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Original article / Оригинальная статья УДК 621.512
DOI: http://dx.d0i.0rg/l0.21285/1814-3520-2020-2-262-274
Developing installation to increase cylindrical part surface hardness
© Semen A. Zaides*, Vu Van Huy**, Doan Thanh Van**
*National Research Irkutsk State Technical University, Irkutsk, Russia **Vietnam-Russia Tropical center, Ho Chi Minh, Vietnam
Abstract: The aim of the study is to develop an installation for increasing the hardness of the surface layer of cylindrical low-carbon steel components. An argon-arc welding apparatus was used as a plasma-arc source. The movements of the burner and the workpieces are provided by a numerical control to perform specific operations according to preprogramed commands, i.e. the unit operates during a work cycle according to a specially-designed program without operator intervention. Thus, the setup is designed for processing parts having complex geometric shapes to a given tolerance. For carburisation, a paste composed of graphite, sodium silicate (waterglass) and water was used. The waterglass is dissolved in water; then, after drying, a colloidal solution is formed with graphite powder. The layout of the installation was elaborated and the main components were selected. The installation comprises the following components: a personal computer for process control; a TIG 250P power source; a plasma arc source; guides fitted with mechanisms for ensuring the movement of tables and burners located on them; a table for affixing flat workpieces; a table equipped with a jaw chuck for securing and rotating cylindrical workpieces. The personal computer used to control the entire process of increasing hardness comprises a key element in the operation of the installation. The results of the study of workpiece samples following processing by means of the designed installation are presented. The installation provides a controlled process for heating the surface layer of a metal workpiece. A light-grey layer of increased hardness is observed on the surface of the hardened metal. The hardness of this layer achieves up to 50-55 HRC, while the roughness is in the range of 3-10 microns. Due to the high accuracy of the plasma carburisation process automated by means of the developed installation, it is possible to significantly reduce the carburisation time and ensure uniform quality properties of the carbu-rised layers.
Keywords: surface hardening, plasma heating, carburizing paste, macrohardness, microhardness, plasma carburisation process
Information about the article: Received February 20, 2020; accepted for publication March 24, 2019; available online April 30, 2020.
For citation: Zaides SA, Vu Van Huy, Doan Thanh Van. Developing installation to increase cylindrical part surface hardness. Vestnik Irkutskogo gosudarstvennogo tehnicheskogo universiteta = Proceedings of Irkutsk State Technical University. 2020;24(2):262-274. https://doi.org/10.21285/1814-3520-2020-2-262-274
Разработка установки для повышения поверхностной твердости цилиндрических деталей
С.А. Зайдес*, Ву Ван Гюи**, Доан Тхань Ван**
*Иркутский национальный исследовательский технический университет, г. Иркутск, Россия **Российско-Вьетнамский Тропический научно-исследовательский и технологический центр, г. Хошимин, Вьетнам
Резюме: Цель - разработка установки для повышения твердости поверхностного слоя цилиндрических деталей из низкоуглеродистых сталей. В качестве источника плазменной дуги использован аппарат аргонодуговой сварки. Движения горелки и детали обеспечиваются числовым программным управлением, позволяющим выполнять определенные операции по командам, т.е. установка работает по режимам специально созданной программы в течение рабочего цикла без вмешательства оператора. Поэтому данная установка позволяет обрабатывать детали сложной геометрической формы с заданной точностью. Для осуществления цементации использовали пасту следующего состава: графит, жидкое стекло, вода. Жидкое стекло растворяется в воде, и после сушки образуется коллоидный раствор с порошком графита. Была разработана компоновка установки и выбраны основные узлы. Установка состоит из: персонального компьютера для управления процессом; источника питания TIG 250P; источника плазменной дуги; направляющих, с расположенными на них механизмами обеспечения движения столов и горелки; стола для закрепления плоской детали; стола, снабженного кулачковым патроном для закрепления и вращения цилиндрической детали. Важным элементом в работе на установке является ПК персональный
компьютер, контролирующий весь технологический процесс повышения твердости. Приведены результаты исследования образцов после обработки на спроектированной установке. Установка обеспечивает контролируемый процесс нагрева поверхностного слоя металла. На поверхности упрочненного металла наблюдается темно-белый слой повышенной твердости. Твердость данного слоя достигается до 50-55 HRC, шероховатость находится в пределах 3-10 мкм. Разработанная установка позволяет автоматизировать процесс плазменной цементации с высокой точностью, следовательно, можно значительно сократить время цементации и обеспечить равномерное качество свойств цементируемых слоев.
