Fig. 1. Atomic configurations of γ-TiAl unit cell (a) and rods with an edge dimple (b), a surface dimple (c), blunt (d) and sharp (e) scratches perpendicular to the [001], and a blunt scratch along [001] loading direction (f). Orientations are indicated in (a) and (b). Atoms in simulation boxes are colored according to their coordination number, with yellow, red, green, pink and purple atoms stand for atoms with coordination number of 12, 11, 10, 9 and 7, respectively.

Fig. 2. Stress-strain relations of the rod with a surface dimple of 120 vacancies under [001] tension at strain rates ranging from 107 s-1 to 1010 s-1 at 300 K.

Fig. 3. Stress-strain relations for γ-TiAl bulk (black), slab (red) and rod (blue) under [001] tension at 108 s-1 at 300 K.

Fig. 4. Atomic process of brittle fracture in perfect γ-TiAl under [001] tension. The simulation is performed under a constant strain rate of 108 s-1 at 1 K. Atoms are colored according to their coordination number.

Fig. 5. Configurations of γ-TiAl bulk (a), slab (b) and rod (c), and the micro-crack (a) and dislocation nucleation from surface (b) and edge (c) as results of [001] tension under 108 s-1 and 300 K. Orientations of perfect slab and rod are the same as that in bulk. Atoms are colored according to their coordination number, with gray atoms on surfaces, red atoms on edges and normal atoms in yellow or invisible.

Fig. 6. Nucleation of 4 partials on the () plane from an edge of a rod forming a superdislocation upon [001] tension at 108 s-1 and 1 K (a). Number 1 to 4 marks the 4 partials. Atomic shifts near the nucleation site due to the slip of each partial (b-f). The blue and green arrows show the Burgers vectors of the partials and superdislocation, respectively. The atoms on the three consecutive () planes are shown, with some atoms colored for easy tracing.

Fig. 7. Generalized stacking fault energy surface of γ-TiAl on the () plane. The red and yellow arrows show the atomic shifts of the four partials and the total Burgers vector.

Fig. 8. Dislocation nucleation in the rods with surface and edge defects of different types and sizes when stretched along [001] direction under 108 s-1 and 1 K. The a, b and c stand for dimple on edge, on surface and scratch on surface, respectively, while 1, 2 and 3 represent small, medium and large defects with diameter of 1, 2 and 4 nm, respectively. The red, green and blue axes are [100], [010] and [001], respectively.

Fig. 9. Dislocation nucleation from edge upon [001] tension at 108 s-1 and 300 K for the rod with a surface dimple containing only one vacancy (a). Defect evolution for a rod with surface dimples of 3 vacancies with different configurations when stretched along [001] at 109 s-1 and 300 K (b-e). The dimples are marked by black circles in (a) and (b). 1 to 4 in (b) stands for dimples of various vacancy configuration: 2 Al + 1 Ti (Dimple1), 1 Al + 2 (Dimple 2) in 2 adjacent (001) planes, 1 Al and 2 Ti (Dimple 3), and 2 Al and 1 Ti (Dimple 4) on 2 adjacent (010) planes.

Fig. 10. Stress-strain relation and deformation microstructure of the rod with a blunt scratch of 2 nm in diameter perpendicular to the loading direction under [001] tension at 109 s-1 and 1 K. The fractured surface is roughly (), with some surface steps.

Fig. 11. Dislocation nucleation process in the rod with a blunt scratch of 2 nm in diameter perpendicular to the loading direction under [001] tension at 108 s-1 and 1 K. The atoms are colored by their coordination numbers and the atoms with normal coordination number of 12 are made invisible. The two red atomic rows enclose the scratch.

Fig. 12. Core dissociation of superdislocation on the () plane for [001] tension under 108 s-1 and 1 K. The Burgers vectors for each partial are marked by black arrows, and the stacking faults between partials are marked by red acronyms.

Fig. 13. Generalized stacking fault energy surface for γ-TiAl on () plane. The red arrows indicate the shifts of atoms for each partial for superdislocation.

Fig. 14. Dislocation and crack nucleation for the rod with a sharp scratch under [001] tension at 108 s-1 and 300 K (a), and the fractured rod (b). The pink atoms in (a) mark the surface step formed on the back surface after dislocation passing by. A crack starts to form on the right hand side from the bottom of the sharp scratch into the sample.

Fig. 15. Local virial normal and shear stress distributions in the rod with a blunt (a, c) and sharp (b, d) scratch under tension along [001] to the critical point. The atomic color shows the stress level. The nucleation sites of superdislocations and micro-crack are marked by the red circles.

Fig. 16. Stress-strain relations for [001] tension of the rods with different volume of edge dimples (a), surface dimples (b) and blunt scratches perpendicular to the loading direction (c) at 108 s-1 and 1 K.

Fig. 17. Yield stress of rods with surface defects of various types and volumes under tension at 108 s-1 and 1 K. The horizontal axis represents the vacancy number in each defect.