Vol. 27 No. 2 2025 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. 27 No. 2 2025 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. 27 No. 2 2025 5 CONTENTS OBRABOTKAMETALLOV TECHNOLOGY Sundukov S.K., Nigmetzyanov R.I., Prikhodko V.M., Fatyukhin D.S., Koldyushov V.K. Comparison of ultrasonic surface treatment methods applied to additively manufactured Ti-6Al-4V alloy................................................................ 6 Kate N., Kulkarni A.P., Dama Y.B. A comparative evaluation of friction and wear in alternative materials for brake friction composites............................................................................................................................................................... 29 Naumov S.V., Panov D.O., Sokolovsky V.S., Chernichenko R.S., Salishchev G.A., Belinin D.S., Lukianov V.V. Microstructure and mechanical properties of Ti2AlNb-based alloy weld joints as a function of gas tungsten arc welding parameters............................................................................................................................................................................. 43 Jatti V.S., Singarajan V., SaiyathibrahimA., Jatti V.S., KrishnanM.R., Jatti S.V. Enhancement of EDM performance for NiTi, NiCu, and BeCu alloys using a multi-criteria approach based on utility function................................................ 57 Stelmakov V.A., Gimadeev M.R., Nikitenko A.V. Ensuring hole shape accuracy in fi nish machining using boring...... 89 EQUIPMENT. INSTRUMENTS Patil N., Agarwal S., Kulkarni A.P., Saraf A., Rane M., Dama Y.B. Experimental investigation of graphene oxide-based nano cutting fl uid in drilling of aluminum matrix composite reinforced with SiC particles under nano-MQL conditions............................................................................................................................................................................. 103 Gimadeev M.R., Stelmakov V.A., Nikitenko A.V., Uliskov M.V. Prediction of surface roughness in milling with a ball end tool using an artifi cial neural network................................................................................................................. 126 Osipovich K.O., Sidorov E.A., Chumaevskii A.V., Nikonov S.N., Kolubaev E.A. Manufacturing conditions of bimetallic samples based on iron and copper alloys by wire-feed electron beam additive manufacturing......................... 142 Babaev A.S., Savchenko N.L., Kozlov V.N., Semenov A.R., Grigoriev M.V. Performance of Y-TZP-Al2O3 composite ceramics in dry high-speed turning of thermally hardened steel 0.4 C-Cr (AISI 5135)...................................................... 159 MATERIAL SCIENCE Sokolov R.A., Muratov K.R., Mamadaliev R.A. Morphological changes of deformed structural steel surface in corrosive environment......................................................................................................................................................... 174 Chernichenko R.S., Panov D.O., Naumov S.V., Kudryavtsev E.A., Salishchev G.A., Pertsev A.S. Eff ect of heterogeneous structure on mechanical behavior of austenitic stainless steel subjected to novel thermomechanical processing............................................................................................................................................................................. 189 Panov D.O., Chernichenko R.S., Naumov S.V., Kudryavtsev E.A., Salishchev G.A., Pertsev A.S. Eff ect of cold radial forging on structure, texture and mechanical properties of lightweight austenitic steel................................................ 206 Deshpande A., Kulkarni A.P., Anerao P., Deshpande L., Somatkar A. Integrated numerical and experimental investigation of tribological performance of PTFE based composite material.................................................................... 219 Vorontsov A.V., Panfi lov A.O., Nikolaeva A.V., Cheremnov A.V., Knyazhev E.O. Eff ect of impact processing on the structure and properties of nickel alloy ZhS6U produced by casting and electron beam additive manufacturing........ 238 Misochenko A.A. Martensitic transformations in TiNi-based alloys during rolling with pulsed current........................... 255 EDITORIALMATERIALS 270 FOUNDERS MATERIALS 279 CONTENTS
