OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 2 2023 solution to this problem is the modification of the working surfaces of steel parts can be used to increase its wear resistance and corrosion resistance, which will increase its service life [1, 2]. In addition, the formation of thin coatings saves a permissible level of ductility of the components. Steel components with cermet coatings based on tungsten carbide (WC) are often used in industries such as oil, aerospace, metallurgical, chemical, and machine building due to its high hardness, wear resistance, and corrosion resistance [3–6]. The main technologies for these materials’ production are HVOF and APS [7–11]. Due to its high hardness and brittleness, WC particles are usually deposited together with a metal binder to form composite coatings. Such coatings combine high ductility, impact strength, and technological effectiveness of the binder (Co, Ni, Ti, Fe, Cu, and others) and high wear and corrosion resistance of ceramics [12, 13]. The change the spraying modes or the characteristics of the sprayed powder allows control the structure, phase composition, and also the properties of the coatings. The authors of [14] established the dependence of the porosity and corrosion resistance of 88% WC-12% Co HVOF coatings on the heating temperature of particles in a carrier gas jet. A higher heating temperature contributed to the formation of an amorphous structure in the coatings and an increase in corrosion resistance. The authors of [15] showed that the change of HVOF modes affect the phase composition, porosity, and hardness of 88% WC-12% Co coatings and allow controlling its tribological characteristics. It is stated in [16–18] that the use of nanostructured WC-Co powder makes it possible to significantly increase the hardness, wear resistance, and corrosion resistance compared to coatings obtained from micron-sized WC-Co powders. The paper [7] shows that the use of pore-free ultrafine-grained WC-Co powder made it possible to obtain coatings consisting only of WC and an amorphous and nanocrystalline Co matrix. Its wear resistance was 4 times higher than that of coatings obtained from a coarser powder. On the other hand, the authors of [19, 20] demonstrated that when deposited by gas-thermal methods, most of the nanosized WC powder has time to decompose in the spray jet, which, in turn, leads to a decrease in the wear resistance of the formed coatings. The paper [5] shows that the composition of the Ar/He or Ar/H2 plasma-forming gas has an influence on wear resistance more than the size of the sprayed particles. For example, the Ar/He plasma jet (with a lower operating temperature) reduced the degree of decarburization of the WC particles and thus increases its volume fraction in the coating. Since the coatings sprayed with Ar/He jet had a higher volume fraction of WC particles, it was characterized by higher values of hardness, wear resistance, and also toughness. The authors also reported that during Ar/He plasma spraying with a jet, coatings made of nanosized powder, rather than made of micron powder, had greater wear resistance. Sum up, the following conclusion can be drawn: nowadays, HVOF and APS methods for obtaining cermet coatings have been investigated in sufficient detail. It is shown that after the development of the technology of deposition of a particular powder, it is possible to clearly control the properties of the resulting coatings. This paper presents the results of studying the effect of HV-APS modes using air as a plasmaforming gas on the structure, phase composition, and properties of WC-Co coatings. Method of experiment A commercial granulated 86% WC-10% Co-4% Cr powder with a dispersion of 15–38 µm was used for the coatings spraying. HV-APS was performed using an electric arc plasma torch PNK-50 developed by the Institute of Theoretical and Applied Mechanics of the Siberian Branch of the Russian Academy of Sciences. Cylindrical substrates for spraying with a diameter of 20 mm and a height of 7.5 mm were prepared from a commercial low carbon Steel 20 (0.2% C). The cermet coatings were sprayed to the frontal surface of the cylindrical substrates, which was precleared by sandblasting. Table 1 shows HV-APS modes. The variable parameter was the spraying distance – 170 and 250 mm and the arc current – 140, 170 and 200 A. Air with the addition of 4 vol.% methane was used as the plasma-forming, transporting, and focusing gas. Samples for structural studies, as well as measurements of microhardness and porosity, were transverse microsections prepared according to the standardmethod: mechanical grinding using suspensions containing Al2O3 particles of various grain sizes (9, 6, 3 and 1 μm) and finishing polishing on cloth using colloidal
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