Abstract—The methods of modern physical materials science are used to study the defective substructure of lamellar pearlite and the properties of rail steel subjected to fracture under uniaxial tension. The ultimate tensile strength is found to be 1247–1335 MPa, and the relative strain to failure is 0.22–0.26. Three zones of fracture surface, i.e., fibrous, radial, and shear zones, are revealed. The deformation of rail steel is accompanied by the destruction of cementite plates in pearlite colonies and the repeated precipitation of tertiary cementite particles ≈8.3 nm in size in the volume of ferrite plates. The scalar dislocation density in ferrite increases from 3.2 × 1010 cm–2 in the initial state to 7.9 × 1010 cm–2 after fracture. Ferrite and cementite plates are fragmented. The average cementite fragment size is ≈9.3 nm.

From the accumulated data on the structure, properties, stability, methods for obtaining high-entropy alloys (HEAs), created at the beginning of the 21st century, a whole range of useful properties were discovered, which allows for promising usages in various industries. A brief review of the literature from the last five years on the analysis of using HEAs in specific knowledge-intensive industries is carried out. In biomedicine, protective coatings made of HEAs (TiZrNbHfTa)N and (TiZrNbHfTa)O possess biocompatibility, a high level of mechanical properties, high wear and corrosion resistance in physiological environments, and excellent adhesion. (MoTa) x NbTiZr products have successfully passed clinical trials when implanted in living muscle tissue. The developed HEAs based on rare earth elements and metals of the Fe group of the YbTbDyAl Me type ( Me = Fe, Co, Ni) have a magnetocaloric effect, have the Curie point close to room temperature, and can be used in modern refrigeration devices. By changing the stoichiometric composition of the CoCrFeNiTi HES, alloying them and conducting heat treatment, it is possible to obtain soft magnetic materials. The application fields of HEAs as catalysts for ammonia oxidation (PtPdRhRuCe), decomposition of ammonia (RuRhCoNiIr), oxidation of aromatic alcohols (Co 0.2 Ni 0.2 Cu 0.2 Mg 0.2 Zn 0.2 ), electrocatalysts for the evolution of hydrogen (Ni 20 Fe 20 Mo 10 Cr 15 CutPi, redox reactions (AlCuNiPtMn and AlNiCuPtPdAu), and methanol/ethanol oxidation are considered. HEAs can be used as electrodes-anodes and cathodes for Li-ion and Na-ion batteries. Synthesized nanoporous AlCoCrFeNi HES have a high bulk density (up to 700 F/cm 3 ) and cyclic stability (>3000 cycles) and are used in supercapacitors. High-entropy oxides of the (MgNiCoCuZn) 0.9 5Li 0.05 O type with high dielectric properties in a wide frequency range can be used in electronic converters. Examples of HEAs application as coatings for parts of watercrafts operating in sea water, dissimilar welded joints—parts of nuclear reactors—are given. Prospects for expanding the areas of HEAs application are noted.

In the past decade the attention of scientists in the field of physical materials science is attracted to studying the high-entropy alloys. By the technology of wire-arc additive manufacturing (WAAM) a high-entropy alloy (HEA) of a nonequiatomic composition was obtained. Deformation curves obtained under uniaxial tension at a rate of 1.2 mm/min at room temperature using Instron 3369 unit were analyzed in two states: initial/after fabrication and after electron-beam treatment (EBT). EBT was conducted to detect its influence on structural-phase states and mechanical properties. The EBP leads to a decrease in strength and plastic properties of the HEA. By means of scanning electron microscope LEO EVO 50, analysis of structure of fracture surface and the near-surface zone was performed. Dependences of the ultimate strength and relative elongation to failure on EBT parameters were revealed, and it was shown that values of strength and plasticity decrease nonmonotonically with an increase in electron beam energy density in the range ES = 10 – 30 J/cm2 at constant values of duration, frequency, and number of pulses. Along with a pit character of the fracture a presence of micropores and microlayering was detected. Investigation of the HEA’s fracture surface after EBP except for areas with a ductile fracture mechanism revealed the regions with a band (lamellar) structure. At ES = 10 J/cm2, the area of such structure is 25 %; it increases nonmonotonically to 65 % at ES = 30 J/cm2. The diameter of pits of detachment in fracture bands varies in the limits of 0.1 – 0.2 μm, which is considerably less than that in the remainder of the HEA samples. After EBP the thickness of the molten layer varies in the limits of 0.8 – 5.0 μm and grows with an increase in the energy density of electron beam. EBT leads to generation of crystallization cells, the sizes of which change within the range 310 – 800 nm as ES increases from 15 to 30 J/cm2. It is suggested that the defects being formed in surface layers in ЕВР may be the reason for decreasing the HEA’s maximum values of strength and plasticity.

