Vol. 24 No. 1 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. 1 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. 23 No. 2 2021 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Kuznetsov V.P., Makarov A.V., Skorobogatov A.S., Skorynina P.A., Luchko S.N., Sirosh V.A., Chekan N.M. Normal force infl uence on smoothing and hardening of steel 03Cr16Ni15Mo3Ti1 surface layer during dry diamond burnishing with spherical indenter............................................................................ 6 Gubin D.S., Kisel’A.G. Calculation of temperatures during fi nishing milling of a nickel based alloys.......... 23 EQUIPMENT. INSTRUMENTS Bratan S.M., Roshchupkin S.I., Chasovitina A.S., Gupta K. The effect of the relative vibrations of the abrasive tool and the workpiece on the probability of material removing during fi nishing grinding................. 33 MATERIAL SCIENCE OzolinA.V., Sokolov E.G. Effect of mechanical activation of tungsten powder on the structure and properties of the sintered Sn-Cu-Co-W material................................................................................................................. 48 Korobov Yu.S., Alwan H.L., Makarov A.V., Kukareko V.A., Sirosh V.A., Filippov M.A., Estemirova S. Kh. Comparative study of cavitation erosion resistance of austenitic steels with different levels of metastability................................................................................................................................................... 61 Vologzanina S.A., IgolkinA.F., PeregudovA.A., Baranov I.V., Martyushev N.V. Effect of the deformation degree at low temperatures on the phase transformations and properties of metastable austenitic steels.......... 73 Filippov A.V., Shamarin N.N., Moskvichev E.N., Novitskaya O.S., Knyazhev E.O., Denisova Yu.A., Leonov A.A., Denisov V.V. Investigation of the structural-phase state and mechanical properties of ZrCrN coatings obtained by plasma-assisted vacuum arc evaporation..................................................................... 87 EDITORIALMATERIALS Guidelines for Writing a Scientifi c Paper ............................................................................................................ 103 Abstract requirements ......................................................................................................................................... 107 Rules for authors ................................................................................................................................................. 111 FOUNDERS MATERIALS 119 CONTENTS
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 Effect of mechanical activation of tungsten powder on the structure and properties of the sintered Sn-Cu-Co-W material Alexander Ozolin a, *, Evgeny Sokolov b Kuban State Technological University, 2 Moskovskaya St., Krasnodar, 350072, Russian Federation a https://orcid.org/0000-0002-0173-1716, ozolinml@yandex.ru, b https://orcid.org/0000-0002-7229-228X, e_sokolov.07@mail.ru Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science. 2022 vol. 24 no. 1 pp. 48–60 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2022-24.1-48-60 Obrabotka metallov - Metal Working and Material Science Journal homepage: http://journals.nstu.ru/obrabotka_metallov ART I CLE I NFO Article history: Received: 14 October 2021 Revised: 02 November 2021 Accepted: 07 December 2021 Available online: 15 March 2022 Keywords: Mechanical activation Nanoparticles Tungsten Liquid phase sintering Metallic binders Diamond abrasive tools Funding The research was carried out with the fi nancial support of the Council for Grants of the President of the Russian Federation for state support of young Russian scientists and for state support of leading scientifi c schools of the Russian Federation, No. SP-5863.2021.1. ABSTRACT Introduction. One of the methods for improving the properties of sintered materials is mechanical activation of powders. It ensures milling the powders, changing its energy state, intensifying the sintering of powder materials, and forming a fi ne-grained structure in it. When tungsten powders are mechanically activated in planetary centrifugal mills, nanoparticles can be formed, which have a high reactive power. The objective of the paper is to study the effect of mechanical activation of tungsten particles on the structure and properties of the sintered Sn-Cu-Co-W powder material. Research technique: Mechanical activation of W16,5 grade tungsten powder is carried out in a planetary centrifugal ball mill AGO-2U for 5…120 minutes with carrier speeds of 400…1,000 rpm. The mixture of tungsten, tin, copper, and cobalt powders are compacted by static pressing in molds and then sintered in vacuum at 820 °C. The morphology and size of powder particles, as well as the structure of the sintered samples, are studied by scanning electronic microscopy, X-ray microanalysis, and optical metallography. Porosity of the sintered samples is identifi ed by the gravimetric