Vol. 26 No. 2 2024 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. 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 Journal “Obrabotka Metallov – Metal Working and Material Science” is indexed in the world's largest abstracting bibliographic and scientometric databases Web of Science and Scopus. 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.
OBRABOTKAMETALLOV Vol. 26 No. 2 2024 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 Aff airs, 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. Korotkov, D.Sc. (Engineering), Professor, Kuzbass State Technical University, Kemerovo; 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, V.P. Larionov Institute of the Physical-Technical Problems of the North of the Siberian Branch of the RAS, Yakutsk; Alexander S. Yanyushkin, D.Sc. (Engineering), Professor, I.N. Ulianov Chuvash State University, Cheboksary
Vol. 26 No. 2 2024 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Gaikwad V., Chinchanikar S. Investigations on ultrasonic vibration-assisted friction stir welded AA7075 joints: Mechanical properties and fracture analysis........................................................................................................................ 6 Sirota V.V., Zaitsev S.V., Limarenko M.V., Prokhorenkov D.S., Lebedev M.S., Churikov A.S., Dan'shin A.L. Preparation of coatings with high infrared emissivity.......................................................................................................... 23 Babaev A.S., Kozlov V.N., Semenov A.R., Shevchuk A.S., Ovcharenko V.A., Sudarev E.A. Investigation of cutting forces and machinability during milling of corrosion-resistant powder steel produced by laser metal deposition............. 38 Dolgova S.V., Malikov A.G., Golyshev A.A., Nikulina A.A. The eff ect of laser surfacing modes on the geometrical characteristics of the single laser tracks............................................................................................................................... 57 Karlina Y.I., Kononenko R.V., Popov M.A., Deryugin F.F., Byankin V.E. Assessment of welding engineering properties of basic type electrode coatings of diff erent electrode manufacturers for welding of pipe parts and assemblies of heat exchange surfaces of boiler units............................................................................................................................. 71 Yanpolskiy V.V., Ivanova M.V., Nasonova A.A., Yanyushkin A.S. Determination of the rate of electrochemical dissolution of U10A steel under ECM conditions with a stationary cathode-tool............................................................... 95 EQUIPMENT. INSTRUMENTS Zakovorotny V.L., Gvindjiliya V.E. The study of vibration disturbance mapping in the geometry of the surface formed by turning............................................................................................................................................................................. 107 Gasanov B.G., Konko N.A., Baev S.S. Study of the kinetics of forming of spherical sliding bearing parts made of corrosion-resistant steels by die forging of porous blanks............................................................................................... 127 Gvindjiliya V.E., Fominov E.V., Moiseev D.V., Gamaleeva E.I. Infl uence of dynamic characteristics of the turning process on the workpiece surface roughness........................................................................................................................ 143 Lobanov D.V., Skeeba V.Yu., Golyushov I.S., Smirnov V.M., Zverev E.A. Design simulation of modular abrasive tool........................................................................................................................................................................................ 158 MATERIAL SCIENCE EroshenkoA.Yu., Legostaeva E.V., Glukhov I.A., Uvarkin P.V., TolmachevA.I., Sharkeev Yu.P. Thermal stability of extruded Mg-Y-Nd alloy structure.................................................................................................................................. 174 Bazaleeva K.O., Safarova D.E., Ponkratova Yu.Yu., Lugovoi M.E., Tsvetkova E.V., Alekseev A.V., Zhelezni M.V., Logachev I.A., Baskov F.A. The infl uence of technological parameters of the laser engineered net shaping process on the quality of the formed object from titanium alloy VT23......................................................... 186 Efi movich I.A., Zolotukhin I.S. Oxidation temperatures of WC-Co cemented tungsten carbides....................................... 199 Pribytkov G.A., Baranovskiy A.V., Firsina I.A., Akimov K.O., Krivopalov V.P. Study of Fe-matrix composites with carbide strengthening, formed by sintering of iron titanides and carbon mechanically activated mixtures................ 212 EDITORIALMATERIALS 224 FOUNDERS MATERIALS 235 CONTENTS
