Abstract

Hybrid shape-memory materials combining structural and magnetic functionalities offer new opportunities for tailoring functional responses through mechanical coupling between dissimilar phases. In this work, a NiTi/NiFeGa bilayer composite was fabricated by high-speed high-pressure torsion (HSHPT), a severe plastic deformation technique enabling the consolidation of dissimilar materials. Although the constituent alloys exhibit martensitic transformations separated by nearly 135 K in their initial states, the HSHPT-processed hybrid displays a single dominant calorimetric transformation despite the absence of measurable chemical interdiffusion, consistent with a cooperative transformation response promoted by strong interfacial mechanical coupling. The microstructure was investigated by scanning electron microscopy, while the martensitic transformation and magnetic properties were characterized by differential scanning calorimetry and magnetometry. SEM observations revealed a well-defined bilayer architecture with a sharp chemically distinct interface. Despite the absence of measurable interdiffusion, the hybrid exhibited a transformation enthalpy approximately twice that of the NiTi constituent (≈20 J g−1 vs. ≈10.35 J g−1), accompanied by a broader thermal hysteresis. The magnetic response was also modified, exhibiting reduced saturation magnetization and increased coercivity. These findings demonstrate that HSHPT provides an effective route for designing hybrid functional materials with tunable thermomechanical and magnetic responses through controlled interfacial interactions between chemically distinct phases.

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