Effect of a-C:H:Si interlayers on the mechanical and superlubricious properties of hydrogenated amorphous carbon films

Abstract

Diamond-like carbon is a promising material due to its outstanding properties. Among them, hydrogenated amorphous carbon (a-C:H) film has attracted many researchers’ interests because of its ability to achieve superlubricity (friction coefficient μ<0.01) in special environments. However, the a-C:H films generally have high internal stress and low chemical affinity with metal alloy substrates, which limits the wide use of a-C:H films in industrial application. In this work, we studied in detail the effects of interlayers on the mechanical properties of a-C:H film, especially the adhesion properties. Different Si-doped a-C:H (a-C:H:Si) interlayers were introduced between a-C:H layer and substrates using ion vapor deposition and prepared by varying the gas flow ratio of Si(CH3)4/C7H8 and the layer number of the interlayer. The gas flow ratio of the interlayer has a great influence on the adhesion of a-C:H film, resulting in different peeling off patterns during the scratch test. The cross-sections of the scratched deformation zone of the ACH-5 (the a-C:H:Si interlayer possesses four sublayers and all contain silicon-dopants) film were analyzed by transmission electron microscope. It was found that there were different failure mechanisms on the titanium and magnesium alloy substrates used. The results of Raman spectra, nanoindentation, nano-scratch and friction tests showed that the ACH-5 film exhibited the lowest ID/IG ratio, the highest hardness, and the strongest adhesion to the substrate and the best superlubricious performance (μ∼0.006).