Vol. 24 No. 3 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. 3 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. 3 2022 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Permyakov G.L., Davlyatshin R.P., Belenkiy V.Y., Trushnikov D.N., Varushkin S.V., Pang S. Numerical analysis of the process of electron beam additive deposition with vertical feed of wire material...................... 6 Ilinykh A.S., Banul V.V., Vorontsov D.S. Theoretical analysis of passive rail grinding.................................. 22 Chinchanikar S. Modeling of sliding wear characteristics of Polytetrafl uoroethylene (PTFE) composite reinforced with carbon fi ber against SS304........................................................................................................ 40 EQUIPMENT. INSTRUMENTS Abbasov V.A., Bashirov R.J. Features of ultrasound application in plasma-mechanical processing of parts made of hard-to-process materials...................................................................................................................... 53 MATERIAL SCIENCE Stolyarov V.V., Andreev V.A., Karelin R.D., Ugurchiev U.Kh., Cherkasov V.V., Komarov V.S., Yusupov V.S. Deformability of TiNiHf shape memory alloy under rolling with pulsed current....................... 66 Vorontsov A.V., Filippov A.V., Shamarin N.N., Moskvichev E.N., Novitskaya O.S., Knyazhev E.O., Denisova Yu.A., Leonov A.A., Denisov V.V. Microstructure and residual stresses of ZrN/CrN multilayer coatings formed by the plasma-assisted vacuum-arc method........................................................................... 76 Ivanov I.V., Safarova D.E., Bataeva Z.B., Bataev I.A. Comparison of approaches based on the WilliamsonHall method for analyzing the structure of an Al0.3CoCrFeNi high-entropy alloy after cold deformation....... 90 Kryukov D.B. Structural features and technology of light armor composite materials with mechanism of brittle cracks localization.......................................................................................................................... 103 EDITORIALMATERIALS 112 FOUNDERS MATERIALS 123 CONTENTS
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 3 2022 Comparison of approaches based on the Williamson-Hall method for analyzing the structure of an Al0.3CoCrFeNi high-entropy alloy after cold deformation Ivan Ivanov 1, a, *, Daria Safarova 1, b, Zinaida Bataeva 2, c, Ivan Bataev 1, d 1 Novosibirsk State Technical University, 20 Prospekt K. Marksa, Novosibirsk, 630073, Russian Federation 2 Siberian State University of water transport, 33 Schetinkina str., Novosibirsk, 630099, Russian Federation a https://orcid.org/0000-0001-5021-0098, i.ivanov@corp.nstu.ru, b https://orcid.org/0000-0002-2811-8292, safarova10ab@mail.ru, c https://orcid.org/0000-0001-5027-6193, bataevazb@ngs.ru, d https://orcid.org/0000-0003-2871-0269, i.bataev@corp.nstu.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. 2022 vol. 24 no. 3 pp. 90–102 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2022-24.3-90-102 ART I CLE I NFO Article history: Received: 13 June 2022 Revised: 29 June 2022 Accepted: 05 July 2022 Available online: 15 September 2022 Keywords: High-entropy alloys Al0.3CoCrFeNi, Plastic deformation Cold rolling Synchrotron X-ray diffraction Peak profi le analysis Microhardness Defect structure Funding This study was funded according to Russian Science Foundation research project No.20-73-10215 «In-situ study of the evolution of the dislocation structure of plastically deformed highentropy alloys under high-pressures and temperatures using synchrotron radiation». Research was conducted at core facility “Structure, mechanical and physical properties of materials”. ABSTRACT Introduction. High-entropy alloys (HEAs) belong to a new and promising class of materials that are attracting the attention of both scientists and engineers from all over the world. Among all alloys of the AlxCoCrFeNi system, HEAs with x ≤ 0.3 attract special attention. Materials with this composition are characterized by the presence of only one phase with a face-centered cubic lattice (FCC). Such alloys have high ductility, excellent corrosion resistance and phase stability at high temperatures. The purpose of this work is to compare several methods of profi le analysis on the example of plastically deformed ingots of a high-entropy Al0.3CoCrFeNi alloy. The methods of investigation. Using several methods of profi le analysis of X-ray diffraction patterns, the