Key Engineering Materials Vol. 909

Abstract: The breakdown mechanism of a number of crystal materials with hydrogen bonds is investigated. The contribution of the proton component is considered and it is shown that the formation of an avalanche-streamer discharge is characteristic of multilayer electrical insulation materials. As a result of the breakdown, a discharge channel is formed, along which the protons that form the reverse proton conductivity will move in the opposite direction. In the process of directed translational diffusion of protons, the formation and decay of H₃O⁺ and OH^- ions occur, which move in opposite directions, resulting in the formation of a reverse positive streamer from the anode to the cathode. For layered samples of phlogopite, muscovite, and magnesium hydrosilicate, it is shown that for thin samples, a volume charge is formed as a result of a multi-avalanche-streamer discharge that significantly exceeds the volume charge that occurs in thick samples, which is determined by the value of high temperature maximum of the spectrum of thermally stimulated depolarization currents. The field of the volume charge reduces the external electric field, as a result of which the breakdown field strength in thin samples increases. That is, the material is electrically strengthened. Based on the results of the research, a non-destructive method of electrical hardening of electrical insulation materials was developed, which was confirmed by the patent.

Abstract: The paper presents a quantitative assessment of the brittleness of highly hardened silicon carbide ceramics. This characteristic is important for predicting the strength characteristics of the material. The analysis of existing methods for determining the brittleness of the material is carried out. During the research, it was assumed that the production of composite materials in the SiC-Al2O3 and SiC-Al2O3-AlN systems would combine high chemical resistance, wear resistance, and low coefficient of friction. These properties inherent in aluminum oxide and nitride, along with high thermal conductivity and strength, are characteristic of silicon carbide. Materials in the SiC-Al₂O₃ system containing 20, 50 and 80 percent of aluminum oxide – Al₂O₃ were selected as objects of research. Their advantages and disadvantages are shown. The results of an experimental study of samples made of highly hardened silicon carbide ceramics are presented. Based on experimental studies, analytical and graphical dependences are proposed that allow determining the crack resistance of ceramics from the crack length at the corners of the Vickers pyramid. It is shown that these dependences change exponentially, which makes it possible to predict the appearance of cracks at various stages of mechanical processing of products made of highly hardened ceramic materials.

Abstract: In this work, we investigated polymer compositions based on epoxy resin cured with polyethylene polyamine and containing ammonium polyphosphate and boric acid as a blowing agent and carbonization stimulator. The UL 94 method was used to determine the ability of a material to burn or extinguish after flame treatment. We determined the ability of the material to burn or extinguish when exposed to a gas burner. Weight loss at characteristic temperatures was determined using a Perkin Elmer STA8000 synchronous DTA / TGA analyzer. The dependence of heat capacity on temperature was determined (calorimeter ITS-400). It has been shown that in modified compositions containing ammonium polyphosphate and boric acid, the heat capacity changes without significant jumps, which is due to a quieter flow of gas formation. The structure of intumescent coatings was studied using atomic force microscopy. The study was carried out on a P4-Solver device NT-MTD. Tests of the samples have shown that the addition of boric acid makes it possible to obtain a more ordered structure of the coke foam, an increase in the heat capacity of intumescent coatings.

Abstract: The relevance of the use of elastic polymers (elastomers) in the structure of vehicle suspension is ensured by reducing the metal content, the unsprung mass and the overall dimensions of the elastic and damping suspension elements, and by increasing ride comfort and resistance to external factors. The aim of the study is to substantiate, theoretically and practically, the advantages of using elastomeric materials in terms of the quality of ride and the increase of the elastic and damping elements power intensity in comparison with standard designs. The comparative analysis of the parameters of standard structures and alternative ones allows us to make a conclusion the advantages of using elastomers in terms of increasing the power intensity of the elastic-damping suspension structure, reducing the values of the unsprung masses.

