Localized Corrosion Research Articles

Corrosion Behavior of Al-Containing CoNiV Medium Entropy Alloy Coating Fabricated by Laser Cladding.

CoNiV medium entropy alloys (MEAs) have been widely recognized for their superior corrosion resistance. Nonetheless, their extensive application has been hindered by high production costs and complex fabrication processes. In this study, CoNiVAlx MEA coatings were synthesized on AISI 304 stainless steel substrates via laser cladding technology. The microstructure, phase composition, corrosion resistance, and corrosion mechanisms of the coatings were systematically investigated by using advanced characterization techniques, including optical microscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffractometry, and electrochemical workstation analysis. The ratio of O2-/OH- in the passivation film of the coated surface exhibited a gradual increase with the addition of Al. The formation of the Al-containing precipitated phase L21 was observed at x = 0.3 and 0.4. The results demonstrated that moderate Al doping (x ≤ 0.2) enhanced corrosion resistance by improving the stability of the passivation film and reducing the thermodynamic tendency toward corrosion. In contrast, excessive Al doping (x > 0.2) led to the formation of the L21 phase, which increased the susceptibility to localized corrosion, thus compromising the overall corrosion resistance.

Effect of Temperature on Passive Film Characteristics of LPBF (Laser Powder-Bed Fusion) Processing on UNS-S31603.

The effect of temperature on the localized corrosion resistance and passive film characteristics of laser powder-bed fusion (LPBF) 316L (UNS S31603) was studied in a buffered 3.5 wt% NaCl solution at 25, 50, and 75 °C. DC techniques such as cyclic potentiodynamic polarization showed lower passive current densities, high breakdown potentials, and a higher resistance to initial breakdown compared with wrought 316L samples at all temperatures. However, LPBF 316L was more susceptible to metastable pitting at potentials before film breakdown and higher damage accumulation post film breakdown. AC techniques, such as Mott-Schottky analysis and electrochemical impedance spectroscopy, showed that the formed passive film was more robust on the LPBF 316L samples at all temperatures, accounting for the higher initial resistance to pitting. However, with increasing temperatures, the film formed had an increasing concentration of defect density. Passive compositions at the various test temperatures studied using X-ray photoelectron spectroscopy (XPS) showed that the LPBF samples showed higher amounts of Cr and Fe oxides and hydroxides compared with the wrought samples, which made the passive films on the LPBF samples more compact and protective. Investigation of the pits formed on the LPBF showed the preferential regions of attack were the melt-pool boundaries and cell interiors due to their being depleted of Cr and Mo when compared with the boundaries and matrix.

Microstructure and corrosion behaviour of structural steel fabricated by wire arc additive manufacturing (WAAM)

Wire arc additive manufacturing (WAAM) is a metal 3D printing technique that allows large-scale elements to be built in a relatively timely and cost-effective manner, well suited to the cost-sensitive construction sector. Despite the potential of this novel technology, the basic properties of WAAM materials remain elusive. This paper presents a comparative study on the microstructure and corrosion behaviour of WAAM steel plates and the conventionally rolled Q345 steel. The WAAM steel exhibited comparable corrosion performance to the conventionally-produced steel within twelve days exposure in 3.5 wt% NaCl solution, including the corrosion current density, and the characteristics of steel/concrete interface, determined through electrochemical impedance spectroscopy (EIS) analysis. Post-corrosion observations revealed that preferential dissolution occurred at (Si, Mn)-rich oxide inclusions, in addition to the general corrosion of surrounding steel matrix. The much higher content of Si and Mn element in the feedstock material WAAM steel resulted in slightly higher susceptibility to localised corrosion, compared to the Q345 rolled steel.

Electrochemical properties and corrosion induced mechanical degradation of biomedical Zn–Cu–Li alloy in simulated body fluid

The electrochemical behavior and corrosion induced mechanical degradation of biodegradable Zn–2Cu–0.03Li alloy were in detail investigated. The results indicated that the corrosion product film presented an increasing corrosion resistance, while the localized corrosion induced by microgalvanic effect was intensified. Corrosion pits, as the typical defect, acted as the crack initiation sites and accelerated the fracture process of the Zn–2Cu–0.03Li alloy. Accordingly, the fracture mode transformed from ductile to brittle failure. Significant loss in ultimate tensile strength and elongation of the alloys occurred due to strong stress concentration at corrosion pit, threatening the mechanical reliability after implantation.

