Abstract: Eutectic high-entropy alloys (EHEAs), as a classification of high-entropy alloys (HEAs), have received worldwide interest due to superior fluidity and attractive properties. However, other than the FCC + B2 EHEA system, most other reported EHEA systems show inherent brittleness during tensile loading at room temperature, which limits their advanced engineering application. In this work, a novel spheroidization + recrystallization (SR) strategy for synergistic strengthening and plasticizing of the brittle CoCrFeNi₂(V₆B₃Si)_0.149 was proposed. The superior combination of strength and ductility was achieved by tailoring spherical M₃B₂ + recrystallized FCC duplex phases. Based on this strategy, the yield strength and elongation were improved from 565 ± 15 MPa and 2.3 % ± 0.3 % to 841 ± 24 - 1278 ± 20 MPa and 14.7 % ± 0.5 % - 22.5 % ± 1.2 %, with an increase of 48 %-126 % and 539 %-878 %, respectively. The synergistic increment in the strength and ductility of SR-FCC+M₃B₂ EHEAs exceeds all reported further strengthened FCC + B2 EHEAs. Meanwhile, such simple thermo-mechanical processing is suitable for large-scale industrial production. The high strength results from the back stress provided by the dual heterogeneity of FCC grain sizes and soft FCC/hard M₃B₂. The good ductility is attributed to the dislocation movement path released by spheroidized M₃B₂ and a more uniform stress distribution caused by the recrystallized FCC. This work provides a new strategy for synergistic strengthening and plasticizing of the brittle EHEAs to meet industrial reliability requirements.

Key words: Eutectic high-entropy alloys, Spheroidization, Recrystallization, Strength, Ductility