Shape Memory Behavior of Ti–22Nb–(0.5–2.0)O(at%) Biomedical Alloys

Abstract

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 1.37 GPa was obtained in the as-rolled Ti–22Nb–2O alloy. The martensitic transformation temperature decreased by 160 K per 1 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.