## 2 Materials and Methods  
### Materials Preparation  
Two CuCrFeMnNi high-entropy alloys (HEAs) with 5 wt. % Cu (I8-6-T) and 10 wt. % Cu (I8-7-T) were selected as sputtering targets. The alloys were cast in an induction furnace and then machined into 2-inch-diameter targets.  
The chemical composition of the cast ingots was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using an Agilent 725 spectrometer (Santa Clara, CA, USA) (Table 1).  
The HEA coatings were deposited using a DC magnetron sputtering method in a hybrid Physical Vapor Deposition (PVD) system (Torr, Auburn, WA, USA). The sputtering system was equipped with a [PERSON] 2-inch TORUS circular magnetron sputtering gun ([PERSON], Jefferson Hills, PA, USA) and a PD500X direct current source ([PERSON], Jefferson Hills, PA, USA) with a maximum power of 1500 W. Three deposition powers (200 W, 250 W, and 300 W) were applied for each HEA composition, resulting in a total of six coating batches, as presented in Table 2.  
Given that the sputtering power level significantly affects the coating thickness, it was opted to deposit at 200 W for 60 min and at 300 W for only 40 min, to achieve comparable coating thicknesses. Greater thickness can introduce other variables such as mechanical stress, cracks, poor adhesion, and the need for substrate heating.  
The deposition of HEA samples for 40 min at 200 W generates thin layers, under 1 \(\upmu\)m, and would be too small for structural characterization (EDS especially). So, a coating thickness of 1.5-2 \(\upmu\)m thickness was targeted for all coating power levels.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Target** & \multicolumn{5}{c}{**Composition, wt. \%**} \\ \cline{2-6}
**Samples** & **Type** & **Cu** & **Cr** & **Fe** & **Mn** & **Ni** \\ \hline \multirow{2}{*}{I8-6-T} & actual & 5.35 & 22.35 & 23.8 & 23.5 & 25 \\  & nominal & 5.1 & 22.27 & 23.92 & 23.53 & 25.14 \\ \multirow{2}{*}{I8-7-T} & actual & 11.18 & 22.36 & 23.07 & 19.21 & 24.18 \\  & nominal & 10.19 & 21.31 & 22.89 & 21.54 & 24.05 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Chemical analyses results for the targets.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Coating** & **Target** & **Sputtering** & **Deposition** & **Argon** & **Deposition** \\
**Samples** & **Samples** & **Power Level** & **Time (min)** & **Pressure** & **Rate** \\  & **Samples** & **(W)** & **(mbar)** & **(nm/min)** \\ \hline \hline I8-6-C1 & & 200 & 60 & & 33 \\ I8-6-C2 & I8-6-T & 250 & 50 & & 36 \\ I8-6-C3 & & 300 & 40 & & 37 \\ I8-7-C1 & & 200 & 60 & \(2.4\times 10^{3}\) & 30 \\ I8-7-C2 & I8-7-T & 250 & 50 & & 34 \\ I8-7-C3 & & 300 & 40 & & 37 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Deposition parameters of DC magnetron sputtering process.  
Deposition rate is measured by dividing the total thickness of the coating with the time of deposition process. Prior to loading the samples, we made several coatings on silicon substrates and measured the obtained layer thickness with a profilometer; if, for example, we obtained 4 \(\upmu\)m thickness layers in 120 min, then we know that if we deposit for 60 min in the same conditions, we will obtain 2 \(\upmu\)m thickness.  
Stainless steel 304L substrates (15 \(\times\) 15 \(\times\) 3 mm) were used for the main deposition, and additional silicon substrates were employed for the SEM-EDS analysis to avoid interference with the morphological and compositional results. The deposition parameters were selected to optimize the microstructure and adhesion of the coatings. The substrate surfaces were prepared by fine grade polishing and ultrasonic cleaning in acetone and isopropyl alcohol. The technological flow for the deposition of the HEA coatings is presented in Figure 1.