Fig. 1. Phase identifications and sampling locations of pillars: (a) EBSD phase map, the colorful and white microregions corresponded to BCC and FCC phases, respectively, the selected FCC, BCC and FCC/BCC interphase were circled with different colors; (b) BSE image of the interface between FCC and BCC phases, the inset images at the bottom left and bottom right corresponded to the initial and ultimate thinned morphologies of a typical interphase pillar before and after fine milling procedures, respectively. The interphase and elliptical precipitations were highlighted by red dotted line and yellow circle, respectively.

Fig. 2. Characterization of performance and microstructure of the bulk HEA: (a) XRD pattern and (b) engineering stress-strain curve and corresponding (c) fracture morphology of a Fe24Co25Ni24Cr23Al4 HEA; (d) and (e) the EBSD inverse pole figure and phase mapping; (f) TEM morphology showing clubbed BCC precipitations embedded in FCC matrix, the SAED patterns showing the existence of FCC and BCC phases; (g) EDS elemental distribution analysis showing a Al-Ni rich BCC phase and Fe-Co-Cr rich FCC phase.

Fig. 3. The elemental distributions of FCC/BCC interphase region.

Fig. 4. Engineering stress-strain curves of FCC, BCC and interphase pillars in uniaxial compressive tests inside SEM, Δx and Δy denoted the amplitudes of strain burst and stress drop, respectively.

Fig. 5. SEM morphologies of post-deformed pillars: (a-c) the first and (d-f) second rows represented the morphologies of pillars with diameters of 800 nm and 1300 nm, respectively, and the first, second and third columns corresponded to the FCC, BCC and interphase pillars, respectively.

Fig. 6. Engineering stress at strains of 5 and 8% strain in terms of FCC, BCC and FCC/BCC interphase pillars with different diameters.

Fig. 7. TEM characterization to explain the stress fluctuation behavior and highly localized plasticity deformation at the interphase: (a) TEM image of the post-deformed BCC pillar with diameter of 1300 nm; (b) an enlarged view of rectangle in (a), the inset showed the SAED patterns of BCC1 and BCC2 phases; (c) high-resolution TEM image located at the BCC1/BCC2 interphase, corresponding to the white rectangle in (b); (d) inverse fast fourier transform (IFFT) image of yellow rectangle in (c) to indicate the drastic dislocations; (e) high-resolution TEM images showed the stacking fault located in the yellow rectangle in (b).