Problem. After the ion nitriding operation, unacceptable geometric deformations of the inner diameter (circular and oval distortions) occur in sucker rod pump (SRP) cylinders, presumably associated with an uneven distribution of residual stresses. Existing methods do not provide non-destructive testing of these stresses throughout the entire volume of the finished product. Aim. To develop a methodology for the ultrasonic assessment of the non-uniformity of residual stresses arising after nitriding in actual SRP cylinders and to establish its relationship with geometric deformation. Methods. The microstructure near the inner surface of the cylinders was investigated after four key stages: delivery (as-received condition), hightemperature tempering, grinding, and ion nitriding, including in deformation zones. For the non-destructive evaluation of residual stresses, the acoustoelasticity method was applied using a SEMA structuroscope and a DIO-1000 PA flaw detector. The acoustoelastic coefficients were determined during compression tests on specimens. Results. It is shown that after nitriding, a heterogeneous nitride zone with coarse inclusions forms in the areas of geometric deformation. The maximum nonuniformity of residual stresses is observed after the as-received and grinding stages. Tempering and nitriding reduce both the absolute stress values and their scatter. A correlation was established between the degree of stress non-uniformity and the wall thickness variation in the deformed cross-section. Conclusions. The discovered correlation between the ultrasonic testing parameters and geometric defects confirms the practical applicability of the acoustoelasticity method for the rapid identification of defective SRP cylinders at the post-nitriding inspection stage. The results make it possible to adjust the technological process to minimize deformations
Abstract: Problem. Intergranular corrosion (IGC) is one of the most dangerous types of corrosion affecting chromium-nickel austenitic steels. With low degrees of IGC damage, the dimensions of the affected surface zones are small, making them reliably detectable only through metallographic examination, which reduces the efficiency and reliability of inspection. Objective. To evaluate the feasibility of increasing the reliability of testing austenitic steels for susceptibility to intergranular corrosion by applying the acoustic emission (AE) method during testing. Methods. The object of study was 12Kh18N9 austenitic steel. Specimens of the steel were subjected to various heat treatments and corrosion treatments to induce intergranular corrosion with varying degrees of damage. The specimens were then tested for resistance to IGC according to GOST 6032–2017 using a static three-point bending test, in which the acoustic emission method was applied in addition to the standard test procedure. Results. The application of the AE method during mechanical testing of austenitic steel specimens made it possible to detect IGC even at low levels of corrosion damage, This was achieved through an up to tenfold increase in AE activity and an increase in AE pulse amplitudes from 60 dB to 90 dB. Moreover, the AE method allows the identification of the sensitised state of austenitic steel by detecting an increase in the proportion of hits with amplitudes exceeding 50 dB (from 0.046 to 0.155), without requiring additional metallographic examination. Conclusions. The AE method can be used during testing of austenitic steel specimens for resistance to IGC to improve the reliability of results, since AE parameters differ significantly between specimens in the initial state, those in the sensitised state, and those with pronounced IGC.
Problem. Alloys of the NiCrBSi system are widely used for gas-thermal spraying of protective coatings due to their low melting point. However, coatings formed by high-velocity gas-thermal spraying are characterised by residual porosity and a layered structure, which limits their strength properties. A literature review revealed a lack of systematic data on the influence of subsequent high-temperature annealing on the transformation of the structural-phase composition, continuity, and the complex of micromechanical characteristics of such coatings. Aim. To evaluate the effect of vacuum annealing at 1050 °C on the structural-phase composition, continuity, and micromechanical properties (microhardness, Martens hardness, contact elastic modulus) of NiCrBSi coatings produced by high-velocity gas-thermal spraying. Methods. NiCrBSi alloy coatings were deposited by high-velocity gas-thermal spraying. The samples were subjected to vacuum annealing at 1050 °C with an isothermal hold of 2 h and subsequent furnace cooling. The study of structural-phase changes was carried out using scanning electron microscopy, X-ray phase analysis, and energy-dispersive X-ray microanalysis. Micromechanical properties were evaluated by measuring microhardness (recovered indentation method) and instrumented microindentation. Results. It was experimentally confirmed that annealing at 1050 °C leads to the formation of a dense homogeneous structure without layering. The formation of large strengthening phases – carbides (Cr7C3 and Cr23C6) and CrB chromium borides – was recorded, which increases the strength characteristics of the coating during indentation by 25–30 %. It was found that the contact elastic modulus increases from 130 to 228 GPa due to the elimination of discontinuities. Additional heating to 900 °C does not cause changes in the structure and hardness, which confirms the high thermal stability of the coating subjected to high-temperature (at 1050 °C) annealing. Conclusions. Hightemperature vacuum annealing at 1050 °C is an effective post-treatment method for sprayed NiCrBSi coatings, providing a 1.3-fold increase in hardness and a 1.7-fold increase in the elastic modulus due to the formation of larger strengthening phases and a reduction in the number of discontinuities.
