Coating Formation on Ti-6Al-4V Alloy by Micro Arc Oxidation in Molten Salt

Abstract

Micro Arc Oxidation (MAO) is an electrochemical surface treatment process to produce oxide protective coatings on some metals. MAO is usually conducted in an aqueous electrolyte, which requires an intensive bath cooling and leads to the formation of a coating containing impurities that originate in the electrolyte. In the current work, we applied an alternative ceramic coating to the Ti-6Al-4V alloy using the MAO process in molten nitrate salt at a temperature of 280 °C. The obtained coating morphology, chemical and phase composition, and corrosion resistance were investigated and described. The obtained results showed that a coating of 2.5 µm was formed after 10 min of treatment, containing titanium oxide and titanium‒aluminum intermetallic phases. Morphological examination indicated that the coating is free of cracks and contains round, homogeneously distributed pores. Corrosion resistance testing indicated that the protective oxide coating on Ti alloy is 20 times more resistive than the untreated alloy.

Microstructure and Wear Properties of Micro Arc Oxidation Ceramic Coatings

“…Wei Song [7] investigated the influence of a stable solid electrolyte mixed with a cellulose additive on the tribological performance of micro arc oxidation coatings. In general, micro arc oxidation is conducted in an aqueous electrolyte, however, Alexander Sobolev [8] applied an alternative MAO ceramic coating to a Ti-6Al-4V alloy in molten nitrate salt at a temperature of 280 • C. Not only the electrolyte type, but also the temperature of the electrolyte had a great influence on the coating quality. Wang Xuefei [9] studied the characterization of micro arc oxidation coatings on an aluminum alloy under different electrolyte temperatures, and found that the thickness and growth rate of the films decreased with the increase in electrolyte temperature, which led to a poor corrosion behavior.…”

Comparative Adsorption of Tungsten and Silicon Oxides by Alumina Matrix

“…Plasma electrolytic oxidation (PEO) as a rule is used to obtain oxides or mixed coatings on aluminium, titanium, magnesium alloys by using aqueous solutions of salts with polymeric anions – silicates 1, phosphates, tungstates, borates of alkali metals. In recent years, a new promising method of obtaining anticorrosion coating on the Ti−6Al−4V alloy in molten nitrate salt at a temperature of 280 °C was proposed …”

Study of the Effect of Current Pulse Frequency on Ti-6Al-4V Alloy Coating Formation by Micro Arc Oxidation

“…The basic principle of the MAO technology is an application of a high voltage between the treated metal and the electrode. During the process, micro-arc discharge migration points appear on the surface lead to the oxide coating formation [5,6,7,8]. Usually, MAO treatment is suitable for the enhanced mechanical properties and corrosion resistance of the alloys’ surface [9,10,11].…”