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Currently, scientists search for new materials for temporary implants that can dissolve in the body, which leads to the fact that there is no need for repeated surgery. In the last decade, scientific interest has focused on zinc-based materials because, unlike other metals, it has suitable corrosion rates and good biocompatibility. The paper describes an experiment for the study of the influence of deformation on the microstructure, strength and corrosion properties of an alloy of the Zn–Fe–Mg system. The authors carried out energy dispersive analysis and calculation of the volume fraction of the second phase of the Zn–Fe–Mg zinc alloy. The corrosion properties of the Zn–Fe–Mg zinc alloy with different microstructures (before and after high-pressure torsion) were studied using the gravimetric method under conditions simulating conditions inside a living organism (temperature, corrosive environment composition). During the tests, the corrosion mechanism was determined, its rate and mass loss of the samples were calculated. The relief of the corrosion surface was studied using scanning electron microscopy. It has been found that the destruction of the material in a corrosive environment occurs through a matrix containing the active Mg metal. The results of calculations of the corrosion rate for the original sample and samples subjected to high-pressure torsion differed due to a more even distribution of second phase particles during severe plastic deformation. In this work, by alloying zinc with iron and magnesium, as well as using high-pressure torsion, it was possible to increase the microhardness of the samples to 239.6±8 HV, which is a high indicator for zinc alloys.

In recent years, the range of silicon-containing steels subjected to hot galvanizing has been expanding. Alloying of steel with 0.5–1 % of silicon leads to the formation of a zinc coating of great thickness with a matte or multi-colored surface. This is associated with the changes in phase reactions between iron and zinc in the Fe–Zn–Si system. The development of ways to neutralize the negative influence of silicon on the formation of zinc coating is an urgent task. The purpose of the work is to study the influence of preliminary plasma cutting and plasma surface hardening of 09G2S (S355J2) steel on the thickness and structure of zinc coating formed on treated surfaces. It was found that after plasma cutting, the structure of the surface layer of steel is martensite, and after plasma surface hardening, it is martensite and ferrite. Analysis of the change in microhardness from the steel surface to the middle showed that the hardened layer depth is 400 μm. A zinc coating consisting of a δ-phase and a ζ-phase is formed on the surface of the steel without pretreatment. On the surface of the steel after plasma treatment, a zinc coating is formed characteristic of low-silicon steels and consisting of the δ-phase, ζ-phase, and η-phase. It was found that the thickness of the zinc coating on the surface after plasma cutting is two times less than on the untreated surface, and the reduction in the coating thickness occurs due to a decrease in the ζ-phase thickness. A hypothesis was suggested that the martensite formation on the steel surface leads to the disappearance of the ordered FeSi phase and changes the phase equilibrium in the Fe–Zn–Si system. Consequently, preliminary plasma treatment of the steel surface allows controlling the structure and thickness of the resulting zinc coating and is therefore recommended for introduction into the hot galvanizing process of silicon-containing steels.

High-chromium martensitic steels are a promising material for the production of elements of boilers and steam pipelines, as well as blades and rotors of steam turbines for new coal-burning thermal generating units. The use of such materials will give an opportunity for the transition to ultra-supercritical steam parameters (temperature of 600–620 °C and pressure of 25–30 MPa), which will allow increasing the efficiency of generating units to 45 %. Modifications of the chemical composition of high-chromium steels have led to significant improvements of high-temperature properties such as 100,000 h creep strength and 1 % creep limit, while resistance to softening due to low-cycle fatigue remains understudied in this field. This work covers the study of low-cycle fatigue at room temperature with different amplitudes of deformation of martensitic high-chromium 10%Cr–3%Co–2%W–0.5%Mo–0.2%Cu–0.2%Re–0.003%N–0.01%B steel. The steel was pre-subjected to normalizing at 1050 °С followed by tempering at 770 °С. After heat treatment, the steel structure was a tempered martensitic lath structure stabilised by the particles of secondary phases of M23C6 carbides, NbX carbonitrides, and M6C carbides. The average width of martensite laths was 380 nm, and the dislocation density was 1.4×1014 m−2. At low-cycle fatigue, with an increase in the strain amplitude from 0.2 to 1 %, the number of cycles before failure significantly decreases, and the value of plastic deformation in the middle of the number of loading cycles significantly increases. Maximum softening (18 %) is observed at a strain amplitude of 1 % in the middle of the number of loading cycles. In general, the steel structure after low-cycle fatigue tests does not undergo significant changes: the width of the laths increases by 18 % at a strain amplitude of more than 0.3 %, while the dislocation density remains at a rather high level (about 1014 m−2) at all strain amplitudes.

One of the important parameters influencing the formation of a weld during friction stir welding is the tool geometry, which affects the processes of heat generation and stirring of metals in their connection zone. These processes influence the formation of a high quality and strength welded joint without continuity defects. In this regard, it is relevant to analyze the influence of tool geometry on the welding mode parameters, at which the welded joint is formed without continuity defects, as well as on the welded joint strength under static tension. The work considers the influence of the cylindrical and conical shapes of the tool pin, as well as the conical shape of the pin with a thread on its outer surface and a spiral groove on the end surface of the tool shoulder on the welding mode parameters, at which the welded joint is formed without continuity defects. The study shows that changing the shape of the pin working surface from cylindrical to a conical one had no effect on the range of welding mode parameters, at which the welded joint is formed without continuity defects. It has been found that the presence of a thread on the pin outer surface and a groove on the end surface of a tool shoulder allows producing welded joints without continuity defects in a wider range of welding mode parameters compared to a simpler tool geometry. The macrostructure of the resulting welded joints was considered. It has been found that the studied tool geometry has almost no influence on the maximum strength values of welded joints produced by friction stir welding and reaches 95 % of the strength of the base metal.

Currently, step quenching of steels in the temperature range of martensitic transformation, including quenching – partitioning, has found wide application in the automotive industry. Step quenching technology is successfully used to increase a set of properties, which most often include temporary tensile strength and relative elongation. The authors carried out a dilatometric study of the supercooled austenite transformations occurring in the 20Cr2Mn2SiNiMo steel, when implementing various options of step quenching with holding in the martensitic region. It was found that after single-stage quenching, single-stage quenching followed by tempering, and two-stage quenching, primary martensite, isothermal bainite, and secondary martensite are formed in various quantitative ratios. Using X-ray diffraction phase analysis, the amount of residual austenite was determined during step quenching. It has been shown that two-stage quenching makes it possible to stabilise up to 14 % of residual austenite, in the structure of the studied steel, at room temperature. Research has revealed that 20Cr2Mn2SiNiMo steel is characterised by a decrease in the crystal lattice parameter of the residual austenite, with an increase in its content in the steel structure. Uniaxial tensile and impact bending tests were carried out, and the values of the mechanical properties were determined. It has been found that during two-stage quenching, higher strength and elongation values, with lower values of relative contraction and impact strength are achieved compared to oil quenching and low-temperature tempering. The study showed that, with regard to the structural reliability of machine-building parts, step quenching is not the optimal heat treatment mode for the steel under study. The best combination of strength, ductility and impact hardness is achieved after quenching and low-temperature tempering.

Nickel coatings consisting of oriented structures have unique catalytic properties. However, the temperature range for the use of such coatings is not determined, and a comprehensive study of their thermal properties in aggressive environments is required. This work studied the influence of the characteristics of the habit of nickel crystals on their reactivity with increasing temperature (thermoreactivity). The authors studied nickel coatings produced by electrodeposition with the addition of inhibitory additives, in the form of alkali metal chlorides to the electrolyte. Differential thermal analysis was used to study the reactivity of coatings in temperature fields. Oxygen was used as an aggressive medium. The phase composition of the samples after heating was determined, using a powder X-ray diffractometer. The introduced additives in the form of alkali metal chlorides allowed forming coatings consisting of crystals of a cone-shaped habit. It was found that the introduction of additives, in the form of alkali metal salts into the electrolyte, makes it possible to change the habit of nickel crystals, and increase the surface area of the coating by approximately 10–15 %. The study showed that electrodeposited nickel coatings, consisting of crystals in the form of micro- and nanocones, have (compared to the control coating) a reduced thermoreactivity. Experimental data allowed concluding that a decrease in the intensity of oxidation on the coatings under study, may be associated with the presence of a preferential development of certain crystallographic faces of the crystals, which causes a change in the nature of the nickel-oxygen interaction, and as a consequence, a change in the oxidation intensity.

