OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 1 2023 separately. Chromium is a fairly common metal, has high corrosion resistance, its carbides and nitrides have high microhardness [9–12]. Chromium forms a continuous series of solid solutions with iron and is widely used as an alloying element. In this regard, chromium-based coatings are a fairly common choice for improving the resistance of machine parts to mechanochemical wear. To apply such coatings, hardening methods such as cladding, flame spraying, electroplating, thermochemical treatment (TCT), etc. are used [13–15]. One of the simplest from a technological point of view, industrially implemented and scalable, cost-effective technologies are thermochemical treatment ones. Amethod of thermodiffusion chromizing is known, when the surface of a part is coated with a chromiumcontaining saturating mixture, and then a coated part is subjected to a soaking at 1,000–1.100 °C, followed by cleaning. The disadvantages of this method include a large degree of contamination of the part’s surface with the remnants of the saturating mixture and coatings’ non-uniformity [16]. Also known is a method of diffusion saturation of structural steels with chromium from molten salts. A common disadvantage of this type of coating is its low adhesion (compared to diffusion coatings) to the base material. Especially if there is a need to form a coating based on carbides or nitrides [17]. One of the promising technologies for forming coatings based on chromium is diffusion saturation from liquid metal medium solutions (DSLMMS) [18–19]. The technology involves saturating the part in a medium of low-melting metals, in which diffusible elements are dissolved in a certain proportion. Coatings are formed due to isothermal selective mass transfer of diffusing elements to the part’s surface and subsequent diffusion and/or chemical interaction with the components of the material being coated. Also, in order to obtain the necessary combination of strength, hardness, wear resistance, and corrosion resistance, the technology of complex diffusion alloying (CDA) of parts’ material surface layers, including DSLMMS and carburizing technologies [20], are promising. The purpose of the work is to reveal the effect of steel composition on the process of formation and elemental composition of diffusion-saturated surface layers (coatings) based on chromium, as well as to establish differences and regularities in the processes of formation of diffusion-saturated coatings after DSLMMS and CDS. Methods Experimental studies were carried out, including the combination of DSLMMS with TCT technologies, to achieve the purpose. Cylindrical specimens with a diameter of 20 mm and a length of 30 mm subjected to DSLMMS. The specimens were made of carbon and alloy steels: low-carbon St3, 20-Cr13, mediumcarbon 40-Cr, 40-Cr13, and austenitic 12-Cr18-Ni10-Ti. Some of the specimens were previously subjected to vacuum carburization. The coatings were deposited by diffusion alloying using the originally developed DSLMMS technology. The process was carried out in an inert medium (argon). DSLMMS is based on the phenomenon of isothermal, selective transfer of coating elements, dissolved in a fusible melt, to the surface of the part, followed by diffusion interaction of the coating elements with the main material of the part. DSLMMS with chromium was carried out at a temperature of 1,025 °C; the soaking time was 5 hours. Iead-bismuth eutectic melt was used as a technological medium (transport melt). Chromiumwas supplied in a given amount into the transport melt. DSLMMS was carried out in a device, designed, produced and patented by us. This device provides the possibility of applying coatings in an open bath with a fusible liquid-metal solution in a cyclic mode, and combines the process of DSLMMS with heat treatment. Before DSLMMS some specimens were subjected to preparatory vacuum carburization at 950 °C during 5 hours. Studies to determine the thickness of coatings and its structure were carried out on the Dura Scan Falcon 500 Microhardness Tester. The elemental composition of the coatings was determined by the method of electron microprobe analysis on a Tescan Lyra 3 scanning electron microscope with the Oxford Ultim MAX PCMA system.
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