Abstract: Problem. Despite the potential of high-entropy alloys (HEAs) as protective coatings under extreme friction conditions, there is insufficient data on the comparative physical-mechanical and tribological properties of CrTiZrNbHf (cathodic arc evaporation) and CuCrMnFeCoNi (magnetron sputtering) coatings on steel substrates at temperatures of −60, 25, and 150 °C, which complicates the selection of the optimal deposition method and coating composition. Aim. To evaluate the tribological behavior (coefficient of friction, wear resistance) and physical-mechanical properties of coatings based on CrTiZrNbHf and CuCrMnFeCoNi high-entropy alloys deposited by cathodic arc evaporation and magnetron sputtering at temperatures of −60, 25, and 150 °C, in order to identify the optimal method and composition with the highest wear resistance and minimal friction. Methods. Coatings were deposited onto a substrate made of 40KhN2MA structural low-alloy steel using a BRV600 vacuum unit by cathodic arc evaporation (CrTiZrNbHf) and magnetron sputtering (CuCrMnFeCoNi). For the CrTiZrNbHf coating, a number of variable parameters were used: reference voltage (US), pressure in the vacuum chamber, argon flow to the chamber, and deposition time. Coating thickness, structure, and composition were determined using a Zeiss EVA MA 18 electron microscope. Based on the determined chemical composition of coatings, the mixing entropy Smix was calculated. Physical-mechanical properties were studied using a Nanotest 600 measuring platform. Tribological characteristics of specimens at −60, 25, and 150 °C were evaluated using the ball-on-disk test method on a specially developed tribometer. The wear crater profile was measured using a Zygo NewView 600 optical profilometer. Conclusions. The CuCrMnFeCoNi coating deposited by magnetron sputtering exhibits superior tribological characteristics compared to CrTiZrNbHf at temperatures of −60, 25, and 150 °C. In particular, the CuCrMnFeCoNi coating demonstrates enhanced stability of the coefficient of friction (μ) and reduced wear intensity (J). For CrTiZrNbHf, optimal mechanical properties are achieved at a substrate reference voltage of US = 105…115 V. Both materials are recommended for friction components, effectively overcoming the strength-ductility trade-off through optimized PVD process parameters.
In the present work, electron beam welding (EBW) was used to produce joints from the VTI-4 alloy based on orthorhombic titanium aluminide (Ti2AlNb), which is a promising material for the aerospace industry. A pulsed EBW mode for butt-welding of 2 mm thick plates of this alloy was proposed, ensuring the formation of a high-quality welded joint. The welding parameters were as follows: welding speed 0.5–1.0 m/min, welding current 15–20 mA, focusing current 500–550 mA, and pulse frequency 25 Hz, with the beam focused on the surface of the workpieces. The phase composition, as well as the grain size and dimensions of the weld zones, were determined using scanning electron microscopy methods. The fusion zone (FZ) consists of the β-phase, while the heat-affected zone (HAZ) can be divided into HAZ1, consisting of β+α2 phases, and HAZ2, comprising β+α2+O phases. In the HAZ1 region, the globular α2-phase is partially retained, since higher heating temperatures are required to complete the α2→β transformation. Furthermore, it was determined that the level of strength properties of the produced welded joints corresponds to ≈90 % of the base metal strength. A comparative analysis of the dendrite size and globular β-grains in the weld, as well as the strength and ductility of joints produced by various fusion welding methods, showed that the EBW joints have a 2–3 times smaller grain size in the fusion zone and the HAZ of the weld. This feature positively affects the set of mechanical properties, where a high weld strength coefficient is achieved during EBW of the VTI-4 alloy, and the elongation at fracture corresponds to 2.8 %.
