Structure and properties of welded joints from various titanium alloys

Aging of the OT4-VT23, VT6-VT23, VT19-VT23 Titanium Welded Pairs

“…The slight hardening in the HAZ of the OT4 alloy after aging in comparison with the state after welding is observed but it disappears near the weld zone. In this case the presence of hardening is mainly due to the decomposition of a certain amount of metastable β-solid solution (up to 10 % according to the data of [6]) formed after welding in the HAZ heated below the temperature of the polymorphic α+β−β-transformation (βtransus temperature, Tβ). In the welding process, the heating of the zone near the weld to a higher temperature (higher then Tβ) in comparison with HAZ, subsequently promotes the formation of the α-phase similar to martensite phase (Fig.…”

“…In the HAZ of the VT23 alloy after aging at 500 °C, the hardening takes place in comparison with the state after welding, which gradually increases in the direction from the parent metal zone to the zone located near the weld with a maximum near the weld. This effect is obviously associated with the process of precipitation of the dispersed α-phase during the decomposition of the metastable α", β-phases formed in the HAZ after welding, the number of which gradually increases with distance from the parent metal zone getting a maximum of 100 % near the weld [6]. Then hardening somewhat decreases due to the coarsening of the metastable structural components owing to the growth of the β-grain.…”

“…%) -OT4 (Ti-3.5Al-1.5Mn), VT6 (Ti-6Al-4.5V), VT23 (Ti-4.5Al-4.5V-2Mo-1Cr-0.6Fe), VT19 (Ti-3Al-5.5Mo-3.5V-5.5Cr-1Zr). According to the previous studies [6,8], various metastable phases (α', α", βm) and their combination are formed in the HAZ and the weld depending on alloy and welded pairs (OT4-VT23, VT6-VT23, VT19-VT23). These metastable phases are prone to decomposition upon subsequent thermal treatment (aging) [16].…”

“…In this case, a more expensive alloyed high strength alloy is used in the welded product zones with increased loads, whereas a cheaper less alloyed and less strong titanium alloy is used in the zones experiencing lower loads [4,5]. As a result, it becomes important to select the heat treatment process of such a welding joint with expressed structural and phase heterogeneity over the joint section especially in the heat affected zones (HAZ) [5][6][7]. It was shown in [8], that the vacuum annealing can be used for the formation of an equilibrium structure and a smooth change of strength properties in the welding joint zone of pseudo-α-and α+βmartensitic class titanium alloys in combination of OT4-VT6, VT20-VT6, VT23-VT6.…”

Microstructure and Properties of High Temperature Titanium Alloys with a High Si Content Prepared by Powder Metallurgy

“…Previous studies have reported improved creep resistance of titanium alloys by using silicon as an alloying element (up to 0.5 mass%) 6,7) . The mechanism by which silicon improves the creep resistance is not clear.…”