Improvement of Superelastic Performance of Ti-Nb Binary Alloys for Biomedical Applications

Beta-Ti alloys consisting of non-cytotoxic elements have been extensively studied for biomedical applications thanks to their thermomechanical properties as shape memory effect and superelasticity. The success of implants is directly related to the principle of osseointegration which depends on the loading conditions at the surrounding bone. The large gap in stiffness between the host bone and the implant material and also the absence of mechanical stress at the surrounding bone induce the stress shielding effect resulting in bone atrophy and loss of implant. The elastic modulus of the implant material should be as close as possible to that of the host bone (10-30GPa). In addition to low Young modulus, high strength is also needed to endure stresses. Our study aims to find the adequate strategies in order to combine superelasticity, relatively high strength and low elastic modulus. The thermomechanical route, based on severe cold rolling deformation followed by a short heat treatment resulting in nano-structure, are shown to be effective to improve strength and superelasticity while keeping low Young’s modulus values. An interesting balance combined a high stress of 900MPa, a low modulus (30GPa) and recoverable strain of 2.7% is achieved. The obtained results are investigated in relation with microstructure evolution during thermomechanical processing according to the temperature and the annealing time.