Effects of Zr content on microstructure and corrosion resistance of Ti–30Nb–Zr casting alloys for biomedical applications

Titanium alloys show attractive properties for biomedical applications where the most important factors are biocompatibility, corrosion resistance, low modulus of elasticity, very good strength-to-weight ratio, reasonable formability and osseointegration. The aim of this study was to investigate the effects of Zr content (7.5 and 15 wt%) on microstructure and corrosion resistance of Ti–30Nb–Zr as-cast alloy samples. The corrosion tests were carried out in a 0.9% NaCl (0.15 mol L−1) solution at 25 °C and neutral pH range. A horizontal centrifuged solidification set-up was used to obtain as-cast samples with a fine dendritic arrangement. In order to evaluate the corrosion behavior, electrochemical impedance spectroscopy (EIS), polarization curves and an equivalent circuit analysis were used. It was found that the as-cast microstructure tends to have the dendrite arm spacings reduced with increasing Zr content. The results have shown that the addition of Zr to a Ti–30Nb alloy has been efficient to stabilize the beta phase. The resulting impedance parameters and passive current densities have shown that the Ti–30Nb alloys sample without Zr addition presents a higher surface reactivity which can induce a better osseointegration than those containing Zr.