Tailoring the microstructure and mechanical properties of metastable Ti–29Nb–13Ta-4.6Zr alloy for self-expansible stent applications

Abstract

In this paper, thin-struts of β-type titanium alloy (Ti–29Nb–13Ta-4.6Zr, wt%) were successfully fabricated by cold rolling, and their elastic behavior and mechanical properties are discussed for different processing conditions. Before cold rolling, the extremely low yield and ultimate tensile strength of the as-cast and solution-treated specimens, result of a notable “double yielding” behavior, make them inadequate to be applied as structural devices. However, after cold rolling plus short time aging, a nonlinear elasticity with a substantial recoverable strain, considered as the intermediate stage between “double yielding” and normal linear elasticity, is obtained and ascribed to a moderate precipitation of nanometer-sized secondary phases. These precipitates strengthen the material by hindering the motion of dislocations while the β-matrix with relatively low content of β-stabilizers can give rise to a low elastic modulus. The ultimate tensile strength, yield strength, Young's modulus and elastic recoverable strain of the cold rolled plus aged specimens were measured as being between 967 and 1192 MPa, 920–1180 MPa, 48–83 GPa and 1.5–2.0%, respectively. As such, the alloy is anticipated to be promising metallic self-expansible stent material by virtue of the unique combination of extraordinarily high elastic strain, high mechanical strength, and excellent biocompatibility [1, 2].