Fig. 1. Standard γ/γ′ microstructure and elemental partitioning behavior of Ni-SXs. Adapted from Ref. [16]. (a) HAADF-STEM microscopy of a Ni-SX. Cuboidal γ′ particles (dark) are separated by thin γ channels (bright); (b) Series of EDX maps showing alloying elements Ni, Al, Ta and Ti partition to the γ′ phase and Co, Cr, Re and W partition to the γ matrix, respectively.

Fig. 2. Effects of lattice misfit on shape of γ′ phase. Adapted from Ref. [65].

Fig. 3. Schematic illustrations of dislocation movements in the γ channels. Adapted from Ref. [72]. (a) Stress components associated with misfit; (b) Effect of an external tensile stress on two dislocation dipoles; (c) Misfit dislocations. (d) Interface dislocations after creep.

Fig. 4. Schematic illustrations of the formation of stacking faults referring to the dislocation glide in γ matrix. Adapted from Ref. [96]. Dislocation decomposition under (1 11) < $\bar{1}$11 > alias shear deformation: a/2[1$\bar{1}$0]→a/6[2$\bar{1}$1]+a/6[$\bar{1}$2 $\bar{1}$] (12→13 + 32).

Fig. 5. Illustrations of dislocation motion in γ′ phase with forming APBs. (a) Dislocations in γ matrix travel in pairs across the γ′ phase; (b) Schematic illustration of the movements of dislocation pairs in the γ′ phase. Figures reproduced from: (a) in Ref. [100] and (b) in Ref. [102].

Fig. 6. Creep curves of Ni-SXs under different temperatures and stresses. (a) Curve of high temperature and low stress creep; (b) Curves of mid temperature and mid stresses creep; (c) Curves of low temperature and high stresses creep. Figures reproduced from: (a) in Ref. [131] and (b, c) in Ref. [133].

Fig. 7. Formation of interfacial grooves during creep of a Ni-SX under 140 MPa at 1120 °C. Adapted from Ref. [73]. (a) HAADF-STEM image of the superalloy after creep for 2 h observed along [010] axis showing many ledges formed at the interfaces; (b) Dislocations at the tip of each groove are indicated by an arrows.

Fig. 8. EDX analysis of dislocation core at the tip of interfacial groove. Adapted from Ref. [73]. (a) EDX mapping of the groove tip showing the elemental inhomogeneity in region near to the groove tip. The arrow denotes the direction of line scan mode as shown in (b); (b) EDS data of line scan across the groove tip; (c) Nearly atomic EDX analysis of the dislocation core at the groove tip showing the enrichment of Re and Co.

Fig. 9. Schematic figure of the stress distribution in the γ/γ′ microstructure. Adapted from ref. [149]. (a) Internal misfit stress generates the stretched stress and compressive stress in the γ′ and γ phases, respectively; (b) Tensile stress gives rise to the release of internal misfit stress in perpendicular γ channels but increases the stress state in paralleled channels.

Fig. 10. Effects of Ti and Ta on APB energy of Ni-SXs. Adapted from ref. [84]. The effects of Ti/Al ratios (a) and Ta/Al ratios (b) on APB energy in Ni-Al-X systems.

Fig. 11. Diffusion coefficients of some strengthening elements in Ni. Adapted from Ref. [161].

Fig. 12. High temperature capabilities of some typical Ni-SXs. Adapted from Ref. [84].

Fig. 13. Effects of Ru addition on TCP precipitation and elemental segregation of refractory elements. (a) SEM micrographs of alloys after isothermal annealing at 950 °C for 1000 h; (b) An APT elemental map of a plate-like TCP precipitate surrounded by a γ′ envelope in the annealed Astra1-21 alloy. Accumulation of Cr, Mo, W and Re in TCP phase is visible. Figures reproduced from: (a) in Ref. [179] and (b) in Ref. [180].

Fig. 14. Effects of Ru addition on creep properties of a Ni-SX. Adapted from ref. [194]. (a, b) Creep curves for the three alloys at 1150 °C /100 MPa; (c-e) Morphology of the interfacial dislocation networks in the alloy; (c) 0Ru, (d) 2Ru and (e) 4Ru after thermal exposure at 1150 °C for 500 h.

Fig. 15. Diagrams of Re distribution in γ phase showing the fluctuation of contribution and ladder behavior. (a) Frequency distribution of the Re concentration represents the binomial distribution expected for a statistically random distribution of Re atoms; (b) Re ions versus total number of detected ions. Figures reproduced from: (a) in Ref. [200] and (b) in Ref. [199].

Fig. 16. Simulation works of Re-Re bonds against the hypothesis of Re clusters. (a) χ(R) spectra obtained from Re L-edge of a Ni-Re sample compared to fits obtained from a Re atom with 12 Re neighbors and a Re atom with 12 Ni neighbors. Arrows show the fitting range; (b) Binding energies between Re-Re, W-W and Ta-Ta pairs in FCC Ni supercell as a function of X-X separation. Figures reproduced from: (a) in Ref. [202] and (b) in Ref. [204].

Fig. 17. Co-segregation of Re and other elements at the γ/γ′ interface. (a) Re concentration as a function of distance with respect to the γ/γ′ interface exhibiting enrichment of Re in the γ matrix near to the γ/γ′ interface; (b-d) Pileup of alloying elements Ni (b) and Ta (c) near to the γ/γ′ interface ahead of the enrichment of Re solutes. Figures reproduced from: (a) in Ref. [207] and (b-d) in Ref. [208].

Fig. 18. V-shape protrusion at the γ/γ′ interface forming by edge dislocations in a crept Ni-SX. Adapted from ref. [33]. (a) HAADF-STEM images of dislocation structures at tip of a V-shaped protrusion; (b) Elemental distribution maps in region near V-shaped protrusion.

Fig. 19. Dislocation configurations within the rafted γ′ phase in 2% Re alloy crept for 155 h up to fracture at 980 °C/300 MPa. Adapted from ref. [209]. (a) g = 022, B= [100], (b) g = 002, B= [100], (c) g = 020, B= [100] and (d) g= $\bar{1}$1$\bar{3}$, B=[30 $\bar{1}$]. It is a reasonable consideration that the dislocations D and E on (100) planes are KW dislocation locks which originate from the cross-slipping of the dislocations from (111) plane to (100) plane.

Fig. 20. Effects of Mo additions on dislocation networks and TCP precipitation. (a, b) TEM pictures showing the dislocation networks at γ/γ′ interfaces of alloy I (a) and alloy II (b); (c, d) SEM images of the TCPs in alloys after exposing at 1100 C for 200 h. The Mo contents in (c) and (d) are 1.5 wt% and 2.5 wt%, respectively. Figures reproduced from: (a, b) in Ref. [68] and (c, d) in Ref. [69].

Fig. 21. Interactions between Ta and W distracted W atoms from γ′ precipitates into γ matrix. Adapted from ref. [219]. (a) Projected 3D-APT reconstructions acquired from: (1) Ni-Al-Cr-W quaternary alloy; (2) Ni-Al-Cr-W-Ta quinary alloy (1 at.% Ta), both aged at 1073 K for 264 h; and (3) multicomponent ME-9 alloy (1.95 at.% Ta); (b) Proximity histograms of the W concentrations across the γ/γ′ interfaces of the three types of alloy in (a); (c) The substitutional formation energies of W and Ta atoms as a function of their distances from the γ/γ′ interface; (d) The binding energies of W-Ta dimers in the γ′ phase and for W-W dimers in the γ phase as a function of interatomic distance (nm).