Significant improvement of corrosion resistance in FeCoNiCrMo coating by in-situ growth of FeNi-LDH

• In-situ FeNi-LDH film formation effectively mitigate surface defects within the FeCoNiCrMo HVAF sprayed coating firstly. • FeNi-LDH with higher Ni content increases interlayer spacing and reduces chloride ion adsorption energy. • The dual anti-corrosion effect in 3.5 wt% NaCl solution was achieved through the synergy of LDH and HEA passivation film. High-entropy alloy (HEA) coatings fabricated via high velocity air–fuel spraying exhibit promising potential for corrosion resistance applications. However, surface defects such as pores and cracks significantly limit their practical utility in marine environments. To address this issue, this study employed a hydrothermal treatment to in-situ grow FeNi layered double hydroxide (FeNi-LDH) on HEA coatings, aiming to repair microscopic surface defects. By modulating the concentration ratio of Fe 3+ to Ni 2+ ions in the hydrothermal solution, LDHs with varying interlayer cation ratios were successfully synthesized, and their effects on the corrosion resistance of the composite coatings were systematically investigated. Electrochemical tests demonstrated that the optimized Fe 1 Ni 4 LDH/HEA composite coating exhibited remarkable corrosion resistance in 3.5 wt% NaCl solution, with the corrosion current density decreasing by more than one order of magnitude (from 4.90 × 10 −6 to 2.18 × 10 −7 A/cm 2 ) compared to the pristine HEA coating. Characterization (TEM/XPS) revealed that FeNi-LDH stores Cl − in its interlayers, while synergistic HEA oxide film/Ni(OH) 2 passivation enhances protection. DFT calculations further confirmed the weak adsorption energy between Fe 1 Ni 4 LDH and Cl − , explaining the excellent chloride resistance. This work provides a novel strategy for defect repair and corrosion resistance enhancement in HEA coatings through in-situ LDH growth.