The modern electrical engineering industry requires cheap and easily reproducible aluminum alloys with advanced mechanical strength and electrical conductivity. This work studies the influence of small (up to 0.3 wt. %) copper additions on the microstructure and physical and mechanical properties, as well as phase transformations in the Al–Fe system alloys with an iron content of 0.5 and 1.7 wt. %, produced by continuous casting into electromagnetic crystallizer. Alloys of the above chemical compositions were produced, and subsequently annealed at 450 °C for 2 h. In all states, the microstructure (via SEM), yield strength, ultimate tensile strength, elongation to failure, and electrical conductivity were studied. It has been shown that copper additions lead to an increase in the strength of both alloys and a slight decrease in their ductility compared to similar materials without copper. An increase in strength and a decrease in ductility due to the copper addition is associated with the formation of more dispersed intermetallic particles in copper-containing Al–Fe system alloys. Additional spheroidizing annealing leads to a decrease in the length of the interphase boundary between the aluminum matrix and iron aluminide particles due to a change in their morphology, which leads to an increase in electrical conductivity. In general, copper-containing alloys showed higher mechanical strength with lower electrical conductivity, as well as higher thermal stability.

The study of the acoustic properties of maraging steels operated under various energy force and temperature actions is a critical task, since it is the method of acoustic structuroscopy that provides the most reliable connection with the structure, stress-strain state and mechanical properties of steels. The paper is devoted to research of the acoustic properties of the 15-5 PH maraging steel samples under various types of heat treatment under the conditions of mechanical tensile and cyclic loads. Samples of the 15-5 PH maraging steel were studied in three structural states: solid solution annealing and subsequent aging at 470 and 565 °C; during tensile tests; during cyclic tension-compression loading. The research used a unique scientific installation “Information-measuring complex for investigation of acoustic properties of materials and products”. It implements the acoustic mirror-shadow multiple reflections method using electromagnetic-acoustic and piezoelectric transducers based on polyvinylidene fluoride film to excite and receive waves and allows determining the velocity of wave propagation with an error of no more than 2 m/s. The acoustic (wave velocity, elastic moduli, electromagnetic-acoustical (EMA) transformation coefficients, acoustic anisotropy coefficients, acoustoelastic coupling coefficients) and electromagnetic (coercive force and electrical conductivity) characteristics of the samples were examined. The samples were studied in the initial state (before loading); stepwise in the process of tensile loads and subsequent unloading; after tensile tests; during cyclic tension-compression loading. It was revealed that the following acoustic parameters of 15-5 PH steel samples are the greatest structural sensitivity to mechanical tensile load and cyclic loading: transverse wave velocity, Poisson’s ratio, double EMA-transformation coefficient, and acoustic anisotropy coefficient.

This study evaluates the use of gingelly oil as an eco-friendly cutting fluid for the turning operation. Experiments were conducted to determine the effect of nose radius, and rake angle on tool wear, surface formation, and cutting force. In addition, different lubrication techniques, such as cutting fluids and bio-oils, were investigated to determine their potential for minimising friction, heat generation, and tool wear during machining. In comparison to dry cutting, and conventional petroleum-based lubricants, the results demonstrate that gingelly oil consistently produces smoother surface finishes, and reduces cutting forces. The relationships between cutting parameters, and surface finish were analysed using statistical modelling, with R-square and p-values used to quantify correlations and predictor significance. The findings highlight the viability of gingelly oil as a cutting fluid and the significance of optimising process parameters for increased machining efficiency.

Friction stir welding is an advanced method of joining various metals and alloys in the aircraft and mechanical engineering industries. This type of welding is used to join materials that are difficult to weld or not weldable by conventional methods. The high-strength D16 aluminum alloy is difficult to weld by fusion, which is associated with the formation of a dendritic structure in the fusion zone leading to a decrease in the mechanical strength of the joint. In the work, the microstructure and microhardness of a welded seam of the D16 aluminum alloy produced by friction stir welding was studied. Using scanning electron microscopy and optical metallography, the authors identified the presence of three zones: the weld core, the thermomechanical impact zone, and the heat effected zone. In the central part of the welded joint (in the core), a laminated onion ring structure was discovered. A change in the chemical composition of the aluminum solid solution was identified in different areas of the weld zones, as well as the presence of a concentration gradient within each zone. In the upper part of the welded seam, the solid solution is silicon-enriched and depleted in copper. Due to the solid solution depletion in alloying elements, the aluminum content in the solid solution in the zone of the welded joint is higher compared to the initial state. The microhardness values in different areas of the welded joint correlate with changes in the chemical composition. In the welded joint zone, a significant decrease in microhardness was found compared to the initial state, and a change in microhardness associated with the chemical composition gradient within each zone was also observed.

The purpose of the work is to study the influence of hafnium additives on the mechanical properties and thermal stability of particles at elevated temperature during heat treatment of aluminum alloys with a high magnesium content. Two modifications of 1570 alloy were chosen for the study: without hafnium content and with its addition of 0.5 % by weight. Both alloys were subjected to homogenizing annealing at a temperature of 440 °C with different exposure modes, which ranged from 2 to 100 h. Microhardness was studied for various heat treatment modes, and the fine microstructure was studied as well using transmission microscopy. As a result, it was possible to identify that during annealing at a short exposure time (2–8 h), the alloy with the hafnium addition has higher microhardness values exceeding those of 1570 alloy by an average of 20 HV units. This is associated with the fact that in 1570 alloy with hafnium additives, during heat treatment, the number of precipitated particles increases while their average size decreases compared to the base alloy. At the same time, in 1570 alloy without hafnium content, when annealed at a temperature of 440 °C, there is no increase in microhardness. This is caused by the fact that in 1570 alloy without hafnium content, when cooled after casting, discontinuous decomposition occurs, which resulted in the fact that most of the scandium precipitates from the supersaturated solid solution in the form of dispersoids. This phenomenon is not observed in the alloy with hafnium additives, which indicates its ability to stop discontinuous decomposition during cooling the ingot after casting.

Biocompatibility makes magnesium alloys attractive functional materials in terms of their use as biodegradable implants. However, the technologies for manufacturing semi-finished products carry a possible diversity of the local strain rate and temperature within a rather wide range, which affects the processed material structure and properties. The purpose of this study is to determine the range of temperatures and resistance to deformation, at which there is no negative effect on the main structural characteristics of the processed material, using the example of a medical purposes alloy of the Mg–Zn–Y alloying system. The authors carried out mechanical tests of a biodegradable Mg–1Zn–2.9Y magnesium alloy at various temperatures and strain rates. The influence of temperatures in the range of 20...400 °C on the structure and properties of the Mg–Zn–Y system alloy is disclosed. Starting from a temperature of 350 °C, the process of dynamic recrystallisation is accompanied both by the complete restoration (return) of the original microstructure and by coarsening of the grain size, which can adversely affect the material functional characteristics. The high thermal stability of the biodegradable Mg–1Zn–2.9Y magnesium alloy is revealed, which probably results from the presence of the LPSO phase in it. The study shows that the deformation process is accompanied by twinning. At a strain rate of 2∙10−2 s−1 over the entire temperature range, the grain size distribution slightly narrows and shifts towards smaller diameters. The application of the obtained results in technological processes for manufacturing medical semi-finished products will help to solve the issue of microstructure instability at the stage of transition from a semi-finished product to a finished product during subsequent thermomechanical treatments.

Unsatisfactory quality of the surface layer of additive products, in particular increased surface roughness, prevents the widespread use of electron beam powder bed fusion (EBPBF). Electrospark treatment (EST) is one of the methods for smoothing and hardening the surface layer. The work shows the possibility of modifying the surface of additive VT6 alloy samples by reactive EST with multicomponent electrodes. For this purpose, the authors used electrodes made of the Fe48Cr15Mo14Y2C15B6 bulk metallic glass forming alloy and the FeCoCrNi2 high-entropy alloy. Based on the results of scanning electron microscopy, it was identified that after EST, both modified layers have a thickness of about 16 μm. X-ray diffraction phase analysis showed that in the case of treatment with an amorphous electrode they contain carboborides of the Ti(B,C) type, and in the case of treatment with a high-entropy electrode – intermetallic of the Ti2(Fe,Ni) type. The modified layers have average hardness values of 19 and 10 GPa and elastic modulus of 234 and 157 GPa, respectively, which significantly exceeds the values of these parameters for the EBPBF-grown VT6 alloy. Electric discharge modification of the surface with multicomponent electrodes led to a decrease in roughness by 8...11 times due to the melting of the protrusions and filling of the dimples with the melt to a depth of more than 50 μm. A comparative analysis of the results of tribological tests showed a change in the wear mechanism as a result of EST of the additive VT6 alloy. Wear resistance increased by 4 and 3 orders of magnitude when using electrodes made of a bulk metallic glass and high-entropy alloy, respectively.

