How a new strain transformable titanium-based biomedical alloy can be designed for balloon expendable stents

Abstract

Although largely used for numerous medical devices, the current titanium medical grades are not adapted for the manufacture of balloon expandable vascular stents due to their low plastic deformation abilities compared to stainless steels and cobalt-chromium alloys. In this study, a new biocompatible Ti-16Nb-8Mo alloy (wt.%) was designed with the objective to obtain large ductility and high strain hardening. In the alloy, a massive twinning and strain-induced martensitic transformation were observed to accommodate the plastic deformation leading to a very large plastic deformation since more than 45% of elongation at fracture were reached by tensile test. This huge plasticity, unusual for titanium alloys, is due to a complex deformation mechanism implying TWinning Induced Plasticity (TWIP) and Transformation Induced Platicicy (TRIP) effects, which were particularly investigated in such strain transformable alloy by electron backscattering diffraction (EBSD), by transmission electron microscopy (TEM) and by in-situ tensile test under synchrotron beam (SXRD).