The effectiveness of 6-(N-morpholino)-2-carboxypyrazine (MCP) as a corrosion inhibitor for mild steel in 1 M hydrochloric acid was systematically assessed using weight loss measurements, electrochemical techniques, and quantum chemical calculations. Various concentrations of the inhibitor (0.0-0.5 mM) and immersion times (1-48 hours) were tested at 303 K, along with temperature variations (303-333 K) to evaluate thermodynamic parameters. The inhibition efficiency increased with concentration, peaking at 81.9% from potentiodynamic polarization and 83.8% from weight loss at 0.5 mM, with moderate enhancement observed at higher temperatures, indicating a chemisorptive interaction. The adsorption behavior followed the Langmuir isotherm, suggesting the formation of a monolayer on the metal surface. Potentiodynamic polarization studies identified MCP as a mixed-type inhibitor, effectively slowing both anodic metal dissolution and cathodic hydrogen evolution. Density functional theory (DFT) computations corroborated these findings by indicating a low HOMO-LUMO energy gap and favorable charge distribution, which align with strong surface adsorption. Together, these experimental and theoretical results position MCP as a thermally stable, electronically active, and surface-affinitive corrosion inhibitor, presenting promising potential for the development of protective coatings for steel structures in acidic environments.
This study demonstrates the comparative properties of titanium chromium nitride (TiCrN) films deposited by direct current magnetron sputtering (dcMS), mid-frequency magnetron sputtering (mfMS), and inductively coupled plasma magnetron sputtering (ICPMS). The crystal structure and microstructure of the deposited films exhibited significant dependence on the sputtering mode employed. The introduction of mfMS and ICPMS deposition processes resulted in a transformation of the film morphology from a porous columnar structure to a denser configuration characterized by finer grains. The surface roughness and crystal grain size of the coated films were assessed using non-contact atomic force microscopy (AFM) and Xray diffraction (XRD) analyses. A high-precision nanoindentation tester was utilized to measure the nano-hardness and elastic modulus of the TiCrN films deposited by three sputtering techniques: dcMS, mfMS, and ICPMS. Additionally, to conduct a comparative analysis of the effects of the sputtering modes on the corrosion resistance of the TiCrN films, a potentiodynamic polarization test was performed, allowing for evaluation of these effects through electrochemical analysis.
This study investigates the effect of minor Mo addition in Cr-bearing ultra-high-strength pipeline steel on microstructure, hydrogen transport behavior, and corrosion response. Two steels with different Mo contents were produced through quenching and tempering, and their characteristics were analyzed using electron backscatter diffraction (EBSD), electrochemical hydrogen permeation testing (HPT), and electrochemical impedance spectroscopy (EIS). EBSD analysis revealed that increased Mo content refined the tempered martensitic lath structure and reduced the prior-austenite grain size, indicating suppressed grain growth during heat treatment, which influences hydrogen transport and trapping behavior in the steel. HPT results demonstrated that hydrogen permeation during the charging stage was similar for both steels; however, a clear difference emerged during the desorption stage. The higher Mo content resulted in a faster decrease in permeation current during the decay transient, indicating greater hydrogen trapping efficiency. This behavior is associated with interactions between hydrogen and microstructural features, including Mo-containing precipitates and associated lattice distortions. EIS results further indicated that the higher-Mo steel exhibited increased polarization resistance during prolonged immersion, suggesting improved long-term corrosion resistance. These results suggest that increasing Mo content enhances hydrogen trapping efficiency and surface stability of the Cr-bearing ultrastrong steels, improving durability for hydrogen transport applications.
In this study, the time-dependent localised corrosion behaviour of UNS K32045 steel in 3.5 wt% NaCl solution was investigated using potentiodynamic polarisation, immersion testing, optical observation, SEM-EDS, and Raman spectroscopy. The microstructure mainly consisted of tempered lath martensitic structure with lath packets distributed across the observed surface, providing heterogeneous sites for corrosion initiation. Potentiodynamic polarisation revealed a continuous increase in anodic current without an active-passive transition, with a slope change near -0.40 V (SSE) . This response indicated that the anodic behaviour was associated with the initiation and propagation of localised corrosion in a chloride-containing environment rather than activation-controlled dissolution. Immersion tests showed that mass loss increased with exposure time, although the increase was not constant. The increase was relatively large during the early stage and became less pronounced after longer immersion in the solution. Optical observation revealed that corrosion products formed and became more widely distributed over time, progressively covering the exposed surface. SEMEDS analysis showed that corroded regions were partially covered with rough, porous corrosion products containing oxygen and chlorine. Raman spectroscopy confirmed that the surface products consisted of mixed iron oxyhydroxides. These results demonstrate that localised corrosion and corrosion-product accumulation developed concurrently with immersion time on the exposed surface.
