Development of thermo-mechanical processing for fabricating highly durable -type Ti-Nb-Ta-Zr rod for use in spinal fixation devices

• Published in: Journal of the mechanical behavior of biomedical materials Vol. 9; pp. 207 - 216
• Main Authors: Narita, Kengo, Niinomi, Mitsuo, Nakai, Masaaki, Hieda, Junko, Oribe, Kazuya
• Format: Journal Article
• Language: English
• Published: 01.05.2012
• Subjects: Biocompatibility; Cold rolling; Orientation relationships; Rods; Surgical implants; Swaging; Thermomechanical treatment; Titanium base alloys
• ISSN: 1751-6161
• DOI: 10.1016/j.jmbbm.2012.01.011

The mechanical strength of a beta titanium alloy such as Ti-Nb-Ta-Zr alloy (TNTZ) can be improved significantly by thermo-mechanical treatment. In this study, TNTZ was subjected to solution treatment, cold caliber rolling, and cold swaging before aging treatment to form a rod for spinal fixation. The { 110 } beta are aligned parallel to the cross-section with two strong peaks approximately 180 [compfn] apart, facing one another, in the TNTZ rods subjected to cold caliber rolling and six strong peaks at approximately 60 [compfn] intervals, facing one another, in the TNTZ rods subjected to cold swaging. Therefore, the TNTZ rods subjected to cold swaging have a more uniform structure than those subjected to cold caliber rolling. The orientation relationship between the alpha and beta phases is different. A [ 110 ] beta // [ 121 ] alpha , ( 112 ) beta // ( 210 ) alpha orientation relationship is observed in the TNTZ rods subjected to aging treatment at 723 K after solution treatment and cold caliber rolling. On the other hand, a [ 110 ] beta // [ 001 ] alpha , ( 112 ) beta // ( 200 ) alpha orientation relationship is observed in TNTZ rod subjected to aging treatment at 723 K after cold swaging. A high 0.2% proof stress of about 1200 MPa, high elongation of 18%, and high fatigue strength of 950 MPa indicate that aging treatment at 723 K after cold swaging is the optimal thermo-mechanical process for a TNTZ rod.