Exceptional strength and ductility in AlCrFe1.5Ni2.6 eutectic medium-entropy alloy by Si induced lamellar to island-like structural transformation

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Changing the lamellar morphology of the brittle phase in the eutectic alloy is beneficial to improving its mechanical properties. In this work, the effect of low-cost Si on the microstructure evolution and mechanical properties AlCrFe 1.5 Ni 2.6 eutectic medium entropy alloys (MEAs) is evaluated. The micro-morphology of the MEAs changes from a lamellar eutectic structure to a dendritic structure with island-like body-centered cubic (BCC) phase dispersed in the interpenetrating face-centered cubic (FCC) matrix, as the Si concentration increases. Additionally, Si alloying significantly increases the tensile strength of the MEA and maintains high elongation. Phase-field simulations were performed to deeply elucidate the underlying mechanisms of this structural transformation, revealing that Si addition produces higher undercooling and significantly enhances the thermodynamic driving force for nucleation. This work is helpful to further optimize the microstructure and mechanical properties of eutectic MEAs.