Deformation of Ti-6Al-4V alloy in the β phase field is generally considered to be trivial since the material is highly workable at these temperatures and does not normally pose problems during processing. In view of this, studies on the hot deformation behavior of β are scanty compared to those on the α−β deformation. This paper is focussed on understanding the β deformation characteristics in Ti-6Al-4V with a view to examine whether such studies help in optimizing the process design and achieving microstructural control. The emphasis has been on the two industrial grades, viz. commercial purity (CP) versus extra-low interstitial (ELI), and also on the effect of starting microstructure (transformed β versus equiaxed α+β). The stress-strain curves obtained in compression exhibited steady-state behavior at strain rates lower than 1 s−1 and oscillatory/softening behavior at higher strain rates. Kinetic analysis of the flow stress data obtained at different temperatures and strain rates has shown that the stress exponent is about 3.6-3.8 and the apparent activation energy is in the range 150-287 kJ/mole, which is comparable to that of self-diffusion in β phase (150 kJ/mol). Dynamic recrystallization (DRX) of β is identified as the microstructural mechanism in all the cases except in ELI grade with transformed β starting structure. The prior β grain size in the DRX region exhibits a good correlation with the Zener-Hollomon parameter. In case of ELI grade, a mechanism of large grained superplasticity involving sliding of prior colony boundaries has been identified. However, deformation close to the transus in ELI grade causes nucleation of voids which may grow during soaking at the deformation temperature under the influence of tensile residual stress. The results clearly show that a study of β deformation mechanisms holds the key during hot working of Ti-6-4. More importantly, the processing schedule used for CP grade Ti-6-4 should not be used for ELI grade to achieve microstructural control and avoid defects.
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July 2001
Technical Papers
A Study of Beta Processing of Ti-6Al-4V: Is it Trivial?
Y. V. R. K. Prasad, Professor,,
Y. V. R. K. Prasad, Professor,
Department of Metallurgy, Indian Institute of Science, Bangalore 560012, India
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T. Seshacharyulu, Visiting Scientist,
T. Seshacharyulu, Visiting Scientist
AFRL/MLMR, Wright-Patterson Air Force Base, OH 45433
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S. C. Medeiros, Research Engineer,
S. C. Medeiros, Research Engineer
AFRL/MLMR, Wright-Patterson Air Force Base, OH 45433
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W. G. Frazier, Senior Engineer,
W. G. Frazier, Senior Engineer,
Miltec Inc., NCPA Coliseum Drive, University, MS 38677
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Y. V. R. K. Prasad, Professor,
Department of Metallurgy, Indian Institute of Science, Bangalore 560012, India
T. Seshacharyulu, Visiting Scientist
AFRL/MLMR, Wright-Patterson Air Force Base, OH 45433
S. C. Medeiros, Research Engineer
AFRL/MLMR, Wright-Patterson Air Force Base, OH 45433
W. G. Frazier, Senior Engineer,
Miltec Inc., NCPA Coliseum Drive, University, MS 38677
Contributed by the Materials Division for publication in the JOURNAL OF ENGINEERING MATERIALS AND TECHNOLOGY. Manuscript received by the Materials Division November 10, 1999; revised manuscript received March 1, 2001. Associate Editor: N. Chandra.
J. Eng. Mater. Technol. Jul 2001, 123(3): 355-360 (6 pages)
Published Online: March 1, 2001
Article history
Received:
November 10, 1999
Revised:
March 1, 2001
Citation
Prasad, Y. V. R. K., Seshacharyulu, T., Medeiros, S. C., and Frazier, W. G. (March 1, 2001). "A Study of Beta Processing of Ti-6Al-4V: Is it Trivial? ." ASME. J. Eng. Mater. Technol. July 2001; 123(3): 355–360. https://doi.org/10.1115/1.1372708
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