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

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 0.8 wt% 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 (M-s) and mechanical properties, including elastic modulus and recoverable strain, was established by compression tests carried out at room temperature. While M-s was close to test temperature, an obvious drop of elastic modulus was observed, which was related to the "beta-alpha" 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 M-s 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. (C) 2015 Elsevier Ltd. All rights reserved,