The paper presents the results of the study of the end milling temperature of low-alloy steel depending on the cutting modes and the type of crystalline structure. The experiment was carried out on a PROMA FHV-50PD universal milling machine. The blanks were processed using a 12-12D-30C-75L-4F HRC55 carbide milling cutter. No cooling was used during processing. The obtained data were statistically analyzed to identify the dependence of the end milling temperature of low-alloy steel on the processing modes and the steel crystalline structure. When creating a mathematical model of cutting temperature, the authors carried out a bootstrap analysis to identify the significance of the parameters of the processing modes. The mathematical model was chosen using the Akaike informative criterion. It was found that mathematical models of the temperature dependence on processing modes for both types of crystalline structure include the cutting depth in the second power. At the same time, for steel in an ultrafine-grained state, both the cutting depth and the feed are statistically significant. It was not possible to detect the influence of cutting speed on temperature in the studied range of processing modes. Thus, when milling this group of materials, the force component primarily determined by the cutting depth exerts the predominant influence on the temperature regime. The level of cutting temperature when processing steel in an ultrafine-grained state is generally higher than when processing steel in a coarse-grained state, which should be associated with the increased physical and mechanical properties of steel with an ultrafine-grained crystalline structure.

The scale of heterogeneity of the structures of steels and alloys can be rather large both within one sample and within a product. The procedure adopted in practice for determining the integral values of crack resistance characteristics cannot always reflect this circumstance. In this regard, it is necessary to develop methods for assessing the crack resistance of a medium with a heterogeneous structure. In this work, the authors determined the crack resistance of large forgings made of heat-hardenable 38KhN3MFA-Sh steel (0.38%C–Cr–3%Ni–Mo–V) based on the critical crack opening δс and the J-integral. The presence of critical stages in the development of a ductile crack during testing was assessed by acoustic emission measurements. In combination with the obtained methods of digital fractography of 3D images of fractures, this allowed relating the shape and position of the leading edge of each crack jump to the load-displacement diagram. Measuring the crack opening geometry during the test showed the possibility of determining directly the coefficient of crack face rotation when estimating δс. In general, this allowed constructing a map of the distribution of parameter δс values over the thickness of the sample and estimating the scale of the scatter in crack resistance within one sample – up to 30 %. Such a localization of measurements, primarily of the δc parameter, is comparable to the scale of heterogeneity in the morphology of various types of structures, which was assessed based on the measurement of digital images of the dendritic structure, the Bauman sulfur print, non-metallic inclusions on an unetched section, and ferrite-pearlite banding in the microstructure. This makes it possible to link local crack resistance values to various fracture mechanisms and their accompanying structural components.

A coating based on a single-phase medium-entropy CrFeNi alloy with a face centered cubic structure has good ductility, relatively high anti-corrosion properties, low cost, but insufficient strength for its widespread use. It is assumed that adding strengthening particles in the form of tungsten carbides and borides to the CrFeNi equiatomic coating will lead to an increase in its mechanical properties. This work studies the influence of tungsten carbide and boride additives on the structure and microhardness of a CrFeNi equiatomic coating. The coatings were formed by layer-by-layer short-pulse laser cladding with preplaced powder on a multifunctional laser installation equipped with a solid-state laser with a lamp pump based on an Nd:YAG crystal. The change in phase composition when adding strengthening particles was detected using X-ray diffraction analysis and transmission electron microscopy (TEM). Both methods confirmed the precipitation of Cr23C6 chromium carbide in the deposited coatings. TEM photographs indicate that the precipitated phase is distributed along the grain boundaries of the γ-solid solution. The study found that the addition of 6 wt. % WC and 3 wt. % WB increases the level of microhardness of the CrFeNi coating by 26 % (from 340±6 to 430±12 HV 0.025). This occurs due to the presence of Cr23C6, WC particles in the structure and possible microdistortions of the crystal lattice of the γ-phase as a result of doping with tungsten atoms released during the dissolution of tungsten borides and carbides in the process of high-temperature short-pulse laser heating.

Magnesium alloys are considered promising materials for the production of bioresorbable implants. Their main disadvantages are low strength and corrosion resistance in biological environment. In the work, the authors studied the effect of severe plastic deformation using the equal channel angular pressing (ECAP) method on the structure, mechanical properties, and corrosion resistance of the Mg–8.6Zn–1.2Zr magnesium alloy. It was identified that one ECAP cycle at 400 °C leads to a substantial hardening of the Mg–8.6Zn–1.2Zr alloy by ~10 %, up to 330 MPa. Structural studies showed that dynamic recrystallisation plays a significant role in the structure transformation. ECAP leads to the formation of a bimodal structure with large deformed grains with an average transverse size of 20±4 µm and recrystallised grains with an average transverse size of 6±2 µm. It was found that with a decrease in the strain temperature up to 250 °С, the process of deformation-induced decay of the supersaturated solid solution takes place. Electrical conductivity of a sample after ECAP at 400 °C amounted 29±2 % according to the International Annealed Copper Standard (IACS), while second ECAP cycles lead to an increase in the electrical conductivity up to 32±2 % IACS. Using the electrochemical corrosion method, the authors found that one ECAP cycle at 400 °C leads to a slight decrease in the corrosion resistance of the alloy under study compared to the initial state. The study showed that the corrosion current increases from 24 to 32 µA/cm2, while the subsequent ECAP cycle at 250 °С increases the corrosion current more than twice (up to 57 µA/cm2).

One of the most effective ways to increase the processing plasticity of advanced superalloys (heat-resistant nickel-based alloys) is the formation of an ultrafine-grained (UFG) microstructure in bulk semi-finished products. Such a microstructure is a necessary condition for the manifestation of the structural superplasticity effect in the technological processes of manufacturing products from such superalloys. One of the most promising methods for producing UFG microstructures is thermomechanical treatment (TMT) according to the multiple isothermal forging scheme. It has been shown that the EK79 superalloy after TMT, with a gradual decrease in the processing temperature from 0.88 to 0.62 Ts (where Ts is the strengthening phase dissolution temperature) leads to the transformation of the initial microduplex fine-grained microstructure into a mixed UFG microstructure. Such a mixed UFG microstructure consists of: 1) relatively coarse (inherited from the fine-grain microstructure) particles – γ'-phase with a size of 3.0±0.8 μm; 2) γ-grains, and incoherent γ'-phase particles with a size of 0.3–0.5 μm; 3) strengthening coherent intragranular γ'-phase particles with a size of 0.05–0.1 μm, released upon cooling from the TMT temperature to room temperature. During uniaxial compression tests, the EK79 superalloy with such microstructure, demonstrates low-temperature superplasticity in the temperature range of 800–1000 °C. It has been found that an increase in the deformation temperature up to 1000 °C, leads to the increase of γ-phase grains to micron size. The maintenance of superplastic properties in the presence of relatively coarse incoherent particles in the microstructure of the second phase (γ'-phase) is apparently related to the fact that the deformation is localised in the UFG component.

The experience of many-year research has shown that optimizing the steel chemical composition and microstructural characteristics, as well as reducing its contamination with non-metallic inclusions (NMI), it is possible to significantly increase the corrosion resistance of oilfield pipeline steels and increase the time of their trouble-free operation. The influence of complex NMIs on the steel corrosion resistance is determined by both the chemical composition of NMIs and their quantitative ratios. Therefore, obtaining metal products of the required quality is possible only when using the “control by structure” principle. In the work, based on the analysis of brightness fields of images (on a sample scale) in 256 shades of gray, the authors proposed digital, metrologically supported procedures for measuring the NMI heterogeneity of low-carbon oilfield steels: eliminating the heterogeneity of field illumination, justifying the criteria for binarization and noise filtering. For low-carbon steels of various types of melting, the authors identified the key role of dispersed non-metallic inclusions ranging in size from 5–10 μm2 to 2 nm2 in the formation of the corrosion resistance of steels. This may explain why, in some cases, there is no interrelation between the corrosion rate and the fracture resistance of steels, the formation of which is determined by larger particles. When representing the NMI as a set of random points on the plane, the distribution of distances between the nearest ones is estimated based on Voronoi polyhedra statistics. The study shows that an increase in the kurtosis coefficient of distributions of polyhedra areas is accompanied by an increase in the corrosion rate of the steels under study. This indicates the negative impact of heterogeneity in the arrangement of dispersed NMIs on the corrosion resistance of steels.

