OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 3 2023 Introduction Intensive wear of parts operating under friction conditions, at elevated temperatures, and in aggressive medium is one of the problems in the engineering equipment operation. To ensure long-term service, materials used in such conditions should possess high wear resistance, heat resistance, corrosion resistance, and fracture toughness. Conventionally used materials based on metal alloys, ceramics or intermetallic compounds cannot always provide the required level of performance characteristics. A new approach based on the fusion of several elements with a concentration of each equal to 5–35 at. % has been actively explored in the last 15 years [1, 2]. Due to the high configurational entropy, such materials are called highentropy alloys (HEAs). This approach leads to an almost limitless number of possible alloy compositions. It was mentioned in studies [3–6] that HEAs can demonstrate an outstanding combination of physical and mechanical properties, such as high strength at elevated and cryogenic temperatures, high ductility, good corrosion resistance, and wear resistance. At the same time, it should be noted that the НEAs are composed of a large number of expensive elements, which increases the product cost. An effective solution to the problem of cost combined with performance consists in the formation of protective layers on its surfaces with properties comparing favorably with those of the base material. The abovementioned peculiarities of HEAs make these materials promising for the protective coatings formation [7, 8]. Various technologies, such as laser surface coating [9–11], plasma spraying [12, 13], and others [7] can be used to fabricate structural coatings based on high-entropy alloys. In this work, for coating formation, the non-vacuum electron-beam surfacing method [14] was applied, which has previously been successfully used to obtain protective coatings on stainless steels [15, 16], titanium [17], and low-carbon steels [18–20]. The CoCrFeNiMn alloy, also known as the Kantor alloy, is one of the well-studied HEAs [21–26]. This alloy is characterized by high plasticity [27], which is retained both at elevated and cryogenic temperatures, as well as high thermal stability, but low strength characteristics. To improve the mechanical properties of the CoCrFeMnNi alloy, various approaches based on cold plastic deformation [28], thermomechanical treatment, optimization of the elemental composition of the alloy [29], and the appending additional elements, such as aluminum or vanadium [30, 31], can be used. Another approach to improving the properties consists in the formation of alloys or coatings with a composite structure formed of a high-entropy matrix reinforced with ceramic particles. At present, TiC [9, 10, 32], SiC [33], WC [34] carbides, as well as oxides and nitrides [35] are used as reinforcing particles in the published works. In the mentioned studies, it was shown that the formation of a composite structure made it possible to improve effectively the strength and tribological properties of high-entropy alloys. Borides are another type of particles that allow increasing the hardness and wear resistance of materials [36, 37]. However, it should be noted that the effect of boron-containing compounds on the structure and properties of high-entropy alloys has not been studied extensively. The purpose of this work was to study the structure and phase composition of CoCrFeNiMn-based HEA coatings reinforced with CrB particles and to estimate the effect of borides on the wear resistance level of the reinforced layers. Materials and methods The specimens with coatings were produced by non-vacuum electron-beam surfacing with the use of an ELV-6M industrial electron accelerator at the Budker Institute of Nuclear Physics, SB RAS. Steel 20 workpieces with a size of 100×50×10 mm3 were used as the base material. The coatings were formed from a powder mixture consisting of metal powders (Co, Cr, Ni, Mn), chromium boride powder, and flux powder. CaF2 was used as a flux to protect the melt pool from interaction with the atmosphere. Commercially pure metal powders were preliminarily mixed by an equiatomic ratio. To obtain a series of experimental specimens, mixtures were prepared with different mass ratios of the CoCrNiMn composition of metal powders to a CrB powder (100:0, 95:5, 90:10, 80:20, 70:30). The mass ratio of the surfacing powders and the flux was constant (7:3). It should be noted that an iron powder was not added to the mixture composition
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