Self-Propagating High-Temperature Synthesis of Porous Nickel-Titanium

Abstract

Porous equiatomic Nickel-Titanium (NiTi) is a strong candidate material for bone engineering applications because its mechanical properties are within the range of bone and its porosity allows for biologic interlock of the material to the surrounding tissue. Self-propagating high-temperature synthesis (SHS) is one method for producing porous NiTi. Nickel and titanium powders, -325 mesh, were mixed for 24 hours then pressed into cylindrical pellets (0.5 inch diameter, 0.5 inch height) to a theoretical green density of approximately 53%. The pellets were preheated in flowing argon for one hour then ignited using a tungsten coil. Scanning electron microscopy and electron dispersive spectroscopy (EDS) show localized differences of stoichiometry suggesting variations in the crystal structure where the Ni to Ti atomic ratio varied between 48.5:51.5 and 50.7:49.3. X-ray diffraction (XRD) (Philips X’Pert PRO) confirmed the presence crystalline equiatomic NiTi as well as other intermetallic compounds including NiTi2 and Ni4Ti3. Nanoindentation (MTS Nano Indenter XP) of this heterogeneous material indicates a mean range indentation modulus of 89.6 ± 9.4 GPa. This is on the same order of magnitude as bone, which has an elastic modulus range of 14-20 GPa.