This study introduces enhanced corrosion performance of the Al-Si-Mg coated 22MnB5 boron steel. Structural changes of the coating after hot-dip-aluminizing and hot-press-forming processes with the presence of Mg included compacter surface with Mg segregation and thicker crack-free layer. Electrochemical corrosion tests indicated higher polarization resistance from the Al-Si-Mg sample compared to the reference Al-Si sample, especially in an early period of immersion. Such enhanced anti-corrosion performance can be attributed to the aforementioned structural changes and pore-filling effect of corrosion products. This study depicts that the Al-SiMg coating can be considered as another option for hot-press-forming steel by its enhanced barrier protection vs. This study introduces enhanced corrosion performance of the Al-Si-Mg coated 22MnB5 boron steel. Structural changes of the coating after hot-dip-aluminizing and hot-press-forming processes with the presence of Mg included compacter surface with Mg segregation and thicker crack-free layer. Electrochemical corrosion tests indicated higher polarization resistance from the Al-Si-Mg sample compared to the reference Al-Si sample, especially in an early period of immersion. Such enhanced anti-corrosion performance can be attributed to the aforementioned structural changes and pore-filling effect of corrosion products. This study depicts that the Al-Si Mg coating can be considered as another option for hot-press-forming steel by its enhanced barrier protection vs. Al-Si coating.

This study introduced an enhanced corrosion performance of an epoxy coated rebar (ECR) embedded with the nanocapsules containing triethanolamine (TEA) as the corrosion inhibitor. Electrochemical corrosion tests indicated a successful protection of the artificially defected area from the sample with encapsulated TEA coating, especially in the initial immersion period, indicating that there was a successful release of TEA from the embedded nanocapsules. A considerably lower surface current density of the encapsulated TEA coating also indicated that the electrochemical reactions were delayed which were further confirmed by surface micrographs that revealed a relatively less degraded artificial defect of the sample with the encapsulated TEA coating. The corrosion product analysis denoted that the inhibiting action has delayed the further oxidation of the exposed surface by having an enhanced barrier protection that helped to maintain a lower O/Fe ratio.

Triethanolamine (TEA), an amine-based corrosion inhibitor, was encapsulated and then embedded into an epoxy coating to provide long-term corrosion protection of aluminum alloy 3003. TEA was encapsulated by means of free-radical polymerization, yielding an average particle size of 450 nm. An applied epoxy coating containing 10 wt % of the nanocapsules successfully protected an artificially defective area for a long period due to TEA adsorption, which resulted in the formation of an inhibiting layer. Electrochemical impedance spectroscopy showed an inhibition efficiency surpassing 85% when the metal experienced mild corrosion in its early stages, and the inhibiting layer started to form by local pH level change, which triggered the release of TEA. On the basis of the results of a scanning vibrating electrode technique, the current density of the metal surface in the presence of an encapsulated TEA coating was significantly lower than that of the control coating with no nanocapsules. Optical microscope and scanning electron microscope images revealed that the sample surface that had encapsulated TEA nearby was considerably less stained after 60 days of testing compared with that of the control sample, which indicated that the metal substrate was protected by an inhibiting layer. Elemental analysis performed by energy-dispersive X-ray spectroscopy further confirmed that the metal surface was well preserved, and a remarkably low oxygen content indicated suppressed metal oxidation. The nuclear magnetic resonance spectra also evidenced a successful release of TEA throughout the experimental period. These findings reflected a spontaneous surface repassivation with the help of encapsulated TEA coating.