Ключевые слова: поверхностное упрочнение, плазменный нагрев, паста, макротвердость, микротвердость, процесс плазменной цементации
Информация о статье: Дата поступления 20 февраля 2020 г.; дата принятия к печати 24 марта 2019 г.; дата онлайн-размещения 30 апреля 2020 г.
Для цитирования: Зайдес С.А., Ву Ван Гюи, Доан Тхань Ван. Разработка установки для повышения поверхностной твердости цилиндрических деталей. Вестник Иркутского государственного технического университета. 2020. Т. 24. № 2. С. 262-274. https://doi.org/10.21285/1814-3520-2020-2-262-274
1. INTRODUCTION
Effecting an increase in the superficial hardness of metals is widely used in various industries to improve the wear resistance of steel parts such as gears, shafts, mill rolls, dies, etc. This is generally achieved by converting the structure of the surface layer of steel from austenite to martensite by heating it above the phase transformation temperature, followed by rapid cooling of the heated metal layer by means of thermal conductivity or the use of various cooling media.
The process is typically carried out using a plasma arc, a laser beam, an electron beam or a gas flame [1-5]. The first attempts to use cold plasma to accelerate the transfer of carbon during carburisation date back to the 1970s [5]. The 1980s were marked by major developments in this process along with the first industrial applications, while the next decade marked the widespread introduction of this technology into various industries. Plasma carburisation offers a promising alternative for increasing hardness and wear resistance [6, 7]. This consists of a thermochemical process [1, 8] applied to accelerate the diffusion of carbon through the surface layer of a metal. At high temperatures, carbon exhibits maximum solubility in the stable austenite equilibrium phase. Carbonised surface layers contain 0.8 and 1.0 wt.% carbon. Following diffusion saturation of the surface layer, cooling is necessary for carbon fixation. Subsequently, the surface carbon-saturated metal layer is reheated to austenitisation temperature and then rapidly
cooled to obtain a martensitic structure having a high degree of hardness. The content of the carbon gradient in the surface layer determines the hardness distribution over the depth of the surface layer, increasing its wear-resistance [5-7]. Plasma carburisation is among preferred alternative procedures for various reasons, including the possibility of its operation in an oxygen-free atmosphere [8]. In this case, active carbon can be formed directly by the ionising effect of the plasma. Therefore, more uniform carburisation throughout the depth of the surface layer of the metal can be accurately controlled by varying flame formation parameters [9-11]. In addition, the fatigue properties of products are improved due to the absence of oxides forming at grain boundaries [8]. The temperature- and time-dependent diffusion process of plasma carburisation follows the square root of the time relation [9, 12-14]. Therefore, it is evident that the results of low-temperature and high-temperature plasma carburisation will depend on the processing time. A known vacuum process uses glow discharge technology to introduce active soluble carbon onto a steel surface for its subsequent diffusion, leading to a greater depth of carburisation than with traditional gas carburisation approaches [8, 9]. On the other hand, despite the higher temperatures that allow plasma carburisation, the control of high temperature and sample geometry is limited by plasma-based methods, especially for industrial applications. Thus, many studies are focused on low-temperature plasma carburisation processes, as well as their effect
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on increasing the hardness of various steels [4, 5, 7, 8, 15, 16]. Most studies emphasise the mechanical and tribocorrosion properties of low-carbon steels obtained through carburi-sation processes carried out at low temperatures. Nevertheless, there are several studies in which the evolution of the microstructure following a plasma carburisation process carried out at a high temperature and over a long period of time was described. So, for example, in [5-7] a coating composition (graphite, wa-terglass, water, oil for cutting fluid) was considered for applying various parts of machines and tools to the surface, which allows the surface of the metal to be saturated with carbon without reflow and with surface reflow [2-5]. Recent works by various authors [4, 5, 7, 1719] demonstrate the potential of plasma-arc carburisation of steel products. At the same time, the number of works devoted to comparing actual industrial plants used for plasma-arc carburisation to their laser and electron-beam processing counterparts, is insignificant [16].
