In Situ Synthesis and Characterization of Shape Memory Alloy Nitinol by Laser Direct Deposition

Nitinol is well known for its unique shape-memory and super-elastic properties along with its excellent biomechanical compatibility and corrosion resistance. In this study, a laser direct deposition technique was explored to synthesize high-quality, near-net-shape nitinol components directly from elemental nickel and titanium powders as opposed to using expensive prealloyed nitinol powder. The systematic characterization of samples was done using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive X-ray spectroscopy (EDS). Transformation temperatures were obtained using differential scanning calorimetry (DSC). With an optimum ratio of nickel and titanium powder mixture, optimal laser parameters, and post-heat treatment, samples with homogeneous and nearly fully dense NiTi phase were synthesized with less unwanted secondary phases occupying less than 3.2 pct volume fraction. Furthermore, these results were compared with those obtained for samples deposited using prealloyed nitinol powder. This technique offers maximum flexibility and cost benefit in the manufacturability of near-net-shape nitinol components.