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In-situ synchrotron diffraction study of the hot deformation behaviour in Ti-64

Tuesday (05.11.2019)
14:40 - 15:00
Part of:

Alpha-beta Ti alloys often show pronounced softening during hot deformation. This softening is often attributed to globularisation of the α-phase, which is thought to occur by a kind of recrystallization mechanism, driven by deformation [1]. However, recent detailed texture and microtexture studies have suggested that this behaviour might instead be due to dynamic phase transformation [2][3]. The lack of a clear explanation is caused in part by the difficulty in interpreting the post-mortem microstructures in these alloy systems. On cooling, the β-phase transforms almost entirely into α, obscuring the deformed microstructure. Unfortunately, softening can only be seen at relatively high strain rates and large strains, making in-situ electron microscopy studies impractical. To avoid these difficulties, we used synchrotron diffraction to measure the internal strains, phase fraction and texture during hot tensile deformation of Ti-64 specimens. Using resistance heating and a fast acquisition rate (10 Hz), we were able to measure the microstructure evolution at a strain rate of about 0.1 /s at different temperatures and therefore different α/β phase contents. Our results showed direct evidence of dynamic phase transformation, during which the texture evolves by a kind of variant selection. Elastic strain measurements suggest that this variant selection is caused by the disappearance of highly stressed α variants during deformation. This finding has important consequences for understanding and controlling the microstructure development in dual-phase Ti alloys during thermomechanical processing.

[1] E. B. Shell and S. L. Semiatin, “Effect of initial microstructure on plastic flow and dynamic globularization during hot working of Ti-6Al-4V,” Metall. Mater. Trans. A, vol. 30, no. 12, pp. 3219–3229, Dec. 1999.

[2] B. Guo, S. L. Semiatin, J. J. Jonas, and S. Yue, “Dynamic transformation of Ti–6Al–4V during torsion in the two-phase region,” J. Mater. Sci., vol. 53, no. 12, pp. 9305–9315, Jun. 2018.

[3] B. Guo, S. L. Semiatin, J. Liang, B. Sun, and J. J. Jonas, “Opposing and Driving Forces Associated with the Dynamic Transformation of Ti-6Al-4V,” Metall. Mater. Trans. A Phys. Metall. Mater. Sci., vol. 49, no. 5, pp. 1–5, 2018.

Dr. Christopher Daniel
The University of Manchester
Additional Authors:
  • Dr. Peter Honniball
    Rolls-Royce plc.
  • Michael Atkinson
    The University of Manchester
  • Dr. Chi-Toan Nguyen
    The University of Manchester
  • Dr. Joao Quinta da Fonseca
    The University of Manchester