OBRABOTKAMETALLOV Vol. 27 No. 2 2025 technology Microstructure and mechanical properties of Ti2AlNb-based alloy weld joints as a function of gas tungsten arc welding parameters Stanislav Naumov 1, a,*, Dmitrii Panov 1, b, Vitaly Sokolovsky 1, c, Ruslan Chernichenko 1, d, Gennady Salishchev 1, e, Dmitry Belinin 2, f, Vasilii Lukianov 3, g 1 Belgorod National Research University, 85 Pobedy Str., Belgorod, 308015, Russian Federation 2 Perm National Research Polytechnic University, 29 Komsomolskiy Prosp., Perm, 614990, Russian Federation 3 NPA “Technopark AT”, 5 Tramvaynaya Str. (bld. 1), Ufa, 450027, Russian Federation a https://orcid.org/0000-0002-4084-8861, NaumovStanislav@yandex.ru; b https://orcid.org/0000-0002-8971-1268, dimmak-panov@mail.ru; c https://orcid.org/0000-0001-5607-2765, sokolovskiy@bsuedu.ru; d https://orcid.org/0000-0002-8619-0700, rus.chernichenko@mail.ru; e https://orcid.org/0000-0002-0815-3525, salishchev_g@bsuedu.ru; f https://orcid.org/0000-0001-5462-0908, 5ly87@mail.ru; g https://orcid.org/0009-0006-3621-3966, lukianovv@bk.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. 2025 vol. 27 no. 2 pp. 43–56 ISSN: 1994-6309 (print) / 2541-819X (online) DOI: 10.17212/1994-6309-2025-27.2-43-56 ART I CLE I NFO Article history: Received: 12 February 2025 Revised: 01 March 2025 Accepted: 21 March 2025 Available online: 15 June 2025 Keywords: Gas tungsten arc welding (GTAW, TIG) Ti2AlNb Ti–Al–Nb–(Zr, Mo)–Si Scanning electron microscopy (SEM) Mechanical properties Funding Thisworkwas supported by theRussian Science Foundation (Agreement No. 19-79-30066) using the equipment of BSU Shared Research Facilities “Technologies and Materials”. ABSTRACT Introduction. Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, is a promising welding method for Ti2AlNb-based alloys, including Ti–Al–Nb–(Zr, Mo)–Si alloy, due to its accessibility and relative simplicity, making it attractive for aerospace applications. However, the application of GTAW to Ti–Al–Nb–(Zr, Mo)– Si alloy is limited by the formation of a coarse-grained microstructure in the weld, leading to reduced mechanical properties of weld joints. Purpose of the work. This study investigates the influence of GTAW modes (using direct current with low- and high-frequency pulses) on the microstructure and tensile properties of Al–Nb–(Zr, Mo)–Si alloy weld joints. Methods. GTAW of plates was carried out using welding currents ranging from 80 to 150 A, employing both low- and high-frequency (>100 Hz) pulses. The microstructure of the weld joints was examined using scanning electron microscopy (SEM). The tensile properties were evaluated through uniaxial tensile testing of the welded joints. The shielding gas flow rate was 12 L/min, while a separate gas flow of 2 L/min was used for blowing. The microstructure of the weld joints was examined using scanning electron microscopy (BSE-EBSD analysis). The tensile properties were evaluated through uniaxial tensile testing of the weld joints. Results and discussion. The weld joints microstructure is characterized by elongated, coarse dendrites in the central and weld bead regions and globular β-grains in the root part of the fusion zone. Tensile testing of the weld joints revealed a strength level approximately 90% of that of the base metal when using pulse mode (σu = 1100 MPa, δ = 1.1 %, 335–390 HV0.2) and not less than 80% when using direct current modes. This level of mechanical properties is achieved using highfrequency pulsed welding, where the maximum length and width of dendrites in the weld joint are 1.06 mm and 0.33 mm, respectively, and the average size of globular grains in the lower part of the weld joint is approximately 130 μm, which is less than that observed when utilizing the same modes, but direct current. For citation: Naumov S.V., Panov D.O., Sokolovsky V.S., Chernichenko R.S., Salishchev G.A., Belinin D.S., Lukianov V.V. Microstructure and mechanical properties ofTi2AlNb-based alloyweld joints as a function of gas tungsten arcwelding parameters. Obrabotkametallov (tekhnologiya, oborudovanie, instrumenty) = Metal Working and Material Science, 2025, vol. 27, no. 2, pp. 43–56. DOI:10.17212/1994-6309-2025-27.2- 43-56. (In Russian). ______ * Corresponding author Naumov Stanislav V., Ph.D. (Engineering), Belgorod National Research University, 85 Pobedy Str., 308015, Belgorod, Russian Federation Tel.: +7 912 580-55-68, e-mail: NaumovStanislav@yandex.ru Introduction Titaniumalloys have foundwidespread application in various industries, including aerospace, mechanical engineering, medicine, and other fields, due to their low density, high strength, corrosion resistance, excellent manufacturability, and other beneficial properties [1–4]. However, the high-temperature applications of titanium alloys are limited by their creep and oxidation resistance up to 500–550 °C [5].
