Corrosion and Materials Degradation

Comprehensive data are presented for corrosion losses of mild steel exposed for up to 5 years, all obtained from exposing steel coupons at one specific severe marine exposure site on the Pacific Ocean coast. The test programme considered the effects of duration of exposure, inclination, orientation, height, shielding, and coupon variability, using multiple, nominally identical mild steel coupons, all under a single local climatic regime. Such a controlled, consistent, natural environment permits unique, valid comparison of the various influences, both for short-term and longer-term exposures, unlike previous tests of some parameters conducted in the short term at disparate sites. In contrast to coupons exposed only on one side, boldly exposed double-sided coupons corroded severely within 3 years. The effects on corrosion behaviour between individual coupons exposed at different heights and vertical continuous single strips of steel are described. Also reported are corrosion losses for continuous strips and for a series of coupons oriented in different directions. Observations of variability in corrosion losses for nominally identically exposed steel coupons are reported. The effect on corrosion losses with continued exposure to 5 years is reported and compared with information available in the literature. Full article

With the increasing number of existing buildings, the implementation of durability-preserving repair procedures is becoming increasingly important. The chemical re-alkalization (CRA) enables the protection of reinforced concrete structures exposed to carbonation by maintaining or restoring the alkalinity in the concrete through the application of an alkaline mortar, such as hybrid alkali-activated binders (HAABs). However, the process of CRA is still insufficiently understood, which means that the requirements for the repair mortars can only be roughly formulated. This paper therefore investigates the process of CRA using laser-induced breakdown spectroscopy (LIBS). Based on the quantitative results of potassium transport in the composite system, a time-dependent attenuation factor can be determined that allows for the adaptation of Fick’s second law of diffusion previously used to predict CRA. The attenuation factor provides further insight into the course of potassium transport, which, based on the results, never follows an ideal diffusion process. Adjusting the diffusion law allows for an improved prediction of the maximum achievable re-alkalization depth depending on the repair mortar, where a potassium content of, e.g., 2.3 wt% leads to a complete re-alkalization of 16 mm. The present study demonstrates the potential of LIBS to quantitatively represent CRA for the first time thus providing new insights into potassium transport and the dynamics of the process. Full article

Polymer-bonded Nd–Fe–B and Sm–Fe–N magnets have excellent magnetic properties, but their corrosion resistance is inferior. Polymer-bonded magnets, the binary alloys Nd–Fe and Sm–Fe, and the metals Fe, Nd, and Sm were investigated in electrolytes with a pH range of 1.8 to 12.8. Potentiodynamic polarisation measurements showed that these materials corrode in acidic (H₂SO₄) and near-neutral (Na₂SO₄ and NaCl) electrolytes. Iron passivates at pH > 9, but Nd and Sm passivate only in strongly alkaline electrolytes (pH > 12). The alloys and magnets combine the characteristics of the individual metals. Scanning electron microscopy with energy-dispersive X-ray spectroscopy characterised the surface layers before and after electrochemical measurements. The speciation and the depth distribution of elements in the surface layers were analysed using X-ray photoelectron spectroscopy. In the H₂SO₄, a non-protective layer was formed. In NaCl, the corrosion products were more abundant, consisting of a mixture of oxides, hydroxides, and chlorides, while in NaOH, an oxide/hydroxide layer was formed. The corrosion product layers formed in the H₂SO₄ and NaCl electrolytes were significantly thicker for the Sm–Fe–N magnet than for the Nd–Fe–B magnet. Understanding the differences and similarities in the electrochemical behaviour of magnets in various electrolytes is essential to overcoming corrosion-related problems. Full article

Chlorides have long been held responsible for the initiation and progression of the corrosion of reinforcing steels in concrete structures, with higher concentrations assumed to cause earlier and more severe subsequent reinforcement corrosion. However, extensive field observations and detailed experimental results show that, in well-compacted, low-permeability concretes, reinforcement corrosion often does not occur even in the presence of high concentrations of chlorides. If corrosion does occur, it has been observed as pitting (and crevice) corrosion primarily at air voids in the concrete at the steel–concrete interface. Herein, it is shown that this is consistent with thermodynamic principles (Pourbaix) for the pitting of steel in practical concretes with high pH and air voids, irrespective of chloride concentration. Any subsequent corrosion becomes inhibited, in part through the formation of corrosion products. The experimental observations also show that there is a separate, concurrent process of the dissolution of calcium hydroxide and its leaching from the concrete. The rate of dissolution is accelerated proportionally to the concentration of chlorides. This is the primary mechanism for longer-term reinforcement corrosion, eventually producing circum-neutral pH at the steel and thereby setting up the thermodynamics permitting general corrosion. The findings question the relevance of a critical chloride concentration as an indicator of the commencement of reinforcement corrosion. Concrete permeability, remaining alkali reserves (or pH), and physical observation of evidence of rust damage are better indicators. Full article

