Nanoscale multilayer WC/C coatings developed for nanopositioning: Part I. Microstructures and mechanical properties

Tungsten Carbide/Carbon (WC/C) multilayers of nanometres in period were developed for applications in the bearings used for nanopositioning. The present work is concerned with the characterization of the microstructure, composition and mechanical properties of the multilayers. Multilayers with a total thickness of 210 nm were sputter deposited on Si substrates. The substrates were covered with a 200 nm thick Cr adhesion layer and a 250 nm thick WC intermediate layer sputter deposited prior to the multilayer coating. The structure and composition were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, Auger electron microscopy, electron energy loss spectroscopy, scanning electron microscopy and transmission electron microscopy. The surface morphology and mechanical properties were examined by atomic force microscopy and nanoindentation techniques. Crystalline β-WC1−x with a carbon content of ∼39 at.% and (200) preferred orientation was found in the WC layers while the C layers were amorphous and contained predominantly sp2 bonds. A sharp interface of 1-2 atomic layers in thickness was observed between the WC and C layers. Hardness and modulus values of the multilayer coatings are between those of the reference single carbon and WC layers. The surface roughness of the multilayer coatings was ∼2 nm, and not depending on the period of the multilayers. The origin of the roughness was due to the columnar growth of the adhesive and intermediate layers.