Surface Characteristics and Indentation Deformation of Porous Anodic TiO2 Layer Before and After Hot Water Treatment

Hot water treatment was performed to modify the surface of porous TiO2 layer prepared by anodic spark oxidation technique for better biocompatibility. The oxide layer without water treatment exhibited a porous surface with few nanometer features and consisted of poorly crystallized oxides. During water treatment, the poorly crystallized oxides were transformed into crystalline anatase gradually and numerous nanoparticles formed on the oxide surface, leading to increased surface roughness at the nanoscale. The indentation deformation behaviors of oxide layer before and after water treatment were investigated and compared. Results show that under the indentation load, the untreated anodic TiO2 layer exhibited good adhesion to the substrate. In contrast, after water treatment, apparent oxides pile-up and spallation were observed around the indentation, indicating decreased adhesion strength.