OBRABOTKAMETALLOV technology Vol. 27 No. 2 2025 A potential solution to the problem of high-temperature service lies in intermetallic compounds and alloys [6]. Alloys based on the orthorhombic titanium intermetallic (ortho-Ti2AlNb alloys) are promising materials in this regard. Ti2AlNb-based alloys exhibit low density (5.1…5.4 g/cm3), high specific strength, oxidation resistance, and creep resistance [7–10]. However, their practical application is complicated by difficulties in welding, which is one of the most significant limiting factors [11]. This is primarily due to the generation of high residual stresses resulting from a cascade of phase transformations in the fusion and heat-affected zones (FZ, HAZ) during welding, low thermal conductivity (6.2 W/(m·K) [10]) and low ductility of Ti2AlNb-based alloys. Therefore, by varying welding parameters to control heat input, it is necessary to ensure the formation of an optimal weld structure and to create conditions for slow cooling of the weld metal to prevent cracking [12–14]. To address these issues, various specialized welding methods with supplementary techniques are employed, such as heating of the workpieces before and during welding (preheating and additional heating). Furthermore, heat treatment is used to improve mechanical properties [15–18]. Despite the wide variety of methods, techniques, and operations used in welding titanium alloys, gas tungsten arc welding (GTAW, TIG welding) remains the most promising for industrial applications, which is determined by the formation of defect-free welds and its wide availability. However, the formation of a coarse-grained structure and a wide weld region limits its application due to the low mechanical properties, namely ultimate tensile strength (σu) and percentage of elongation (δ), of the welded joints [19, 20]. Currently, leveraging the accumulated global experience in GTAW of titanium alloys, it is possible to enhance the mechanical properties of welded joints made from Ti2AlNb-based alloy by employing GTAW with speed-up direct current and using low- and high-frequency pulsing. This allows for the regulation of the heat spot power and, consequently, the heat input into the workpiece, creating conditions to prevent the growth of dendritic structures in the weld metal [21]. Therefore, the purpose of this research is to investigate the influence of GTAW conditions on the microstructure and mechanical properties of welded joints made from Ti2AlNb-based alloy. To achieve the set purpose, it is proposed to solve several problems. Namely, the first problem is to select GTAW weldig conditions using direct current and with the application of low- and high-frequency pulsing to obtain defect-free welded Ti2AlNb-based alloy joints. Subsequent problems involve studying the microstructure, microhardness, and mechanical properties of the obtained welded joints compared to the properties of the base material. Methods The chemical composition of the initial Ti2AlNb-based alloy is presented in Table 1. The hot-forged workpiece of the Ti2AlNb-based alloy in the initial state exhibits the following properties: ultimate tensile strength (σu) = 1,230 MPa, offset yield strength (σ0.2) = 1,190 MPa, percentage of elongation (δ) = 3.5 %, and microhardness = 400 ± 10 HV0.2. The microstructure of the initial material (Fig. 1) consisted of large β-grains elongated perpendicular to the forging direction and 300 ± 50 μm in size. Furthermore, a globular α2-particles (Ti3Al) with a size of 