Fig. 1. Initial microstructure of DS Ni-Co-based superalloys used in this study: (a) optical image showing the columnar grains; (b) SEM-SE image showing the γ′ phase characteristics.

Fig. 2. (a) Geometry and preparation process of hot compression samples used in this study; (b) hot compression test process along with photographs of the specimens before and after compression.

Fig. 3. (a) DTA curves of Ni-Co based superalloys used in this study, (b) temperature increment under various deformation directions at 1120 °C/1 s-1.

Fig. 4. True stress-strain curves and morphologies of the samples deformed up to a 0.693 true strain at 1120 °C/1 s -1.

Fig. 5. (a) Statistical results of GOS distributions for acquiring the threshold value; (b-d) IPF color-coded maps and (e-g) GOS color-coded maps of the samples under various deformation directions: (b,e) 0°, (c,f) 45°, (d, g) 90° (For interpretation of the references to color in this figure, the reader is referred to the web version of this article.).

Fig. 6. Misorientation angle along the lines marked in Fig. 5: (a) A1, (b) A2, (c) B1, (d) B2, (e) C1, (f) C2.

Fig. 7. TEM micrographs and diffraction pattern of the samples under various deformation directions: (a,b) 0°, (c) 45°, (d) 90°.

Fig. 8. Compression direction along the columnar grain: (a) TEM images of dense dislocations in the γ matrix; (b) microstructures of dense MTs and the corresponding diffraction pattern; (c) MTs with different extended directions; (d) MTs formed close to the edge of the LAGB.

Fig. 9. HRTEM images of (a) a dislocation reaction in the γ matrix; (b) the front end of the deformation twin; (c) detailed view containing the ITB and two twins, T1 and T2, on both sides.

Fig. 10. An HRTEM image of a typical SF in the γ matrix.

Fig. 11. Specimens with different deformation directions: (a) 45°, (b) 90°; (c,d) corresponding longitudinal sections along the slip traces of the 45° and 90° deformed specimens; (e) schematic of the deformation direction.