Vol. 24 No. 2 2022 3 EDITORIAL COUNCIL EDITORIAL BOARD EDITOR-IN-CHIEF: Anatoliy A. Bataev, D.Sc. (Engineering), Professor, Rector, Novosibirsk State Technical University, Novosibirsk, Russian Federation DEPUTIES EDITOR-IN-CHIEF: Vladimir V. Ivancivsky, D.Sc. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Vadim Y. Skeeba, Ph.D. (Engineering), Associate Professor, Department of Industrial Machinery Design, Novosibirsk State Technical University, Novosibirsk, Russian Federation Editor of the English translation: Elena A. Lozhkina, Ph.D. (Engineering), Department of Material Science in Mechanical Engineering, Novosibirsk State Technical University, Novosibirsk, Russian Federation The journal is issued since 1999 Publication frequency – 4 numbers a year Data on the journal are published in «Ulrich's Periodical Directory» Journal “Obrabotka Metallov” (“Metal Working and Material Science”) has been Indexed in Clarivate Analytics Services. We sincerely happy to announce that Journal “Obrabotka Metallov” (“Metal Working and Material Science”), ISSN 1994-6309 / E-ISSN 2541-819X is selected for coverage in Clarivate Analytics (formerly Thomson Reuters) products and services started from July 10, 2017. Beginning with No. 1 (74) 2017, this publication will be indexed and abstracted in: Emerging Sources Citation Index. Journal “Obrabotka Metallov” (“Metal Working & Material Science”) has entered into an electronic licensing relationship with EBSCO Publishing, the world's leading aggregator of full text journals, magazines and eBooks. The full text of JOURNAL can be found in the EBSCOhost™ databases. Novosibirsk State Technical University, Prospekt K. Marksa, 20, Novosibirsk, 630073, Russia Tel.: +7 (383) 346-17-75 http://journals.nstu.ru/obrabotka_metallov E-mail: metal_working@mail.ru; metal_working@corp.nstu.ru
OBRABOTKAMETALLOV Vol. 24 No. 2 2022 4 EDITORIAL COUNCIL EDITORIAL COUNCIL CHAIRMAN: Nikolai V. Pustovoy, D.Sc. (Engineering), Professor, President, Novosibirsk State Technical University, Novosibirsk, Russian Federation MEMBERS: The Federative Republic of Brazil: Alberto Moreira Jorge Junior, Dr.-Ing., Full Professor; Federal University of São Carlos, São Carlos The Federal Republic of Germany: Moniko Greif, Dr.-Ing., Professor, Hochschule RheinMain University of Applied Sciences, Russelsheim Florian Nürnberger, Dr.-Ing., Chief Engineer and Head of the Department “Technology of Materials”, Leibniz Universität Hannover, Garbsen; Thomas Hassel, Dr.-Ing., Head of Underwater Technology Center Hanover, Leibniz Universität Hannover, Garbsen The Spain: Andrey L. Chuvilin, Ph.D. (Physics and Mathematics), Ikerbasque Research Professor, Head of Electron Microscopy Laboratory “CIC nanoGUNE”, San Sebastian The Republic of Belarus: Fyodor I. Panteleenko, D.Sc. (Engineering), Professor, First Vice-Rector, Corresponding Member of National Academy of Sciences of Belarus, Belarusian National Technical University, Minsk The Ukraine: Sergiy V. Kovalevskyy, D.Sc. (Engineering), Professor, Vice Rector for Research and Academic Affairs, Donbass State Engineering Academy, Kramatorsk The Russian Federation: Vladimir G. Atapin, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Victor P. Balkov, Deputy general director, Research and Development Tooling Institute “VNIIINSTRUMENT”, Moscow; Vladimir A. Bataev, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Vladimir G. Burov, D.Sc. (Engineering), Professor, Novosibirsk State Technical University, Novosibirsk; Aleksandr N. Gerasenko, Director, Scientifi c and Production company “Mashservispribor”, Novosibirsk; Sergey V. Kirsanov, D.Sc. (Engineering), Professor, National Research Tomsk Polytechnic University, Tomsk; Aleksandr N. Korotkov, D.Sc. (Engineering), Professor, Kuzbass State Technical University, Kemerovo; Evgeniy A. Kudryashov, D.Sc. (Engineering), Professor, Southwest State University, Kursk; Dmitry V. Lobanov, D.Sc. (Engineering), Associate Professor, I.N. Ulianov Chuvash State University, Cheboksary; Aleksey V. Makarov, D.Sc. (Engineering), Corresponding Member of RAS, Head of division, Head of laboratory (Laboratory of Mechanical Properties) M.N. Miheev Institute of Metal Physics, Russian Academy of Sciences (Ural Branch), Yekaterinburg; Aleksandr G. Ovcharenko, D.Sc. (Engineering), Professor, Biysk Technological Institute, Biysk; Yuriy N. Saraev, D.Sc. (Engineering), Professor, Institute of Strength Physics and Materials Science, Russian Academy of Sciences (Siberian Branch), Tomsk; Alexander S. Yanyushkin, D.Sc. (Engineering), Professor, I.N. Ulianov Chuvash State University, Cheboksary
