Dynamic coupling of TRIP effect and hetero-deformation-induced (HDI) hardening in a hierarchical eutectic high-entropy alloy

Overcoming the pervasive strength-ductility trade-off in metallic materials requires the synergistic activation of multiple deformation mechanisms. Heterostructural design offers an effective strategy to regulate strain partitioning and evoke extra deformation mechanisms. Here, we designed a hierarchical heterostructured eutectic high-entropy alloy featuring alternating equiaxed grain regions (EGR) and lamellar grain regions (LGR). This architected microstructure gives rise to a pronounced TRIP-assisted hardening behavior and delivers an outstanding strength-ductility synergy, achieving an ultimate tensile strength of ∼1.57 GPa together with a uniform elongation of ∼24% at room temperature. The exceptional tensile properties originate from the hierarchical heterostructure and the associated martensitic transformation activated in the EGR, which sustains a high work-hardening rate throughout tensile deformation. Hetero-deformation between EGR and LGR generates elevated internal stresses, thereby triggering martensitic transformation in the EGR, particularly near disrupted K-S interfaces. This transformation effectively redistributes strain and mitigates local stress concentrations. The occurrence of martensitic transformation is directly verified by in-situ synchrotron X-ray diffraction. Moreover, the formation of L1₀ martensite introduces additional phase boundaries and mechanical contrast, which promote dislocation storage and sustain hetero-deformation-induced (HDI) hardening, thereby delaying the onset of necking. This study demonstrates that hierarchical heterostructure design not only enables HDI hardening but also facilitates the activation and utilization of unconventional deformation mechanisms via increased internal stresses, providing a new paradigm for the development of high-performance eutectic high-entropy alloys.