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Study of the susceptibility to corrosion on Ti6Al4V alloy coating with hydroxypatite in simulated body fluid (SBF)

Abstract:

In this study the susceptibility to corrosion was evaluated in a Ti6Al4V alloy with three coatings of hydroxyapatite: R1 = thermal passivation 600 °C, 1 hr, 7 days in a simulated body fluid solution (SBF) concentrated with calcium ions (SBFCa); R2 = thermal passivation 600 °C, 1 hr, 7 days in saline phosphate buffer solution (SBFP) and R3 = NaOH 5M treatment, 70 °C, 24 h, thermal passivation 600 °C, 1 hr, 7 days in SBSCa. Then, these samples were exposed to electrochemical tests in SFCS for 0, 120 and 240 h and analyzed by Scanning Electron Microscopy (SEM) and X-ray Spectroscopy in the Energy Dispersive (EDS), revealing the formation of a nonuniform layer apatite on the surface of the alloy. However, R3 presented a more extended apatite layer on the surface, associated with the formation of a hydrogel layer of titanium sodium more bioactive than the titanium oxide layer when exposed to a SFCS by 7 days. Potentiodynamic polarization curves showed that after 240 h SBF immersion, the coating R2 proved more resistant to corrosion than R1 followed by R3. The characterization of the products formed on the electrochemically tested coatings showed that after 240 hr of immersion, the coating R1 had higher bioactivity than R2, followed by R3, associated with the property of the formed apatite layer, which acts as precursor in precipitation of new calcium phosphate, offering the best combination of properties for biomedical applications.