OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 monotonically with a decrease in the copper concentration in the Cu-Ti coatings. At the same time, all samples with Cu-Ti coatings had a smaller radius of the capacitive arc than the untreated substrate. As follows from the Bode impedance diagram, the spectrum of the Ti-6Al-4V alloy in the mid-frequency range (10−1–103 Hz) has a wide linear region, which indicates the formation of a single-layer passive layer in the SBF solution (Fig. 3 b). In the coatings, the linear region narrowed with increasing copper concentration, which indicates the formation of additional passive layers. It is shown that with an increase in the copper concentration in the NE, the capacitance of the barrier layer on the coating surface decreases, as indicated by a decrease in the slope of the corresponding curves in the logarithmic coordinates. It is known that, in the general case, the anticorrosive properties of the material are in direct proportion to the resistance of the barrier layer and inversely dependent on its capacitance [30]. The compactness of the formed oxide film is determined by the convexity magnitude in the mid-frequency range on the Bode phase angle graph (Fig. 3 c). For the Ti-6Al-4V alloy, the convexity value was higher than 75°. It is known that the phase angle а b c Fig. 3. Impedance plots of Cu-Ti coatings in Nyquist coordinates (a), total Bode impedance (b) and phase angle (c)
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