Growth mechanism of anodic oxide film on Ti6Al4V alloy

The growth mechanism of anodic oxide film on Ti6Al4V in HF and CrO3 solution was investigated. The surface morphology of the oxide film was observed by FESEM, and the V-t and i-t curves in different electrolytes were measured with an electrochemistry workstation. The results show that there exist two critical values of HF concentration to form a compact-porous structure under certain CrO3 concentration and applied current. A compact film is formed when the HF concentration is below the minimum critical value and a porous film is formed when the HF concentration is greater than the maximum critical value. The compact-porous structure can be obtained in solutions with HF concentration between the two critical values. It experiences a continuous nucleation process in the solution without HF and the film presents a nonporous structure. An instantaneous nucleation process is found in solutions with HF concentration ranged from 0.3% to 4.4% and the film is porous. The formation of titanium alloy anodic oxide film follows the mechanism of 3D nucleation.