Austenitic stainless steels are characterized by paramagnetic properties, good ductility, toughness and corrosion resistance. However, their strength properties are relatively low. Nitrogen alloying is an effective way to increase their strength. The increased nitrogen and manganese content in steels of this class makes it possible to reduce the nickel content. The presence of delta ferrite in the structure of austenitic steels can improve their resistance to the formation of hot cracks. Wire arc additive manufacturing is a modern method of producing parts from austenitic steels. The authors have developed a flux-cored wire for wire arc additive manufacturing, which makes it possible to deposit metal containing nitrogen in chemical composition, high chromium and manganese content, low nickel content, and providing a structure of austenite and a small amount of δ-ferrite. The aim of the work was to certify the deposited material, including t he determination of structural features, micromechanical characteristics, and mechanical properties under conditions of static tensile loading and cyclic loading in the low cycle fatigue testing. As a result of multilayer depositing, deposited layers were obtained with a composition (by wt. %): <0.1 C; 21.1 Cr; 3.3 Ni; 5.0 Mn; 2.0 Mo; 2.8 Cu; 0.239 N. According to the results of X-ray and EBSD analyses, the structure of the deposited layers consists of austenite and 6 wt. % δ-ferrite. The properties of the studied material are compared with those of the widely used austenitic stainless steel AISI 321. Higher strength properties of the studied material are shown both during instrumental microindentation (HM=2.7 GPa; HIT=3.1 GPa) and static tensile testing (σ0,2=595 MPa; σВ=790 MPa; δ=28 %). The transition to multi-cycle fatigue of the developed material occurs at a stress amplitude within 550 MPa.
Problem. Currently, in the field of research on alloys based on orthorhombic Ti 2AlNb aluminide, there are no data on the relationship between heat treatment modes, structural parameters, and mechanical characteristics to ensure a balance of strength and ductility. Aim. To establish the relationship between heat treatment modes, microstructural characteristics (O-phase sizes, α2-phase volume fraction) and mechanical characteristics at room temperature, as well as to determine the heat treatment mode that provides the best balance of strength and ductility for the VTI-4 alloy. Methods. In this work, the method of isothermal multidirectional forging was applied to form a fine-grained globular structure in order to improve the ductility characteristics of the alloy. Subsequent two –stage heat treatment was carried out in the α2+β+O-phase region. Mechanical characteristics were determined by tensile testing. Results. The influence of quenching and aging temperature on the size and volume fraction of α2 and O-phase particles was investigated. The choice of heat treatment modes aimed at forming a structure that ensures high strength and ductility properties of the VTI-4 alloy is substantiated. It was established that when heating for quenching to T=900 °C, O-phase precipitates are retained at triple junctions along β-grain boundaries; during subsequent aging, O-phase particles and interlayers are formed, the thickness of which increases with rising temperature, leading to a decrease in strength and ductility. It was also established that heating for quenching from the upper part of the α2+β+O-phase region (T=960 °C) preserves the globular microstructure, leading to the dissolution of O-phase particles and, accordingly, saturating the β-phase with alloying elements. Increasing the quenching temperature also reduces the volume fraction of α2-phase particles and prevents the formation of O-phase interlayers along β-grain boundaries during aging in the temperature range of 760–800 °C. Conclusions. The study of the influence of aging temperature in the range of 760–840 °C revealed that the lower the temperature, the smaller the thickness of O-phase particles, the higher the strength, and the lower the ductility. The optimal heat treatment mode was determined: quenching at T=960 °C for τ=2 h and aging at T=800 °C for τ=6 h. After such heat treatment, the wrought VTI-4 alloy demonstrates high strength and ductility (σ0.2=1180 MPa, σв=1300 MPa, δ=6.2 %).