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 Oxidation temperatures of WC-Co cemented tungsten carbides Igor Efimovich a, *, Ivan Zolotukhin b Tyumen Industrial University, 38 Volodarskogo, Tyumen, 625000, Russian Federation a https://orcid.org/0000-0002-9060-4988, egor_kosin@mail.ru; b https://orcid.org/0000-0002-1517-9117, zolotuhinis@tyuiu.ru 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. 2024 vol. 26 no. 2 pp. 199–211 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2024-26.2-199-211 ART I CLE I NFO Article history: Received: 29 January 2024 Revised: 26 February 2024 Accepted: 20 March 2024 Available online: 15 June 2024 Keywords: Elevated temperatures High-temperature oxidation Tungsten cemented carbides WC-Co Dilatometry Thermal expansion Temperature of oxidation Gas corrosion Chemical destruction ABSTRACT Introduction. Products containing WC-Co cemented tungsten carbides are commonly used in various industries. It is often operates at elevated temperatures, at which, as noted in the literature, tungsten carbides are susceptible to severe oxidation in air. However, no sufficiently accurate values of oxidation temperatures and dependence of these temperatures and the oxidation rate of tungsten carbides on the cobalt content with its wide variation have been established. The subject of the study is the oxidation process of WC-Co cemented tungsten carbides. The purpose of the work is to obtain the oxidation temperatures of WC-Co cemented tungsten carbides with different cobalt content by weight in the range of 3–20 %. Methods. The dynamics of oxidation was studied in air. Specimens of the same length were heated to a temperature of 850 °C and cooled at the same rate in the furnace of a push-rod dilatometer Netzsch 402 PC while its expansion was simultaneously recorded. The oxidation rate of the specimens was determined by the difference in its length before heating and after cooling. The values of oxidation temperatures were obtained by mathematical analysis of relationships of the expansion on temperature. Results and discussion. Experimental dependences of expansion of WC-Co cemented tungsten carbides on temperature in the range from 20 to 850 °C, and for WC-8Co – up to 1,150 °C, were obtained. The oxidation rate of WC-Co cemented tungsten carbides increased linearly with increasing concentration of tungsten carbides (decreased with increasing cobalt content). During heating, two characteristic temperatures were identified: the onset of oxidation (631±4 °C) and the transition to active oxidation (804±11 °C). The established temperatures were the same for different ratios of tungsten carbides and cobalt. The results can be used when choosing temperature conditions for products made from WC-Co cemented tungsten carbides. For citation: Efimovich I.A., Zolotukhin I.S. Oxidation temperatures ofWC-Co cemented tungsten carbides. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2024, vol. 26, no. 2, pp. 199–211. DOI: 10.17212/1994-6309-2024-26.2199-211. (In Russian). ______ * Corresponding author Efimovich Igor A., Ph.D. (Engineering), Associate Professor Tyumen Industrial University, 38 Volodarskogo, 625000, Tyumen, Russian Federation Tel.: +7 3452 50-49-15, e-mail: egor_kosin@mail.ru Introduction Tool WC-Co cemented tungsten carbides are widely used in various industries. Products containing these alloys are often used in a range of elevated temperatures, which determines the relevance of studying its performance under these conditions. The properties of most materials change significantly as temperature increases, and an increase in chemical activity plays a special role, in particular, when interacting with atmospheric oxygen. The fact of high-temperature oxidation of WC-Co cemented tungsten carbides is confirmed by a number of researchers. The oxidation of WC-Co cemented tungsten carbides is weak up to 600–650 °C [1–3], only cobalt is slightly oxidized [4]. In the temperature range of 650–800 °C, there is a sharp increase in the oxidation rate [3, 5–8], which is confirmed by the curves obtained by the thermogravimetric analysis (TGA). At temperatures above 800 °C, intense oxidation begins. The longer the thermal exposure time (even at constant temperature), the greater the thickness of the oxide layer, which is confirmed by all researchers.