Laser chemical vapor deposition of fluorinated diamond thin films for solid lubrication

Abstract

A laser chemical vapor deposition process for growing fluorinated diamond thin films and the solid lubrication behavior of such films on two bearing materials (SiC and 440C stainless steel), were investigated. Raman spectroscopy analysis revealed that the films deposited on SiC consisted of a mixture of diamond and graphite, while the films deposited on 440C steel were composed of diamond-like carbon and graphite. X-ray photoelectron spectroscopy analysis revealed the presence of significant amounts of C–F compounds, both in the surface and subsurface layers, in addition to carbon. Tribological tests (ball-on-disc and pin-on-disc) of laser-grown films under ambient environment indicated a friction coefficient in the range 0.1–0.3, depending on the wear couple, sliding speed and load, confirming the effectiveness of these films as solid lubricants for moving mechanical assemblies in space structures. Fluorination of carbon films has the following attributes: passivation of the surface of diamond-graphite films from adsorption of water or oxygen, reduction of surface energy needed for shearing of the film during solid lubrication and protection from corrosive environments.