Effects of NaOH Concentration on Section Structures of Oxide Films Based on TC4 by Anodic Oxidation Process

Abstract

The section structure and growth mechanism of oxide films on titanium alloys Ti-6Al-4V (TC4) in the oxalate, silicate and phosphate hybrid electrolyte system by anodic oxidation method were investigated. Using TC4 as anodic, stainless steel as cathode, oxide films on the surface of TC4 titanium alloy were prepared by anodic oxidation process. X-ray diffract meter, spiral-micrometer, eddy current thickness meter and scanning electron microscope were used to measure the crystal structure, thickness, microstructure and chemical composition of the film . The experimental results indicate that NaOH concentration has almost no effects on the crystal structure of oxide films which are amorphous state. The oxide films on TC4 grow through three stages. At anodic oxidation primary stage, a thicker TiO2films on TC4 are able to form due to an abundant oxygen atmosphere. At anodic oxidation middle stage, a middle TiO1.5films form due to a not enough oxygen atmosphere. At anodic oxidation latest stage, a thin TiO1.5films form due to a heavily insufficient oxygen atmosphere. With NaOH concentration increasing, the ingrowth velocity (VOA) of the interface between TC4 and oxide film is faster than dissolution rate (VAD) of the surface oxide film resulting in a slight oxide film growth. The thickness of oxide film no longer varies when VOAis equal to VAD.