method. Microhardness of the structural constituents and macrohardness of the sintered materials are measured, too. Results: in the modes under study, mechanical activation is accompanied by the formation of tungsten nanoparticles with the minimum size of 25 nm. Alongside this, the powder is exposed to cold working, which hinders further milling. Tungsten nanoparticles, characterized by high surface energy, have a signifi cant effect on the dissolution-precipitation of cobalt during liquid-phase sintering of Sn-Cu-Co-W powder material. Addition of nanodispersed tungsten into the material slows down the growth of cobalt particles during sintering and contributes to the formation of a fi ne-grained structure. The sintered Sn-Cu-Co-W material, containing mechanically activated tungsten, features higher hardness of 105…107 HRB, which is explained by cold working of tungsten particles and dispersion hardening. The results can be applied for improving mechanical properties of Sn-Cu-Co-W alloys used as metallic binders in diamond abrasive tools. For citation: Ozolin A.V., Sokolov E.G. Effect of mechanical activation of tungsten powder on the structure and properties of the sintered Sn-Cu-Co-W material. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2022, vol. 24, no. 1, pp. 48–60. DOI: 10.17212/1994-6309-2022-24.1-48-60. (In Russian). ______ * Corresponding author Ozolin Alexander V., junior researcher Kuban State Technological University 2 Moskovskaya St., 350072, Krasnodar, Russian Federation Tel.: 8 (918) 058-56-54, e-mail: ozolinml@yandex.ru Introduction Sn-Cu-Co and Sn-Cu-Co-W alloys are used as metallic binders in diamond abrasive tools manufactured by the powder metallurgy process [1–3]. Binders of the sintered diamond tools have to be physically and chemically compatible with diamond, strong, and highly resistant to abrasion wear.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 One of the methods for enhancing the properties of sintered materials is mechanical activation of powders. It provides milling of the powders, changing its energy state, intensifi ed sintering of the powder materials, and forming a fi ne-grained structure in it [4–7]. When certain powders are mechanically activated in planetary centrifugal mills, nanoparticles having a high reactivity can be formed [8]. Works [9–13] demonstrate that addition of nanoparticles into metallic binders ensures dispersion hardening of the binders and helps enhance operational properties of the diamond tools considerably. For this purpose, nanopowders of carbon-based materials, boron nitride, and high-melting oxides and carbides (ZrO2, WC) are used. The melting temperature of nanoparticles is known to be lower than that of micropowders [14]. So, to ensure dispersion hardening, nanoparticles have to be preserved in the structure of the material after sintering. An important characteristic of metallic binders is its adhesion activity to diamond, which provides strong retention of diamond grains in the binders. Nanoparticles located on the matrix-fi ller interface are known to be able to produce a considerable effect on mechanical properties of the composite material [15–17]. With regard to this, one can suppose that addition of nanodispersed particles of carbide-forming metals to the binder will allow enhancing its adhesion to diamond essentially. One more factor contributing to adhesion activity of binders can be the changed energy state and higher reactivity of the powders after its mechanical activation. Tungsten is one of the most refractory metals. Annealed tungsten of high purity has the hardness of 225–300 HB, ultimate strength of 800–1,200 MPa, and its relative elongation is close to zero [18]. Such properties make it possible to mill tungsten mechanically to nanosized particles [8, 19]. The authors of this work have conducted preliminary experiments [20] demonstrating the possibility of obtaining 25–90 nm sized particles of tungsten in milling the PVT and W16,5 grade powders with a planetary centrifugal mill. With tungsten being a carbide-forming element, adding it into the powder material enhances diamond adhesion activity of the binder. However, under certain conditions, the additive can prevent the binder from sintering, which leads to increase in its porosity while also reducing its hardness and strength [21]. The objective of this work is to study the effect of mechanical activation of tungsten particles on the structure and properties of the sintered Sn-Cu-Co-W powder material. Research technique For the experiments, the following powders were used: PO1 tin powder (up to GOST 9723-73), PMS-1 copper powder (up to GOST 4960-75), and Diacob-1600 cobalt powder with the particle size of 1–2 μm (by Dr. Fritsch Kg., Germany). It was the W16,5 special tungsten powder (by Pobedit JSC) containing not less than 99.9% W with particles sized 19–24 μm (technical specifi cations TU 48-19-417-8) that was exposed to mechanical activation. Mechanical activation was performed in