structures of the cold-worked high-entropy alloy Al0.3CoCrFeNi are studied. In addition to the classical Williamson-Hall method, the analysis was carried out using a modifi ed one, as well as a method that takes into account the anisotropy of the elastic properties of the crystal lattice. Research material. Ingots of the high-entropy Al0.3CoCrFeNi alloy deformed by cold rolling with a maximum reduction ratio of 80% were used as the object of the study. Samples were cut from the obtained blanks, which were studied by the method of synchrotron radiation diffraction according to the “transmission” scheme along two (longitudinal (RD) and transverse (TD)) directions of rolled products. Results and discussion. It is shown that the use of the classical Williamson-Hall method leads to a signifi cant error in the approximation of experimental results. The modifi ed Williamson-Hall method has the smallest approximation error and can be recommended for studying the Al0.3CoCrFeNi alloy. An analysis of deformed samples using this method made it possible to reveal several features of the formation of defects in the crystalline structure, which are in good agreement with the classical concepts of the mechanisms of plastic deformation. First, an increase in the degree of deformation of the high-entropy Al0.3CoCrFeNi alloy leads to an almost uniform increase in the number of twins and stacking faults. Secondly, with an increase in the degree of reduction, there is a decrease in the fraction of edge dislocations and an increase in the fraction of screw dislocations in the material. The results obtained correlate well with the results of microhardness measurements. For citation: Ivanov I.V., Safarova D.E., Bataeva Z.B., Bataev I.A. Comparison of approaches based on the Williamson–Hall method for analyzing the structure of an Al0.3CoCrFeNi high-entropy alloy after cold deformation. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2022, vol. 24, no. 3, pp. 90–102. DOI: 10.17212/1994-6309-2022-24.3-90-102. (In Russian). ______ * Corresponding author Ivanov Ivan V., Ph.D. (Engineering) Novosibirsk State Technical University, 20 Prospekt K. Marksa, 630073, Novosibirsk, Russian Federation Tel.: 8 (383) 346-11-71, e-mail: i.ivanov@corp.nstu.ru
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 3 2022 Introduction High-entropy alloys (HEAs) represent a new and promising class of materials that are attracting the attention of both scientists and engineers from all over the world. [1, 2]. The most common and studied are alloys based on a combination of cobalt, chromium, iron, nickel and an additional element. In particular, many scientifi c works are devoted to such alloys as CoCrFeMnNi (Cantor’s alloy) and AlxCoCrFeNi alloys [3–5]. Special attention of researchers attracts AlxCoCrFeNi alloys with x ≤ 0.3. Materials with this composition consist of only one face-centered cubic (FCC) phase. Such alloys have high ductility, excellent corrosion resistance and phase stability at high temperatures. At the same time, these materials possess low hardness and yield strength. The strength of these alloys can be signifi cantly improved by plastic deformation with subsequent heat treatment. According to a number of literary sources, the thermomechanical processing of the Al0.3CoCrFeNi alloy leads to its strengthening and an increase in hardness but allows retaining a reasonable level of ductility [6–8]. One of the effective methods for studying the structure of plastically deformed alloys is the peak profi le analysis of the X-ray diffraction patterns. This technique makes it possible to evaluate the defects in the crystal structure of alloys. The most common peak profi le analysis approach is the classical WilliamsonHall method. The use of this method makes it possible to estimate the distortions of the crystal lattice and the size of coherent scattering regions (CSRs). However, the Williamson-Hall method is known to have a high approximation error during the analysis of materials with high anisotropy of elastic properties. Therefore, special corrections are introduced during the analysis, that take into account the dependence of elastic properties on the direction in the crystal lattice. Even though these methods are widely used in the analysis of metals and alloys, there are no examples of exhaustive comparative analysis of peak profi le analysis methods for studying the structure of high-entropy alloys. In this study, several peak profi le analysis