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This work presents the research results of the impact of plasma electrolyte hardening (PEH) on the structure and properties of structural 40HN and 20H2N4A steels. Thermal surface hardening of steel parts is one of the most effective and efficient ways to increase the service life of loaded elements of machines and mechanisms, also to reduce their material consumption. In this case, only the most loaded working surface of the part is strengthened, leaving the core intact. The PEH process was carried out in an electrolyte from an aqueous solution containing 20% ​​sodium carbonate and 10% urea. It has been established that a modified layer after PEH is formed with a thickness of 0.5-0.7 mm which consist of a hardened layer of fine-grained martensite and an intermediate layer of perlite and martensite. Microhardness increases by 2 times, wear resistance increases by 3 times after PEH. The conducted research showed the promise and feasibility of using the developed method to improve the operational properties of parts operating under friction and wear. This method, which consists in heating the part for 2 s, is recommended for hardening gears made of 40HN and 20H2N4A steels without additional heat treatment. PEH ensures the achievement of a technical and economic effect due to the use of simple equipment, not expensive aqueous solutions, reduction of processing time, and also as a result of increased wear resistance and microhardness of steels.

The features of the formation of low-temperature plasma and its interaction with a metal surface were studied in this work. A qualitative model of the interaction of low-temperature plasma with the steel surface during nitriding has been developed by summarizing the available research results and taking into account the specific features of the electrolyte plasma process. In accordance with this model, in the first moments of the interaction of low-temperature plasma with the steel surface in the near-surface layer, which accelerated formation of the Feα(N) solid solution occurs due to the action of directed bombardment of charged particles, which enhances the adsorption and diffusion of nitrogen into the interior of the material, then dispersed particles of nitride of alloying elements are formed as further saturation in places with an increased level of free energy (at lattice defects, at grain boundaries, etc.). Subsequently, transformations occur in the surface zone of the layer when the limiting solubility of nitrogen in iron is exceeded, which leading to the formation of nitrides of the γ′-phase (Fe4N) and ε-phase (Fe2–3N) in it. Thus, electrolyte plasma nitriding opens up many new possibilities, in particular: varying the nitriding temperature over a wide range (400–700 ºC), targeted production of a nitrided layer consisting only of a diffusion layer without a layer of compounds, while obtaining a diffusion layer with particles γ’-phase (Fe4N) of plate form and with finely dispersed nitrides MN (CrN). The use of an electric discharge in an electrolyte (low-temperature plasma) makes it possible to increase the heating rate and diffusion saturation of the material surface. This work is of practical importance, since the studied method of electrolytic-plasma nitriding makes it possible to obtain a modified surface layer on steels with high physical and mechanical properties.

This work presents the results of the study of tribological and corrosion properties of powder coatings based on VN, TiN, SiC and Cr2N obtained by mechanochemical synthesis on the surface of steel balls ShKh15. The idea of this method is using the impact energy of moving balls to apply coatings on metal surfaces. Based on the conducted research, it was proved using the method of mechanochemical synthesis possible to obtain a coating of VN, TiN, SiC, and Cr2N on the surface of steel balls. The optimal parameters for coating were chosen: amplitude of the oscillation 3.5 mm; frequency of the oscillation 50 Hz; volume of filling of the chamber 50 %, the diameter of the ball 6 mm; ratio mass of the powder to the mass of the balls mp:mb=1:30, processing time by mechanochemical synthesis is 1 hour. It is established that the change in the haracteristics of coatings directly depends on the stiffness and physical and mechanical properties of the source material (substrate) and surface roughness. The results of the tribological study showed that a wear-resistant coating was formed on the surface of the steel balls.

The results of experimental studies of changes in the structure, microhardness, and wear resistance of the AMG6 aluminum alloy during equal channel angular pressing (ECAP) are presented in this work. The evolution of the fine structure and the formation of secondary phases in the AMG6 alloy during ECAP were studied. The dark-field image of the structure of the AMg6 alloy in the matrix reflex showed the splitting of the material into small disoriented fragments of about 0.5 μm in size with a small-angle disorientation boundary (about 2–5°). Optimal method and modes of ECAP of the AMG6 aluminum alloy were selected of the bases of experimental research, which make it possible to obtain a workpiece with enhanced tribological and mechanical characteristics. It was established that the most intensive grinding of the grain structure in the AMG6 alloy occurs at ECAP-12 at a channel angle intersection of 120°. It is shown that with a decrease in grain size, the microhardness of the alloy AMG6 after ECAP increases by 4 times, compared with the initial state.The results of the test samples for abrasive wear showed a decrease in mass loss after 12 passes of ECAP, which indicates an increase in the wear resistance of the alloy AMG6 by 13–14 %, compared with the initial state.

The paper presents research into the surface morphology, helium cluster formation and mechanical properties of high-purity tungsten after the high fluence and low-energy helium ion implantation and subsequent annealing. Investigations are based on scanning electron and atomic force microscopy observations and thermal desorption measurements. Because of the local stresses appearing within the energy loss straggling of helium ions, atoms migrate at distances significantly increasing the ion projective range, and create mobile coalescence of helium atoms and immobile helium-vacancy clusters. The latter form helium bubbles in the energy loss straggling which cause the surface blistering. Local stresses induced by helium coalescence and helium-vacancy clusters beyond the energy loss straggling result in the material strengthening or hardness increase. Subsequent 600°С annealing provides the size growth of blisters on the metal surface irradiated with helium ions and high helium desorption due to the migration of mobile coalescence of helium atoms. With the increasing annealing temperature from 600 to 1000°С, the layer corresponding to the projective range of helium ions fully fractures due to the interstitial helium atoms releasing from immobile helium-vacancy clusters. After 1000°С annealing, the tungsten hardness returns to its initial value.

The paper presents results of material testing of the full-scale corium (melt of fuel and structural materials of the reactor core), obtained in the in-pile experimental device. Tests were carried out in the research reactor IGR (Impulse Graphite Reactor) at simulation of the final stage of severe accident of the fast power reactor with sodium coolant. The investigations include metallographic analysis of structure condition of corium ingot fragments. They are partly supplemented by the results of X-ray phase analysis of the powders made from those fragments.