This study investigates the effectiveness of calcined magnesium–aluminium layered double hydroxide (CLDH) as a functional additive for mitigating carbonation-induced corrosion in alkali-activated slag concrete (AASC). Mixtures incorporating different CLDH contents (0%, 2%, 4%, 6%, and 8%) were evaluated under accelerated CO₂ exposure (3%, 65% RH, 25 °C) for 90 days. Mechanical characterisation was carried out through 28-day compressive strength tests to assess the potential impact of CLDH on the structural performance of the material. Performance characterisation included electrochemical impedance spectroscopy (EIS) to assess the corrosion of embedded steel, phenolphthalein spraying to determine the carbonation depth, and complementary techniques such as X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and scanning electron microscopy (SEM/EDX) for assessments of the microstructural evolution. The results demonstrate that CLDH significantly enhances resistance to CO₂ ingress, increasing the polarisation resistance (Rp) to over 55 kΩ·cm² (at 6% CLDH) and reducing the carbonation depth by more than 50% compared to the reference mix. These improvements are attributed to the memory effect-induced regeneration of LDH-type lamellar phases, controlled release of OH⁻ and CO₃²⁻ anions, and progressive densification of the microstructure, thereby limiting the ingress of aggressive agents. The optimal dosage was identified as 6%, as higher contents offered no further improvement and evidenced the formation of residual phases such as MgO. This work highlights the potential of CLDH as an effective and sustainable strategy to enhance the durability of alkali-activated cementitious materials against degradation processes driven by carbonation and corrosion. Full article

This research investigates the impact of incorporating montmorillonite-based nanoclay additives on the anti-corrosive properties of a polyester/triglycidyl isocyanurate (polyester/TGIC) powder coating on phosphated steel. The self-repairing capability facilitated by the swelling and expansion of nanoclay was demonstrated to enhance the corrosion resistance of the coatings significantly. A statistical Mixture Design methodology was employed to establish the optimal combination of nanoclay dosage and coating film thickness. Nineteen experiments were conducted using Design of Experiments, and two regression models were developed using the measured polarization resistance (R_p) and specular gloss values as responses. The mathematical maximization of the R_p value predicted an optimal nanoclay dosage of 4.1% with a corresponding film thickness of 80 µm. Statistical and experimental verification validated the results obtained from the regression models. Notably, the optimized coating demonstrated an R_p value one order of magnitude higher than the coating with 4% nanoclay and a standard film thickness of 60 µm. The behavior of the newly developed coatings was analyzed and compared through measurements of open circuit potential, polarization resistance, and electrochemical impedance spectroscopy. The findings confirm the substantial improvement in the anti-corrosive and self-repairing properties of the polyester/TGIC powder coating with the incorporation of montmorillonite-based nanoclay additives. Full article

Corrosion has a significant impact on the economic and environmental sustainability of metal-based infrastructure and products. This position paper explores the intrinsic relationship between corrosion protection and sustainability, examining the economic costs, environmental impacts and technological strategies involved. While corrosion results in resource waste, energy loss, and increased CO₂ emissions, effective corrosion management can extend the service life of metallic components, thus preserving resources and minimizing environmental burden. The approaches such as Total Cost of Ownership (TCO) and Life Cycle Analysis (LCA) can provide a framework for selecting the most cost-efficient and environmentally friendly corrosion protection method in view of the required lifetime. The paper emphasises the crucial role of material selection, design optimization, recyclability and environmentally friendly coatings. Regulatory pressures and new trends such as machine learning are also discussed. Achieving sustainability goals requires greater awareness, education, interdisciplinary collaboration, and continued innovation in corrosion protection strategies. Full article

