## 3 Results and Discussion
This may be attributed to the higher initial surface roughness, which provided more active sites for corrosion. The 12 M HF treatment generally led to more dramatic surface reconstruction, forming more complex multi-scale structures. Figure 4 shows the surface morphology of the Ti-64 alloy in its original state and after shot peening treatment with various parameters. The untreated Ti-64 surface (Figure 4a) exhibited extremely smooth characteristics, consistent with the surface morphology after mechanical polishing. While this smooth surface may have advantages in certain applications,  
Figure 3: SEM images of Ti-6 Al-4V surfaces after sandblasting and subsequent HF etching: (**a**) 80-grit sandblasted and etched with 3 M HF; (**b**) 80-grit sandblasted and etched with 12 M HF; (**c**) 120-grit sandblasted and etched with 3 M HF; and (**d**) 120-grit sandblasted and etched with 12 M HF. All etching processes were conducted at 5 \({}^{\circ}\)C. The images reveal the significant influence of sandblasting grit size and HF concentration on the resultant surface morphology, demonstrating a range of micron- and nano-scale features potentially beneficial for biomedical applications. it might not be optimal for osseointegration in biomedical implants. After shot peening treatment, the Ti-64 surface morphology underwent significant changes. The sample treated at 2 kg/cm\({}^{2}\) pressure for 5 s (Figure 4b) displayed pronounced plastic deformation features, characterized by numerous irregular protrusions, depressions, and microcracks. This structure likely resulted from rapid surface deformation due to high-energy impacts. As the treatment pressure decreased and duration increased, the surface structure gradually became more uniform and refined. The sample treated at 1 kg/cm\({}^{2}\) pressure for 10 s (Figure 4c) exhibited smaller-scale pits and protrusions, while the sample treated at 0.5 kg/cm\({}^{2}\) pressure for 20 s (Figure 4d) formed a more delicate and uniform structure, comprising numerous minute pits and angular features. These results demonstrate that precise control over Ti-64 surface morphology can be achieved by modulating shot peening parameters such as pressure and duration. As the treatment pressure decreased and duration increased, the surface structure tended to become more refined and uniform. This trend may have significant implications for the material's biological performance. Particularly, the coexistence of micron- and submicron-scale structures observed in Figure 4c,d may be more conducive to mimicking the hierarchical structure of natural bone tissue, thereby promoting cell adhesion and osseointegration processes [66; 67]. Shot peening treatment significantly increased the surface area and roughness of the material, which may be beneficial for increasing cell attachment sites and enhancing bioactivity. However, different treatment parameters may lead to variations in surface and subsurface stress distribution, potentially affecting the material's fatigue performance and corrosion resistance. Therefore, further research is needed to evaluate the specific effects of these different surface structures on cellular behavior, as well as their potential impact on the long-term performance of the material. Figure 5 shows the SEM surface morphology of the Ti-64 alloy after various surface treatments, including sandblasting and shot peening, followed by immersion corrosion in low-concentration HF solution. These treatments aim to create bioactive surfaces with optimized characteristics for potential biomedical applications. The surface treated with  
Figure 4: SEM images of Ti-6 Al-4V surfaces. (**a**) Untreated surface; (**b**) surface treated with zirconia beads at 2 kg/cm\({}^{2}\) for 5 s; (**c**) surface treated at 1 kg/cm\({}^{2}\) for 10 s; (**d**) surface treated at 0.5 kg/cm\({}^{2}\) for 20 s. The images reveal the progressive changes in surface morphology with varying shot peening parameters.