Vol. 24 No. 2 2022 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Timofeev S.P., Grinek A.V., Hurtasenko A.V., Boychuk I.P. Machining technology, digital modelling and shape control device for large parts..................................................................................................................... 6 Shlykov E.S. ,Ablyaz T.R.. Muratov K.R. Theoretical simulation of the process interelectrode space fl ushing during copy-piercing EDM of products made of polymer composite materials................................................ 25 Loginov Yu.N., Shimov G.V., Bushueva N.I. Deformations in the nonstationary stage of aluminum alloy rod extrusion process with a low elongation ratio.............................................................................................. 39 Sundukov S.K. Features of the superposition of ultrasonic vibrations in the welding process........................ 50 EQUIPMENT. INSTRUMENTS Podgornyj Yu.I., Martynova T.G., Skeeba V.Yu. On the issue of limiting the irregular motion of a technological machinewithin specifi ed limits.................................................................................................... 67 MATERIAL SCIENCE Burkov A.A., Kulik M.A., Belya A.V., Krutikova V.O. Electrospark deposition of chromium diboride powder on stainless steel AISI 304..................................................................................................................... 78 Gulyashinov P.A., Mishigdorzhiyn U.L., Ulakhanov N.S. Infl uence of boriding and aluminizing processes on the structure and properties of low-carbon steels........................................................................ 91 EDITORIALMATERIALS Guidelines for Writing a Scientifi c Paper ............................................................................................................ 102 Abstract requirements ......................................................................................................................................... 107 Rules for authors ................................................................................................................................................. 111 FOUNDERS MATERIALS 119 CONTENTS
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 Electrospark deposition of chromium diboride powder on stainless steel AISI 304 Alexander Burkov 1, a, *, Maria Kulik1, b, Alexander Belya 1, c, Valeria Krutikova 2, d 1 Institute of Materials Science of the Khabarovsk Scientifi c Center of the Far-Eastern Branch of the Russian Academy of Sciences, 153 Tikhookeanskaya, Khabarovsk, 680042, Russian Federation 2 Institute of Tectonics and Geophysics, Far Eastern Branch of the Russian Academy of Sciences, 65 Kim Yu Chen street, Khabarovsk, 680000, Russian Federation a https://orcid.org/0000-0002-5636-4669, burkovalex@mail.ru, b https://orcid.org/0000-0002-4857-1887, marijka80@mail.ru, c https://orcid.org/0000-0001-8795-3346, whitewolf-97@mail.ru, d https://orcid.org/0000-0001-9977-2809, nm32697@gmail.com Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2022 vol. 24 no. 2 pp. 78–90 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2022-24.2-78-90 ART I CLE I NFO Article history: Received: 24 February 2022 Revised: 15 March 2022 Accepted: 23 March 2022 Available online: 15 June 2022 Keywords: Electrospark deposition Stainless steel AISI 304 Chromium boride Wettability Corrosion Oxidation resistance Wear Acknowledgements Research were partially conducted at core facility “Structure, mechanical and physical properties of materials”. ABSTRACT Introduction. Austenitic stainless steel AISI 304 is the most widely used type of stainless steel. However, it is subject to wear due to relatively low hardness, and also begins to oxidize intensively in air at a temperature above 800 °C. The use of coatings based on chromium boride can improve its tribotechnical properties and oxidation resistance. The purpose of the work: to study the effect of chromium diboride concentration in the anode mixture on the structure, wear behavior, oxidation resistance and corrosion properties of electric spark coatings on AISI 304 steel. The research methods. Electric spark treatment of AISI 304 steel was carried out in a mixture of iron granules with the addition of CrB2 powder in amount of 5, 10 and 15 vol.