Bulletin PNRPU. Mechanical engineering, materials science

Steel 25Mn2Si is widely used in long sections of long products. Since in the process of operation the structures made of sections must meet a number of requirements for such characteristics as ductility and strength, special requirements are imposed on them, which have reinforcing steel 25Mn2Si. The paper considers the rolled section by production method: hot rolling of smooth and periodic profile with controlled cooling in the flow of the rolling mill, and making of anchor heads on reinforcing elements, carried out by upsetting process. However, if the necessary requirements of the technological process for manufacturing anchor heads by upsetting are observed, their destruction occurs during the tensile test. In order to establish the possible causes of destruction, tests were carried out to determine the chemical composition of reinforcement steel, fractrogrographic analysis of fracture surfaces of upsetting heads after fracture, their metallographic examination with determination of microhardness, as well as the initial structure of bars and the structure of upsetting reinforcement. The results of macro- and microstructural studies, as well as the mechanical characteristics of bars of 25Mn2Si steel and upset heads are presented. According to the results of investigations, it has been established that different batches of reinforcement have different microstructure and hardness. Rebars with low-tempered martensite structure in the surface layer and bainite in the middle have higher hardness on the average from 355 HV to 340 HV and are prone to brittle failure under increased stresses and the presence of stress concentrators on the surface. Fracture of the reinforcement at the border of the dislocated part under loading follows the brittle mechanism. This is due to the initial structure of the reinforcement and to the formation of brittle quenching structures with a hardness higher than that of the reinforcement rod, which has a high level of internal stresses and a small ductility margin.

Electron beam wire-feed additive manufacturing is one of the most promising methods to produce large-sized products. Its main advantages are the presence of vacuum protection of molten and heated metal, as well as high performance. Currently, this method is actively developing, but despite this, not enough attention is paid to the definition of modes and especially to the study of the influence of technological electron beam oscillations on the bead shape and the properties of the metal. The article presents the results of a study of the influence of the main parameters of the wire deposition mode, as well as the shape and oscillation parameters on the shape of the beads, the stability and efficiency of the deposition process using SPT-2 titanium alloy wire and VT6 alloy substrate. It was found that an increase in the deposition rate leads to an increase in the efficiency of the deposition process and an increase in the penetration of the substrate. It is shown that an increase in the size of the heat source due to an increase in the diameter of the concentric circles oscillation allows you to adjust the width of the bead, but within certain limits. When using a wire with a diameter of 1.2 mm, it has been possible to increase the width of the roller from 5.97 mm to 9.32 mm - by 1.5 times. When surfacing using a zigzag oscillation at frequencies from 3.5 to 100 Hz, it has been noted that stable formation is guaranteed at the highest frequencies-70 and 100 Hz, and in the low frequency region, the stability of the bead formation depends on the frequency non-linearly - at 3.5 Hz, the formation is stable, and at 7 and 35 - not. A decrease in the power of the electron beam leads to an increase in the height of the bead and a decrease in its width.

Special protective coatings currently provide the highest operational properties of quartz fibers. One of the best coatings is polyimide, which combines high mechanical characteristics and heat resistance (up to 350 °C). At an operating temperature of 350 °C and above, fibers with metal coatings are used, which allow increasing the temperature range up to 600 °C. The object of the study was optical fibers without coatings, with polyimide and with copper coatings. The aim of the work was to determine the strength, hardness and crack resistance of optical fibers without coatings, with polyimide and with copper coatings. The values of crack resistance and hardness of quartz fibers were measured by the indentation method. The crack resistance of K 1c optical fibers was determined using the semi-empirical dependence of A. Niihara, the crack size using scanning electron microscopy. The strength limit of the fibers was determined by the method of axial stretching and the method of two-point bending, at a constant loading speed of 100 mm/min. A graph of the dependence of the ultimate strength on crack resistance is constructed, which shows a comparison of the methods of two-point bending and axial stretching. The two-point bending method gives overestimated results compared to the reference method, we believe this is due to the distribution of defects along the length of the optical fiber. The highest strength was observed in an optical fiber with a copper coating from 6.7 to 9.0 GPa. Low strength, as expected, was obtained for an uncoated optical fiber from 0.3 to 2.3 GPa. The increase in strength and crack resistance of coated fibers is determined by compressive stresses on the surface when copper and polyimide are applied to quartz fibers.