Dispersion-strengthened composite materials belong to the group of promising structural materials characterised by a diverse combination of properties. The paper considers examples of the creation and heat treatment of composite materials based on aluminium alloys strengthened by the titanium carbide dispersed phase characterised by high hardness, elastic modulus, and good melt wettability. At present, self-propagating high-temperature synthesis (SHS) is the most accessible, inexpensive and effective way to obtain them. The authors substantiate the expediency and show their successful experience of the formation in the composition of the AMg2 and AMg6 industrial alloys of a titanium carbide dispersed phase with a particle size of 130 nm in an amount of up to 10 wt. % using the SHS method, which makes it possible to increase the hardness of the alloys. Additional heating of the AMg2–10%TiC and AMg6–10%TiC samples after synthesis also contributes to the further increase in hardness. The complex of studies of physical, mechanical and operational characteristics presented in the paper was carried out to compare the properties of the work-hardened matrix alloys and the samples of composite materials before and after heating. The test results showed that heat treatment reduces the porosity of the composites and significantly increases their hardness and microhardness. A slight decrease in compressive strength at a significant increase in wear resistance is observed. It was found that composite materials are characterised by high corrosion resistance to carbon dioxide and hydrogen sulfide corrosion corresponding to the level of matrix alloys. The results obtained allow recommending the developed materials for the production of parts of the connecting rod and piston group, bearings and other wear-resistant parts of friction units.

The Fe–Ga alloy is a promising magnetostrictive material thanks to of the optimal combination of functional properties and relatively low price due to the absence of rare-earth elements in the composition. To obtain the maximum magnetostriction in Fe–Ga polycrystals, it is necessary to create a crystallographic texture with a predominance of the direction, since the tetragonal magnetostriction constant is the largest. Traditional methods of thermomechanical treatment do not lead to the formation of such a texture in a bcc alloy. In this paper, for the first time, the authors propose to use inclined rolling to increase the proportion of favorable texture components. Warm rolling with a deformation degree of 70 % was carried out at angles of 0, 30 and 90° to the direction of hot rolling. The deformation texture was examined using X-ray texture analysis and the texture and structure of the material after recrystallization was analyzed by electron backscatter diffraction (EBSD) on a scanning electron microscope. Quantitative texture analysis was carried out using the orientation distribution function (ODF) method using the ATEX software. The volume fraction of some texture components was calculated. The study shows that a significant change in the deformation textures and primary recrystallization occurs during rolling at an angle of 90°. The sample after such rolling contains the largest amount of the planar component {100}. The study identified a relationship between the texture of deformation and recrystallization in Fe–Ga: to increase the proportion of components with the crystallographic direction during recrystallization, the presence of planar components {111} in the deformation texture is necessary, which is associated with the predominant growth of favorable components in the deformation matrix with such a texture.

Currently, to increase the hardness, strength and wear resistance of thermally non-hardenable austenitic chromium-nickel steels, such methods as frictional treatment with a sliding indenter and liquid carburizing have been used. However, along with an effective increase in mechanical characteristics, the application of these types of treatment may be accompanied by a decrease in the corrosion resistance of austenitic steels. Therefore, it is reasonable to study the influence of frictional treatment and liquid carburizing on the general corrosion resistance of Cr–Ni austenitic steels. In this work, the surface microhardness of the 12Cr18Ni10Ti and AISI 321 steels was determined using the recovered indentation method after electropolishing, mechanical grinding, frictional treatment, and liquid carburizing at a temperature of 780 °C. Using scanning electron microscopy and optical profilometry, the authors studied steel surfaces subjected to the specified types of treatment and determined their roughness. The corrosion resistance of steel was studied by testing for general corrosion using the gravimetric method. When testing for general corrosion, it was found that hardening (up to 710 HV 0.025) frictional treatment leads to an increase in the corrosion rate of the 12Cr18Ni10Ti austenitic steel compared to the electropolished state (from km=0.35 g/(m2•h) to km=0.53–0.54 g/(m2•h)). The corrosion rate of the ground steel is km=0.58 g/(m2∙h), while mechanical grinding does not provide a significant increase in the microhardness of the steel under study (from 220 to 240 HV 0.025). It is shown that the corrosion behavior of 12Cr18Ni10Ti steel subjected to various types of treatment is determined by the following factors: the presence/absence of strain-induced α'-martensite in the structure, the quality of the formed surface and, apparently, the dispersion of the formed structure. Liquid carburizing of the AISI 321 austenitic steel leads simultaneously to an increase in its microhardness to 890 HV 0.025 and a certain increase in corrosion resistance compared to fine mechanical grinding. This is related to the fact that carbon embedding atoms stabilize the electronic structure of iron (austenite and martensite), thereby increasing its corrosion resistance.

Self-propagating high-temperature synthesis (SHS) is one of the promising methods for producing strong and wear-resistant composites. The use of copper as a matrix due to the unique combination of electrical and thermal conductivity is of particular interest. Monolithic SHS composites of the Cu–Ti–C–B and Cu–Ti–C systems are currently little studied. The information on the phase composition of such composites is contradictory, and data on micromechanical properties is practically absent. The paper presents the results of a comparative analysis of the structure and micromechanical properties of composites of the Cu–Ti–C and Cu–Ti–C–B systems. It is found that the matrix of both composites is a copper-based solid solution supersaturated with titanium, in which nanosized Cu4Ti intermetallic compound particles precipitate upon cooling. TiC particles (Cu–Ti–C composite) and TiC and TiB2 particles (Cu–Ti–C–B composite) are the strengthening phases resulting from SHS. In the Cu–Ti–C–B composite, the original particles of unreacted B4C boron carbide were preserved, the microhardness of which was 3680 HV 0.1. The most ductile structural constituent in the Cu–Ti–B system composite is the Cu+Cu4Ti mechanical mixture, due to which further plastic deformation is possible to obtain parts of a given shape. During the study of micromechanical properties, the maximum strength indicators of HIT, HV, We, Re, HIT/E* were recorded in the Cu–Ti–C–B system composite, which allows expecting high wear resistance of products made of it.

Microarc oxidation is a promising technology for producing wear-resistant anticorrosive coatings for goods made of valve metals and alloys and is used in many industries. One of the main problems of this technology is low controllability caused by the complexity and interconnectedness of physical and chemical phenomena occurring during the coating process. To solve such problems, digital twins are currently actively used. The paper covers the development of mathematical models that are advisable to use as structural elements of the digital twin of the microarc oxidation process. An equivalent electrical circuit of a galvanic cell of microarc oxidation is given, which takes into account the electrolyte resistance, the part coating resistance in the form of a parallel connection of nonlinear active resistance and capacitive reactance. The authors propose a mathematical model describing the behavior of the equivalent electrical circuit of a galvanic cell of microarc oxidation. A technique for determining the parameters of this model was developed, including the construction of a waveform of changes in the resistance of the cell and its approximation, estimation of the values of resistances and capacitance of the galvanic cell equivalent circuit. The authors proposed a calculation method and developed a Simulink model of the microarc oxidation process, which allows simulating the current and voltage waveforms of a galvanic cell. The analysis of the model showed that the model is stable, controllable and observable, but poorly conditioned, which leads to modelling errors, the maximum value of which is 7 % for voltage and 10 % for current. By the parametric identification method using experimental current and voltage waveforms, the dependences of the parameters of the galvanic cell equivalent circuit on the oxidation time are obtained. It is found that the change in the period average of the galvanic cell active resistance correlates with the coating thickness.

Currently, an active increase in requirements for fuel efficiency and specific gravity of aircraft turbojet engines is observed. Existing coatings based on zirconium dioxide intended for protecting engine parts are largely outdated and have exhausted their development potential, so new ceramic systems for the production of protective coatings based on them are an area of research. The authors carried out a study of a heat-resistant two-layer coating based on the Y–Al–O system (outer layer) and the Ti2AlC MAX phase of the Ti–Al–C system (sublayer) produced using vacuum-arc deposition on the Inconel 738 heat-resistant nickel alloy and molybdenum by alternate deposition of layers based on Ti–Al–C and a Y–Al–O layer. Using synchrotron radiation, phase transformations in the coating were examined when samples were heated to 1400 °C in a vacuum and to 1100 °C in the atmosphere to study the process of oxidation and coating formation in the presence of oxygen. Using scanning electron microscopy, the authors studied the microstructure and chemical composition of the coating. The study identified that heating the coating in a vacuum and in the atmosphere causes various phase transformations in it, but in both cases, the formation of a mixture of oxides of the Y–Al–O group and destabilization of the Ti–Al–C-based sublayer are observed. After heating the coating in the atmosphere without preliminary heat treatment, the coating was destroyed upon cooling, which was not observed when the coating was heated in a vacuum.

