OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 highest bactericidal activity. The Cu50 sample is the most optimal in terms of low concentration of released copper ions and sufficient antibacterial activity. The results of tribological tests of copper-titanium coatings in comparison with Ti-6Al-4V alloy in SBF solution at normal loads of 10 and 25 N are shown in Figure 5. It was found that with an increase in the applied load from 10 to 25 N, the average values of the friction coefficient (COF) of the titanium alloy Ti6Al-4V decreased from 0.45 to 0.36 (Fig. 5 a). Similarly, the friction force during the wear of Cu-Ti coatings decreased with an increase in the specific load. Thus, the average COF values of Cu-Ti coatings at load of 10 N were in the range from 0.39 to 0.55, while at 25 N it was in the range from 0.28 to 0.40 (Table 6). This leads to the conclusion that part of the applied load is compensated by the pressure of the oncoming liquid flow. The highest values of COF at both loads were observed for the Cu70 sample, while the lowest values of COF were for Cu50 sample. The use of the latter allows reducing the friction force of the Ti-6Al-4V alloy by 14–21 %. Previously, at a load of 25 N, we found that COF of copper-titanium coatings without SBF was much higher and was in the range from 0.73 to 0.96. Moreover, COF of the coatings under dry friction was significantly higher than that of the Ti-6Al-4V alloy [19]. Fig. 5 b shows the diagrams of wear rate values of titanium alloy samples with copper-titanium coatings in SBF solution. The wear rate of samples with Cu-Ti coatings was within the range from 0.71×10−5 to 2.70×10−5 mm3/Nm under a load of 10 N and from 0.70×10−5 to 1.79×10−5 mm3/Nm under a load of 25 N. Under both loads, the Cu50 coating had the highest wear resistance, which is explained by its lowest friction coefficient. Under a load of 10 N, the wear rate of the Ti-6Al-4V alloy in SBF solution was 3.58×10−4 mm3/ Nm, and under 25 N it was 3.99×10−4 mm3/Nm. Thus, the wear resistance of the alloy was 13 to 57 times lower than that of the coatings. It is characteristic that the wear of the Ti-6Al-4V alloy under dry sliding conditions at 25 N was 0.75×10−4 mm3/Nm [20], which is 5.3 times lower than that in the SBF solution, which is consistent with the results of work [36]. Thus, the SBF solution repeatedly accelerates the wear of the titanium alloy due to its interaction with the electrolyte according to the oxidative wear mechanism [36]. Oxidative products, and primarily rutile, can act as abrasive particles, accelerating the wear of the titanium alloy. Comparison of the wear intensity of Cu-Ti coatings under a load of 25 N showed that most of the samples also had increased wear in the SBF solution compared to the dry sliding mode, with the exception of the Cu50 and Cu70 coatings, which had very close wear values in SBF and dry environments. Thus, the use of Cu-Ti coatings for products made of titanium alloy Ti-6Al-4V allows reducing its wear many times over and lowering the coefficient of friction when used in SBF solution. Fig. 4. Antibacterial activity (AA)
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