Vol 23, No 2 (2021)
- Year: 2021
- Articles: 10
- URL: https://ered.pstu.ru/index.php/mm/issue/view/259
- DOI: https://doi.org/10.15593/.v23i2
ARTICLES
Surface modification of ultrafine ZrO2 powders chromium oxide compounds
Abstract
The paper presents a comparative characteristic of the results of surface modification of ZrO2 powders stabilized with Y2O3 by impregnation with an aqueous solution of CrO3 followed by heat treatment. The studied powders were industrial powders ZYO-7-10-80, TZ-3Y-E and laboratory powder synthesized at the Research Center of Powder Materials Science of the Perm National Research Polytechnic University - ZrO2-5 wt% Y2O3. To modify the surface, we chose the option of impregnation with a 10 % aqueous solution of hexavalent chromium oxide, followed by calcination at temperatures of 270, 400, and 700 °C for 1 h in air. The phase composition of the obtained powders was determined by Raman spectroscopy (Raman spectroscopy). According to Raman spectroscopy data, it was found that all powders are mixtures of tetragonal and monoclinic modifications. The content of the monoclinic modification in the ZYO-7-10-80 powder during calcination is practically unchanged (10-12 %); this result can be explained by the fact that the amount of the stabilizer - yttrium oxide - in the powder is rather high, 7 wt. %, which means that the powder is close to the cubic modification and, accordingly, contains mainly a tetragonal phase that cannot be converted into a monoclinic one. The content of monoclinic modification in TZ-3Y-E powder is 31-38 %, laboratory ZrO2 powder - 5 wt. % Y2O3-51-58 %, it can be argued that there is a partial loss of the stabilizer and the formation of new compounds. On the surface of zirconium dioxide stabilized with yttrium oxide, after impregnation with an aqueous solution of CrO3 and calcining, the peaks of CrO3, Cr2O3 and intermediate phases are identified. The spectrum of the ZYO-7-10-80 powder also shows peaks of zircon. At low temperatures, the formation of a high-temperature compound YCrO4 is noted, which can be explained by its structural similarity to zircon.
Bulletin PNRPU. Mechanical engineering, materials science. 2021;23(2):5-12
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Effective Power of Polarities in non-constricted arc with variable current pulses
Abstract
The basis for this research was a review of papers related to the effective efficiency of non-consumable and consumable electrode arc welding of various metal products in argon. The result shows that the variation of effective efficiency values is essential. It was found that the stable arc effect on aluminum parts is the least understood. In most works, the effective efficiency is given without arc voltage values that complicate its use in practical engineering. The most preferred concept from the point of welding thermal efficiency is the specific effective power per 1 A of the arc current. Nowadays, the most promising method of aluminum alloy welding is Tungsten Inert Gas Welding (TIG) with the application of variable square wave current pulses (VP-GTAW). Numerical mathematical models developed for this welding method show contradicting results. The contribution of arc polarities to the total effective power is not well studied. This makes it difficult to choose optimal ratios for polarity duration and a period. To determine the role of polarities, we apply the method of aluminum parts calorimetry at the same pulse current and different ratios of the pulse duration of straight and reverse polarities. The experiments made it possible to compose several systems of equations for the total arc effective power. Equations solving showed high convergence of data on the specific effective power of polarities. If the current is about 100 A, the specific effective power of the reverse polarity arc is about twice higher when compared to the straight polarity arc. This result accord with data on the ratio of aluminum wire fusion rate at consumable electrode hardfacing.
