Structure and mechanical properties of electron beam welded joints of orthorhombic titanium aluminide alloy VTI-4

In the present work, electron beam welding (EBW) was used to produce joints from the VTI-4 alloy based on orthorhombic titanium aluminide (Ti2AlNb), which is a promising material for the aerospace industry. A pulsed EBW mode for butt-welding of 2 mm thick plates of this alloy was proposed, ensuring the formation of a high-quality welded joint. The welding parameters were as follows: welding speed 0.5–1.0 m/min, welding current 15–20 mA, focusing current 500–550 mA, and pulse frequency 25 Hz, with the beam focused on the surface of the workpieces. The phase composition, as well as the grain size and dimensions of the weld zones, were determined using scanning electron microscopy methods. The fusion zone (FZ) consists of the β-phase, while the heat-affected zone (HAZ) can be divided into HAZ1, consisting of β+α2 phases, and HAZ2, comprising β+α2+O phases. In the HAZ1 region, the globular α2-phase is partially retained, since higher heating temperatures are required to complete the α2→β transformation. Furthermore, it was determined that the level of strength properties of the produced welded joints corresponds to ≈90 % of the base metal strength. A comparative analysis of the dendrite size and globular β-grains in the weld, as well as the strength and ductility of joints produced by various fusion welding methods, showed that the EBW joints have a 2–3 times smaller grain size in the fusion zone and the HAZ of the weld. This feature positively affects the set of mechanical properties, where a high weld strength coefficient is achieved during EBW of the VTI-4 alloy, and the elongation at fracture corresponds to 2.8 %.