OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 3 2024 Figure 6 shows SEM images of wear track of Cu-Ti coatings after tribological testing in SBF solution. It shows that on the worn surface of the Ti-6Al-4V alloy, as a result of plowing up, were formed tracks that look like wide grooves and scratches, which indicate abrasive wear. At the same time, there are signs of adhesive wear, such as areas with delamination and strong deformation. The images clearly show that the worn surface of the Ti-6Al-4V alloy is rougher, and the surface of the Cu-Ti coatings is smoother. The smoothest surface was observed in the case of the Cu50 sample (Fig. 6 c), and the most relief one was observed in the case of the least wear-resistant Cu90 coating (Fig. 6 e). In contrast to dry friction in the SBF solution, no oxide wear flakes were observed on the surface of the coatings. This indicates that, during friction in liquid, the oxidative products are actively removed from the friction zone. Therefore the protective tribooxide layer is not preserved, which is expressed in increased wear rate values, compared to dry friction. Wear products were preserved only in surface depressions such as pores and cracks. According to the results of EDS analysis, the wear products contain iron, tungsten and chromium, which were deposited on the coating surface as a result of intensive wear of the counterbody made of high-speed steel M45 (Table 7). A significant amount of oxygen indicates oxide accumulations, which is a consequence of oxidative wear [37]. The presence of Cl, S and P elements is explained by the participation of the SBF solution in the formation of wear products. The oxygen concentration decreased in the wear products with an increase in the copper content in the coatings, which is explained by a higher standard electrode potential of copper compared to titanium. Thus, the main wear mechanism of copper-titanium coatings was a combination of oxidation and abrasive wear, while for titanium alloy the adhesive wear mechanism was more typical. a b Fig. 5. Friction coefficient (a) and wear rate (b) of Cu-Ti coatings and Ti-6Al-4V alloy in SBF solution under various loads Ta b l e 6 Averaged COF values of samples with coatings in SBF solution Load, N Samples Ti-6Al-4V Cu10 Cu30 Cu50 Cu70 Cu90 10 0.449 0.430 0.480 0.387 0.548 0.425 25 0.361 0.346 0.358 0.284 0.399 0.320
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