Assessment of corrosion resistance of nano-structured stainless steel in marine environments

Thesis Abstract

Marine environments pose significant challenges to the longevity and structural integrity of stainless steel due to aggressive corrosion processes, which reduce the service life of maritime infrastructure and increase maintenance costs. This study aims to comprehensively assess the corrosion resistance of nano-structured stainless steel, focusing on how nanostructuring influences corrosion behavior in saline marine conditions. The primary objectives are to evaluate the corrosion rates, analyze surface morphology changes, and identify the electrochemical mechanisms underlying corrosion resistance enhancements attributable to nanostructuring. The research adopts a mixed-methods approach combining empirical laboratory experiments with field testing. The population comprises commercially available 304 and 316 stainless steel samples, which are subjected to nanostructuring via electrodeposition and severe plastic deformation techniques to produce nano-structured variants. A total of 60 samples—30 nano-structured and 30 conventional stainless steel samples, with 15 of each type tested in laboratory salt-spray chambers and 15 deployed in real marine settings for six months—are used. Data collection involves electrochemical measurements through potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), surface characterization via scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy-dispersive X-ray spectroscopy (EDS). Corrosion products are identified using X-ray diffraction (XRD). Validity and reliability of the electrochemical instruments are ensured through calibration and repeated measurements, adhering to ASTM standards. Data analysis employs statistical tools such as ANOVA to compare corrosion rates, regression analysis to model the influence of nanostructure parameters, and thematic analysis for qualitative surface morphology observations. The anticipated findings indicate that nano-structured stainless steel exhibits significantly reduced corrosion rates compared to conventional variants, with electrochemical data showing higher polarization resistance and greater impedance values. Surface analyses are expected to reveal denser passive oxide layers and fewer corrosion initiation sites in nano-structured samples. The study hypothesizes that nanostructuring enhances passive film stability and promotes uniform corrosion resistance by increasing grain boundary areas, consistent with the corrosion theories grounded in the Passive Film Theory and the Electrochemical Stability Theory. These results are hypothesized to confirm that nanostructuring refines the passivation process, thereby increasing material durability in saline marine environments. This research contributes novel empirical evidence on the tangible benefits of nanostructuring techniques applied to stainless steel for marine applications, filling a significant gap in the literature concerning long-term corrosion performance in real-world settings. It advances understanding of the microstructural-electrochemical correlations that dictate corrosion resistance, providing a scientific basis for the development of more durable, corrosion-resistant stainless steel materials. The study’s findings are expected to influence industrial practices in maritime construction and maintenance, promoting the adoption of nano-engineered steels for subsea and coastal infrastructure. In conclusion, nano-structured stainless steel demonstrates a marked improvement in corrosion resistance within marine environments, attributable to microstructural modifications that enhance passive film formation and stability. Based on the findings, the study recommends further exploration of scalable nanostructuring methods and long-term field assessment across diverse marine conditions. It also advocates for integrating nanostructuring techniques into corrosion protection standards, supporting sustainable maritime infrastructure development. Future research should investigate the synergistic effects of nanostructuring combined with coatings and other corrosion mitigation strategies to further extend the service life of marine-grade stainless steels.