Effect of fluoride on the corrosion behavior of nanostructured Ti-24Nb-4Zr-8Sn alloy in acidulated artificial saliva

The surface of titanium dental implants is highly susceptible to aggressive fluoride ions in the oral environment. Nanotechnology has proven an effective approach to improve the stability and corrosion resistance of titanium by applying a passive film. In this study, we investigated the effects of fluoride on the corrosion behavior of nanostructured (NS) Ti-24Nb-4Zr-8Sn (Ti2448) alloy in acidulated artificial saliva (AAS) at 37 °C, and then conducted comparisons with its coarse grained (CG) counterpart. Electrochemical techniques, such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), as well as surface analysis including X-ray photoelectron spectroscopy (XPS) with argon ion sputtering, and scanning electronic microscopy (SEM) were employed to evaluate the effects of fluoride on sensitivity to pitting and the tolerance of Ti2448 to fluoride in AAS solution. The results demonstrate that corrosion current density increased with F− concentration. In all respects, the NS Ti2448 alloy presented corrosion resistance superior to that of its coarse grained (CG) counterpart at low F− concentrations (≤0.1%). Furthermore, a high content of F− (1%) was shown to promote the active dissolution of both alloys by increasing the rate of corrosion. Following immersion in the fluoridated AAS solution for 60 days, a tissue-friendly compound, Ca3(PO4)2, was detected on the surface of the NS when F− = 0.01% and Na2TiF6 was identified as the main component in the corrosion products of the CG as well as NS Ti2448 alloys when F− = 1%. High concentrations of F− produced pitting corrosion on the CG alloy, whereas NS Ti2448 alloy presented general corrosion in the form of lamellar separation under the same conditions. These findings demonstrate the superior corrosion resistance of the NS Ti2448 alloy as well as lower pitting sensitivity and higher tolerance to fluoride due mainly to grain refinement.