Fig. 1. EBSD IPF maps of the CoCrFeMnNi HEA annealed at 1023 K (a), 1273 K (b) and 1473 K (c), respectively. TBs, which were shown with red lines, were seen frequently.

Fig. 2. (a) A typical SEM image shows slip bands passing through TBs as pointed by with arrows and (b) a typical TEM morphology presents planar slips bands as indicated by the black arrows, in the HEA fatigued under a total strain amplitude of 0.4%.

Fig. 3. Typical SEM images of (a) SB cracking and (b) TB cracking in the HEA with intermediate grains fatigued under a total strain amplitude of 0.4% (similar morphologies can be observed in the HEA with fine and coarse grains); (c) A typical IPF map showing the interaction between SBs and TBs (the white areas were not indexed due to the SB or TB cracking or severe extrusion/intrusion); (d) Determination of the slip planes in twin (top) and matrix (bottom) derived from (c) for the calculation of the DSF between matrix and twin.

Fig. 4. (a) Influence of DSF and grain size on the competition between SB cracking and TB cracking in the CoCrFeMnNi HEA; (b) Relationship between the spacing of SBs with extrusions/intrusions and grain size (The inset image demonstrates the measurement of SB spacing in the HEA); (c) Typical SEM images indicate that the SBs spacing increases with grain sizes.

Fig. 5. Schematic illustration of the effect of grain size on the SB-TB interactions and TB cracking.