Tribological properties of lubricants with dispersions of multi-walled carbon nanotubes (MWCNTs)

Multi-walled carbon nanotubes (MWCNTs) present interesting tribological properties under boundary lubrication leading to attractive and promising possibilities. In this study, MWCNTs synthesized by chemical vapour deposition and arc-discharge method were dispersed in two types of base oils used for metal forming applications. The dispersion of MWCNTs was carried out by using a probe type ultra sonicator. The tribological properties of the resultant oils with different concentrations of MWCNTs were evaluated using a four-ball tribo-test apparatus and measured in terms of the scar diameter and extreme pressure characteristics of the oil. Results confirmed that antiwear performance and load carrying capacity of the oils was significantly raised and the friction coefficient decreased. This could be attributed to the excellent mechanical properties and efficient dispersion of MWCNTs in oil, which resulted in the MWCNTs acting as tiny bearings between sliding surfaces during lubrication. The wear surfaces of the steel balls used for tribo-testing were analyzed using scanning electron microscope and showed the presence of carbon nanotubes. These preliminary results indicate that oils with MWCNTs dispersed in them can be used as excellent lubricants in metal forming applications.