Low friction and wear resistant a-C:H/a-Si1-xCx:H multilayer coatings

Amorphous hydrogenated carbon a-C:H and silicon alloyed a-C:H (a-Si1-xCx:H) films were combined into a multilayer coating by alternatively adding silane to methane in a conventional capacitively coupled parallel plate r.f. plasma assisted chemical vapour deposition process (r.f. PACVD). The multilayer structures were revealed by Rutherford backscattering spectroscopy (RES) and their mechanical properties were determined by depth sensing indentation. The tribological behaviour of various multilayer combinations was studied by ball-on-disk testing. The r.f PACVD technique allowed to produce multilayer coatings with varying composition modulations and sharp interfaces. The mechanical properties of the a-C:H/a-Si1-xCx:H multilayer coating were situated in between those of its constituents. By optimising the a-Si1-xCx:H sublayer composition, sublayer thicknesses and thickness ratios, top layer composition and total thickness of the multilayer, a true low friction and wear resistant coating was obtained showing a friction coefficient below 0.1 under a relative humidity of 50% in air together with a wear resistance comparable with that of pure diamond-like carbon.