The high-entropy alloy (HEA) of Al - Co - Cr - Fe - Ni system of nonequiatomic composition is obtained by the technology of wire-arc additive manufacturing (WAAM) in atmosphere of pure nitrogen. By the methods of modern physical materials science it is shown that in the initial state the alloy has dendritic structure indicating nonhomogeneous distribution of alloying elements. It is a multiphase material whose main phases are Al3NCr3C2 , (Ni, Co)3Al4 . Nonadimensional particles (Ni, Co)3Al4 of cubic shape are located along interfaces of submicron phases Al3Ni and Cr3C2 . The HEA irradiation by pulsed electron beams with energy density Es = 10 + 30 J/cm2, pulse duration of 50 is, frequency of 3 Hz and pulse number of 3 leads to high-velocity melting and subsequent crystallization of surface layer. If Es = 10 J/cm2, no failure of dendritic crystallization structure happens. Interdendritic spaces are enriched in chemical elements Al, Ni and Fe, and dendrites themselves - in chromium atoms. The most liquating element of the alloy is Al, the least one is Co. If Es = 20 J/cm2, a nanocrystalline structure is formed in the layer 15 inn thick in bulk of grains. Size of crystallization cells amounts to 100 - 200 nm, size of inclusions in cell junctions is 20 - 25 nm, and along cell boundaries it is 10 - 15 nm. Cells of high-velocity crystallization are enriched in Al and Ni. The Co atoms are homogeneously distributed along the surface layer volume. The most liquating element is Cr, the least liquating one is Co. The increase in energy density of electron beam to 30 J/cm2 doesn't lead to substantial (as compared to Es = 20 J/cm2 ) variations in surface layer structure. The irradiation mode (Es = 20 J/cm2, 50 is, 3 pulses, 0.3 Hz) is detected that allows formation of the surface layer with the highest level of homogeneity of chemical element distribution in the alloy.

Surface treatment by an electron beam is a method of improving the mechanical properties of metals. Rapid heating, vaporization, recrystallization, and plastic deformation in the surface produce dislocations with high density. That results in increase in physicomechanical properties such as the hardness and wear resistance. Since high-entropy alloys are a relatively new class of materials, the influence of a high-intensity pulsed electron beam on the dislocational structure has yet to be established. In the present work, a nonequiatomic high-entropy Co–Cr–Fe–Mn–Ni alloy produced by additive wire-arc technology undergoes surface treatment using a high-intensity pulsed electron beam (energy density 30 J/cm2). Investigation of thin foil by means of a transmission electron microscope indicates that this treatment has no effect on the chemical composition of the alloy. However, the dislocational substructure is profoundly changed. The scalar dislocation density varies nonmonotonically, reaching a maximum of 5.5 × 1010 cm–2 at a distance of 25 μm from the irradiated surface. At this distance, a somewhat oriented cellular dislocation substructure (cell size 400–600 nm) is formed. At greater distances from the surface (up to 45 μm), the dislocation substructure changes from cellular to cellular–reticular. At a distance of 120–130 μm, no effect of the electron beam is seen: the substructure corresponds to that of the initial alloy with a chaotic distribution of the dislocations.

