Tribological behavior and lubricating mechanism of Cu nanoparticles in oil

Nanosized Cu, modified by an organic compound containing S and P was synthesized using a surface-modification method. The size and structure of the Cu nanoparticles were characterized by means of a transmission electron microscope (TEM) and electron diffraction (ED). Their tribological behavior was evaluated on a four-ball machine. The results showed that Cu nanoparticles as an oil additive have better friction-reduction and antiwear properties than ZDDP, especially at high applied load. Meanwhile, they can also strikingly improve the load-carrying capacity of the base oil. The rubbed surface was investigated by electron probe microanalysis (EPMA) and X-ray photoelectron spectroscopy (XPS). It was found that the boundary film on the worn surface consisted of a Cu nanoparticle deposited film and a tribochemical reaction film containing S and P. A synergistic effect between the deposited film and tribochemical reaction film contributes to the good tribological properties of oil.