## 3 Results and Discussion
### Comparison of Corrosion Resistance of Different Samples
For hydrophilic samples, the entire surface will be wetted when immersed in water, and the corrosive medium will directly contact the substrate, as shown in Figure 11a, so the corrosion reaction is more likely to happen. However, when a superhydrophobic sample is immersed in water, an air film will be formed on the surface of the superhydrophobic microstructure. As shown in Figure 11b, this film blocks the direct contact between corrosive media and the metal matrix and improves the corrosion resistance of the sample. Observing the above experimental results, we can also find that the corrosion resistance of the 3D printed sample is worse than the polished surface. The reasons for this phenomenon may be as follows: First, the surface of the sample obtained by 3D printed is hydrophilic without modification. The increase of the microstructure makes the actual solid-liquid contact area larger than the polished surface, that is, the actual contact area between the sample and the corrosive medium increases. Second, the polished sample used in the corrosion resistance test is a commercially available 316L plate. Compared with the sample obtained by laser printing, it has higher density and fewer defects, so the corrosion resistance is better. In order to further study the corrosion resistance of the prepared superhydrophobic surface immersed in simulated seawater, the superhydrophobic samples obtained by 3D printing + modification and 3D printing + corrosion were immersed in simulated seawater solution for 1 day, 3 days, 5 days, and 7 days, then the electrochemical workstation was used to measure the changes of its Tafel curve and AC impedance curve. The measurement results are as follows:  
Figure 12 shows the Tafel curve of 3D printed + modified superhydrophobic samples immersed in simulated seawater for 1 day, 3 days, 5 days, and 7 days, respectively. It can be seen from the figure that the Tafel curve does not change obviously as the immersion time increases. Combined with Table 3, the corrosion potential decreased from \(-0.342\) V for 1 day of immersion to \(-0.369\) V for 7 days of immersion. The magnitude of the change was small, and it was still greater than the corrosion potential of the polished surface \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & **Rs** & **Rf** & **Cp** & **Rct** & **CPE-T** & **CPE-P** & **Ws** \\  & **(\(\Omega\cdot\)cm\({}^{2}\))** & **(\(\Omega\cdot\)cm\({}^{2}\))** & **(\(\mu\)F\(\cdot\)cm\({}^{2}\))** & **(\(\Omega\cdot\)cm\({}^{2}\))** & **(\(\mu\)F\(\cdot\)cm\({}^{2}\))** & **(\(\Omega\cdot\)cm\({}^{2}\))** \\ \hline
3D printed & 8.764 & 68.54 & 53.63 & 29,540 & 89.52 & 0.6 & - \\ polished & 9.364 & - & - & 75,550 & 67.26 & 0.8 & - \\
3D printed + corroded & 9.43 & 80.22 & 0.98 & 178,902 & 20.76 & 0.6 & 0.0003 \\
3D printed + modified & 10.51 & 83.03 & 0.22 & 207,600 & 6.64 & 0.7 & 0.0001 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Parameters of equivalent circuit components of different samples. Figure 10: Equivalent circuit models of different samples. (**a**) Polished sample; (**b**) 3D-printed sample; (**c**) 3D-printed + corroded and 3D-printed + modified samples. (\(-\)0.383 V, see Table 1), and the corrosion current density increased from 0.319 uA\(\cdot\)cm\({}^{-2}\) after immersion for 1 day to 0.743 uA\(\cdot\)cm\({}^{-2}\) after immersion for 7 days, which was still lower than the corrosion current density of the polished surface (2.834 uA\(\cdot\)cm\({}^{-2}\), see Table 1). Therefore, it can be concluded that the 3D-printed + modified superhydrophobic samples still have excellent corrosion resistance after immersion in simulated seawater for 7 days. Figure 13 shows the Nyquist diagram and Bode diagram of the 3D-printed + modified samples immersed in simulated seawater for 1 day, 3 days, 5 days, and 7 days, respectively. It can be seen from the figure that as the immersion time increases, the changes in the Nyquist diagram and Bode diagram are not obvious.