Frictional and wear characteristics of Polytetrafluoroethylene (PTFE) thin-film coatings deposited by hot filament-chemical vapor deposition (HFCVD)

Abstract

Polytetrafluoroethylene (PTFE) is a widely used engineering polymer, which exhibits notable characteristics including low coefficient of friction (COF), chemical inertness as well as low dielectric constant. These unique characteristics motivate the development of deposition methods for applying PTFE as an ultra-thin film to micromechanical and medical devices. The aim of this work is to experimentally investigate the frictional and wear characteristics of PTFE coatings deposited on a relatively rigid substrate using HFCVD method. The ball-on-plate configuration was used to measure the COF values of PTFE coated on aluminum plates. It was found that the COF of PTFE coating exhibits the dependence sliding speed, normal force and surface roughness of the substrate. In particular, the COF value decreases at slower sliding speeds and increases with increased roughness. Moreover, comparative studies of friction and micro-indentation experiments qualitatively indicate that the fracture toughness or cohesive energy at the interface of the coating and the substrate influences the COF values. We also examined the wear characteristics of PTFE coating deposited on glass substrate using ball-on-disk configuration. The effects of normal force, sliding velocity and substrate surface conditions were investigated. A fairly clear trend associated with the wear characteristics of the PTFE film was obtained where reducing the normal force or increasing the sliding speed improves the durability of PTFE thin-film coating.