Controlled nanoscale precipitation to enhance the mechanical and biological performances of a metastable β Ti-Nb-Sn alloy for orthopedic applications

Toward engineering a new generation of low modulus titanium alloys for orthopedics, we present new insight into the control of nanoscale precipitation in a metastable β Ti-32Nb-2Sn alloy. Nanoscale α precipitates from β phase were obtained by one-step heat treatment at 500 °C. The nanoscale precipitates markedly improve the tensile strength (≈ 1070 MPa) while affording lower modulus (≈ 82 GPa) than conventional metallic biomaterials. Besides age-hardening at 500 °C, an unexpected phenomenon of age-softening is observed even in the presence of nanoscale α precipitates when aged at 600 °C. This effect is attributed to significant softening of the β phase due to compositional changes, as revealed by the elemental mapping in transmission electron microscopy (TEM). TEM elemental mapping reveals that Sn partitions preferentially in the β phase on aging at 500 °C and does not show any preferential partition on aging at 600 °C. The passive layer at the surface enriches in Sn content after aging at 500 °C and consequently affects the electrochemical behavior of the alloy. The alloy supports the proliferation, and osteogenesis of human mesenchymal stem cells. This study provides new understanding for processing Ti-Nb-Sn alloys in biomedical applications.