%. The structure of the coatings was studied by X-ray analysis, scanning electron microscopy, and electron dispersion spectroscopy analysis. The wear resistance of the coatings was studied under dry friction condition at a load of 10 N. The oxidation resistance test was carried out at a temperature of 900 °C for 100 hours. Results and Discussion. According to X-ray analysis, it is shown that under the conditions of electric spark exposure, CrB2 interacts with iron melt; this has resulted in the formation of chromium and iron borides. Corrosion properties, microhardness, coeffi cient of friction and wear are investigated in comparison with AISI 304 steel. Samples with coatings showed a lower corrosion potential and corrosion current density compared to the substrate in 3.5% NaCl solution and from 5 to 15 times higher oxidation resistance. The microhardness of the coatings increased from 6.25 to 7.60 GPa with an increase in the addition of chromium diboride in the electrode mixture. The coeffi cient of friction and the wear rate of all coatings were lower than that of AISI 304 stainless steel, while the coating prepared with the addition of 5 vol.% chromium diboride had the best tribotechnical characteristics. For citation: Burkov A.A., Kulik M.A., Belya A.V., Krutikova V.O. Electrospark deposition of chromium diboride powder on stainless steel AISI 304. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2022, vol. 24, no. 2, pp. 78– 90. DOI: 10.17212/1994-6309-2022-24.2-78-90. (In Russian). ______ * Corresponding author Burkov Alexander A., Ph.D. (Physics and Mathematics), Senior researcher Institute of Materials Science of the Khabarovsk Scientifi c Center of the Far-Eastern Branch of the Russian Academy of Sciences, 153 Tikhookeanskaya, 680042, Khabarovsk, Russian Federation Tel.: 8 (914) 1618954, e-mail: burkovalex@mail.ru Introduction Austenitic stainless steel AISI 304 has excellent mechanical properties and good oxidation resistance, as well as high corrosion resistance in a wide variety of media. Because of this, AISI 304 is the most widely used type of stainless steel and is used as structural components subject to corrosion. So it is used in the manufacture of nuclear reactors, in the medical fi eld and in the food industry [1]. However, due to low hardness (~2 GPa), AISI 304 steel is highly susceptible to wear [2]. The addition of carbon can increase the
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 hardness of stainless steel, but at the same time reduces its ductility. Application of hardening coatings can increase the surface hardness of stainless steel and improve its tribological behavior [3-4]. Cermet materials (MC) are a composite of ceramic phases embedded in a metal matrix [5]. Due to ceramic inclusions, MC coatings have a high hardness, and a plastic metal bond provides high strength and adhesion to the substrate, which together leads to high wear resistance [6–7]. Transition metal borides have high hardness and, therefore, are considered as a ceramic component of MC coatings [8]. Thus, it was shown in [9] that FeCrB coatings improve the microhardness and wear resistance of ASTM 283-C steel. It was shown in [10] that an increase in the content of boride ceramics in MC coatings leads to an increase in its microhardness. According to the paper [11], the microhardness of AISI 304 borated steel can reach 17 GPa. Electrospark deposition (ESD) is widely used to form MC coatings on metal base [12–14]. ESD is based on the phenomenon of polar metal transfer from the anode to the cathode in the process of exposure tomultiple microarc discharges [15]. Due to the high cooling rate of the material, a coating with an exceptionally fi negrained structure is formed after the termination of the discharge [16]. In addition, ESD is characterized by high adhesion of the formed layer to the base without thermal infl uence on the bulk characteristics of the substrate material [17]. The modifi ed ESD method with a non-localized electrode in a mixture of granules with ceramic powder has a number of advantages over traditional ESD, since it does not require additional operations for the preparation of MC electrodes and allows coating parts with a curved surface in automatic mode [18]. In addition, the method of ESD with a non-localized electrode is characterized by a low cost of equipment compared to other methods of deposition of MC coatings. In this work to obtain Fe-CrB MC coatings, AISI 304 stainless steel was processed in a mixture of iron granules with different concentrations of chromium diboride powder in order to establish the effect of the CrB2 powder concentration in the anode mixture on the structure, wear behavior, oxidation resistance and corrosion properties of the formed ESD coatings. Methods Three anode mixtures of steel granules (St3 steel) in the form of cylinders (d = 4±0.5 mm, h = 4±0.5 mm) and CrB2 powder