10 ± 5 μm were located along the β-grain boundaries. Particles of the acicular O-phase (Ti2AlNb) particles with a length of 8 ± 3 μm and a thickness of 1–3 μm were uniformly distributed throughout the entire volume of the material under study. TIG welding was performed on INVERTEC V405-T pulse equipment (Lincoln Electric, USA) using a WP-9 flex welding torch (Start, Russia) and WT-20 electrodes (Start, Russia). Argon was used as the shielding gas. Gas shielding was implemented using a 12 mm diameter gas lens at the welding site and Ta b l e 1 Chemical composition of Ti–Al–Nb–(Zr, Mo)–Si alloy Element Al Nb V Zr Mo Si Ti at. % 23.0 23.0 1.4 0.8 0.4 0.4 base
OBRABOTKAMETALLOV Vol. 27 No. 2 2025 technology additional blowing into the weld root (Fig. 2, a). The shielding gas flow rate was 12 L/min, and the gas for blowing rate was 2 L/min. The workpieces for GTAW (25×15×2 mm) were cut from the forged piece using VL400Q and VL600Q wire electrical discharge machines (Sodick, China). The surface of the workpieces was prepared before GTAW using abrasive paper: the abutting surfaces were ground with FEPA P1000 (18 μm, GOST No. M20) abrasive paper, and the remaining surfaces were ground with FEPA P220 (68 μm, GOST No. 6) abrasive paper. Welding of the 2 mm thick plate workpieces was performed in a butt joint configuration. Welding was performed using speedup welding condition. Low- and high-frequency pulsed welding was also used in the study (Table 2). A feature of gas tungsten arc welding using low- and high-frequency pulsing is that additional pulses with a specified amplitude are superimposed on the effective constant welding current, forming energy peaks that exceed the background current. At the same time, the formation of the welds occurs sequentially in a droplet mode, which eliminates metal spatter and allows for the production of thin-walled welded joints without burn-through. Arc ignition was performed on the edge of the workpieces being welded due to the absence of runoff plates. The welding current range was 80…150 A. Fig. 1. Initial microstructure of the Ti–Al–Nb–(Zr, Mo)–Si alloy a b c Fig. 2. GTAW welding fixture (a), specimens for mechanical testing (b) and microhardness testing specimens (c) of the welded joint of Ti–Al–Nb–(Zr, Mo)–Si alloy Specimens for uniaxial tensile testing, microstructural analysis, and microhardness testing were ground with silicon carbide-based abrasive papers FEPA P 220–2000 (Struers, Denmark) on a grinding and polishing machine (Chennai Metco BAINPOL, India). The polishing was carried out on a 200 mm polishing wheel made of MD-Nap cloth from Struers using O.P.S (MetCata, Germany) or OP-S (Struers, Denmark) 0.05 μm suspension. To determine the mechanical properties of the welded joints made of Ti–Al–Nb–(Zr, Mo)–Si alloy, uniaxial tensile tests were performed using a 5882 universal testing machine (Instron, USA). The test temperature corresponded to room temperature. The strain rate during tensile testing was set to 10–4 s–1. The shape and dimensions of the uniaxial tensile test specimens are shown in Fig. 2. The microhardness was measured in the cross-section of the welded joints using a 402MVD microhardness tester (Instron, Netherlands) equipped with a diamond indenter. The load applied to the indenter corresponded to 200 g with a holding time of 10 sec. The distance between measurements was 100 μm. The measurement was carried out along one line in the center of the specimen, i.e., at a depth of 1 mm, as shown in Fig. 2, c.
