Abstract
Deformation behaviour of laser-welded tube blank of TA15 Ti-alloy at elevated temperature was investigated by both hot tensile tests and high pressure gas forming(HPGF). The hot tensile tests were carried out with four different specimens at 800 ∘ C with an initial strain rate of 1.00×10 −2 s −1 and HPGF test was performed at 800 ∘ C with a constant pressure of 9.5MPa. The tensile results show that base material with equiaxed microstructure exhibited good formability and grain boundary sliding (GBS) accompanied with dynamic recrystallization (DRV) was the main deformation mechanism. However, because the weld bead has coarse columnar grains with fine acicular α′ in the β matrix, when the loading direction is parallel with the weld bead, the fine acicular α′ transformed into thicker α lamella and the aspect ratio decreased greatly, and voids formed along the initial coarse β grain boundaries. When the loading direction is vertical with the weld bead, the welded materials deformed little and the lamella structure thickened obviously after deformation. HPGF tests demonstrate that the laser-welded TA15 tube had a very good formability at 800 ∘ C, and the maximum bulging ratio was as high as 77.4%.
Highlights
One can see that the weld bead has the highest strength and the lowest ductility, which is consistent with the microstructure characteristic of the coarse columnar grains with fine acicular ’ in the matrix
The maximum perimeter along the hoop direction after deformation is 220 mm, so the bulging ratio of the welded tube is 77.4%. Another interesting thing is that the tube failed at base material rather than weld bead and the crack which happened during the tensile deformation when the loading direction is parallel with the weld bead, did not occur in the high pressure gas forming process (HPGF)
Deformation behaviour of laser-welded tube blank of TA15 Ti-alloy at elevated temperature was investigated by both hot tensile tests and high pressure gas forming (HPGF)
Summary
The welded Ti-alloy joints have lamellar microstructure in the weld zone, and continuous globularization ensures a good superplasticity of the material, so full globularization happened after superplastic deformation. To reduce cycle time and increase productivity, forming process at higher strain rate and lower temperature should be developed. [11] formed Ti-3Al-2.5V parts with seamless tube at temperature around 8000C by high pressure gas forming process (HPGF) successfully. Few reports were found about the deformation behaviour of laser-welded Ti-alloy tube blank within this kind of forming process, especially for Ti–6.5Al–2Zr–1Mo1V (TA15) alloy
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