Effect of NaOH Concentration on the Microhardness and Corrosion Resistance of Titanium by Acid-Hydrothermal Method

To enhance the microhardness and corrosion resistance of modified pure titanium, TiO₂ nanostructure has been prepared on titanium substrate by acid-hydrothermal method. The morphology of the titanium surface underwent change from nanosheets to nanorods with the increase of NaOH concentration, which was performed by the scanning electron microscope (SEM). A mixture of the anatase TiO₂ and rutile TiO₂ were formed on the synthesized titanium surface measured by X-ray diffraction (XRD). Microhardness was measured by microhardness tester and the hardness rose sharply and then declined gradually as the increase of NaOH concentration, showing a considerably high hardness value of 361HV with NaOH concentration of 5 M (PAN-5). In addition, the corrosion resistance was examined in SBF by electrochemical methods. The polarization curve demonstrated that the corrosion resistance was optimal when the NaOH concentration was 5 M. Therefore, the hardness and corrosion resistance of titanium, with the appropriate morphology of nanorods, were optimized as the NaOH concentration was 5 M.