Corrosion of steel reinforcement is one of the primary causes of deterioration in reinforced concrete structures, significantly impacting their durability and structural performance. This review comprehensively examines various techniques used to evaluate rebar corrosion, categorizing them into electrochemical, physical, and advanced non-destructive methods. Each method is discussed with respect to its operational principles, advantages, limitations, and field applicability. This comparative overview aims to support the selection of suitable evaluation strategies tailored to diverse structural conditions. Full article

We investigated the protective properties of ultrathin laminated coatings, comprising three pairs of Al₂O₃ and TiO₂ sublayers with coating thicknesses < 150 nm, deposited on AISI 310 stainless steel (SS) and Si (100) substrates at 80–500 °C by atomic layer deposition. The coatings were chemically etched and subjected to corrosion, ultrasound, and thermal shock tests. The coating etching resistance efficiency (R_e) was determined by measuring via XRF the change in the coating sublayer mass thickness after etching in hot 80% H₂SO₄. The maximum R_e values of ≥98% for both alumina and titania sublayers were obtained for the laminates deposited at 250–400 °C on both substrates. In these coatings, the titania sublayers were crystalline. The lowest R_e values of 15% and 50% for the alumina and titania sublayers, respectively, were measured for laminate grown at 80 °C on silicon. The coatings deposited at 160–200 °C demonstrated a delay in the increase of R_e values, attributed to the changes in the titania sublayers before full crystallization. Coatings grown at higher temperatures were also more resistant to ultrasound and liquid nitrogen treatments. In contrast, coatings deposited at 125 °C on SS had better corrosion protection, as demonstrated via electrochemical impedance spectroscopy and a standard immersion test in FeCl₃ solution. Full article

Ultrahigh-temperature ceramic composites based on hafnium diboride have a wide range of applications, including as components for high-speed aircraft and energy generation and storage devices. Consequently, developing methodologies for their fabrication and studying their properties are of paramount importance, in particular in using them as an electrode material for energy storage devices with increased oxidation resistance. This study investigates the behavior of ceramic composites based on the HfB₂-HfO₂-SiC system, obtained using 15 vol% Ti₂AlC MAX-phase as a sintering component, under the influence of subsonic flow of dissociated air. It was determined that incorporating the modifying component (Ti₂AlC) altered the composition of the silicate melt formed on the surface during ceramic oxidation. This modification led to the observation of a protective antioxidant function. Consequently, liquation was observed in the silicate melt layer, resulting in the formation of spherical phase inhomogeneities in its volume with increased content of titanium, aluminum, and hafnium. It is hypothesized that the increase in the high-temperature viscosity of this melt prevents it from being carried away in the form of drops, even at a surface temperature of ~1900–2000 °C. Despite the established temperature, there is no sharp increase in its values above 2400–2500 °C. This is due to the evaporation of silicate melt from the surface. In addition, the electrochemical behavior of the obtained material in a liquid electrolyte medium (KOH, 3 mol/L) was examined, and it was shown that according to the value of electrical conductivity and specific capacitance, it is a promising electrode material for supercapacitors. Full article

In the framework of hydrogen production and storage for clean energy generation, the resistance to hydrogen embrittlement of a newly developed austenitic stainless steel is presented. Gas-atomized metal powders prepared from secondary-sourced metals were employed to manufacture test specimens with Laser Powder Bed Fusion (LPBF) technology. After machining and exposure to a controlled, pressurized hydrogen atmosphere at high temperature, the effect of hydrogen charging on the mechanical performance under static and dynamic conditions was investigated. The stabilizing effect of the optimized chemical composition is reflected in the absence of degradation effects on Yield Stress (YS), Ultimate Tensile Stress (UTS), and fatigue life observed for specimens exposed to hydrogen. Moreover, despite a moderate reduction in the elongation at fracture observed by increasing the hydrogen charging time, ductility loss calculated as Relative Reduction of Area (RRA) remains substantially unaffected by the duration of exposure to hydrogen and demonstrates that the austenitic steel is capable of resisting hydrogen embrittlement (HE). Full article

Graphene, graphene oxide, reduced graphene oxide, and few-layer graphene as functional coating materials for corrosion protection in devices for electrochemical energy conversion and storage are reviewed. Reported applications are briefly described, enabling the reader to make an informed decision about the protective options based on the reported achievements. Full article

