###### Abstract
When a high-energy ion beam bombards the target, after melting, sublimation, and evaporation, the deposition of the target takes place. Since each element's saturated vapor pressure is different, the coating composition on the surface sample will change. When placed in a thin, homogeneous layer, vapor-deposited coatings are dense. These types of coatings result in a decrease in the quantity of gas or moisture that can pass through the film. Consequently, these coatings are perfect for corrosion reduction in a nuclear environment. This applies to Generation IV reactors, such as SCW-type or liquid metal-cooled reactors, as well as existing LWR reactors (BWR, PWR) and CANDU reactors [11; 12]. In this paper, 310H stainless steel has been selected for testing because the tests carried out so far, as well as the data from the literature, proved that this type of steel has a high oxidation resistance in water at high temperatures and pressures, while remaining susceptible to intergranular corrosion [13; 14; 15] and sigma phase precipitation when exposed to aggressive conditions like 550 \({}^{\circ}\)C and 25 MPa for a longer period of time [16]. Therefore, applying protective ceramic or metallic layers on the surface of this alloy has proven to be one of the ways to improve corrosion resistance. Ceramic materials such as nitrides, carbides, silicones, transition metal oxides, and metallic materials--such as McArIY (M = Ni, NiCo, CoNi, or Fe)--show good resistance in corrosive environments, and are thus recommended for applications in water at supercritical temperatures. NiCrAIV-based coatings, widely used as independent layers or bond layers in TBCs (thermal barrier coatings), are selected in this paper based on their good adhesion, high modulus, high strength, and good oxidation resistance [17; 18; 19]. The development of a corrosion-resistant layer (Cr2O3, and Al2O3) on the material's surface, which shields the deposited layer and the base material (substrate), is what gives the material its high oxidation resistance [20]. Additionally, dense layers rich in \(\alpha\)-Al2O3-forming serve as a protective barrier, thus effectively preventing the diffusion-controlled oxidation process and rapid deterioration of the coated superalloys [21]. In recent years, only a few authors have studied the oxidation behavior of coated austenitic alloys under extreme conditions [22], even though knowledge of the oxidation of austenitic steel 316 L at high temperatures [23] is more present in the literature [24; 25; 26]. An example of this is the corrosion behavior of CrNx-coated 310H SS before and after exposure to water under supercritical pressure and temperature (550 \({}^{\circ}\)C and 25 MPa) for up to 2160 h [22; 27; 28]. The present paper aims to study the corrosion behavior of the NiCrAJY-coated 310H alloy in thermally degassed demineralized water (2 ppm O2) at a temperature of 550 \({}^{\circ}\)C and a pressure of 25 MPa for up to 2160 h. After oxidation, all tested samples were characterized by the following various methods: gravimetric analysis, grazing incidence X-ray diffraction (GIXRD), or scanning electron microscopy (SEM). The corrosion susceptibility has been assessed using the following two electrochemical techniques: linear potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The motivation for choosing such an investigation is based on the fact that the selected 310H alloy coating was not sufficiently studied at high temperatures despite its remarkable behavior. It is also crucial to mention the novel character of this article, which has a detailed electrochemical investigation of NiCrAJY film on 310 alloys studied in aggressive temperature and pressure conditions. The electrochemical aspect has not been studied until now. The original character of this article is not only the fabrication, but also the characterization for a longer time. All such aspects are important for us to gain more knowledge about nuclear material candidates for generation IV reactors.