## 3 Results and Discussion
In the low wavenumber range (250-700 cm\({}^{-1}\)), the spectral features primarily reflect the crystalline structure of TiO\({}_{2}\). Samples treated with different electrolytes exhibit distinct spectral characteristics, suggesting diversity in the surface oxide layer structures. Notably, samples treated with HNO\({}_{3}\) and NaF show characteristic peaks at approximately 450 cm\({}^{-1}\) and 610 cm\({}^{-1}\), respectively. These peaks can be attributed to the Eg mode of anatase and the A1g mode of rutile TiO\({}_{2}\) phases [73]. In contrast, samples treated with H\({}_{2}\)SO\({}_{4}\) and HF lack distinct crystalline phase peaks in this range, indicating the possible formation of amorphous or highly defective oxide layers. The spectral features in the high wavenumber range (1000-2000 cm\({}^{-1}\)) provide information about surface defects and second-order scattering processes. All samples exhibit broad features in this range, but with varying intensities and shapes. These differences reflect the impact of different electrolyte treatments on the surface microstructure and chemical composition. Notably, the HNO\({}_{3-}\) treated sample shows the strongest spectral response between 1300 and 1600 cm\({}^{-1}\), which may be related to oxygen vacancies in non-stoichiometric TiO\({}_{2}\), suggesting a complex surface defect structure. Comprehensive analysis indicates that the choice of electrolyte significantly influences the structure and composition of the oxide layer on the Ti-64 surface. The HNO\({}_{3}\) treatment appears to induce the most pronounced surface oxidation, potentially forming a mixed structure of anatase and amorphous TiO\({}_{2}\). The NaF treatment tends to promote the formation of the rutile phase, which may affect surface stability and biocompatibility. The H\({}_{2}\)SO\({}_{4}\) and HF treatments likely result in more disordered or amorphous surface structures, which may have advantages in certain biological applications, such as enhanced protein adsorption capability. Figure 7: SEM images of Ti-6 Al-4V surfaces after electrochemical corrosion in different electrolytes: (**a**) 0.5 M HF, showing a highly porous honeycomb-like structure; (**b**) 0.5 M H\({}_{2}\)SO\({}_{4}\), exhibiting a relatively smooth surface with shallow pits; (**c**) 0.5 M NaF, presenting a highly uniform and smooth surface; and (**d**) 0.5 M HNO\({}_{3}\), featuring scattered circular pits of varying sizes. This study further investigated the effects of mixed electrolytes on the electrochemical corrosion of Ti-64 alloy surfaces. Figure 9 shows SEM images of surfaces treated with four different mixed electrolytes, revealing the unique effects of composite electrolytes in surface modification. Treatment with a 0.5 M NaF/0.5 M H\({}_{2}\)SO\({}_{4}\) mixed electrolyte (Figure 9a) produced a highly porous and complex surface structure. The surface exhibits an irregular honeycomb-like morphology, with pore sizes ranging widely from submicron to several micrometers. This structure likely results from the synergistic action of F\({}^{-}\) and SO\({}_{4}\)\({}^{2-}\) ions, where the former promotes the dissolution of the TiO\({}_{2}\) protective layer, while the latter may accelerate the corrosion process [76]. This multi-scale porous structure is expected to significantly increase the surface area, potentially enhancing cell adhesion capability and osseointegration. The 0.5 M NaF/0.5 M HNO\({}_{3}\) mixed electrolyte treatment (Figure 9b) generated a more uniform porous structure. The pores are relatively consistent in size, with diameters ranging approximately from 1 to 2 \(\upmu\)m. This morphology may result from a balance between the strong oxidizing action of NO\({}^{3-}\) ions and the selective dissolution effect of F\({}^{-}\) ions [77]. Such a uniform porous structure might be beneficial for even cell distribution and growth. In contrast, the 0.5 M HCl/0.5 M HNO\({}_{3}\) mixed electrolyte treatment (Figure 9c) produced a relatively smooth surface with only a few scattered pits and protrusions.