Advanced Characterization of Beta Ti and Mg-based Alloys for implant applications

Abstract

The addition of Nb to Ti yields to the stabilization of the β phase (bcc), and the addition of Zr to the Ti-Nb system increases the β stabilizing effect and lead to a decreasing in modulus (E = 55 to 80 GPa). Mg-based alloys usually show low elastic modulus values as well around E ~ 45 GPa, being an attractive option for temporary implants is small parts. Nanostructured Mg-Zn, Mg-Zn-Ca, Mg-Li-Y and Mg-Y-RE alloys system processed through severe plastic deformation by high pressure torsion (HPT) were obtained and characterized as well, showing nanorystalline grains, depending on the composition. In addition, β Ti alloys obtained by HPT were characterized in comparison with thin films by sputtering of β Ti-Nb-based alloys for biomedical applications with nanograins from the β Ti phase, and nanometric precipitates of w and a phases. New processing routes can be used to obtain metallic biomaterials for implant with suitable properties, such as selective laser melting (SLM) which is a AM process that produce a metal parts by melting the micrometric metal powder layer-by-layer. In this context, the metastable β Ti-15Nb alloy (wt.%) appears, processed through selective laser melting (SLM) and arc melting, since this is free of cytotoxic elements and shows lower Young modulus down to 60 GPa. Chemical, structural, and morphological analyses were performed by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and atomic force microscopy (AFM). The characterization was carried out by scanning and transmission electron microscopy (STEM) coupled with energy-dispersive X-ray spectroscopy (EDS) and transmission electron microscopy (TEM) coupled to ASTAR - automatic crystal orientation mapping (ACOM). The Mg-1Zn-0.5Ca and Mg-4Y-3RE alloys displayed low strain rate sensitivity and are prone to strain localization during high pressure torsion processing. Non homogeneous grain refinement was obtained along radial distance and severe corrosion localization takes place in different levels depending on the Mg-based alloy composition. The application of HPT on the P/M samples generated nanostructured β-Ti alloys without porosity and with a grain size of approximately 50 nm. Magnetron sputtering has proved to be an effective technique for alloying relatively large amounts of immiscible Mg to Ti-Nb and in nanoscale.