Fig. 1. Macro/microstructure of the DS high Nb containing TiAl alloys: (a) macrostructure image of the longitudinal section of Ti46Al7Nb alloy; (b) macrostructure image of the longitudinal section of Ti46Al7Nb0.4W0.6Cr0.1B alloy; (c) metallographic microstructure image of the DS stable growth zone of the microalloyed high Nb containing TiAl alloy; (d) SEM image of the cross-section of the DS columnar crystal region in (b).

Fig. 2. Creep curves (a) and creep rate and strain curves (b) of the DS Ti46Al7Nb and Ti46Al7Nb0.4W0.6Cr0.1B alloys at the condition of 760 °C and 275 MPa.

Fig. 3. TEM images of microalloyed DS high Nb containing TiAl alloy after creep tests: (a) dislocation entanglement and γ recrystallization, (b) dislocation entanglement induces subgrain boundary formation, (c) intersection between high-density dislocations and twins, (d) twin intersections.

Fig. 4. Typical mechanical twin structure of DS TiAl alloy lamellar structure after creep deformation: (a) bright field image of deformation microstructure, (b) selected area electron diffraction (SAED) pattern of the white cycle in (a), (c) high resolution TEM (HRTEM) of twin, (d-g) fast fourier transform (FFT) diagrams of the white boxes in (c), respectively.

Fig. 5. Schematic diagram of superlattice intrinsic stacking fault (SISF) and twin formation in γ phase: (a) ABCABC stacking sequence; (b) ABCAC'ABC stacking sequence; (c) twin formation on (-110) plane.

Fig. 6. Twin intersections in lamellar structure of DS TiAl alloy after creep deformation: (a) twin intersection in the γ lamellae, (b) the magnified figure of the yellow box in (a), (c) twin intersection across γ lamellae, (d) the magnified figure of the red box in (c), (e) SAED pattern of twin intersection in (d), (f) calibration of SAED in (e).

Fig. 7. HRTEM images of twin intersection in DS TiAl alloy after creep deformation: (a) twin intersection and stacking faults, (b-e) FFT images of area b, c and d in (a), respectively, (e) center position of the intersection of (a).

Fig. 8. Schematic diagram of twin intersection with stacking faults.