Fig. 1. Engineering stress-strain curves (a) of three alloys and uniform elongation versus yield strength of Co51Cr25Al8Fe8Ni8 alloy in comparison with previous FCC based TRIP HEAs (light blue area) and FCC alloys with precipitation strengthening (lime green area) (b). The grey stars in (a) denote the interrupted test for TEM and EBSD observation (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).

Fig. 2. EBSD and TEM results showing different microstructure in the annealed alloy: (a) EBSD phase-map displaying the distribution of FCC and NiAl phase, solid lines in the phase-map indicate the various boundary. (b) bright-field TEM (BFTEM) image of stacking faults. (c) BFTEM images of NiAl (grain 1 and 2) and FCC matrix, the insert SADP confirmed that there is a K-S relationship between grain 1 and matrix, and the corresponding interface (solid blue lines) is shown in (d). ∑3 twin (e, f) also exists in the annealed alloy (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).

Fig. 3. Qualitative STEM-EDS showing elemental distribution of NiAl phase and FCC matrix.

Fig. 4. Low angle annular dark field (LAADF) images showing the visibility of partial dislocations in the case of corresponding operation vectors: (a) both the partial dislocations are visible and the width marked as 6.59 nm, (b) Only the dislocation above is visible, (c) another dislocation is visible.

Fig. 5. EBSD images showing the distribution of phases (red: FCC, yellow: NiAl, aqua: HCP) and ∑3 twin boundaries (lime green) under different strains ((a-f) represents local strain of 0, 10%, 20%, 30%, 40% and > 50% respectively). TD is the transverse direction and RD is rolling direction (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).

Fig. 6. Length of ∑3 twin boundaries and ratio of HCP phase versus local strain.

Fig. 7. TEM and HAADF-STEM images showing the interaction of stacking faults with themselves (a, b), twin boundary (c, d) and NiAl phase (e) after ～10% deformation. The inserted SADP in (a) are shown to highlight the streaky lines due to edge-on SFs.

Fig. 8. HAADF-STEM images showing the nucleation position (a: stacking faults, b: ∑3 twin boundaries) of HCP phase after ～20% deformation (For interpretation of the references to color in this figure, the reader is referred to the web version of this article.).

Fig. 9. HCP phase interacts with NiAl phase after > 50% deformation (a) and the atomic arrangement of HCP phase (b).

Fig. 10. Corresponding schematic diagram of deformation mechanism.