Mechanical Properties of Implant Rods made of Low-Modulus β-Type Titanium Alloy, Ti-29Nb-13Ta-4.6Zr, for Spinal Fixture

Abstract

Installing a spinal fixture using implant rods is one of the effective operations for spinal diseases. Most of the implant rods are made of Ti 6Al 4V ELI alloy (Ti64). However, some problems regarding the Ti64 rod have been pointed out; it contains vanadium, which is considerably toxic to the human body, and exhibits a much higher Young's modulus than that of the cortical bone. Ti 29Nb 13Ta 4.6Zr alloy (TNTZ) developed by the authors exhibits good biocompatibility due to its nontoxicand allergy free elements, and has a lower Young's modulus than that of Ti64. In addition, the mechanical properties of TNTZ can be changed drastically according to various heat treatments. The mechanical properties of TNTZ rods subjected to various heat treatments have been investigated in this study.The as solutionized TNTZ rod consists of a single b phase. Isothermal v phase and a phase precipitate in the b phase of the TNTZ rod aged at 673 K for 259.2 ks. Only a phase precipitates in the b phase of the TNTZ rod aged at 723 K for 259.2 ks. Tensile strength and 0.2 proof stress become larger in order of as solutionized TNTZ rod, TNTZ rod aged at 723 K for 259.2 ks and TNTZ rod aged at 673 K for 259.2 ks, while elongation is smaller in order of as solutionized TNTZ rod, TNTZ rod aged at 723 K for 259.2 ks and TNTZ rod aged at 673 K for 259.2 ks. Young's modulus become larger in order of as solutionized TNTZ rod, TNTZ rod aged at 723 K for 259.2 ks and TNTZ rod aged at 673 K for 259.2 ks.

Effect of alloying elements on microstructural evolution in oxygen content controlled Ti-29Nb-13Ta-4.6Zr (wt%) alloys for biomedical applications during aging

“…This effect may retard the kinetics of  and  phase formation, and as such their nucleus size could be very small compared with those in the 0.1 alloy. Consequently, the sizes of  and  phases may be large in the 0.1 alloy aged for 24 h. In general, both the  and  phases enhance the strength of -type Ti alloys [25], and hence we can conclude that the peak hardness is obtained due to concurrent precipitations of the  and  phases.…”

Specific characteristics of mechanically and biologically compatible titanium alloy rods for use in spinal fixation applications

“…Finally, each TNTZ was peeled to remove the oxidized outer layer and machined flaws, producing a rod with a diameter of 5.0 mm. The elemental mechanical properties of TNTZ-ST, TNTZ-673 K and TNTZ-723 K have been reported in a reference paper [10]. Three conventional biomaterials, CP-Ti, Ti-64, and SUS316L were prepared as comparison materials.…”

Bending Fatigue and Spring Back Properties of Implant Rods Made of β-Type Titanium Alloy for Spinal Fixture

“…Therefore, TNTZ is highly expected to be applied to the above-mentioned implant rod practically. The development of the practical implant rod made of TNTZ is being proceeded currently [8].…”