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
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