were used as a non-localized electrode (Table 1). The diameter of the powder particles was signifi cantly smaller than the diameter of the area affected by the discharge ~0.8 mm, and was in the range from 25 to 134 μm with a median of 62 μm (Fig. 1). The substrate (cathode) of stainless steel AISI 304 (Table 2) was made in the form of a cylinder (d = 12 mm, h = 10 mm). The layout of the installation for the deposition of coatings with a non-localized anode with the addition of powder is described in detail in [19]. The IMES-40 discharge pulse source generated rectangular current pulses with amplitude of 110 A, duration of 100 μs, and frequency of 1000 Hz at voltage of 30 V. To prevent oxidation of the samples surface the argon was supplied to the working volume of the container with rate of 10 L/min. The mass transfer kinetics was studied by successively weighing the cathode every 120 s of ESA on a Vibra HT120 analytical balance with an accuracy of 0.1 mg. The total processing time for one sample Ta b l e 1 The content of CrB2 in the anode mixture, designation and characteristics of coatings CrB2 concentration, vol.% 5 10 15 Designation of samples Cr5 Cr10 Cr15 Coating characteristics Thickness, μm 35.7±2.3 33.5±5.7 30.7±6.1 Roughness (Ra), μm 7.1±0.88 7.4±1.14 9.1±0.60 Water contact angle, o 70.2±8.6 58.1±5.8 57.6±10.6
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 Fig. 1. Distribution of chromium diboride powder particles by diameter: 1 – integral; 2 – differential Ta b l e 2 Chemical composition of AISI 304 steel Element Fe Cr Ni Mn Cu P C S Concentration, wt. % 66.3‒74 18 8 ≤ 2 ≤ 1 ≤ 0.045 ≤ 0.03 ≤ 0.03 was 600 s. To ensure reproducibility of the results the cathode weight gain was studied for three samples from each series. The structure of the formed coatings was studied using a Sigma 300 VP scanning electron microscope (SEM) equipped with an INCA Energy dispersive spectroscopy (EDS) analyzer and a DRON-7 X-ray diffractometer in Cu-Kα radiation. The roughness of the coatings was measured on a TR 200 profi lometer. The contact angle of wetting with water was measured at room temperature according to the sessile drop method [20]. Polarization tests were carried out in a three-electrode cell in a 3.5% NaCl solution using a P-2X galvanostat (Electro Chemical Instruments, Russia) with a scanning rate of 10 mV/s. A standard Ag/AgCl electrode served as a reference electrode, and a paired ETP-02 platinum electrode was used as a counter electrode. Before recording the samples were held for 30 minutes to stabilize the current of open circuit potential. Cyclic oxidation resistance tests were carried out in a muffl e furnace at a temperature of 900 °C in air. Cube samples with an edge of 6 mm were kept at a given temperature for ~6 hours, then removed and cooled in a desiccator to room temperature. The total testing time was 100 hours. During the oxidation resistance test, the samples were placed in ceramic crucibles to take into account the mass of exfoliated oxides. The change in the weight of the samples was measured using a laboratory balance with a sensitivity of 10–4 g. The weight gain Δm for steel AISI 304 and coatings after the oxidation resistance test was calculated by formula: , w m S where Δw – weight gain and S – sample area.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 The hardness of the coatings was measured on a PMT-3M microhardness tester at a load of 0.5 N using the Vickers method. The wear resistance and coeffi cient of friction of the samples were tested following the ASTM G99-17 procedure under dry friction condition with speed of 0.47 ms–1 under load of 25 N. The testing time was 20 minutes. Discs made of M45 high-speed steel with a hardness of 60 HRC were used as a counterbody. Wear was measured gravimetrically. The sample of each type was tested three times. Results and discussion The study of mass transfer during ESD is important for establishing the fact of a positive weight gain of the cathode, otherwise ESD is not effective. In addition, the coating thickness is a function of the cathode weight gain [21]. During the ESD, electric discharges arose between steel granules and the substrate, which resulted in a liquid-phase transfer of the metal from the granules surface to the substrate. The powder particles that appeared on the surface of the electrodes at the moment of development of the discharge channel were fused with the metal. This was accompanied by a monotonous increase in the weight gain of the cathode (Fig. 2, a). With an increase in the processing time for all mixtures, a slowdown in the weight