Hot press forming (HPF) steels are widely used in automotive applications; however, their corrosion performance is significantly influenced by the coating microstructure. Although Al-Si and Zn-based coatings are commonly applied, the relationship between microstructural characteristics and electrochemical behavior is not yet well understood. This study investigates the corrosion behavior of Al-Si-coated and Zncoated HPF steels using an integrated approach that combines electron backscatter diffraction (EBSD) analysis with electrochemical techniques. Microstructural characteristics were directly correlated with electrochemical responses obtained from open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and galvanostatic testing. The Al-Si-coated HPF exhibited a dense and continuous Fe-Al intermetallic multilayer structure, which provides effective barrier-type protection and stable electrochemical behavior. In contrast, the Zn-coated HPF displayed a heterogeneous microstructure with Fe-Zn phases and surface oxides, leading to localized electrochemical activity. EIS results indicated a simple and stable response for the Al-Si coating, while the Zn coating exhibited complex behavior associated with adsorption-related processes. These findings were consistent with polarization and galvanostatic results, confirming higher corrosion activity in the Zn coating. Overall, this study demonstrates that the corrosion behavior is strongly governed by coating microstructure, highlighting its importance in understanding corrosion mechanisms.
This investigation assessed the mechanical, electrochemical, and cavitation-erosion properties of Al-Mg alloys subjected to multi-step anodization under marine conditions. The results of indentation tests showed a significant increase in surface hardness with more anodization cycles, indicating the formation of a thicker, more compact oxide layer. Potentiodynamic polarization measurements demonstrated a decrease in corrosion current density, attributed to the enhanced barrier effect of the thicker oxide film, which effectively reduces seawater penetration and ionic transport. Cavitation-erosion tests in natural seawater revealed that anodized specimens experienced significantly less weight loss compared to the bare substrate, indicating improved resistance to material degradation. However, despite the increased hardness, the ceramic-like oxide layer was prone to crack initiation and propagation under repeated cavitation impacts, leading to localized brittle fractures and partial delamination of the coating. Overall, while increasing the number of anodization cycles greatly enhanced both corrosion and cavitation-erosion resistance, the structural integrity of the oxide layer remains a crucial factor for long-term durability.
In this research, we investigated the effects of mechanical polishing conditions prior to anodizing in a sulfuric acid electrolyte on the characteristics of the anodized oxide film of a 5083-O aluminum alloy. Experimental results indicated that as the polishing process became finer, the height and Vickers hardness of the Al2O3 oxide film increased, while surface roughness decreased. Electrochemical experiments showed that with finer polishing, the corrosion potential shifted in a noble direction, the corrosion current density decreased, and the anodic Tafel slope increased. In sliding friction and wear experiments, the coefficient of friction increased rapidly during the initial running-in period under all conditions. Specifically, the coarse polishing condition maintained a high coefficient of friction, while a relatively low coefficient was observed under fine polishing conditions as the frictional distance increased. Consequently, mechanical polishing prior to anodizing a 5083-O aluminum alloy significantly enhances corrosion and wear resistance by controlling the growth and microstructure of the oxide film.
The localised corrosion behaviour of UNS A93003 aluminium alloy was investigated in a seawater acetic acid test solution (SWAAT: 4.2 wt% NaCl + 1.0 wt% CH3COOH). Specimens were immersed for 169 h, and the surface morphology was examined using optical microscopy. Maximum and average depths were measured by 3D profilometry, and the corroded area fraction was quantified through image analysis. Al- Mn-Fe-Si intermetallic compounds (IMCs) were distributed throughout the alloy matrix. Localised corrosion was observed at the IMC-matrix interfaces, particularly around coarse IMCs (approximately 10 mu m). Both the average and maximum depths increased with immersion time, while the maximum-toaverage depth ratio decreased towards unity. This trend indicated a reduction in depth localisation and an increase in the number of localised corrosion sites. Initiation was preferentially associated with the interfaces of coarse IMCs and later extended to the interfaces of finer IMCs. Initially, localised corrosion areas were isolated but eventually became connected or merged. SKPFM analysis showed a higher contact potential difference (CPD) on IMCs than on the matrix; the Delta CPD values were consistent with a micro-galvanic driving force for early initiation.
