Chloride Ion-Induced Passive Film Breakdown in 18%Ni High-Strength Steel | | #WorldResearchAwards

Introduction

The corrosion resistance of ultra high strength steels is a critical issue for their reliable application in marine, aerospace, and defense environments. Among them, 18%Ni high strength steel is widely used due to its excellent mechanical performance, yet it remains vulnerable to chloride induced corrosion. Chloride ions are known to destabilize passive films, promote localized corrosion, and reduce long term durability. Understanding how different chloride concentrations influence corrosion behavior and passive film characteristics is therefore essential. This research focuses on the systematic investigation of corrosion mechanisms and passive film evolution of 18%Ni high strength steel in NaCl solutions with varying chloride ion concentrations, providing insight into degradation processes under aggressive environments.

Experimental Design and Corrosion Evaluation

The corrosion behavior of the steel was comprehensively evaluated through standardized chemical immersion tests and electrochemical measurements. Immersion tests conducted under controlled conditions allowed for the assessment of corrosion rates and surface degradation over extended exposure. Electrochemical techniques, including electrochemical impedance spectroscopy and Tafel polarization, provided quantitative information on charge transfer resistance, corrosion current density, and overall electrochemical stability. This combined methodology ensured a reliable evaluation of corrosion kinetics under increasing chloride ion concentrations.

Electrochemical Response in Chloride Environments

Electrochemical results demonstrate a strong dependence of corrosion behavior on chloride concentration. As chloride content increases, polarization resistance decreases significantly, indicating reduced protection efficiency of the passive layer. Simultaneously, corrosion current density increases, confirming accelerated anodic dissolution. These findings highlight the aggressive role of chloride ions in disrupting electrochemical equilibrium and promoting active corrosion on the steel surface.

Passive Film Semiconducting Properties

The semiconducting behavior of the passive film was analyzed using Mott–Schottky measurements. The results reveal a systematic shift in flat band potential toward more positive values with increasing chloride concentration. This shift indicates a higher density of point defects within the passive film, which compromises its stability. The increase in defect concentration weakens the self healing ability of the passive layer, making it more susceptible to localized breakdown and pitting initiation.

Microstructural Evolution and Corrosion Products

Microstructural observations show that pitting corrosion dominates the degradation mechanism in chloride containing solutions. The corrosion products evolve from loose and porous outer layers composed mainly of α FeOOH and γ FeOOH to denser inner layers consisting of Fe3O4 and β FeOOH. The formation of these dense inner corrosion products plays a dual role, initially slowing anodic reactions by acting as a diffusion barrier, while still reflecting the progression of localized corrosion damage.

Mechanism and Research Implications

The overall corrosion mechanism is governed by the interaction between chloride ions and the passive film. Higher chloride concentrations increase defect density, destabilize the passive layer, and promote pit nucleation and growth. Although dense corrosion products can locally inhibit anodic reactions, they cannot fully prevent degradation under aggressive chloride conditions. The findings of this research provide valuable insights for materials design, surface treatment strategies, and predictive models aimed at improving the corrosion resistance of high strength steels in chloride rich environments.

Hashtags

#corrosionresearch #materialsengineering #electrochemicalanalysis #passivefilm #chloridecorrosion #steelresearch #pittingcorrosion #surfacechemistry #electrochemistry #materialsdegradation #metallurgy #engineeringresearch #advancedmaterials #researchinnovation #scientificstudy #worldresearchawards #worldresearchawards2025 #worldresearchawards_global #worldresearchawards_science #worldresearchawards_engineering

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