Vacuum arc deposition of metal/ceramic coatings on polymer substrates

Thin metal/ceramic coatings were deposited onto polysulfone S2010 substrates using a triple-cathode vacuum arc plasma source connected to a magnetized plasma duct in order to improve the tribological properties of the surface. Various combinations of multi-layer coatings having Ti, Zr, or Nb sub-layers, and nitrides of Ti, Zr, and multi-component (Ti,Zr)N as wear-resistant layers, were deposited and evaluated. The deposition parameters (arc current, magnetic field strengths, deposition time) were optimized (1) to obtain the required deposition rate and coating thickness, while preventing substrate damage under the high-energy ion flux exposure, and (2) to obtain good adhesion of the coating to the substrate at low substrate temperatures. The structure and composition of the coatings were studied using XRD, AES, and SEM. Scratch tests were used to evaluate 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. It was shown that TiN layers possessed a nanocrystalline structure or a mixture of an amorphous and a nanocrystalline structure with random orientation, whereas the ZrN and (Ti,Zr)N had a more defined crystalline nature. The lowest wear rate was observed for Ti/TiN bilayer coatings. The Zr/ZrN coatings failed completely because of poor adhesion to the substrate. It was observed that carbide formed at the interface of the Ti coating and the substrate. In contrast, Zr intermediate layers did not form a carbide, and the coatings had poor adhesion and wear resistance. The results suggest that the formation of a carbide interface improves the coating adhesion.