Beta type Ti-Mo alloys with changeable Young's modulus for spinal fixation applications

To develop a novel biomedical titanium alloy with a changeable Young's modulus via deformation-induced omega phase transformation for the spinal rods in spinal fixation devices, a series of metastable beta type binary Ti-(15-18)Mo alloys were prepared. In this study, the microstructures, Young's moduli and tensile properties of the alloys were systemically examined to investigate the effects of deformation-induced omega phase transformation on their mechanical properties. The springback of the optimal alloy was also examined. Ti-(15-18)Mo alloys subjected to solution treatment comprise a beta phase and a small amount of athermal omega phase, and they have low Young's moduli. All the alloys investigated in this study show an increase in the Young's modulus owing to deformation-induced omega phase transformation during cold rolling. The deformation-induced omega phase transformation is accompanied with {332}(beta) mechanical twinning. This resulted in the maintenance of acceptable ductility with relatively high strength. Among the examined alloys, the Ti-17Mo alloy shows the lowest Young's modulus and the largest increase in the Young's modulus. This alloy exhibits small springback and could be easily bent to the required shape during operation. Thus, Ti-17Mo alloy is considered to be a potential candidate for the spinal rods in spinal fixation devices. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.