Anodic growth and pre-calcification on β-Ti-40Nb alloy: Effects on elastic modulus, electrochemical properties, and bioactivity

This study evaluated the surface optimization of β-Ti-40Nb alloy in terms of corrosion and bioactivity properties. Electrochemical anodization at different voltages was used to synthesize (Ti,Nb)O2 nanostructures (nanopores (NPs)) and (nanotubes (NTs)) on samples' surfaces, allowing the analysis of their influence on performances related to those properties. Then, (Ti,Nb)O2 NPs and NTs were annealed at 550 °C to crystallize the previously obtained amorphous (Ti,Nb)O2 into a mixture of anatase and rutile. Also, a pre-calcification process (PC) was applied on annealed (Ti,Nb)O2 NPs and NTs. SEM micrographs showed the presence of NTs (10 V) and NPs (20 V) after anodization. After annealing, the morphology of (Ti,Nb)O2 NPs and NTs remained constant for both diameter and length. XRD analysis confirmed that as-anodized amorphous (Ti,Nb)O2 was crystallized, after annealing, into a mixture of anatase-rutile phases. Corrosion properties were evaluated through the open circuit potential (OCP), potentiodynamic polarization curves, and electrochemical impedance spectroscopy (EIS). Samples were immersed in a simulated body fluid (SBF) solution for one to 14 days to assess the bioactivity. The bioactivity evaluation was carried out by mass gain. Also, the amount of apatite precipitated on the sample's surface was determined through SEM-EDS. The results showed that PC samples presented similar corrosion properties compared to the annealed samples. However, PC processing improved the bioactivity (apatite formation) of (Ti,Nb)O2 NTs and NPs modified β-Ti-40Nb alloy.