the AGO-2U planetary centrifugal mill for 5, 15, 60, and 120 minutes at the carrier rotation frequencies of 400, 800, and 1,000 RPM. Using the above powders, mixtures were prepared containing two kinds of tungsten powders – mechanically activated and non-activated; the proportion of the components was as follows (% wt.): 20 Sn; 43 Cu; 30 Co; 7 W. The 20 g weighted samples were compacted by single-action static pressing in an all-steel mould at the 12 t/cm2 press power. The resulting cylindrical samples of 21 mm diameter were sintered in vacuum at the temperature of 820 °C for 20 minutes. After that, the sintered samples were weighed with the Adventurer AR2140 assay balance (by OHAUS) to fi nd out its density as the ratio of weight to volume. Next, the structure of sintered materials was examined by scanning electron microscopy and optical metallography. For this, the authors used the JSM-7500F (by JEOL) ultrahigh resolution
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 scanning electron microscope, the EVO HD 15 electron microscope (by ZEISS), and the AxioObserver.A1m metallographic microscope (by ZEISS). As for distribution of elements within the samples, it was studied by X-ray microanalysis using the EVO HD 15 electron microscope. Microhardness of the structural constituents was measured by indentation of a tetrahedral diamond pyramid under the load of 10 g (HV0,01) with the DuraScan80 hardness meter (by EmcoTest). Hardness of the materials was measured according to the Rockwell method (scale B) using the TK-2M hardness meter. Results and discussion Effect of mechanical activation on the shape and size of tungsten particles In Figure 1, one can see the changed shape of tungsten powder particles after mechanical activation. Before the activation, the particles of tungsten were equiaxial polyhedra. After being mechanically activated for 60 min at the 800 RPM, most particles have the equiaxial shape and rough surface. A small quantity of the particles has the splintery shape. As the duration of mechanical activation is increased, the quantity of splintery particles goes down. a b Fig. 1. Shape of tungsten particles: a – before mechanical activation; b – after mechanical activation Sizes of the particles were measured using the images obtained with the electron microscope. After the described mechanical activation mode, it ranges within 0.025–12 μm. The particles are distributed according to sizes as follows: d10 = 67 nm; d50 = 220 nm; d90 = 750 nm. Meanwhile, in the mechanically activated powder, the share of nanoparticles sized up to 100 nm exceeds 20% (Figure 2). The minimum size of the particles, which equals to 25 nm, was obtained at the 800 RPM and the mechanical activation duration of 60–120 min (Table 1). After mechanical activation, the signifi cant proportion of the powder sticks together forming loose aggregates of up to 80 μm size. The aggregation of nanoparticles is explained by the presence of numerous uncompensated interatomic bonds on its surface. Combining such particles into aggregates contributes to a decrease in its free energy [13]. The shape and size of the resulting powders indicate the following processes occurring duringmechanical activation: large particles are split up; the fragments are rolled and gain the rounded shape; small particles
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 Ta b l e 1 Minimum size (nm) of tungsten W16,5 particles depending on mechanical activation mode Rotation speed, rpm Duration of mechanical activation, min 5 15 60 120 400 160 132 90 83 800 137 116 25 25 1,000 128 85 90 102 Fig. 2. Size distribution of tungsten particles after mechanical activation are aggregated. Alongside this, the material is exposed to work hardening, which hinders further milling. It can be seen fromTable 1 that increasing the duration of milling from 30 to 60 min practically does not lead to a decrease in particle size. Apparently, this is explained by work hardening of the particles. Increasing the rotation frequency leads to centrifugal forces and the kinetic energy of grinding media building up that results in the above milling processes getting intensifi ed. In particular, aggregation leading to large particle sizes mounts. Due to this, an increase in the carrier rotation frequency (from 800 to 1,000 RPM) does not give any positive effect. Effect of mechanical activation of tungsten on the structure of sintered Sn-Cu-Co-W materials Figure 3 shows the microstructure of two kinds of sintered materials: ones with tungsten not exposed to mechanical activation and ones with mechanically activated tungsten. Phase composition of the materials containing non-activated tungsten and its crystallization mechanism are described in works [3, 21]. After sintering, the materials contain the following phases: solid solution of tin and cobalt in copper (Cu), the Cu3Sn intermetallic compound, cobalt particles, and tungsten particles. Sintering of the materials at 820 °C proceeded with a large quantity of the liquid phase forming. Upon cooling after sintering, a Cu3Sn compound with a melting point of 755–798 °C was formed from the liquid phase [22]. X-ray microanalysis has shown that in the examined materials, the Cu3Sn intermetallic phase has almost the same composition, % wt.: 63.2 Cu; 33.5 Sn; 3.3 Co.