Abstract: The paper presents the results of studies of a new cast high-strength austenitic corrosion-resistant steel, which can be successfully used in shipbuilding for the manufacture of fittings. The authors included data on the structural-phase state of steel, the results of evaluating the mechanical properties, wear and corrosion resistance of the metal of castings in the cast and heat-treated state. The mechanical properties of steel are considered in detail in a wide temperature range. The impact strength was considered at low temperatures and static strength at 20 to 350 ° C. It is shown that steel has higher mechanical and corrosive properties in a wide temperature range than those of traditional stainless steels. The corrosion resistance of steel is considered. This is intergranular and pitting corrosion; the main types of corrosion are peculiar for shipbuilding. It has been shown that cast steel is superior to traditional corrosion-resistant steels in pitting corrosion resistance estimated by the pitting coefficient PREN and the critical temperature of pitting. The new cast steel has the same wear resistance as Hadfield steel.

Abstract: Corrosion-resistant steels with a high nitrogen content are used as structural materials for high-load critical products. Their high strength and ductility, austenite stability, corrosion and wear resistance are highly relevant for parts and structures operating in marine environments. In addition to a high level of operational properties, they are subject to the requirement of manufacturability, including weldability. Welding of such steels, due to the high concentration of nitrogen, is a complex technological operation, and it is necessary to avoid the appearance of gas nitrogen pores, hot cracks, a sharp drop in mechanical properties in any zones of welded joint. In this work, we investigated the regularities of changes in microhardness in different zones of welded joints (base metal, heat-affected zone of the weld, fusion zone and weld metal) of two grades of austenitic Cr-Ni-Mn-Mo-N high-strength steels with a high equilibrium nitrogen content (up to 0.6%). They fundamentally differ in the structural state of the base metal being welded: deformed (hot-rolled sheet) and cast (metal of a heat-treated cast plate). It has been shown that despite the use of different welding methods (MIG, MMA and TIG), the options for welding fillers and the type of weld groove, there are general patterns for each of the two types of base metal. The work also evaluated the correlation between these regularities and such basic characteristics of the structure and properties of rolled and cast metal of welded joints, such as the grain size and values ​​of the yield stress.

Abstract: This work shows readability of the QR code of the structural alloy Ti2 surface after the thermal influence. The main goal is the readability estimation after exposure to temperatures exceeding operating alloy temperatures and in destruction crash conditions. Contrast and readability were measured by using a Samsung smartphone and the program Adobe Photoshop CC 2017. The graphs of contrast change depending on the heating temperature were drawn. These graphs illustrate that significant changes in contrast are observed in the range from 500 to 600°C due to darkening of the base metal and the substrate, as well as fading of the dark elements of the code.

Abstract: The article presents the results of studies of aluminum alloys connected by a welded joint obtained by friction stir welding. During this kind of welding a recrystallized fine-grained microstructure is formed in the joint. The pictures of the weld area microstructure are presented, and the eddy current probe signal variations when scanning the joint are shown. The resulting parameter of the eddy current probe was the local electrical conductivity of the weld area. It is demonstrated that the average grain size of the welded joint microstructure varies in the area of weld defects, which was determined by the signal variation of the eddy current probe. The microstructure peculiarities formed in the weld area where the defects are located, and their influence on the mechanical properties of welded joints are discussed. The results of a series of experiments allow concluding about the qualitative characteristics of the obtained welded joints.

Abstract: Electric current has a significant effect on the transfer of matter in liquid layers that grow during contact melting. Depending on the direction of the current, both an increase and a decrease in the rate of contact melting can be observed. In this case, the growth of liquid interlayers does not obey the well-known parabolic law, in contrast to the usual (current-less) contact melting in a nonstationary diffusion mode and other diffusion processes. The paper considers the question of the influence of direct electric current on the concentration distribution in the melt formed during contact melting, as well as on the process of movement of interphase boundaries. A solution is obtained for the diffusion equation for a liquid layer growing in the process of contact melting in the presence of a constant electric current in the system. It is shown that the concentration distribution curves and their gradients for the two modes of the process under consideration (accelerating and decelerating) will have a rather different form, while the movement of the interphase boundaries occurs according to a complex law.