OBRABOTKAMETALLOV technology Vol. 27 No. 2 2025 The microstructure was evaluated using scanning electronmicroscopy (BSE and EBSD analysis), namely, evaluation of the presence of internal defects (pores, cracks, lack of fusion), identification of phases, and geometric dimensions of the microstructure elements in the weld metal and heat-affected zone (HAZ). BSE and EBSD analysis was performed using a Q600 3D instrument (FEI, Czech Republic) using TSL OIM Analysis 9 software with a scanning step of 3 μm and an accelerating voltage of 30 kV. Results and discussion Fig. 3 shows the appearance of welded joints. The welded joints obtained in the selected modes (Table 2) do not have external cracks, pores or heat colors. The presence of defects at the beginning and end of the welds is attributed to the absence of run-off plates (Fig. 3). At currents of 80–85 A (mode No. 1), a fine scaling pattern is observed on the weld bead. A localized lack of fusion was found in the weld root, which could potentially be eliminated by a more uniform welding speed. In speed-up welding condition at I = 150…155 A (mode No. 2), burn-through of the plates occurred; furthermore, the liquid metal locally accumulated under the force of surface tension, forming a drop-shaped weld bead. Thus, burn-through occurred on part of the plate, while a wide weld formed on another part. This mode is not suitable for GTAW of Ti–Al–Nb–(Zr, Mo)–Si alloy plates 2 mm thick. At increased currents of 110…115 A (mode No. 3), defects did not form, ensuring a uniform, fine-ripple weld with full fusion of the plates (Fig. 3, b). However, the weld width (mode No. 3) is 1.5 times wider compared to mode No. 1, and the melting of the plate edges is more intense. On average, the weld width obtained with direct current was 5…8 mm. Ta b l e 2 Modes of GTAW for Ti–Al–Nb–(Zr, Mo)–Si alloy plates No. Current, A Pulse frequency, Hz Shielding gas, L/min Blowing L/min Comments 1 80–85 – 12 2 local lack of fusion 2 150–155 – 12 2 burn-through 3 110–115 – 12 2 – 4 80–85 2 12 2 coarse scaling 5 80–85 >100 12 2 fine scaling 6 110–115 >100 15 2 fine scaling a b c d e Fig. 3. Appearance of Ti–Al–Nb–(Zr, Mo)–Si alloy weld joints produced by GTAW under: a – direct current (mode No. 1); b – direct current (mode No. 3); c – low-frequency pulse (mode No. 4); d – highfrequency pulse (mode No. 5); e – high-frequency pulse (mode No. 6)
OBRABOTKAMETALLOV Vol. 27 No. 2 2025 technology During GTAW with a low-frequency pulse of 2 Hz at currents of 80–85 A (mode No. 4), a coarse scaling pattern formed on the surface of the weld bead under the dynamic effects of the pulsed current (Fig. 3, c). Since the effects of the pulsed current allows reducing the welding speed, it promotes more intensive fusion of the weld root at the same current values as in mode No. 1. Welded joints obtained in modes No. 5 and No. 6 were obtained using a high-frequency pulse of more than 100 Hz. These modes provided a fine scaling pattern on the surface of the weld bead; however, when the current is increased to 110…115 A, melting of the plate edges occurred. The weld width obtained with pulsed currents was 5…7 mm. The reduction in the weld width can be explained by the influence of the welding current, namely, the effect of the pulsed current reduces the average power in the heat heating spot [22]. A typical morphology of the weld cross-section is shown in Fig. 4. In the upper part of the weld, a wide fusion zone (FZ) of the metal formed (Fig. 4, a) because of the action of the electric arc [23]. The weld metal consists entirely of β-grains (Fig. 4, b). The intense heating of the weld metal caused by the