Abstract: Problem. The low ductility of binary Fe-Ga alloys significantly limits their thermomechanical processing capabilities and industrial application as magnetostrictive materials. Although alloying with rare-earth metals improves performance characteristics, the influence of temperature and hot deformation conditions on the behaviour of Fe-Ga-based alloys has been insufficiently studied, which prevents the optimisation of technological regimes for manufacturing sheet products without the risk of fracture and the formation of undesirable microstructures. Aim. To determine the influence of hot deformation temperature (700, 850, and 1000 °C) on the deformation behaviour, microstructure, and crystallographic texture of Fe80Ga20 alloys with additions of 0.1 and 0.2 % Ce, and to establish the optimal hot deformation temperature. Methods. The binary Fe80Ga20 alloy and two doped (Fe80Ga20)99.9Ce0.1 and (Fe80Ga20)99.8Ce0.2 alloys were studied. Physical simulation of hot rolling was carried out using a Gleeble 3800 simulator under plane strain conditions at temperatures of 700, 850, and 1000 °C with a strain degree of 75 %. The structure and texture were studied using optical metallography and scanning electron microscopy with EBSD analysis. Results. The addition of cerium significantly improves the ductility of the alloys at temperatures of 850 and 1000 °C. At 700 °C, intense strain hardening and crack formation are observed in all alloys. At 1000 °C, intense grain growth and the formation of a heterogeneous structure occur. The differences in the behaviour of the alloys with 0.1 and 0.2 % of Ce are insignificant. Conclusions. Cerium alloying significantly improves the ductility of the binary Fe80Ga20 alloy. The optimal hot deformation temperature for Fe-Ga-Ce alloys is 850 °C.
Problem. Prolonged annealing of high-nitrogen austenitic steels leads to the precipitation of secondary phases, which significantly affects the structure and properties of the material. However, the nature of phase precipitates and their influence on the mechanical properties of VNS-53-Sh steel have been insufficiently studied. Aim. The aim of this work is to investigate the effect of long-term annealing at 700 °C on the microstructure and mechanical properties of VNS53-Sh high-nitrogen austenitic steel and to determine the phase composition and characteristics of the formed secondary phases. Methods. VNS-53-Sh steel samples were subjected to annealing at 700 °C for 100 hours. Microstructural investigation was carried out using optical metallography, scanning and transmission electron microscopy with a quantitative assessment of the secondary phase fraction. Mechanical properties were determined by uniaxial tensile testing followed by analysis of changes in strength and ductility characteristics. Results. After annealing, grain-boundary and intragranular precipitates of M23C6-type carbides were revealed, formed by the discontinuous austenite decomposition mechanism. Estimates of the area occupied by carbides give values of less than 5 %. Meanwhile, the proportion of a pearlite-like structure represented by lamellar particles and a chromium-depleted matrix is approximately 23 %. The yield strength decreases by 111 MPa, the ultimate tensile strength – by 62 MPa, and the relative elongation increases by about 7 %. Conclusions. Long-term annealing of VNS-53-Sh steel at 700 °C leads to the formation of M23C6 carbide precipitates and partial relaxation of the dislocation structure, which is accompanied by a moderate reduction in strength properties while simultaneously increasing the ductility of the material.
Abstract: Problem. The influence of the degree of cold deformation on the morphology and precipitation of T-phase particles (Al20Cu2Mn3) in Al–Cu–Mn system alloys (ALTEK) during final annealing has been insufficiently studied. This complicates the prediction of properties and the optimisation of thermomechanical processing of sheets and foils for electrical engineering applications. Objective. To establish the patterns of the influence of the cold rolling deformation degree (50 and 90 %) on the formation, morphology, and size of T-phase (Al20Cu2Mn3) particles, as well as on the complex of mechanical and electrical properties of sheets and foils made of ALTEK alloy of the Al–2%Cu–2%Mn system, produced by the following scheme: hot rolling → cold rolling → annealing at 400 C. Methods. Ingots were produced by chill casting and subjected to hot rolling, intermediate annealing, and cold rolling. A portion of the specimens was annealed at 400 °С for 3 hours. The microstructure was studied using transmission electron microscopy. Electrical conductivity (EC) and mechanical properties were measured. Results. It was found that the majority of Al20Cu2Mn3 particles is formed during hot rolling. Cold deformation causes dislocation hardening and fragmentation of existing particles. Regardless of the degree of deformation (50 or 90 %), annealing at 400 °С forms an identical microstructure with lamellar T-phase precipitates measuring 120–200 nm. The electrical conductivity increases from 14.6–14.8 MS/m to 29.6 MS/m after annealing. Conclusions. The degree of cold deformation in the investigated range does not affect the volume fraction of T-phase particles after annealing. The main increase in electrical conductivity and softening are caused by a reduction in dislocation density and further decomposition of the solid solution with coagulation of particles formed during the hot rolling stage.
