No 3 (2025)

The durability of industrial components is largely determined by the materials they are made of. Often, the materials used must be resistant to wear, corrosion, and high temperatures. Advanced materials, such as high-strength alloy steels, are expensive and have limited weldability, which complicates the restoration of worn components. Fe–Al alloys having high corrosion resistance, wear resistance, and heat resistance at a lower cost are considered as an alternative. The objective of this study is to increase the wear resistance and heat resistance of low-carbon steel components by studying the processes of arc surfacing of iron aluminides and their properties. The study methodology included single-arc and double-arc surfacing using aluminium and steel electrode wires, analysis of the chemical composition of the deposited coatings, their hardness, wear resistance, and heat resistance. The results showed that single-arc surfacing forms alloys based on FeAl₃ and α-Al phases with Fe₂Al₅ and FeAl₃ inclusions, while double-arc surfacing produces alloys more saturated with iron with an α-Fe matrix phase and a Fe₃AlC_x carbide phase. The resulting alloys demonstrate a hardness of up to 58 HRC, a relative wear resistance of up to 2.5 units, and a weight loss of no more than 5 % with an aluminium content of up to 20 %, which indicates their potential for use under high loading conditions. The results confirm the feasibility of using iron aluminides as an inexpensive alternative to expensive coatings, which expands the possibilities for increasing the wear resistance and heat resistance of components in industry.

The study covers the problem of early elimination of tool resonant vibrations through preliminary mathematical modelling. In particular, the problem is considered for the case of milling with an end mill on a vertical milling centre. The paper presents processed experimental data and results of mathematical modelling containing information on the rigidity of the FKC 4257 mill, its natural frequencies on the spectrum and vibration modes. The constructed finite element mathematical model covers the mill itself, the gripping collet and the collet chuck attachment. The model describes the static rigidity of the mill with an error of 2.2 %, and the position of its natural frequencies on the spectrum – with an error of about 7 % relative to the experimental results. By constructing the amplitude-frequency characteristic and conducting a modal analysis, it is shown that the first two vibration modes (80 and 112 Hz) are the most critical for the mill, both in terms of the amplitude of vibrations and in terms of their shape. The vibration shapes in the first modes are bending. During the modal analysis, the vibration shapes in the remaining modes are considered and estimated. To improve the convergence of the frequency analysis results, it is proposed to introduce the coefficient K_k1=0.9, which takes into account the lower rigidity of a real mill in comparison with an idealized mathematical model, when applying which the convergence is improved to 2.5 %. Thanks to the applied technique, it is possible to obtain reliable data on the frequency zones of instability used in practice to avoid resonance phenomena. In the future, based on such data, taking into account the correction factors, it is possible to train neural network models predicting the tool response under specific processing conditions and solving the inverse problem of selecting rational tool geometry for specific tasks.

The use of friction stir treatment (FST) to modify the physical and mechanical properties of age-hardenable low-alloyed bronzes is a promising and at the same time complex task due to the wide temperature range of its implementation. The difficulty is that friction stir treatment of bronzes can result in the formation of fundamentally different types of microstructures with a wide range of grain sizes and various combinations of types of strengthening phases and their various morphologies. Moreover, options are possible when friction stir treatment leads to degradation of properties of bronzes. A favorable combination of properties can be achieved by low-temperature friction stir treatment. In this work, the main microstructural changes in promising Cu–Cr–Zr–Y bronze were analyzed during low-temperature friction stir treatment with a tool rotation speed of 1000 rpm and a feed rate of 25 mm/min (ensuring a temperature in the stir zone of ≈350 °C). Scanning electron microscopy and EBSD analysis revealed the mechanisms of formation of an ultrafine-grained structure with predominantly high-angle boundaries, as well as the development of two types of simple shear crystallographic textures. It is shown that the Cu_x(Y,Zr) phase observed in the initial structure can undergo mechanical destruction or retain its geometric parameters depending on its initial morphology and location. It is shown for the first time that excess Cr particles (the equilibrium fraction at the heating temperature for quenching) may not be destroyed, but plastically deformed with a strong change in their morphology. During friction stir treatment of the bronze under study, particles of a new Y-containing phase are released. The paper considered the relationship of the distribution of microhardness and electrical conductivity and the observed changes in the microstructure of a new promising material.

Study of the temperature field of the milling process with the imposition of ultrasonic vibrations (USV), under various ratios of the vibration amplitude to the depth of tooth penetration into the blank, will allow predicting the efficiency of the milling process with USV under various processing modes. The purpose of this study is to develop physical and mathematical models of the milling process with the imposition of USV, allowing identifying the influence of ultrasonic vibrations on the efficiency of the milling process under various ratios of the vibration amplitude to the depth of tooth penetration. Three sources of heat generation are considered: in the deformation (chip formation) area and in the zones of contact of the chip with the cutting plate (cutter tooth) and the plate with the blank. The authors have developed heat transfer models that take into account, in particular, the change in boundary conditions on the surfaces of the cutting plate and the blank under the USV imposition. When the plate is in contact with the blank, heat flows are directed to the blank, chips and cutter tooth, and the conditions of thermal interaction within the zones of contact of the plate with the chips and the blank are described by boundary conditions of the 2^nd type. When the plate leaves the contact with the blank during the ultrasonic imposition and the chip formation process stops, then on all surfaces of the tooth (plate) and the blank that are in contact with the environment (cutting fluid or air), the convective heat transfer is described by the Newton–Richmann law (boundary conditions of the 3^rd type). The results of numerical modelling are presented, confirming the assumption that the effect of using ultrasonic vibrations is higher at high values of the ratio of the ultrasonic vibration amplitude to the depth of tooth penetration into the blank.

Copper alloys based on the Cu–Zn system, in particular L68 brass, are promising structural materials. However, to improve their reliability and expand the scope of application, it is necessary to enhance their strength characteristics. In this work, the influence of a combination of rotary swaging (RS) and subsequent annealing on the structure, strength and ductility of L68 brass was studied. For this purpose, the alloy microstructure was studied in the quenched and deformed states, mechanical tests for uniaxial tension, a Brinell hardness study, and an assessment of structural and phase transitions using differential scanning calorimetry were carried out. It was found that during rotary swaging, both α-phase grains elongated along the deformation direction and an ultrafine-grained structure inside them consisting of subgrains, deformation twins and shear bands are formed. Subsequent annealing at 450 °C leads to an increase in the grain size to 3–5 μm due to static recrystallization. After rotary swaging, an increase in the offset yield strength (σ_0.2) and ultimate tensile stress limit (σ_B) by ~10 and ~3.5 times, respectively, is observed with a decrease in the relative elongation value by more than 6 times. Subsequent annealing at 450 °C, which caused the formation of a recrystallised structure, led to a decrease in the strength characteristics of L68 brass relative to the deformed state with a simultaneous increase in the relative elongation value compared to both the deformed and the initial state of the alloy. However, it is worth noting that σ_0.2 and σ_B of L68 brass after rotary swaging and subsequent annealing at 450 °C exceed the values for the quenched alloy by an average of ~2.5 and ~1.7 times, respectively, and exceed the values regulated by GOST 494-90, GOST 1066-2015, GOST 931-90, and GOST 5362-78.