Diamond like carbon (DLC) coatings have attracted great attention for use in various applications in automobile industry and machinery because they have excellent properties such as low friction coefficient and ultra high strength. The low friction coefficient of DLC comes from anti-adhesion with other materials, smooth surface, lubrication of graphite structure at the contacting point of films, and the hydrogen content of the films. Many researches have been focused on the microstructure effects on the tribological properties of DLC films but few have been reported on the effect of hydrogen content. In this study, the effect of hydrogen content on the friction coefficient of DLC films has been investigated.
DLC films have been deposited on D2 steel by plasma enhanced CVD (Pulsed DC PECVD) method with different precursor gas of C2H2 and CH4 and different gas pressure. The effects of gas composition on the hydrogen content in DLC films and the resulting tribological properties have been reviewed. Si interlayer was deposited on D2 to improve adhesion of DLC on steel substrates. The characteristics of microstructure were evaluated by Raman spectroscope and composition was measured by RBS and EDS. The tribological behaviors of DLC films were investigated using ball on disk tribometer. The hardness of films was examined by nano-indenter. The failure mechanism of DLC deposited on steel substrates was examined using optical microscope and SEM/EDS. The results showed that the friction coefficient of DLC films deposited with C2H2 was 0.06 and that of the film with CH4 was 0.15. The friction coefficient improved with decreasing hydrogen content in DLC films.