Tribological properties improvement of H-DLC films through reconstruction of microstructure and surface morphology by low-energy helium ion irradiation

Abstract

The hydrogenated diamond-like carbon (H-DLC) films were deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) technique and implanted with 60 keV He ion (He+) over a wide dose ranges. A two-steep model for the evolution of tribological properties of H-DLC films after irradiation has been proposed and discussed. Firstly, at the He+ doses range from 0 to 3 × 1016 cm−2, irradiation treatment induced structural transformation of graphitization in the H-DLC films modification layer due to the increase of sp2/sp3 ratio, which led to the upgradation of tribological properties owing to the lubrication effect of graphite. The decreases of the root mean square roughness (Sq) led to a decrease in the resistance to the relative movement of the friction pair. Therefore, the reduction of friction coefficient and wear rate of H-DLC was contributed to be the combined effect of graphite phase transition and low Sq value. As the dose was increased to 1 × 1017 cm−2, the degradation of tribological properties was evidenced, which could be ascribed to the formation of irradiation-induced He bubbles and holes on the surface of films. In addition, when the irradiation dose increased from 1 × 1016 cm−2 to 3 × 1016 cm−2 and then to 1 × 1017 cm−2, the variation of H/Ef value also indicated that the anti-wear properties of H-DLC film first increased and then decreased. Based on the experimental results, the H-DLC film that irradiated by the He+ at the dose of 3 × 1016 cm−2 shows the best tribological properties with low friction coefficient and high anti-wear properties while maintaining agreeable mechanical properties.