Strength and ductility enhancement of high-entropy FeCoNi₂Al_0.9 alloy by ultrasonically refining eutectic structures

The solidification process of high-entropy FeCoNi₂Al_0.9 alloy was modulated by 20 kHz power ultrasound with maximum 13 μm amplitude. The statically solidified eutectic structures were composed of L1₂ and B2 phases growing by K-S synergistic relationship. With the increase of ultrasound amplitude, the eutectic cell width and regular lamellar spacing were significantly refined, the proportion of strictly semi-coherent L1₂/B2 interfaces increased, and the solute concentration fluctuation in each eutectic phase was obviously suppressed. The steady-state cavitation and acoustic flow displayed remarkable influences on eutectic microstructure evolution. The yield strength, ultimate strength, and total elongation were increased by 23%, 21%, and 19% as compared with statically solidified alloy. This provided an effective approach to promoting the mechanical properties and overcoming the strength-ductility trade-off for those high-entropy alloys with eutectic structures.