Thin coatings of the pure metals Ti, Zr, Cu, and multi-layer metal-nitride coatings Ti/TiN and Ti/ZrN of 0.2-1 μm thickness were deposited onto polysulfone S2010 substrate using a multi-cathode vacuum arc plasma gun connected to a magnetized straight plasma duct. A few Ti coatings were also deposited with the aid of transverse current injection (TCI). The structure and composition of the coatings were studied by means of X-ray diffraction, Auger electron spectroscopy and scanning electron microscopy (SEM) analysis. Scratch tests were used for evaluation of the adhesive strength between the substrate and the coating, and reciprocating wear tests against a steel ball were used to study the friction and wear rates of the coated samples. The wear tracks were examined by SEM. The nitride coatings possessed a nanocrystalline structure or a mixture of amorphous and nanocrystalline structures. The TiN and the ZrN coatings were stoichiometric. The adhesive strength was found to be dependent on the pre-coating treatment and the nature of the metallic bond layer. The Ti/ZrN coating exhibited improved tribological properties as compared to uncoated polysulfone. For this coating a negligible wear rate and a coefficient of friction of 0.1 against a steel ball (lower than the uncoated substrate) was obtained. In addition, TCI significantly reduced the wear rate of the Ti films by a factor of 5 to 6.5.
- Hard coating
- Tribological properties