It has been documented that the corrosion behavior of AZ91 (Mg–9Al–1Zn, wt.%) alloy is strongly influenced by the morphology, distribution, and volume fraction of secondary phases, however, the proposed corrosion mechanisms are questioned due to new experimental findings. The present study focused on providing a more detailed understanding of the corrosion mechanism of a peak-aged AZ91 alloy exposed to a chloride environment by using scanning Kelvin probe force microscopy, immersion testing, optical microscopy, scanning and transmission electron microscopy techniques and electrochemical microcell technique. It was found that corrosion was simultaneously initiated in the interior of α-Mg grains and in the local α-Mg phase within the α + β lamellar precipitate; furthermore, the lamellar precipitate/α-Mg matrix boundary acted as a barrier for corrosion propagation. The proposed corrosion initiation mechanism is opposed to previous investigations reporting the development of micro-galvanic coupling between the β-Mg17Al12 phase and the adjacent α-Mg matrix, which cannot be supported by our experimental findings. The corrosion propagation in the peak-aged alloy was dominated by the preferential anodic dissolution at the interior of the α-Mg matrix due to its faster corrosion reaction kinetics compared to the micro-galvanic corrosion process between the β-phase and the local α-Mg phase occurring inside the lamellar precipitate.

A good combination of mechanical properties and corrosion performance is desired when employing Mg alloys in engineering applications. Therefore, it is essential to investigate both the mechanical properties and corrosion resistance of processed Mg alloys to determine the optimum combinations of materials properties. This study investigates the microstructure, mechanical properties, and corrosion resistance of AZ91 (Mg–9Al–1Zn, wt.%) alloys in chloride-containing environments under different processing conditions. The findings revealed that the AZ91 alloy exhibits good mechanical properties combined with high corrosion resistance after microstructure modification through equal channel angular pressing (ECAP). This microstructure was characterized by a bimodal grain structure with the formation of a high volume fraction of well dispersed β-Mg17Al12 precipitates. The superior mechanical properties of the AZ91 alloy after ECAP process were mainly attributed to the combined effect of significant grain refinement and high volume fraction of fine β-Mg17Al12 precipitates that provided grain boundary and precipitation strengthening and promoted a more uniform plastic deformation. The enhanced corrosion resistance of the fine-grained AZ91 alloy was related to the presence of a highly protective oxide layer, the formation of a highly adherent and compact layer of corrosion products, and the development of uniform corrosion with shallow corrosion pits. This simultaneous improvement in strength, ductility, and corrosion resistance of fine-grained AZ91 alloys can serve as a guide for future alloy design and represents a promising alternative for industrial applications.

Here, we present a numerical approach to analyze the integrity of a vessel that was subject to a weld repair. A Post-Weld Heat Treatment (PWHT) process was implemented to a vessel undergone weld repair due to leakage. Due to the thick wall of the welded bottom head, this welding process must be followed by the PWHT to relieve the residual stress, as well as to improve the material properties. PWHT process was performed by heating the welded area to reach 675 °C temperature. A numerical approach using finite element analysis (FEA) method was performed to analyze the integrity of the vessel. Based on the analysis, the structure is still stable within the applied load. PWHT process does not lead to buckling on the main structure and the load is still lower than the load required for the occurrence of buckling. A sensitivity analysis was also performed with reduced temperatures to 630 °C or reduction of PWHT area width. These changes were found to have negligible effects in reducing the stress and strains in the vessel. After PWHT is completed, the structure is still considered to be safe to be operated, as indicated by its strain that is still below the allowable strain and only relatively small deflection was occurred.

In this work, a bioresorbable Mg-ZKQX6000 (Mg-6Zn-0.6Zr-0.4Ag-0.2Ca (wt%)) alloy was severely plastically deformed via equal channel angular pressing (ECAP) according to three unique hybrid routes at low temperatures (200 degrees C to 125 degrees C). The roles of ECAP processing on microstructure, and ensuing mechanical properties and corrosion rates, are assessed. Microstructurally, ECAP induces a complex plethora of features, especially variations in grain sizes and precipitates' sizes, distributions, and morphologies for individual cases. Mechanically, ECAP generally refined grain size, resulting in ultra-high strength levels of about 400 MPa in ultimate tensile strength for several cases; however, deformation via ECAP of precipitates induced embrittlement and low elongation to failure levels. Corrosion testing, conducted in simulated bodily fluid at bodily pH levels to mimic conditions in the human body, revealed consistent corrosion rates across several techniques (mass loss, hydrogen evolution, and electrochemical impedance spectroscopy (EIS)), showing that severe plastic deformation deteriorates corrosion resistance for this material. In-situ corrosion monitoring explained that corrosion accelerated after ECAP due to the creation of heterogeneous, anodic shear zones, which exhibited dense regions of refined grains and fine precipitates. Suggestions for future design and thermomechanical processing of Mg alloys for bioresorbable orthopedic implants are provided.

