Bulletin PNRPU. Mechanical engineering, materials science

The determination of effective power qiof a welding arc is significant, because this value makes it easier to calculate temperatures in the welded products. Usually, effective efficiency factor η is used to determine qi of free welding arc. However, data of a number of studies dedicated to the values of this coefficient for direct polarity arc in argon with non-consumable electrode are η = 0.21…0.9, which is not enough at the up-to-date requirements to the calculation accuracy of thermal cycles of a weld and heat-affected zone that determine the structure of welding joints. To calculate qi of a free welding arc, we use the temperature formula from a heat point source fixed on the surface of a flat layer, and measured values of spot face sizes after welding them on a high-alloy steel plate of 3.7 mm thickness. The determination of qi by the spot size was carried out by solving of equation with a help of software programmed on С#. For calculation, the dichotomy method was used. As coefficients of a model equation, we use average values recommended in the list of references. The measured values of the effective power were determined by calorimetric study of the samples heated by the fixed welding arc at currents of 80 and 100 А. The comparison of designed and measured specific effective powers per 1 А of the arc current showed that the designed powers are 10-12 % less than the measured powers. It follows that the calculations of sizes of weld penetration with the use of calorimetric power need to be adjusted regarding volumetric heat capacity of the metal in comparison with the used average volumetric heat capacity, which is recommended in the list of references. This approach allows estimating the applicability of any math model of the process for the calculation of temperatures in a product.

The paper presents the results of a study of the conditions for the deagglomeration of carbon-containing suspensions based on various hydrophilic media. As carbon raw materials, multi-walled carbon nanotubes (MWNTs) of the Taunit trademark (NanoTechCenter, Tambov) were used. The key technique of the presented experiments is liquid-phase exfoliation of carbon structures under the influence of ultrasound. The studies were performed by photon correlation spectroscopy, Raman spectroscopy, atomic force and scanning electron microscopy, and X-ray diffraction analysis. It was established that the treatment of nanotubes in an ultrasonic bath for 30 minutes does not ensure their uniform dispersion in a hydrophilic medium. Agglomerates of various types are formed depending on the type of stabilizing additive. The best dispersion medium for introducing MWCNTs into ceramic matrices is an aqueous solution of nonionic surfactant (nonionic surfactant) Tween-80. When the suspension of a dispersed MWCNT suspension is kept for 7 days, the intensity of the peaks in the Raman spectra characteristic of carbon nanostructures increases. A suspension based on polyvinyl alcohol (PVA) can only be used in a freshly prepared state. The number of layers in a MWCNT corresponds to the starting material. Ultrasonic treatment in the environment of the oxidizing agent (NH4)2S2O8 for 30 min leads to the formation of a thin film on the surface, rather than agglomerates uniformly distributed in the dispersion medium. The crystallite size, interlayer distance, number of layers in MWCNTs, inner diameter, and average size of nanotubes after dispersion in an oxidizing medium were calculated using well-known formulas. Exposure of such suspensions for 7 days leads to a denser film of oxidized nanotubes on the surface.

Multilayer films Ti1-х Al x N were deposited on carbide plates using cathodic arc evaporation of Ti and Al cathodes. Cathodes were cooled down by most often used industrial methods: by flowing or recirculated water. The results show that the aluminum evaporation at the temperature above melting and insufficient cathode cooling is accompanied by phase transformation: solid-liquid, stiffness loss and cathode spot volume increase, melt displacement from the craters with the formation of microjets and a large number of defective microdroplets on the surface and in the film body, a phase and elemental composition redistribution over the surface of a substrate and a cathode. Such phenomena are caused by a thermal conductivity decrease of Al in the cathode spot by 2.5 times, its density by 15 %, strength by 30 times, viscosity by 7 times, crystallographic anisotropy acceleration, a sharp decrease in shear modulus, a 2-fold increase in entropy and enhance in thermal expansion coefficient. A temperature increase of a Ti cathode spot with low thermal conductivity accelerates various dynamics of thermal expansion coefficient and Young's modulus and leads to the appearance of thermal and mechanical stresses. A model of the thermophysical and physicomechanical properties of cathode materials has been established to predict the behavior of cathodes during their evaporation.