gain of the cathode was observed, which is also characteristic of the traditional ESD [22]. This is explained by the accumulation of defects in the coating and the intensifi cation of its electrical erosion with an increase in the specifi c number of discharges [23]. The largest gain of the cathode after 600 seconds of ESA was observed for the anode mixture of Cr5, and in the case of mixtures of Cr10 and Cr15, taking into account the error bars, the gain can be considered close. This behavior of mass transfer can be explained by the deterioration of the electrical contact and a decrease in the frequency of discharges with an increase in the powder concentration in a mixture of granules, which was previously observed for silicon powder [24]. Therefore optimal concentration of CrB2 powder in a mixture with iron granules is about 5 vol.% from the standpoint of achieving the maximum coating thickness. a b Fig. 2. AISI 304 stainless steel cathode weight gain during ESD (a) and X-ray diffraction patterns of deposited coatings (b) Figure 2, b shows the results of X-ray analysis of the prepared coatings. From this it follows that the composition of the coatings was dominated by a solid solution of chromium in iron, which forms a metal binder of the coating, and ceramic phases of chromium (Cr5B3, Cr2B) and iron (Fe23B6) borides are also present. This indicates that the original CrB2 phase was not retained in the coating due to its high reac-
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 a b Fig. 3. SEM image of the elements of the cross-section of the Cr5 coating in the back scattered electrons mode (a) and EDS distribution of elements in depth (b) tivity with iron and chromium melts under electric discharge conditions. Thus, in this case the mechanism of crystallization of ceramic phases from the melt after the terminated discharge is realized. Figure 3, a shows a cross-sectional image of the Cr5 coating and element distribution profi le data according to EDS analysis. The coating has a slightly darker shade compared to the substrate due to the enrichment with boron, which was not fi xed by the EDS analysis. Figure 3b shows a sharp transition between the deposited layer and the substrate. It also indicates a decrease in the concentration of substrate elements in the coating structure that is explained by the transfer of iron from the granules. The coating had a dense homogeneous structure with a small amount of small pores. With an increase in the powder concentration in the anode mixture, the average coating thickness decreased monotonically from 35.7 to 30.7 μm, and the roughness (Ra) increased from 7.1 to 9.1 μm (Table 1). Water contact angle (WCA) was measured to study the hydrophobic properties of the coating surface. The WCA is inversely proportional to the surface energy. As shown in Table 1, the WCA decreased from 70.2 to 57.6° with an increase in the concentration of CrB2 in the anode mixture that means decrease in the hydrophobicity of its surface. However, in general electrospark Fe-Cr-B coatings had lower surface energy and higher hydrophobicity compared to AISI 304 stainless steel (WCA 48.9°). Figure 4 shows the results of polarization testing of samples in 3.5% NaCl solution at room temperature. It shows that the potentiodynamic curves of all coatings have signifi cantly higher corrosion potential of Ecorr compared to AISI 304 steel. For detailed description of the corrosion behavior of the samples, the corrosion current Icorr was calculated from the slopes of the Tafel portions of the potentiodynamic curves (Table 3). It follows from Table 3 that with an increase in the amount of CrB2 powder in a mixture of granules, the corrosion current of the coatings monotonically decreased, which indicates an improvement in the anticorrosion behavior. Thus, saturation of the AISI 304 steel surface with chromium boride improves its anti-corrosion behavior. This is explained by the barrier action of a thin Cr2O3 fi lm inevitably formed on the surface of metallic chromium [25]. In addition, ceramic phases limit the contact area of the metal with the electrolyte [6]. Fig. 4. Tafel polarization curves of coatings and substrate