The physics of plasticity and strength are largely based on dislocation physics. The study of the defective substructure after plastic deformation was carried out using an electron microscope. For the study, polycrystals of fcc copper-based alloys were used. The Mn content varied from 0.4 to 25 at. %. The average grain size in the samples is 100 µm. Samples of alloys for research were subjected to tension at room temperature. The sequence of changes in the types of dislocation substructures in alloys is established. In the Cu + 0.4 at. % Mn alloy, the following sequence of dislocation substructures (DSS) is observed: dislocation tangles, cellular without misorientations, cellular with misorientations, in which the misorientations between cells are greater than 0.5°, micro-bands. In alloys with a Mn content of more than 6 at. %, a different sequence of DSS transformation is observed: chaosic dislocations, dislocation pile-ups, nondisoriented network, cell-networks without misorientations, misoriented cellular-reticulated, micro-band. The type of DSS formed at a certain degree of deformation is characterized by its quantitative parameters and distribution of dislocations. A quantitative measurement of the parameters of each type of substructures was carried out. The presence of at least two types of DSS at a given degree of deformation at the same time indicates the presence of "two-phase" in the material. An increase in the degree of deformation contributes to an increase in the density of dislocations in the material. In this case, the volume of the substructure that was formed at small degrees of deformation decreases, and the newly formed substructure occupies a larger volume in the material than the previous DSS. The newly formed DES continues to develop with increasing deformation. In this case, the value of the dislocation density takes on critical values. The accumulation of dislocations in each formed substructure ρcom is much higher than in the previous ones. The paper reveals the relationship between the parameters of the DSS and the average scalar dislocation density. It was found that most of the parameters of the DSS can be the parameters of "phase" transformations. The observed dependences are characteristic of order-disorder transformations. In this case, the "phase" is a definite organization of dislocations in a dislocation ensemble.

Additive processes are innovative technological processes, the use of which significantly reduces the number of stages of modern production. At present, scientists are actively studying the issues of creating products using various surfacing technologies, issues of structure formation of deposited layers and the dependence of the composition of the deposited material on surfacing modes. Despite the active development of methods for the additive layer-by-layer formation of workpieces and products from metallic materials, the issues of reducing heat input into the product during the formation of layers, the possibility of processing materials of different classes, reducing the defectiveness of the deposited material, ensuring the required properties have not been fully resolved so far. The structure and properties of layered materials are largely determined by the features of heat transfer to the product during surfacing, including when working with active materials, which include titanium and its alloys. Titanium alloys have a number of structural features, in particular, the formation of elongated large grains of the beta phase, which can form as a result of the long-term presence of the metal in the region of elevated temperatures and the appearance of large martensitic phases, the formation of which is facilitated by a high cooling rate. The peculiarities of the structure of titanium alloys must be taken into account in surfacing technologies in the formation of physical and mechanical properties. The paper considers the influence of various methods of plasma surfacing technology on the structure and properties of a two-phase titanium alloy during additive formation of blanks. The workpieces were built up by plasma surfacing in a chamber with a controlled atmosphere according to a single-arc and double-arc scheme. High-quality formation of blanks from a titanium alloy with obtaining stable geometric characteristics is possible by plasma surfacing of a wire material with a direct arc of direct polarity. The use of a technological chamber filled with an inert gas makes it possible to provide the most effective protection of the molten and heated titanium alloy from the effects of the environment. The research results showed that the use of a two-arc plasma cladding scheme in a controlled atmosphere can reduce the total heat input in comparison with a single-arc scheme while ensuring the same productivity and process stability.

The article discusses an integrated approach to improving the reliability of oilfield and drilling equipment through the use of technological and design solutions for machining threads and subsequent controlled assembly of connections. In the modern production process of hydrocarbon production, the method of directional and horizontal drilling of oil and gas wells is widely used. At the same time, there is an increased reservoir pressure in the well, the effect of high temperatures on equipment and other complicating factors that affect the stable operation of products. In this regard, the design and manufacturing technology of critical parts of oilfield and drilling equipment requires the use of more durable and reliable products with high technical characteristics. Causal relationships have been built that affect the reliability of the thread and threaded connection. Reasons are disclosed and effective solutions to the problem of low durability of threaded connections are shown. Various methods of surface hardening are considered. The most promising methods of surface plastic deformation based on thread rolling with a special profile roller are proposed. It is noted that the quality of the surface layer mainly characterizes the resource indicators of surface and underground equipment used in the oil and gas industry. The key operations of the technological process of manufacturing a part on which its geometric and physical-mechanical properties are formed are identified. Improving the durability of threaded products is one of the main tasks of modern mechanical engineering. Electromechanical machining is considered as a highly effective method that increases the wear resistance of a thread. Experimental studies are carried out to improve the reliability of threaded connections, comparative fatigue tests of drill pipe samples with and without thread hardening are considered. The studies were carried out on a special stand and using a new technique. It should be noted that the development of methodological foundations and practical recommendations is important for the technological process of blade processing, the subsequent hardening of thread valleys and assembly of joints. The analysis of early studies of scientific schools and production experience of oil engineering enterprises showed that a comprehensive assessment of reliability should take into account the efficiency of the threading process and assembly of threaded connections with an optimal torque. In the manufacture of special drill pipes, casing and tubing, as well as other highly loaded parts of oilfield and drilling equipment, it is important to meet the technological requirements and predict the output parameters of the threading process. Thus, the creation of the theoretical foundations for the design and technological provision of the reliability of threaded connections is an urgent scientific task in the manufacture of drill pipes and has an important practical significance for the national economy of the Russian Federation.