Deformation behavior and strengthening mechanism analysis of newly designed Co_31.5Fe_18.5Ni_31.5Al_18.5 eutectic high-entropy alloy by calculating solidification paths

A novelCo_31.5Fe_18.5Ni_31.5Al_18.5 eutectic high-entropy alloy (EHEA) is designed through computational prediction of solidification paths using JMatPro. The microstructure features eutectic dendrites and cells, with the two-phase eutectic showing characteristic lamellar structures of alternating NiAl-rich B2 (ordered BCC) and CoFeNi-rich L1₂ (ordered FCC) phases. TEM analysis reveals a semi-coherent relationship between BCC and FCC phases, i.e., [011]_FCC// [1‾11] _BCC and (1‾1‾1) _FCC//(011‾) _BCC. The Co_31.5Fe_18.5Ni_31.5Al_18.5 EHEA exhibits a yield strength of 571 ± 15 MPa and an ultimate strength of 975 ± 5 MPa with a ductility of 6.9 ± 0.3 %. Deformation behavior is well understood through comprehensive analysis of fracture surface morphology, side surface characteristics, and tensile-induced substructure evolution. Extensive plastic deformation in the FCC phase is evidenced by pronounced necking, fine shear bands, and high-density dislocation networks. In contrast, the BCC phase displays quasi-cleavage fracture characteristics with limited dislocation activity, indicating restricted plastic deformation capability. The strengthening mechanisms (like mixing rule, interface strengthening and HDI stress strengthening) are discussed in detail. In particular, the investigation of the mechanical properties of FCC and BCC individual phases represents the most significant highlight of this work, which provides critical insights into the strengthening mechanisms of EHEAs.