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 This leads to a significant increase in the size of the specimen [3, 9, 10], which is due to the porosity of oxides formation, which favors unhindered access of oxygen. Oxidation occurs not only during a long-term isothermal process [11, 12], but also during a short-term exposure to laser radiation [13]. It is noted in [14] that the oxidation rate increases with increasing temperature; however, the study [15] revealed a local inversion in the dynamics of oxidation in the temperature range of 528–630 °C. The oxidation rate also increases with the increasing heating rate [1, 5], which is confirmed by a shift in the curves of the dependence of mass on temperature. However, this may be due to the specifics of the experiment. It is noted in [6] that in the temperature range up to 650 °C a linear oxidation law is observed (dependence of the increase in mass on temperature), and above 800 °C it is quasi-parabolic. In other words, the oxidation rate increases linearly with increasing temperature above 800 °C. Increased oxygen [1, 12] and air flow rates accelerate oxidation [1], but at high flow rates this effect weakens due to cooling of the specimen. Recent studies have shown that WC-Co cemented tungsten carbides undergo several stages of oxidation when heated [16]: extremely weak oxidation of cobalt and carbides (up to 600 °C), the onset of oxidation (above 600 °C) of cobalt (CoO, Co3O4), and simultaneous oxidation of cobalt and carbides (above 700 °C) with the formation of tungsten oxides (WO2, WO3) and double oxides of tungsten and cobalt (CoWO4) [1, 7, 16]. A similar pattern is observed not only for sintered materials, but also for a mixture of powders [17]. A number of studies have noted that cemented carbides with a higher cobalt content oxidize more slowly than those with a lower content [1, 18, 19]. In [7], the authors discovered that the hardness of WC-10Co with particularly fine grains drops significantly during oxidation. However, the Vickers hardness of a surface cleaned of oxides after cooling may either not change at all or even increase [20]. During oxidation, the bending strength of cemented carbides decreases [12, 21, 22], which is largely due to the degradation of the surface layer. This was indirectly confirmed in [23], where the influence of oxidation on the development of surface cracks was noted. Coatings have a protective function [3, 24] and prevent oxidation of the cemented carbide base. However, when heated (due to thermal stresses caused by differences in the thermal coefficient of linear expansion), cracks appear in the coatings, allowing oxygen access to the base. In addition, coatings themselves are also oxidized [25]. Not only specially prepared specimens with a ground surface were used, but also commercially produced cutting inserts [26], including those with coatings [24] were used to study the oxidation process of cemented carbides. The results presented coincide with the results obtained on special specimens. Oxidation can be used to purposefully reduce the strength of a cemented carbide in order to improve its machinability [27]. In the work [8] it is even proposed to use oxidation to recycle worn multifaceted cutting tool inserts. However, when using cemented carbides as cutting tool materials, its high-temperature oxidation can play an important [28–30] or decisive role in the wear of cutting tools [26, 31, 32]. Having studied the literature, we can see that the above experiments mainly used isothermal heating with a large step of temperature change (500, 600 °C, etc.). The accuracy of the determined oxidation onset temperatures was not sufficient, and the influence of cobalt content on the value of these temperatures and on the dynamics of oxidation with wide variations in the composition of WC-Co cemented tungsten carbides was not established. The quantitative study of oxidative processes can be performed in various