During the 1940s in the USSR, a test was conducted on the use of a welding arc obtained via a graphite electrode for the surface hardening of steel [17]. Although the use of an alternating field to produce an oscillating arc prevents the surface from melting [2], this technology was not industrially implemented due to the significant accumulation of heat in the treated workpiece. An approach for the automation of an argon-arc welding process used in the USA involved a continuous supply of additional metal (powder) to the arc [18, 19]. During the 1980s, plasma devices started to become widely used in industry for welding, cutting, spraying and hardening parts such as mine equipment and automobile camshafts [19-21]. Equipment for arc welding in an inert gas medium with a non-consumable tungsten electrode can also be used to produce a plasma arc [20]. Although relatively simple and widely available, the use of this type of equipment for surface treatments (quenching, carburisation) is limited due to plasma arcs obtained in this way having a small heating spot, resulting in a very narrow hardened track (~ 5-8 mm). The use of a magnetic field to perform oscillations of the arc, expanding the
track width to 15-20 mm is described in the works [2, 7, 17-20]. It should be noted that an arc generated from plasma arc welding equipment (direct arc) is highly sensitive to changes in the parameters of the combustion mode on the metal surface. As a result, the process of surface hardening without melting easily deviates from the optimal mode during manual hardening, causing fusion of the surface, which is unacceptable according to the principles of classical surface hardening. Thus, in order to eliminate this phenomenon, it is necessary to automate the process of hardening machine parts and tools.
The aim of the present work is to develop an apparatus for automating a selective surface carburisation (hardening) process using a graphite coating and an electric (plasma) arc as used in the TIG welding process.
2. MATERIALS AND METHODS
An argon-arc welding apparatus was used for forming a plasma arc. Here, the movements of the burner and the parts are provided by a computer numerical control (CNC) to perform specific operations according to the commands, i.e. the unit functions during a work cycle according to a specially-designed program without operator intervention. Thus, the setup is designed for the to a high-tolerance processing of workpieces having complex geometric shapes.
The plasma carburisation process was carried out by applying to the samples a hard coating having the following composition: graphite, waterglass, water. After dissolving the waterglass in water and subsequent drying, a colloidal solution is formed with graphite powder. The composition of the graphite, wa-terglass and water coating paste is described in detail in [5-7]. Due to its high electrical conductivity, the use of graphite as the main saturating component makes it possible to reduce the electrical resistance at the interface between the contact between the heating spots of the plasma arc and the coating. The mechanical strength of the coating is achieved by the use of a waterglass-based adhesive mass as a binder. The experiments reported in [5, 7,
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13, 14] showed that a solution consisting of 40% waterglass, 30% graphite and 30% water provides the best adhesion of the graphite coating (before drying) to the surface of cylindrical workpieces. The order of preparation of the paste was as follows: a fine-grained form of the powder was combined to form an even mixture. The pastes were made by mixing the mixture of powders in silicate cement at a volume ratio of 1:1. The resulting paste was applied with a thickness of about 1 mm onto the cylindrical surface of the workpiece samples. Following plasma processing, samples were cut on a Polilab P100A automatic cutting machine. A Polilab C50A press was used to fabricate the metallographic sections. For polishing the surface of microsections, a Polilab P12M grinding and polishing machine was used. Prior to carrying out the microstructure examination, the samples were etched in 5% nitric acid. The microstructure was observed using a Micromed MET-2 optical microscope (Russia) and a JEOL JIB-4501 scanning electron microscope (Japan). Microhardness was measured using a Lonroy HBRV-187.5 (China) and Emcotest DuraScan G5 series hardness tester (Germany).
3. RESULTS AND DISCUSSION
Based on the analysis of literary sources [1-22], the schematic configuration was determined and the main units of the in-
stallation were selected. The installation (Fig. 1, 2) consists of: a personal computer (PC) (1) for controlling the process; a TIG 250P (2) -power source; a plasma arc source; guides (3) fitted with mechanisms for ensuring the movement of tables and burners located on them (4); a table (5) for affixing flat workpieces; a table (6) equipped with a K80 jaw chuck (7) for securing and rotating cylindrical work-pieces. An important element in the operation of the installation is the PC (1), which provides the signals for the installation commands and supports the uninterrupted operation of the equipment. The computer (1) is installed with the Mach 3 software package, comprising an economical installation management station. The Mach 3 software runs on a PC with a Windows 2000, Windows XP, or Windows 7 32-bit operating system. The developers of the program recommend using a computer with a processor of 1 GHz or more and at least 1 Gb of RAM. The TIG-250P welding source is a commercially-available inverter power source designed for argon-arc welding of materials such as stainless-, carbon- and alloy-steels, aluminium, alloys of titanium, nickel, copper, brass, etc, using a non-consumable tungsten electrode. The frame (3) of the installation (Fig. 2) is made of seamless aluminium profile (wall cross section 30 mm). The reinforced profile of the frame allows it to withstand heavy loads, while maintaining reliability and structural rigidity.