The degradation of ultra-fine grained aluminum alloys involves multiple localized corrosion mechanisms at once which make its understanding complex. Here we investigate the electrochemical response of a partially recrystallized ultra-fine grained AA6061 alloy after a low-temperature post-aging treatment. Our results show that the anodic current density, the severity of the filiform corrosion along the shear direction, and the intergranular corrosion are significantly influenced by the precipitation within the shear bands, being the highest at peak aging. Also, passivation is enhanced but the passive film is less stable after ECAP regardless of the low- temperature post-aging treatment. because of the high density of dislocation, precipitates, and grain boundary in the extruded material.

We present the preparation and inhibition behavior of rebar in the presence of calcium nitrate (CN)-containing microcapsules with concentrations of 0.50, 2.00, and 5.00 wt.% in concrete. From both open circuit potential (OCP) and electrochemical impedance spectroscopy spectra, it was found that an addition of microcapsules containing CN corrosion inhibitor into concrete beams successfully repassivated or maintained the passivity of the rebar when the concrete was cracked. This corrosion inhibitor repassivated the rebar by forming a passive layer on the rebar surface under the crack. This repassivation process was evident by an increase of OCP values to more positive values or by stable OCP values at around -100 mV vs SCE. An increase in phase angle after corrosion activation for the sample with 2.00 wt.% microcapsule clearly showed this repassivation process. The optimum concentration for maintaining the passivity on rebar in the cracked concrete was found to be 5.00 wt.%.

We present the preparation and inhibition behavior of rebar in the presence of microencapsulated calcium nitrate (CN) with concentrations of 0.5, 2.0, and 5 wt.% in concrete. From both open circuit potential (OCP) and electrochemical impedance spectroscopy spectra, it was found that an addition of CN corrosion inhibitor-containing microcapsules into concrete beams successfully repassivated or maintained the passivity of the rebar when the concrete was cracked. This corrosion inhibitor healed the rebar by forming a passive layer on the rebar surface under the crack. This healing process was evident by an increase of OCP values to more positive values or by stable OCP values at around -100 mV vs SCE. An increase in phase angle after corrosion activation for CN C 2% clearly showed this healing process. The optimum concentration for maintaining the passivity on rebar in the cracked concrete was found to be 5 wt.%.

In this study, corrosion response of the 2060-T8E30 alloy was analyzed in the following environments: EXCO (an immersion test in accordance with ASTM G34), modified EXCO, and modified ASTM acetic acid salt intermittent spray (MASTMAASIS), which were used to predict the alloy system's exfoliation corrosion (EFC) susceptibility. Here, results show that exposure to the first two environments failed to accurately predict EFC during seacoast exposure while the latter was successful. The final attacks in the 2060 alloy varied from solution to solution. In EXCO solution with a pH of 0.25 and chloride content of 4 M, a severe attack of EFC occurred in the 2060 alloy. In modified EXCO solution with a pH of 3.4 and chloride content of 1.1 M, intergranular corrosion was present. Pitting corrosion appeared on the 2060 alloy in MASTMAASIS environment with pH of 3 and chloride content of 1 M. Additionally, electrochemical impedance spectroscopy signature, video capture microscopy images, and scanning electron microscope images revealed the formation of a new interface on the 2060 alloy resulting from grain lifting in the EXCO solution. Here, it is shown that there is a synergistic action between the corrosion product wedging and the pressure of hydrogen gas during the grain lifting.