ways: by weight changes of the specimen – thermogravimetric analysis (TGA); by temperature difference – differential thermal analysis (DTA); by changes in heat flux – differential scanning calorimetry (DSC); by changes in the parameters of thermal radiation – infrared spectroscopy [15]; by changes in the properties of reflected radiation – optical or scanning electron microscopes (SEM). However, these methods do not always provide trustworthy information about the oxidation rate, and its accuracy is limited by the nature of the experiment. For instance, in thermogravimetric analysis, due to the absorption of gases and the appearance of volatile oxides in addition to solid oxides, the change in the mass of the specimen can be ambiguous.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 Since the density of the substance changes during chemical reactions, the dimensions of the specimen also change. This makes it possible to quantify oxide layers directly by comparing the dimensions of the specimen before and after heating. However, this requires interrupting the heating process and removing the specimen from the furnace. Dilatometers designed to determine the thermal coefficient of linear expansion (TCLE) of a material can also be used to measure the thickness of oxide formations directly during heating [33, 34]. This paper is a continuation of the work of the authors [35] on dilatometry of WC-Co cemented tungsten carbides and its purpose is to determine the temperatures at which the oxidation of these cemented carbides with different cobalt content begins, as well as to establish the relationship of cobalt content with the oxidation temperatures and the dynamics of oxide formation. Achieving this purpose requires studying the dynamics of the WC-Co oxide growth with a wide variation in cobalt content by heating to high temperatures in a laboratory furnace and by dilatometry. Methods Small specimens were heated in a laboratory furnace in air atmosphere to qualitatively assess the dynamics of oxidation. For this purpose, six specimens with cobalt content Co = 3, 6, 8, 10, 15, 20 wt. % were prepared. These specimens were made from commercially produced carbide cutting tool inserts and cylindrical blanks for milling cutters. The composition of WC-Co cemented tungsten carbides corresponded to the VK (WC-Co) group of the Russian Standard [36]. The Fisher grain size of tungsten carbide powders was 4.0–9.0 μm (according to the manufacturer). The specimens’ sizes ranged from 3.5 to 5 mm. In the furnace, the specimens’ were placed on a corundum substrate and heated to 900 °C at a rate of 7 °C/min in air, after which, without holding at the maximum temperature, naturally cooled to 20 °C without removing them from the furnace. The most common and reliable push-rod dilatometer Netzsch 402 PC was used in this work to quantify the dynamics of oxidation. The dilatometer’s push rod and specimen holder are made of alumina ceramics (Al2O3). Tests were carried out in air. The specimen was heated and cooled at a rate of 7°C/min. The contact force of pressing the push rod against the specimen was 0.35 N. To measure the temperature of the specimen, an S-type thermocouple was used, located in close proximity to it. Nitrogen was supplied to its housing at a flow rate of 30 ml/min to protect the displacement sensor. Specimens for dilatometry with a 5×5 mm square cross section were made from the same blanks as the specimens for heating in the furnace. The nominal length of the specimens corresponded to the length of the reference specimen used to calibrate the dilatometer and was 25±0,001 mm. To remove the surface layer obtained during sintering of the workpieces, the ends of the specimens in contact with the holder and push rod were polished with a diamond grinding wheel. The initial length of each specimen was determined at room temperature using a micrometer with a 1 μm scale division in three dimensions. Prior to the experiment, the dilatometer was calibrated at a constant heating rate of 7 °C/min to 1,200 °C using a standard Al2O3 reference specimen. The test specimens were heated at the same rate to 850 °C. One specimen with cobalt content Co = 8 % was heated to 1,150 °C. Cooling to room temperature was carried out at the same rate as heating. Thus, the time of thermal exposure of the specimen was the same for all specimens heated to 850 °C. Simultaneous