## 3 Results
### Characterization of the Coatings
The average values in the fluctuation of the friction coefficient (COF) with the Rockwell diamond indenter applying 10 N normal and tangential contact force are also shown in Table 3. The highest mean friction coefficients were measured for the bare substrate and \(-100\) V biased coating that delaminated under the applied force, and both friction coefficient values resulted from adhesion at the contact interface. With the increase in bias from \(-25\) V to \(-75\) V and the consequent increase in hardness, a decrease in the COF values from about 0.27 down to 0.20, \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **KH\({}_{0.005}\)**, & **L\({}_{\text{c}}\)** & **COF** \\  & **kgf/mm\({}^{2}\)** & **(N)** & **COF** \\ \hline Substrate & \(778\pm 39\) & - & 0.43 \(\pm\) 0.040 \\ \(-25\) V & \(1365\pm 16\) & 8.4 \(\pm\) 0.8 & 0.27 \(\pm\) 0.012 \\ \(-50\) V & \(2108\pm 207\) & 37.5 \(\pm\) 1.1 & 0.23 \(\pm\) 0.008 \\ \(-75\) V & \(2164\pm 195\) & \(>\)50 & 0.20 \(\pm\) 0.010 \\ \(-100\) V & \(3031\pm 115\) & 5.4 \(\pm\) 0.6 & 0.40 \(\pm\) 0.022 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Microhardness (KH\({}_{0.005}\)), critical loads (Lc), and coefficients of friction (COF) \(\pm\) standard deviation of the examined substrate and sputtered coatings. Figure 7: Representative microscopic images of the scratch track on the oxide coatings deposited at (**a**) \(-25\) V, (**b**) \(-50\) V, (**c**) \(-75\) V, and (**d**) \(-100\) V bias voltage. The normal load increases from 0 to 50 N from left to right. respectively, is found. This phenomenon is a result of a better penetration resistance of these films, reducing the contact area of the indenter. The improved mechanical characteristics of the \(-50\) V and \(-75\) V biased samples were predicted to offer enormous potential for application in implant coatings or artificial bone/dental materials. Wettability is another important aspect of implant surfaces that influences interactions between cells and materials. We measured the water wettability of Cu-doped TiO\({}_{2}\) coatings deposited to the Ti6 Al4V substrate. For reference, the ground and etched substrate's water contact angles were also assessed, and they came out to be substantially different at \(-55.8^{\circ}\) and \(85.5^{\circ}\), respectively. For this reason, the WCAs of both grounded and etched-coated samples were explored and presented in Figure 8. Because the WCA values for each coating on the ground substrates were less than 90, all deposited thin films were hydrophilic. The WCA increased from \(48.5\) (\(-25\) V) to \(86.5\) (\(-100\) V) with an increase in bias values during sputtering. Therefore, the anatase phase was found to be more hydrophilic than rutile. Similar observations were reported by [39]. A comparable inclination was observed for the etched and coated surfaces but with higher WCA values, indicating that the surface topography and crystal phases have a major influence on the contact angle values. The inevitable deterioration of numerous medical devices in clinical settings is widely recognized. Corrosion at the interface of the implant surface with the surrounding physiological medium, particularly after implantation into the human body, has a major impact on the implant's biocompatibility and longer lifespan. To determine the Cu-TiO\({}_{2}\) films' corrosion resistance, anodic polarization tests have been conducted. Figure 9 and Table 4 show typical potentiodynamic polarization curves and the resulting data that follow for the bare titanium alloy and coated samples in SBF solution. Compared to the bare alloy, the corrosion potentials (E\({}_{\text{corr}}\)) recorded from the coated samples shift somewhat negatively, while the \(-50\) V biased coating shows almost no shift in corrosion potentials. The greatest surface hydrophilicity of the \(-25\) V biased specimens and their highest copper content, which some authors found to increase the corrosion rate [18], may be connected to the larger E\({}_{\text{corr}}\) negative shift.