In this study, we investigated exfoliation corrosion (EFC) of the alloy 2060 T3E80 in an aggressive solution, namely EXCO. The pH value increased from 0.25 at the initial time point to 3.45 after 96 h of testing. In Stage 1 (0.25 < pH < 3.00), the pH value increased significantly and the aluminum surface experienced anodic dissolution. During this step, a massive hydrogen evolution reaction was observed, and pits formed due to the galvanic effect between the anodic and cathodic sites. The electrochemical impedance spectroscopy (EIS) test and equivalent analogs suggest that the inductive loop at low Nyquist frequencies and phase angle plots correspond to the adsorbed intermediates in the reduction reaction. In Stage 2 (3.00 < pH < 3.45), the pH value slowly increased. The continuous pits along the grain boundaries produced intergranular corrosion (IGC) during this stage. A small amount of delamination occurred at this stage. In Stage 3, pH remains constant and IGC extensively propagate, allowing the accumulation of white gelatinous corrosion products under the grains. These, along with hydrogen bubbles underneath the grain, exerted pressure to the grain that was attacked by IGC, resulting in a lifting of the grain. The grain lifting at this stage was abundant. It is clear from the cyclic potentiodynamic polarization and scanning electron microscopy images that the pits formed on this alloy surface in the EXCO solution can be attributed to fall-out of particles instead of passive film breakdown. (C) 2015 Elsevier B.V. All rights reserved.

This study focuses on the transpassivity of super austenitic stainless steel (UNS N08367) in a LiBr solution using electrochemical techniques, i.e., cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy tests combined with the surface analysis technique, i.e., x-ray photoelectron spectroscopy (XPS). The transpassivity of UNS N08367 in 2.5 M LiBr solution corresponds to the dissolution of Cr, Mo, and Ni at high potentials. This study illustrates how the adsorption of intermediate Mo species is responsible for the appearance of an inductive loop in the Nyquist plot at low frequencies. The addition of alloying elements such as Cr and Mo successfully prevents localized corrosion; however, these alloying elements increase the susceptibility of this material to general corrosion by the formation of an anodic film. Nickel does not directly contribute to the formation of passive film in this alloy, as illustrated by the absence of passivation in the CPP curve and by the weak XPS sig...

Aluminum Alloys are widely used for aircraft application in both commercial and military fields. The increasing development in performance and efficiency has led to Al-Cu-Li Alloys, as these are capable of being lighter while achieving similar or superior levels of mechanical properties of their commonly used counterparts. The need to evaluate new alloys such as Al 2060 to their susceptibility to corrosion, especially Exfoliation Corrosion (EFC), becomes evident as this corrosion mechanism is known to be one of the main reasons of failure of aluminum alloys. The aim of this paper is to use electrochemical and surface analysis techniques to evaluate the susceptibility to EFC in Al 2060 in the Exfoliation Corrosion (EXCO) solution proposed in ASTM G34, propose a mechanism and describe the different stages of the damage evolution of the material. Electrochemical techniques include Open Circuit Potential (OCP), Cyclic Potentiodynamic Polarization (CPP), Galvanostatic Polarization (GS), Electrochemical Impedance Spectroscopy (EIS) and Electrochemical Noise (EN).

We investigate the transpassivity of super-austenitic stainless steel UNS N08367 in 2.5 M LiCl solution by using cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and X-ray photoelectron spectroscopy (XPS). The CPP curve exhibits negative hysteresis, which indicates a transpassive dissolution process instead of pitting corrosion. The transition from the passive region to the transpassive region is characterized by EIS and equivalent circuit analysis. During the transpassive dissolution of the N08367 alloy, two reactions of adsorbed intermediates are dominant, as indicated by the two inductive loops at the transpassive region. The first inductive loop is associated with the faster reaction, i.e., the adsorption of Fe intermediates. This fast reaction is significantly influenced by the preferential dissolution of Fe during the transpassive dissolution. The second inductive loop is correlated with the adsorption of the Cr intermediate. In contrast to Fe, the Cr content on the surface increases in the transpassive region compared with the content in the passive region. The XPS spectra support the time and frequency domain approach for the preferential dissolution, and the dominant species resulted from the interfacial processes at the transpassive region.

