Ti₂AlNb-based alloys are promising materials for operation at high temperatures in aerospace industry. Meanwhile, the existing difficulties of weldability restrict opportunities of their application. This work is devoted to studies of welded joints from Ti₂AlNb-based VTI-4 alloy, obtained using pulsed laser welding (PLW). The optimum PLW modes have been determined providing uniform faultless joint. The features of formation of external defects, internal pores, cracks and non-uniform penetration depth were detected depending on welding conditions. The main PLW parameters influencing on formation of welded joint are voltage and duration of laser pulse. It was demonstrated that at insufficient medium and high peak powers sawtooth seam roots and internal pores can be formed. However, at higher rates of energy input thermal hydraulic processes in welding bathe are violated, accompanied by metal splashing (spattering), heterogeneity of pulse imposition is observed. This leads to formation of cracks, higher porosity, heterogeneity of melting zone, and as a consequence, poor mechanical properties. Microstructure analysis of the welded joints obtained by means of PLW has demonstrated that the melting area is comprised of long dendritic grains of β phase, and the heat affected zone from two regions of β + α₂phases and β + α₂+ O phases. Herewith, the achieved joint strength equals to ~80 % of the base metal produced using the optimum PLW mode.

In the present paper, the effect of diffusion bonding (DB) and post-bond heat treatment on a microstructure and mechanical properties of a Ti₂AlNb-based alloy VTI-4 was studied. DB was carried out using an SPS 10–3 selective plasma sintering system. The optimum mechanical properties of DB-joints (σ_u = 1240 MPa, σ_0.2 = 1070 MPa, δ = 4.6%) were achieved after DB at temperatures of 940°C and 960°C, a holding time of 120 minutes, and a pressure of 15–25 MPa. The obtained mechanical properties were equal to that of the initial material (σ_u = 1230 MPa, σ_0.2 = 1190 MPa and δ = 3.5%, 400 ± 10 HV_0.2). After DB at 940–960°C, microhardness was 395 ± 30 HV_0.2, which was higher than that after DB at 920°C (360 ± 25 HV_0.2). DB provoked an increase in the volume fraction of the O-phase along the joint interface compared to the base material. Post-bond heat treatment resulted in an additional increase in the volume fraction of the O-phase that increased strength and hardness.

Using keyhole plasma arc welding, welded joints of a Ti₂AlNb-based alloy, VTI-4, were obtained, and their structure and mechanical properties were studied. It has been established that the dynamic effect of a keyhole arc had a positive effect on the quality of the welded joint; namely, lack of penetration, porosity, and microcracks were eliminated. The welded joint consisted of a fusion zone (FZ), a heat-affected zone (HAZ), and a base metal (BM). Depending on the phase composition and morphology of the obtained phases, the HAZ can be divided into four zones: HAZ1 with large β-phase grains near the melting line, HAZ2 with large β-phase grains + α₂, HAZ3 with more fragmented β-phase grains retaining more α₂-phase, and HAZ4 with the phase composition β + α₂ + O. Subsequent heat treatment (HT: quenching at 920 °C for 2 h, cooling in air, followed by aging at 800 °C for 6 h, cooling in air) preserved the zone structure of the weld but led to the formation of the O-phase within β-grains. The microhardness of the weld in the zone corresponds to 360±15 HV0.2, but after HT, it increased to 382±20 HV0.2. The strength properties of the welded joint after HT were above 90 % of the base metal (σ_ucs = 1120 MPa, σ_0.2 = 1090 MPa), while elongation to failure is close to the initial condition (δ = 2.1 %).

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.

Introduction. The low yield strength of austenitic stainless steels is a factor significantly limiting their industrial applications. In turn, the formation of a heterogeneous structure is a promising method for achieving a synergy of mechanical properties. At the same time, an effective way to obtain a bulk heterogeneous structure is cold radial forging. However, the underlying mechanisms for the improved mechanical properties of materials with a heterogeneous structure formed in the process of cold radial forging are currently poorly understood. Purpose of the work is to investigate the effect of a heterogeneous structure obtained by deformation and heat treatment on the mechanical properties of austenitic stainless steel 0.08 C-17 Cr-13 Ni-2 Mn-Ti. Methods. Uniaxial tensile tests were performed on specimens obtained by cold radial forging followed by heat treatment at 600–700°C, using an Instron 5882 testing machine at room temperature with a strain rate of 1.15 × 10–3 s–1. A VIC-3D visual inspection system was used to measure elongation during testing. The fine structure was examined on perforated foils with a diameter of 3 mm using a JEOL JEM-2100 transmission electron microscope at an accelerating voltage of 200 kV. Results and discussion. It was shown that, after thermo-mechanical treatment, a twin-matrix austenite structure was obtained in the center of the rod, while an ultrafine-grained structure with isolated recrystallized austenite grains of approximately 1 μm in size was obtained at the edge. It was established that a two-component axial austenite texture / is formed in the center of the rod, which transformed into a shear texture B/B̅ towards the rod surface. It was determined that the formation of a heterogeneous structure led to additional strengthening due to back stresses. It was found that, after heat treatment at 700°C, the specimen with a heterogeneous structure exhibited the highest yield strength, equal to 1054 MPa, with a relative elongation of 16%. Thus, the employed thermo-mechanical treatment may be a promising method for obtaining large-sized rod stocks from austenitic stainless steel 0.08 C-17 Cr-13 Ni-2 Mn-Ti with high mechanical properties.