Nickel and titanium alloys and in particular nitinol (~55% Ni, ~45% Ti) are widely used as biomaterials for medical implants due to their unique properties, such as the shape memory and elasticity. They provide a unique opportunity to make novel surgical implants and instruments for vascular and orthopedic surgery. However, a high nickel content in these alloys could cause the problem of biocompatibility because of nickel toxic effect. Thus, it is necessary to improve the corrosion resistance of nitinol that can be achieved with applying of protective porousless niobium coating.

Previously, we obtained tantalum coatings on nitinol stents. For obtaining of niobium coatings the NaCl-KCl-NaF(10 wt.%)-K₂NbF₇(8 wt.%) melt was used at the temperature 750°С. Direct and pulsed current was supplied for electrodeposition. The adhesion of coatings to substrate was measured by cross-sections method using a tester of adhesion Elcometer 107. The porosity of niobium coatings was determined by Erhard’ technique based on measuring the current dissolution at a certain potential, in which dissolves the substrate material and the coating remains passive. Corrosion resistance of the composition nitinol - niobium coating was studied in dilute mineral acids and 0.9% solution of NaCl.

In these experiments the formation of some intermediate layers between the coating and substrate was observed, but their thickness was not enough for the determination of the composition by microanalysis. To solve this problem, the conditions for electrodeposition of niobium coatings were significantly changed. The electrolysis time was increased (from 10 or 30 min to 4 h.) and the cathodic current density decreased (from 100 mA cm^-2 to 5 mA cm^-2), which made it possible to obtain intermediate layers of sufficient thickness for studying their composition.