Electron beam freeform fabrication (EBF3) has been used to produce Ni-rich NiTi parts and the effect of thermal treatments on the superelastic response was evaluated. The as-built EBF³ deposition resulted in samples with alternating regions of coarse columnar and equiaxed grains, with Ni-rich precipitates and Ti-rich eutectic structures. A solution treatment at 950 °C for 6 hours was performed on some as-built samples to dissolve precipitates and anneal residual stresses after the EBF3 deposition. The solution treatment dissolved Ni-rich precipitates from the as-built sample and globalized Ti-rich structures. In uniaxial compression testing, the superelasticity of both the solution-treated and as-built samples showed a moderate initial strain recovery of 45% and 80% during the first cycle, and 49% and 36% after ten cycles, respectively. Thereafter, some as-built and solution-treated samples were aged at 350 °C and 450 °C for 1, 6, and 12 hours. The heat treatments showed a significant influence on the phase transformation and superelastic response of the as-built and solution-treated samples. X-ray diffraction detected precipitates of Ni₄Ti₃ in the heat-treated samples, resulting in intermediate R-phase transformation between the low-temperature martensitic and high-temperature austenitic phases. Furthermore, as-built or solution-treated samples aged at 350 °C provided excellent superelasticity, greater than those aged at 450 °C. Outstanding superelasticity was achieved by aging the solubilized samples at 350 °C for 12 hours, with 97% strain recovery after one compression cycle and 86% after ten compression cycles at 860 MPa. The findings demonstrate that solution treatments and tailored aging parameters can greatly enhance the superelasticity of EBF³ manufactured parts, opening the door for superelastic material applications such as torque tubes in airplanes. 

 Keywords: Electron beam freeform fabrication, superelasticity, NiTi alloys, heat treatments