Fig. 1. Configuration of plasma surface hardening installation Рис. 1. Комплектация установки для плазменного поверхностного упрочнения
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The movement of the burner (4) (see Fig. 2) in forward, backward, right, left, up and down directions relative to the tables (5, 6), according to the coordinate system (X, Y, Z), is performed using leadscrew actuators (8, 9, 10), consisting of a screw having a diameter of 12 mm, two screw brackets, a GFD-12 nut holder and R12-5T4-FSI nuts. The use of these leadscrews eliminates play when moving coordinates, providing high precision processing and positioning, as well as smoothness and good wear resistance. The rotation of the K80 type cam chuck is provided by a toothed belt drive (11), consisting of a driving
pulley, driven pulleys and a belt having a width of 10 mm. To move along the axes, 57x42 stepper motors having a step of 0.8-1.8 degrees with a rotation moment of 3 nm are used, allowing the manipulation of workpieces with a weight of up to 15 kg. The main advantage of stepper motors consists in their accuracy and low cost. Tables (5), (6) are used to fasten the workpieces for processing on the installation. The T-shaped grooves in the aluminium table allow the workpiece to be attached using clamps in any working area. Installation parameters are given in the table.
Main technical parameters of the installation
Основные технические пар оаметры установки
Axis travel XxYxZ (mm) 750x550x300
Table size, XxY (mm) 200x200; 200x300
Overall dimensions of the machine, XxYxZ (mm) 800x600x600
Frame seamless aluminium profile
Table type grooved aluminium table
Control system Mach 3
Free movement on axes X, Y, Z (mm/min) 1500
X, Y, Z axis guides Leadscrew actuators
A axis guides Toothed belt drive
Drive type stepper motors
Operating system Windows XP / 7 (32)
Power Source 220V ~ 50 Hz
Fig. 2. View of movement and rotation mechanisms of a plasma hardening installation Рис. 2. Внешний вид механизмов перемещения и вращения установки для плазменного упрочнения
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Installation operation procedure:
1. A "computer numerical control" is created. The CNC, generally presented in the form of a G-code file, contains a set of commands by which surface cementation will be performed. The G-code language comprises two groups of commands: G-commands and M-commands. G-commands specify the coordinate system and working plane, as well as the origin and type of movement (accelerated, working), the type of motion trajectory (linear, circular), positioning coordinates, cartridge rotation speed and processing speed. A group of auxiliary commands referred to as M-commands are used to turn the plasma arc on and off. G-code control programs can be compiled manually or by using computer-aided design CAD/CAM application.
2. The CNC file is then transferred to the installation control program (in this case, Mach 3).
3. The control program reads the CNC, translates it into a language that the installation control system understands and uses the information to control the tool that processes the workpiece with a graphite coating. The Mach 3 program, which runs on a PC, sends the signals to the drive cards (controllers).
4. The signals from the control program are amplified by the axle drive circuit boards in such a way that they are supplied with power and an appropriate duration to control the motors mounted on the machine axes.
5. Movement along the machine axes is carried out using helical (X, Y, Z axis) and belt (axis A) gears, whose rotation is transmitted from stepper motors.
An example of a control program for carburising a cylinder having a diameter of 10 mm is given below.