Magnesium alloys with a strengthening long-period stacking ordered structure (LPSO-phase) offer outstanding mechanical properties, but their low corrosion resistance necessitates additional surface protection. The work investigates the influence of adding ZrO2 nanoparticles at a concentration of 1–4 g/l to the electrolyte on the thickness, structure, composition, wettability, and anticorrosion properties of oxide layers formed during plasma electrolytic oxidation (PEO) of the Mg97Y2Zn1 alloy with the LPSO-phase. It was found that during PEO, under the influence of an electric field, ZrO2 nanoparticles penetrate into the forming oxide layer and reduce its porosity. The study revealed a decrease in the quantity and size of pores near the barrier layer in places where the alloy LPSO-phase comes out to the interface with the oxide layer. Low concentrations of ZrO2 nanoparticles (1–2 g/l) reduce the corrosion rate of the alloy up to two times compared to the base case. The minimum corrosion current density icorr≈14 nA/cm2 and the highest polarization resistance Rp≈2.6 MΩ•cm2 are found in the sample formed in an electrolyte with the addition of 1 g/l of ZrO2 nanoparticles. Calculation of the barrier zone parameters of oxide layers showed that an increase in the ZrO2 concentration in the electrolyte leads to an increase in the barrier layer thickness and in its specific conductivity, which negatively affects the corrosion resistance of the formed oxide layers – the barrier zone resistance of the layer obtained by adding 4 g/l of ZrO2, drops by ~20 % compared to the base case (up to ~1 MΩ•cm2).

The data of a comparative analysis of the structure and hardness of pure metals with a face-centered cubic lattice – aluminum, nickel and copper, subjected to complex thermomechanical treatment (TMT), including isothermal cryogenic rolling at liquid nitrogen temperature and subsequent high-density electropulse treatment (EPT) were presented. The main stages, features and advantages of TMT, which first ensure strong work hardening of the processed material due to deformation at low temperatures and then its ultra-fast contact electropulse heating up to a specified temperature, were considered. A multi-level analysis of the metals structure evolution due to TMT was carried out using modern methods of scanning electron microscopy and X-ray diffractometry, recording a wide range of its linear and angular parameters. The kinetics and nature of the processes of the metals structure evolution under cryogenic rolling and EPT, their driving forces and controlling factors, as well as general patterns and temperature intervals of activation of the deformation structure recovery and recrystallization influenced by an electric pulse are identified and discussed. Based on the results of the analysis of the structural and mechanical behaviour of metals, it was concluded that the combination of severe plastic cryogenic deformation and a single-step treatment with ultrashort alternating current pulses is an effective way to obtain semi-finished products with controlled parameters of their structure and properties, including high-strength ultrafine-grain rolled products. At that the phenomenology and nature of the strengthening/softening of metals during cryogenic rolling and subsequent electropulsing are similar to those observed under cold rolling and furnace annealing.

The main problem of submicrocrystalline (SMC) materials formed as a result of large plastic deformation is their thermal stability. The large stored energy and the formation of strongly disordered microcrystallites in the structure lead to a decrease in the recrystallization onset temperature and, therefore, possibly decrease the structure stability. In the work, severe plastic deformation by high-pressure torsion and annealing of pure nickel and an alloy containing 2 at. % chromium were carried out. The structure of both deformed and annealed material was studied by scanning and transmission electron microscopy. The dependence of hardness on the square root of true strain and structure evolution were analyzed to identify the boundaries of the stages of structural states. The energy stored during deformation was estimated using differential scanning calorimetry by the amount of absorbed heat energy. The author studied the behaviour of materials during annealing depending on the stored strain energy at the SMC structure stage. Three stages of structural stats were identified in pure nickel: cellular, mixed, and SMC structure, while in the alloy containing 2 at. % chromium, a cellular structure stage was not detected. A decrease in the stored strain energy was found at the stage of the SMC structure for both materials. Alloying nickel with 2 at. % chromium increases its thermal stability, which increases the temperature when the grain growth becomes intensive by 150 °C. The amount of stored strain energy affects grain growth in the alloy containing 2 at. % chromium, whereas in pure nickel no effect was detected. In the Ni–Cr alloy, greater stored energy corresponds to larger recrystallized grain size.

The paper studies the Al–Mg–Si alloy that does not contain scandium and zirconium, as well as the silicon-rich Al–Mg–Si–Sc–Zr alloy. Multistage thermal treatment was carried out for the Al0.3Mg1Si0.3Sc0.15Zr alloy, which included annealing at a temperature of 440 °C for 8 h, high-temperature annealing at 500 °C for 0.5 h, and artificial aging at a temperature of 180 °C with soaking for 5 h. The Al0.3Mg1Si alloy was annealed at 550 °C for 8 h, and then artificial aging was carried out similarly to the alloy with Sc and Zr additives. To study the fine structure, transmission electron microscopy was used. In the as-cast condition and after each stage of thermal treatment, the mechanical properties of the alloys were determined. It has been found that in an alloy doped with Sc and Zr, the formation of Al3Sc particles occurs already at the stage of formation of the cast structure. During subsequent artificial aging, the supersaturated solid solution decomposes with the formation of β" (Mg5Si6) particles improving mechanical properties. It has been found that in the scandium-containing alloy, fewer β" (Mg5Si6) particles are formed, as a result of which its strength properties are slightly worse than those of the base alloy are. Moreover, these particles are larger than in an alloy that does not contain scandium. This is explained by the fact that complete quenching is impossible for an alloy with scandium additives.

Layered double hydroxides (LDH) can be classified as promising materials due to the ease of synthesis, as well as their wide scope of application. However, the process of LDH synthesis, depending on the LDH chemical composition, can take from tens of hours to several days. It was previously identified that ultrasound exposure during the LDH production significantly reduces the synthesis time, and LDHs produced in this way are interesting in relation to the study of their physicochemical properties and sorption capacity. In this work, the authors produced Mg/Fe LDHs in nitrate form by the traditional method and by the combined action of ultrasound and increased hydrostatic pressure. The resulting samples are characterized by a complex of physicochemical methods of analysis, including scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray phase analysis (XRD), and thermal gravimetric analysis (TGA) with differential scanning calorimetry (DSC). Experiments were carried out to study the sorption capacity of the obtained Fe/Mg LDH samples in relation to chromate ions under normal conditions and under the influence of ultrasound, including in combination with increased hydrostatic pressure. A photoelectric photometer was used to obtain and analyze data with quantitative values of the sorption process. Data of comprehensive analysis of the finished product indicate that the synthesized material is a Mg/Fe layered double hydroxide. X-ray phase analysis identified that the LDH synthesis using ultrasound and pressure increases the crystallinity degree of the finished product. It has been found that the sorption properties of LDHs produced by the conventional method and LDHs produced under the influence of ultrasound and pressure are different. In Mg/Fe LDHs synthesized by the conventional method, chromate sorption proceeds better than in samples synthesized using ultrasonic treatment in combination with increased hydrostatic pressure. The study shows that the sorption process of the examined LDH samples is described by different mathematical models.

Magnesium alloys are an ideal material for creating lightweight and durable modern transport systems, but their widespread use is limited due to some physical and chemical properties. This paper considers the effect of nonlinear elastic unloading of the MA14 (ZK60, Mg–5.4Zn–0.5Zr) magnesium alloy in a coarse-grained state after recrystallisation annealing. The study found that the nonlinearity of the unloading characteristic, is formed when reaching a certain threshold stress level. It is expected that the effect under the study is associated with the deformation behavior of the alloy, during which the twin structure formation according to the tensile twinning mechanism is observed. The sample material microstructure was determined, by scanning electron microscopy using electron backscattered diffraction analysis. Determination of the threshold stress, for the formation of unloading nonlinearity was carried out by two methods: 1) by the value of the loop area formed by the nonlinearity of the unloading mechanical characteristics and the repeated loading (mechanical hysteresis) characteristics, and 2) by analysing the acoustic emission recorded during failure strain. A comparison of the results obtained, allows suggesting that the unloading nonlinearity is caused by twinning in grains, in which an unfavorable configuration (low Schmidt factor), for dislocation slip is observed. Rotating the twinned crystal at an angle close to 90° does not contribute to an increase in the Schmidt factor and activation of dislocation slip systems to secure the deformed structure through the dislocation strengthening mechanism. With a subsequent decrease in the external stress, detwinning and partial restoration of the crystal lattice configuration occur.

