Fig. 1. (a) The XRD pattern of the CoCrFeNiTa0.395 E-HEA containing a Laves phase and a FCC phase. (b) A secondary-electron SEM image and (c) a low magnification HAADF-STEM image of CoCrFeNiTa0.395 E-HEA. The dark region is the FCC phase and the light platelets are the Laves phase. (d) High-resolution HAADF-STEM image of the inter-phase and the FFT (inset) of FCC phase along the [011] zone axis. (e) High-resolution HAADF-STEM image and corresponding FFT (inset) of the Laves phase along the [0001] zone axis. Superlattice diffraction spots are indicated by red circles in the FFT image. (f) The low magnification HAADF-STEM image of the dual phase lamellar eutectic structure and the corresponding EDX maps.

Fig. 2. (a) Representative true stress-strain curves obtained from the compression tests for E-HEA micropillars with similar diameters (～3 μm), but varying orientations, i.e., the lamellae oriented approximately 0°, 45°, and 90° angles relative to the loading direction. SEM morphologies of pre- and post-compression micropillars with similar diameters (～3 μm), but different orientation angles between the lamellae and the loading direction: (b, c) 0°, (d, e) 45°, and (f, g) 90°.

Fig. 3. (a) Representative true stress-strain curves for the 0° pillars with diameters ranging from 3.08 μm to 1.01 μm. Note that the curves are shifted along the abscissa for improved clarity. (b) Variations of the yield stress and strain hardening rate at a plastic strain of 2% as a function of the pillar diameter. Typical SEM images of compressed 0° micropillars with different diameters: (c) 3.08 μm, (d) 2.81 μm, (e) 1.68 μm, and (f) 1.01 μm, showing the deformation mode transforming from kinking/buckling to through-sample shear banding as the pillar diameter decreases.

Fig. 4. HAADF STEM images of the post-compressed 0° pillar with a diameter of 3.08 μm showing (a) the local kinking deformation of the Laves lamellae, accommodated by multiple small slip bands within the Laves lamellae. (b) Slip bands are confined inside the Laves lamellae. (c) Slip bands cut through the Laves/FCC interface. (d) A bright field TEM image of the post-compressed 0° pillar with a diameter of 2.81 μm showing the buckling of the Laves phase via profuse slip bands and dislocation accumulation in the FCC phase.

Fig. 5. (a) Representative true stress-strain curves for 45° pillars with diameters ranging from 3.02 μm to 0.42 μm. Note that the curves are shifted along the abscissa for improved clarity. Large strain bursts in the smallest pillar are indicated by black arrows. (b) Variations of the yield stress and strain hardening rate at a plastic strain of 2% as a function of the pillar diameter. Note the strain hardening rates for the sub-micron diameter pillars are not provided because they show negative values. Typical SEM images of compressed 45° micropillars with different diameters: (c) 3.02 μm, (d) 1.61 μm, (e) 1.02 μm, and (f) 0.42 μm, showing that the deformation mode reflected by the level of the FCC extrusion changes as the pillar diameter decreases.

Fig. 6. (a) TEM images of the post-compressed 45° pillar with a diameter of 3.02 μm. (b) Dislocations bands marked by arrows inside the FCC lamellae. (c) A TEM image of the post-compressed 45° pillar with a diameter of 0.42 μm.

Fig. 7. Schematic illustration of deformation modes in the E-HEA pillars with different diameters. (a-c) The deformation mode of 0° pillars transforms from pillar kinking or buckling to large shear banding as the diameter decreases. (d-f) The deformation mode of 45° pillars transforms from shear deformation along the interface to within the FCC lamellae as the diameter decreases.

Fig. 8. (a) SEM images of undeformed (left) and compressed (middle) micropillar with a diameter of 3 μm milled from the monolithic FCC phase sample, and its corresponding uniaxial compressive true stress-strain curve (right). (b) SEM images of undeformed (left) and compressed (middle) micropillar with a diameter of 3.1 μm milled from the monolithic laves phase sample, and its corresponding uniaxial compressive true stress-strain curve (right).