G0 Y0 (accelerated movement of the burner to position Y0)
G0 X0 (accelerated movement of the burner to position X0)
G0 Z3 (accelerated movement of the burner to position Z3 - with a distance between the electrode and the surface of the workpiece of 3 mm)
M3 (Actuation of plasma arc)
G91 (assignment of relative
positioning)
G1 A355 F2800 (rotation of workpiece by 355° at a speed of 2800 deg/min)
G1 X2 F1000 (movement of the burner 2 mm along the axis O X)
G1 A355 F2800 (rotation of workpiece by 355° at a speed of 2800 deg/min)
G1 A350 F2800 (rotation of workpiece by 355° at a speed of 200 mm/min)
G1 X4 F1000 (movement of the burner 2 mm along the OX axis)
M5 (Deactuation of the plasma arc) G90 (assignment of absolute positioning)
G0 Z20 (burner raised by 20 mm along the OZ axis)
G0 X0 Y0 (movement of the burner at X = 0 Y = 0)
M30 (Process shutdown) The workpiece in the form of a cylinder rotates at a speed of 2800 rpm; the burner can move in the range of 0.5-2 mm per revolution. An important condition for the movement of the burner consists in the diameter of the heating spot and the length of the cylinder [2]. This fact must be considered when setting the hardening rate. The practical part is as follows: following mixing, the solution is stirred with an AREX / F20520163 heating magnetic stirrer for 15 minutes to form a colloidal solution. Samples are immersed in the resulting solution (held for 5 s and rotated through 360°), removed and placed in a JP Selecta 2000367 furnace, heated to a temperature of 50°C, for 1 h. Following this stage, graphite from the solution is firmly adhered to the surface of the samples. Coating by this method ensures uniform thickness along the sample length. Coating thickness is measured along the length of the samples using a Defelsko Positector 6000 FNS coating thickness gauge.
Initially, an operation was carried out to control the plasma carburisation process on rectangular test pieces. A hard coating with a different carbon content was applied to the surface of these samples. Hardness measurements were carried out on the upper part of the control sample (surface open to the plasma), as well as on the lower part (surface not
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exposed to the plasma). Following low-temperature plasma carburisation, a significant increase in the hardness of the material as when comparing the values measured at the top of the sample (carbonised) with those measured at the bottom (untreated). A change in the carbon content in the hard coating in the range from 0.25% to 1.00% led to a slight increase in the hardness of the upper surface of the sample from 589 to 638 HV0.3. On the other hand, an average value of 375 HV03 was obtained on the lower surface as a result of the tempering effect from heating the sample during processing. These values are very similar to those obtained for other samples in [25], which can be attributed to the carburisation effect, since the upper part is exposed to the physicochemical plasma environment. In contrast, where it came into contact with the holder, the lower surface of the sample showed a significant decrease in hardness due to a lack of interaction with the plasma medium. It is well-known [5, 8] that it is necessary to carry out tempering immediately following quenching in order to reduce the residual stresses caused by the martensitic transformation. In the present work, carburisation, leading to an increase in hardness, is carried out simultaneously with hardening. At the same time, due to the accumulation of heat and consequent decrease in hardness, a tempering effect is possible. Since they are thermally activated, both effects are directly dependent on the processing temperature. The increase in hardness may be due to the formation of carbide or even to the obtaining of other phases. In the converse case, the decrease in hardness will be associated with the martensite tempering effect. The above results clearly indicate that low-temperature carburisation is effective for surface hardening, with no martensite tempering. The carburisation rate - and, consequently, the hardness of martensite - is affected by various processing parameters, including voltage, the distance between arc source and samples, arc current, as well as the time of the carburisation process [5, 7].
Fig. 3 shows the change in coating thickness along the length of the workpiece during testing of the installation. When using a
coating with 40% waterglass, it can be seen that the thickness is in the range of 104-112 ^m; following processing, no surface fusion was detected. After that, the samples are subjected to plasma treatment at a plasma arc current of 90 A, an arc length of 3 mm and an argon flow rate of 5 l/min. A visual representation of the processing process is shown in Fig. 4.
Fig. 5 shows the appearance of the cylindrical part before processing (right side) and after processing (left side). A dark white layer of increased hardness can be observed on the surface of the coated part following plasma heating. The hardness of this layer reaches 50-55 HRC, which agrees with the figures in [2-4, 7, 14, 21], while the roughness is in the range of 3-10 microns [24].
It was determined that the thickness of the carbonised layers increases with increasing arc source current. From this it follows that high arc currents lead to the formation of a high-density plasma, involving significant flows of active particles that bombard the surface of the sample, and, consequently, to the rapid formation of carbonised surface layers. With increasing distance between the arc source and samples, the thickness of the carburised layers decreased. This result can be explained by the fact that greater distances result in a lower ion current, leading to a high probability of ion scattering and, consequently, to a loss of energy of the ions used to bombard carbon ions. All this will lead to a decrease in the carbonisation rate. In the course of the experimental studies, it was demonstrated that the carburisation rate increases with increasing arc voltage. This can be attributed to the high fluxes of ions bombarding the surface of the samples resulting in the deposition of carbon particles. In addition, intense ion bombardment will lead to a high density of structural defects on the surface of the sample and, consequently, to the creation of channels for the rapid diffusion of carbon atoms into the steel. At the same time, carbon diffusion also accelerates with increasing temperature.
