Effect of base oil lubrication in comparison with non-lubricated sliding in diamond-like carbon contacts

Abstract

Diamond-like carbon (DLC) coatings are, nowadays, used in various mechanical systems, including highly stressed and lubricated applications. However, a lot is still unknown about the interactions between lubricants and DLC coatings. For example, what is the role of base oil in DLC contact? Do base oils adsorb to the DLC surface, or are they only a passive element in the contact? In this study, self-mated DLC–DLC contacts were employed, and steel–steel contacts were used as a reference for the expected lubrication mechanisms, which are well known for steel. In tribological experiments, low velocity boundary lubrication conditions were applied to eliminate any velocity related effects. Low viscosity polyalphaolefin base oil was used as a lubricant, and some tests were made also without the use of the lubricant in the contact. Results showed that the friction of boundary lubricated DLC contacts is always lower than the friction of steel contacts. However, in the low speed boundary lubrication regime, the friction of the lubricated DLC contacts increased in comparison with the non-lubricated conditions, which is the opposite of steel behaviour. Nevertheless, oil was required to stabilise the friction behaviour and to prevent high wear and removal of the DLC coating.

Keywords:

• DLC
• Boundary lubrication
• Base oil
• Adsorption