Corrosion, combined with cyclic loading, is inevitable and becomes a challenging problem, even when inherently corrosion-protected materials have been selected and applied based on established in-house experience. Aero engine mount structures are exposed to dusty and salty environmental conditions during both operational and non-operational periods. It is becoming tough to predict the remaining useful corrosion fatigue life due to the unascertainable material strength degradations under service conditions. As such, a rationalized approach is currently being used to assess their structural integrity, which produces more wastages of the flying parts. This paper presents a novel approach for predicting corrosion fatigue by proposing a random-parameter model in combination with validated experimental data. The two-random-parameter model is employed here with the probability method to determine the time-independent corrosion fatigue life of a magnesium structural casting, which is used heavily in engine front-mount aircraft systems. This is also correlated with experimental data from the literature, validating the proposed stochastic corrosion fatigue model that addresses the technical variances that occur during service to increase optimal mount structure usage using an automated data system. Full article

Measuring interfacial roughness is essential in evaluating the adhesion of coatings and thermally grown oxides. Conventional contact methods are often impractical for such analyses, especially when the interface lies beneath a nonremovable layer. This study proposes a semi-automated method combining an ImageJ macro and an R-language script to assess interfacial roughness from images obtained through scanning electron microscopy (SEM), leveraging chemical contrast between substrate and oxide. The approach preserves user input where interpretation is critical while standardizing measurement to reduce variability. Applied to 21 images from seven experimental conditions, the algorithm successfully reproduced the roughness ranking obtained from manual measurement while also significantly reducing measurement dispersion. Though it underestimates absolute roughness values compared with the user measurements (which should also happen with conventional contact methods), it offers a robust, flexible, and reproducible alternative for interface characterization. Full article

Hydrogen embrittlement (HE) can significantly degrade the mechanical properties of steels. This phenomenon is particularly relevant for high-strength steels where large elastic stresses lead to detrimental localized concentrations of hydrogen at defects. In this study, unnotched rotating bending specimens of the bearing steel SAE 52100 (100Cr6) quenched and tempered at 180 °C and 400 °C were electrochemically charged with hydrogen. Charged and non-charged specimens then underwent rotating bending fatigue testing, either immediately after charging or after aging at room temperature up to 72 h. The hydrogen-charged specimens annealed at 180 °C showed a sizeable drop in fatigue limit and fatigue lifetime compared to the non-charged specimens with cracks mainly originating from near-surface non-metallic inclusions. In comparison, the specimens annealed at 400 °C exhibited a moderate drop in fatigue limit and lifetime due to hydrogen charging with cracks originating mostly from the surface. Aging had only insignificant effects on the fatigue lifetime. Notably, annealing of charged samples for 2 h at 180 °C restored their lifetime to that of non-charged specimens. Full article

In a recent investigation the corrosion-fighting potential of five benzaldehyde derivatives were explored: 4-Formylbenzonitrile (BA1), 4-Nitrobenzaldehyde (BA2), 2-Hydroxy-5-methoxy-3-nitrobenzaldehyde (BA3), 3,5-Bis(trifluoromethyl)benzaldehyde (BA4), and 4-Fluorobenzaldehyde (BA5). Benzaldehyde derivative (BA-2) showed a maximum inhibition efficiency of 93.3% at 500 ppm. Several techniques were used to evaluate these compounds’ ability to protect mild steel from corrosion in a 1 M HCl solution, including potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), adsorption isotherms, and computational methods. Supporting techniques Fourier transform infrared spectroscopy (FTIR) and ultraviolet–visible (UV-Vis) spectroscopy were also employed to validate the results. Despite sharing a common benzene ring, the molecules differ in their substituents, allowing for a comprehensive examination of the substituents’ impact on corrosion inhibition. PDP analysis disclosed that the inhibitors exhibited mixed-type inhibition behavior, interacting with anodic as well as cathodic reactions, influencing the corrosion process. EIS analysis revealed that benzaldehyde derivatives formed a protective passive film on the metal, exhibiting high corrosion resistance by shielding the alloy from corrosive attacks. The benzaldehyde inhibitors followed the Langmuir adsorption isotherm, with high R² values near one, indicating a monolayer adsorption mechanism. DFT results indicate that BA 2 is the most effective inhibitor. FTIR and UV-vis spectroscopy revealed the molecular interactions between metal and benzaldehyde derivative molecules, providing insight into the binding mechanism. Experimental results support the outcomes obtained from the molecular dynamic (MD) simulations. Full article