High-current pulsed electron beam surface treatment is a method of materials modifying, which improves the mechanical properties of metal materials. Due to high-speed heating, evaporation, recrystallization, as well as plastic deformation, dislocations with high density are formed in the surface and, as a result, an increase in indicators of various physical and mechanical properties, such as hardness, wear resistance, etc., is observed. Since currently high-entropy alloys are a relatively new class of materials, the effect of pulsed electron beam treatment on the dislocation substructure has not yet been established. In this work, a non-equiatomic high–entropy alloy of the Co – Cr – Fe – Mn – Ni system, made using a wire-arc additive manufacturing, was subjected to surface treatment using a high-current pulsed electron beam with an energy density of 30 J/cm2. By the method of studying thin foils using transmission electron microscopy, it was found that the treatment does not affect the chemical composition of the alloy, but leads to serious changes in the dislocation substructure. A nonmonotonic change in the scalar density of dislocations was revealed, reaching a maximum value of 5.5·1010 cm–2 at a distance of 25 µm from the irradiation surface. It is shown that an undirected cellular dislocation substructure with cell sizes from 400 nm to 600 nm is formed at this distance from the surface. With further distance from the surface at a distance of up to 45 µm, the dislocation substructure changes from cellular to cellular-mesh. At a distance of 120 – 130 µm, the effect of a high-current pulsed electron beam is not observed – the substructure corresponds to the substructure of the initial alloy with a chaotic distribution of dislocations.

A coating of high-entropy Cantor alloy FeCoCrNiMn of nonequiatomic composition was formed on a 5083 aluminum alloy substrate by wire-arc additive manufacturing (WAAM). The methods of physical materials science were applied to analyze the structure, elemental composition, microhardness, and wear resistance of the coating–substrate system. The deposition of the FeCoCrNiMn high-entropy coating on the 5083 alloy surface is accompanied by the formation of microhardness and elemental composition gradients. Microcracks and micropores were revealed in the cross section of the coating. Microhardness in the volume of the coating is 2.5–3.5 GPa and increases to 9.9 GPa at the boundary with the substrate. In the middle part of the coating, the wear factor is 2.3 × 10–4 mm3/N m; the friction coefficient is 0.7. A transition layer up to 450 µm thick is formed at the interface between the coating and the substrate. We analyzed the elemental composition gradient of the transition layer and noted a high level of chemical homogeneity of the coating. The found doping of the coating with substrate elements (aluminum) leads to the formation of a FeC-oCrNiMnAl high-entropy coating, causing a lamellar structure at the interface between the transition layer and the substrate.

The article considers a brief review of the last years of Russian and foreign research on the possibilities of improving mechanical properties of the Cantor quinary high­entropy alloy (HEA) with different phase composition in wide temperature range. The alloy, one of the frst created equimolar HEAs with FCC structure, needs mechanical properties improvement in accordance with possible felds of application in spite of its high impact toughness and increased creep resistance. It has been noted that bimodal distribution of the grains by sizes under severe plastic torsional strain at high pressure of 7.8 GPa of cast alloy and subsequent short­time annealing at 873 and 973 K can change strength and plastic properties. Nanodimensional scale of the grains surrounded by amorphous envelope has been obtained for HEA produced by the method of magnetron sputtering and subsequent annealing at 573 K. In such a two­phase alloy nanohardness amounted to 9.44 GPa and elasticity modulus – to 183 GPa. Using plasticity effect induced by phase transformation in (CrMnFeCoNi)50Fe50 alloy obtained by the method of laser additive technology the ultimate strength of 415 – 470 MPa has been reached at high level of plasticity up to 77 %. It has been ensured by FCC → BCC diffusionless transformation. It is shown that difference in mechanisms of plastic strain of cast alloy at 77 K and 293 K (dislocation glide and twinning) determines a combination of increased “strength­plasticity” properties. Samples for generation of twins prestrained at 77 K exhibit increased strength and plasticity under subsequent loading at 293 K in comparison with the unstrained ones. For HEA obtained by laser additive technology this way of increasing properties is also true. The way of improving mechanical properties at the expense of electron beam processing is noted. The attention is paid to the necessity of taking into account the role of entropy, crystal lattice distortions, short­range order, weak diffusion and “cocktail” effect in the analysis of mechanical properties.

