## 3 Electrodeposition
### Properties Relevant to Applications
#### 3.3.5 Mechano-Structural Properties  
Some electrodeposited high-entropy alloys have been characterized to evaluate their mechanical properties and structural performance [32; 46; 65; 66]. Compared to conventional nanocrystalline materials, HEAs show enhanced stability as the number of constituent elements increases, due to their high configurational entropy and complex atomic interactions. [PERSON] et al. [32; 65] investigated the microstructural behavior of electroplated Al-CoFeMnNiCu alloys after heat treatment at 600 \({}^{\circ}\)C. They observed a transformation from a globular morphology, with a refinement of grains, an increase in compactness, and a subsequent enhancement of coating hardness. Other studies [16; 59] confirmed the trans  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Alloy** & **Structure** & **Coercivity, Oe** & **Saturation Magnetization, emu/g** & **Ref.** \\ \hline \multirow{6}{*}{Bi19 Fe21 Co19 Ni22 Mn19} & \multirow{2}{*}{FCC} & 20 \({}^{\circ}\)C: 0 & – & \\ \cline{3-5}  & & \(-\)268 \({}^{\circ}\)C: 100 & – & [15] \\ \cline{3-5}  & & 20 \({}^{\circ}\)C: 658 \({}^{1}\) & – & \\ \cline{3-5}  & & 20 \({}^{\circ}\)C: 121 & – & \\ \cline{3-5} Fe7 Ni48W17 Mo27 Mn0.1 & \multirow{2}{*}{cubic} & 20 \({}^{\circ}\)C: 103 \({}^{2}\) & – & [26] \\ \hline Co20 Cu21 Fe19 Ni17 Zn23 & FCC + BCC & 20 \({}^{\circ}\)C: 19 & 20 \({}^{\circ}\)C: 82 & [43] \\ \hline AlCrFeNiTi & FCC + BCC & 20 \({}^{\circ}\)C: 0 & 20 \({}^{\circ}\)C: 83–106 & [46] \\ \hline FeCoNiMoW & FCC + amorphous & 20 \({}^{\circ}\)C: 7–34 & 20 \({}^{\circ}\)C: 42–107 & [47] \\ \hline \hline \end{tabular} \({}^{1}\) Alloy annealed at 600 \({}^{\circ}\)C. \({}^{2}\) Alloy annealed at 200 \({}^{\circ}\)C.  
\end{table}
Table 4: Magnetic properties of some as-deposited high-entropy alloys.  
formation of amorphous as-deposited coatings into solid solution crystalline structures upon annealing.  
[PERSON] et al. [66] systematically analyzed the mechanical and structural properties of nanocrystalline NiFeCoW, amorphous NiFeCoMo, and nanoglass NiFeCoMoW alloys. Their findings showed that grain size stability improved with the addition of elements, with the following order of enhancement: Ni \(<\) NiCo \(<\) NiFeCo \(<\) NiFeCoW \(<\) NiFeCoMo \(\sim\) NiFeCoMoW. The five-element alloy did not result in further improvements compared to the four-element precursor due to the limitations of the compositional flexibility of molybdenum and tungsten during electroplating. They also observed a significant improvement in thermal stability in the electrodeposited HEAs, as indicated by a doubling of the activation energy for grain growth in NiFeCoW and NiFeCoMoW (both about 3 eV) compared to nanocrystalline Ni (1.3 eV). Additionally, these HEAs exhibited a 60% increase in hardness after annealing at about 500 \({}^{\circ}\)C, reaching maximum hardness (8.4 GPa). This hardening trend followed an inverse Hall-Petch relationship, where grain boundary relaxation and nanoglass structural breakdown played a dominant role in the inverse regime.  
[PERSON] et al. [68] demonstrated the influence of zinc content on the mechanical properties of electrodeposited CoFeNiZn alloys with FCC structure. They reported that for Zn concentrations in a range of 25-44 at%, the coatings exhibited a hardness of approximately 4.5 GPa and an elastic modulus of around 130 GPa. At lower zinc contents (down to 18 at%), both parameters decreased. These values were significantly lower than those reported for other electrodeposited CoFeNiZn coatings produced in a similar bath, which was attributed to the presence of not only FCC but also the BCC and amorphous phases reported in the earlier study [67].