Electrochemical corrosion behavior of niobium alloys as metallic bio-implants

Alloying is one of the most important methods to improve the corrosion resistance and mechanical properties of metals. Previous studies show that the corrosion resistance of niobium Nb could be increased by Ta alloying in alkali solutions. Nevertheless, compared with Ti alloys, only a few Nb alloys were reported to increase their corrosion resistance. In this work, the mechanical properties and microstructure of Nb-Ta-Re, Nb-Re, Nb-Pd, and Nb-Pt alloys were studied by nano-indentation measurements and X-ray diffraction, respectively. The corrosion behavior of these alloys was compared by electrochemical methods, including open circuit potential measurement, potentiodynamic, and electrochemical impedance spectroscopy, in phosphate buffered saline (PBS) and sodium fluoride solutions. The properties of the passive films formed on these alloys were characterized by X-ray photoelectron spectroscopy. The results showed that Ta or Re alloying could increase the hardness and elastic modulus of Nb, however, these alloying elements did not significantly modify the phase structure of Nb. All of these Nb alloys show high corrosion resistance in PBS and NaF-containing PBS solutions, and no pitting behavior was observed. Re and Ta alloying could further increase the corrosion resistance of Nb, however, small amounts of Pd and Pt alloying did not significantly affect the corrosion resistance of Nb.