No 1 (2026)

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 produce 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 temperatures 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 an 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.

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 subsequent processing. Aim. To determine the rational range of wave deformation hardening (WDH) modes when 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 with a hydraulic pulse generator. In a three-stage experiment, the sample heating temperature (300–700 °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.

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; H_IT=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. 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.