Vol 24, No 3 (2022)

Introduction. At present, additive technologies are actively developing all over the world and are becoming more and more widely used in industrial production. The use of electron beams in additive processes of directed energy input, the so-called Directed Energy Deposition (DED) technologies, has several advantages, the main ones being the flexibility of controlling the spatial and energy characteristics of the thermal source and the presence of a vacuum protective environment. The standard scheme for additive electron beam deposition is melting of a wire filler material fed from the side into the electron beam affected area, but this additive electron beam deposition pattern does not provide a uniform thermal impact in the deposited area. The most effective method for electron-beam deposition is vertical wire feeding, which provides the most stable formation of the liquid metal bath and, consequently, the deposited beads. At the same time, so far there are no results of numerical analysis of this process in order to determine its main regularities. The aim of the work is to carry out numerical experiments for qualitative analysis and determination of the regularities of formation of deposited beads and transfer of filler material, the dependence of the geometric characteristics of the obtained beads on the influence of vapor pressure forces, direction and value of the azimuthal angle of heat sources. The research methods were a series of numerical experiments, which analyzed variants of the electron-beam surfacing process at the location of the surfacing rate vector in the action plane of electron beams and perpendicular to this plane to determine the basic regularities of deposited beads formation and transfer of filler material, dependence of geometric characteristics of obtained beads on the influence of vapor pressure forces, direction of heat sources and the azimuth angle of heat sources. Results and discussion. It is found that the geometric characteristics of the deposited beads significantly depend on the relative position of the deposition velocity vector with respect to the plane of the electron beams, and consideration of the vapor pressure has a significant influence on the results of numerical simulation of the weld pool formation and the hydrodynamic processes occurring in it. In this case, the location of the deposition velocity vector perpendicular to the action plane of the electron beams, there is a more uniform geometry of the deposited metal beads, and increasing the azimuthal angle of the heat sources increases the probability of spitting to the periphery of the deposited bead, which is associated with limitation of the melt motion in the longitudinal direction by the vapor pressure forces.

Introduction. Over the last decade, composite materials based on polytetrafluoroethylene (PTFE) have been increasingly used as alternative materials for automotive applications. PTFE is characterized by a low coefficient of friction, hardness and corrosion resistance. However, this material has a high wear rate. A group of researchers attempted to improve the wear resistance of PTFE material by reinforcing it with different fillers. The purpose of the work: This study experimentally investigates the dry sliding wear characteristics of a PTFE composite reinforced with carbon fiber (35 wt.%) compared to SS304 stainless steel. In addition, experimental mathematical and ANN models are developed to predict the specific wear rate, taking into account the influence of pressure, sliding speed, and interface temperature. The methods of investigation. Dry sliding experiments were performed on a pin-on-disk wear testing machine with varying the normal load on the pin, disk rotation, and interface temperature. Experiments were planned systematically to investigate the effect of input parameters on specific wear rates with a wide range of design space. In total, fifteen experiments were carried out at a 5-kilometer distance without repeating the central run experiment. Sliding velocities were obtained by selecting the track diameter on the disk and corresponding rotation of the disk. A feedforward back-propagation machine learning algorithm was used to the ANN model. Results and Discussion. This study finds better prediction accuracy with the ANN architecture having two hidden layers with 150 neurons on each layer. This study finds an increase in specific wear rates with normal load, sliding velocity, and interface temperature. However, the increase is more prominent at higher process parameters. The normal load followed by sliding velocity most significantly affects the specific wear rate. The results predicted by the developed models for specific wear rates are in good agreement with the experimental values with an average error close to 10%. This shows that the model could be reliably used to obtain the wear rate of PTFE composite reinforced with carbon fiber (35 wt.%) compared to SS304 stainless steel. This study finds scope for further studies considering the effect of varying ANN architectures, different amount of neurons, and hidden layers on the prediction accuracy of the wear rate.

