## 3 Results and Discussion
### Corrosion Susceptibility Assessment Tests
#### 3.3.2 Potentiodynamic Linear Polarization  
To study the corrosion behavior of the 310H stainless steel samples coated with a layer of NiCrAJY using the EB-PVD method after exposure for different periods in the specific environment of an SCW reactor, the potentiodynamic polarization plots were recorded \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Sample Type**} & **Polarization Resistance (From the** & **i0 (Calculated from** \\  & **Extrapolation of Nyquist Diagrams),** & **Polarization Resistance).** \\  & **(M\(\Omega\)\(\times\) cm\({}^{2}\))** & **(n\(\lambda\)\(\times\) cm\({}^{-2}\))** \\ \hline
310H\_uncoated & 0.0342 & 370 \\
310H/NiCrAJY\_0 h & 0.039 & 320 \\
310H/NiCrAJY\_720 h & 0.297 & 42.6 \\
310H/NiCrAJY\_1440 h & 0.389 & 32.6 \\
310H/NiCrAJY\_2160 h & 0.514 & 24.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Rp and i0 values obtained for unoxidized and oxidized NiCrAJY-coated 310H samples for different periods in water at 550 \({}^{\circ}\)C and 25 MPa. starting from a potential of \(-\)0.250 V vs. OCP up to +1.0 V. A scan rate of 0.5 mV/s was used. The obtained potentiodynamic polarization plots are shown in Figure 10.  
Following the shape of the polarization plots shown in Figure 10, it can be seen that in the case of the samples coated with a layer of NiCrAlY and oxidized for 2160 h, more electropositive values of the corrosion potential and lower corrosion current density values were recorded, which indicate a better corrosion resistance of these samples compared to unoxidized ones or those oxidized under the same conditions for a shorter period of time. These observations indicate that the oxide films are more protective and provide better corrosion resistance, which is also evidenced by the EIS analysis. The electrochemical parameters determined from potentiodynamic polarization plots using the Tafel slopes extrapolation and polarization resistance (Rp) methods, as well as the protection efficiency (P\({}_{\text{i}}\)) and porosity (P) values, are presented in Table 7.  
As this table shows, similar values of the electrochemical parameters were obtained by the Tafel and R\({}_{\text{P}}\) methods. Thus, it is observed that the sample coated with a layer of NiCrAlY and oxidized for 2160 h has the best corrosion protection, which is indicated by the lowest corrosion current density value (4.62 nA \(\times\) cm\({}^{-2}\)) and the corrosion rate \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample Type**} & \multicolumn{6}{c}{**Electrochemical Parameters**} \\ \cline{2-7}  & \multicolumn{3}{c}{**Tafel Slopes Method**} & \multicolumn{3}{c}{**Rp Method**} & **Pi,** & **P,** \\ \cline{2-7}  & **E\({}_{\text{corr}}\)** & **i\({}_{\text{corr}}\)** & **V\({}_{\text{corr}}\)** & **R\({}_{\text{P}}\)** & **i\({}_{\text{corr}}\)** & **[\%]** & **[\%]** \\  & **[mV]** & **[mA \(\times\) cm\({}^{-2}\)]** & **[mm \(\times\) year\({}^{-1}\)]** & **[K\(\Omega\)\(\times\) cm\({}^{2}\)]** & **[mA \(\times\) cm\({}^{-2}\)]** & & \\ \hline uncoated & \(-\)256 & 1030 & 0.011 & 26.07 & 1190 & - & - \\
0 h & \(-\)219 & 200 & 0.002 & 82.61 & 227 & 80.58 & 0.135 \\
720 h & \(-\)164 & 8.43 & 8.9 \(\times\) 10\({}^{-5}\) & 2.5 \(\times\) 10\({}^{3}\) & 8.14 & 99.18 & 1.25 \(\times\) 10\({}^{-3}\) \\
1440 h & \(-\)161 & 7.17 & 7.5 \(\times\) 10\({}^{-5}\) & 3.6 \(\times\) 10\({}^{3}\) & 7.25 & 99.30 & 8.01 \(\times\) 10\({}^{-4}\) \\
2160 h & \(-\)123 & 4.62 & 4.8 \(\times\) 10\({}^{-5}\) & 7.3 \(\times\) 10\({}^{3}\) & 4.29 & 99.55 & 1.67 \(\times\) 10\({}^{-4}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Electrochemical parameter values calculated from Tafel slopes and Rp methods, Pi and P values determined for NiCrAlY-coated 310H stainless steel samples unoxidized and oxidized for different periods in water at 550 \({}^{\circ}\)C and 25 MPa. Figure 10: Potentiodynamic plots for NiCrAlY-coated 310H steel samples before and after oxidation for 720 h, 1440 h, and 2160 h in water at 550 \({}^{\circ}\)C and 25 MPa.