Microstructure and mechanical properties of Ti2AlNb-based alloy weld joints as a function of gas tungsten arc welding parameters

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 high-frequency 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.