Martensitic transformation, shape memory effect and superelasticity of Ti–xZr–(30–x)Nb–4Ta alloys

Martensitic transformations, mechanical properties, shape memory effect and superelasticity of Ti–xZr–(30–x)Nb–4Ta (x = 15, 16, 17 and 18; at%) alloys were investigated. X-ray diffraction (XRD), optical microscopy (OM) and transmission electron microscopy (TEM) results indicated that the Ti–16Zr–14Nb–4Ta, Ti–17Zr–13Nb–4Ta and Ti–18Zr–12Nb–4Ta alloys were mainly composed of α″-martensite, while the Ti–15Zr–15Nb–4Ta alloy was characterized by predominant β phase. The reverse martensitic transformation temperatures increased when Nb was replaced by Zr, indicating stronger β-stabilizing effect for the former. The Ti–15Zr–15Nb–4Ta alloy displayed superelasticity during tensile deformation with a recovery strain of 3.51%. For the other three alloys with higher Zr content, the martensitic reorientation occurred during tensile deformation, resulting in shape memory recovery upon subsequent heating. The maximum shape memory effect was 3.46% in the Ti–18Zr–12Nb–4Ta alloy.