The paper presents the results of the X-ray diffraction analysis of structural-phase states in the weld zone of a titanium alloy Grade2 in micro-and submicrocrystalline states. It is established that the structural-phase state in the weld zone and in the heat-affected zone depends on the state of samples of the alloy Grade2 before welding. It is shown that formation process of metastable phases ω-Ti and α′′-Ti occurs in the submicrocrystalline state in the alloy Grade2 in the weld zone and in the heat-affected zone. Investigations of the features of the microhardness distribution in the weld zone in alloys Grade2 in micro-and submicrocrystalline states are carried out. Different character of microhardness distributions in the weld zone in the samples depending on the structural-phase state of welded plates made of alloy Grade2 is determined.
The paper reports changes in strain fields on welded sample surfaces from commercial pure titanium, joined by both laser beam welding (LBW) and gas tungsten arc welding (GTAW) procedures, under uniaxial tensile loads. Their dynamics were investigated by the digital image correlation method using a ‘Vic-3D’ optical system. In addition, stress-strain curves were drawn in both σeng-εeng and σtrue-εtrue coordinates. It was shown that the laser welded sample was characterized by a higher ultimate tensile strength to yield point ratio than the as-received one. The GTAW sample fractured under much less stresses than the LBW one.
The structural-phase state of weld joints of the samples of Grade 2 alloys with micro- and submicrocrystalline structure is studied using methods of X-ray diffraction analysis. The weld joint was obtained by joining plates with a thickness of 2 mm using the electron-beam welding method. It is established that the transfer of the titanium alloy Grade 2 from the microcrystalline state into the submicrocrystalline state during the process of gradual grinding of grains in the samples by the abc-pressing method at a parallel stepwise decrease of the temperature in the range of 750-500 °C leads to an intensive introduction of oxygen atoms into the crystalline lattice of the solid solution a-Ti. The presence of an increased content of oxygen atoms in the crystalline lattice of the solid solution a-Ti in the submicrocrystalline state in the Grade 2 alloy in the weld zone and in the heat-affected zone promotes the formation of metastable phases w-Ti and α''-Ti. The obtained results made it possible to assume that in the process of electron-beam welding in the Grade 2 alloy in the submicrocrystalline state, an increased concentration of interstitial oxygen atoms in the crystalline lattice of the solid solution based on a–Ti plays a significant role in the formation of a wide range of structural-phase states in the weld zone and in the heat-affected zone.
This paper presents the results of structural studies for a welded joint of the Grade 2 titanium alloy in submicrocrystalline and microcrystalline states produced by electron beam welding when joining 2-mm-thick plates. Microhardness distribution patterns of the Grade-2 titanium alloy in micro- and submicrocrystalline states are identified in the weld zone and heat-affected zone. These patterns reflect a difference in structural phase states. It is assumed that one of the key factors affecting both the structural state and microhardness distribution in the weld zone and heat-affected zone during electron-beam welding is high concentration of oxygen atoms embedded into the crystal lattice of α–Ti-based solid solution.
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