Corrosion Current Density Research Articles

AZ31-calcium-deficient hydroxyapatite (CDHA) composites produced by friction stir processing: controlling the degradation by enhancing the biomineralisation

ABSTRACT In the present work, calcium deficient hydroxyapatite (CDHA) was dispersed into the surface of AZ31 Mg alloy within the solid state by friction stir processing and the role of the refined microstructure and the presence of nano-CDHA on biomineralization and corrosion performance was investigated. Fine grains (1.6 ± 2.1 µm) have been produced in AZ31-CDHA composite compared with base alloy (41 ± 6.1 µm) and nano-CDHA was observed as reinforced into AZ31 matrix. X-ray diffraction analysis confirms the texture change due to FSP in the composite. Wettability studies carried out by measuring contact angles on the surface of the composites indicated increased surface energy (37.27 ± 5.1 mJ/m2) compared with the base alloy (20.55 ± 3.4 mJ/m2) . From the potentiodynamic polarization studies, lower corrosion current density (1.69 ± 1.13 × 10-5 A/cm2) was observed for the composite. From the immersion studies in simulated body fluids, higher level of biomineralization on the composite helped to decrease the degradation rate as reflected from the lower weight loss (7.5 ± 1.1 %) compared with the base alloy (12.1 ± 1.3 %). The results demonstrate the promising role of enhanced biomineralization on controlling the degradation of AZ31-CDHA composite..

Ex-situ Characterization of Nb-Ti Alloy/Pt Coated Stainless Steel Bipolar Plates for Proton Exchange Membrane Fuel Cells

Metallic bipolar plates are crucial for the development of compact and lightweight proton exchange membrane fuel cell stacks; however, most of them encounter durability and conductivity challenges in the fuel cell environment. In this study, Nb-Ti alloy/Pt coatings are deposited on SS316L plates to enhance corrosion resistance, surface wettability, electrical and thermal conductivity, with reduced interfacial contact resistance. Corrosion resistance is assessed by exposing test samples to a 1M H2SO4 acidic environment at 25 °C and 80 °C, respectively, via potentiostatic and potentiodynamic polarization tests. It is found that Nb-Ti alloy/Pt coatings exhibit exceptional stability, with corrosion potential increased by 2.5 (at 25 °C) and 0.5 (at 80 °C) times and corrosion current density reduced by orders of magnitude; and their anti-corrosion performance far exceeds the technical targets set by the US Department of Energy, with a protective efficiency of 99.98 % at both temperatures tested. The coated samples have reduced water affinity, indicated by significantly larger contact angle values compared to the uncoated samples in both pre-and post-corrosion tests. The incorporation of Nb-Ti alloy/Pt coatings on SS316L increases the in-plane electrical conductivity by 42.6 % and thermal conductivity by 3.5 %; surpassing the US Department of Energy's technical targets in these categories as well. At a compaction force of 140 N/cm2, the interfacial contact resistance for the coated samples is about 2.5 times lower than the Department of Energy's requirements. These results indicate the viability of Nb-Ti alloy/Pt coated SS316L bipolar plates for fuel cell applications.

Enhanced Intrinsic Self-Healing Performance of Mussel Inspired Coating via In-Situ Cation Capture.

Under damp or aquatic conditions, the corrosion products deposited on micro-cracks/pore sites bring about the failure of intrinsically healable organic coatings. Inspired by mussels, a composite coating of poly (methyl methacrylate-co-butyl acylate-co-dopamine acrylamide)/phenylalanine-functionalized boron nitride (PMBD/BN-Phe) is successfully prepared on the reinforcing steel, which exhibits excellent anti-corrosion and underwater self-healing capabilities. The self-healing property of PMBD is derived from the synergistic effect of hydrogen bonding and metal-ligand coordination bonding, and thereby the continuous generation of corrosion products can be significantly suppressed through in situ capture of cations by the catechol group. Furthermore, the corrosion protection ability can be remarkably improved by the labyrinth effect of BN and the inhibition role of Phe, and the desired interfacial compatibility can be formed by the hydrogen bonds between BN-Phe and PMBD matrix. The corrosion current density (icorr) of PMBD/BN-Phe coating is determined as 7.95×10-11Acm-2. The low-frequency impedance modulus (|Z|f = 0.0 1 Hz is remained at 3.47×109Ωcm2, indicating an ultra-high self-healing efficiency (≈89.5%). It is anticipated to provide a unique strategy for development of an underwater self-healing coating and robust durability for application in anti-corrosion engineering of marine buildings.

