Mechanical Properties and Shape Memory Behavior of Ti-Nb Alloys

TLDR

The study investigates Ti‑Nb alloys (20–29 at % Nb) to develop Ni‑free biomedical shape‑memory materials. Ti‑Nb alloys were produced by arc melting, then cold‑rolled to 95 % thickness reduction and solution‑treated at 1173 K for 1.8 ks. Increasing Nb content lowers the martensitic transformation temperature by 43 K per at % and yields room‑temperature shape‑memory in 22–25 at % Nb and superelasticity in 25.5–27 at % Nb, with a maximum 3 % recovered strain, small transformation enthalpy, large Ms–Mf gap, and heat treatment at 573 K for 3.6 ks further stabilizes superelasticity by raising the critical slip stress.

Abstract

Mechanical properties and shape memory behavior of Ti-(20—29)at%Nb alloys were investigated in order to develop Ni-free biomedical shape memory alloys. The Ti-Nb alloys were fabricated by arc melting method. The ingots were cold-rolled with a reduction up to 95% in thickness and then solution treated at 1173 K for 1.8 ks. The martensitic transformation temperature decreased by 43 K per 1 at% increase of Nb content. The shape memory effect and superelastic behavior were observed at room temperature in the Ti-(22—25)at%Nb alloys and Ti-(25.5—27)at%Nb alloys, respectively. A small enthalpy of the martensitic transformation and a large difference between Ms and Mf were observed in the Ti-Nb alloys compared to Ti-Ni shape memory alloys. The maximum recovered strain of 3% was obtained at room temperature in solution treated Ti-(25−27)at%Nb alloys. The heat treatment at 573 K for 3.6 ks stabilized superelastic behavior of Ti-Nb alloys by increasing the critical stress for slip.