Augmentation of Polymer-FeCO3 Microlayers on Carbon Steel for Enhanced Corrosion Protection in Hydrodynamic CO2 Corrosion Environments.

Carbon dioxide (CO2) internal corrosion of carbon steel pipelines is a significant challenge and is typically managed by adding corrosion inhibitors. In certain operational conditions, a natural protective layer of iron carbonate (FeCO3) can form on the internal walls of the pipeline, offering inhibition efficiency comparable to that of standard surfactant inhibitors. However, incomplete coverage of the FeCO3 layer on carbon steel can sometimes trigger localized corrosion. Our previous research demonstrated that poly(allylamine hydrochloride) (PAH) can work synergistically with FeCO3 when the corrosion product partially covers X65 carbon steel surfaces in an aqueous CO2 corrosion environment. In this study, we utilize rotating cylinder electrode (RCE) tests along with electrochemical measurements to investigate the FeCO3-PAH hybrid structure in a dynamic environment. We characterize the general and localized corrosion behavior as well as the surface properties of both naturally formed FeCO3 and FeCO3-PAH hybrid layers using interferometry and focused ion beam scanning electron microscopy.

The corrosion behavior of carbon steel under coexistence of carbon dioxide and SRB.

The corrosion behavior of carbon steel under the coexistence of carbon dioxide and SRB was studied by means of corrosion weight loss, SEM, EDS, in situ pH test, and other methods. The results showed that Chloride ions, temperature, pH, and oxygen coexist with iron bacteria will affect the corrosion under the coexistence of CO2 and SRB, and SRB tends to grow in a favorable environment for itself, and the corrosion rate of X52N at 42days is slightly higher than that at 21days. However, the pitting depth increased sharply from 21.20µm in 21days to 39.79µm in 42days. So that the corrosion can be divided into two stages. First, SRB catalyze the dissolution of FeCO3, leading to local uniform corrosion. Second, SRB directly obtain electrons from the metal surface, resulting in local pitting. In addition, the environment under the stable mineralized biofilm was found to be slightly alkaline.

Pressurized water reactor fuel corrosion-related unidentified deposit and its related safety issues – I. Corrosion product deposition and heat transfer

CRUD depositions on fuel cladding are the main cause of power shift and localized corrosion in nuclear power plants. This paper is the first of a three-part study concerning the formation mechanism of CRUD depositions and its related heat transfer issues. In this paper, CRUD depositions are obtained under subcooled boiling conditions in 2 × 2 rod array channels via accelerated deposition method to explore corrosion product deposition and its feedback on heat transfer. Imbalance of deposition and erosion at initial stage causes fouling resistance to increase first and then decrease. CRUD growth is proposed as a relatively pure fouling process combining soluble precipitation and particulate aggregation. Through high-resolution characterizations, boiling chimney diameters span from 3 μm to a dozen microns. Principal components are nickel ferrite and nickel elemental with Fe/Ni ratio of 1.9:1. Static contact angle decreases to less than 30°. Effective CRUD thermal conductivity decreases with the increase of heat flux with 1.3866 W/(m × K) on average. The results of this study provide a precise method for understanding corrosion product deposition and its impact on heat transfer to further establish accurate CRUD-related models and predict CRUD-related safety issues.

On the formation trajectory of diverse corrosion morphologies associated with T phases in an Al-Cu-Li alloy

Four different types of localized corrosion morphologies associated with Al20Cu2Mn3 dispersoids (T phases) in an AA2195 alloy were traced using atom-resolved characterizations and quasi-in-situ experiments. At the atomic scale, we demonstrated that the rod-shaped T dispersoid is homogeneous within the grain but enriched with Cu on the side surfaces, leading to a depletion of T1 precipitates nearby and an abundance near the tips. This plays a significant role in the initiation of galvanic corrosion between T dispersoids and the matrix. Combined with heterogeneous nucleation, the subsequent redeposition of noble metal clusters results in four typical corrosion morphologies.