A 45 degrees-built laser powder bed fusion (LPBF) 316L stainless steel specimen, heat-treated at 900 C for 2 hours in argon, was investigated in a 3.5 wt% NaCl solution at room temperature. Surface-exposed pores were observed on both the build-direction (BD) and transverse-direction (TD) planes; however, EDS mapping did not reveal pronounced elemental segregation around the pores. Optical microscopy indicated predominantly equiaxed grains. EBSD kernel average misorientation (KAM) analysis showed that misorientation above 1 persisted over a substantial area after heat treatment. SEM analysis following anodic polarisation, terminated at 100 mu A cm , confirmed that localised corrosion primarily initiated and/ or propagated at pore openings and in the adjacent substrate regions on both planes. Electrochemical impedance spectroscopy (EIS) responses exhibited comparable impedance values between the BD and TD, a phase maximum near -70 , and a low-frequency inductive feature. This low-frequency inductive behaviour suggested the influence of pore-related local environments on the interfacial response of PBF 316L stainless steel under chloride exposure.
This paper presents an artificial neural network (ANN) model designed to predict the potentiodynamic polarization behavior of S31803 duplex stainless steel (DSS) in marine environments. A full factorial experimental design was utilized to gather data on the effects of temperature, salinity, and pH on corrosion behavior. Potentiodynamic polarization (PDP) tests were performed to create a comprehensive database across a wide potential range. The ANN model uses temperature, salinity, pH, and overpotential as input variables, while the output layer predicts the corresponding current density under overpotential. Based on the dataset obtained from the PDP curves, a multilayer ANN model was developed and optimized to forecast polarization curves. The optimized ANN model demonstrated high predictive accuracy, with determination coefficients of 0.993, 0.987, and 0.987 for the training, validation, and test datasets, respectively. These results suggest that the proposed ANN model is an effective tool for predicting corrosion behavior, contributing to corrosion monitoring and condition-based maintenance in marine systems.
In this study, three coating conditions were applied to carbon steel specimens: (1) galvalume-coated specimens, (2) galvalume-coated specimens treated with trivalent chromium (Cr ) chemical conversion treatment (Galvalume+ Cr3+ ), and (3) polymer top-coated specimens applied over the Galvalume+ Cr3+ treated layer (Galvalume+Top). The electrochemical corrosion behavior, surface morphology, and mechanical properties of each specimen were systematically evaluated to clarify the role of each surface modification step. The electrochemical measurements included monitoring the open-circuit potential, conducting cyclic potentiodynamic polarization tests, and performing Tafel extrapolation analysis to determine corrosion potential and corrosion current density. Surface characteristics were examined to identify coating integrity and defect evolution after testing. Mechanical properties were assessed through scratch and indentation tests to evaluate hardness, adhesion strength, and creep resistance. The results indicated that the Galvalume+Top specimens exhibited the highest corrosion resistance, characterized by the lowest corrosion current density. The Galvalume+ Cr (3+) specimens showed the greatest hardness and excellent creep resistance, while the Galvalume+Top specimens demonstrated superior adhesion strength due to the polymer overlayer. Overall, the combined application of Cr3+ chemical conversion treatment and polymer coating effectively enhanced both corrosion resistance and mechanical performance of the galvalume coatings.
Anodic aluminum oxide (AAO) is commonly utilized in functional surface engineering, yet the influence of alloy composition on AAO growth behavior, pore-widening (PW) characteristics, and structural stability remains poorly understood. This study investigates AAO films formed on Al 1050, Al 3003, Al 5052, and Al 6061 through anodization for 1 hour under identical conditions, followed by PW in phosphoric acid for varying durations. Despite the same anodizing conditions, significant differences were noted in pore diameter, oxide-film thickness, and AAO growth rates based on alloy composition. Al 5052 demonstrated the highest growth and PW rates, while Al 3003 exhibited the lowest. During the PW process, all alloys initially experienced increased porosity and enhanced wettability; however, extended PW led to distinct collapse behaviors of the oxide film that were dependent on the alloy. These behaviors ranged from gradual structural transformation to rapid oxide removal. Notably, wettability enhancement occurred only while a stable porous structure was intact; once the oxide film collapsed or was removed, wettability reverted. These findings indicate that the PW rate and structural stability are governed by different mechanisms, highlighting the critical role of alloy composition in influencing AAO growth, collapse behavior, and wettability.
