Low Friction Property of Boron Doped DLC under Engine Oil

Abstract

DLC films are of significant interest for automobile parts, because they possess the potential to improve the friction property under oil lubricated conditions. In order to obtain further low friction, we focused on the combination of boron doped DLC (B-DLC) and the Mo-trimer as a lubricating oil additive, and the influence of the boron concentration on the friction property of the B-DLC films was evaluated by a block on ring type test. Compared to DLC films without boron, the B-DLC films exhibited an extremely low friction coefficient below 0.03 ranging from 2 to 12 at% in boron concentration under the lubricating condition using the engine oil containing the Mo-trimer. It was found that the surface roughness of the B-DLC films rubbed in the oil containing the Mo-trimer became particularly smooth below 2 nm measured by an atomic force microscope. On the wear surface of the B-DLC films, Mo3S7- derived from the Mo-trimer was selectively confirmed as having a uniform distribution by time-of-flight secondary ion mass spectrometry. Based on the obtained results of surface measurements and analyses, it was suggested that the B-DLC films exhibited a low friction property primarily caused by the nano-scale smooth surface, disturbing the adsorption of the other additives and the transfer reaction products from the counter parts by forming a selective adsorbed Mo-trimer film on the B-DLC surface.

Keywords

• dlc
• boron
• low friction
• engine oil
• additive
• mo-trimer