface tension σl of different oils were investigated. 1 wt% dibenzyldisulfide (DBDS) was added to base oils as an extreme-pressure agent or anti-wear additive to make blend oil each. Then one of the wetting parameter the work of adhesion (WA) was calculated using each polar components and dispersive components of σs and σl. It was found that the WA had the negative correlation to the coefficient of friction obtained on PEO lubricated with the various oils. DBDS increased the WA which means that the blend oil adheres on PEO film stronger than the base oil, and as a result it reduced the friction coefficient.

Keywords: Wetting, friction, work of adhesion, Plasma electrolytic oxidation, esters, polyglycols