## 1 Introduction
The flexibility of HEA coating fabrication allows control over the coating properties--such as thickness, density, and surface quality--by adjusting process parameters like deposition temperature, laser power, and sputtering power. Additionally, HEA coatingsare compatible with a range of substrates, including steel, aluminum alloys, magnesium alloys, and titanium alloys, providing uniform coverage and consistent performance even on complex shapes [17; 18]. In terms of functionality, HEA coatings excel in environments requiring resistance to corrosion, erosion, and wear [16]. This makes them suitable for challenging conditions, such as marine and extreme cold environments, as well as high-radiation and high-altitude applications. Overall, the versatility, economic benefits, and enhanced protective qualities of HEA coatings position them as a promising solution for extending the service life of metal substrates in demanding applications. Additive manufacturing methods such as selective laser melting (SLM) have recently enabled the fabrication of complex high-entropy alloy (HEA) components, as highlighted by [PERSON] et al. [19], who demonstrated the machinability and enhanced mechanical properties of CoCrFeMnNi HEAs produced via SLM. However, challenges related to surface quality and subsequent processing remain significant, necessitating further investigation into alternative fabrication and processing techniques, such as sputtering and coating technologies. The deposition of HEA coatings through direct current (DC) magnetron sputtering has proven advantageous for producing dense, uniform films with tailored properties. Magneton sputtering involves bombarding a target with high-energy ions to eject atoms, which are then deposited as a thin film on the substrate. Studies by [PERSON] and [PERSON] [20] provide an overview of sputtering technology, highlighting its benefits in achieving controlled thickness and composition in thin-film coatings. More recent work [21] demonstrates that DC magnetron sputtering can precisely control the microstructure of HEA coatings, which is essential for optimizing their corrosion resistance in marine environments. Notably, researchers found that the dense microstructures achieved through sputtering inhibit the penetration of corrosive ions and exhibit superior stability in chloride exposure, common in marine applications. The limitation of this coating technique could be the poor uniformity on large and complex geometry substrates, but its good structural accuracy presents high interest for industry. Marine materials, including carbon steels, stainless steels, and titanium, are highly susceptible to microbial colonization and biofilm development, which contribute to microbially influenced corrosion (MIC) and biofouling. To mitigate MIC, researchers have extensively explored incorporating antimicrobial elements, such as copper (Cu), into these materials [22; 23]. Recent studies highlight the potential of copper (Cu) as a beneficial addition to HEA systems, especially for marine corrosion resistance. Copper can enhance passivation by promoting stable oxide layer formation on HEA surfaces, which is crucial for applications in chloride-rich marine environments. [PERSON] et al. [24] demonstrated that Cu-doped HEAs exhibit improved resistance to localized corrosion due to the protective passivation layer that Cu facilitates. Additionally, [PERSON] et al. [25] observed that Cu additions can significantly mitigate pitting corrosion, a common degradation mode in saline conditions, thus extending the alloy's service life in harsh environments. High-entropy alloy (HEA) coatings present a promising solution for such applications due to their customizable composition and ability to incorporate elements with antimicrobial properties. HEA coatings not only improve the corrosion resistance of substrates but also allow the integration of elements like Cu, which can effectively reduce microbial adhesion and biofilm formation.