Influence of anions in phosphate and tetraborate electrolytes on growth kinetics of microarc oxidation coatings on Ti6Al4V alloy
(1. Powder Metallurgy Research Institute, Central South University, Changsha 410083, China;
2. Department of Mechanical and Energy Engineering, Shaoyang University, Shaoyang 422000, China;
3. Key Laboratory of Hunan Province for Efficient Power System and Intelligent Manufacturing, Shaoyang University, Shaoyang 422000, China)
2. Department of Mechanical and Energy Engineering, Shaoyang University, Shaoyang 422000, China;
3. Key Laboratory of Hunan Province for Efficient Power System and Intelligent Manufacturing, Shaoyang University, Shaoyang 422000, China)
Abstract: The growth kinetics of microarc oxidation (MAO) coatings on Ti6Al4V alloy was studied by designing an electrolyte with low content and high content, using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and potentiodynamic polarization. The results showed that increased the spark intensity and dissolved most of the oxides at high temperatures. Then, a thicker barrier layer at the coating/substrate interface was produced, which increased the polarization resistance of the coating. at a low concentration also promoted the uniform growth of the MAO coating and the formation of hat-shaped holes in the outer deposition layer. The thickness of the MAO coatings obtained in Na2B4O7 electrolytes exhibited an exponential increase with time at spark discharge stage, while that of the MAO coating obtained in phosphate–tetraborate electrolytes showed a linear trend as the content increased.
Key words: Ti6Al4V alloy; microarc oxidation; phosphate; tetraborate; electrolyte; anions; growth kinetics