EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Despite Ti alloys are biocompatible and non-allergenic, their use in blood contact applications including stent was rarely reported, mainly due to their low strength-ductility trade-off. In this work, two strengthening strategies were investigated to achieve Ti alloys with required mechanical properties for stent applications. The first tackled the increase of oxygen content in the TWIP (twinning induced-plasticity)/TRIP (transformation induced-plasticity) Ti-12Mo alloy. The second, aimed to design Ti-Mo-Fe alloys to combine TWIP/TRIP effects. Ti-12Mo-0.04O, Ti-12Mo-0.18O, Ti-8Mo-2Fe, Ti-9Mo-1Fe and Ti-10.5Mo-1Fe (wt.%) were produced by casting, swaging and solution treatment. Mechanical properties were assessed by tensile tests, while microstructures and deformation mechanisms by optical microscopy, X-Ray diffraction, transmission electron microscopy and electron backscatter diffraction. Hemocompatibility and direct cytotoxicity (endothelial and smooth muscle cells) were investigated. Results shown that the increase of O content in Ti-12Mo was responsible for an increase of nominal strength from 687 to 841 MPa, and for a decrease of uniform elongation from 39 to 28%. The increased strength of 0.18O alloy is associated to its superior work hardening rate (WHR) caused by the solid solution strengthening effect of oxygen. All the alloys showed plastic deformation by twinning and stress-induced martensitic (SIM) α" transformation. The twin density and area fraction of SIM α" were different for each alloy, affecting their WHR and mechanical properties. Concerning Fe, it resulted effective in strengthening Ti-Mo alloys. Ti-8Mo-2Fe and Ti-10.5Mo-1Fe exhibited high strength (986 and 823 MPa) and large uniform elongation (22 and 34%). The two strengthening strategies studied in this work leaded to Ni-free Ti alloys showing the high strength and high ductility required for stent applications. In particular, Ti-8Mo-2Fe appeared as potential candidate, showing strength comparable to L605 and elongation to failure up to 30%.