This study assessed the enhancement of cavitation erosion resistance in gray cast iron, a common material used for marine diesel engine cylinder liners, through the application of electroless nickel plating (ENP). EDS and XRD analyses revealed that the ENP coating contained approximately 6.4 wt% phosphorus and displayed broadened Ni diffraction peaks, suggesting an amorphous or microcrystalline structure. Cavitation erosion tests were performed following ASTM G32 standards using an ultrasonic vibratory apparatus set to an amplitude of 50 & micro;m. The gray cast iron substrate exhibited a rapid increase in cumulative weight loss with exposure time, reaching about 1.2 mg after 90 minutes, along with a significant rise in surface roughness and maximum damage depth. In contrast, the ENP-coated specimen showed a much slower rate of material loss, with cumulative weight loss limited to approximately 0.4 mg even after 240 minutes. Three-dimensional surface profiling further confirmed that the ENP coating effectively inhibited the growth and coalescence of erosion pits, resulting in lower surface roughness and shallower damage depth compared to the substrate. These findings indicate that ENP is an effective surface treatment for improving the cavitation erosion resistance and durability of marine diesel engine cylinder liners in coolant environments.
Hydraulic actuators in gas turbine (GT) inlet guide vane (IGV) systems are crucial for the stable operation of combined heat and power (CHP) plants. This study systematically investigates the internal damage and corrosion behavior of a GT IGV hydraulic actuator recovered after long-term service in a district heating CHP plant. The manifold block, cylinder tube, and piston were disassembled and analyzed to assess the effects of lubricant degradation and water contamination. Visual and cross-sectional examinations revealed localized corrosion pits, oxide accumulation, and uneven material thinning on lubricant-contacting surfaces, with maximum pit depths measuring 0.18 mm in the manifold block, 0.13 mm in the cylinder tube, and 0.07 mm in the piston. The chromium plating, approximately 18 mu m thick, effectively suppressed degradation of the cylinder tube; however, localized coating damage led to interfacial corrosion and accelerated substrate degradation. Lubricant analysis showed fluctuations in water content, particle contamination, and PQ index, indicating a lubricant environment susceptible to hydrolysis, additive depletion, and tribocorrosion. These findings demonstrate that monitoring lubricant properties alone is insufficient to accurately represent the evolution of internal damage and provide direct experimental evidence linking lubricant degradation and water contamination to the internal corrosion of hydraulic actuators.
This study investigates the influence of minor Cu addition on the CO2 corrosion behavior of API-grade HSLA steel in CO2-saturated aqueous environments. Two types of steel were examined: one Cu-free and one containing 0.5 wt% Cu, under neutral (pH approximate to 6) and mildly acidic (pH 4.0-4.5) conditions. The methods used included electrochemical LPR measurements, microstructural characterization, and surface analyses. The addition of Cu did not significantly alter the ferritic microstructure but allowed for limited precipitation of metallic Cu. Under neutral conditions, Cu accelerated initial Fe dissolution and the formation of CuO/Cu2O, which suppressed stable FeCO3 deposition and decreased corrosion resistance. In contrast, under mildly acidic conditions, preferential Fe dissolution led to pronounced Cu enrichment at the surface. The resulting Cu and Cu-oxide layers increased the local pH and promoted more stable FeCO3 formation during prolonged immersion, resulting in lower corrosion rates compared to the Cu-free steel. These findings demonstrate that while Cu plays a detrimental role in neutral solutions, it enhances corrosion resistance in acidic CO2 environments, indicating the potential applicability of Cu-microalloyed steel for acidic CO2 transport conditions.
In pursuit of greener corrosion control, this study evaluates Trametes versicolor (Turkey Tail Mushroom) extract as a corrosion inhibitor for mild steel in 1 M HCl. Using experimental and theoretical approaches, the extract achieved up to 92.1% inhibition efficiency at 800 mg/L, though efficiency declined with higher temperatures, suggesting predominantly physical adsorption with possible chemisorption. GC-MS/MS and FTIR analyses revealed various bioactive compounds-mainly flavonoids and polyphenols-containing functional groups like hydroxyl, carbonyl, and amine that promote protective film formation on the metal tions at the interface. To support these results, DFT, MD, and MC simulations provided molecular-level insights into adsorption behavior, highlighting myricetin and rutin as key compounds with strong binding affinities and favorable electronic properties. A QSAR model with 22 molecular descriptors was developed to predict adsorption energies, identifying frontier orbital energies and surface area as major factors influencing inhibitor performance. These findings demonstrate the potential of T. versicolor extract as an eco-friendly corrosion inhibitor and offer valuable molecular insights for designing bio-based corrosion control strategies.