recording of temperature and specimen expansion was conducted continuously one time per second. The data obtained during dilatometrywere approximated by cubic splines. The characteristic temperatures of oxidation were determined from the inflection points of both lines (heating and cooling) of the thermal expansion curves by finding the extrema of the first and second derivatives. The resulting (after cooling) thickness of the oxide layers was determined using the thermal expansion curves that have a characteristic hysteresis to determine the average oxidation rate of each specimen. The experimental results were processed using standard tools in MS Excel by fetching subroutines specially written in MATLAB with the built-in functions for working with splines using the Spreadsheet Link plugin.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 Results and discussion Table 1 presents the results of heating the specimens of WC-Co cemented tungsten carbides with different cobalt content by weight in a laboratory furnace to 900 °C. The top row of the table shows the initial appearance of the specimens, and the bottom row – its appearance after heating and cooling. As we can see from the photographs, all WC-Co cemented tungsten carbides are highly oxidized. The oxide layers are of considerable thickness and in some cases peel off from the base. The cross sections of these layers correspond to the shape of the surfaces on which they are formed. All specimens changed color. None of the specimens had traces of interaction with the corundum substrate. The experimental results confirm that WC-Co cemented tungsten carbides highly oxidize with the material structure being destroyed when heated to temperatures above 800 °C. These results are consistent with the data obtained by other researchers for other cobalt contents [3, 5–8]. Ta b l e 1 Results of heating WC-Co specimens with different cobalt content in air in a laboratory furnace Со, % 3 6 8 10 15 20 20 °С 900 °С Fig. 1 shows the results of heating a specimen of a WC-Co cemented tungsten carbides with a cobalt content of Co = 8 % in a dilatometer to a temperature of 1,150 °C. The appearance of the specimen before heating is shown in Fig. 1, a and after completion of the experiment in Fig. 1, b. The last photo demonstrates that the specimen has significantly deteriorated and lost its shape. The surfaces of the specimen holder and push rod were covered with a blue coating. Fig. 1, c shows the relationship between the specimen expansion Δl and temperature T. The curve shows three characteristic temperature ranges: slight expansion up to about 650 °C, a sharp increase in size from 650 °C to approximately 950 °C, and destruction of the specimen at a higher temperature. In all these ranges there are sections of the curve close to the linear law. In the first range, changes are caused almost exclusively by the thermal expansion of the specimen with a slightly increasing TCLE [35]. In the second range, thermal deformation is accompanied by the growth of the oxide layer, which begins to dominate. If in the range of 20–650 °C the specimen increased by only 0.096 mm, in the range of 650–1050 °C the specimen increased by 1.534 mm. In the third temperature range, the increase in specimen size slows down and then the specimen shortens, which can be explained by loss of shape and destruction of the specimen. Fig. 2 shows relationships between the expansion and temperature for WC-Co specimens with different cobalt content, obtained by heating to 850 °C and subsequent cooling to room temperature. All the curves are similar and have a characteristic hysteresis, indicating permanent elongation due to the presence of oxide layers. The section of the curves corresponding to cooling looks like a mirror image of the heating section. The first two characteristic temperature ranges of slight expansion and a sharp increase in specimen size are observed.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 a b c Fig. 1. View of the specimen (Co = 8 %) in the dilatometer before heating (a) and after heating (b); graph of the dependence of the specimen expansion on temperature (c) Fig. 2. Dependences of the expansion on temperature for WC-Co specimens with different cobalt content
