Dislocation self-interaction in TiAl: Evolution of super-dislocation dipoles revealed by atomistic simulations

doi:10.1016/j.jmst.2020.03.091

Abstract

Abstract:

As one of the fundamental outcomes of dislocation self-interaction, dislocation dipoles have an important influence on the plastic deformation of materials, especially on fatigue and creep. In this work, super-dislocation dipoles in γ-TiAl and α₂-Ti₃Al were systematically investigated by atomistic simulations, with a variety of dipole heights, orientations and annealing temperatures. The results indicate that non-screw super-dipoles transform into locally stable dipolar or reconstructed cores at low temperature, while into isolated or interconnected point defect clusters and stacking fault tetrahedra at high temperature via short-range diffusion. Non-screw super-dipoles in γ-TiAl and α₂-Ti₃Al exhibit similar features as fcc and hcp metals, respectively. Generally, over long-term annealing where diffusion is significant, 60° super-dipoles in γ-TiAl are stable, whereas the stability of super-dipoles in α₂-Ti₃Al increases with dipole height and orientation angle. The influence on mechanical properties can be well evaluated by integrating these results into mesoscale or constitutive models.

Key words: TiAl, Dislocation, Dipole, Mechanical property, Atomistic simulation

Z. Zhen, H. Wang, C.Y. Teng, C.G. Bai, D.S. Xu, R. Yang. Dislocation self-interaction in TiAl: Evolution of super-dislocation dipoles revealed by atomistic simulations[J]. J. Mater. Sci. Technol., 2021, 69: 138-147.

Figures/Tables 12

Fig. 1. (a1 and b1) Correspondence of super-dipole orientation and atom row in γ-TiAl and α2-Ti3Al. (a2 and b2) Construction of super-dipoles by removing atoms of the selected thickness and merging the remaining two parts.

Fig. 2. $[11\bar{2}]$ projection of super-dislocation dipolar configurations with orientations 30°, 41°, 60°, 74°, and 90° and with heights of 1d to 6d after 50 ps annealing at 1 K in γ-TiAl. Atoms are colored by their coordination number (magenta: 9, green: 10, red: 11, yellow: 12, blue: 13 and white: 14).

Fig. 3. $[1\bar{1}00]$ projection of super-dislocation dipolar configurations with orientations 30°, 41°, 60°, 74°, and 90° and with heights of 1d to 6d after 50 ps annealing at 1 K in α2-Ti3Al. Atoms are colored by their coordination number (magenta: 9, green: 10, red: 11, yellow: 12, blue: 13 and white: 14).

Fig. 4. (a1 and b1) Formation energy for super-dipoles with height 1d to 6d and orientation 30° to 90° in γ-TiAl and α2-Ti3Al, respectively. (a2 and b2) Formation energy per vacancy of a1 and b1, respectively.

Fig. 5. [111] projection of super-dipoles after 1700 K annealing for 1 ns in γ-TiAl, with orientation from 90° to 30° and heights of 1d to 6d. Atoms are colored by their coordination number (magenta: 9, green: 10, red: 11, blue: 13 and white: 14). Atoms with coordination number 12 are not shown.

Fig. 6. [0001] projection of super-dipoles after 1700 K annealing for 1 ns in α2-Ti3Al, with orientation from 90° to 30° and heights of 1d to 6d. Atoms are colored by their coordination number (magenta: 9, green: 10, red: 11, blue: 13 and white: 14). Atoms with coordination number 12 are not shown.

Table 1 The formation energy per vacancy of super-dislocation dipoles with orientation from 30° to 90° and heights of 1d to 6d in γ-TiAl. And the formation energy of Ti and Al in single crystalline γ-TiAl.

	1d	2d	3d	4d	5d	6d	Ti	Al
30°	2.52	1.79	1.14	1.26	1.26	1.14	1.49	0.72
41°	2.45	1.65	1.28	1.06	0.94	1.00	1.49	0.72
60°	2.32	1.52	1.18	1.02	0.98	0.90	1.49	0.72
74°	2.55	1.60	1.26	0.83	1.00	0.92	1.49	0.72
90°	2.49	1.60	1.26	0.91	1.01	0.92	1.49	0.72

Table 2 The formation energy per vacancy of super-dislocation dipoles with orientation from 30° to 90° and heights of 1d to 6d in α2-Ti3Al. And the formation energy of Ti and Al in single crystalline α2-Ti3Al.

	1d	2d	3d	4d	5d	6d	Ti	Al
30°	2.35	1.90	1.62	1.54	1.21	1.21	1.47	1.36
41°	2.22	1.73	1.24	1.22	1.05	0.95	1.47	1.36
60°	2.15	1.61	0.97	1.08	0.92	0.85	1.47	1.36
74°	2.13	1.61	1.17	1.03	0.88	0.81	1.47	1.36
90°	2.12	1.58	1.16	1.02	0.88	0.81	1.47	1.36

Fig. 7. Point defect clustering in 30° to 90° and 1d-2d super-dipoles in γ-TiAl. Atoms are colored by their number of normal nearest neighbors (invisible: 12, red: 11, orange: 10, yellow: 9, yellow green: 8, green: 7, cyan: 6, light blue: 5 and blue: 4.).

Fig. 8. Point defect clustering in 30° to 90° and 1d-2d super-dipoles in α2-Ti3Al. Atoms are colored by their number of normal nearest neighbors (invisible: 12, red: 11, orange: 10, yellow: 9, yellow green: 8, green: 7, cyan: 6, light blue: 5 and blue: 4.).

Fig. 9. Energy path of the 30°-90° 1d-2d super-dipoles in γ-TiAl calculated with the ART method. The configurations at high temperature are shown in the (a)-(j) insets.

Fig. 10. Energy path of the 30°-90° 1d-2d super-dipole in α2-Ti3Al calculated with the ART method. The configurations at high temperature are shown in the (a)-(j) insets.

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