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 a b Fig. 5. Oxidation resistance of coatings at a temperature of 900 оС in air (a) and X-ray patterns of the samples surface after the oxidation resistance test (b) Ta b l e 3 Corrosion parameters of coatings Parameters Samples AISI 304 Cr5 Cr10 Cr15 Ecorr, V –0.777 –0.646 –0.603 –0.489 Icorr, μA/сm2 42.24 20.66 14.80 11.47 Figure 5, a shows the results of cyclic testing of Fe-Cr-B coatings for oxidation resistance at a temperature of 900 °C. The weight gain of samples with coatings, according to the results of 100 hours of testing, ranged from 17 to 51 g/m2. The smallest gain was observed for the Cr15 sample, and the largest for Cr10, however, in this case, the weight gain is not an unambiguous criterion for the oxidation intensity. Thus, the inset to Figure 5a shows that uncoated AISI 304 steel gained weight in the fi rst test cycle, and monotonically substrate weight loss in subsequent cycles. This cannot be explained by the delamination of oxide layers, as was the case in [26], due to the presence of samples in ceramic crucibles during the oxidation resistance test. Therefore, the only explanation for the observed weight loss of AISI 304 steel can be the burnout of carbon, phosphorus and sulfur included in its composition (Table 2). It is noteworthy that in the above work, for 100 hours of testing at 900 °C, the weight gain of AISI 304 steel was only 6.5 g/m2, and in [27] – 22.2 g/m2 for 90 hours. The oxidation rate of the Cr5 sample was the highest among the coatings up to 65 hours, and then the weight gain stopped, that can be explained by the action of two differently directed processes: weight loss by the substrate and weight gain of the coating. Thus, the oxidation resistance of the Cr5 coating can be qualifi ed as the worst. The Cr15 coating had the best oxidation resistance. The gain in the process of high-temperature oxidation is due to the fi xation of oxygen on the surface of the samples with the formation of magnetite Fe2O3 and hematite Fe2O3 (Fig. 5, b). According to X-ray data, ferrochrome Fe0.52Cr1.36 was also observed on the surface of the samples after the oxidation resistance test, the intensity of the refl ections of which monotonically increased from the sample Cr5 to Cr15. It is explained by a decrease in the thickness of the oxide layer and confi rms the improvement in the oxidation resistance of coatings with an increase in CrB2 in the anode mixture. In general, the use of electrospark Fe-Cr-B coatings makes it possible to increase the oxidation resistance of AISI 304 stainless steel from 5 to 15 times.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 Figure 6 shows that the deposition of Fe-Cr-B coatings makes it possible to increase the surface hardness of AISI 304 steel by 2.2–2.7 times. With an increase in the concentration of CrB2 powder in the anode mixture, the average microhardness of the coating surface increased from 6.25 to 7.6 GPa. This can be explained by an increase in the content of chromium and boride phases in the coating. Nevertheless, mild hardness values, compared with high hardness of borides, indicate a low volume fraction of ceramic phases in the coatings. That is consistent with the phase analysis data. In general, these results are consistent with the data obtained in [9], where the microhardness of wire-arc spraying Fe87-xCr13Bx coatings increased from 7.9 to 9 GPa with increase in the boron content from 1 to 4 wt.%. The kinetics of the change in the coeffi cient of friction of the samples during the wear test under dry friction condition is shown in Figure 7, a. The average values of the coatings coeffi cient of friction were lower than those of stainless steel and were in a narrow range from 0.69 to 0.71. However, for the Cr10 and Cr15 samples deposited with a high powder content in the anode mixture, narrow ravines were observed in the friction coeffi cient curves, while the curve was smooth for the Cr5 coating. In the case of steel, a high noise level was observed on the graph of the coeffi cient of friction that is usually associated with its high plasticity and with periodic deposition and delamination of the material transferred between the rubbing surfaces [28]. Thus, in particular, in samples Cr10 and Cr15, noise can be caused by delamination of microsections of the coating due to defi ciency of plastic metal binder. The results of coating wear tests showed that the wear rate was in the range of 0.76–1.7 × 10–5 mm3/ Nm (Fig. 7, b). It was lower than that of AISI 304 steel, from 1.6 to 3.7 times. The lowest wear values were demonstrated by the Cr5 coating that is consistent with the data on the coeffi cient of friction. At a higher concentration of CrB2 in the mixture of granules, the wear of the samples increased, that is caused by a de- a b Fig. 7. Dynamics of the coeffi cient of friction from the sliding path (a) and the wear rate (б) of coatings compared to AISI304 stainless steel Fig. 6. Microhardness of coatings compared to AISI 304 steel