The article is devoted to understanding the experimental results obtained on the basis of thermodynamic calculated phase diagrams of Fe-N for conclusions and prognostic estimates in the study of the interaction of nitrogen and pure iron at various temperatures. The previously considered α-γ' equilibrium model does not work well at temperatures below 200 °C. Apparently, when deriving the equations for the corresponding equilibrium, some features of the interaction of α-γ' were not evaluated correctly and accurately. In this study, the thermodynamic estimation of the iron - nitrogen diagram was given using the model of two sublattices for solid phases. A description of interstitial solid solutions with sufficient accuracy is possible by using the molar parts of occupied and unoccupied places in the lattice as concentration units. Free energy was considered as the sum of the free energies of hypothetical sections of filled and unfilled interstitial spaces. The equilibrium of the α-γ' system was calculated and the solubility of nitrogen in a-Fe was determined at temperatures of 100-600 °C. The data obtained led to a revision and refinement of the α-g 'equilibrium model. Based on the performed calculations, the tendency to increase the solubility of nitrogen in a-Fe with decreasing temperature to a level below 190 °C was confirmed. It has been suggested that there is a new phase obtained as a result of the peritectoid reaction (a-phase + g'-phase = b-phase) at a temperature in the range of 180-170°C. It has been shown that there are zones on the state diagram of Fe-N that are not adequately described in existing thermodynamic models, and much work remains to be done in this direction.

Ensuring a given performance of electrical discharge machining with minimal wear of the electrode tool is an urgent scientific and technical task that determines the efficiency of the process. The aim of the work is to study the influence of the structure of the electrode-tool on the efficiency of erosion treatment of materials. The technological process of processing workpieces by electroerosion methods is based on the physical effect of electric discharge pulses on the surface being treated. The output parameters of the processing process depend on the physicomechanical properties of the electrode-tool and the electrode-part. Based on the literature, it was found that ensuring a uniform structure of the material of the electrode-tool allows you to increase its operational characteristics. A more efficient electrical discharge machining of the metal can be carried out upon receipt of an electrode-tool with a given directional structure. One of the main parameters affecting the electrical discharge properties of an instrument is electrical conductivity. The electrical characteristics of the electroerosion process of material processing affect the productivity and quality of processing. The microstructure of the electrode-tool has an active influence on their change in electrical characteristics. The nature of its erosive destruction and the nature of erosive destruction of the processed material depend on the initial structure of the electrode-tool, however, these processes have fundamental differences. With an increase in the energy of a single pulse, the rate of erosive destruction of the electrode has a pronounced non-monotonic character, while the rate of volumetric removal of the processed material monotonously increases. In the work, to study the influence of the microstructure of the electrode material on the process of erosion treatment, three types of cast billets made of brass LC40S were obtained, two of which were obtained using refrigerators. According to the results of metallographic analysis, we can conclude that the use of refrigerators made it possible to obtain a microstructure with a predominant columnar structure. Three cuts were made with each electrode. As a result, the microstructure with a predominant columnar structure, obtained using refrigerators, allowed to obtain higher rates for the efficiency of the erosion treatment process. When using electrodes obtained by technology that provides higher electrical conductivity and higher microhardness, the technological time is reduced.

The relevance of the study is due to modern trends in higher education and the ever-growing competition among national research universities in Russia. The assessment of the quality of higher education is presented in the provisions of State programmes and requires constant study at the university level. At present, there is no single (recommended) methodology for assessing the educational activities of the university for a number of reasons. Consequently, there is a need to develop a methodology for the internal evaluation of educational activities within a particular university, taking into account its organizational and process structure. In order to elaborate on this issue, the article considers the concept of quality from the point of view of the educational organization of higher education. Methods of analysis were used, including content analysis of sites, systematization, design and modeling, as well as visual presentation of data. The components of quality of educational activity of the university by levels: technical, technological, production, management, ethical and world. The main elements determining the quality of educational service in the university were analyzed. The peculiarities of the educational service from the point of view of consumers are defined. Elements of an internal system of assessment of the quality of educational activities characterizing educational services of the university for consumers and other interested parties have been developed. Based on the studies carried out, the scheme of internal and external factors and elements determining the quality of educational service in the university was modeled. The system of assessment of the quality of educational services of the university based on a process trip in the quality management system of the university is proposed, which is a set of criteria elements: the quality management system of the university; Performance of processes, educational program, competences of students, indicators of the department; Satisfaction of consumers of educational services and stakeholders, success of graduates. Objects and valuation levels are defined. An algorithms mic block diagram for assessing the quality of educational services has been developed.