Characterization and fatigue damage of TiO ₂ layer on spark-anodized titanium before and after hot water treatment

Spark anodizing of titanium in phosphoric acid solution produced porous TiO ₂ layer on its surface, and subsequent hot water treatment was performed to modify the surface characteristics of resultant oxide layer. Results show that water treatment not only transformed the original amorphous TiO ₂ into crystalline anatase, but also resulted in a nanostructured surface. Also, the influence of spark anodizing treatment on fatigue behavior of titanium and the fatigue damage of TiO ₂ layer before and after water treatment was investigated. Results show that the present spark anodizing at 200 V had no significant influence on the fatigue life of titanium. However, significant fatigue damage was induced in the TiO ₂ layer. Before water treatment, tensile fatigue loading first caused transverse cracking to occur in the TiO ₂ layer, and then inclined spallation of oxide layer driven by slip bands in the titanium substrate was observed at a maximum cyclic stress of 140 MPa. In comparison, after water treatment, TiO ₂ layer exhibited severer fatigue damage, and extensive cracking and delamination of TiO ₂ layer occurred at a lower maximum cyclic stress of 120 MPa.