Introduction. Structural materials, including materials made of heat-resistant and hard-to-work steels, are widely used in various branches of mechanical engineering. To increase the efficiency of manufacturing parts of thermal equipment from heat-resistant and hard-to-work steels, the technological method of cutting with preliminary plasma heating of the workpiece is used. There is also a technological method of cutting metals, including hard-to-process materials by ultrasonic turning. Proceeding from this, in order to increase the efficiency of plasma machining of hard-to-process materials, it is necessary to investigate the technological possibilities of using ultrasonic turning of hard-to-process materials during plasma machining. The purpose of the work: to investigate the wear of cutting tools when using ultrasound in the conditions of plasma-mechanical processing of parts made of hard-to-process materials. The paper investigates the features of the plasma-mechanical processing under ultrasonic cutting conditions and determines the wear values of carbide cutters VK8, T5K10 and T15K6 when processing steels of grades 20Cr13Ni18 and 20Cr25Ni20Si2(cast). And also the wear of these cutters was determined under the conditions of conventional turning of the same materials to compare the results of wear of the cutters in different processing conditions. The research method is to determine the linear wear of carbide cutters along the back surface with conventional, plasma-mechanical and plasma-mechanical cutting assisted with ultrasonic cutting using an instrumental microscope and visual estimation with a 10x magnifying glass.  Results and discussion. The paper presents the results of experimental studies to determine the wear of cutting tools when processing heat-resistant steels of the 20Cr13Ni18 and 20Cr25Ni20Si2(cast) grades with carbide cutters of the VK8, T5K10 and T15K6 grades. Studies were carried out to determine the wear of carbide cutters as with conventional mechanical cutting, plasma-mechanical cutting, as well as plasma-mechanical cutting using ultrasound. The experiments were carried out when turning these materials on a modernized lathe mod.1A64. A rectifier with a controlled choke and a plasma torch mod.APR-403 are connected to the lathe; a plasma holder is placed on the lathe carriage. A semiconductor rectifier serves as a power source with a compressed electric arc of current. The arcing takes place between the cathode (plasma torch) and the anode (blank) at the point of the plasma-forming gas; compressed air passes through the nozzle channel of the plasma torch. During the experiments, the position of the plasma torch was adjusted relative to the part rotation axis. When conducting experiments on studying the wear of cutters under conditions of ultrasonic plasma-mechanical cutting, ultrasound was applied to the cutting edge using a device developed by the authors. When processing heat-resistant steels under the usual turning condition, processing modes were adopted: cutting speed V = 10 m/min, cutting depth t = 3...4 mm, longitudinal feed Sl = 0.31 mm/rev. It is found that when processing steel grade 20Cr13Ni18 by conventional cutting, the back surface of the carbide cutter made of T5K10 wears out to 1 mm in size within 10 minutes, and for the cutter made of VK8 – within 15 minutes. During plasma machining, the cutting speed and the feed rate were increased 2 times; the results of the wear of the cutters show that at the same time T5K10 wears out to 1 mm within 20 minutes, VK8 – within 25 minutes. Plasma-mechanical processing using ultrasound show that the carbide cutter T5K10 wears out by 0.50 mm in less than 50 minutes of cutting, and VK8 wears out by 0.35 mm. The same results are obtained when processing heat-resistant steel 20Cr25Ni20Si2(cast). Thus, the study of wear of carbide cutters in the processing of heat-resistant steels shows that the use of ultrasonic cutting in plasma-mechanical processing of steels can significantly reduce the amount of tool wear. The presented results confirm the prospects of using ultrasonic plasma-mechanical cutting of heat-resistant steels with blade tools.

Introduction. The deformation capacity of materials is one of the main mechanical characteristics that determine the possibility of its production using various technological processes for metal forming. Among intermetallic compounds, a special role belongs to alloys with a high-temperature shape memory effect (SME) based on TiNi with the addition hafnium. Most of these alloys are not only difficult to deform, but also quite brittle. Therefore, the development of any technological schemes to increase the deformation capacity of these alloys is relevant. The purpose of the work: to study the deformation capacity and the possibility of using electric pulsed current during cold rolling of the TiNiHf alloy. This processing method has not previously been applied to these alloys. In this work, the deformation capacity during cold rolling of a strip 2 mm thick made of a hard-to-deform high-temperature TiNi-based shape memory alloy with the addition of hafnium is studied. To increase the deformability, an external action in the form of a high-density pulsed current of more than 200 A/mm2 is investigated. The research methods are: X-ray analysis to assess the initial phase state; analysis of the evolution of true and engineering deformation to failure (appearance of visible macrocracks in the deformation zone); optical microscopy with magnification from 50 to 100 and measurement of Vickers hardness at room temperature. Results and discussion. An increase in the deformability under the influence of a pulsed current compared to rolling without current and the achievement of a maximum strain of 1.7 (true) and 85% (engineering) are established. The initial coarse-grained equiaxed martensitic microstructure (50 μm) is transformed into a microstructure elongated along the rolling direction, while the hardness increases by 50%. The absence of noticeable structural changes and the observed hardening may indicate a nonthermal effect of the current in increasing the deformability. Thus, the results of the conducted studies indicate the prospects of the method of rolling with a current of a hard-to-deform TiNiHf shape memory alloy as a method of metal forming.

Introduction. High-entropy alloys (HEAs) belong to a new and promising class of materials that are attracting the attention of both scientists and engineers from all over the world. Among all alloys of the AlxCoCrFeNi system, HEAs with x ≤ 0.3 attract special attention. Materials with this composition are characterized by the presence of only one phase with a face-centered cubic lattice (FCC). Such alloys have high ductility, excellent corrosion resistance and phase stability at high temperatures. The purpose of this work is to compare several methods of profile analysis on the example of plastically deformed ingots of a high-entropy Al0.3CoCrFeNi alloy. The methods of investigation. Using several methods of profile analysis of X-ray diffraction patterns, the structures of the cold-worked high-entropy alloy Al0.3CoCrFeNi are studied. In addition to the classical Williamson-Hall method, the analysis was carried out using a modified one, as well as a method that takes into account the anisotropy of the elastic properties of the crystal lattice. Research material. Ingots of the high-entropy Al0.3CoCrFeNi alloy deformed by cold rolling with a maximum reduction ratio of 80% were used as the object of the study. Samples were cut from the obtained blanks, which were studied by the method of synchrotron radiation diffraction according to the “transmission” scheme along two (longitudinal (RD) and transverse (TD)) directions of rolled products. Results and discussion. It is shown that the use of the classical Williamson-Hall method leads to a significant error in the approximation of experimental results. The modified Williamson-Hall method has the smallest approximation error and can be recommended for studying the Al0.3CoCrFeNi alloy. An analysis of deformed samples using this method made it possible to reveal several features of the formation of defects in the crystalline structure, which are in good agreement with the classical concepts of the mechanisms of plastic deformation. First, an increase in the degree of deformation of the high-entropy Al0.3CoCrFeNi alloy leads to an almost uniform increase in the number of twins and stacking faults. Secondly, with an increase in the degree of reduction, there is a decrease in the fraction of edge dislocations and an increase in the fraction of screw dislocations in the material. The results obtained correlate well with the results of microhardness measurements.