Optimization of Cr and O contents in beta-type Ti-Cr-O alloys for obtaining both larger changeable young's modulus during deformation and higher strength for use in spinal fixation applications

In order to meet the requirements of patients and surgeons simultaneously for spinal fixation applications, β-type Ti-Cr based alloys with self-tunable Young's modulus due to deformation have been developed to prevent the stress-shielding effect for patients and to suppress springback for surgeons. In this study, the effects of Cr and O on the deformation-induced ω phase transformation were investigated to optimize the Cr and O contents in ternary Ti-Cr-O alloys in order to achieve a large increase in Young's modulus via deformation-induced ω phase transformation with good mechanical properties. The Young's modulus of the alloys with same Cr content after solution treatment increases with increasing O content because of solid-solution strengthening effect of O. The increase in Young's modulus during cold rolling is larger for the alloys with lower O and Cr contents because larger amount of deformation-induced ω phase is formed. With regard to tensile properties, the tensile strength of the alloys subjected to solution treatment increases and the elongation of them decreases with increasing O content and decreasing Cr content because of both the effects of solid-solution strengthening of O and the deformation-induced ω phase strengthening.