Preparation and high temperature oxidation resistance of microarc oxidation ceramic coatings formed on Ti2AlNb alloy

Microarc oxidation (MAO) was used to produce oxide ceramic coatings on Ti2AlNb alloy. The influences of NaOH and NaF additives in the electrolyte on microstructure and high-temperature oxidation resistance of MAO ceramic coatings were investigated. MAO ceramic coatings formed on Ti2AlNb alloy exhibit a volcanic-like porous structure, and consist of Al2TiO5, R-TiO2, γ-Al2O3 and small amounts of α-Al2O3, Nb2O5. NaOH additive in the electrolyte enhances the densification of ceramic coatings and the relative content of Al2TiO5. NaF additive in the electrolyte not only increases the thickness of coatings, but also promotes the formation of Al2TiO5. In the case of static oxidation at 800 °C for 100 h, MAO coatings improve high temperature oxidation resistance of Ti2AlNb alloy. The oxidized products after thermal exposure to 800 °C for 100 h in air exhibit a multiple-layered oxide structure, and are main composed of R-TiO2, γ-Al2O3 and Al2TiO5.