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 Fig. 3. Dependences of the specimen change in length Δ (after heating and cooling) on cobalt content As a result of processing the data shown in Fig. 2, a dependence of the specimen change in length Δ (after heating and cooling) on cobalt content was obtained (Fig. 3) by linear approximation (coefficient of determination R² = 0.897). Since the testing time is the same for all specimens, the residual elongation corresponds to the average oxidation rate. Thus, the average oxidation rate is inversely proportional to the cobalt content and increases with increasing content of tungsten carbides. This dependence is close to the linear law in the considered range of changes in the cobalt content in the alloy. Data on the effect of cobalt content on the oxidation rate for the tungsten carbides considered are consistent with the results of previous studies obtained for: WC-6Co and WC-12Co [1]; WC-6Co, WC-10Co and WC-18Co [12]; WC-15Co and WC-25Co [18] under isothermal conditions. Figs. 4 and 5 show curves of the first and second derivatives (for heating and cooling, respectively, see Fig. 2) of the dependences of expansion Δl on temperature T for WC-Co specimens with different cobalt content for the range of 550–850 °C, which is of greatest interest. The graphs generally confirm the inverse dependence of the average oxidation rate on cobalt content based on residual elongation. The second derivatives have two characteristic inflections: around 630 °C (T1) and 800 °C (T2). Before T1, the first derivative has a horizontal section, and the values of the second derivative are close to zero. Closer to T1, both derivatives begin to increase significantly, which indicates the emergence of new chemical processes (mainly, carbide oxidation with WO3 formation and cobalt oxidation) that affect the change in size. This point corresponds to the onset of oxidation of the cemented carbides. Around T2, an extremum at the maximum value of the second derivative of the heating line, as well as an extremum of the second derivative of the cooling line are observed. The obtained temperature values at T2 correlate with the temperature values of characteristic points on the curves of the heat flux changes obtained in previous studies [3, 5–7] using the differential scanning calorimetry (DSC) method. T2 corresponds to the transition to the active oxidation of the carbide, after which the ratio of CoWO4 in the total weight of the oxide layer probably begins to increase. The beginning of the graphs’ slowdown after T2 can be explained by the higher density of CoWO4 compared to WO3. Domination of CoWO4 at high temperatures is confirmed by spectral analysis of the oxide layer after heating WC-Co [3]. а b Fig. 4. Graphs of the first (a) and second (b) derivatives of the relationship of expansion Δl on temperature T for WC-Co specimens with different cobalt content obtained during heating
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 а b Fig. 5. Graphs of the first (a) and second (b) derivatives of the relationship of expansion Δl on temperature T for WC-Co specimens with different cobalt content obtained during cooling An intermediate extremum in the lines of the second derivative for heating may result from the errors caused by the mechanism of the dilatometer and is not observed in cooling. Table 2 summarizes the values of characteristic points T1 and T2 for all WC-Co cemented tungsten carbides obtained during heating (Fig. 4) and cooling (Fig. 5). Fig. 6 shows graphs of the dependence of T1 and T2 on cobalt content, where the black lines show the average values and the red lines show the root-meansquare (RMS) deviations from these values. Ta b l e 2 Temperatures T1 and T2 during heating (↑) and cooling (↓) of WC-Co with different cobalt content Temperature Co, % Mean value 3 6 8 10 15 20 Т1 ↑ 638.8 626.2 630.6 628.6 628.4 633.7 631.1 ↓ 628.1 627.7 631.6 634.6 631.2 634.1 Т2 ↑ 793.5 803.9 791.2 815.1 789.6 809.7 804.1 ↓ 818.5 816.8 801.4 818.5 797.5 793.8 Analysis of the results shows that the values of T1 and T2 during heating and cooling for different cobalt content are very similar. For T1, the maximum deviations from the average value were 1.2 %, and for T2 the maximum deviations from the average value were 1.8 %; the RMS deviations were 0.6 % and 1.4 %, respectively. In absolute terms, the RMS deviations for T1 were ±4 °C, and for T2 the standard deviations were ±11 °C. At the same time, changes in actual temperature values depending on cobalt content is insignificant and random, which is apparently due to experimental errors. Thus, we can conclude that the quantitative composition of WC-Co cemented tungsten carbides has virtually no effect on the temperatures of the onset of oxidation and the transition to active oxidation. Fig. 6. Dependences of characteristic temperatures T1 and T2 on cobalt content, obtained during heating (↑) and cooling (↓)