Incorporating GO in PI matrix to advance nanocomposite coating: An enhancing strategy to prevent corrosion

Abstract This research endeavors to advance the anti-corrosive characteristics, mainly the physico-mechanical properties, by incorporating graphene oxide (GO) into a polyimide (PI) matrix. So, a nanocomposite coating is fabricated for an aluminum alloy substrate. Results reveal that the coating was uniformly dispersed across the surface signifying that the inclusion of GO increased the PI dispersion. The π–π stacking interactions between the aromatic rings of PI and GO contribute to their stability and improved anticorrosive properties. The incorporation of GO to PI films significantly enhances hydrophobicity, as evidenced by the increased contact angles. Assessing the corrosion resistance of the coating in a 3.5 wt% NaCl solution through electrochemical impedance spectroscopy and potentio-dynamic polarization establishes a prominent correlation between the percentage of GO and the anticorrosion efficiency of the composite coating. Precisely, the nanocomposite coating containing 5 wt% GO exhibits an impressive impedance modulus value of 107, and the corrosion current density (I cor) is drastically reduced by over three orders of magnitude, reaching 4.8 × 10−9 A cm−2, as indicated by the polarization curve. Also, prolonged immersion tests confirm the exceptional protective ability of the S5 coating (5 wt% GO), effectively shielding the metal for up to 100 h. After conducting diagnostic measurements, the hybrid nanocomposites of GO/PI examined in this study showcased their effectiveness as inhibitors in anticorrosive coatings. These composites played a vital role to hinder the oxidation of underlying aluminum alloy when exposed to oxidizing chemicals, water, or air, thereby extending the protective duration.

Investigation on the Passive Behavior of Ti-9Mn Alloy in 3.5 wt% NaCl Solution

Abstract Ti-9Mn alloy, widely used in aerospace and hydrogen storage, was recently introduced for use in marine and offshore structures because of its competitive mechanical characteristics. In this study, passive behavior of Ti-9Mn alloy was compared to the commercially pure titanium (cp-Ti). Ti-9Mn exhibited lower charge-transfer resistance than cp-Ti. Under steady-state condition, resistivity at metal /oxide film interface for Ti-9Mn alloy, which increased as fa unction of applied passive potential in range of 0.5 to 1.5 VSCE, was found to be lower than that of cp-Ti. Complex-capacitance (C∞) value for Ti-9Mn alloy was higher than that of cp-Ti. Presence of Mn in the alloy induced significant increase in current density when potential exceeds 1.5 VSCE. Corrosion current density of Ti-9Mn (16.2 ± 4.0 nA cm-2) was three times higher than that of cp-Ti (4.57 ± 0.7 nA cm-2) after 21 days immersion in 3.5 wt% NaCl. The study may allow us to realize the full potential passivation behavior of Ti-9Mn for future marine and offshore applications.

Effect of solution pH value on the corrosion resistance of Co-Fe LDHs coating developed on MAO treated magnesium alloy AZ31

As a post-treatment method of MAO coating, layered doubled hydroxides (LDHs) can improve the corrosion/degradation resistance of magnesium (Mg) alloys. This study innovatively prepared Co-Fe LDHs coatings on MAO treated Mg alloy AZ31, and investigated the effect of pH value on the corrosion/degradation resistance of the coatings. The results indicate that the corrosion/degradation resistance of LDHs coatings first increase and then decrease with the increase of pH. The best corrosion/degradation resistance occurred for pH = 12, with a corrosion current density (icorr) of 5.18×10–8 A∙cm–2. The icorr after immersing in NaCl solution for 14 days was 1.65×10–6 A∙cm–2. The Co-Fe LDHs nanosheets (pH = 12) effectively sealed the pores of the MAO coating, resulting in increased coating density and hindering the diffusion of corrosive media, thereby effectively protecting the Mg alloy. This study is of great significance for the corrosion protection and rapid degradation prevention of Mg alloys and other alloys.

One-step hydrothermal preparation of corrosion-resistant coatings with microsphere structure

Rapid corrosion rate is limiting the engineering application of magnesium alloys. In this paper, an attempt was made to produce a corrosion resistant coating on the surface of AZ91D magnesium alloy using hydrothermal method. The coating surface is covered with microspheres and has a dense structure, which effectively isolates the contact between the outside world and the substrate. The corrosion potential(E) raised from −1.57 V to −0.45 V compared to the bare sample. The corrosion current density and corrosion rate of the coating can be reduced by 6 orders of magnitude, and the polarization resistance raised by 6 orders of magnitude. The thickness of the coating is 45.4 μm at the moment, with a minimum of defects on the surface, resulting in excellent corrosion resistance in the immersion test. The coating also has good adhesion strength at 4B, which can expand the application range of magnesium alloy in corrosive environments.

