In the present work, surface-coated Cu nanoparticles with FCC structure and an average
size of 40 nm were prepared by reducing reaction and surface modification technique. The
morphology and phase structure of the nano-copper were characterized by transmission electron
microscope (TEM). The ball-on-disc tester and ring-on-block tester were performed to study the
tribological properties of surface-coated Cu nanoparticles as oil additive. The tests were carried out
under the lubrication of 50CC oil alone and oil containing surface-coated nano-copper additives. The
morphologies and elementary distributions of the worn surfaces were analyzed by scanning electron
microscope (SEM) and energy dispersive spectrometry (EDS), respectively. Results indicate that
surface-coated nano-copper additives can significantly improve the wear resistance and load-carrying
abilities of 50CC oil, as well as reduce friction coefficient. A soft copper protective film is formed on
the worn surface lubricated with oil containing nano-copper additives, which separates the worn
surfaces, avoids their direct contact and reduces friction and adhesive wear. Besides, the grooves and
small valleys on the worn surfaces are found to be partly filled and repaired by nano-copper, as makes
the worn surface repaired and smoother.