methods are compared by using the plastically deformed ingots of an Al0.3CoCrFeNi high-entropy alloy as an example. Using various methods, defects in the crystal structure were evaluated and its relationship with the microhardness of the deformed alloy was shown. Samples preparation. Methods for studying the structure and properties of materials In this work, the ingots of the Al0.3CoCrFeNi high-entropy alloy were used. The ingots were obtained from commercially pure metals by argon-arc melting in a water-cooled copper crucible. To distribute chemical elements evenly, remelting was carried out at least 10 times. Weight loss during smelting did not exceed 0.2 %. The elemental composition of the ingots was evaluated by energy dispersive X-ray spectroscopy using a scanning electron microscope EVO50 XVP (Carl Zeiss) equipped with detector X-Act (Oxford Instruments). According to data obtained, the deviation of the actual composition did not exceed 0.6 at. %. It is well known that the structure of materials obtained by melting and casting methods is characterized by the presence of large dendrites, as well as a heterogeneity of the chemical composition (i.e., dendritic segregation). In order to obtain a more homogeneous composition and a fi ne-grained structure, thermomechanical processing of ingots was carried out. It was carried out by cold rolling with a reduction of 20 % and long-term low-temperature annealing (400 °C during 24 hours). The higher annealing temperatures were not used because some high-entropy alloys of the AlxCoCrFeNi system have a phase transition with formation of the B2 and L12 ordered phases (space group 3 ) Pm m at temperatures exceeding 400 °C [6, 9]. The results of X-ray diffraction analysis indicate that this thermomechanical processing contributed to the relaxation of the structure and did not lead to the formation of new phases (Fig. 1). After the thermomechanical treatment, the high-entropy alloy ingots were subjected to cold rolling with reduction of 20; 40; 60 and 80 %. The reduction during the single rolling pass was ~ 2 %. Afterall, the samples were cut for X-ray diffraction analysis and microhardness testing. The structure and properties of materials along the rolling direction (RD) и transverse direction (TD) were investigated.
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 3 2022 The X-ray diffraction analysis was carried out by the synchrotron X-ray diffraction method in transmission using the beamline P07 of Petra III source of Deutsches Elektronen-Synchrotron (DESY). The wavelength of the radiation used was 0.14235 nm. It corresponds to energy of 87.1 keV. A 2D PerkinElmer XRD 1621 detector was used to record the diffraction patterns. The screen resolution of the detector was 2048 × 2048 px. The screen area was 409.6 mm × 409.6 mm. The distance from the sample to the detector was 1.05 m. The resulting diffraction patterns were reduced to a one-dimensional form by azimuthal integration using the pyFAI library [10]. Examples of the obtained two-dimensional and one-dimensional diffraction patterns are shown in Fig. 1. For peak profi le analysis, one-dimensional diffraction patterns were described by a function of the following form: 10 7 i 1 i 0 (2 ) (2 ) (2 ) , j pattern i j I I a (1) where the fi rst sum determines the contribution to the intensity of ten diffraction maxima, and the second sum is a 7th order polynomial to describe the background. In turn, the profi le of each of the diffraction maxima was described by the pseudo-Voigt function, which is generally written as: 0 (2 ) (2 ) (1 ) (2 ) , i I I L G (2) where I0 – the value of the maximum intensity of the diffraction peak; η – Lorentz function contribution; L(2θ) and G(2θ) – Lorentz and Gauss functions, respectively. These functions look like: 2 2 2 0 0.5 [1 ] (2 ) 0.5 [1 ] (2 2 ) A L A (3) and 2 0 2 (2 2 ) (2 ) exp , 0.5 [1 ] / ln 2 G A (4) where 2θ0 – angular position corresponding to the maximum value of the peak intensity; β – full width at half maxima (FWHM); A – diffraction peak asymmetry parameter (–1 ≤ A ≤ 1). The instrumental contribution was taken into account by using the Caglioti function. The parameters of the function were determined by analyzing the diffraction pattern of the HEA sample after cold rolling and long-term annealing at 400 C. To carry out X-ray diffraction analysis the classical Williamson-Hall model was used. According to this model, the peak broadening depends on the parameters of the sample