OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 4 2023 enables the use of structural carbon, low- and medium-alloy steels instead of high-alloy ones in equipment operating in aggressive environments. With regard to increase the corrosion resistance of structural materials, elements such as Ni, Cr, Al, Ti, Cu, etc. are of interest [7–9]. At the same time, the current trend in the formation of functional coatings is the use of elemental compositions based on two or three or more components [10]. From the variety of possible elemental compositions, it is worth highlighting compositions based on nickel and chromium. Nickel forms a continuous series of solid solutions with iron. Nickel coatings are often used as corrosionresistant, heat-resistant, high-temperature resistant ones. Chromium also forms a continuous series of solid solutions with iron. However, chromium is a carbide-forming element, which allows it to be considered not only for elements that form corrosion-resistant coatings, but also wear-resistant ones. Therefore, the formation of coatings based on the Ni-Cr composition is promising. There are numerous techniques for forming coatings based on Ni and Cr, namely: CVD, PVD, flame spraying, galvanic methods, and thermochemical treatment (TCT) [11–15]. At the same time, it is worth paying attention to TCT technologies in connection with the following technological capabilities: simplicity of processing methods; the ability to coat products of complex shapes; a high degree of compatibility of the coating and the material being coated; ensuring a smooth gradient of concentration and properties from the coating to the material being coated [16–17]. Among the promising TCT technologies, diffusion alloying from the medium of low-melting liquid metal solutions (DALMMS) stands out. The technology is based on the phenomenon of isothermal mass transfer of coating elements in a medium of low-melting metals [18–19]. The melt of low-melting metal acts as a transport medium for bringing the diffusant to the coated product’s surface. Simultaneously, the melt elements are unable to diffuse into the specimen being coated. Isothermal mass transfer of a diffusing element consists of the following elementary processes: dissolution of diffusing elements in the melt; its diffusion to the coating material in the liquid phase; adsorption on the surface; diffusion in the solid phase. Based on previous studies, it is worth noting that an important factor influencing the formation of a coating is the elemental composition of the materials being coated. The microstructure of the specimens has less influence on the formation process due to the fact that the DALMMS technology is characterized by high temperatures (900–1,100 °C) and duration (60–600 minutes), which causes phase transformations to occur in the specimen, bringing the structure to an equilibrium state. The formation of coatings based on two-component diffusion saturation with nickel and chromium using DALMMS technology has not been extensively studied. Previous studies indicate that coatings were formed on materials like Armco, Steel 10, Cr6WV, 12Cr18Ni10Ti [20, 21]. The purpose of this work is to identify the features of the coatings formation with simultaneous diffusion saturation of nickel and chromium structural steels using the DALMMS technology. The research objectives are as follows: 1) to identify the influence of the elemental composition of steels on the structure of the surface layers of the coated specimens after DALMMS process. 2) to identify the influence of the elemental composition of steels on the microhardness of the coatings obtained. 3) to identify the influence of the elemental composition of steels on the concentration distribution of coating elements. Methods Cylindrical specimens with a diameter of 20 mm and a length of 30 mm were subjected to DALMMS. The composition of the steels is shown in table. These steels were selected due to the possibility of detecting the influence of carbon and other alloying elements (in particular, chromium, nickel) on the DALMMS process. The DALMMS was carried out in a facility developed by our team, in a Pb-Li eutectic melt. Chromium powder (5 wt. %) and nickel powder (10 wt. %) were added to the melt [20]. The coated products were kept
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