Indirect determination of martensitic transformation temperature of sintered nickel-free Ti–22Nb–6Zr alloy by low temperature compression test

• Ms and Mf of sintered Ti–22Nb–6Zr alloy were indirectly determined.
• A superelasticity of as high as 5.9% was achieved at −85 °C.
• Guidance was provided for the future design of porous Ti–Nb–Zr SMAs as implants.

Nickel-free Ti–22Nb–6Zr alloys were fabricated by conventional powder metallurgy sintering method. X-ray diffractometer (XRD) investigation showed that the as-sintered alloys mainly consisted of β phase, with a few needle-like α phase precipitates. Differential scanning calorimetry (DSC) measurement in the temperature ranging from −70 °C to 400 °C and constant stress thermal cycling test by dynamic mechanical analysis (DMA) were unable to reveal the martensitic start temperature of sintered Ti–22Nb–6Zr alloys. Therefore low temperature compression tests were carried out to evaluate their phase transformation behavior indirectly. There was an obvious drop of both Young’s modulus and recoverable strain at −85 °C ∼ −80 °C in the Young’s modulus-temperature and recoverable strain–temperature curves of sintered Ti–22Nb–6Zr alloys respectively, which was attributed to the occurrence of thermal elastic martensitic transformation at this temperature. At the testing temperature of −85 °C, a superelasticity of as high as 5.9% was achieved in the sintered alloys. The results had revealed that sintered Ti–22Nb–6Zr alloys own a great superelasticity intrinsically and would exhibit a much greater superelasticity at room temperature if their martensitic transformation start temperature (Ms) were closer to room temperature. Along with their noble biocompatibility, sintered nickel free Ti–22Nb–6Zr alloys are thus thought to be potentially competitive biomaterials for biomedical applications.