Fig. 6 shows the microstructures and distribution of microhardness along the width of the hardening zone in the mode without surface melting at a degree of overlap of the
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Е 250 Е
<о 200
(Л
ф с
о 150
100 50
0
0 5 10 15 20
№ 1 № 2 № 3
25 30
Length, mm
b
Fig. 3. Results of cylindrical sample coating (40% - waterglass, 30% - graphite, 30% - water): a - sample after drying; b - coating thickness distribution along the length of the cylindrical surface Рис. 3. Результаты покрытия цилиндрического образца (40% - жидкое стекло, 30% - графит, 30% - вода): а - образец после сушки; b - распределение толщины покрытия
по длине цилиндрической поверхности
Fig. 4. Plasma treatment on the installation Рис. 4. Процесс плазменной обработки на установке
hardened tracks of 25%. The structure of the carburisation zone of the surface layer is presented: ledeburite + residual austenite + martensite (up to the overlap zone) and martensite and residual austenite in the overlap zone. Microhardness was measured to a depth of 30 ^m from the surface. It can be seen that the distribution of microhardness is relatively uniform, without significant cavities, as indicated in [2-4].
A thin and continuous carbon-rich surface layer was obtained for all experimental conditions. The results show that the outer layer becomes thicker with increasing carbon content in the hard coating. It can also be noted that carbon diffusion in the bulk material does not appear to cause significant microstructural modifications at the interface between the carbon-saturated layer and the base metal. The surface carburisation layer consists
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b
Fig. 5. Sample after processing: a - after plasma treatment; b - after coating removal Рис. 5. Образец после обработки: а - после плазменной обработки; b - после удаления покрытия
mm
Fig. 6. Microhardness distribution at 25% overlap of hardening tracks under modes without surface melting Рис. 6. Распределение микротвердости при 25% перекрытии дорожек упрочнения при режимах без оплавления поверхности
of a diffusion layer and a phase transformation layer. This suggests that the higher flux of atomised carbon formed by an increased plasma discharge temperature results in a higher flux of carbon impinging on the surface, while all the diffused carbon dissolves in solid solution in the diffusion layer of the surface layer of the metal. It was shown in [5] that the quantity of carbon capable of diffusing into the surface during plasma carburisation depends on the temperature and thickness of the hard coating. Therefore, the best approach for controlling this phenomenon in plasma carburisation is to transfer as much carbon as possible to the surface and maintain this high carbon flux until the carbon content on the surface reaches the solubility limit in the austenite of the steel. At the same time, it is known [2-8] that carburisation is a thermochemical diffusion process in which carbon atoms diffuse in the form of in-terstitials through an iron matrix, creating typical diffusion profiles depending on temperature and time. With increasing temperature, the depth of diffusion increases along with the carbon content on the surface, which reflects the increased solubility of the matrix of /-iron for carbon. Thus, the carbon flux to the surface is dependent not only on gas and plasma, but also - significantly - on the temperature of the workpiece. This suggests that a higher diffusion flux caused by an elevated temperature leads to a higher carbon flux impinging on the surface. To date, the question remains open concerning how carbon penetrates the surface of a workpiece during plasma carburisation.
In terms of the physical process, flows of active carbon particles with high dynamic energies are used to bombard the surface of the steel, with the penetration of carbon atoms into the samples beginning at individual points and only then spreading throughout the volume of the surface layer to all surfaces (diffusion of carbon atoms will occur homogeneously within the samples). However, the detailed mechanism for this carbon transport cannot be fully described. It is known that approximately 70% of carbon particles from a graphite coating source can be ionised during an arc process [8]. The ion energy is 30-40 eV [8] depending on the voltage across the arc. Ions or
carbon particles will accelerate under voltage to the substrate (sample); intense bombardment of the surface of the sample will lead to a large number of defects on its surface. It is significant that a large number of point defects should form in the cascades of collisions, significantly increasing the diffusion of carbon atoms. It was suggested in [5, 7] that the carburisation process will begin with the formation of cementite inside the plasma column and then condense on the surfaces of the samples. Subsequent decomposition of the precipitate then becomes a source of carbon atoms [5, 7]. Some authors believe that the use of plasma will not affect the diffusion rate of carbon atoms in steel [2-4]. However, due to a high rate of transfer of carbon particles in the plasma leading to a rapid increase in the concentration of carbon on the surface, carbon diffusion will begin earlier, which will lead to a reduction in processing time [5, 9].