Methods of modern material physics were used for the formation and evolution of the structural and phase state during electron-beam treatment and multiple-cycle fatigue in 20Cr23Ni18 stainless steel. Patterns of the structure, phase composition, and defective substructure of 20Cr23Ni18 austenite steel at the multicycle failure load were determined as well as the gradient character of evolution of the structural and phase states and defective substructure of steel irradiated by electron beams under different conditions.

The number of cycles to failure for 08X18H10T, 20X23H18, 2X13, and Э76Ф steel and Silumin (Al–12% Si alloy) may be increased by a factor of 3.5 by electron-beam treatment with the following parameters: energy density of the electron beam 10–40 J/cm2; pulse length 50–150 µs; 3–5 pulses; and pulse frequency 0.3 s–1. By scanning and transmission electron-diffraction microscopy, the structure and phase states and defect substructure of these materials may be investigated. The increase in the fatigue life of the steel is due to the transformation of the surface structure of the material under the action of the intense pulsed electron beam. In physical terms, the influence of the multilevel structure and phase state on the mechanical properties of the surface layer indicates redistribution of the elastic energy both on account of the interaction of the elastic fields of structural elements at different scale levels and on account of the reduction of the scale level corresponding to localization of the plastic deformation.

The electron-beam treatment of different classes of steels (Fe– 0.1C–18Cr–10Ni–1Ti, Fe–0.2C–23Cr–18Ni, Fe–0.2C–13Cr, Fe– 0.76C–1V) and silumin (Al – 12 % Si) with the parameters: electron beam energy density 10 – 40 J/cm2, pulse duration 50 – 150 μs, pulse number 3 – 5, frequency 0.3 Hz) leads to the increase of cycle numbers up to the fracture in ~ 3.5 times. The studies of structure-phase states and defect substructure of these materials were carried out using the methods of scanning and transmission electron diffraction microscopy. It was shown that the increase in fatigue life of steel is due to the transformation of the structure of the surface layer of the material occurring during irradiation of samples high-intensity pulsed electron beam. It was suggested that the physical sense of the impact of multi-level structure-phase state on the mechanical properties of the surface layer of the material is in the redistribution of elastic energy as due to the interaction of the elastic fields of structural elements of different scale levels, and by reducing the scale level of plastic strain localization.

The structure, phase composition and dislocation substructure of 20Cr23Ni18 steel subjected to electron-beam treatment and subsequent multicycle fatigue loading until destruction were studied by scanning and transmission electron microscopy. It was shown that electron-beam treatment with an energy density of 20 J/cm2 increases the fatigue durability by a factor of 2.1. The cause of steel fatigue destruction is analyzed and a way of further increasing the fatigue durability is proposed.

The treatment of 20Cr13-grade hardened steel (0.2% C, 13% Cr) with an electron beam whose energy density is 10–30 J/cm 2 results in an increase in the fatigue life by a factor of 1.9. The irradiated surface is investigated by scanning electron microscopy; substantial refinement of the grain structure and a change in the Cr content in the surface layer are revealed.

Optical and scanning and transmission electron microscopy have been used to study structural and phase states of steel 08Kh18N10T failed under fatigue conditions. Structural factors that reduce the fatigue life of a material have been revealed. To increase the fatigue life of the steel, it is recommended to treat the surface of the material by concentrated energy fluxes.

Методами оптической и электронной микроскопии проведены исследования структурно-фазовых состояний стали 08Х18Н10Т, подвергнутой импульсной электронно-пучковой обработке в режиме плавления поверхностного слоя. Выявлено закономерное изменение фазового состава и состояния дефектной субструктуры по мере удаления от поверхности облучения на глубину до 200 мкм.