Structural and tribological properties of hard carbon film synthesized by heat-treatment of a polymer on graphite substrate

Hard carbon films have been synthesized by heat-treating a polymer-poly(phenylcarbyne) at various temperatures (800-1100°C) for different times (0.5-2 h) in Ar ambient. The influences of heat-treatment temperature and time on the structural and tribological properties of the hard carbon films on graphite substrate were investigated by Raman spectroscopy, scanning electron microscopy (SEM), nanoindenter and pin-on-disk tribometer. The position of D bands and the relative intensity (I_D/I_G) of D and G band in the Raman spectra are related to the heat-treatment temperature and time. The hardness is approximately 6-8 GPa, which is lower than that of diamond like carbon (DLC) films (10-20 GPa) and higher than that of glassy carbon (3 GPa). The evolution of the coefficient of friction for the hard carbon films against sliding distance is similar to the DLC and not graphite-like carbon. The coefficient of friction is in the range from 0.14 to 0.19 at room temperature and a relative humidity of 40%. The wear rate is approximately 10^-15 m³ N^-1 m^-1. The hardness, coefficient of friction and wear rate are all dependent on the heat-treatment temperature and time. From the SEM, it was found that the soft graphite substrate makes the films crack at the edge of wear track but the spallation does not occur due to their strong adhesion.