Remarkable superelasticity of sintered Ti–Nb alloys by Ms adjustment via oxygen regulation

• Published in: Materials & design 2015-12, Vol.87, p.466-472
• Main Authors: Lai, M., Gao, Y., Yuan, B., Zhu, M.
• Format: Article
• Language: English
• Subjects: Alloys; Biocompatibility; Biomedical alloy; Elastic modulus; Martensitic transformation; Martensitic transformations; Oxygen content; Recoverable strain; Sintered titanium alloy; Sintering; Superelasticity; Surgical implants; Titanium base alloys
• ISSN: 0264-1275; 1873-4197
• DOI: 10.1016/j.matdes.2015.07.180

Nickel-free Ti–Nb alloys were fabricated by conventional powder metallurgy sintering method. The oxygen content of sintered Ti–Nb alloys were successfully decreased to around 0.8wt.% by putting TiH2 powders aside the samples during the sintering process. For the first time, the phase transformation behaviors of these sintered Ti–Nb alloys were observed by differential scanning calorimetry (DSC) measurement. The relationship between martensitic transformation start temperature (Ms) and mechanical properties, including elastic modulus and recoverable strain, was established by compression tests carried out at room temperature. While Ms was close to test temperature, an obvious drop of elastic modulus was observed, which was related to the “β-α” transformation. In the meantime, a remarkable recoverable strain as high as 5% was obtained at room temperature, which is the highest value reported in sintered Ti–Nb alloys until now. The results of this study reveal that the recoverable strain can be further improved by adjusting Ms close to the service temperature, which was neglected in the reported studies before and will provide some guidance for the future design and fabrication of porous Ni-free Ti-based shape memory alloys for biomedical application. Sintered Ti–Nb alloys with relatively low O and Nb content, which were fabricated via oxygen regulation and Nb adjustment, exhibit obvious martensitic transformation behavior and a remarkable recoverable strain of as high as 5% at room temperature. [Display omitted] •Ms and Mf of sintered Ti–Nb alloys were detected by DSC for the first time.•A superelasticity of as high as 5% was achieved at room temperature.•Guidance was provided for the future design of porous Ti–Nb SMAs as implants.