## 3 Results and Discussion
However, when shot peening is combined with HF immersion corrosion, the resulting spectrum presents the most complex features. Multiple peaks appear in the 300-700 cm\({}^{-1}\) range, with peaks at 447 cm\({}^{-1}\) and 612 cm\({}^{-1}\) potentially corresponding to the Eg and A1g modes of rutile phase TiO\({}_{2}\), respectively [73]. This composite treatment leads to the coexistence of both anatase and rutile TiO\({}_{2}\) phases, forming a more complex oxide layer structure. Raman spectral analysis in the 1000-2000 cm\({}^{-1}\) range also provides valuable insights into the surface characteristics of the Ti-64 alloy (Figure 6b). This spectral region is particularly sensitive to titanium oxidation states and structural changes, aiding in a deeper understanding of the effects of different treatment methods on surface modification. The polished Ti-64 surface presents a relatively flat spectrum, indicating a predominantly metallic surface with minimal natural oxidation. In contrast, chemically and mechanically treated surfaces exhibit significant spectral changes, reflecting the formation and evolution of titanium oxide layers. HF immersion corrosion results in an overall increase in spectral intensity, especially in the 1300-1600 cm\({}^{-1}\) range. This broad feature suggests the formation of an amorphous or highly defective TiO\({}_{2}\) layer. Shot peening further enhances this effect, with a more pronounced broad peak in the same spectral region. The most significant spectral changes are observed in samples subjected to combined shot peening and HF corrosion treatment. The strong broad peak in the 1300-1700 cm\({}^{-1}\) range can be attributed to second-order Raman scattering of TiO\({}_{2}\), while the weak feature near 1100 cm\({}^{-1}\) may correspond to Ti-O-Ti vibrations [74]. This complex spectral profile indicates the formation of a more extensive and structurally diverse oxide layer, potentially combining amorphous \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Sample Conditions**} & **Surface Roughness Ra** & **Surface Roughness** & **Surface Hardness** \\  & **(\(\upmu\)m)** & **Rq (\(\upmu\)m)** & **(HR15N)** \\ \hline As polished Ti64 & 0.09 \(\pm\) 0.01 & 0.16 \(\pm\) 0.01 & 79.8 \(\pm\) 0.4 \\ \hline
3 M HF immersion corrosion & 0.23 \(\pm\) 0.02 & 0.30 \(\pm\) 0.02 & 78.5 \(\pm\) 0.5 \\ \hline
12 M HF immersion corrosion & 0.32 \(\pm\)0.03 & 0.39 \(\pm\)0.03 & 78.5 \(\pm\) 0.9 \\ \hline
80-gtri Zr, 45\({}^{\circ}\) & 2.25 \(\pm\) 0.41 & 2.92 \(\pm\) 0.02 & 84.3 \(\pm\) 0.4 \\ \hline
120-gtri Zr, 45\({}^{\circ}\) & 1.20 \(\pm\) 0.13 & 1.67 \(\pm\) 0.08 & 83.1 \(\pm\) 0.2 \\ \hline
80-gtri Zr, 45\({}^{\circ}\)/3 M HF immersion corrosion & 2.23 \(\pm\) 0.36 & 2.85 \(\pm\) 0.07 & 79.5 \(\pm\) 0.5 \\ \hline
80-gtri Zr, 45\({}^{\circ}\)/12 M HF immersion corrosion & 1.43 \(\pm\) 0.27 & 1.90 \(\pm\) 0.03 & 79.0 \(\pm\) 1.0 \\ \hline
120-gtri Zr, 45\({}^{\circ}\)/3 M HF immersion corrosion & 1.28 \(\pm\) 0.14 & 1.79 \(\pm\) 0.08 & 80.3 \(\pm\) 0.4 \\ \hline
120-gtri Zr, 45\({}^{\circ}\)/12 M HF immersion corrosion & 0.85 \(\pm\) 0.19 & 1.56 \(\pm\) 0.09 & 79.3 \(\pm\) 0.8 \\ \hline Zr SP: 2 kg/cm\({}^{2}\), 5 s & 0.85 \(\pm\) 0.03 & 1.69 \(\pm\) 0.03 & 83.8 \(\pm\) 0.8 \\ \hline Zr SP: 1 kg/cm\({}^{2}\), 10 s & 0.79 \(\pm\) 0.03 & 1.46 \(\pm\) 0.10 & 83.3 \(\pm\) 0.4 \\ \hline Zr SP: 0.5 kg/cm\({}^{2}\), 20 s & 0.72 \(\pm\) 0.06 & 1.23 \(\pm\) 0.07 & 82.5 \(\pm\) 0.5 \\ \hline Zr SP: 2 kg/cm\({}^{2}\), 5 s/3 M HF immersion corrosion & 0.97 \(\pm\) 0.05 & 1.70 \(\pm\) 0.06 & 79.4 \(\pm\) 1.0 \\ \hline Zr SP: 1 kg/cm\({}^{2}\), 10 s/3 M HF immersion corrosion & 0.93 \(\pm\) 0.04 & 1.53 \(\pm\) 0.15 & 79.5 \(\pm\) 0.5 \\ \hline Zr SP: 0.5 kg/cm\({}^{2}\), 20 s/3 M HF immersion corrosion & 0.87 \(\pm\) 0.06 & 1.67 \(\pm\) 0.17 & 79.7 \(\pm\) 0.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Surface characteristics of the Ti-6 Al-4V alloy under various surface treatment conditions.