Effect of plasma nitriding on structure and biocompatibility of self-organised TiO2 nanotubes on Ti–6Al–7Nb

Abstract

TiO₂ nanotubes formed by anodic oxidation of Ti–6Al–7Nb were nitrided in a nitrogen plasma. The samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nano hardness testing (NHT) and field emission scanning electron microscopy (FESEM). The corrosion behaviour of the substrate, plasma nitrided substrate, substrate with self-organised TiO₂ nanotubes (TNT) and with plasma nitrided TiO₂ nano tubes (TNT + PN) was investigated through electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies in simulated body fluid (Hanks' solution). The investigations show that the native oxide on the sample is replaced by a self assembled nano array by an anodisation process. XPS spectra of the TNT plasma nitrided sample show the presence of oxy nitride and nitride on the surface. The nano hardness of the samples was increased after nitriding. FESEM images of samples immersed in Hanks' solution show that growth of calcium phosphate phases is more and the size of the deposits are larger on TNT and nitrided TNT samples, as compared to the untreated substrate. XPS spectra of TNT and nitrided TNT samples immersed in Hanks' solution show a higher amount of calcium, phosphorous and oxygen than on the substrate. Electrochemical studies show that nitriding decreases the corrosion resistance.