Fabrication of hydrophobic corrosion-resistant microarc oxidation titanium alloy through pore-sealing treatment with secondary growth of ZIF-8 seed crystals

Abstract

The inherent porous structure of Micro-arc oxidation (MAO) coatings may facilitate penetration of corrosive ions into the substrate, thereby compromising its corrosion resistance. In this work, the metal-organic framework (MOF) ZIF-8 was employed to seal the micropores in the MAO coating of titanium alloy (MAO-Ti) through a secondary growth method involved initially physically pre-loading crystal seeds into the micropores, followed by solvent thermal synthesis. Consequently, an excellent cohesive pore-sealing coating known as ZIF-8@MAO was successfully developed. The anchoring effect between ZIF-8 in the micropores and the substrate forms a solid blocking layer, which can effectively avoid the issue of traditional sealing layers detaching easily. Additionally, the arranged ZIF-8 crystals on the surface of MAO-Ti imparts excellent hydrophobicity and high stability to the alloy, evidenced by contact angle tests conducted under various solution environments, where the water contact angles (WCAs) exceeded 140°. Moreover, ZIF-8 microcrystals act as effective sealants for the micropores of MAO-Ti, effectively safeguarding the internal titanium alloy matrix against chloride ion infiltration and ensuring long-term corrosion resistance. Electrochemical tests assessing the corrosion resistance of the coatings revealed a significant improvement in the corrosion resistance of the ZIF-8@MAO pore-sealing coating compared to the primary MAO-Ti coating. The charge transfer resistance (R_ct) increased from 2.05 × 10⁴ Ω/cm² to 1.287 × 10⁹ Ω/cm², while the current density (I_corr) declined from 2.03 × 10⁻⁸ A/cm² to 2.65 × 10⁻¹³ A/cm².