Deformation-induced changeable Young's modulus with high strength in β-type Ti-Cr-O alloys for spinal fixture.

Abstract

In order to meet the requirements of the patients and surgeons simultaneously for spinal fixation applications, a novel biomedical alloy with a changeable Young's modulus, that is, with a low Young's modulus to prevent the stress-shielding effect for patients and a high Young's modulus to suppress springback for surgeons, was developed. In this study, the chromium and oxygen contents in ternary Ti(11, 12 mass%)Cr-(0.2, 0.4, 0.6 mass%)O alloys were optimized in order to achieve a changeable Young's modulus via deformation-induced ω-phase transformation with good mechanical properties. The Young's moduli of all the examined alloys increase after cold rolling, which is attributed to the deformation-induced ω-phase transformation. This transformation is suppressed by oxygen but enhanced with lower chromium content, which is related to the β(bcc)-lattice stability. Among the examined alloys, the Ti-11Cr-0.2O alloy shows a low Young's modulus of less than 80GPa in the solution-treated (ST) condition and a high Young's modulus of more than 90GPa in the cold rolled (CR) condition. The Ti-11Cr-0.2O alloy also exhibits a high tensile strength, above 1000MPa, with an acceptable elongation of ~12% in the ST condition. Furthermore, the Ti-11Cr-0.2O alloy exhibits minimal springback. This value of springback is the closest to that of Ti64 ELI alloy among the compared alloys. Therefore, the Ti-11Cr-0.2O alloy, which has a good balance between large changeable Young's modulus, high tensile strength, good plasticity, and minimal springback, is considered to be a potential candidate for spinal fixation applications.