Impact of ruthenium on microstructure and corrosion behavior of β-type Ti–Nb–Ru alloys for biomedical applications

Corrosion behavior and microstructure of as-cast metastable b-type Ti-20Nb-xRu (x = 0, 0.5, 1.0, 1.5 at.%) have been investigated using linear polarization and transmission electron microscopy (TEM), respectively. Ruthenium (Ru) was confirmed to be a b-phase stabilizer as a titanium (Ti) alloying element which served to suppress both x precipitation and elemental segregation; the prominence and degree of elemental segregation between the Nb-rich primary dendrites and the interdendritic areas rapidly decreased with minor Ru addition, yielding a more homogenous microstructure overall. Additionally, even minimal Ru additions significantly altered the corrosion potential (Ecorr), yielding a 0.3 V shift in the noble direction over the Ru-free controls, along with a comparable shift in the potential at which the initial passive region begins to fail (Einc). The present result suggests Ru addition can confer a greater resistance to corrosion in b-Ti alloys.