Reinforced concrete structures in marine environments frequently experience premature deterioration due to corrosion, particularly of the steel reinforcement, which is a leading cause of degradation in these structures, including bridges and marine airports. In recent years, developed countries have increasingly turned to offshore spaces-such as floating wind farms, floating solar power plants, and floating waste treatment facilities-for infrastructure development, driven by a shortage of available urban land. This trend is also observable in our country, where, despite being surrounded by the sea on three sides, usable land in urban centers is extremely limited. To mitigate corrosion in reinforced concrete structures, various cathodic protection methods are employed, including sacrificial anode cathodic protection (SACP) and impressed current cathodic protection (ICCP). Among these, ICCP is the preferred method due to the high electrical resistivity of concrete. In this study, we applied an ICCP system powered by self-generated energy sources-such as wind power, solar power, and ocean thermal energy-to floating reinforced concrete offshore structures. The performance of the ICCP system was assessed by measuring the cathodic protection current, cathodic protection potential, and depolarization potential.
This study aimed to enhance the corrosion resistance of Al-10Si-based plated steel by incorporating Mg and Zn-elements known for their low corrosion potentials-into the plating layer. We analyzed the effects of varying the content of these elements on both the microstructure and corrosion behavior. Using a Central Composite Design method, we developed nine plating compositions that combined Zn (0, 7.5, 15 wt%) and Mg (0, 2.5, 5 wt%). We evaluated the electrochemical properties of the plating layers through potentiodynamic polarization tests in a 3.5 wt% NaCl aqueous solution and examined the microstructures before and after corrosion using optical microscopy and SEM-EDS. The results of the potentiodynamic polarization tests revealed corrosion potentials ranging from-0.93 V to-0.56 V. Corrosion rates increased with Mg content, ranging from 2.36 x 10(-6 )A/cm to 2.9 x 10(-5 )A/cm(2) . Statistical analysis indicated that Zn content primarily influenced corrosion potential, while Mg content affected the corrosion rate. Cross-sectional observations post-corrosion testing confirmed micro-galvanic corrosion behavior, characterized by the selective dissolution of eutectic Al-Si phases surrounding Si-rich phases within the plating layer.
This study examines the impact of Zr-based electroplating on the discoloration behavior of Zn-Mg alloy coatings, which are considered for use in aqueous ion-battery electrodes and electronic components. The as-coated Zn-Mg alloy on steel showed significant surface darkening after being exposed to boiling water, simulating a high-temperature and high-humidity environment. To suppress this surface degradation, a Zr-O-Carbonate composite film was created through electroplating. In this process, Zr-Carbonate complexes were transformed into hydroxides and then dehydrated to produce a protective surface layer. The resulting film, approximately 500 nm thick, effectively reduced discoloration by limiting the formation of oxide species responsible for darkening. This was evidenced by significantly smaller decreases in lightness (L*) and a more stable surface morphology compared to uncoated samples, even after prolonged exposure. These findings indicate that Zr-based electroplating offers a straightforward and effective approach to enhance the environmental durability of Zn-Mg alloys, potentially expanding their use in energy and electronic device materials.
Wire bonding is still prevalent in conventional semiconductor packaging. However, degradation can occur during use or storage due to factors such as humidity, acidity, and ionic contamination. This study investigates the corrosion behavior of packaging structures with Al and Au bond pads combined with Au and Cu wires in sulfate-based environments. Electrochemical evaluations, including individual polarization and galvanic tests, were performed in de-aerated 1% Na SO solutions with varying H SO concentrations. Tafel analysis provided data on corrosion potential (E ), corrosion current density (i ), galvanic potential/current density, and total charge. Additionally, a Temperature-Humidity Test (85 C/85% RH) was conducted under 1% Na SO with either 0% or 1% H SO conditions, using PCB unit specimens that featured a 1 ball bond on an Al pad and a 2 stitch bond on an Au pad, bonded with either Au or Cu wires. The surface morphology and elemental distribution were qualitatively analyzed before and after exposure using a 3D optical microscope and FE-SEM/EDS.