Problem. The widespread adoption of additive manufacturing technologies, particularly the WAAM method, is hindered by the insufficient level of mechanical properties of synthesized products: microstructural heterogeneity, porosity, and high residual stresses. A promising direction for solving this problem is the application of hybrid technologies combining additive manufacturing with ubsequent processing. Aim. To determine the rational range of wave deformation hardening (WDH) modes hen used in hybrid technology for synthesizing products by the WAAM method, ensuring an increase in the mechanical properties (hardness and impact toughness) of the synthesized product. Methods. Samples of 08G2S steel produced by the WAAM method were subjected to WDH using a specialized setup ith a hydraulic pulse generator. In a three-stage experiment, the sample heating temperature (300– C), the overlap coefficient of plastic imprints (0.3–0.7), and the processing frequency (every layer, every third, every fifth, and every seventh deposited layer) were varied. Vickers hardness through the depth, the degree of hardening, and KCU impact toughness were measured. Results. It was established that maximum hardening is achieved at a temperature of 500 °C, an overlap coefficient of 0.3–0.6, and processing of every third deposited layer. This made it possible not only to increase the material hardness by 8–13 % at a depth of more than 12 mm and increase impact toughness by up to 14 %, ensuring uniformity of properties throughout the product volume, but also to improve the productivity of the hybrid process. Conclusions. The developed methodology makes it possible to control effectively the mechanical properties of WAAM products by determining rational parameters of wave deformation hardening. The proposed approach can be used in the manufacture of critical components in mechanical engineering.
Abstract: Problem. Cold-resistant chromium-nickel stainless steels possess low strength properties. Their replacement requires using steels with enhanced strength characteristics and lower cost. Steels alloyed with nitrogen and carbon meet these requirements; however, their crystal structure at low temperatures has been insufficiently studied. Aim. To determine the influence of low temperatures and low-temperature deformation on the crystal structure parameters of a nickel-free austenitic steel with a high content of interstitial elements. Methods. The crystal structure of cast CrMnCN steel with a (С+N) content of 1.27 wt. % was investigated by X-ray diffraction methods in the temperature range from −190 to 20 °C. The steel was preliminarily homogenised at 1000 °С, then heated to 1150 °С and quenched in water. Tensile tests were carried out at temperatures from −196 to 20 °С. After testing, the crystal structure was analysed. Results. After quenching, the dendritic structure of the steel consists of austenite with a lattice parameter а=3.6405 Å and clusters of dispersed particles. Upon cooling of the steel, the FCC lattice parameter decreased, while in specimens tested in tension, it increased as the test temperature decreased. At cryogenic test temperatures, the crystal lattice exhibits auxetic behaviour. During cooling and low-temperature deformation, stacking faults (SFs) form in the steel. After testing at −196 °С, the SF concentration is twice as high as in steel cooled to the same temperature. The combination of low ductility of the steel at −196 °С, a small amount of plastic deformation work, and a high dispersion of coherent scattering regions (CSRs) indicates the onset of martensitic transformations. Conclusions. Upon cooling of the steel, the lattice parameter decreases. Conversely, during low-temperature deformation, the FCC lattice parameter increases, and at −196 °С the steel exhibits auxetic behaviour. A feature of the response of the crystal structure to low-temperature deformation is an increase in the SF concentration and a small CSR size.
