## 3 Electrodeposition
### Properties Relevant to Applications  
#### 3.3.1 Corrosion Resistance  
High-entropy alloys often exhibit excellent corrosion resistance, which is attributed to their unique multicomponent composition and stable solid solution structures. Although their corrosion behavior depends strongly on alloy composition and post-processing conditions (Table 2), HEAs are considered promising materials for use in marine environments due to the formation of stable passive layers [26; 27]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Alloy** & **Structure** & \(\mathbf{i_{corr}}\)\(\mathbf{\mu A/cm^{2}}\) & \(\mathbf{E_{corr}}\)\(\mathbf{V}\) & **Ref.** \\ \hline Fe7 Ni50W17 Mo27 Mn0.1 & FCC & 40 & \(-\)0.40 & [26] \\ Fe7 Ni48W17 Mo27 Mn0.1 (annealed 200 \({}^{\circ}\)C) & FCC & 17 & \(-\)0.16 & [26] \\ \hline Fe(36–47)Co(23–25)Ni(3–8)Mo(7–13)W(16–20) & – & 92 & \(-\)0.95 & [28] \\ \hline Fe18 Co18 Ni16 Mo17W31 & FCC & 4.4 & \(-\)0.83 & [27] \\ \hline Fe22 Co13 Ni8 Mo12W22 Cr21 & FCC & 3.5 & \(-\)0.34 & [27] \\ \hline Fe32 Co24 Ni27W7 Cr10 & FCC & 2.9 & \(-\)0.65 & [29] \\ \hline Fe18 Co19 Ni21 Cr42 & FCC & 1.4 & \(-\)0.32 & [30] \\ \hline \hline \multirow{2}{*}{Fe24 Co28 Ni25 Cr23} & \multirow{2}{*}{amorphous} & 1.7 & \(-\)0.45 & \\ \cline{3-5}  & & 12 & \(-\)0.33 \({}^{1}\) & [31] \\ \cline{3-5}  & & 1.4 & \(-\)0.74 \({}^{2}\) & \\ \hline Fe22 Co19 Ni30 Cr29 & FCC & 33 & \(-\)0.51 & \\ \hline Fe23 Co20 Ni21 Cr15 Mn20 & FCC & 58 & \(-\)0.40 & [55] \\ \hline Fe23 Co15 Ni26 Cr14 Al20 & FCC & 18 & \(-\)0.39 & \\ \hline Fe24 Co26 Ni14 Cr9 Mn27 & no data & 3.3 & \(-\)0.23 & [56] \\ \hline Fe41 Co27 Ni4 Cr27 Mn0.3 & no data & 1.1 & \(-\)0.53 & [38] \\ \hline Fe37 Co27 Ni10 Cr25 Mn0.6 & no data & 8.5 & \(-\)0.75 & [38] \\ \hline Al15 Fe26 Cr21 Ni27 Ti14 & FCC+BCC & 0.09 & \(-\)0.77 & [46] \\ \hline \hline \end{tabular} \({}^{1}\) In 1M H\({}_{5}\)SO\({}_{4}\), \({}^{2}\) In 1M NaOH.  
\end{table} 
Table 2: Corrosion properties of some high-entropy alloys in 3.5% NaCl (except as indicated). Figure 5: Effect of cathode geometry and increased zinc concentration in the electrolyte (red arrow) on the increased zinc concentrations at various points (red dots, red arrow) on the cathode surface (**a**) and the morphology (**b**) of CoFeNiZn alloy. Reproduced from [68] under license CC BY 4.0. [PERSON] et al. [26] compared the corrosion properties of FeNiWMoMn alloys electrodeposited galvanostatically (10 mA/cm\({}^{2}\)) from a sulfate-citrate bath. They observed that extending the electrolysis time (30-90 min) caused a slight decrease in iron content (by 4 at%) and a corresponding increase in nickel content (by 5 at%), which resulted in only a minor increase in corrosion current density and a shift in corrosion potential. Annealing the alloy (200 \({}^{\circ}\)C) reduced the corrosion current density by half, which was attributed to microstructural refinement and a reduction in defect density, both contributing to the formation of a more protective passive layer. [PERSON] et al. [28] analyzed FeCoNiMoW alloys (DC, chloride-sulfate-citrate bath) deposited at different current densities. Although the alloy composition varied slightly and the resulting coatings exhibited some cracking, the corrosion current densities were significantly reduced compared to the substrate (304 stainless steel) by 32-67%. In turn, [PERSON] et al. [27] investigated the effect of chromium incorporation into FeCoNiMoW alloy (DC, 40 mA/cm\({}^{2}\), chloride bath). This modification led to a significant positive shift in corrosion potential (by 0.5 V), while the corrosion current density remained nearly unchanged. Both HEAs markedly improved the corrosion resistance of the multiphase nickel-aluminum bronze substrate, enhancing it by more than 36%. On the other hand, [PERSON] et al. [29] showed that the incorporation of tungsten (about 7 at%) into the chromium-containing FeCoNiW alloy did not significantly improve corrosion resistance, but it increased the coating's microhardness by about 180 HV (up to 675 HV) and enhanced its wear resistance. [PERSON] et al.