Current trends in the development of mechanical engineering impose increasingly stringent requirements for the performance characteristics of manufactured goods. The main parameters characterizing the quality of a product as a whole are the physical, mechanical, and geometric indicators of the working surfaces of the compound units. In domestic practice, a machined surface is mainly characterized by a rather limited number of parameters (no more than 6), such as the average microroughness height, the microroughness height at 10 points, etc. However, their use is not enough to manufacture competitive products in the modern conditions. For example, international ISO/ASME/DIN standards include a much broader set of parameters required to accurately describe the performance properties of a surface. The paper analyzes the approaches to the formation of requirements for the microgeometry of the working surfaces of parts used in modern mechanical engineering. Based on the analysis, the author proposed and mathematically substantiated a general approach to modelling surface texture characteristics, which allows describing adequately the surface using a new parameter – the profile physical coefficient, since it is virtually impossible to directly compare the technologies developed in Russia with foreign analogues based on the current standards. First, the profile physical coefficient was determined at the section level. Next, it was decomposed into a Fourier series for the two-dimensional and three-dimensional cases. The paper presents the analysis of the new parameter applicability on the example of a product obtained by honing. The author concluded about the applicability of this parameter and the necessity to develop a comprehensive methodology based on it for evaluating the surface after machining.

Aerospace applications can benefit from additive manufacturing (AM), which is highly advantageous for prototyping and rapid manufacturing. It also offers cost and weight savings, as well as integrated design capabilities. As of now, there are only a few AM standards available, many materials and equipment are involved, resulting in many variables that hinder certification and adoption. As a result, nonstandard testing is making AM in the airborne materials less appealing due to its costly and time-consuming nature. The main objective of this work is to manufacture the Selector Valve Body parts of military and civil aircraft through Laser Powder Bed Fusion (LPBF) process using AlSi10Mg powder. Further, this paper has been carried out the metallurgical properties, non-destructive and destructive testing as well as the clear explanation about the certification procedures. Moreover, this underscores the need for the developing guidelines, and standards that cover all aspects of manufacturing from design to manufacturing to operation. A comprehensive analysis from liquid penetration test shows defects are within the permissible level. In addition, it exhibits higher yield strength, ultimate strength, and elongation of (259±4) MPa, (323±4) MPa, and (12.5±1.5) % respectively, along with factual evidence that the precipitation hardened AlSi10Mg indigenously developed and produced is equal in properties to the equivalent precipitation hardening aluminium alloys produced by internationally renowned manufacturers.

The problem of increasing the efficiency of mechanical treatment within modern automated production is relevant for many branches of the processing industry. This problem requires a deep study of the physical processes occurring during cutting. The urgency of the problem increases even more with the development of digital production in our country. Today, in the presence of a wide range of products, enterprises are forced to create conditions for reducing the technological cycle when manufacturing a particular product. To carry out the study, an experiment was conducted in which the U8 carbon steel was used as the processed material, and the T15K6 alloy was used as the tool material. During the experiment, the authors observed a change in the roughness of the machined surface depending on the cutting speed. The paper considers the possibility of assessing the quality of the surface layer during cutting based on fractal and neural network modeling. It is identified that the fractal dimension shows the regularity of the reproduction of the machined surface roughness during cutting. The calculated fractal dimension of the machined surface roughness correlates well with the values of the machined surface roughness (correlation coefficient is 0.8–0.9). A neural network structure has been developed, which allows controlling the machined surface quality depending on the cutting conditions. The authors studied the possibility of using neural network models to control technological systems of cutting treatment. When creating digital twins, it is proposed to take into account factors affecting the quality of the treated surface and processing performance, which are poorly accounted for in modeling, as well as when conducting full-scale experiments during machining. Such factors are wear of the cutting tool, the process of plastic deformation, and cutting dynamics.

Analysis of the processing equipment structures when designing according to the temperature criterion is a necessary guarantee of ensuring the required performance characteristics. The presence of a significant number of parts in the processing equipment units and mechanisms requires, when designing, the prediction of the heat flow passage through the joints. When simulating contact thermal resistance, the variety of requirements for a joint can be taken into account by introducing a pseudolayer into the contact zone. The paper presents test results of the proposed regression dependence of the temperature change when the heat flow goes through the pseudolayer obtained considering four significant factors: the pseudolayer thickness, the nominal pressure, the material yield strength, and the actual contact zone location. The adequacy of the specified regression dependence was verified experimentally and applying numerical simulation using large-block finite elements. To describe the process of heat transfer in the thermal model elements, the authors determined contact thermal resistances for several conditions for the heat flow propagation: from one finite element to another within one part; from one finite element to another located in an adjacent part; heat flow passing through closed cavities; heat flow propagation into the environment for finite elements located on the outer (free) contour of the part. The experiments showed a good agreement between the experimental data and the simulation results. The application of large-block finite elements based on the proposed contact thermal resistance model allowed bringing the FE simulation technique to engineering use without complex software.

Resistance welding in large-scale manufacturing is carried out with a significant number of disturbances, the cumulative effect of which may exceed the capabilities of modern control equipment. Most resistance welding control systems used in industry to compensate for existing disturbances provide welding current phase control depending on the measured parameters characterizing the process of welded joint formation. The efficiency of such controllers is largely determined by the accuracy of measuring and setting the phase control parameters, which include the opening and conduction angles of welding thyristors. The paper shows that when switching on a contact machine, a phase shift of the mains voltage occurs in the load mode relative to the mains voltage in the idle mode. Using a simplified electric equivalent circuit of a contact welding machine, the paper describes the nature of the phase shift of the mains voltage. Circuit active resistance and inductance are selected as parasitic parameters of the mains. The authors simulated the electrical processes in the contact machine according to the three-loop equivalent circuit. The study shows the influence of mains parasitic parameters on the phase regulation stability, the features of the obtained current and voltage oscillograms. Depending on the mains and contact welding machine parameters, the phase shift magnitude ranges from fractions to units of an electrical degree. With welding current parametric stabilization by the mains voltage, the influence of mains parasitic parameters can be neglected. When the regulator operates in the mode of maintaining the secondary current numerical value, a decrease in the generated current relative to the specified one is observed. The authors proposed and tested a technique for determining the parasitic parameters of the supply mains based on the results of a short circuit test.

Currently, there is a request from aerospace and aircraft for the construction materials with sufficiently high mechanical strength, thermal creep, corrosion and oxidation resistance. The conventional alloys used for these purposes are too heavy. At the same time, alternative light materials such as Ti–Al-based alloys have many flaws, when they are produced by conventional methods. This work considers the possibility to produce the Ti–Al-based alloys by the method of a wire-feed electron-beam additive manufacturing (EBAM). We study the chemical and phase compositions, microstructure and microhardness of a bimetallic Ti–Al alloy, obtained by this method. It is found the formation of five characteristic regions between titanium and aluminum parts of the bimetallic billet. The mixing zone consists of TiAl and TiAl3 intermetallics, that is confirmed by the investigation of microstructure, chemical and phase compositions. According to XRD (X-ray diffraction) and EDS (energy-dispersive X-ray spectroscopy) analyses, it can be assumed that TiAl intermetallic prevails over TiAl3 one. The average microhardness of the mixing zone equals to 450 HV (≈4.4 GPa). This zone has developed dendritic microstructure, and even distribution of the phases without link to dendritic and inter-dendritic zones. The cracks appearing in this area are filled with the material of the upper layers, so the whole material is poreless and defect-free. Thus, the results of this work have shown a fundamental possibility to produce the intermetallic Ti–Al alloys with the use of the EBAM.

Magnesium alloys are promising materials for aviation, automotive engineering, and medicine, however, due to the low resistance to stress corrosion cracking (SCC), their wide application is limited. To create alloys with high resistance to SCC, a comprehensive study of this phenomenon nature is required. Previously, it was suggested that diffusible hydrogen and corrosion products formed on the magnesium surface can play an important role in the SCC mechanism. However, the contribution of each of these factors to the SCC-induced embrittlement of magnesium and its alloys is understudied. Since the influence of diffusible hydrogen on the mechanical properties of metals increases with the strain rate decrease, the study of the strain rate sensitivity of the SCC-susceptibility of magnesium alloys is a critical task. In this work, the authors studied the effect of the strain rate in the range from 5•10−6 to 5•10−4 s−1 on the mechanical properties, the state of the side and fracture surfaces of the as-cast commercially pure magnesium and the AZ31 alloy before and after exposure to a corrosive environment and after removal of corrosion products. The study identified that the preliminary exposure to a corrosive medium leads to the AZ31 alloy embrittlement, but does not affect the mechanical properties and the fracture mode of pure magnesium. The authors found that the AZ31 alloy embrittlement caused by the preliminary exposure to a corrosive medium appears extensively only at the low strain rate and only if the layer of corrosion products is present on the specimens’ surface. The study shows that a change in the strain rate has little effect on the mechanical properties of pure magnesium. The authors concluded that the main cause of the AZ31 alloy embrittlement after soaking in a corrosive medium is the corrosion products layer, which presumably contains the embrittling agents such as hydrogen and residual corrosive medium.

