Enhanced salt spray corrosion resistance of Fe-based amorphous coatings via sealing treatment

Abstract Fe-based amorphous coatings are promising for corrosion protection in marine environments, yet their long-term performance after sealing treatment under salt-spray exposure remains unclear. In this study, two atmospheric plasma-sprayed Fe-based amorphous coatings, APS3 and APS5, prepared at different H ₂ flow rates, were sealed using a brush-applied nano-alumina sealant. The microstructure and corrosion behavior of the coatings, before and after sealing, were systematically evaluated by porosity analysis, scanning electron microscopy, x-ray diffraction, potentiodynamic polarization, and electrochemical impedance spectroscopy during 3 weeks of salt-spray exposure. The results showed that the as-sprayed coatings retained a predominantly amorphous structure and exhibited porous features. Sealing treatment reduced the porosity of APS3 and APS5 from (4.76 ± 0.5)% to (2.64 ± 0.5)% and from (3.32 ± 0.5)% to (1.58 ± 0.5)%, respectively. During the first two weeks of exposure, the sealed coatings showed higher corrosion potentials, lower corrosion current densities, and larger impedance responses than the corresponding unsealed coatings. APS5 consistently exhibited superior corrosion resistance, attributed to its lower porosity and denser microstructure. After 21 d, sealant degradation and detachment became evident, accompanied by a marked decline in corrosion resistance. These findings indicate that sealing treatment can effectively improve the salt-spray corrosion resistance of Fe-based amorphous coatings for approximately two weeks, and provide guidance for the design and durability evaluation of protective coating systems intended for marine service environments.