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 α″ 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 β 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°) and Ti–25Nb–11Sn (46°) 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, β-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.