Adhesion and corrosion of Al-N doped diamond-like carbon films synthesized by filtered cathodic vacuum arc deposition

Diamond-like carbon (DLC) films (thickness: ~118 nm) doped with Al and N on AISI 4140 steel were synthesized using a filtered cathodic vacuum arc technique. The adhesion and corrosion of the ta-C, ta-C:N, ta-C:Al, and ta-C: Al:N films were examined in terms of structure and bonding. X-ray reflectivity, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy revealed that the Al-doped and Al and N co-doped films had lower densities and internal stresses than the other films, as indicated by their higher ID/IG ratios and graphite cluster size (La) and lower sp3 relative fractions. All DLC films exhibited improved corrosion resistance as compared to AISI 4140, as indicated by their decreased corrosion rate and increased corrosion potential and polarization resistance. The corrosion resistances of ta-C:Al:N and ta-C:Al films were high owing to the combined effect of sp3 C-N and Al2O3, as confirmed by near-edge X-ray absorption fine structure spectroscopy and XPS. All doped DLC films exhibited improved adhesion performance compared to the ta-C film owing to their improved lubrication performance (increased sp3-hybridized C-N bonds) and improved toughness (formation of Al2O3).