## 3 Results and Discussion
Both treated surfaces exhibited significant plastic shear strain characteristics, manifested as material flow and accumulation. This non-uniformly distributed strain layer not only increases the effective surface area but also stores a substantial amount of strain energy in the material surface. This stored strain energy may play a catalytic role in subsequent acid etching processes, serving as a crucial factor in driving non-uniform surface corrosion. Notably, the sandblasted surfaces display multi-scale roughness features, ranging from micron-scale major protrusions to nano-scale fine structures. This multi-scale surface structure may have complex effects on subsequent biological performance, potentially promoting the attachment and proliferation of certain cell types while also influencing the material's fatigue properties and corrosion behavior [63,66]. The 45\({}^{\circ}\) angle sandblasting treatment successfully created complex morphologies on the Ti-64 surface, laying the foundation for subsequent surface modifications and biological applications. However, the observed differences in surface morphology resulting from different grit sizes suggest that the selection of optimal treatment parameters should consider a combination of factors, including surface roughness, strain energy distribution, and potential biological effects. These findings underscore the importance of carefully controlling sandblasting parameters to achieve the desired surface properties. Future studies should focus on quantifying the relationship between sandblasting parameters (such as grit size, pressure, and angle) and the resulting surface characteristics. Additionally, investigating the biological response to these modified surfaces through in vitro and in vivo experiments would provide valuable insights into their potential for enhancing implant performance. Figure 2: SEM images of Ti-6 Al-4V surfaces after 45\({}^{\circ}\) angle sandblasting treatment. (**a**) Surface treated with 80-grit zirconia sand, showing larger deformation features and pronounced plastic shear strain. (**b**) Surface treated with 120-grit zirconia sand, exhibiting finer and more uniform texture. Both surfaces demonstrate complex 3D structures with evident plastic deformation, providing potential sites for subsequent chemical etching and cell attachment. Figure 3 illustrates the surface morphology of the Ti-64 alloy subjected to a two-step surface modification process, sandblasting at a 45\({}^{\circ}\) angle using zirconia sand of different grit sizes (80 and 120 grit), followed by low-temperature (5 \({}^{\circ}\)C) immersion corrosion in HF solutions of varying concentrations (3M and 12M). This composite treatment aims to create bioactive surfaces with multi-scale structural features. Comparing Figure 3a,b, we observe the significant influence of HF concentration on surfaces initially treated with 80-grit sand. The 3 M HF treatment (Figure 3a) produced relatively uniform etch pit structures, resulting in micron-scale surface features that may promote cell adhesion. In contrast, the 12 M HF treatment (Figure 3b) led to more aggressive corrosion, forming deeper and wider etch pits with superimposed nano-scale secondary structures. This multi-level surface architecture may be more conducive to the osseointegration process [66; 68]. A comparison of Figure 3c,d reveals the effects of different HF concentrations on surfaces initially treated with 120-grit sand. The 3 M HF treatment (Figure 3c) preserved more of the original sandblasted texture while forming uniformly distributed micro-pits on the surface. The 12 M HF treatment (Figure 3d) resulted in more pronounced surface reconstruction, creating a more complex three-dimensional network structure. This structure may provide a larger specific surface area and more cell attachment sites [52; 55; 56]. Comparing all four treatment methods, we observe that surfaces initially treated with 80-grit sand exhibited greater changes during subsequent corrosion.