External corrosion direct assessment includes four steps in the SP ECDA standard practice as a recommended methodology. The first step in the process is the pre-evaluation and the fourth step is the post assessment; we propose the first step to include the integration of macro-parameters, such as rainfall, water accumulation, chemistry of the soil, and soil corrosiveness. These parameters are associated with indirect measurement influencing corrosion (as time-dependent threats) for underground pipelines. Real time macro-modeling was used to enhance the pre-assessment and indirect assessment and clustering analysis was performed to aid in the pre-evaluation and post assessment steps. This work aims to provide a case study for pre-evaluation assessment based on dynamic macro-modeling previously introduced for external corrosion direct assessment of a buried pipeline that is 110 km (68.35 miles) in length and 457.2 mm (18in) in diameter. The macro-modeling concept was previously presented and was based on the parameters affecting the soil properties in different regions during four seasons due to the climate, rainfall, soil properties and environmental parameters. The noise of the field data obtained from indirect surveys and direct assessments can be reduced based on a statistical approach (principal component analysis), and the soil and environmental properties are then grouped into similar clusters via clustering models in order to increase accuracy of the estimation of the corrosion rate in an underground pipeline. The statistical analysis helped to develop the pre-evaluation and post assessment step for the ECDA process.

A brine storage tank was reported to have visible and severe localized corrosion 1 year after installation. The material used for this tank was UNS S31603 stainless steel. The corrosion was mainly noticeable at various points/areas along the welded joint, and there was also some pitting on the base metal at the bottom of the tank. Corrosion was also found at the welded joint at the hatch wall. Indications of severe corrosion that resulted in deep metal loss were found at some points along the welded joint. The results of an oxalic acid etch test in the heat-affected zone (HAZ) showed the interdendritic ditches, which are considered to be prone to intergranular corrosion/weld decay. The results of a double-loop electrochemical potentiokinetic reactivation (DL-EPR) test and 3D multiscale images were in agreement with the results of an oxalic acid etch test that indicated the intergranular corrosion susceptibility of the HAZ. The base metal, in contrast, did not show any intergranular corrosion. (C) 2014 Elsevier Ltd. All rights reserved.

We studied crevice corrosion of UNS S32003 using a single-boss crevice former. This crevice assembly with a single boss at the center is a modification of the commonly used multiple-crevice assembly (MCA). This design effectively prevents unwanted crevice corrosion outside the crevice of interest. Our single-boss crevice assembly produces comparable repassivation potentials obtained using cyclic potentiodynamic polarization (CPP), Tsujikawa-Hisamatsu Electrochemical (THE), potentiodynamic-galvanostatic-potentiodynamic (PD-GS-PD), and potentiostatic (PS) techniques. Considering the degree of attack, we found that the THE technique is the most powerful for forming a deep, wide, and continuous crevice corrosion site, while the PS technique is the least powerful technique at potentials slightly above the repassivation potential. A galvanostatic hold in step 2 of the THE and PD-GS-PD techniques successfully grows a deep localized corrosion site, as indicated by a deep crevice corrosion attack found in samples tested with these techniques. The PS step (step 3) in the THE technique allows the grown localized corrosion site formed by a previous step (a galvanostatic hold) to propagate inward and along the crevice mouth, creating a wide and continuous crevice corrosion attack along the crevice mouth. Metastable pits play a role in crevice corrosion of UNS S32003 alloy in this study, as indicated by a large number of metastable pits in the crevice region. The ferrite phase is preferentially attacked by metastable pits. (C) 2014 Elsevier B.V. All rights reserved.

The purpose of this research was to study the synthesis of TiO2 nanotubes on Ti-10Ta-10Nb thin film and the effect of applied potential on the tube size, length and morphology. The Ti-10Ta-10Nb thin film was deposited by dc magnetron sputtering on the CP Ti substrate. The anodization of this Ti-10Ta-10Nb thin film was performed in the solution containing 1M H3PO4 + 1.5wt.% HF at the potential readings of 4, 6, 8 and 10 V for 10 minutes. The results showed that there was a slight increase in the tube diameter from approximately 25 nm at 4 V to 50 nm at 8 V. The length of nanotube varied from 700-900 nm. Interestingly, at the potential of 10 V, the nanotube diameters were damaged with slight decreases in nanotube lengths (500 nm).