Abstract: Problem. Calciothermic reduction of zirconium dioxide is one of the promising methods for producing zirconium powders. To reduce the synthesis temperature and modify the product morphology, calcium chloride is often introduced into the charge; however, its influence on phase formation and the final powder characteristics is insufficiently studied. Aim. To investigate the influence of calcium chloride introduced into the charge during the calciothermic reduction of zirconium dioxide on the phase composition, morphology, dispersity, and reactivity of the resulting zirconium powder. Methods. A comparative analysis was performed on two series of samples obtained with and without flux (CaCl2). Chemical composition was determined by arc atomic emission analysis; phase composition – by X-ray diffraction analysis; particle size distribution – by laser diffraction; specific surface area – by the BET method; particle morphology – by scanning electron microscopy; and active zirconium content – by gravimetric method. Results. It was shown that the addition of calcium chloride to the charge by wetting in an alcohol solution increased the specific surface area of the powder from 0.56 m2/g (without CaCl2) to 2.9 m2/g (with CaCl2) while maintaining the average particle size (d50 ~5 μm). However, this was accompanied by the retention of the calcium zirconate (CaZrO3) phase in the product, which was not removed during standard hydrometallurgical processing, leading to an increased residual calcium content (1.10 wt.% vs. 0.05 wt.%) and a decrease in active zirconium content (64.7 % vs. 96.9 %). Conclusions. The obtained results indicate the need to optimise process parameters when using CaCl2 as a flux. The calciothermic method without flux additives made it possible to produce a powder with characteristics comparable to literature data.
Problem. Despite numerous studies on the problems of rotary friction welding of dissimilar materials, there is a lack of data on the influence of welding parameters on the formation of brittle phases in the mating zone of carbon and austenitic steels, which affect the structural strength of the joints. Aim. The objective of this study is to evaluate the influence of the friction force on the impact toughness of the mating zone of welded joints made of 32G2 and 10Kh11N23T3MR steels. Methods. Welded hollow cylindrical workpieces made of these steels with an outer diameter of 73 mm and a wall thickness of 12 mm were performed with friction force varying from 70 kN to 210 kN. The remaining parameters were held constant: forging force of 280 kN, friction speed of 600 rpm, upsetting during heating of 6 mm, and forging time of 3 s. Optical and scanning electron microscopy with EBSD and X-ray spectral analysis were used to study the microstructure of welded joints. Impact toughness tests were conducted on specimens with a V-shaped stress concentrator in the joint zone at room temperature. A detailed factual analysis of the fractured specimens was conducted, including an analysis of the chemical composition of individual characteristic areas with distinct fracture morphologies. Results. It was established that the presence of a titanium carbide phase, which forms in the joint zone during diffusion of elements during welding, leads to embrittlement of the joint and a decrease in impact toughness. Reducing the heating force to 70 kN increases the volume of metal extruded during forging, effectively removing the brittle phase and ensuring toughness in the joint zone comparable to that of austenitic steel. Conclusions. The obtained results demonstrated the fundamental possibility of producing joints from 32G2 and 10Kh11N23M3TR steels, which have high viscosity, are of practical interest and can be useful in developing technological modes for welding electric motor shafts and turbocharger rotors.
Abstract: Problem. Increasing the productivity of additive manufacturing (Binder Jetting technology) is limited by the low speed of powder layer deposition while maintaining high geometric accuracy of the products. Traditional systems often lead to defects such as shear deformations, formation of local voids, and interlayer delamination. Aim. To develop and study a mathematical model of a mechatronic system for powder layer formation that allows improving the productivity and quality of 3D printing. Methods. A comparative analysis of deposition systems (blade, rotating roller, and the proposed mechatronic module) was carried out using analytical modeling and computer simulation in Altair EDEM 2023 and MatLab Simulink software. Results. The developed mathematical models describe the dynamics of granular material flows and the dependencies of powder flow rate on the motion parameters of the actuating elements. It was established that the proposed mechatronic system allows achieving a deposition speed of 2800 mm/s with a shear value of 1.98 mm. This is 14 times faster than when using a squeegee (200 mm/s, shear 5 mm) and 3.3 times faster than when using a rotating roller (850 mm/s, shear 2.4 mm), while maintaining Class 7 dimensional accuracy according to GOST 26645-85. Conclusions. The resulting mathematical models of granular material flow dynamics can form the basis for the physics of powder layer formation and research in the field of improving the quality of printed products.
