Korozní vlastnosti DLC vrstev legovaných zirkoniem / Corrosion properties of DLC layers alloyed with zirconium

Various forms of diamond-like carbon layers have been widely used in industrial applications and there are numerous potential opportunities of their utilisation in biomaterial applications. The DLC layers are bio-inert. It is assumed that a certain level of bioactivity could be achieved by alloying with bioactive metals (Ti, Zr, etc.). The paper studied the impact of DLC layers alloying with zirconium on corrosion properties of coated systems and on the interaction with a simulated body fluid. The tests were performed in a physiological solution (untreated pH, pH=4.2, pH=4.2+200 ppm F-) and simulated body fluid. Composition of the surface was assessed by photoelectron spectroscopy (XPS), the electrochemical response was evaluated by electrochemical impedance spectroscopy (EIS). The concentration of zirconium was 7.4 % at. on the surface of the layers and the metal was in an oxidised form. Corrosion response of alloyed layers differed significantly from that of the unalloyed DLC, the behaviour of which corresponded more to zirconium. The systems showed high corrosion resistance in saline solutions, however, the presence of fluoride ions destabilised the layers. After the exposure to the simulated body fluid, XPS tests indicated a slight increase of Ca-P concentration on the surface of alloyed specimens compared to the unalloyed specimens. This result was confirmed by EIS tests. DLC layers alloyed with zirconium are highly resistant to corrosion under ambient conditions and in the environment with lowered pH (as a result of inflammation). The results imply that alloying lead to changes in terms of bioactivity. Further testing is required to confirm these results.