Shape memory behavior of Ti-22Nb-(0.5-2.0)O(at%) biomedical alloys

In order to develop new biomedical shape memory alloys, mechanical properties and shape memory behavior of Ti-22Nb-(0.5-2.0)O(at%) alloys were investigated by tensile tests at various temperatures and X-ray diffraction measurement. The Ti-Nb-O alloys were fabricated by an arc melting method and then homogenized at 1273 K for 7.2 ks. The ingots were cold-rolled with a reduction up to 98.5% in thickness and solution treated at 1173 K for 1.8 ks. The fracture stress of both as-rolled specimen and Solution treated specimen increased with increasing oxygen content. A fracture stress of 1.37GPa was obtained in the as-rolled Ti-22Nb-2O alloy. The martensitic transformation temperature decreased by 160 K per I at% increase of oxygen content. Superior shape memory effect and superelastic behavior were observed at room temperature in the Ti-22Nb-(0.5-1.5)O alloys. The addition of oxygen stabilized superelastic behavior of Ti-Nb alloys by increasing the critical stress for permanent deformation. The maximum shape recovery strain of 4.0% and the critical stress of 900 MPa for permanent deformation were obtained in the Ti-22Nb-0.5O and Ti-22Nb-1.5O alloys, respectively.