Fig. 1 Structure of the needle-like precipitates in the Ni-based SX superalloy: a low-magnification STEM-HAADF image of sample after 1100 °C-160 h heat treatment along [001]γ direction. Precipitates are indicated by black arrows; b a precipitate lying in the γ′ phase; c a precipitate lying across the γ/γ′ interface; d-f 2D slices cut from the diffraction volume of the precipitation reconstructed on the basis of 3D electron diffraction data. d Viewing along a*. e Viewing along b*. f Viewing along c*. Vector a* is in blue, vector b* is in green and vector c* is in red. Note that these are projections of a 3D diffraction volume and not conventional 2D in-zone diffraction patterns

Fig. 2 Different interfaces: a Hf2S precipitate in the γ phase; b Hf2S precipitate in the γ′ phase; c Hf2S/γ interface; d Hf2S/γ′ interface

Fig. 3 Atomic occupancy in the Hf2S precipitate: a atomic scale EDS mapping of a Hf2S precipitate; b mixed map of Hf and S. Orange and blue balls represent Hf and S atoms, respectively; c atomic model of Hf2S along [100]Hf2S direction; d high-resolution HAADF-STEM image of the precipitate along [100]Hf2S direction. Insets are the simulated HAADF-STEM image of Hf2S and the atomic model of Hf2S

Fig. 4 Interfacial segregations: a high-resolution HAADF-STEM images of Hf2S phases. Bright dots at the Hf2S/γ′ interface are indicated by yellow arrows; b HAADF image of a Hf2S precipitate with dark contrast line areas; c corresponding overlapped Ni, Cr and Hf maps of a; d-f atomic structure of the Hf2S/γ′ interface and corresponding elemental map of e Hf and f Ni. The bright dot at the Hf2S/γ′ is circled by orange dashed line

Fig. 5 Structural evolutions of the Hf2S/γ′ interface. a High-resolution HAADF-STEM images of a Hf2S precipitate. Bright dots are arranged regularly along the interface between Hf2S phase and the matrix, indicated by yellow arrows. b-d Different interface structures along (001)Hf2S plane. The left side of the picture is the Hf2S phase, while the right side is the γ′ phase. Yellow arrows indicate noticeable segregations of Hf atomic columns on the γ′ side of the Hf2S/γ′ interface and white arrows indicate Hf segregations at the transition region. e-h Atomic model for the interfacial evolutions between the Hf2S phase and the γ′ phase