A numerical analysis of the mechano-electrochemical effects on localised corrosion in pipelines using a multi-physical field coupling approach

In this study, we used a multi-physics coupling approach integrating the electrochemical and solid mechanics fields to develop a three-dimensional finite element model. This model was specifically designed to investigate the effects of mechano-electrochemical (M-E) effects on pipeline corrosion. The boundary conditions for the finite element simulation were established using experimental data, enabling the model to effectively predict the corrosion potential and current density, which aligned well with the experimental findings. Subsequently, the validated model was applied to examine the M-E effects near the pipe corrosion defects, considering various depths of corrosion defects and axial strain. Our results indicate that the stress concentration at the core of the defect increases with increasing axial tensile strain and deepening corrosion. The investigation of the correlation between the corrosion potential and net current density revealed that mechanical forces significantly impact metal corrosion rates, thus influencing pipeline longevity. When the metal structure of the pipeline is deformed within the elastic deformation range, the impact of the M-E effects on corrosion is minimal. However, when a tensile strain is applied or the defect geometry induces plastic deformation at the defect site, a notable increase in the local corrosion activity is observed.

Effect of Ti on the corrosion resistance of Al-Cr-Fe-Mn-Mo-Ni single and multi-phase CCAs

Five Al0.3Cr0.5Fe2Mn0.25Mo0.15Ni1.5Tix compositionally concentrated alloys were synthesized, forming alloys with an FCC matrix. At Ti concentrations of 5 at% and above, an L21 phase enriched in Al, Ti and Ni was present within the FCC matrix. At Ti concentrations of 9.6 at% Ti and above, a three-phase microstructure containing FCC+L21+Laves phases was formed, with the Laves third phases enriched in Cr and Mo. Ti(IV) was a prominent constituent in the passive film. Resistance to localized corrosion improved with Ti concentration before reaching an optimal concentration and beginning to decrease, likely due to the formation of new phases.

A new facile strategy for addressing the localized corrosion issue at damaged coating via a wind-driven triboelectric nanogenerator

Metal substrate at the damaged coating, exposed directly to the corrosive medium, is susceptible to the localized corrosion, due to the formation of occluded corrosion cells. Herein, a new facile strategy for addressing the localized corrosion issue at damaged coating using a triboelectric nanogenerator (TENG) was proposed. The wind-driven TENG with a simple double-layer structure was designed. The output performance of the TENG can be controlled by adjusting structural parameters and the wind speeds, with the maximum short circuit current, output voltage and corresponding power reaching approximately 102.5 μA, 814 V and 7.6 mW, respectively, at a wind speed of 7.5 m/s. The electrons generated by the TENG can be transferred to the metal substrate at the damaged coating, inducing the cathodic polarization of the metal and providing effective cathodic protection. The reduction reaction, with the consumption of O2 and the formation of OH-, occurs at the metal substrate at the damaged coating. A protective local environment is created by the combination of increased pH and removal of Cl- under the electric field of the TENG. To evaluate the corrosion behavior, immersion experiments and electrochemical measurements were conducted in 3.5 wt% NaCl when the Q235 steels covered the damaged coating were coupled with and without the wind-driven TENG at different wind speeds. Meanwhile, the influence of TENG’s output performance on the cathodic protection effect for the metal substrate at the damaged coating is discussed. This study expands the application of the TENG in the field of corrosion resistance.

Pit initiation in quenching and partitioning processed martensitic stainless steels

The present article investigates the influence of chemical composition and phase fractions on the corrosion behaviour of industrially produced quenching and partitioning (Q&P) martensitic stainless steels. Localised corrosion was analysed by scanning Kelvin probe force microscopy (SKPFM) and scanning electrochemical microscopy (SECM) in 3.5 wt.% NaCl solution. SKPFM revealed a Volta-potential difference of around 40 mV between inclusions and the matrix, which is larger than the Volta potential variations within the matrix. This difference in surface potential is a driving force for selective dissolution (corrosion initiation) at inclusions and inclusion/matrix interfaces. SECM detected early pitting initiation, particularly in alloys containing MnS and TiN inclusions. Results suggest that pitting initiation and propagation occur at those specific regions. This study emphasised that irrespective of chemical composition and phase fraction, localised corrosion initiation in Q&P-processed martensitic stainless steels is predominantly governed by the presence of inclusions.

Influence of impurity content on corrosion behavior of Al-Zn-Mg-Cu alloys in a tropical marine atmospheric environment

The influence of impurity content on the corrosion behavior of Al-Zn-Mg-Cu alloys in a tropical marine atmospheric environment was systematically investigated. Combined with experimental measurements and theoretical calculations, it has been elaborated that the Volta potential difference is the main reason for the localized corrosion. The composition-property correlation has been established between the impurity contents, the type, size, and quantity of precipitates, and the corrosion behavior. The effects of impurity contents on the volume fraction of precipitates and corrosion parameters such as corrosion rate and average pit depth have been quantified, offering quantitative guidance to develop novel Al-Zn-Mg-Cu alloys.