electric arc and, as a consequence, the wide weld (5–8 mm) also led to the formation of a wide HAZ. Depending on the phase composition, the HAZ can be divided into HAZ1 and HAZ2. HAZ1 consists of large β-phase grains 150 ± 50 μm (Fig. 4, c), whereas HAZ2 consists of β (80 ± 30 μm) + α2 (4 ± 2 μm) grains. It is known that with a greater distance from the fusion line, the phase composition in the HAZ (β+ α2) also additionally contains the O-phase [24]. The weld metal formed at direct and pulsed currents possesses a microstructure in the form of columnar grains at the bead and globular grains in the root part of the weld (Fig. 5). Primary crystallization begins when heat is removed to the base material, originating along the FL. The primary crystallization of the weld metal proceeds periodically, and a layered structure can be found (Fig. 4, a). The main volume of the а b c d Fig. 4. BSE-analysis of a Ti–Al–Nb–(Zr, Mo)–Si alloy weld joint obtained by GTAW according to mode No.4: a – general view showing the locations of BSE and EBSD analyses (FL – fusion line; FZ – fusion zone; HAZ – heat-affected zone); b – FZ; c – HAZ with coarse β-grains (HAZ1); d – HAZ with β + α2 phase composition (HAZ2)
OBRABOTKAMETALLOV technology Vol. 27 No. 2 2025 molten pool is concentrated in the immediate vicinity of the welding arc, so columnar dendrites formed in the central and upper part of the weld, where the maximum heat removal is observed. The maximum length (Lmax) and width (Hmax) of dendrites in welds made at currents of 110–115 A is ≈ 1.39 mm and 0.43 mm (mode No. 3), with a decrease in current (mode No. 1), the Lmax and Hmax of dendrites are ≈ 0.99 mm and 0.23 mm, respectively (Table 3). With an increase in the welding current, the width of the zone with globular grains decreases; however, the average grain size does not change and remains within 140 ± 50 μm (Fig. 5, a, b). In welding mode No. 3, localized incomplete fusion (lack of fusion) is observed at the root of the weld (Fig. 5, a), which was confirmed previously during visual inspection of the weld appearance. Ta b l e 3 Maximum dendrite length and width (Lmax, Hmax) and average globular grain size in the weld joint metal as a function of GTAW modes Welding modes No.1 No.2 No.3 No.4 No.5 No.6 Lmax (mm) 0.99 – 1.39 0.98 0.61 1.06 Hmax (mm) 0.23 – 0.43 0.27 0.23 0.33 Average globular grain size (μm) 140 ± 50 – 140 ± 50 190 ± 40 140 ± 40 130 ± 45 а b c d e Fig. 5. EBSD maps in cross-section of Ti–Al–Nb–(Zr, Mo)–Si alloy weld joints, obtained by GTAW according to: a – mode No. 1; b – mode No. 3; c – mode No. 4; d – mode No. 5; e – mode No. 6
OBRABOTKAMETALLOV Vol. 27 No. 2 2025 technology When welding in low-frequency pulsed modes, the FZ structure does not differ from the structure of welds obtained in modes No. 1 and No. 3. The Lmax and Hmax of dendrites in the weld, obtained in the low-frequency pulse mode (mode No. 4), are ≈ 0.98 mm and 0.27 mm, respectively, and the average size of the globular grains is ≈ 190 μm (Fig. 5, c). However, when using high-frequency pulsed current (mode No. 5), the Lmax and Hmax of dendrites in the weld decreases to ≈ 0.61 mm and 0.23 mm, and the average size of the globular grains is ≈ 140 μm (Fig. 5, d). In welding mode No. 5, a localized lack of fusion of 100…150 μm can be observed (Fig. 5, d), which is smaller than at the same welding current parameters in mode No. 1 (300…500 μm). With an increase in the high-frequency current values (mode No. 6), the Lmax (1.06 mm) and Hmax (0.33 mm) of the β-phase dendrites increases, while the average size of the globular β-grains in the lower part of the weld remains at ≈ 130 ± 45 