Tuning the wettability, mechanical and tribological properties of NbN films by doping rare earth cerium

Transition metal nitride (TMN) films with high hardness, high melting point and excellent chemical inertness have been widely used for protecting surfaces from scratch, wear and corrosion, but they are generally hydrophilic. On the other hand, rare earth oxides are considered as intrinsically hydrophobic ceramics, but with much lower hardness relative to TMN. In this study, solid-solution Nb–Ce–N films were fabricated by doping Ce atoms into NbN, and the effects of solute Ce atoms on the wettability, mechanical and tribological properties of NbN films were evaluated. The results show that the incorporation of only a small number of solute Ce atoms (Ce/Nb atom ratio, R = 0.02) into NbN film can induce the switch from hydrophilic to hydrophobic due to the formation of hydrophobic CeO2 on the surfaces, coupled with enhanced hardness and toughness, reduced friction and improved wear resistance ability. However, the incorporation of more solute Ce atoms remarkably worsens the hardness and wear resistance ability of NbN films despite maintaining a hydrophobic surface.