Corrosion resistance of anodic oxides on the Ti–50Zr and Ti–13Nb–13Zr alloys

Electrochemical analyses on the biocompatible alloys Ti–50Zr and Ti–13Nb–13Zr, as-cast and heat-treated, in distinct electrolytes (simulating or not physiological media: pH 7, Ringer, PBS, phosphate buffer and Na2SO4 solutions; pH 1, H2SO4, HNO3, CH3SO3H, HClO4 and H3PO4 solutions) are reported. Analyses of the open-circuit potential values indicated that either as-cast or heat-treated samples of both alloys present the same tendency to spontaneously form an oxide film on their surfaces and that the oxide grown in the Na2SO4 solution presents better protection characteristics than those formed in the phosphate buffer, Ringer and PBS solutions, in this order. Cyclic voltammograms obtained in the Ringer and PBS solutions showed that the Ti–13Nb–13Zr alloy does not transpassivate up to potentials of 8 V (versus SCE), while the Ti–50Zr alloy presents corrosion at potentials lower than 2 V (versus SCE), indicating that this alloy is less resistant to corrosion in solutions simulating physiological conditions. The obtained pit potential values showed that the heat treatment has very little influence on the corrosion behavior of the alloys. Finally, both alloys did not present transpassivation at potentials up to 8 V (versus SCE) in the H2SO4, HNO3, CH3SO3H and H3PO4 solutions; however, when immersed in the HClO4 solution the Ti–50Zr alloy underwent pit corrosion while the Ti–13Nb–13Zr alloy remained corrosion resistant in this potential range.