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

• Published in: Materials & design Vol. 126; pp. 226 - 237
• Main Authors: Bahl, Sumit, Krishnamurthy, Akash S., Suwas, Satyam, Chatterjee, Kaushik
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15.07.2017
• Subjects: Aging; Biocompatibility; Biomedical alloys; Corrosion; Ti-Nb-Sn; Titanium alloys; Aging; Titanium alloys; Biocompatibility; Corrosion; Biomedical alloys; Ti-Nb-Sn
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2017.04.014

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 (≈1070MPa) while affording lower modulus (≈82GPa) 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. [Display omitted] •One-step ageing treatment matrix of Ti-32Nb-2Sn alloy yields nanoscale precipitates of α phase in β matrix•High strength (> 1 GPa) with low elastic modulus (~ 75 GPa) is achieved by ageing at 500° C•Unexpected age-softening is seen when alloy is aged at 600° C•Morphology, distribution and composition of the precipitates govern the strengthening in the alloy•A comprehensive microstructure-processing-biomaterial properties relationship is established