In-Situ Synthesis of Shape Memory Alloy-Nitinol for 3D Parts by Laser Direct Deposition and Its Property Characterization

Nitinol has unique Ni-Ti shape-memory and super-elastic properties along with excellent bio-mechanical compatibility and corrosion resistance.  However, it is very difficult to fabricate complex geometries from this material. Nitinol properties are highly sensitive to the processing history used to fabricate the final component, and due to its poor machinability machining of Nitinol by conventional techniques is very difficult.   We have been successful in synthesizing Nitinol in-situ using the laser direct deposition, directly from the elemental Nickel and Titanium powder for the first time.  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% volume fraction. Further, these results were compared with those obtained for samples deposited using pre-alloyed nitinol powder. This technique offers maximum flexibility and cost benefits in the manufacturability of near-net-shape nitinol components.  It is shown that the synthesized Nitinol is as good as those produced by other current techniques in homogeneity and resultant properties.  This processing capability is more cost effective than using pre-alloyed Nitinol powder and it also allows one to fabricate near net-shaped complex geometries without the need of building moulds, tools or fixtures and hence making the process rapid.  Synthesized material is characterized using Scanning electron microscopy, Energy Dispersive Spectroscopy, X-ray Diffraction and compression testing.  By changing the ratio of nickel and titanium powders, different phase transformation temperatures are achieved. Differential Scanning Calorimeter is used to determine the characteristic transformation temperature of Nitinol.