Corrosion and Materials Degradation

The formation and evolution of secondary phases, such as sigma (σ), chi (χ), Laves, carbides (M₂₃C₆), and nitrides (Cr₂N), have a fundamental impact on the corrosion resistance of stainless steels. These stages alter the matrix’s local chemistry, compromise the passive film’s quality, and promote micro-galvanic interaction, which enhances localized corrosion issues. The thermodynamic stability, precipitation kinetics, and corrosion consequences of secondary phases in austenitic, ferritic, duplex, and lightweight (Fe–Mn–Al–C) stainless-steel systems are thoroughly reviewed and discussed in this paper. Advances in high-resolution characterization techniques, such as TEM, EBSD, atom-probe tomography, and in situ synchrotron techniques, have made it possible to map corrosion problems caused by secondary phases at the nanoscale. Computational thermodynamics (CALPHAD, DICTRA, TC-PRISMA) and emerging machine-learning models now provide quantitative prediction of phase formation and dissolution. Strategies for mitigation through alloy design, thermal treatment, and surface engineering are summarized, together with additive-manufacturing approaches for microstructural tailoring. Finally, this review highlights the integration of multi-scale modeling and sustainable alloy design to ensure phase-stable, corrosion-resistant stainless steels that enhance asset integrity and infrastructure reliability as per Sustainable Development Goals.

It goes without saying that when studying the corrosion behaviour of a component or structure, the experimental conditions should reflect the service environment to which the object will be exposed. However, all too frequently, “accelerated” conditions are used, involving applied potentials, elevated temperature, high solute concentrations, excessive strain or strain rates, etc., which complicates the prediction of the in-service behaviour or component lifetime. At best, it is necessary to extrapolate the results of these accelerated laboratory measurements to more realistic conditions, ideally based on a mechanistic understanding of the processes involved. At worst, accelerated laboratory tests may suggest corrosion processes that are not feasible or relevant to the service environment, potentially disqualifying a given material or design from consideration that would otherwise provide acceptable behaviour in service. Examples of the need to properly take into account the service environment and the potential negative consequences of accelerated testing are given for the case of the corrosion behaviour of nuclear waste container materials. For example, the use of bulk solutions to study the corrosion of copper by sulfide in the laboratory involves high sulfide fluxes and leads to localized corrosion and stress corrosion cracking mechanisms that are not possible under actual repository conditions. Similarly, accelerating the effects of γ-irradiation using high absorbed dose rates runs the risk of changing the mechanism of radiation-induced corrosion. Above all, it is imperative to develop a sound mechanistic understanding of the underlying corrosion mechanisms in order to confidently apply the results of short-term laboratory observations to the prediction of the long-term performance of nuclear waste containers.

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