Fig. 1. Representative EBSD micrographs. (a) Area where the micropillars were fabricated. The black unindexed lines are scratch marks utilized to locate the area of interest in FIB and the dashed rectangle marks the area characterized in Fig. 1(c). Inverse pole figure (IPF) maps of (b) SC and (c) BC and TC micropillars, with the higher magnification images of the (d) BC and (e) TC pillars.

Fig. 2. Representative SEM images of the as-fabricated (a) [111]-oriented SC, (b) BC, and (c) TC pillars, respectively.

Fig. 3. Representative microstructures of the CoCrFeNi HEA showing (a) an EBSD IPF map, (b) the boundary distribution (where red and green lines represent the high-angle grain boundaries and the twin boundaries, respectively), and (c) a higher magnification BSE image of the microstructure. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article).

Fig. 4. Representative true stress-true strain responses obtained from the uniaxial (a) compression and (b) tension tests on the PC specimens. (c) Double logarithmic plots of the yield strength versus strain rate for both compression and tension tests. The lines mark the linear fits of the double logarithmic plots. (For interpretation of the references to color in this figure, the reader is referred to the web version of this article).

Fig. 5. Morphologies of the compressed SC pillars, characterized by SEM and schematics of the slip systems with the maximum Schmid factors, SFmax. (a) [111], (b) [114], and (c) [101] oriented pillars deformed at $\dot{\varepsilon }$ = 10-3 s-1.

Fig. 6. Representative engineering stress-strain responses of (a) [111], (b) [114], and (c) [101] SC micropillars subjected to uniaxial compression at 10-2 and 10-3 s-1 strain rates.

Fig. 7. Morphologies of the compressed (at $\dot{\varepsilon }$ = 10-3 s-1) (a) BC and (b) TC micropillars, with (c) the corresponding list of the activated slip systems in both the pillars.

Fig. 8. Representative engineering stress-strain responses of (a) BC and (b) TC micropillars subjected to uniaxial compression at 10-2 and 10-3 s-1 strain rates.

Fig. 9. Double logarithmic plots of yield strength versus logarithmic strain rate for different micropillars tested in this work: [111], [114], [101] SC pillars and [111] / [114] BC and TC pillars.

Fig. 10. Variation of the average stress drop magnitude with the average work hardening rate at the strain rates of 10-2 and 10-3 s-1 for different micropillars tested in this work: [111], [114], [101] SC pillars and [111]/[114] BC and TC pillars.

Fig. 11. Schematic illustrations of the effects of high-angle grain boundary (HAGB) and twin boundary (TB) on the dislocation motion.

Fig. 12. Schematic illustrations of the dislocation density evolution at 10-3 and 10-2 s-1 strain rates in the [111], [114], and [101] SC pillars. Red dots represent the dislocation pinning points and red arrows point out the single-arm dislocation source. (For interpretation of the references to color in this figure, the reader is referred to the web version of this article).

Fig. 13. Variations of the strain-rate sensitivity (m) and grain size (d). Literature data for pure ?Ni [[10], [11], [12], [13],17,63], along with ??CoCrFeNi [8,15,17,67], ???CoCrFeMnNi [15,17,19,22,70], and ????Al0.3CoCrFeNi HEAs [18,68,69].