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 26 No. 2 2024 This is apparently due to the properties of the tungsten carbides, which do not significantly depend on the concentration of the cobalt phase. The resulting temperatures of the onset of oxidation (631±4 °C) and the transition to active oxidation (804±11 °C) are in good agreement with the ranges of characteristic temperatures of oxidation obtained by other researchers using methods other than the one used here. Conclusions 1. Oxidation of WC-Co cemented tungsten carbides with a wide variation in cobalt content (Co = 3–20 wt. %) heated to elevated temperatures was studied. 2. After heating in a laboratory furnace to 900 °C, strong oxidation of these tungsten carbides was observed, with the material structure being destroyed. 3. Dilatometric studies resulted in obtaining experimental graphs of the expansion of WC-Co cemented tungsten carbides specimens at temperatures up to 850°C. The graphs have a characteristic hysteresis, indicating permanent elongation due to the presence of oxide layers. The two characteristic temperature ranges of slight expansion and a sharp increase in specimen size are observed. 4. For a specimen with a cobalt content of 8 %, an additional experiment was carried out with heating to 1,150 °C; as a result, it was completely destroyed. 5. The average rate of oxidation of WC-Co cemented tungsten carbides increases with increasing content of tungsten carbides (decreases with increasing cobalt content) and this relationship is linear. 6. Two characteristic temperatures were identified: the onset of oxidation (631±4 °C) and the transition to active oxidation (804±11 °C). These temperatures are the same for different ratios of tungsten carbides and cobalt. References 1. Basu S.N., Sarin V.K. Oxidation behavior of WC-Co. Materials Science and Engineering, 1996, vol. 209 (1–2), pp. 206–212. DOI: 10.1016/0921-5093(95)10145-4. 2. Hidnert P. Thermal expansion of cemented tungsten carbide. Journal of Research of the National Bureau of Standards, 1936, vol. 18, pp. 47–52. Available at: https://nvlpubs.nist.gov/nistpubs/jres/18/jresv18n1p47_A1b.pdf (accessed 04.04.2024). 3. Verkhoturov A.D., Gordienko P.S., Konevtsov L.A., Panin E.S., Potapova N.M. Temperaturnoe okislenie vol’framokobal’tovykh tverdykh splavov [Thermal oxidation of tungsten-cobalt hard alloys]. Perspektivnye materialy = Advanced Materials, 2008, no. 2, pp. 68–75. (In Russian). 4. Chen L., Yi D., Wang B., Liu H., Wu C., Huang X., Li H., Gao Y. The selective oxidation behaviour of WCCo cemented carbides during the early oxidation stage. Corrosion Science, 2015, vol. 94, pp. 1–5. DOI: 10.1016/j. corsci.2015.02.033. 5. Chen L., Wang B., Yi D., Liu H. Non-isothermal oxidation kinetics of WC-6Co cemented carbides in air. International Journal of Refractory Metals and Hard Materials, 2013, vol. 40, pp. 19–23. DOI: 10.1016/j. ijrmhm.2013.02.003. 6. Liu S. Oxidation behavior of WC-Co cemented carbide in elevated temperature. Materials Research Express, 2018, vol. 5 (9). DOI: 10.1088/2053-1591/aad535. 7. Shi X., Yang H., Shao G., Duan X., Wang S. Oxidation of ultrafine-cemented carbide prepared from nanocrystalline WC-10Co composite powder. Ceramics International, 2008, vol. 34, pp. 2043–2049. DOI: 10.1016/j. ceramint.2007.07.029. 8. Gu W.-H., Jeong Y.S., Kim K., Kim J.-C., Son S.-H., Kim S. Thermal oxidation behavior of WC-Co hard metal machining tool tip scraps. Journal of Materials Processing Technology, 2012, vol. 212, pp. 1250–1256. DOI: 10.1016/j.jmatprotec.2012.01.009. 9. Lofaj F., Kaganovskii Y.S. Kinetics of WC-Co oxidation accompanied by swelling. Journal of Materials Science, 1995, vol. 30, pp. 1811–1817. DOI: 10.1007/BF00351615. 10. Bagnall C., Capo J., Moorhead W. Oxidation behavior of tungsten carbide-6% cobalt cemented carbide. Metallography, Microstructure, and Analysis, 2018, vol. 7, pp. 661–679. DOI: 10.1007/s13632-018-0493-7.
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