Superelasticity and tensile strength of Ti-Zr-Nb-Sn alloys with high Zr content for biomedical applications

In this study, Ti-xZr-8Nb-2Sn (x = 40, 45, 50) (at.%) alloys were fabricated by arc melting method and then microstructures, martensitic transformation behavior, superelasticity and mechanical properties were investigated by means of optical m icroscopy, electron microscopy, X-ray diffraction, tensile test and Vickers hardness test. The alloys consisted of beta phase only at room temperature and exhibited strong (200)(beta) texture after solution treated at 1173 K for 1.8 ks. Athermal omega phase was not observed from transmission electron microscopy in the alloys. The stress induced beta ->alpha '' transformation and the reverse transformation occurred on loading and unloading, respectively. Transformation temperature (Ms(C-C)) decreased from 188 K to 77 K with increasing Zr content from 40 at.% to 50 at.%. The maximum recoverable strains for 40Zr, 45Zr and 50Zr alloys were 7.1%, 7.5% and 7.3%, respectively, which was due to a combined effect of the large lattice deformation and a strong recrystallization texture. All alloys were fractured in ductile manner with fracture strains larger than 25%. Ultimate tensile strength of 835 MPa and superelastic recovery strain of 5.5% were obtained at room temperature in the solution treated Ti-40Zr-8Nb-2Sn alloy.