Bulletin PNRPU. Mechanical engineering, materials science. 2021;23(2):13-19
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Influence of current frequency during pulse layer plasma surface on the structure and properties of high-alloy steel during additive formation of products
Abstract
Ensuring the proper microstructure of the synthesized material and eliminating defects is a problem in additive technologies. An active influence on the structure and properties of the formed metal allows the use of methods of additional impact on the weld pool and the weld metal. The results of the study of the influence of the current frequency during pulsed layer-by-layer plasma surfacing on the stability of the formation of beads, the structure and mechanical characteristics of high-alloy heat-resistant austenitic steel 308LSi during the additive formation of products are presented. The influence of the frequency of the impulse action was evaluated. It was found that the best results on the stability of the formation of beads are provided by plasma surfacing with a current frequency of 500 and more than 10000 Hz. The most uniform penetration depth is observed when surfacing with impulse action at frequencies of 5000, 10 000 and 15 000 Hz. Columnar crystallites of a cellular-dendritic structure are formed along the entire height of the ridge, and their size gradually decreases from the root to the upper part. To assess the effect of the frequency of impulse action on changes in the crystallite size along the height of the beads, a quantitative metallographic analysis of the deposited samples was carried out. The most complete leveling of the crystallite growth rate is manifested during surfacing with a pulse frequency of more than 5000 Hz. The studies carried out allow us to conclude that the best results in terms of the stability of the formation of beads, structure and mechanical characteristics are provided by plasma surfacing with a current frequency of more than 5000 Hz. The mechanical properties of the synthesized material without impulse action are at the level of a standard material, and when a current impulse is applied, it is 15-20 % higher.
Bulletin PNRPU. Mechanical engineering, materials science. 2021;23(2):20-26
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Improvement of valve rods thread connection run life at cyclic loading
Abstract
The problem of the reliability at the promotion of modern advanced types of thin wall API pumps was investigated. Pumps that are still rare in the Russian Federation. The difference from the traditional heavy wall pumps, including an elevated exploitation stresses at the valve rods are counted and the typical failures of such model sucker rod pumps are discussed. The review of fatigue fractures of threaded connections is carried out for the search of effective methods to improve their reliability and durability. The classical procedure for determining failures has been shown, including examination of the quality of the rod, metallographic examination of bars typical for the oil industry and special fractography. Observing destructions cases of the rods happened at different operating conditions was done an assumption about their similarity. To explain the systematic nature of the failures is performed a stress calculation by the modified Inglis formula. At paper is presented nonlinear stress distributions at microvolumes under the API tapered thread profile. The most significant stresses under the thread roots are considered in detail and here is shown in five times higher stresses in respect to the body of the rod behind the thread. Based on the graphical interpretation of the Goodman modified law is presented for tapered thread rod connections API LP are build safe stresses diagram contained stresses regions with proper reliability and durability of products. The approach for fatigue crack prediction is explained based on the comparation the real cyclic stresses and the safe region, limited according the Goodman modified law and dependent on load parameters and mechanical properties of the rods. The necessary mechanical properties level of the thread material is assessed and explained that method of safe region diagram developing. A review and analysis of approaches for achieving the requested reliability and durability of cyclic loaded parts thread is carried out. Investigated the interconnection between the static and cyclic plastic zones and the minimum material volume of thread rod ends have to be local strengthened. Described the calculation methods for that zones needed to be improved. Highlighted especially effective improvements, discussed the possibility of their combination. The insufficiency of the classical methods of metallurgy for investigated rods quality improving is explained.
Bulletin PNRPU. Mechanical engineering, materials science. 2021;23(2):27-35
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Influence of tallium on the kinetics of oxidation of aluminum alloy AMg2 in the solid state
Abstract
Oxidation of metals and alloys is studied due to the fact that they play an important role in various fields of technology, however, information of this kind is insufficient. Since pure metals are rarely used as structural materials, the issues of oxidation of alloys, especially methods of increasing their resistance to oxidation, are, from an applied point of view, the most important aspects of high-temperature oxidation of alloys. The increased interest of researchers and manufacturers in aluminum-magnesium alloys is associated with their widespread use in industry. However, the development of such alloys is inextricably linked to the problem of their oxidation. There is limited information in the literature on the effect of the third component on the oxidizability of aluminum-magnesium alloys. The oxidation process of the alloys was investigated in air under isothermal conditions by the thermogravimetric method with continuous fixation of the sample mass for an hour at temperatures of 773K; 823K and 873K. On the basis of the experimental data, kinetic curves of oxidation were constructed and the values of the specific increase in mass from the amount of thallium in the AMg2 alloy, time and temperature were determined. It is shown that thallium additions and an increase in temperature increase the rate of oxidation of the initial alloy in the solid state. The apparent activation energy of the oxidation process of the aluminum alloy AMg2 is 100 kJ/mol and decreases to 47.90 kJ/mol for the alloy with 1.0 wt% thallium. The oxidation curves of the AMg2 aluminum alloy with thallium in the solid state are described by polynomials indicating the hyperbolic mechanism of this process.
