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Narrow dislocation dipoles in deformed intermetallic gamma-TiAl

Tuesday (27.09.2016)
15:45 - 16:00
Part of:

Dislocation dipoles play important roles in the plastic deformation of materials. For instance, the formation of a stable dipole locks the two constituent dislocations and contributes to work hardening; dipole annihilation after dragging a jogged screw dislocation produces vacancy- or interstitial-type defects, which contribute to deformation localization; etc. In intermetallic gamma-TiAl, dislocation dipoles in the form of faulted dipoles are frequently encountered in deformed samples [1], but their fine structure and transformation into point defects remain largely undocumented. In the present work, narrow dipoles in gamma-TiAl with height lower than 6d (with d the {111} interplane spacing) are systematically investigated using atomistic simulations. The stability of narrow dipolar configurations are unraveled by interatomic potential and ab initio calculations, showing the stability of faulted dipoles over other forms. The results are compared with transmission electron microscopy observations [2]. Subsequent direct molecular dynamics simulations indicate that at elevated temperature, these dipoles transform into individual defects, e.g., vacancy clusters, stacking fault tetrahedra and interstitial loops, depending on dipole height and orientation. Employing saddle-point search methods, activation energies of the atomic processes therein are obtained and the lifetime of the deformation debris is estimated, showing the stability of certain narrow dipoles on the experimental timescale. Lastly, the influence of stable narrow dipoles on plastic deformation is discussed.

[1] F. Grégori, P. Veyssière. Properties of <011]{111} slip in Al-rich gamma-TiAl II. The formation of faulted dipoles. Philosophical Magazine A 80, 2933 (2000)

[2] F. Appel, D. Herrmann, F. D. Fischer, J. Svoboda, E. Kozeschnik. Role of vacancies in work hardening and fatigue of TiAl alloys. International Journal of Plasticity 42, 83 (2013)

Dr. Hao Wang
Chinese Academy of Sciences
Additional Authors:
  • Prof. Dongsheng Xu
    Institute of Metal Research
  • Prof. David Rodney
    Université Lyon 1
  • Prof. Rui Yang
    Institute of Metal Research