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• Dental implant showed the scratches in the vertical direction made by machine. • Sandblasted surface showed the indented trace instead of mechanical scratch. • In surface by plasma electrolytic oxidation, the pore shape was different on implant parts. • Nanotubes were uniformly well-formed in the α-phase but not well in the β-phase. • The surface with pores showed low corrosion potential and high current density. In this study, the corrosion behaviors of macro/micro/nano-scale surface modifications of Ti-6Al-4V dental implant for bio-implants were investigated. For this purpose, macro/micro/nano-scale surface roughness was formed on the surface of Ti-6Al-4V alloy using plasma electrolytic oxidation (PEO), anodization, and sandblasting. Potentiodynamic and potentiostatic methods were used to investigate the corrosion behavior of the samples. The surface properties of the alloy were observed using field-emission scanning electron microscopy and X-ray diffractometry. The bulk sample exhibited scratches in the vertical direction created by the machine. The sandblasted sample showed an indented trace instead of a machined scratch. The PEO-treated sample showed different pore shapes in the screw valley, screw flank, and screw top. Nanotubes were uniformly formed in the α phase but not well formed in the β phase. In the case of nanotubes on sandblasting, the nanotubes were not well formed in the defect areas formed during the sandblasting process. In a corrosion test, the corrosion potential significantly increased with no surface treatment, whereas it significantly decreased when defects or pores were formed on the surface. The current density–time curves revealed that the sandblasted specimen showed the most unstable film behavior and in the case of the nanotube and nanotube-on-sandblasting specimens, the current density increased with time. [ABSTRACT FROM AUTHOR]

• Nanotube formation of Ti-6Al-4V alloy in electrolyte containing fluoride ion. • Uniform nanotube formed in alpha phase and irregular formed in β-phase of Ti-alloy. • Stable passivation formed on nanotube-formed surface, and corrosion resistance increased. • Corrosion occurred between α−phase and β phase. In this study, the nanotube formation and corrosion behavior of Ti-6Al-4V alloy with α - and β -phases were researched with various experimental instruments. For this study, nanotube formation on the sample was performed using the anodic oxidation method by applying a voltage of 30 V using a direct current power supply for 1 h using a 1.0 M H 3 PO 4 + 0.8 wt.% NaF solution at 25 °C. The corrosion properties of specimens were examined by potentiodynamic testing (potential range of -1000–1500 mV) in a 0.9% NaCl solution using a potentiostat. The nanotube morphology of the alloys was observed by field-emission scanning electron microscopy, X-ray diffractometry, and energy dispersive X-ray spectroscopy. The nanotubes in the α -phase were uniformly formed on the surface of the Ti-6Al-4V alloy, but nanotubes in the β -phase were irregularly formed. The nanotube-formed alloy had a wider passivation range and higher corrosion current density than the bulk alloy. The morphologies of the corrosion surfaces show that the edge trace around the β -phase was reduced, and the anatase phase increased on the corroded surface. In cross-sectioned nanotube layer after corrosion test, a deep pit was observed in the part where the nanotubes were removed. XRD analysis showed that the anatase and rutile phases were not formed in bulk alloys, but anatase and rutile phases were detected in the nanotube formed alloy, and the peak of the anatase increased on the corroded surface. From the result of potentiostatic test, the variation of current density from the beginning is almost the same, but the current density of the nanotube formed surface was slightly higher than that of non-nanotube formed surface with time. [ABSTRACT FROM AUTHOR]

• Nanotube diameter and layer formed on Ti-alloy increased as applied voltage increased. • Hydroxyapatite- and Sr-coating layer was formed thicker than that of the HA coating layer. • Surface roughness of alloy increased in order of non-, HA and Sr-, and HA-coating. • Contact angle of HA- and Sr-coating increased, as applied voltage increased. In this study, morphology of hydroxyapatite and Sr coatings deposited using radio frequency- magnetron sputtering method on nanotube formed Ti-6Al-4V alloy was researched. For this study, nanotube formation on the samples was performed using anodization and then the hydroxyapatite (HA) and Sr thin film was coated using a RF magnetron sputtering system. For characterization of nanotube surface, the surface was observed using various instruments. The diameter of the nanotube increased and the nanotube layer increased as the applied voltage increased. The anatase phases were well formed on the surface and significantly increased as the applied voltage increased. HA and Sr coating layer was formed thicker than that of the HA coating layer and nanotubes were covered with HA and Sr. The surface roughness of the alloy increased as the voltage increased in the order of non-coating, HA and Sr coating, and HA coating. The contact angle of the alloy surface decreased in non-coating and HA coating, whereas, contact angle of HA and Sr coating increased as the applied voltage increased. [ABSTRACT FROM AUTHOR]