Bulletin PNRPU. Mechanical engineering, materials science. 2021;23(2):36-42
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Analysis and selection testing methods for sulfide stress corrosion cracking of steels in H2S environment
Abstract
Sulfide stress corrosion cracking is one of the most harmful factors destroying production equipment. Currently the amount of the corrosive H2S oil wells increases and the use of corrosion inhibitors does not bring the expected effect. The selection of resistant materials is the main effective way to increase the reliability of equipment and run life in an aggressive H2S environment. Often, downhole conditions are a set of complicating factors that have a interferential impact to materials. In this regard, a number of tests have been developed to assess the materials susceptibility to SSCC. The results of these tests can be used to compare the sensitivity of different alloys under specific conditions and select the best one. At paper presented a general theoretical information about aggressive impact of hydrogen sulfide environment, Russian and international standards for the selection and test methods, laboratory equipment, procedures and standard samples. Significant achievements in the development of standards belong to the American National Association of Corrosion Engineers (NACE), which currently operates in 130 countries around the world. The first international conference in Russia was held relatively recently. Today the international experience of material test in the H2S environment has been almost not known in the Russian Federation. Therefore, much attention paid to the international aproach.
Bulletin PNRPU. Mechanical engineering, materials science. 2021;23(2):43-54
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Comparison of efficiency of contact search algorithms for discrete element method
Abstract
The aim of the work is investigation of granular media movement in a rotating cylinder with the formation of agglomerates and granules. To investigate this process, computer modeling by the method of discrete elements is used. One of the important problems requiring large calculations is the problem of finding contacts for one particle. The search for contacts can require significantly more computational time than direct calculations of the results of particle interactions. To reduce the search area for contacts when modeling granular media by the method of discrete elements, the divide of the entire physical volume into cells using 2D- or 3D-lattice overlay is usually used. Determining the most efficient lattice generation method for dividing the area under consideration and selecting the lattice characteristics can significantly reduce the computation time. The search for contacts for each particle is limited to an area consisting of neighboring cells. In this paper, we investigate the efficiency of the numerical method for different characteristics of the computational lattice. As a result of comparing the methods for constructing the lattice, the following conclusions were obtained. To simulate the movement of granular media in a rotating cylinder with a horizontal axis and a limited depth of the cylinder, the most effective search algorithm is a 2D-lattice with a cell side size equal to the radius of the minimum particle. To simulate the movement of granular media in a rotating cylinder with a cylinder depth that is larger than the cylinder diameter, the most effective search algorithm is a 3D-lattice with a cell side size equal to the radius of the maximum particle.
Bulletin PNRPU. Mechanical engineering, materials science. 2021;23(2):55-61
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Thermokinetic analysis of phase composition of welds aluminum alloy 1420 system Al-Mg-Li. Part 2. Thermokinetic analysis of phase composition of the weld made with AMg-6 wire
Abstract
Aluminum alloys 1420 belong to the complex alloying system Al-Mg-Li. The use of alloys of this group is not limited to the aviation industry, and also finds in other areas to create welded structures. Welding technologies of aluminum alloys are actively developing, in spite of a number of difficulties arising in the welding of aluminum alloys. For each welding method, the difficulties are usually overcome by using different technological solutions. Among these solutions, the welding material - the welding wire, which provides the formation of the weld, plays a rather important role. The paper considers metallographic studies and thermokinetic calculations of the phase composition of a welded seam of aluminum alloy 1420 obtained by argon-arc welding with the use of welding wire Sv-Amg-6. Metallographic studies revealed the dendritic structure of the weld of aluminum alloyed complex alloying system with the separation of phases significantly changing in the areas from the center of the weld to the fusion line. Thermostatic and kinetic calculations made it possible to establish that the start temperature of aluminum crystallization in the weld pool TL = 622 °C and the end temperature of crystallization TS = 551.5 °C. It has been revealed that at temperature T = 642 °С the phase Al6(Mn,Fe) starts to form from the liquid, and by the moment of the beginning of crystallization of Al in the weld pool its content in the weld melt is 1,39 %. By the end of crystallization the following phases are released: Al3Mg2 14.29 %, Al6(Mn,Fe) 4.64 %, (Al-Mg-Zn-Cu) 1.62 %, Mg2Si 1.09 %, Al3(Fe) 0.05 %.
