Low friction coatings of diamond-like carbon with silicon prepared by plasma-assisted chemical vapor deposition

Amorphous carbon-silicon (a–C–Si) coatings with smooth surface and adhesion to steel substrate were deposited at 550°C by a dc glow discharge method from reactant gases of CH₄, SiCl₄, H₂, and Ar at a deposition rate of 1–3 μm h⁻¹. Diamond-like carbon was detected by laser Raman spectroscopy in the coatings with high hardness of Hv 2000 and more than 70 at. % carbon. Ball-on-disk type and Ohgoshi-type apparatuses were used to measure the tribological properties. Ball-on-disk tests revealed that the a–C–Si coatings showed a friction coefficient as low as 0.04 against steel with no lubricant in an ambient atmosphere of 70% relative humidity, which was one-third that of an i–C coating. The wear rate of the steel ball against the coated disk was an order and three orders of magnitude smaller than that against i–C coated and uncoated disks, respectively. Both types of tests showed that the wear rate of the a–C–Si coating itself was also very small.