OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 Fig. 2. Polarization plots of Cu-Ti coatings and Ti-6Al-4V alloy in SBF solution Ta b l e 4 Copper concentration in the composition of Cu-Ti coatings and its corrosion parameters in SBF solution Parameter Samples Ti-6Al-4V Cu10 Cu30 Cu50 Cu70 Cu90 Ecorr, V −0.38 −0.23 −0.34 −0.33 −0.36 −0.61 Icorr, μA/cm2 9.00 3.46 7.05 8.75 8.45 17.57 Copper concentration, at.% – 12.5 24.3 36.8 61.4 74.1 that the Cu10–Cu70 coatings have a higher corrosion potential than the substrate, i.e. these coatings are more noble. Because of this, a galvanic couple can be formed between the coating and the substrate, where the substrate will undergo anodic corrosion. The corrosion current density determines the corrosion rate of the material. With an increase in the titanium concentration in the coatings, Icorr decreased from 17.570 to 3.455 μA/cm2. It was shown that for all coatings except Cu90, I corr was lower than that of the Ti-6Al-4V alloy. Thus, polarization tests indicate an increase in the corrosion resistance of the Ti-6Al-4V alloy when using ESD Cu-Ti coatings with a copper content of less than 70 at. %. The corrosion resistance of Cu-Ti compositions is usually associated with the passivation film of Cu2O, which is resistant to the effects of Cl − ions due to the formation of insoluble copper (I) chloride [27]. For a more detailed research of the corrosion characteristics for all samples, electrochemical impedance spectroscopy (EIS) was used, which can be classified as a non-destructive testing method due to the low voltage and low current flowing through the sample [28]. Fig. 3 shows the experimental results on EIS. As a rule, the capacitive arc on the Nyquist plot is explained by charge transfer reactions occurring at the metal/solution interface or associated with the features of the surface passive layer. It is known that with an increase in the radius of the capacitive arc, charge transfer is hindered, which has a positive effect on the corrosion resistance of the material [29]. The radius of the capacitive arc of the samples increased in the series: Cu90, Cu70, Cu50, Cu30, Cu10 (Fig. 3 a, b). That is, charge transfer became more difficult
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