Bulletin PNRPU. Mechanical engineering, materials science. 2021;23(2):62-69
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Possibilities of additive technologies application in designing and manufacturing of weapons of military equipment
Abstract
One of the priority areas for the development of modern mechanical engineering is the transition to advanced digital and intelligent production technologies, and additive technologies dominate in them. Today, the direction of development of additive technologies has gone beyond the framework of research and development work, which in turn allows us to consider them as an independent production process or, at least, the implementation of technological production processes. An integral part of modern domestic mechanical engineering is the production of weapons, military and special equipment. Additive technologies are considered in the article as a promising cost-effective method of manufacturing metal products in order to improve the manufacturability of production processes for the manufacture of modern weapons, military and special equipment. The advantages of the production of metal products by the layer-by-layer synthesis method are shown in comparison with the already existing and well-established methods used in special mechanical engineering at the present time. The comparison of the categories of additive technologies with different methods of implementation, different sources of thermal energy and different forms of material is carried out. Possible ways of increasing the operational characteristics of reliability and durability of both existing models of weapons of military and special equipment, and those in the process of design and pilot production through the use of additive technologies in the manufacture of parts and assembly units from metals and alloys that have not previously been used from for low economic efficiency in traditional technologies. The analysis of the possibility and feasibility of using additive technologies as the implementation of technological processes for the production of weapons of military and special equipment by enterprises of the domestic military-industrial complex.
Bulletin PNRPU. Mechanical engineering, materials science. 2021;23(2):70-78
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Equations of motion of the universal joint
Abstract
There are two known approaches to solving the problems of cardan transmission kinematics. In the first case, the cardan transmission is considered as a spatial mechanism with constant angles between the axes of the cardan shafts. This approach is acceptable when considering the cardan drive when driving in curved sections of the path of a small radius. In the second approach, the cardan drive is considered as a flat driveshaft with variable angles between the axles of the driveshafts. Quite often, cardan drives are used in cases when the bending angle or the distance between the axes of the driving and driven shafts of the transmission can change during the operation of machines. In such conditions, the kinematic and dynamic characteristics of the transmission significantly depend on the modes of its movement. With an increase in the angle of fracture of the propeller shaft, the unevenness of rotation increases noticeably and the average value of the angular velocity decreases. Since with an increase in the angle of fracture of the cardan drive, the unevenness of rotation of the driven shaft increases, due to the unevenness of angular velocities, the area of their applicability decreases, and a decrease in the level of torsional vibrations is achieved only through the use of torsional vibration dampers. The cardan transmission, consisting of one cardan joint, is considered, the equation of motion of the cardan joint is obtained, taking into account the bend angle of the cardan gear and the graph of the dependence of the angle of rotation of the cardan joint per revolution on the skew angle of the cardan shafts and the angular speed. Calculated dynamic models have been developed and the values of natural frequencies of vibrations of a cardan transmission with one cardan joint and a cardan transmission with two cardan joints are obtained. The graphs of the dependence of the angles of fracture of the cardan transmission on the frequency of natural vibrations of the cardan transmission with one cardan joint and with two cardan joints were obtained.
Bulletin PNRPU. Mechanical engineering, materials science. 2021;23(2):79-86
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