Martensitic Transformation and Superelastic Properties of Ti-Nb Base Alloys

Abstract

Ti-Nb base alloys have been proposed as prospective candidates for Ni-free biomedical superelastic alloys due to their excellent mechanical properties with good biocompatibility, and many kinds of Ti-Nb base alloys exhibiting shape memory effect or superelasticity have been developed up to now. However, typical Ti-Nb base superelastic alloys show a small recovery strain which is less than one third of the recovery strain of practical Ti-Ni superelastic alloys. Over the last decade there have been extensive efforts to improve the properties of Ti-Nb base superelastic alloys through microstructure control and alloying. Low temperature annealing and aging are very effective to increase the critical stress for slip due to fine subgrain structure and precipitation hardening. The addition of interstitial alloying elements such as O and N raises the critical stress for slip and improves superelastic properties. In this paper, the roles of alloying elements on the martensitic transformation temperature, crystal structure, microstructure and deformation behavior in the Ti-Nb base alloys are reviewed and the alloy design strategy for biomedical superelastic alloys is proposed.

Low Young’s Modulus Ti–Nb–O with High Strength and Good Plasticity

“…It has been reported that non-linear elastic behaviour are due to the formation of nano-domain lattice distortion induced by interstitial oxygen atoms. 10,11) The • 0.2 in TN0.13O and TN 0.24O is related to the first yield stress, which corresponds to the stress for SIMT and is affected by the M s temperature. Oxygen reduces the M s temperature and thereby increases…”

Twinning behavior of orthorhombic-α” martensite in a Ti-7.5Mo alloy

“…One characteristic of these materials is the martensitic transformation from body centered cubic (bcc)-β to orthorhombic-αʺ martensite upon quenching or deformation, which strongly depends on the content of β-stabilizing elements such as Mo, Nb, and Ta [4][5][6][7]. αʺ martensite has been reported to play a key role in several mechanical properties of β-Ti alloys [7][8][9].…”

Several Issues in the Development of Ti–Nb-Based Shape Memory Alloys

“…Over the past decade, there has been significant progress not only in understanding the martensitic transformation behavior of Ti-based alloys but also in developing novel biocompatible shape memory alloys [1][2][3]. In binary Ti-Nb alloys, superelasticity has been reported to occur when the Ni content is in the range of 26-27 at.% [4,5].…”

“…It has been concluded that the small recovery strain is mainly due to the intrinsic small transformation strain of the b-a 00 transformation. [3,5]. Another drawback of Ti-Nb alloys to be mentioned is low critical stress for slip.…”