Fig. 1. (a) XRD pattern, (b) EBSD phase mapping and (c) EBSD grain mapping of the as-cast CrFeCoNiAl0.7 HEA.

Fig. 2. (a) SEM micrograph, (b) TEM-BF micrograph, SAD patterns of (c) FCC phase and (d) B2 phase of the as-cast CrFeCoNiAl0.7 HEA.

Fig. 3. TEM-EDS results of the FCC and BCC phase in the as-cast CrFeCoNiAl0.7 HEA.

Fig. 4. (a) Tensile engineering stress-strain curve and (b) tensile true stress-strain and work-hardening rate vs. strain curves of the as-cast CrFeCoNiAl0.7 HEA.

Fig. 5. (a) and (b) HR-TEM images of FCC/BCC phase interfaces (the dotted line in (b) indicates the phase interface), (b1) and (b2) interplanar spacings of (111)FCC and (440)BCC, (c) and (d) the inverse fast-Fourier-transformed images of the HR-TEM image of area marked by a blue box in (b) (symbol “⊥” means a dislocation).

Fig. 6. TEM-BF microstructures of the cast CrFeCoNiAl0.7 HEA after tension to failure with the FCC matrix of relatively (a) low and (b) high dislocation densities. The red arrows indicate dislocations slips impeded by FCC/B2 phase interfaces.

Fig. 7. Tensile fracture surface of the cast CrFeCoNiAl0.7 HEA (a) low- and (b) high-magnification SEM images. The inset in (a) shows the river patterns.

Fig. 8. Representative TEM-BF micrographs from the gauge sections of interrupted tensile test specimens of the cast CrFeCoNiAl0.7 HEA after different tensile strains: (a) and (b) a small strain of ～2 %, (c) and (d) dislocation tangle in the microstructure after an intermediate tensile strain of ～7 %.

Fig. 9. TEM-BF micrographs of the cast CrFeCoNiAl0.7 HEA tensioned to failure: (a) dislocation morphologies in FCC and B2 phases, (b)-(d) different morphologies of dislocation walls.

Fig. 10. (a) TEM-BF micrograph and (b) HR-TEM image of the stacking fault in the FCC phase. (b1)-(b4) filtered images of the stacking faults.

Fig. 11. Schematic diagram illustrating the deformation twin formation through overlapping of stacking faults in FCC phase, (a) projection of a perfect FCC lattice along <111> plane showing a stacking sequence of ABCABC, (b) stacking fault generated by a dissociation reaction of a perfect dislocation showing a stacking sequence of ABCBCABC, (c) a deformed twin formed by dynamic overlapping of four stacking faults by repeating the process in (b) showing a stacking sequence of ABCBABABC.