## 3 Results and Discussion
### Electrochemical Assessment
#### 3.2.3 EIS Analyses  
EIS assessments (Figure 5) showed the corrosion mechanism evolution of the samples. Both samples presented a similar corrosion mechanism evolution over time, indicating its high stability. The equivalent circuit method was utilised to analyse the corrosion mechanism. The horizontal curve at the high frequency range (from 10\({}^{4}\) Hz to 10\({}^{5}\) Hz) in Bode plots of the impedance modulus (\(Z_{\rm m}\)) in function to frequency (\(\upsilon\)) indicated the presence of a resistance in the equivalent circuit. The resistance was similar for all immersion times and samples, meaning that this element corresponds to the solution resistance (R\({}_{\rm s}\)) [24]. The double peak in Bode plots of phase angle vs. \(\upsilon\), the tilted curve with two slopes in \(Z_{\rm m}\) against the \(\upsilon\) plot, and the two loops in the Nyquist plots indicate two overlapped constant times. The double peak was difficult to be distinguished due to the significant overlapping between peaks, resulting in a flattened aspect. These time constants are formed of a constant phase element (CPE) and a resistance in parallel with each other. Note that CPE has a power element (\(\eta\)) due to this not being an ideal capacitor [24]. The resistance of the time constant at a medium frequency range (from 10\({}^{4}\) Hz to 1 Hz) is in serial to the CPE of the time constant at a low frequency range (from 10\({}^{-1}\) Hz to 10\({}^{-2}\) Hz). Both time constants were in series with R\({}_{\rm s}\). The resistances represent the resistance to the charge transference of the samples, while CPEs represent the double layer generated by the alignment of the material and dissolution charges [7; 25]. The time constant at a medium frequency range corresponds to the passive film (R\({}_{\rm pass}\), CPE\({}_{\rm pass}\), and \(\eta_{\rm pass}\)), whilst the bared material is rendered by the constant time at a low frequency range (R\({}_{\rm bared}\), CPE\({}_{\rm bared}\), and \(\eta_{\rm bared}\)). The equivalent circuit was thus composed of three time constants, as can be seen in Figure 6. This is a common equivalent circuit used for 316L stainless steel [7; 25]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{\(I_{corr}\) (**nA/cm\({}^{2}\))**} & \(C.R._{corr}\) (**\(\mu\)A/cm\({}^{2}\))** & \(I_{pass}\) (**\(\mu\)A/cm\({}^{2}\))** & \(C.R._{pass}\) (**\(\mu\)A/cm\({}^{2}\))** & \(\beta_{c}\) (**mV/A Decade**) & \(\beta_{a}\) (**mV/A Decade**) & \(R_{p}\) (**M\(\Omega\)/cm\({}^{2}\))** \\ \hline \multirow{2}{*}{Wrought} & \multirow{2}{*}{9.260} & \multirow{2}{*}{70.646} & \multirow{2}{*}{1.860} & \multirow{2}{*}{19.403} & \multirow{2}{*}{\(-\)0.028} & \multirow{2}{*}{0.693} & \multirow{2}{*}{1.253} \\  & & & & & & \\ \hline LPBF & 10.900 & 90.230 & 0.743 & 5.671 & \(-\)0.029 & 0.065 & 2.325 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Sample corrosion characteristics of the PPC. Figure 5: EIS analyses of the wrought sheet (**a**) and LPBF (**b**) 316L stainless steel samples in 0.6 M NaCl. Table 3 lists the values of the equivalent circuit elements according to the samples and immersion time. R\({}_{\mathrm{s}}\) was similar for the various immersion times and samples. The solution's electrochemical features usually remained constant because the corrosion process mainly occurs on the metallic material [25]. CPE\({}_{\mathrm{pass}}\) was similar for all immersion times and sample kinds, meaning the sample passive film thickness was constant over the times and similar for both samples. The thickness of the passive film (\(d\)) and coating are proportional to \(\mathit{CPE}_{\mathrm{pass}}\), as shown in Equation (6) [7; 12; 20]. \[d=\frac{E_{p}\times E_{o}}{\mathit{CPE}_{\mathrm{pass}}} \tag{6}\]  
where \(E_{p}\) is the diiron trioxide dielectric constant (17.85) and \(E_{o}\) is the vacuum permeability (8.854 \(10^{-14}\) Fcm\({}^{-1}\)[7]). \(d\) was around 1 nm for both samples, being similar to the passive film thickness observed in other works [7].