Fig. 1. (a) Shape and geometry of flat dog-bone shaped micro-tensile specimens. (b) Four steps to prepare micro-tensile specimens. (c) Schematic view of the in-house built micro-tensile testing setup at KIT [27].

Fig. 2. Representative tensile engineering stress-strain curves of micro- and macro-samples of CoCrFeMnNi deformed at (a) RT and a strain rate of 3 × 10-4 s-1, (b) 550 °C and different strain rates (1 × 10-2, 3 × 10-4 and 8 × 10-5 s-1). The inset in (a) displays as-recrystallized and failed micro-samples, for comparison one-cent euro coin is also shown. The error bar in (a) and (b) refers to the variation of UTS and uniform elongation from multiple tests.

Fig. 3. Representative normalized working hardening rate versus (σt-σYS)/G curves of micro- and macro-samples at both RT and 550 °C for CoCrFeMnNi.

Fig. 4. SEM micrographs from the surface of a sample tested at RT: (a) an overview of the deformed surface. Marked are grains that show single-slip (white lines) and double-slip (black lines) traces. Respective higher magnification micrographs are shown in (b) single-slip and (c) double-slip bands/traces.

Fig. 5. Representative inverse pole figures (IPF) along the longitudinal direction (LD) of (a) an as-recrystallized/undeformed sample, deformed samples at (b) RT, and (c-e) 550 °C (under different strain rates) as well as their corresponding (f-j) KAM maps. The scale/color bar in (a, f) is valid for all corresponding maps. For deformed samples, all scans are obtained on uniformly deformed area of the gauge section.

Fig. 6. Kernel average misorientation (KAM) distributions of as-recrystallized/undeformed and deformed CoCrFeMnNi samples at RT and 550 °C (under different strain rates), obtained from scans in Fig. 5. As evident, a narrow KAM distribution for undeformed sample became wider and shifted towards higher values upon deformation. This evolution is more prominent at RT than at 550 °C.

Fig. 7. Typical bright-field TEM micrographs from the micro-samples tested at 550 °C and (a) 1 × 10-2 s-1 and (b) 8 × 10-5 s-1. Arrows in (a) mark smooth dislocations that seem to have under-gone steadily unrestricted motion. Triangles in (b) refer to the curved/unsmooth dislocations with pinned segments that appear to be pinned by solute clouds.

Fig. 8. HAADF-STEM micrographs along with its corresponding EDX maps from a sample tested at 550 °C and strain rate of 8 × 10-5 s-1 showing Cr-enriched secondary phases and MnNi-enrichment and Cr-depletion along marked grain boundary (GB).

Fig. 9. (a) IPF map (//LD) shows deformation twins (DTs) formation in the necking region of a sample tested at RT and strain rate 3 × 10-4 s-1. (b) A higher magnification scan from the marked area in (a) clearly reveals DTs. (c) The point-to-origin misorientation profiles along marked lines 1 and 2 confirm the presence of Σ3 twin boundaries (with ~60° misorientation). Black points indicate unindexed severely deformed regions.

Fig. 10. SEM micrographs presenting fracture surfaces of samples tested at RT and 550°C under different strain rates: (a-c) overviews, along with (d-f) enlarged views of the respective marked area in (a, b, c), present fine and coarse dimples. The pre-existing micro-particles are embedded inside coarse dimples. (g-i) Tested samples surfaces (which were ground and polished to remove surface oxides) also show micro-particles and deformation-induced cavities. The cavities were found at lower strain rates and 550 °C.