Microstructure and mechanical behavior of superelastic Ti-24Nb-0.5O and Ti-24Nb-0.5N biomedical alloys.

In this study, the microstructure and the mechanical properties of two new biocompatible superelastic alloys, Ti-24Nb-0.5O and Ti-24Nb-0.5N (at.%), were investigated. Special attention was focused on the role of O and N addition on α(″) formation, supereleastic recovery and mechanical strength by comparison with the Ti-24Nb and Ti-26Nb (at.%) alloy compositions taken as references. Microstructures were characterized by optical microscopy, X-ray diffraction and transmission electron microscopy before and after deformation. The mechanical properties and the superelastic behavior were evaluated by conventional and cyclic tensile tests. High tensile strength, low Young's modulus, rather high superelastic recovery and excellent ductility were observed for both superelastic Ti-24Nb-0.5O and Ti-24Nb-0.5N alloys. Deformation twinning was shown to accommodate the plastic deformation in these alloys and only the {332}<113> twinning system was observed to be activated by electron backscattered diffraction analyses.