Friction properties of surface-modified polished chemical-vapor-deposited diamond films under boundary lubrication with water and poly-alpha olefin

To reduce the friction coefficient of chemical-vapor-deposited diamond films, the films were surface modified by fluorination, oxidation, or nitrogen ion implantation. Surface modification of diamond surface structures (especially of the N+-implanted diamond film) was confirmed by Raman spectroscopy. Fluorinated diamond film demonstrated the lowest surface free energy, whereas the nanoindentation hardness and nanowear resistance were lowest in the N+-implanted diamond film. Boundary lubrication properties were evaluated by an oscillating friction test. The friction coefficient and surface damage of the oxidized and N+-implanted diamond films (with high surface free energies) were effectively reduced by boundary lubrication. Fluorinated and untreated diamond films exhibited low-friction and little damage under dry and boundary lubrication.