Unveiling strength-ductility synergy in eutectic high-entropy alloys via directional solidification
Eutectic high-entropy alloys (EHEAs) combine multi-principal-element compositions with regular lamellar microstructures, offering exceptional high-temperature stability and mechanical properties. However, conventional casting yields random solidification microstructures and inhomogeneous phase distributions, constraining strength-ductility synergy. This study employs directional solidification (DS) on Al19Fe20Co20Ni41 EHEA to achieve precise microstructural control, constructing a multi-level lamellar architecture with a herringbone-like alternating arrangement. This tailored microstructure refines interlamellar spacing, eliminates detrimental isolated B2 phases, and promotes slip continuity at interfaces, enhancing coordinated dislocation motion and uniform distribution across multiple slip systems. Consequently, the DS EHEA exhibits superior mechanical properties compared to most reported thermomechanically processed and directionally solidified HEAs. Micro-mechanistic analysis reveals that homogenized geometrically necessary dislocation (GND) density, interface-assisted crack deflection, and multi-stage strain-hardening from sequential dislocation activation collectively contribute to outstanding strength-ductility synergy. This work demonstrates that programming solidification paths enables design of unique multi-level lamellar architectures, serving as intrinsic microstructural composites that optimize dislocation management and crack propagation, offering a novel paradigm for developing ultra-robust EHEAs for extreme service environments.