Effect of interlayer remelting on damping and mechanical properties of EBF³-fabricated NiTi alloys

Electron-beam freeform fabrication (EBF³) of NiTi alloys commonly exhibits a trade-off between tensile ductility and damping capacity. In this study, a low-beam current interlayer remelting strategy is introduced to modify the thermal history during deposition, thereby influencing the microstructural evolution and phase transformation behavior. The results indicate that interlayer remelting enhances nanoscale compositional fluctuations and redistributes internal strain fields. These effects stabilize the R-phase transformation and modify the morphology of Ti₄Ni₂O_x precipitates. The stabilization of the R-phase increases the transformation interface density and improves reversibility, thereby contributing to enhanced the transient (Q_Tr⁻¹) and intrinsic (Q_Int⁻¹) internal friction components. Concurrently, the spheroidized oxides are suggested to mitigate local stress concentration, and stabilized R-phase interfaces may act as compliant stress buffers that promote a more homogeneous homogenize stress-induced martensitic transformation (SIMT) and delay strain localization. As a result, the remelted alloy exhibits an increased damping capacity, with a loss factor (Q⁻¹) value of 0.34 at 0.1 Hz together with an improved tensile elongation of 8.1 ± 0.5%. These findings suggest that controlled interlayer thermal reconfiguration can influence phase transformation process in NiTi alloys, providing a potential pathway to improve the balance between damping capacity and tensile ductility in additively manufactured shape memory alloys.