Experimental, analytical, and numerical quantification of the Marangoni effect in static refractory finger test

This study investigated the local corrosion of alumina and magnesia refractory in CaO–Al2O3–SiO2–MgO slag due to the Marangoni effect, which is a key factor for localized wear in different industrial processes, using experimental, analytical, and numerical approaches. The objective is to explore the Marangoni effect using computational fluid dynamics simulation aiming to provide insights into the dominant slag flow patterns influencing refractory corrosion and to determine whether the observed corrosion groove can be attributed solely to the Marangoni effect. Static finger tests were conducted at temperatures of 1500 and 1550 °C employing a continuous wear testing device. A two-dimensional axisymmetrical section model of the test assembly was created, incorporating concentration-dependent surface tension gradients and surface tension forces to replicate the Marangoni flow. As the surface-tension simulation required time steps in the order of 10−5 s, modeling up to the experimental time scale cannot be realized. Consequently, the simulation outcomes were extrapolated to anticipate the groove radii of the experimental corrosion steps. Corrosion rates were derived from measurements and analytical methodologies. Established analytical equations for corrosion under surface-tension-flows were adapted to enhance the accuracy of corrosion rate estimation. However, the analytical considerations yielded poor estimates. Meanwhile, the employed simulation model successfully generated plausible predictions of the Marangoni flow. Drawing from the extrapolated simulation outcomes, the projected groove radii exhibited a close correspondence to the measured values, demonstrating a relative error of approximately 3 %, 11 %, and 15 % for the magnesia system at 1500 °C and alumina systems at 1500 and 1550 °C, respectively. Taking into account the uncertainties inherent in the methodological approach, the disparities in the alumina values suggest the involvement of mechanisms beyond the Marangoni effect in the localized wear. Consequently, this study effectively clarifies the impact of the Marangoni effect on the local wear of the examined material systems.

Scanning Electrochemical Probe Lithography for Ultra-Precision Machining of Micro-Optical Elements with Freeform Curved Surface.

Two challenges should be overcome for the ultra-precision machining of micro-optical element with freeform curved surface: one is the intricate geometry, the other is the hard-to-machining optical materials due to their hardness, brittleness or flexibility. Here scanning electrochemical probe lithography (SECPL) is developed, not only to meet the machining need of intricate geometry by 3D direct writing, but also to overcome the above mentioned mechanical properties by an electrochemical material removal mode. Through the electrochemical probe a localized anodic voltage is applied to drive the localized corrosion of GaAs. The material removal rate is obtained as a function of applied voltage, motion rate, scan segment, etc. Based on the material removal function, an arbitrary geometry can be converted to a spatially distributed voltage. Thus, a series of micro-optical element are fabricated with a machining accuracy in the scale of 100 s of nanometers. Notably, the spiral phase plate shows an excellent performance to transfer parallel light to vortex beam. SECPL demonstrates its excellent controllability and accuracy for the ultra-precision machining of micro-optical devices with freeform curved surface, providing an alternative chemical approach besides the physical and mechanical techniques.

Effect of Corrosion Inhibitors on Bond Strength of Reinforced Concrete Structures

Corrosion of steel reinforcement is a major factor affecting the durability and strength of reinforced concrete structures. This study investigated the influence of plant-derived corrosion inhibitors, applied as coatings, on the bond strength between reinforcing steel and concrete. Thirty-six 150 mm concrete cubes with 12 mm diameter embedded steel bars were prepared and divided into uncoated, corrosion inhibitor coated, and control groups. The samples were immersed in 5% sodium chloride solution over 360 days to accelerate corrosion. Pull-out testing measured the bond strength and failure load. The corroded samples showed 31-26% lower bond strength and 82-87% higher maximum slip than controls, indicating corrosion damage at the steel-concrete interface. However, inhibitor-coated samples displayed 24-36% higher bond strength and 42-43% lower maximum slip versus corroded samples. Although the coatings did not fully restore original bond strength, this demonstrates their effectiveness at protecting bond properties. Microscopic analysis revealed non-uniform, localized corrosion preferentially initiated at steel defects. Statistical correlations confirmed the direct relationship between steel weight loss and reductions in post-corrosion rebar weight due to material loss. While nominal rebar diameters showed minimal differences between sample types, localized diameter reductions and cross-sectional area increases in corroded samples highlighted discrete corrosion effects. These were mitigated in coated samples. Together with direct weight loss measurements, this proves corrosion occurred in unprotected samples. Overall, the significant recovery of bond strength, slip resistance, diameter, area, and weight in coated samples validates the success of the natural corrosion inhibitors in reducing steel deterioration and interface degradation. The results provide new insights on optimizing inhibitor coatings to maximize corrosion protection for reinforced concrete structures.

