## 3 Results and Discussion
### SEM and EDS Analysis Results  
The microstructural characteristics of the HEA coatings with 5 wt. % and 10 wt. % Cu, deposited at different power settings, were examined using scanning electron microscopy (SEM) to assess morphology, surface uniformity, and deposition quality. First, Figures 2 and 3 present SEM images of the HEA coatings, compared with the SEM images of the HEA targets. The as-cast samples present well defined interdendritic (ID) and dendritic phases (DR). Impurities are also found in the target structure (IMP). The deposited samples did not show an obvious phase structure compared to the as-cast targets. Figure 2: SEM images of the target I8-6-T (**a**) and coating I8-6-C3 (**b**). Semi-quantitative spot EDS analysis results (Table 3) confirmed the presence of Cr, Mn, Fe, Ni, and Cu, consistent with the composition of the alloy targets determined by ICP-OES spectroscopy (Table 1). The as-cast samples contain two major phases (DR and ID) with concentrations varying mainly by the Mn and Ni content. The thin film coatings displayed a homogeneous distribution of elements, closely matching the target composition, with only minor variations. The most notable differences were observed in the concentration of Mn and Ni, versus the actual target concentration. This can be attributed to their differential sputtering yields and deposition rates, which may lead to slight variations in the final elemental distribution on the coating surface. The sensitivity of Mn and Ni to sputtering yields and deposition rates is driven by:  
* Atomic properties like binding energy and mass. * The sputtering yield being dependent on the mass ratio between the incident ion (e.g., Ar) and the target atoms. Mn, being lighter than many other alloy constituents, is more easily ejected, while Ni, being intermediate in mass, is also moderately affected. * Mn, being relatively light compared to many transition metals, being preferentially sputtered. This occurs because lighter elements require less momentum transfer to overcome their binding energy. * Mn having a relatively higher vapor pressure compared to Ni and many other elements in high-entropy alloys (HEAs). This means that Mn is more likely to evaporate or redistribute during deposition, leading to fluctuations in its deposition rate. * Ni atoms, due to their intermediate mass and relatively high binding energy, may undergo more re-deposition, where sputtered atoms are redeposited back onto the target or substrate. * Cascade and energy transfer mechanisms during sputtering. Figure 3: SEM images of the target 18-7-T (**a**) and coating 18-7-C3 (**b**). \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Samples** & **State** & \multicolumn{5}{c}{**Composition, wt. \%**} \\  & **Cu** & **Cr** & **Fe** & **Mn** & **Ni** \\ \hline \multirow{2}{*}{18-6-T} & Phase ID & 4.66 & 20.16 & 20.89 & 28.85 & 25.44 \\  & Phase DR & 2.34 & 47.13 & 23.00 & 18.62 & 8.91 \\  & Spot 1 & 4.50 & 21.19 & 22.85 & 28.78 & 22.68 \\  & Spot 2 & 5.07 & 21.54 & 22.42 & 27.54 & 23.43 \\  & Spot 3 & 4.47 & 22.39 & 21.75 & 28.90 & 22.49 \\  & Phase ID & 14.53 & 14.12 & 15.18 & 28.02 & 28.16 \\  & Phase DR & 1.88 & 43.75 & 29.99 & 12.90 & 11.48 \\  & Spot 1 & 10.64 & 20.08 & 21.10 & 25.98 & 22.20 \\  & Spot 2 & 10.59 & 20.42 & 20.14 & 26.15 & 22.70 \\  & Spot 3 & 10.26 & 20.25 & 21.33 & 25.49 & 22.67 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: EDS analysis results of HEA targets and coatings. These factors collectively make Mn and Ni more prone to compositional variations in sputtering-based thin film deposition processes. Overall, the coatings exhibited dense, uniform surfaces with an even thickness and strong adhesion to the substrates, as evidenced by the cross-sectional SEM image (Figure 4) that shows an absence of significant voids, cracks, or signs of delamination. An improved adhesion is crucial for maintaining the coatings' integrity under operational stresses, suggesting effective bonding achieved through the controlled deposition process.