Fig. 1. (a) Schematic of FSP, geometry of extracted tensile and tool, as well as external shape of FSPed GH4068 alloy; PD, ND, and TD correspond to processing, normal, and transversal directions, respectively. Macrostructure of the transversal cross-section of FSPed GH4068 alloy: (b) 400-50, SZ and BM are stir zone and base material, respectively; (c) 600-50, the red dotted rectangle is tensile specimen gauge location.

Fig. 2. (a)-(c) EBSD images showing grain structures of BM, 400-50, and 600-50, respectively; (b) inset is an enlarged image of the part marked with the rectangle; (b), (c) black rings are the characteristic bulging grain boundaries; (d)-(f) corresponding size statistical distributions of grains in (a), (b), and (c), respectively.

Fig. 3. EBSD images showing the corresponding distribution of grain boundary misorientation angle and arrangement of the sigma three (Σ3) twin boundaries: (a) and (d) BM, (b) and (e) 400-50, (c) and (f) 600-50.

Fig. 4. TEM micrographs of twin structure in the 400-50: (a) submicron twin lamellas (annealing twins), (b) nanoscale twin lamellas, (c) HR TEM micrograph showing microstructures in (b).

Fig. 5. TEM micrographs and corresponding size distributions of γ′ precipitates: (a) and (d) BM, (b) and (e) 400-50, (c) and (f) 600-50.

Fig. 6. Engineering stress-strain curves of BM, FSP samples 400-50 and 600-50, and wrought GH4068 alloy: (a) RT, (b) 400 °C.

Fig. 7. STEM micrograph of microstructure in the 600-50. A is the dislocation-free grain, B is the grain with a high dislocation density.

Fig. 8. The schematic of DDRX: (b), (c), and (d) is the enlarged image of the part marked by the yellow dotted rectangle in (a).

Fig. 9. Configuration of dislocations and precipitates during weak-pair coupling cutting and strong-pair coupling cutting, and relative critical shear stress because of each mechanism vs precipitate size. Adapted from Huther and Reppich [52].

Fig. 10. STEM micrographs of deformation microstructures of BM after tensile fracture at room temperature: (a) slip bands cut through γ′ precipitates and the matrix, (b) microstructures of APB in γ′ precipitates at higher magnification.

Fig. 11. SEM microstructure of the wrought GH4068 alloy. Inset is the enlarged image of the part marked with the rectangle.

Fig. 12. Relationship between elongation and UTS for superalloys prepared by FSW, FSP, and wrought methods. 1 are the BM conditions, 2 are processed conditions. FSW In 600, 625, and 718 are the properties in the weld nugget(previous studies) [29], [30], [31].

Fig. 13. TEM micrographs of deformation microstructures in the 600-50 after tensile fracture at 400 °C: (a) substructures of dislocations and microtwins at low magnification, (b) deformation substructures of twinning at higher magnification.