Due to the improved strength properties compared to the equiatomic Cu–50 at. % Au alloy, non-stoichiometric Cu–56 at. % Au alloy can be used both in dentistry and as a corrosion-resistant conductor of weak electrical signals in tool engineering. The work studies the kinetics of the disorder→order phase transformation in the Cu–56Au alloy, during which the disordered fcc lattice (A1-phase) is rearranged into an atomically ordered one with the L10 superstructure. The initial disordered state of the alloy was obtained in two ways: applying plastic deformation by 90 % or quenching at a temperature of above 600 °C (i. e., from the region of the A1-phase existence). To form the L10 superstructure, annealing was carried out at temperatures of 200, 225, and 250 °C. The annealing duration ranged from 1 h to 2 months. Resistometry was chosen as the main technique to study the kinetics of the disorder→order transformation. The temperature dependences of the electrical resistivity of the alloy in various structural states are obtained. The authors constructed the graphs of the electrical resistance dependence on the annealing time logarithm, based on which, the rate of the new phase formation was estimated. To evaluate the structural state of the alloy at various transformation stages, the authors used X-ray diffraction analysis (XRD). The crystal structure rearrangement during the transformation is shown by the example of splitting the initial cubic A1-phase peak (200) into two tetragonal ordered L10 phase peaks – (200) and (002). Based on the resistometry and X-ray diffraction analysis data, the authors carried out a quantitative assessment of the rate of the disorder→order phase transformation in the alloy under the study. It is established that the values of the converted volume fraction (resistometry) and the long-range order degree (X-ray diffraction analysis) are close. The study shows that in the temperature range of 200–250 °C, the rate of atomic ordering according to the L10 type in the nonstoichiometric alloy Cu–56 at. % Au is maximum at 250 °C. It is identified that the disorder→order transformation in the initially quenched specimens of the investigated alloy proceeds approximately an order of magnitude faster than in preliminarily deformed specimens.

In the process of formation of composite coatings, partial dissolution of strengthening particles (most often carbides) in the matrix is possible; therefore, in some cases, the material creation mode is chosen taking into account the volume fraction of primary carbides not dissolved during coating deposition. The methods currently widely used for calculating the volume fraction of carbides in the structure of composite coatings (manual point method and programs implementing classical computer vision methods) have limitations in terms of the possibility of automation. It is expected that performing semantic segmentation using convolutional neural networks will improve both the performance of the process and the accuracy of carbide detection. In the work, multiclass semantic segmentation was carried out including the classification on the image of pores and areas that are not a microstructure. The authors used two neural networks based on DeepLab-v3 trained with different loss functions (IoU Loss and Dice Loss). The initial data were images of various sizes from electron and optical microscopes, with spherical and angular carbides darker and lighter than the matrix, in some cases with pores and areas not related to the microstructure. The paper presents mask images consisting of four classes, created manually and by two trained neural networks. The study shows that the networks recognize pores, areas not related to the microstructure, and perfectly segment spherical carbides in images, regardless of their color relative to the matrix and the presence of pores in the structure. The authors compared the proportion of carbides in the microstructure of coatings determined by two neural networks and a manual point method.

The formation of representative databases determines the interest in forecasting and managing the quality of metal based on data mining using special software products often based on regression analysis and not always taking into account the statistical nature of an object of study itself. This can lead to misinterpretation of the results or incomplete extracted information reducing the efficiency of statistical processing. Based on the analysis of the production database of the technology for producing 13G1S-U sheet steel, the authors evaluated the possibilities of multiple linear regression for predicting the quality of a steel sheet. The study shows that the type of distribution of the values of control parameters, the distribution nature of which was estimated based on the determination of the skewness and kurtosis coefficients, limits the regression forecast depth. Due to the great deviation of the predicted models from the experimental values in the right tail area of the distribution of the impact strength values, in this work, the authors developed the methods for separating data arrays and proposed criteria to compare the obtained results. To assess the accuracy of the results obtained, arrays with a deliberately asymmetric distribution were selected from the initial sample, against which the statistical characteristics were also compared. Based on the proposed techniques, the authors identified the dominant chemical elements that contribute to the difference in the distribution of the values of acceptance properties existing within the same standard technology. The study shows that the proposed separation method can be used as a variation of cognitive graphics techniques to identify areas with a dependence dominant type based on the correlation of skewness and kurtosis coefficients.

Friction stir processing is one of the modern methods of local modification of the surface of aluminum alloys in the solid-phase state, which provides the dispersion of structural components. In heat-hardened aluminum alloys with a matrix type structure, heat treatment following after friction stir processing can lead to abnormal grain growth in the stir zone. However, in alloys with the structure close to microduplex type, a fine-grained structure can be formed after friction stir processing and heat treatment. This work is aimed at evaluating the possibility of increasing the microstructure thermal stability of the AK4-1 (Al–Cu–Mg–Fe–Si–Ni) matrix-type aluminum alloy. For this purpose, AK12D (Al–Si–Cu–Ni–Mg) aluminum alloy with the structure close to microduplex type was locally mixed into the studied alloy by friction stir processing. Subsequent Т6 heat treatment was carried out according to the standard mode for the AK4-1 alloy. Studies showed that the stir zone had an elliptical shape with an onion-ring structure. This structure comprised alternating rings with different amounts and sizes of excess phases. At the same time, in the stir zone center, the width of rings and the average area of excess phases were larger compared to the stir zone periphery, where the width of rings and the average area of particles were smaller. The average area of excess phases in the rings with their higher content was smaller than in the rings with their lower content. This distribution of excess phases leads to the formation of a fine-grained microstructure, where the average size of grains depends on the interparticle distance in the α-Al solid solution.

An effective way to protect valve metals and their alloys is the micro-arc oxidation method (MAO), which is currently used in various industries. However, to achieve the desired characteristics and properties of oxide coatings, a large number of experiments are required to determine an optimal oxidation mode, which makes the MAO method labor-intensive and resource-consuming. One of the ways to solve this problem is the search for an informative parameter or several parameters, the use of which during the oxidation process monitoring allows identifying a relationship between the MAO modes and the specified characteristics of oxide coatings. This paper studies the influence of the specified technological MAO modes (current density, oxidation time, amplitude of acoustic emission (AE) signals recorded during MAO) on the morphology and parameters of oxide coatings (thickness δ and surface roughness Ra) deposited on the D16AT aluminum alloy clad with pure aluminum. Multivariate planning of an experiment and the performed regression analysis allowed establishing a relationship between two oxidation factors (current density and oxidation time) and the parameters of the produced coatings. The authors proposed an additional factor, which is determined in the monitoring mode during the oxidation process as the time from the moment when the maximum or minimum of the acoustic emission (AE) amplitude recorded in the MAO process is reached until the end of the oxidation process. The study established that the introduction of an additional factor allows increasing significantly the reliability of the dependence between the coating parameters obtained experimentally and by the computational method based on the regression analysis. The authors note that when performing MAO, with the additional use of the MAO process monitoring by recording the AE amplitude, it is possible to achieve a high reliability between the calculated and actual values of the parameters of oxide coatings.

One of the important parameters ensuring the production of a welded joint without continuity defects during friction stir welding is the provision of the required temperature in the metal bonding zone. Significant difficulties arise when determining experimentally the temperature directly in the stir zone of metals using thermocouples. In this regard, the application of numerical methods describing the distribution of temperature fields during friction stir welding is relevant. In the work, numerical modeling of temperature fields during friction stir welding was used, which was based on the finite element method using Abaqus/Explicit software. Modeling was carried out taking into account the coupled Euler – Lagrange approach, the Johnson – Cook plasticity model, and the Coulomb friction law. Using the finite element method, the models of a part, substrate, and tool were constructed taking into account their thermophysical properties. To reduce the computation time, an approach based on the metal mass scaling by recalculating the density of the metal and its thermal properties was used. The authors matched coefficients of scaling of the material mass and heat capacity for the selected welding mode parameters. To evaluate the validity of the results of numerical modeling of temperature fields during friction stir welding, the experimental research of the temperature fields using thermocouples was carried out. The paper shows the possibility of numerical modeling of temperature fields during friction stir welding with the help of the coupled Euler – Lagrange approach and Abaqus/Explicit software. Due to the application of the approach associated with material mass scaling, the calculation time is reduced by more than 10 times.