microstructure as follows: 0.9 2 , K K D (5) where 2sin K – reciprocal coordinate; cos 2 K ; ε – relative lattice distortion; λ – wavelength; D – average «visible» size of CSRs. As noted in the introduction, the anisotropy of the elastic properties of materials causes a high error in the approximation of diffraction data using the classical methods of peak profi le analysis. Therefore, in this work, in addition to the classical Williamson-Hall model, several other models were used. In some cases, the approximation error can be reduced by introducing a correction based on the assumption that crystal lattice distortions in one of the directions depend on the elastic modulus of the crystal along this direction [11]. This model can be written in the following way:
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 3 2022 0.9 , hkl K K D E (6) where σ is isotropic elastic stress; Ehkl – modulus of elasticity along the normal direction to the plane (hkl). In addition, the obtained data were analyzed using a model based on the assumption of the dislocation nature of crystal lattice distortions. This approach is called the modifi ed Williamson-Hall method [12]. In the case of cubic polycrystalline materials, the equation underlying this model has the following form: 2 2 00 2 ( ) / [1 ], h K W g a AC qH K (7) where α = (0.9/D)2; β – parameter that shows the probability of detecting stacking faults and twins; W(g) – coeffi cients depending on crystallographic direction indices [hkl] [13, 14]; a – lattice parameter; A – parameter depending on the average density of dislocations, the average length of the Burgers vector and the arrangement of dislocations; 00 h C – average dislocation contrast factor along [h00] direction; q – parameter depending on the elastic properties of the material; H2 = (h2k2 + h2l2 + k2l2) / (h2 + k2 + l2)2. According to literature, the modifi ed Williamson-Hall method has the lowest approximation error [11, 15]. A more detailed description of the implementation of this method is described elsewhere [11, 15, 16]. The microhardness of the samples was evaluated by using the Vickers method on a Wolpert Group 402MVD semi-automatic hardness tester. The load on the tetrahedral diamond indenter was 0.98 N, the holding time under load was 10 s. Research results It is believed that the multielement composition of high-entropy alloys leads to signifi cant distortions of its crystal lattice even before plastic deformation. This feature can possibly cause an additional broadening of the diffraction peaks of undeformed samples. In addition, the instrumental broadening of diffraction maxima arises due to the instrument which is used for the diffraction experiment. In order to take into account, the contribution of both factors and analyze only the effects caused by a change in the structure of the samples, an undeformed HEA sample of the same composition with a homogeneous structure was used as a reference. For this purpose, preliminary thermomechanical processing of HEA was carried out. This processing consisted in plastic deformation and subsequent long-term low-temperature annealing.According to the results shown in Fig. 1 a, b, the structure of the alloy after the deformation and low-temperature annealing is characterized by a more uniform spatial orientation of crystallites (which is evidenced by the presence of complete diffraction rings) and a low level of microstresses (which is evidenced by the small width of diffraction maxima). Subsequent cold rolling (Fig. 1, c, d) leads to a signifi cant broadening of the diffraction maxima, which indicates an increase in the number of defects in the crystalline structure. The peak profi le analysis of diffraction patterns of plastically deformed alloys makes it possible to estimate the number and the type of defects in the crystal structure based on the parameters of diffraction maxima. Thus, the assessment of the width of diffraction maxima using the classical Williamson-Hall method (Equation 5) makes it possible to determine the relative distortions of the crystal lattice and the CSRs sizes. However, it is known that this method is the least accurate with the signifi cant error of the approximation of experimental results. Therefore, some corrections based on the anisotropy of crystal properties are often introduced during the analysis of X-ray diffraction data by using the peak profi le analysis methods. The simplest way to account for anisotropy is to introduce into the calculation the elastic modulus for the normal to the planes (hkl) crystallographic directions (Equation 6). Table shows the values of the elastic moduli of the Al0.3CoCrFeNi alloy for the diffraction maxima analyzed in the work. Another, less common, but in many cases more effective way to improve the approximation accuracy is to use a model based on the dislocation theory of elastic distortions of the crystal lattice. This type of models is called modifi ed in the literature. They were described in detail in the works of