This study investigates the tensile behaviors of wrought 44W steel, Monel 400, 304L austenitic stainless steel, and arc-directed energy deposited (arc-DED) 308L austenitic stainless steel under simulated hydrogen environments to evaluate their endurance to hydrogen embrittlement (HE). The specimens were subjected to cathodic hydrogen charging in an alkaline solution, followed by uniaxial tensile testing at a strain rate of 0.2 min⁻¹. Based on measurements of elongation and toughness, the resistance to HE was ranked as follows: 304L stainless steel > Monel 400 > arc-DED 308L stainless steel > 44W steel. Notably, no significant changes were observed in the yield strengths, ultimate tensile strengths, or elastic modulus of 304L austenitic stainless steel, Monel 400, and 44W steel across all the levels of hydrogenation. However, the arc-DED 308L stainless steel exhibited a slight increase in these properties, attributed to its unique microstructural characteristics and strengthening mechanisms inherent to additive manufacturing processes. These outcomes contribute to a better understanding of the mechanical performance and suitability of these structural alloys in hydrogen-rich environments, highlighting the superior HE resistance of 304L stainless steel and Monel 400 for such applications. Full article

The decommissioning and dismantling of nuclear research reactors can lead to a large amount of low- and intermediate-level radioactive waste. For repositories, the materials must be kept confined and safety must be ensured for extended time spans. Waste is encapsulated in concrete, which leads to alkaline conditions with pH values of 12 and higher. This can be advantageous for some radionuclides due to their precipitation at high pH. For other materials, such as reactive metals, however, it can be disadvantageous because it might foster their corrosion. The Studsvik R2 research reactor contained an AlMg3.5 alloy with a composition close to that of commercial Al5154 for its core internals and the reactor tank. Aluminum corrosion is known to start rapidly due to the formation of an oxidation layer, which later functions as natural protection for the surface. The corrosion can lead to pressure build-up through the accompanied production of hydrogen gas. This can lead to cracks in the concrete, which can be pathways for radioactive nuclides to migrate and must therefore be prevented. In this study, unirradiated rod-shaped samples were cut from the same material as the original reactor tank manufacture. They were embedded in concrete with elevated water–cement ratios of 0.7 compared to regular commercial concrete (ca. 0.45) to ensure water availability throughout all of the experiments. The sample containers were stored in pressure vessels with attached high-definition pressure gauges to read the hydrogen-induced pressure build-up. A second set of samples were exposed in simplified artificial cement–water to study similarities in corrosion characteristics between concrete and cement–water. Additionally, the samples were exposed to concrete and cement–water in free-standing sample containers for deconstructive examinations. In concrete, the corrosion rates started extremely high, with values of more than 10,000 µm/y, and slowed down to less than 500 µm/y after 2000 h, which resulted in visible channels inside the concrete. In the cement–water, the samples showed similar behavior after early fluctuations, most likely caused by the surface coverage of hydrogen bubbles. These trends were further supported by mass loss evaluations. Full article

This study investigated the effects of alternating current (AC) interference on pipeline steel under cathodic protection (CP). In a simulated solution, real-time electrochemical measurements and corrosion rate analysis were conducted on two steel types (C1018 and X60) under various levels of AC interference with CP. Due to the complexity of AC-induced corrosion, relying on the shift in DC potential alone cannot accurately demonstrate the corrosion behavior in the presence of AC interference. In fact, such an approach may mislead the predictions of corrosion performance. It is observed that AC interference reduced the effectiveness of CP and increased the corrosion rate of the steel, both in weight loss and Tafel Extrapolation (Tafel) measurements. The study concluded that conventional CP standards used in the field were inadequate in the presence of high AC-level interference. Furthermore, this study found that a more negative CP current density (−0.75 A/m²) could reduce the effect of AC interference by 46–93%. This is particularly shown in the case of low-level AC interference, where the reduction can reach up to 93%. Utilizing the experimental data obtained by the two measurement methods, probabilistic models to predict the corrosion rate were developed with consideration of the uncertainty in the measurements. The sensitivity analysis showed how AC interference impacts the corrosion rate for a given CP level. Full article