Corrosion behavior of Cr/RE alloyed rebar in carbonated simulated concrete pore solutions with chloride ions

This study investigated the effect of the addition of Cr and RE microalloying regarding the steel rebar's resistance to corrosion in the co-existence of carbonation and chloride ions using electrochemical tests, scanning electron microscopy and confocal laser scanning microscopy. The best corrosion resistance of the Cr/RE microalloying rebar was found by the reduction in corrosion rates and the diminution of the rust layer. And during the initial stages of localized corrosion, the corrosion pits' depth was minimized, showing lateral expansion trends, which was supported by confocal laser scanning microscopy. Additionally, XPS analysis revealed that Cr/RE microalloying rebar can change the structure of the surface oxide film with a higher Fe(II)/Fe(III) ratio, which enhanced the surface oxide film's protective qualities.

Investigating microstructure, mechanical properties, and pitting corrosion resistance of UNS S32760 super duplex stainless steel after linear friction welding

High-performance alloys such as super duplex stainless steels (SDSS) are of interest to the oil and gas industry, especially in deep and ultra-deep reservoirs where high pressures and highly corrosive environments are prevalent. SDSS have high nitrogen contents and pitting resistant equivalent number (PREN) values greater than 40, however, fusion welds of these alloys can exhibit unsuitable microstructures and defects that may result in failure during usage. Solid-state linear friction welding (LFW) offers an alternative for the effective joining of SDSS with a less detrimental effect on microstructure and properties. In this work, four LFW joints in UNS S32760 SDSS were produced and investigated by evaluating the process parameters required to achieve a high-quality joint with the desirable metallurgical, mechanical, and localized corrosion properties. These properties were assessed through metallography (optical microscopy and scanning electron microscopy), tensile and microhardness tests, and corrosion analysis according to the ASTM G48A standard. Results indicated that one specific combination of LFW parameters led to a defect-free joint, and that the mechanical properties of the weld in this case were comparable to those of the base material. Additionally, an adequate balance between ferrite and austenite phases was achieved throughout the microstructural gradients seen in the weld region. Microhardness values were below 350 HV, thus complying with the DNV–OS–F101 standard. Furthermore, no pitting corrosion was observed in this joint under the testing conditions suggested by ASTM G48A.

Study of the corrosion behavior of N80 and TP125V steels in aerobic and anoxic shale gas field produced water at high temperature

In this study, the corrosion behavior of N80 and TP125V steels was delved firstly into produced water from shale gas fields containing CO2-O2. Moreover, the localized corrosion of these steels was investigated to elucidate the effects of aerobic and anoxic on steel corrosion. The results indicated that the corrosion rates of N80 and TP125V steels under aerobic conditions were lower compared to those in the presence of CO2-O2. Specifically, at temperature of 100 °C and with dissolved oxygen (DO) concentration of 4 mg/L in the CO2-O2 environment, the N80 and TP125V steels exhibited the highest corrosion rate, with values of 0.13 mm/y and 0.16 mm/y, respectively, as determined by specific weight loss measurements. Conversely, these rates decreased to 0.022 mm/y and 0.049 mm/y under aerobic conditions. Furthermore, severe localized corrosion of N80 and TP125V steels with a DO concentration of 4 mg/L was also observed in the CO2-O2 environment. Finally, it was evident that pitting corrosion is the predominant type of corrosion affecting N80 and TP125V steels in the produced water from shale gas fields.

Wet corrosion of incinerators under chloride deposits: Insights from experimental study on stainless steels and nickel-based alloy weldments

The deliquescence of the corrosion species produced by nuclear waste incineration, in particular ZnCl2, makes wet corrosion possible even in dehumidified atmosphere complicating the corrosion risk management of the equipment. A specific cyclic corrosion test was used to assess the compatibility of corrosion resistance alloys to such conditions. Thereby, AISI 316 L welds resisted somehow to pitting but experienced severe stress corrosion cracking, while UR66™ showed only pitting in the heat affected zone. Hastelloy® C22 exhibited better performance, with localized corrosion only in the fusion zone, that was greatly influenced by the composition of the filler materials and welding techniques.