Abstract: Problem. Despite the uniquely high long-term rupture creep of 114 MPa at temperature of 650 °C for 100,000 hours of the new advanced creep -resistant 10Kh10K3V2MFBR steel, its practical application is limited by the lack of technologies for producing high-quality permanent joints. Traditional fusion welding technologies lead to degradation of mechanical properties due to hydrogen embrittlement, formation of -ferrite, and porosity. Objective. To determine experimentally the main aspects of microstructure formation (phase composition, phase morphology, martensite crystallography) and mechanical properties (hardness and strength) of 10Kh10K3V2MFBR steel after friction stir processing (FSP) with high heat input, as well as to establish the reasons for hardening in the stir zone and softening in the heat-affected zone, in order to assess the suitability of this steel for friction stir welding. Methods. Plates of 10Kh10K3V2MFBR steel 3.2 mm thick after normalization at 1060 °C and tempering at 770 °C were subjected to FSP using the parameters of 800 rpm – 5 mm/min. Optical metallography, SEM, EDS, and EBSD methods were used to reveal the mechanisms of microstructure formation in the stir zone (SZ) after FSP. Results. The possibility of producing a material with a fully martensitic structure in the processing zone and a minimal softening effect in the heat-affected zone after FSP was established. It was found that FSP with the parameters of 800 rpm – 5 mm/min leads to heating of the material in the stir zone above the Ас3 temperature (>985 °C). The extreme thermomechanical conditions of FSP contributed to the refinement of the prior austenite grains from 35 to 10 μm. The formation of a fine-grained martensitic microstructure, as well as mechanical alloying with wear products in the stir zone, contributed to an increase in microhardness from 230 to 420 HV in the center of the stir zone and to ≈760 HV on the advancing side of the stir zone. After FSP, the yield strength decreased by 55 MPa, the ultimate tensile strength decreased by 30 MPa, and the percentage elongation decreased by 6 %. Conclusions. High-temperature FSP of 10Kh10K3V2MFBR steel ensures the formation of a martensitic microstructure but is accompanied by intensive wear of the hard alloy tool and a reduction in tool service life.
Problem. Currently used materials for ureteral stents are unable to eliminate inflammation, exhibit low strength, and require a second surgery for removal. Metallic bioresorbable stents can reduce the burden on the patient’s body and eliminate additional operations for product removal. Aim. To roduce a new biocompatible Zn-1 %Cu-1 %Mn alloy and, using equal-channel angular pressing at elevated temperature, to develop an improved set of mechanical properties for potential application as a material for ureteral stents. Methods. The Zn-1 %Cu1 %Mn alloy was subjected to equal-channel angular pressing at 200 °C (8 passes, route Bc). The microstructure and elemental composition were studied using transmission electron microscopy with energy-dispersive analysis. Mechanical properties were evaluated under uniaxial tension (strain rate of 10–3 с –1 , at least 3 samples per each condition), Vickers microindentation with construction of hardness distribution maps, and fractographic analysis of fracture surfaces using a scanning electron microscope. Results. By indexing diffraction patterns, it was established that the deformation processing promotes the precipitation of MnZn13 phase particles, which may have a strengthening effect. Fractographic analysis of fractured samples after tension showed a change in the fracture character from brittle to ductile with deep dimples. Carrying out equal-channel angular pressing (ECAP) for 8 passes at elevated temFrontier Materials & Technologies. 2026. № 1 17 Абдрахманова Э.Д., Хафизова Э.Д., Поленок М.В. и др. «Влияние высокотемпературного РКУП на структуру и механические…» peratures allowed increasing the ultimate tensile strength by 2.3 times, the offset yield strength by 3 times, and the percentage elongation by 8 times. The distribution of microhardness values becomes more uniform with a n increase in passes from 2 to 8, and the gap between the smallest and largest values decreases. Conclusions. It was established that the deformation method (ECAP, 8 passes) for the new biocompatible Zn-1 %Cu-1 %Mn alloy develops an improved set of mechanical properties, which opens up possibilities for its application in medical purposes.