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 3 2022 a b c d Fig. 1. X-ray diffraction patterns of the Al0.3CoCrFeNi high-entropy alloy in pre-deformed state (a); after annealing at 400 C (b); after cold rolling with 40 % (c) and 80 % (d) reduction Ta b l e 1 Young’s modulus of Al0.3CoCrFeNi alloy in different directions Direction [111] [200] [220] [311] [222] [400] [311] [420] [422] [333] Ehkl, GPa 432 178 318 246 432 178 345 248 318 432 Ungar et al. [17, 18]. In particular, such models include the modifi ed Williamson-Hall model used in this work (Equation 7). It is known that the structural defects are the reason of occurrence of stresses of the crystal lattice. The most common defects in the crystal structure are point defects, dislocations, stacking faults, twins, as well as grain and subgrain boundaries [19]. In addition to reducing the approximation error, the use of the modifi ed Williamson-Hall method makes it possible to obtain additional information about the features of the defect structure of the crystal lattice. Thus, in the case of the analysis of polycrystalline materials with a cubic crystal lattice, it becomes possible to determine such microstructure parameters as the distribution of dislocations by type (screw/edge), as well as the probability to fi nd stacking faults and twins. Experimental data and fi gures obtained using various models are presented in Figs. 2, 3 and 4. From the presented fi gures it can be concluded that the entering of adjustments allows reducing the variance of values and bringing the trend closer to a linear one. This conclusion is confi rmed by the analysis of
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 3 2022 Fig. 2. Williamson-Hall plots for Al0.3CoCrFeNi alloy after cold rolling for (a) RD and (b) TD directions a b a b Fig. 3. Williamson-Hall corrected by elastic modulus plots for Al0.3CoCrFeNi alloy after cold rolling for (a) RD and (b) TD directions a b Fig. 4. Modifi ed Williamson-Hall plots for Al0.3CoCrFeNi alloy after cold rolling for (a) RD and (b) TD directions
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 3 2022 the values of the coeffi cient of determination (R2). According to Fig. 5, the values of the coeffi cient 2 R in the case of the classical Williamson-Hall method can be lower than 0.5. This fact indicates that only half of the variance of the values ΔK is described by the model. The entering of adjustments signifi cantly reduces the approximation error. The best result is observed for the modifi ed Williamson-Hall method. a b Fig. 5. The coeffi cient of determination for various peak profi le analysis methods used in this study: the classical Williamson-Hall (WH) method; classical method corrected for the modulus of elasticity (WHEhkl); modifi ed Williamson-Hall (mWH) method. The results for RD (a) and TD (b) directions are presented A number of parameters of the modifi ed Williamson-Hall model make it possible to evaluate the features of defects in the crystal structure of the materials. So, the dynamics of the parameter q (Equation 7) makes it possible to draw conclusions about the change of the relative fraction of edge/screw dislocations. Furthermore, the values of the parameter β (Equation 7) are directly related to the formation of stacking faults and twins in the material. An increase in the number of twins and stacking faults is indicated by an increase in the values of the parameter β. At the same time, the decrease in the parameter q values indicate a decrease in the relative fraction of edge dislocations. The Fig. 6 shows the results of the analysis of the dislocation density and the parameter β depending on the degree of plastic deformation, as well as its relationship with the measured values of microhardness. It can be seen that plastic deformation leads to a signifi cant increase of the number of twins and stacking Fig. 6. Relative fraction of edge dislocations, parameter β and microhardness of the Al0.3CoCrFeNi alloy during cold rolling
OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 24 No. 3 2022 faults. The values of the parameter β increase by more than an order of magnitude with an increase of the deformation degree up to 60 %. A further increase of the deformation degree leads to a slight decrease in the number of defects of this type. The effect of an increase of the number of twins and stacking faults during cold plastic deformation is known and well-studied for many high-entropy alloys with a FCC lattice [20, 21, 22]. The last stage (the stage of slight decrease) is apparently associated with the saturation of the structure with defects of this type. Furthermore, it can be seen that at the stage of increasing the deformation degree up to 60 %, the material is characterized mainly by the presence of screw dislocations. A further increase of the deformation degree leads to a decrease of the relative fraction of this type of defects. The effect of the dominance of screw dislocations at relatively low strains was demonstrated by Schafl er et al. on the example of commercially pure copper deformed by equal channel angular pressing [23]. According to the obtained results, an increase of the deformation degree leads to a gradual decrease in the fraction of screw dislocations and an increase of the fraction of edge dislocations. A similar effect was also observed in the study of the dislocation structure of the aluminum alloy Al-5.9Mg-0.3Sc-0.18Zr with FCC crystal lattice [24]. This alloy was deformed by high-pressure torsion, and an increase of the number of revolutions from 0.5 to 5 led to a decrease in the proportion of screw dislocations in the system from 30 to 8 %. The obtained results of microstructural studies correlate well with the values of microhardness. It can be seen (Fig. 6) that an increase of the deformation degree leads to a signifi cant increase of the microhardness. It can be noted that the Al0.3CoCrFeNi alloy has a high capacity for work hardening. Conclusions 1. In this study the possibilities of peak profi le analysis methods for assessing defects in the crystal structure are shown by using the high-entropy alloy Al0.3CoCrFeNi as an example. Due to the presence of internal stresses associated with the nature of HEA, it is advisable to take into account the instrumental contribution using a preliminarily prepared annealed alloy of the same composition as the investigated samples. 2. The anisotropy of the elastic properties of the Al0.3CoCrFeNi alloy leads to an error of the approximation of the results by using the classical Williamson-Hall method. Entering of adjustments is an effective way to reduce the approximation error. 3. The smallest approximation error is typical for the modifi ed Williamson-Hall method. The use of this method makes it possible to obtain the most reliable results concerning the defective structure of the Al0.3CoCrFeNi alloy. Plastic deformation by cold rolling leads to an increase of the number of stacking faults and twins. Screw dislocations dominate in the structure of the alloy at a deformation degree up to 60 %, and an increase in the fraction of edge dislocations occurs only with an increase of the deformation degree up to 80 %. This dynamics of defects in the crystal structure is in good agreement with the data provided in the literature. The Al0.3CoCrFeNi alloy has a high tendency to work hardening. References 1. Bataeva Z.B., Ruktuev A.A., Ivanov I.V., Yurgin A.B., Bataev I.A.Obzor issledovanii splavov, razrabotannykh na osnove entropiinogo podkhoda [Review of alloys developed using the entropy approach]. Obrabotka metallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2021, vol. 23, no. 2, pp. 116–146. DOI: 10.17212/1994-6309-2021-23.2-116-146. 2. Zhang F., Lou H., Cheng B., Zeng Z., Zeng Q. High-pressure induced phase transitions in high-entropy alloys: a review. Entropy, 2019, vol. 21 (3). DOI: 10.3390/e21030239. 3. Wang W.R., Wang W.L., Yeh J.W. Phases, microstructure and mechanical properties of AlxCoCrFeNi high-entropy alloys at elevated temperatures. Journal of Alloys and Compounds, 2014, vol. 589, pp. 143–152. DOI: 10.1016/j.jallcom.2013.11.084. 4. WangW.R.,WangW.L.,Wang S.C., TsaiY.C., Lai C.H.,Yeh J.W. Effects ofAl addition on themicrostructure and mechanical property of AlxCoCrFeNi high-entropy alloys. Intermetallics, 2012, vol. 26, pp. 44–51. DOI: 10.1016/j. intermet.2012.03.005.
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