Microstructure, elastic deformation behavior and mechanical properties of biomedical β-type titanium alloy thin-tube used for stents

• Thin-tube of β-type titanium alloy is reported for the first time.
• Cold-rolled tubes shows nonlinear elastic behavior.
• Appropriate amount of α phase improves the superelasticity.
• Maximal recoverable strain (εmax-R) of above 2.0% corresponds to Vα of 3–10%.
• Elastic behavior probably relates to “mechanical” stabilization of the alloy.

Cold-deformability and mechanical compatibility of the biomedical β-type titanium alloy are the foremost considerations for their application in stents, because the lower ductility restricts the cold-forming of thin-tube and unsatisfactory mechanical performance causes a failed tissue repair. In this paper, β-type titanium alloy (Ti–25Nb–3Zr–3Mo–2Sn, wt%) thin-tube fabricated by routine cold rolling is reported for the first time, and its elastic behavior and mechanical properties are discussed for the various microstructures. The as cold-rolled tube exhibits nonlinear elastic behavior with large recoverable strain of 2.3%. After annealing and aging, a nonlinear elasticity, considered as the intermediate stage between “double yielding” and normal linear elasticity, is attributable to a moderate precipitation of α phase. Quantitive relationships are established between volume fraction of α phase (Vα) and elastic modulus, strength as well as maximal recoverable strain (εmax-R), where the εmax-R of above 2.0% corresponds to the Vα range of 3–10%. It is considered that the “mechanical” stabilization of the (α+β) microstructure is a possible elastic mechanism for explaining the nonlinear elastic behavior.