Shape memory effect and superelasticity of Ni-free Ti-Nb-based alloys

Abstract

Ni-Free Ti-Nb-based alloys have potential application as non-toxic shape memory and superelastic alloys. The shape memory behavior and superelasticity of free-Ni Ti-Nb-based alloys were described and discussed in this paper. It was shown that the excellent shape memory behavior and superelasticity can be obtained by a reasonable chemical composition and heat treatments. β-Ti-Nb alloys undergo a martensitic transformation when the alloys are rapidly cooled from the β phase region at high temperatures. This transformation produces α , or α ,, martensite. The transformation from β phase to α ,, martensite is a thermoelastic one and thereby produces shape memory effect and superelasticity. The start temperature of martensitic transformation (Ms) decreases with increasing Nb contents. Nb contents are located between 22-26 (at.%) among the reported Ti-Nb alloys since the superelasticity at room temperature exists when the Ti-Nb alloys have the compositions of 22-26at.%Nb. The addition of the elements such as Zr, Sn, O and Al has influences on the shape memory effect and superelasticity of Ti-Nb alloys, which decreases Ms and increases superelasticity. Ti-22Nb-4Zr (at.%) and Ti-24Nb-3Al (at.%) possesses large recovery strain. The maximum recovery strain is 4.3% for the former and 4.7% for the latter, respectively.