Microstructure and corrosion behavior of Ti–10Mo–6Zr–4Sn–3 Nb (Ti-B12) alloys as biomedical material in lactic acid-containing Hank's solution

Due to the growing interest in Ti and its alloys in the biomedical field, Ti–10Mo–6Zr–4Sn–3 Nb (Ti-B12) alloys have promising potential for orthopedic applications. However, although much work is related to the microstructures and mechanical properties of Ti-B12 alloys, their corrosion behavior, especially in the solution containing lactic acid, is still unclear. This work investigated the microstructures and electrochemical corrosion behavior of Ti-B12 alloys in Hank's solution with varying lactic acid concentrations. As-cast, deformed, and annealed Ti-B12 alloys were used as the samples. The results show that lactic acid plays a detrimental role in the corrosion resistance of the alloys. When the lactic acid concentration of Hank's solution is 0.075 wt% (pH = 3), the Ti-B12 alloys exhibit the highest corrosion current densities of 0.055 μA·cm⁻², 0.078 μA·cm⁻², and 0.098 μA·cm⁻², for the annealed, as-cast and deformed samples, respectively. Correspondingly, in such a situation, the impedances of the passive films formed after open circuit potential are 1.46 MΩ·cm², 1.28 MΩ·cm^2, and 0.95 MΩ·cm², which is about two-thirds of those in the Hank's solution with pH of 7. The lactic acid dissolves the outer layer of the passive film, resulting in an increased density of oxygen vacancies. The annealed sample exhibits refined grains in the microstructure, crucial for enhancing corrosion resistance. The as-cast samples display coarser grains. The grains are broken and elongated in the rolling direction in the deformed sample, leading to inferior performance in corrosive environments. This research provides critical insights into the potential applications of Ti-B12 alloys in biomedical environments.