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 Mechanically activated tungsten occurs in the material in the form of separate particles sized 25 nm and more and sintered agglomerates having the cross dimension of up to 0.4 mm. In Figure 4 b, one can see nanoparticles of tungsten located within the sintered agglomerate of cobalt and at the interface of cobalt and the Cu3Sn intermetallic phase; its cross dimension is around 100 nm. Thus, in spite of its higher reactivity and lower melting temperature, tungsten nanoparticles did not get dissolved either in cobalt or in the liquid phase during sintering. Figure 5 demonstrates that mechanical activation of tungsten contributes to its more uniform distribution in the sintered material. Apparently, the uniform distribution of fi nely dispersed particles of the carbideforming tungsten must have a positive effect on adhesion of the binder to the surface of diamond and contribute to stronger retention of diamond grains in the binder [23]. In Figure 3, the effect of mechanical activation of tungsten on the size of cobalt particles can be seen. As a rule, during liquid phase sintering of systems with limited solubility of components, what occurs in it a b Fig. 3. Structure of the sintered Sn-Cu-Co-W material: a – without mechanical activation of tungsten; b – with mechanically activated tungsten a b Fig. 4. Particles of mechanically activated tungsten in the sintered material structure: a – submicron, b – nanosized
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 is the dissolution-reprecipitation process. This process consists in small particles of the solid phase getting dissolved in the liquid phase and its substance reprecipitating against the surface of larger particles [24, 25]. In the material with tungsten not exposed to mechanical activation, the size of cobalt particles has increased owing to dissolution-reprecipitation from 1.6 μm up to 9–15 μm (see Figure 3 a). In the sintered material containing mechanically activated tungsten, cobalt particles are smaller, about 3–10 μm (Figure 3 b). The effect of mechanical activation of tungsten on the dissolution-reprecipitation of cobalt is explained by the following. In systems containing two solid metals and a liquid phase, the mass transfer is directed toward the metal having the largest free energy [26]. In the ascending order of the surface energy, the components of the system in question are located as follows: Sn, Cu, Co, W [27]. Under such conditions, it is transfer of cobalt via the liquid phase to tungsten particles that is the most favorable in terms of energy. The mass transfer of cobalt to tungsten through the liquid phase is confi rmed by component distribution maps given in Figure 5. In the maps, one can see sintered agglomerates of tungsten particles; notably, spaces between the particles are mainly fi lled up with cobalt. Obviously, cobalt penetrated deep into the tungsten agglomerates together with the liquid phase. Precipitation of cobalt led to blocking of pores of the agglomerates. After that, cobalt could fi nd its way deep into the agglomerates owing to its diffusion over the surface of tungsten particles. The mass transfer of cobalt to tungsten through the liquid phase occurs without mechanical activation of tungsten, too. In Figure 4 a, it can be seen that particles of tungsten not exposed to mechanical activation are surrounded by “enclosures” formed as a result of precipitation of cobalt from the liquid phase. Fig. 5. Element distribution maps for the material with mechanically activated tungsten: 1 – intermetallic compound Cu3Sn; 2 – cobalt particles; 3 – tungsten particles
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 As it has been demonstrated above, mechanical activation has led to higher fi neness of tungsten powder, with the area of its free surface increasing, respectively. As a result, precipitation of cobalt from the liquid phase against the particles of tungsten has intensifi ed. Thus, mechanical activation of tungsten has reduced the mass transfer from small cobalt particles to larger ones and contributed to the formation of the more dispersed, fi ne-grained structure in the sintered material. The effect of high-melting nanoparticles on dissolution-reprecipitation of another solid phase during liquid phase sintering needs further investigation. This phenomenon opens up new opportunities for acting on structure formation in sintering to obtain materials with the required structure and properties. Effect of mechanical activation of tungsten on the porosity of sintered Sn-Cu-Co-W materials In the sintered Sn-Cu-Co-W materials, there is a minor quantity of isolated closed pores. The material with non-activated