μm (Fig. 5, e), which is smaller than at the same currents without the pulsed mode No. 3. The above results show that the pulsed welding current demonstrates periodic changes in the dynamic effects of the arc, which can enhance the effect of mixing the molten pool and thereby reduce the grain size in the weld [25]. The microhardness profile in the cross-section of welded joints obtained with direct current along the entire length is at the same level, since the weld width varies within 5…8 mm and the values correspond to the microhardness of the FZ and the HAZ1 with globular β-phase grains (Fig. 6, a, b). The range of values varies from 335 to 390 HV0.2. The range of microhardness values of welds obtained with pulsed currents is in the range of 340…380 HV0.2 (Fig. 6, c, d, e). Tensile tests of welded joints obtained GTAW (Fig. 7) showed that the strength level of the joints welded in mode No. 6 reaches ≈ 90 % of the base metal (σu = 1,100 MPa, δ = 1.1 %), and is not lower than 80 % of the base metal in modes No. 4 and No. 5 (σu = 1070 MPa, δ = 1.49 %) (Fig. 7, a). However, the ductility of the welded joint obtained in mode No. 5 is absent (σu = 960 MPa, δ = 0 %), and for the welded joints obtained in modes No. 4 and No. 6, it drops by 2–3 times in relation to the base metal and amounts to no more than 2 % (Fig. 7, b). a b c d e Fig. 6. Cross-sectional microhardness profiles of Ti–Al–Nb–(Zr, Mo)–Si alloy GTAW joints according to: a, b – DC mode; c, d, e – pulsed mode
OBRABOTKAMETALLOV technology Vol. 27 No. 2 2025 a b Fig. 7. Results of uniaxial tensile testing of Ti–Al–Nb–(Zr, Mo)–Si alloy weld joints as a function of GTAW modes: a – tensile stress-strain diagram; b – graph of mechanical properties In welded joints obtained with direct current welding, the joints perform extremely low ductility and strength properties. In welds obtained in mode No. 1, a localized lack of fusion was observed, which led to a decrease in strength to less than 80 %. In addition, the strength of the welded joint obtained in mode No. 3 is ≈ 40 % of the strength of the base metal. This is due to the fact that in this mode, the maximum grain size of the dendritic structure of the FZ was found, which exceeds by 1.5 times the maximum sizes of dendrites in the FZ of welded joints obtained with low- and high-frequency pulsed modes. When welding in mode No. 5, the decrease in the strength properties of the welded joint is possibly related to the localized lack of fusion that was found in the root part of the weld (Fig. 5, d). Fracture of the welded joints always occurs along the fusion line, and a river line pattern is visible on the fracture surface, mainly caused by the fracture of large β-grains (Fig. 8). The fracture surface of the sample welded in mode No. 6 has 2 zones, namely: a fracture area of large (dendritic structure of the FZ) and small grains. The phenomenon indicates the fracture of globular β-grains, which were formed in the root area of the weld (Fig. 8). A similar fracture pattern is observed on the remaining samples. Fig. 8. Fracture surface morphology of specimens after uniaxial tensile testing as a function of Ti–Al–Nb–(Zr, Mo)–Si alloy GTAW mode
