PSI - Issue 65

V.A. Bryzgalov et al. / Procedia Structural Integrity 65 (2024) 25–31 Bryzgalov V.A., Korznikova E.A. / Structural Integrity Procedia 00 (2024) 000–000

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Superalloys, a class of advanced metallic materials, have emerged as crucial components in sectors such as aerospace, power generation, and petrochemical industries due to their exceptional mechanical properties and resistance to severe environmental conditions. These alloys are high-performance metallic materials composed of at least two elements, which are exploited for their exceptional temperature and chemical resistance, as well as their mechanical properties (Selvaraj et al. (2021); Su et al. (2023); Zhan et al. (2023)). These alloys are employed in a multitude of applications in environments that are subject to extreme conditions, including those encountered in the medical (Detrois, (2020)), aerospace (Gloria et al. (2019)) and chemical processing industries (Grange et al. (2020); Reed (2006), Ilgamov et al. (2024), Dmitriev et al. (2024)). Devices made from such alloys are operated in environments that contain corrosive species, such as sulfur, chlorine- or carbon-containing compounds, water vapor, etc. At elevated temperatures, such environments present an even greater challenge, as even in air, the oxidation of many superalloys is insufficient for continuous operation. The oxide grows at an accelerated rate on the surface of the alloy, resulting in a change to the subsurface zone of the alloy and a subsequent loss of mechanical strength. Higher additions of alloying elements for corrosion protection such as Cr, Al or Si cannot be used effectively due to them either leading to embrittlement of the alloy or lowering its melting point. The only effective method of dealing with such high-temperature environments is to employ high-temperature coatings to protect the alloy from the aggressive atmosphere. The physical mechanisms of mass transport mechanisms capable to assist the formation of coatings are discussed in Babicheva (2019), Kistanov (2019), Moradi Marjaneh (2018), Shepelev (2020). Cao et al. (Cao et al. (2024)) employed a Pt coating to markedly enhance the combustion resistance of a Ni-based superalloy, impeding the oxidation and combustion of an Al phase within an alloy with the highest combustion heat. In (Lei et al. (2024)) used a high-entropy alloy NbCrFeNiCoMox as a coating for GTD-111 superalloy to increase its corrosion resistance. One of the most frequently utilized and effective materials for the coating of superalloys is chromium (Bestor et al. (2011); Ledoux et al. (2011)). Chromium forms a dense protective Cr2O3 oxide scale that significantly improves oxidation resistance at high temperature, and provides solid solution strengthening when diffused into the superalloy (Kruk et al. (2020)). It also can be combined with other elements like aluminium (in Cr-Al coatings) to further enhance protective properties). In addition to the aforementioned advantages, chromium coatings are also highly compatible with superalloys. This is due to the fact that chromium is already a key component in many superalloys, which allows for chromium coatings to be highly compatible with the substrate (König et al. (2022); Ma et al. (2023)). This compatibility helps to reduce unwanted reactions and diffusion issues between the coating and substrate. This paper provides an overview of research on chromium coatings used to protect superalloys from extreme environments. This paper will describe the application methods of chromium and chromium-based coatings and present the mechanisms that make these coatings so effective in protecting superalloys at high temperatures. Diffusion coating is a process whereby metal components are coated with a non-corrosive material to enhance their resistance to high temperatures, corrosion and wear. As with all diffusion processes, the parameters time, temperature and phase composition are of critical importance. It is essential that the process conditions are optimized for each material, as the phase composition and the microstructural evolution of diffusion coatings are highly dependent on the substrate which is coated, Galetz (2015). Figure 1 illustrates the general concept of diffusion coatings. 2. Diffusion coatings