Pore Control in Porous NiTi Alloy Produced by Combustion Synthesis Method with the Utilization of Space Holders

Abstract

Nitinol (NiTi) is an intermetallic compound and a member of the shape memory alloy family. This widely used material has unique properties such as biocompatibility, superelasticity, good corrosion resistance, and abrasion resistance, which distinguish it from the other shape memory materials. The most common applications of this alloy in medical engineering are in the manufacture of orthodontic wires, orthopedic implants, and guide wires in cardiovascular surgery. The production of orthopedic implants requires porous structures and bone-like tissue. In the present study, sodium chloride, polystyrene beads, and sawdust were used as space holder during the combustion synthesis process to produce porous NiTi alloy. The effect of space holder type on the percentage, distribution, and size of porosity of the synthesized samples were investigated. The sample's porosity percentage without the space holder was 30% and increased to 52, 36, and 37% by using sodium chloride, polystyrene beads, and sawdust spacers, respectively. The microstructure and phases of the specimens were examined using scanning electron microscopy (SEM) equipped with x-ray energy diffraction (EDS) spectroscopy and x-ray diffraction (XRD) analysis in samples with NaCl space holders with higher percentages and more controlled porosity. The microstructure of the synthesized sample without the space holder consisted of NiTi, NiTi₂, Ni₃Ti, and Ni₄Ti₃, and the addition of the sodium chloride did not change the phases. The Young's modulus and compressive strength of the synthesized sample without a space holder were 0.4 GPa and 59.7 MPa, respectively, which decreased with the addition of sodium chloride particles to 0.2 GPa and 25.5 MPa.

Graphical abstract