Eutectic Topology Regulates Deformation Pathways Enabling Synergistic Superelasticity and Strength in EBF 3 ‐Fabricated NiTiNb Alloys

ABSTRACT The deformation behavior of NiTiNb shape memory alloys is governed by microstructural heterogeneity, specifically the interconnected topology of the β‐Nb phase. The regulatory role of the eutectic structure in load partitioning and the evolution of deformation mechanisms, particularly in high‐Nb systems, has not been clearly understood. This study systematically investigates NiTiNb alloys with varying Nb contents within the NiTi matrix and inter‐lamellar eutectic regions, elucidating the crucial role of a topologically interlocking eutectic structure in modulating mechanical responses. The formation of a β‐Nb eutectic skeleton fundamentally reconstructs load transfer pathways and imposes significant geometric constraints, effectively retarding the kinetics of stress‐induced martensitic transformation (SIMT) within the NiTi matrix. Microstructural analysis reveals that deformation prior to phase transformation is predominantly governed by {123}<111> dislocation slip. Subsequently, during the martensitic transformation, distinct strain‐dependent twinning modes are activated for strain accommodation. Specifically, (001) compound twins and (100) deformation twins are preferentially activated in the early stages of transformation, whereas (20) twins are triggered in regions experiencing severe lattice distortion or extensive deformation. The cooperative activation of these twin variants promotes the evolution of wedge‐shaped martensitic structures, effectively coordinating local strain incompatibility. Benefiting from this unique load‐partitioning mechanism, the Nb15 alloy achieves an improved strain recovery ratio of 43.72% during the first superelastic cycle at a fixed strain of 4%, while maintaining a high critical stress of 564.25 ± 6 MPa for the martensitic transformation. These findings demonstrate that microstructural topological engineering provides an effective pathway for tailoring local stress distributions and transformation behaviors, offering new insights into the design of next‐generation high‐performance shape memory alloys.