Microstructural mechanisms imparting high strength-ductility synergy in heterogeneous structured as-cast AlCoCrFeNi2.1 eutectic high-entropy alloy

The dual-phase AlCoCrFeNi2.1 eutectic high-entropy alloy (EHEA) presents a promising solution to the strength-ductility trade-off dilemma, making it a highly desirable option for structural materials with vast potential applications. However, the relationship between the mechanical properties and the unique as-cast heterostructures needs to be further revealed. Here, we conducted in-situ tensile experiments of the as-cast EHEA to unveil the mesoscopic/microscopic microstructural mechanisms of strength-ductility synergy via investigating the dynamic real-time plastic deformation behaviors and crystallographic information evolution, as well as characterizing the deformed microstructures via transmission electron microscopy. The results indicate that the sequential dominant heterogeneous deformation induced hardening resulting from the incompatible plastic deformation between different types of heterogeneous microstructures is the primary source of its remarkable strength-ductility synergy. Moreover, the unique elongated lamellar microstructures of the as-cast EHEA offer numerous phase boundaries, and the growth twins in the face-centered cubic (FCC) phase generate abundant twin boundaries, all of which contribute to boundary strengthening and further enhance the strength and ductility of the as-cast EHEA. Furthermore, abundant cross-slip and dislocation substructures in the FCC phase provide strain hardening for as-cast EHEA, while body-centered cubic phase contributes to the high strength through precipitation hardening. Consequently, the heterostructure induced multiple strengthening mechanisms are responsible for the high strength-ductility synergy in the as-cast EHEA. The present work provides a new perspective to explain the strength-ductility synergy of similar heterogeneous structured alloys.