Ni4Ti3 precipitates formed in NiTi alloy modulated by powder bed fusion and their effects on mechanical and electrical deformation

Abstract

In this study, NiTi alloys featuring different distributions and morphologies of Ni4Ti3 precipitates were developed via powder bed fusion (PBF) technology. The effects of these Ni4Ti3 precipitates on the mechanical, resistive, and electrical deformational properties of the alloys were also studied. With increasing laser energy density, a coarsening behavior of the semi-coherent Ni4Ti3 precipitates was observed, with these precipitates transitioning from needle-like to disk-like structures. Consequently, their coherence with the B2 matrix diminished, thus weakening the surrounding strain field. The presence of dislocations and uniformly dispersed Ni4Ti3 precipitates, endowed the NiTi alloy with enhanced resistivity (7.294 μΩ·m) and stable tensile recovery strain (2–4 %) during stress-controlled loading and unloading. Employing PBF, a NiTi spring actuator was produced, capable of lifting loads over 145 times its weight, with a shape-memory recovery efficiency of 76.80 % at a current of 3.0 A. This study demonstrated the versatility of PBF technology in tailoring the microstructure of NiTi alloys by adjusting the laser energy density, providing a laboratory reference for advanced applications in electrically induced deformation.