A comprehensive study on different silicon-containing interlayers for a-C:H adhesion on ferrous alloys

Silicon-containing interlayers can be used to promote adhesion of a-C:H thin films on ferrous alloys substrates. In contrast to chromium and titanium intermediate layers, which are often deposited by well-established technologies such as physical vapor deposition (PVD), the deposition of silicon interlayers is more compatible with plasma enhanced chemical vapor deposition (PECVD) techniques since most of the precursors are usually presented as liquids in stantard conditions. In this work, different silicon-containing interlayers were deposited on AISI 4140 steel using three different precursors in a PECVD chamber equipped with electrostatic confinement. The tribological behavior was correlated with the chemical structure of the interlayer. The critical load for delamination depends more strongly on Si/O and C/O ratios than on deposition temperature. In a general way, low oxygen content in the silicon-containing interlayer is leading to high adhesion. The best adhesion was achieved by using hexamethyldisiloxane as precursor when a critical load for delamination of 3.6 N was observed.