## 3 Results and Discussion
The  
Figure 9: SEM images of Ti-6 Al-4V surfaces after electrochemical corrosion in different mixed electrolytes: (**a**) 0.5 M NaF/0.5 M H\({}_{2}\)SO\({}_{4}\), showing a highly porous honeycomb-like structure with varied pore sizes; (**b**) 0.5 M NaF/0.5 M HNO\({}_{3}\), exhibiting a uniform porous surface with consistent pore diameters; (**c**) 0.5 M HCl/0.5 M HNO\({}_{3}\), presenting a relatively smooth surface with scattered small pits; and (**d**) 0.5 M HF/0.5 M HNO\({}_{3}\), featuring large, interconnected etched pits forming a complex 3D network. NaF/H2 SO4 treatment tends to promote the formation of the rutile phase, which may affect surface stability and biocompatibility. The HCl/HNO3 and NaF/HNO3 treatments may produce more complex or inhomogeneous surface structures, which could have advantages in certain biological applications. Table 2 summarizes the surface roughness parameters (Ra and Rq) and surface hardness (HR15N) of the Ti-64 alloy under various electrochemical corrosion conditions. These data reveal the significant impact of different electrolytes on the surface characteristics of Ti-64. The original polished Ti-64 surface exhibited extremely low roughness (Ra = 0.09 \(\pm\) 0.01 \(\upmu\)m), consistent with the smooth surface expected after mechanical polishing. However, after various electrochemical corrosion treatments, both surface roughness and hardness changed significantly. The single electrolyte treatment results show that the 0.5 M NaF electrolyte produced the highest surface roughness (Ra = 2.25 \(\pm\) 0.41 \(\upmu\)m) and hardness (84.3 \(\pm\) 0.4 HR15N). This may be due to the selective dissolution of the TiO2 protective layer by F- ions, simultaneously promoting the formation of a surface oxide layer. In contrast, the 0.5 M HF and 0.5 M H2 SO4 treatments resulted in relatively lower roughness (Ra of 0.23 \(\pm\) 0.02 \(\upmu\)m and 0.32 \(\pm\) 0.03 \(\upmu\)m, respectively) and slightly decreased surface hardness (78.5 \(\pm\) 0.5 HR15N). This suggests that these electrolytes may have led to more uniform surface corrosion. The 0.5 M HNO3 treatment achieved moderate levels of roughness (Ra = 1.20 \(\pm\) 0.13 \(\upmu\)m) and hardness (83.1 \(\pm\) 0.2 HR15N), possibly due to its strong oxidizing nature, promoting oxide layer formation alongside corrosion. The mixed electrolyte treatments yielded interesting results. The 0.5 M NaF/0.5 M H2 SO4 and 0.5 M NaF/0.5 M HNO3 combinations produced surface roughness (Ra of 0.23 \(\pm\) 0.02 \(\upmu\)m and 0.32 \(\pm\) 0.03 \(\upmu\)m, respectively) similar to the single HF or H2 SO4 treatments, but with slightly reduced hardness. This indicates that mixed electrolytes may lead to more complex surface reactions, affecting the final surface characteristics. Notably, the 0.5 M HCl/0.5 M HNO3 combination generated high roughness (Ra = 2.25 \(\pm\) 0.41 \(\upmu\)m) and hardness (84.3 \(\pm\) 0.4 HR15N) similar to the single NaF treatment. This synergistic effect may result from the interplay between the localized corrosion action of Cl- ions and the oxidizing effect of NO3- ions. The 0.5 M HF/0.5 M HNO3 combination produced moderate roughness (Ra = 1.20 \(\pm\) 0.13 \(\upmu\)m) and relatively high hardness (83.1 \(\pm\) 0.2 HR15N), possibly due to the strong corrosive action of HF being partially counteracted by the oxidizing effect of HNO3. These results demonstrate that through the selection of appropriate electrolyte combinations, precise control over the roughness and hardness of Ti-64 surfaces can be achieved. Different electrolyte combina  
Figure 10: Raman spectra of Ti-6 Al-4V surfaces at (a) short wavenumber range (250–700 cm\({}^{-1}\)) and (b) longer wavenumber range (1000–2000 cm\({}^{-1}\)) under various treatment conditions. tions produced a wide range of roughness scales, from submicron to micron levels, offering diverse options to meet the requirements of various biomedical applications.