tungsten has the density of 8.16 g/cm3 (porosity of 8%). Meanwhile, the material with milled tungsten has the density of 7.72 g/cm3 (porosity of 13 %). With its high chemical activity, fi nely dispersed tungsten tends to adsorb atmospheric gases and get oxidized. The WO2 tungsten oxide is decomposed when heated in vacuum up to the temperature of 800 °C [28]. Apparently, at the temperature of sintering, oxides are decomposed, and gases are extracted in the closed pores subsequently. The pressure of gases in the closed pores prevents it from healing, which results in higher porosity of the sintered material. Effect of mechanical activation of tungsten on the hardness of sintered Sn-Cu-Co-W materials It is clear from Table 2 that the hardest structural constituent of Sn-Cu-Co-W materials is particles of tungsten. Mechanically activated tungsten has a 1.8–2.2 times higher hardness. For technical reasons, hardness of nanoparticles cannot be measured with the 10 g indenter load. As for larger tungsten particles, having the cross dimension of 10–12 μm, its microhardness is 823–1,162 HV0,01. Higher hardness of mechanically activated tungsten is associated with work hardening of its particles. Recrystallization temperature of tungsten is known to be much higher than 820°C, so during sintering of the material, work hardening of tungsten particles was retained. Ta b l e 2 Microhardness HV0,01 of the structural constituents of the sintered Sn-Cu-Co-W material Sintered material Microhardness HV0,01 of the structural constituents (Cu) Cu3Sn Co W without mechanical activation of tungsten 245±12 367±7 137±16 496±29 with mechanical activation of tungsten 259±22 384±14 140±16 992±169 Apart of mechanically activated tungsten occurs within the material in the form of sintered agglomerates; its structure is given in Figure 6 (the light image; the sample was treated with the solution containing 5 g of ferrichloride, FeCl3, 15 ml of hydrochloric acid, HCl, and 100 ml of water). It can be seen that necking was formed between contact tungsten particles during sintering. Microhardness of the agglomerates was measured at the 100–500 g indenter load; meanwhile, hardness impresses have been obtained with the diagonal length exceeding the size of individual tungsten particles (see Figure 6). When the indenter was pressed in, the particles of tungsten did not get disconnected or crumbled away. In spite of its porous structure, the agglomerates feature high microhardness of 582–1,223 HV. In the structure of the materials under study, particles of tungsten occupy a small volume (less than 5 %), so its hardness has little effect on the general hardness of the material. In Figure 5, it can be seen that the largest volume in the structure of the materials belongs to the Cu3Sn intermetallic phase. In the material with mechanically activated tungsten, hardness of the Cu3Sn intermetallic compound is much higher
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 1 2022 Fig. 6. Microstructure of the sintered tungsten agglomerates (see Table 2). Obviously, this is associated with hardening of the intermetallic compound by fi nely dispersed tungsten particles. The sintered material containing tungsten not exposed to mechanical activation has the macrohardness of 101–102 HRB. Meanwhile, the material with mechanically activated tungsten features the higher hardness of 105–107 HRB, which is associated with work hardening of tungsten particles and dispersion hardening of other structural constituents. Conclusions 1. The effect of mechanical activation on the morphology of particles and fi neness of the W16,5 grade tungsten powder has been studied. In the examined modes, mechanical activation is accompanied by the formation of tungsten nanoparticles with the minimum size of 25 nm. Alongside this, the powder is exposed to work hardening, which hinders further milling. 2. With its high surface energy, tungsten nanoparticles produce a noticeable effect on cobalt dissolving and depositing in liquid phase sintering of the Sn-Cu-Co-W powder material. Introducing nanodispersed tungsten into the material slows down the growth of cobalt particles and helps to obtain a fi ne-grained structure. 3. The sintered Sn-Cu-Co-W material containing mechanically activated tungsten features higher hardness of 105–107 HRB, which is explained by work hardening of tungsten particles and dispersion hardening of other structural constituents. References 1. Konstanty J. Powder metallurgy diamond tools. Oxford, Elsevier, 2005. 152 p. ISBN 978-1-85617-440-4. DOI: 10.1016/B978-1-85617-440-4.X5077-9. 2. Novikov M.V., Mechnyk V.A., Bondarenko M.O., Lyashenko B.A., Kuzin M.O. Composite materials of diamond−(Co–Cu–Sn) system with improved mechanical characteristics. Part 1. The infl uence of hot re-pressing on the structure and properties of diamond−(Co–Cu–Sn) composite. Journal of Superhard Materials, 2015, vol. 37, pp. 402–416. DOI: 10.3103/S1063457615060052.
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