Simultaneous doping of TiNi alloy with copper and zirconium by substituting zirconium for titanium and copper for nickel while maintaining the quasi-binary (Ti35Zr15)(Ni35Cu15) composition enables the formation of two fundamentally different phase states – amorphous and crystalline – as a result of exposure of the material to low- and medium-energy ion beams. An amorphous layer synthesised from the same alloy on the surface of a medical implant made of a Ti–Ni–Cu–Zr alloy, not functional (stents, occluders), but structural (intervertebral discs, orthopedic braces), will allow protecting effectively the implant from the permanent effects of aggressive biological environments of any type (biological fluids, soft tissue, and bone). However, ion-beam modification of the Ti–Ni–Cu–Zr alloy surface can induce residual stresses that can change the properties of the original material. According to X-ray diffraction analysis, niobium ion treatment results in the formation of a layered structure with an amorphous-crystalline surface layer, a B2 matrix phase, and secondary (Ti,Zr)2(Ni,Cu) and TiZr phases. It was found that the B2 phase is a superposition of two phases, one of which, B2core, predominates in the deeper layers of the sample, while B2surf, conversely, is formed primarily in the surface layers. Analysis of the elastic stress state revealed that beneath the ion-modified surface layer, the B2surf phase is in a tensile state, while the B2core phase is in a compressed state, which indicates a complex interaction between the phases and the fact that the stresses in them can mutually compensate for each other. The obtained results are important for understanding the influence of ion implantation on the structure and properties of Ti35Ni35Cu15Zr15 alloys and optimising processing modes for medical applications.
The most rational approach in the production of friction units is not to manufacture the entire part from high-quality materials but to apply thin coatings (up to hundreds of micrometers) from expensive materials onto steels already widely used in industry. One such expensive material is Ta. This paper presents the results of a study on the structure of coatings formed by short-pulse laser cladding of Ta, SiC, B4C, and BN powders onto 40Kh steel. The results demonstrate the technical feasibility of producing coatings of such composition using short-pulse laser radiation. Coatings based on the Ta and SiC powder mixture without B4C and BN additions exhibit large pores that connect into channels after cladding, while the chemical elements are distributed uniformly over the surface. In particular, Fe atoms, which were not part of the initial powder mixture, were transferred from the steel substrate, indicating strong adhesion between the coating and the substrate. The addition of B4C and BN powders led to the formation of separate elliptical pores within the coating. The coating with the lowest content of the Ta and SiC powder mixture demonstrated the smoothest surface. Wear resistance tests revealed a positive influence of B4C and BN on the tribological properties of the coating based on Ta and SiC powders. The minimum mass loss values for both the “pin” and “plate” specimens were obtained after testing the coating with the maximum B4C and BN content. Although the TaSiC coating without additives experienced significantly greater mass loss, it was still 1.8 times lower than that of the uncoated 40Kh steel.
The application of a circuit with a common pulse current source for surfacing with two electrode wires increases the energy efficiency of the arc process and the welding arc technological properties, but requires a more detailed study of the influence of the mode parameters on its stability. In this regard, this paper focuses on studying the dynamics of formation and transfer of metal drops under various modes of pulsed power supply of the welding arc. Using high-speed video filming of the welding arc and synchronized recording of current and voltage signals, a mode was set (average current value was 250 A, maximum current value in pulse was 600 A, arc voltage was ~30 V), which ensured a stable process of transfer of electrode metal by a drop common to two wires without short circuits. It was found that the common drop under the action of electrodynamic forces acquires centripetal acceleration, which contributes to its directed transfer to the weld pool and allows minimizing the amount of spatter on the surface of the base metal. Using mathematical modeling, the nature of the interaction of welding arcs on two wires was confirmed and it was found that even at the stage of the current pulse “hot” phase (600 A, t=0.8 s), the arc pressure on the plate surface is less than when welding with one wire at direct current. The identified effect is associated with a change in the direction of the plasma flow to perpendicular to the wire axis due to an increase in the electrodynamic attractive force of the magnetic fields around the two wire conductors. Together with a decrease in the arc temperature and pressure on the plate surface during the “heat input control” phase of the current pulse (180 A, t=1.4 s), this should help to reduce the heat input and the depth of penetration of the base metal, and, consequently, reduce the degree of dilution of the deposited alloy by the substrate metal. The latter is especially relevant when solving problems of creating a technology for surfacing of relatively thin layers of corrosion-resistant alloys, in particular, on the surface of petrochemical equipment products.