Increasing the resistance of steel products to sulfide stress cracking (SSC) is one of the topical issues of the oil and gas industry. Among various factors determining the SSC resistance of a material is the structure-phase state of the material itself and the crystallographic texture associated with it. This paper analyzes these features using the scanning electron microscopy (SEM), transmission electron microscopy (TEM), and microroentgen electron backscattered diffraction (EBSD) techniques. As the research material, a production string (PS) coupling made of medium-carbon steel was selected, which collapsed by the mechanism of hydrogen embrittlement and subsequent SSC. For the first time, by the SEM method, using the location and mutual orientation of cementite (Fe3C) particles, at high magnifications, the authors demonstrated the possibilities of identifying the components of upper bainite, lower bainite, and tempered martensite in steels. The presence of the detected structural components of steel was confirmed by transmission electron microscopy (TEM). Using the EBSD method, the detailed studies of microtexture were conducted to identify the type and nature of the microcrack propagation. It is established that the processes of hydrogen embrittlement and subsequent SSC lead to the formation of {101} , {100} , {122} , {013} , {111} < 00>, {133} < 1>, {3 } grain orientations. It is shown that the strengthening of orientations of {001} , {100} , {112} , and {133} < 1> types worsens the SSC resistance of the material. Using the EBSD analysis method, the influence of coincident site lattice (CSL) grain boundaries on the nature of microcrack propagation is estimated. It is found that the Σ 3 CSL grain boundaries between the {122} and {111} < 00>, {012} < 0>, {100} plates of the upper bainite inhibit the microcrack development, and the Σ 13b, Σ 29a, and Σ 39a CSL grain boundaries, contribute to the accelerated propagation of microcracks. For comparative analysis, similar studies were carried out in an unbroken (original) coupling before operation.

There is a strong belief that hydrogen absorbed by magnesium alloys during corrosion can cause their stress corrosion cracking. One of the characteristic markers indicating the involvement of diffusible hydrogen into the fracture mechanism of metals is the negative strain rate dependence of the embrittlement degree. Recent studies show that the loss of ductility of the ZK60 alloy specimens subjected to a short-term (1.5 h) pre-exposure in a corrosive medium actually decreases with the increasing strain rate. However, after the removal of corrosion products from the surface of the specimens, the strain rate dependence of the ductility loss becomes positive, which indicates the absence of hydrogen in the bulk of the metal. At short-term exposure in a corrosive environment, the deep penetration of hydrogen into a metal could be limited due to the insufficient time for hydrogen diffusion. The paper studies the mechanical behavior of the ZK60 alloy subjected to a longer (12 h) pre-exposure in a corrosive medium followed by tensile testing in air at various strain rates. The authors consider the effect of strain rate, long-term pre-exposure in a corrosive medium, and subsequent removal of corrosion products on the strength, ductility, stages of work hardening, and localized deformation, as well as on the state of the side and fracture surfaces of specimens. It is established that the ductility loss of the specimens pre-exposed in a corrosive medium for 12 h decreases with the increasing strain rate, regardless of whether the corrosion products have been removed from their surface or not. It is shown that in this case, the negative strain rate dependence of the ductility loss is associated not with hydrogen dissolved in the bulk of a metal but with the presence of severe corrosion damage of the specimens’ surface. An explanation for the effect of corrosion damage on the mechanical properties and their strain rate sensitivity is proposed.

Polypropylene is one of the most popular thermoplastic materials used in industry. To produce goods from this material, the ultrasonic welding method is often used. However, despite a large number of scientific papers, the influence of some parameters of the ultrasonic welding mode on the strength characteristics of polypropylene joints remains unstudied. The paper presents the results of experimental studies of contact spot ultrasonic welding of plates 3 mm thick made of 01003-26 grade polypropylene. The authors considered the process of gradual penetration of the ultrasonic tool working face into polypropylene to a depth equal to the total thickness of the welded plates. Statistical dependences of the depth of the tool face penetration into the material and the force of material separation on the ultrasound exposure time are obtained. The influence of the depth of the ultrasonic tool working face penetration on the tearing force of welded specimens is determined. A significant increase in the tearing force from 150 to 400 N was found at the tool penetration depth of more than 3.5 mm due to an increase in the nominal area of mutual mixing of the material between the welded plates caused by the flow of molten material into the gap. The authors proposed a hypothesis about the flow of the molten material in the direction opposite to the direction of penetration of the working tool by forming traveling Rayleigh waves. However, its confirmation requires additional studies of the influence of the ultrasonic welding mode parameters and the size of the gap between the parts to be joined on the rate of the molten material flow into the gap.

Rotary friction welding (RFW) is used in the production of drill pipes for solid mineral prospecting. The need for the creation of the lightened drill strings for high-speed diamond drilling of ultradeep wells dictates the necessity of a greater focus on the study of a weld zone and setting the RFW technological parameters. This paper presents the results of experimental studies of a welded joint of a drill pipe of the H standard size according to ISO 10097, made of the 30ХГСА (pipe body) and 40ХМФА (tool joint) steels under the cyclic loads. The authors evaluated the influence of the force applied to the workpieces in the process of friction of the contacting surfaces (force during heating), and postweld tempering at a temperature of 550 °С on the cyclic life of welded joints, under the conditions of alternate tension-compression at the cycle amplitude stress of ±420 MPa. The study determined that with an increase in the force during heating, the microstructure changes occur in the zone of thermomechanical influence, contributing to an increase in the fatigue strength of welded joints. The authors identified the negative effect of postweld tempering on the fatigue strength of welded joints, which is expressed in the decrease in the number of cycles before failure by 15–40 %, depending on the magnitude of the force during heating. The optimal RFW mode of the specified combination of steels is determined, which provides the largest number of cycles before failure: the force during heating (at friction) Fh=120 kN, forging force Ffor=160 kN, rotational frequency during heating n=800 Rpm, and upset during heating l=8 mm. A series of fatigue tests have been carried out at various values of the cycle amplitude stress of the welded joint produced at the optimal mode and the 30ХГСА steel base metal; limited endurance curves have been plotted. It is shown that the differences in the limited endurance curves of the pipe body material (30ХГСА steel) and the welded joint are insignificant. The obtained results are supplemented by the microhardness measurement data and fractographs of fractured samples, revealing the mechanism of crack propagation under the cyclic loads.

The paper covers the development and analysis of a model of the true viscous lubricant movement in the working gap of a radial sliding bearing with a non-standard support profile having a fluoroplastic composite polymer coating with a groove on the shaft surface. The authors obtained new models based on the classical equation in the approximation for the “thin layer” and the continuity equation describing the laminar pattern of movement of a lubricant with the viscous rheological properties. The results of the numerical analysis of the developed models allowed obtaining a quantitative assessment of the efficiency of the bearing bush support profile and the polymer-coated shaft with an axial groove. To complete the set of studies and verify theoretical insights, the authors carried out the experimental research. The novelty of the work lies in the development of an engineering calculation technique that allows determining the magnitude of the main tribotechnical parameters of a radial sliding bearing (hydrodynamic pressure, load capacity, and friction ratio) and expanding the area of practical application of the developed engineering calculations. The design of the radial bearing with a fluoroplastic antifriction composite polymer coating, a 3 mm wide groove, and a special support profile ensured the stable shaft ascent on the hydrodynamic wedge, which experimentally confirmed the correctness of the results of theoretical studies of sliding bearings with a diameter of 40 mm at a sliding speed of 0.3–3 m/s and a load of 13–65 MPa.

The continuous increase in the speed and load of railway transport operating in a wide range of climatic zones of the Russian Federation creates a need to develop new friction materials with the improved performance properties that can ensure high functioning reliability of the electric switch mechanisms. The paper presents the results of the study of the microstructure, physical, mechanical, and operational properties of a new material for friction inserts based on an iron matrix for the switch gear clutches. The new material composition includes such components as Fe, Cu, BaSO4, SiO2, C, and Zn. The authors propose a technique for selecting materials with the specified performance properties based on the results of the research carried out using the experiment factorial planning. For this purpose, the authors carried out the studies and established a relationship between the values of microstructure indicators, physical, mechanical and operational properties of the materials with different quantitative composition of components. The grain boundary density was proposed as an indicator of the dissipative properties of the material, and the possibility of its application as a structural parameter for evaluating the friction material performance characteristics. To assess the friction material performance characteristics, which determine the possibility of its application as a part of the friction clutches of the electric switch mechanism, the authors proposed a new parameter – the endurance period t. Another service property was the deviation of the friction coefficient Dƒ values in the range of values of the clamping force of the electric switch mechanism. According to the results of bench tests of a new friction material within the friction clutches of the electric switch mechanism, the authors identified a high wear resistance of the material and the possibility of its use in severe climatic conditions. The proposed testing technique allows predicting the performance properties of new materials at the stage of studying the microstructure based on the obtained dependences, which can significantly narrow the search range.