The structure and mechanical properties of as-cast Ti-25Nb-xSn alloys for biomedical applications

The effects of tin on the structure and mechanical properties of a Ti-25Nb-based system were studied with an emphasis on improving the strength/modulus ratio. Commercially pure titanium (c.p. Ti) was used as a control. As-cast Ti-25Nb and a series of Ti-25Nb-xSn (x = 1, 3, 5, 7, 8, 9, 10, 11, 13, and 15 wt%) alloys prepared using a commercial arc-melting vacuum pressure casting system were investigated. The experimental results showed that the as-cast Ti-25Nb has an alpha '' phase, and when 1-5 wt% Sn was introduced into the Ti-25Nb alloy, the structure remained essentially unchanged. However, with 7-15 wt% Sn, retention of the metastable beta phase began. Among the developed Ti-25Nb-xSn alloys, all the alloys had good ductility, and Ti-25Nb-8Sn and Ti-25Nb-9Sn alloys had lower bending moduli (52 and 53 GPa, respectively) than c.p. Ti (99 GPa) and the other Ti-25Nb-based alloys (61-133 GPa). Moreover, Ti-25Nb-9Sn and Ti-25Nb-11Sn alloys exhibited higher bending strength/modulus ratios, as large as 20.5 and 20.6, respectively, higher than those of c.p. Ti (8.5) and the Ti-25Nb alloys (19.8). The Ti-25Nb-10Sn (41 degrees) and Ti-25Nb-11Sn (46 degrees) alloys had superior elastically recoverable angles, about 17.0 and 15.2 times greater than that of c.p. Ti, respectively. In the current search for a better implant material, beta-phase Ti-25Nb-(8-11)Sn alloys show considerable promise due to their low moduli, ductile properties, excellent elastic recovery capability, reasonably high strength (or high strength/modulus ratio), and better shape memory effect. (c) 2013 Elsevier B.V. All rights reserved.