Tribological behaviour of Si–DLC coatings

Abstract

Amorphous silicon containing diamondlike carbon (Si–DLC) films were prepared by Ar⁺ ion beam assisted deposition (IBAD) on silicon wafers, with coating thickness ranging from 0·6 to 4·0 μm. The films were examined with SEM, TEM, and FTIR spec troscopy. The TEM analysis showed that the films were mainly amorphous and composed of diamondlike and graphitelike domains. The relative amounts of sp³ and sp² bonding types in Si–DLC were determined by IR spectroscopy and the sp³/sp² ratio was found to depend strongly on the current density in the ion beam, ranging from 1·4 for 163 μA cm^-2 to 5·4 for 85 μA cm^-2. Infrared absorption features correspond ing to Si–H and Si–C bonds were observed, illustrating the role of Si atoms in a DLC structure. Pin on disc experiments were conducted to characterise the tribol ogical behaviour of the Si–DLC films. The results showed that the films exhibit high wear resistance and low coefficient of friction. The results suggest that the wear behaviour is affected by film thickness and its diamondlike character. Thick films with low sp³/sp² ratios demonstrated ultralow wear rates in short duration tests. However, films with high sp³/sp² ratios may be suitable for long duration applications since they exhibit slower transformation kinetics.