Microstructural evolution accompanying mechanical properties change by aging treatment at 723 K in cold swaged Ti 29Nb 13Ta 4.6Zr were investigated in order to obtain an optimized aging condition for getting excellent mechanical properties.The precipitate free zone exists in Ti 29Nb 13Ta 4.6Zr after aging treatment for various time periods. Such the precipitate free zone corresponds to Nb and Ta enriched region according to the result of element distribution analysis. With the increase in aging time, the area of the precipitate free zone decreases.Two types of a phase, acicular and ellipsoidal ones, are observed in Ti 29Nb 13Ta 4.6Zr after aging treatment for various time periods. The acicular a phase is precipitated in the Tiand Zr enriched region. While the size increases, the area fraction barely changes with aging time for acicular a phase, On the other hand, the ellipsoidal a phase precipitates at b grain boundary and its subgrain boundary. Both the size and area fraction increase with the increase in aging time for the ellipsoidal a phase.The lattice correspondence between acicular a phase and b matrix is Tensile strength of Ti 29Nb 13Ta 4.6Zr subjected to aging treatment after cold swaging is around 1200 GPa, regardless of aging time. On the other hand, elongation of those are decreased by the aging treatment up to 86.4 ks, increased at ones over 259.2 ks.
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 nontoxicand 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.
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