Fig. 1. Microstructures of the binary Ti48Al intermetallic alloys, BSE SEM micrographs: (a) as-extruded (longitudinal); (b) as-extruded (transverse); (c) as-heat treated (longitudinal); (d) as-heat treated (transverse).

Fig. 2. Plan view fractography, SE SEM after fracture at a) room temperature (RT), (b) RT and prior 800°C soak followed by water quenching (WQ), (c) RT and prior 800°C soak followed by air-cooling (AC), (d) 800°C, and detail from the equiaxed region (e) RT, (f) 800°C, and the lamellar region, (g) RT and (h) 800°C, respectively.

Fig. 3. Side view SE SEM fractography of fracture specimens;(a) RT (low magnification), (b) 800°C (low magnification), (c) detail RT, lamellar colony, (d) detail RT, equiaxed region, (e) detail 800°C, lamellar colony and (f) detail 800°C, equiaxed region. The direction of the tensile axis is vertical in all the micrographs as indicated by the arrow next to (a) and (b).

Fig. 4. Low magnification overview TEM micrograph, multiple g, BD ≈[01], depicting the various constituents of the partially lamellar microstructure after fracture at RT.

Fig. 5. Equiaxed region after room temperature deformation: γ-grains in: (a) g=002, BD≈[010] (only SD) and (b) g=202, BD≈[010] (both SD and OD), and α₂-grains in (c) g=0002 and (d)g=220 ,both for BD≈[100].

Fig. 6. TEM micrographs typical of the lamellar regions after RT fracture: (a) BD≈[01], g_γ=111 parallel to g_α2=0002, and detail from a γ-lamella (b) g=200, and (c) g=220, and detail from an α₂-lamella (d) g=0002, BD≈[110], and (e) g=220, BD≈[010].).

Fig. 7. Defect substructure in α₂-lamellae after room temperature fracture: (a) 220, BD≈ off [010] to [0001], (b) 201, BD≈ off [110] to [012], (c) 0002, BD≈[140], and (d) 20, BD≈ off [012] to [110]. The labels A and B relate to two different types of <a>-dislocations, and X and Y are fudicial markers.).

Fig. 8. Low magnification overview multiple beam bright field TEM micrographs of the Ti-48Al specimen after fracture at 800°C exhibiting high defect desities in (a) the equiaxed region and (b) in the lamellar region with bent γ- and α₂-lamellae.

Fig. 9. TEM weak beam micrographs of the defect substructure typical of the α₂-lamellae after fracture at 800°C, (a) g=0002, and (b) g=201, both with BD≈[112].

Fig. 10. Dense defect populations in an α₂-lamellae of the 800°C fractured sample. The images have been recorded with (a) g=0002, BD≈[110],(b) g=0002, BD≈[010], (c) g=[110], BD≈[011], (d) g=202, BD≈[110]; (e) g=200, BD≈[110].

Fig. 11. Defect substructure typical of the α₂-lamellae after 2.5% tensile straining at 800°C, (a) g=0002, (b) g=201, both for an approximate BD≈[110], and, (c) weak beam, g=200, BD≈[111]. Note the presence of the <c>-component dislocations labeled A, B and tangles of <a>-dislocations.).

Table 1. Mechanical data from tensile tests to fracture