Threefold enhancement of ductility in dual-phase L1₂–B2 high-entropy alloys via interface-orientation-weakening-induced B2→BCT phase transformation

Interfaces play a crucial role in strain hardening, slip accommodation, and plastic flow stability of dual-phase alloys. The orientation relationship (OR) between phases critically governs the crystallographic discontinuity and imposes geometric constraints on the activation of deformation modes. In dual-phase 19Al-20Fe-20Co-41Ni high-entropy alloys, we demonstrate that weakening the Kurdjumov-Sachs (K-S) OR between the L12 and B2 phases via moderate plastic deformation and recrystallization, significantly improves ductility without sacrificing strength. The threefold increase in ductility compared to the as-cast alloy is attributed to a B2→body-centered tetragonal (BCT) transformation, promoted by weakening the interface OR. In contrast, the as-cast alloy with K-S OR constrained B2 remains untransformed. In situ synchrotron tensile testing confirms the phase transformation evolves progressively. Our analysis of the expected strain contribution reveals that transformation preferentially occurs in B2 grains adjacent to highly deformable neighbors. These findings highlight the critical role of OR in governing phase transformation and deformation. The orientation relationship between phases governs crystallographic discontinuity and imposes constraints on the activation of deformation modes. Here, weakening the orientation relationship between L12 and B2 phases in a dual-phase high-entropy alloy via plastic deformation and recrystallization significantly improves ductility without sacrificing strength.