Surface characterization of TiO2 nanotube arrays produced on Ti6Al4V alloy by anodic oxidation

A highly well-ordered TiO2 (titanium dioxide) nanotube arrays were prepared at different voltages (20 V, 30 V, 40 V, 50 V, 60 V, 80 V and 100 V) for 60 min on Ti6Al4V (titanium alloy) substrate in the ammonium fluoride-containing ethylene glycol electrolyte by a DC (direct current) power supply through AO (anodic oxidation) technique. The anatase-based TiO2 phases were observed at post-heat treatment although the titanium phase was obtained on TiO2 nanotube surfaces at post-production AO technique. Up to 40 V, the nanotube structures were uniformly distributed and the surface roughness increased. The roughness and thickness of the nanotube surfaces were measured as 7.57 nm - 47.08 nm and 0.18 mu m - 0.83 mu m, respectively. The nanotube array surfaces indicated hydrophobic properties compared to uncoated titanium surface. The hardness and elastic modulus of plain titanium alloy and TiO2 nanotube surfaces were investigated under a Berkovich indenter by a nano-indentation test device. The elastic modulus values of TiO2 nanotube surfaces were close to bone structure with respect to plain Ti6Al4V substrate. Moreover, hardness values of nanotube surfaces were measured between similar to 203.7 MPa and similar to 932.2 MPa. The adhesion properties such as critical load of the nanotube surfaces were investigated by micro scratch tester. Adhesion strengths of the nanotube surface were obtained between similar to 2.2 N and similar to 4.6 N.