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 2 2022 crease in the volume of the plastic metal binder in these coatings and increasing brittleness under friction. In addition, when analyzing the wear resistance of a Cr5 sample, it is worth considering the large thickness of this coating compared to other samples, as indicated by the data on the cathode weight gain (Fig. 2, a). Conclusion Cermet Fe-Cr-B coatings were formed on AISI 304 stainless steel by electrospark treatment in a mixture of iron granules and 5-15 vol.% CrB2 powder. The largest cathode weight gain and coating thickness were in case of using an anode mixture with 5 vol.% CrB2. The X-ray data indicate the cermet structure of the coatings, where the role of the binder is performed by ferrochrome, and the role of ceramics are performed the Cr5B3, Cr2B, and Fe23B6 phases. The borides were formed as a result of the complete destruction of CrB2 upon interaction with an iron melt under the conditions of an electric discharge. With an increase in the concentration of CrB2 in the anode mixture, an improvement in the anticorrosion properties of Fe-Cr-B coatings in a 3.5% NaCl solution and an increase in oxidation resistance compared to AISI 304 steel from 5 to 15 times were observed. The use of electrospark Fe-Cr-B coatings on AISI 304 stainless steel makes it possible to increase its surface hardness, reduce and stabilize the friction coeffi cient, and improve wear resistance by 3.7 times. References 1. Mahdavi A., Medvedovski E., Mendoza G.L., McDonald A. Corrosion resistance of boronized, aluminized, and chromized thermal diffusion-coated steels in simulated high-temperature recovery boiler conditions. Coatings, 2018, vol. 8, iss. 8, p. 257. DOI: 10.3390/coatings8080257. 2. Frutos A. de, Arenas M.A., Fuentes G.G., Rodríguez R.J., Martínez R., Avelar-Batista J.C., Damborenea J.J. de. Tribocorrosion behaviour of duplex surface treated AISI 304 stainless steel. Surface and Coatings Technology, 2010, vol. 204, iss. 9–10, pp. 1623–1630. DOI: 10.1016/j.surfcoat.2009.10.039. 3. Ushashri K., Masanta M. Hard TiC coating on AISI304 steel by laser surface engineering using pulsed Nd: YAG laser. Materials and Manufacturing Processes, 2015, vol. 30, iss. 6, pp. 730–735. DOI: 10.1080/10426914.20 14.973593. 4. Sahoo C.K., MasantaM. Microstructure andmechanical properties of TiC-Ni coating onAISI304 steel produced by TIG cladding process. Journal of Materials Processing Technology, 2017, vol. 240, pp. 126–137. DOI: 10.1016/j. jmatprotec.2016.09.018. 5. Golyshev A.A., Orishich A.M. Issledovanie vliyaniya rezhimov fokusirovki lazernogo izlucheniya na geometricheskie i mekhanicheskie svoistva metallokeramicheskikh trekov [Study of the laser radiation focusing modes effect on geometrical and mechanical properties of metal-ceramic tracks]. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Materials Science, 2019, vol. 21, no. 1, pp. 82–92. DOI: 10.17212/1994-6309-2019-21.1-82-92. 6. Yan D., He J., Wu J., Qiu W., Ma J. The corrosion behaviour of a plasma spraying Al2O3 ceramic coating in dilute HC1 solution. Surface and Coatings Technology, 1997, vol. 89, iss. 1–2, pp. 191–195. DOI: 10.1016/S02578972(96)02862-9. 7. Berger L.-M. Application of hardmetals as thermal spray coatings. International Journal of Refractory Metals and Hard Materials, 2015, vol. 49, pp. 350–364. DOI: 10.1016/j.ijrmhm.2014.09.029. 8. Mishigdorzhiyn U.L., Sizov I.G., Polaynsky I.P. Formirovanie pokrytii na osnove bora i alyuminiya na poverkhnosti uglerodistykh stalei elektronno-luchevym legirovaniem [Formation of coatings based on boron and aluminumon the surface of carbon steels by electron beamalloying]. Obrabotkametallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Materials Science, 2018, vol. 20, no. 2, pp. 87–99. DOI: 10.17212/1994-63092018-20.2-87-99. 9. Yao H.H., Zhou Z., Wang Y.M., He D.Y., Bobzin K.,· Zhao L., Öte M., Königstein T. Microstructure and properties of FeCrB alloy coatings prepared by wire-arc spraying. Journal of Thermal Spray Technology, 2017, vol. 26, iss. 3, pp. 483–491. DOI: 10.1007/s11666-016-0510-9. 10. Kılıç M. Microstructural characterization of Ni-based B4C reinforced composite coating produced by tungsten inert gas method. Archives of Metallurgy and Materials, 2021, vol. 66 (3), pp. 917–924. DOI: 10.24425/ amm.2021.136398. 11. Turkoglu T., Ay I. Investigation of mechanical, kinetic and corrosion properties of boridedAISI 304, AISI 420 and AISI 430. Surface Engineering, 2021, vol. 37, iss. 8, pp. 1020–1031. DOI: 10.1080/02670844.2021.1884332.
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