Shear deformation in TiAl: Atomic dynamic and static simulations
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Q. Wang Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China
H.Q. Ye Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, People’s Republic of China; and Electron Microscope Lab, Peking University, Beijing 100871, People’s Republic of China (Received 19 January 2007; accepted 8 March 2007)
The dynamic shear deformation process and the related stacking fault transitions in TiAl have been systematically investigated using both the molecular dynamics and ab initio methods. The details of the dislocation initiation and microstructural evolution are presented, and the concomitant potential energy variation and the radial distribution functions have been analyzed. The results show, interestingly, that some deformation-induced hexagonal close-packed (hcp) structures are metastable, and that a higher velocity field promotes more hcp segments. The phenomena are interpreted based on ab initio calculations of the detailed energy variation at the different fault transition stages, i.e., superlattice intrinsic stacking fault (SISF) → TWIN, SISF → hcp, and hcp → TWIN. The intrinsic factor that governs the deformation process is discussed. The results promote new understanding of the stress-induced interfaces and dislocation behaviors in experimental observations.
I. INTRODUCTION
Research on Ti–Al alloys has been conducted for many years because of their wide application as materials of major importance in the aerospace and automotive industries. Thus, they are highly attractive from the technological as well as the basic point of view. It is recognized that the two-phase (␥–TiAl + ␣2–Ti3Al) alloys possess improved ductility and toughness over the singlephase alloys.1–3 In the duplex phase materials, a basic understanding of the micromechanisms of phase transformation (␣2 ↔ ␥) and interface (␣2/␥, ␥/␥) behavior under deformation is necessary and significant. During the past decades, different deformation methods such as extruding, compression, ball milling, thermomechanical treatment, and torsion straining under high pressure, etc., were adopted to induce the phase transformation (␣2 ↔ ␥) at room temperature.4–10 Experimental observation showed the homogeneous generation of gliding dislocaa)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2007.0218 J. Mater. Res., Vol. 22, No. 6, Jun 2007
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tions along the [112¯] direction and extensive deformation twins.4,11 Ye et al.12 observed a stress-induced diffusionless phase transformation ␥ → ␣2 in the intermetallic compound Ti–50Al48Cr2, and Ti3Al was formed as a metastable phase. Nevertheless, the inherent mechanism of the Ti3Al formation and the corresponding vanishing behavior need to be explored further. As for the theoretical work, some calculations have been conducted to study the interfaces in view of the fault
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