OBRABOTKAMETALLOV Vol. 27 No. 2 2025 technology Conclusion The effect of GTAW modes on the quality of welded joints made of the Ti2AlNb-based alloy Ti–Al– Nb–(Zr, Mo)–Si alloy is studied. Based on the results obtained in this work, the following conclusions are drawn: – A defect-free weld is formed in welding modes at direct and pulsed currents in the range of 80–115 A and with a gas flow rate of 12–15 L/min. At lower welding currents, incomplete penetration (lack of fusion) was detected, while at higher currents, burn-through occurred. – The welds, depending on the welding modes, have the following microstructure: elongated, large dendrites with a size of 0.23–1.39 mm in the center of the weld; and globular β-grains with a size of 130–190 μm in the root area of the weld. The main volume of the liquid pool is concentrated near the impact of the welding arc. Therefore, columnar dendrites are formed in the central and upper part of the weld, where the maximum heat removal occurs. – Mechanical testing of Ti–Al–Nb–(Zr, Mo)–Si alloy welded joints showed a high strength level of ≈ 90 % of the base metal strength when using the pulsed welding mode (σu = 1100 MPa, δ = 1.1 %, 340–380 HV0.2) and not less than 80 % when using direct current modes (σu = 1070 MPa, δ = 1.49 %, 335–390 HV0.2). References 1. ZhaoQ., SunQ., Xin S., ChenY.,WuC.,WangH., Xu J.,WanM., ZengW., ZhaoY. High-strength titaniumalloys for aerospace engineering applications: a review on melting-forging process. Materials Science and Engineering: A, 2022, vol. 845, p. 143260. DOI: 10.1016/j.msea.2022.143260. 2. Marin E., Lanzutti A. Biomedical applications of titanium alloys: a comprehensive review. Materials (Basel), 2024, vol. 17 (2), p. 114. DOI: 10.3390/ma17010114. 3. Ezugwu E.O., Wang Z.M. Titanium alloys and their machinability – a review. Journal of Materials Processing Technology, 1997, vol. 68 (3), pp. 262–274. DOI: 10.1016/S0924-0136(96)00030-1. 4. Pasang T., Tao Y., Azizi M., Kamiya O., Mizutani M., Misiolek W. Welding of titanium alloys. MATEC Web of Conferences, 2017, vol. 123, pp. 1–8. DOI: 10.1051/matecconf/201712300001. 5. Veiga C., Davim J.P., Loureiro A. Properties and applications of titanium alloys: a brief review. Reviews on Advanced Materials Science, 2012, vol. 32 (2), pp. 133–148. 6. Kim Y.-W., Dimiduk D.M. Progress in the understanding of gamma titanium aluminides. JOM, 1991, vol. 43, pp. 40–47. 7. ShagievM.R., Galeyev R.M., Valiakhmetov O.R. Ti2AlNb-based intermetallic alloys and composites. Materials Physics and Mechanics, 2017, vol. 33 (1), pp. 12–18. DOI: 10.18720/MPM.3312017_2. 8. Nandy T.K., Banerjee D. Creep of the orthorhombic phase based on the intermetallic Ti2AlNb. Intermetallics, 2000, vol. 8 (8), pp. 915–928. DOI: 10.1016/S0966-9795(00)00059-5. 9. Dadé M., Esin V.A., Nazé L., Sallot P. Short- and long-term oxidation behaviour of an advanced Ti2AlNb alloy. Corrosion Science, 2019, vol. 148, pp. 379–387. DOI: 10.1016/j.corsci.2018.11.036. 10. Xu J., He L., Su H., Zhang L. Tool wear investigation in high-pressure jet coolant assisted machining Ti2AlNb intermetallic alloys based on FEM. International Journal of Lightweight Materials and Manufacture, 2018, vol. 1 (4), pp. 219–228. DOI: 10.1016/j.ijlmm.2018.08.007. 11. Chen W., Li J.W., Xu L., Lu B. Development of Ti2AlNb alloys: opportunities and challenges. AM&P Technical Articles, 2014, vol. 172 (5), pp. 23–27. DOI: 10.31399/asm.amp.2014-05.p023. 12. Panov D.O., Naumov S.V., Sokolovsky V.S., Volokitina E.I., Kashaev N., Ventzke V., Dinse R., Riekehr S., Povolyaeva E.A., Alekseev E.B., Nochovnaya N.A., Zherebtsov S.V., Salishchev G.A. Cracking of Ti2AlNb-based alloy after laser beam welding. IOP Conference Series: Materials Science and Engineering, 2021, vol. 1014, p. 012035. DOI: 10.1088/1757-899X/1014/1/012035. 13. Li Y.-J., Wu Ai-P., Li Q., Zhao Y., Zhu R.-C., Wang G.-Q. Mechanism of reheat cracking in electron beam welded Ti2AlNb alloys. Transactions of Nonferrous Metals Society of China, 2019, vol. 29 (9), pp. 1873–1881. DOI: 10.1016/S1003-6326(19)65095-8.
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