When designing the installation, all the above theoretical aspects of the saturation of metals with carbon were considered. In particular, the introduction of automatic control over the saturation process by setting commands in the program unit allowed processing errors involving overlapping hardening tracks to be minimised.
Thus, the above-presented research results demonstrate the possibility of surface plasma carburisation using the developed installation, where the significant technological parameters are the thermal power of the plasma arc, the coefficient of overlap of the hardening tracks, the composition of the car-burising paste (coating) and the cooling rate of the surface metal layer. Adjustment of technological parameters is provided by a combination of installation design parameters and the ability to automatically control them using a computer program.
4. CONCLUSION
Thus, as a result of the studies, a design for the plasma carburisation of cylindrical parts was developed and implemented. The developed installation for increasing surface hardness permits automatic control of the
ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(2):262-274
technological surface hardening parameters. Plasma carburisation, in which an arc discharge plasma is used as a heating source, is more efficient than conventional processes due to the bombardment of intense energy carbon ions generated by a direct current arc discharge and accelerated by a bias voltage to the sample surface, resulting in increased carbon diffusion due to the high defect density
caused by the bombardment.
Taking cognisance of the important effect that other parameters of plasma processing can have on the properties of the treated surface, experiments were carried out in order to evaluate the effect of gas pressure and applied voltage on the plasma carburisa-tion process in automatic mode.
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Authorship criteria
Zaides S.A., Vu Van Huy, Doan Thanh Van declare equal participation in obtaining and formalization of scientific results and bear equal responsibility for plagiarism.
Conflict of interests
The authors declare that there is no conflict of interests regarding the publication of this article.
шлицевых соединений // Вестник машиностроения. 2009. № 8. С. 87-89.
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Критерии авторства
Зайдес С.А., Ву Ван Гюи, Доан Тхань Ван заявляют о равном участии в получении и оформлении научных результатов и в равной мере несут ответственность за плагиат.
Конфликт интересов
Авторы заявляют об отсутствии конфликта интересов.
ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(2):262-274
The final manuscript has been read and approved by all the co-authors.
INFORMATION ABOUT THE AUTHORS
Semen A. Zaides,
Dr. Sci. (Eng), Professor, Head of the Department of Mechanical Engineering Technologies and Materials, Irkutsk National Research Technical University, 83 Lermontov St., Irkutsk 664074, Russia; H e-mail: zsa@istu.edu
Vu Van Huy,
Cand. Sci. (Eng), Researcher,
Vietnam-Russia Tropical center,
3, Road 3/2, District 10, Ho Chi Minh, Vietnam;
e-mail: huy241989@gmail.com
Doan Thanh Van,
Cand. Sci. (Eng), Researcher,
Vietnam-Russia Tropical center,
3, Road 3/2, District 10, Ho Chi Minh, Vietnam;
e-mail: doanvan.ttndvn@gmail.com
Все авторы прочитали и одобрили окончательный вариант рукописи.
СВЕДЕНИЯ ОБ АВТОРАХ
Зайдес Семен Азикович
доктор технических наук, профессор,
заведующий кафедрой машиностроительных
технологий и материалов,
Иркутский национальный исследовательский
технический университет,
664074, Россия, г. Иркутск, ул. Лермонтова, 83,
Россия;
Н e-mail: zsa@istu.edu Ву Ван Гюи,
кандидат технических наук,
научный сотрудник,
Российско-Вьетнамский Тропический
научно-исследовательский
и технологический центр,
г. Хошимин, 3, ул. 3/2, район 10, Вьетнам;
e-mail: huy241989@gmail.com
Доан Тхань Ван,
кандидат технических наук,
научный сотрудник,
Российско-Вьетнамский Тропический
научно-исследовательский
и технологический центр,
г. Хошимин, 3, ул. 3/2, район 10, Вьетнам;
e-mail: doanvan.ttndvn@gmail.com
ВЕСТНИК ИРКУТСКОГО ГОСУДАРСТВЕННОГО ТЕХНИЧЕСКОГО УНИВЕРСИТЕТА 2020;24(2):262-274
