Fig. 1 Microstructures of FC specimens: a OM image; b primary γ′ and secondary γ′ in dual-phase zone observed by SEM; c primary γ′ and secondary γ′ observed by TEM, the inserted images show magnitude image of primary γ′ and secondary γ′ of red outline region and the SAED image of primary γ′ along [11-2] zone axis; d split primary γ′ and dislocations around split primary γ′ (TEM); e HRTEM image of the red outline region in d along [-110] zone axis; the inserted image shows the FFT image of red outline region; f IFFT image (extra atomic planes marked by yellow dashed frame) of the red outline region in e

Fig. 2 Microstructures of AC specimens: a OM image; b primary γ′ in dual-phase zone observed by SEM; c primary γ′ observed by TEM; d γ channel of red outline region in c

Fig. 3 Microstructures of WC specimens: a OM image; b primary γ′ in dual-phase zone observed by SEM; c primary γ′ observed by TEM; d magnitude image of γ channel between primary γ′ in c; e vacancies observed by HRTEM

Fig. 4 Primary γ′ number and particle length (within an area of 5 μm×5 μm) under different cooling conditions

Fig. 5 a Shape parameter ratio of a spherical primary γ′ in WC; b shape parameter ratio of a concave cuboidal primary γ′ in FC; c shape parameter ratio η1 increase with the shape transformation; d shape parameter ratio η2 increases with the shape transformation

Fig. 6 XRD results of WC, AC and FC specimens: a identification of γ′ and γ; γ/γ′ (200) deconvolution diffraction peak of WC b, AC c and FC d using Pseudo-VoigtA as fitting function

Fig. 7 a Primary γ′ observed by TEM under AC condition; b area between γ′ edge and γ of HRTEM image; c area between γ′ corner and γ of HRTEM image; d area between primary γ′ and γ in corner area in AC, the inserted images show the FFT image γ′ and γ; e area between primary γ′ and γ in edge area in AC; the inserted images show the FFT image γ′ and γ

Fig. 8 a EDS along the diagonal path of primary γ′ and adjacent γ matrix in FC; the inserted image is the concentration of Ni, Al, Cr, and Fe along AB; b concentration of Ni, Al, Cr, and Fe (EDS line profile) corresponding to diagonal path in a

Fig. 9 a, c, e Temperature as a function of time (t) and concentration (C); b, d, f temperature as a function of nucleation rate (NR)

Fig. 10 Schematic diagrams of lattice parameter evolution of primary γ′ and γ under three different cooling conditions: a, c, f lattice parameter of γ under solid solution state; b lattice parameter of primary γ′ and γ during growth under WC condition; d, e lattice parameter of primary γ′ and γ during growth under AC condition; g-i lattice parameter of primary γ′ and γ during growth under FC condition; j lattice parameter of primary γ′; k unconstrained lattice parameter of primary γ′

Fig. 11 a Arrangement of extra atomic planes from Fig. 1f and schematic diagrams of dislocation reaction; (111) and (-1-11) planes are depicted by red and dark blue dash line, and zone axis is [-110]; b three-dimensional lattice structure of γ matrix; solid balls and the hollow balls represent different layers of atoms parallel to the (1-10) plane

Fig. 12 Schematic diagrams of primary γ′ evolution under different cooling rates of a 1270 °C×9 h+WC; b 1270 °C×9 h+AC; c 1270 °C×9 h+FC