Enhanced tribological performance of alumina composites reinforced with acid-treated carbon nanotubes under water lubrication

Abstract Alumina composites reinforced with acid-treated multiwalled carbon nanotubes (MWCNTs) are prepared, and the tribological properties of the composite are investigated under water-lubricated conditions using a ball-on-disk technique against an alumina ball. The coefficient of friction (COF) in the steady-state region of the composite with acid-treated MWCNTs is found to be 0.06, which is 32–37% lower than that of the monolithic alumina and the composite with pristine MWCNTs. Microstructural observations and in-depth Raman spectroscopy analyses of the disk samples and counterparts before and after the friction tests reveal that the MWCNTs located in pits on the disk surface pull-out and that the resultant MWCNT fragments adhere to the friction surface of the counterparts. The enhanced tribological performance shown in the composite with acid-treated MWCNTs is mainly because the negatively charged functional groups adsorbed on the MWCNTs participate in the hydrogen-bond network of the hydrodynamic lubrication film and lead to acceleration of the transformation from a boundary lubrication regime to a mixed lubrication regime.