Study on the effects of nano-copper addition on the properties of epoxy resin/graphite composite bipolar plates

Bipolar plates (BPs) are vital components in Proton Exchange Membrane Fuel Cells (PEMFCs), and their performance and cost significantly impact fuel cell stack efficiency and affordability. BPs require excellent conductivity, strength, and corrosion resistance depending on usage conditions. Common graphite and metal-based BPs offer good conductivity, but they have their drawbacks. Graphite lacks strength and is costly to process, while metal-based BPs need additional surface treatments to prevent corrosion. In recent years, composite bipolar plates have gained widespread attention due to their excellent conductivity, mechanical properties, and outstanding corrosion resistance. In this study, we used natural graphite flakes as the main conductive filler and nano-copper as the secondary conductive filler, with epoxy resin as the binder. The composite bipolar plate was prepared using a hot-pressing method. The study found that adding 1 wt% of nmCu can increase the conductivity of the composite BP by 75.2%, but it decreases the flexural strength by 26.84%. The prepared nmCu/G/EP composite BP exhibits an ASR of only 4.00 mΩ cm2 and a corrosion current density of 2.615 × 10−7 A/cm2, meeting the DOE 2025 expectations. After conducting Cu2+ leaching experiments on the prepared composite BP, single-cell performance testing showed a maximum power density of 0.556 W/cm2. This study expands the range of conductive fillers for composite BPs, no longer limited to carbon-based conductive fillers.

Dual-Function Hybrid Coatings Based on Polytetrafluoroethylene and Cu2O for Anti-Biocorrosion and Anti-Wear Applications

Corrosion and wear issues of motion components exposed to water-based corrosion mediums, e.g., naval vessels and oil extraction equipment, pose challenges for the lifespan and reliability of the motion systems. In this work, epoxy-based coatings modified with polytetrafluoroethylene (PTFE) and cuprous oxide (Cu2O) nanoparticles were prepared. The anti-corrosion performance of the coatings was comparatively investigated by electrical impedance spectroscopy and Tafel tests in sterile and sulphate-reducing bacteria (SRB) mediums. Moreover, the tribological behaviors of the coatings were examined under water lubrication conditions. Our results demonstrate that the epoxy coatings lower significantly the corrosion current density icorr and the charge transfer resistance of the electrical double layer Rct of the carbon steel substrate. Interestingly, the hybrid coatings filled with both PTFE and Cu2O exhibit excellent anti-corrosion and anti-wear performance. After being immersed in the SRB medium for 18 days, the icorr of the pure EP coating and hybrid coatings are 1.10 × 10−7 Amp/cm2 and 0.3 × 10−7 Amp/cm2, and the Rct values are 1.04 × 103 Ω·cm2 and 3.87 × 103 Ω·cm2, respectively. A solid tribofilm forms on the stainless steel counterface sliding against the hybrid coating, which is surmised to be essential for the low friction coefficients and wear. The present work paves a route for formulating the dual-function coatings of anti-biocorrosion and anti-wear.

Application of MgO/ZrO2 coating on 309 stainless steel to increase resistance to corrosion at high temperatures and oxidation by an electrochemical method

Abstract 309 stainless steel is one of the steels that have the highest resistance to corrosion and thermal oxidation compared to other steel grades, but it should not be used at temperatures higher than 980°C if there are temperature fluctuations. Additionally, 309 stainless steel is not designed for use in wet environments and has the least corrosion resistance. This study aims to cover 309 stainless steel with MgO/ZrO2 particles using a two-step electroplating deposition method and then sintering to increase its resistance to wet corrosion and oxidation in temperature fluctuations. The intermediate ZrO2 coating makes the outer MgO layer about two times thicker and reduces the corrosion current density. The morphology of the coatings was determined using scanning electron microscopy and X-ray diffraction, and oxidation resistance was determined using cyclic oxidation tests and the wet corrosion test of the corrosion solution. 3.5% NaCl was used. The results showed that the coated samples, due to the use of TiO2 middle layer and MgO protective layer in the electrochemical method, have a 2-fold increase in wet corrosion and an increase in hardness of about 77%, as well as an increase in oxidation resistance of 1.8% compared to the sample without coating. Also, the reason for using the electrochemical deposition method is for better surface smoothness and less porosity of the coating as well as its use on all metals compared to thermal spray methods.

Study on the properties of Ni-W-CrN thin films on X80 pipeline steel: Effect of current density and deposition time

X80 pipeline steel, an essential material for oil and gas pipelines, faces challenges in maintaining its integrity due to internal friction and exposure to corrosive environments. Addressing this issue, our study utilized electrodeposition to create a nano Ni-W-CrN composite protective coating on its surface for the first time, enhancing resistance to such wear and corrosion. The results indicate that the film prepared under a current density of 3 A dm−2 and deposition time of 60 min exhibits the finest structure, with a smooth surface, and an average thickness of 35 μm. The microcrystalline size ranges in the 8–15 nm range and the maximum hardness of 813 HV. Under these conditions, the lowest wear rate achieved was 1.16 mm3 (N m)−1. Electrochemical measurements show that the corrosion current density reached a minimum of 6.14 × 10−7 A dm−2, indicating excellent corrosion resistance. Simultaneously, the ratio of microhardness to Young's modulus (H3/E2) reached a maximum of 0.051, indicating the film's optimal resistance to deformation. This provides significant support for the fabrication of high-performance films on the surface of X80 pipeline steel.

Corrosion Inhibition Performance of Brachystegia eurycoma Leaf Extract on Mild Steel in Acid Media

The aim of this work is to investigate the corrosion inhibition of B. eurycoma leaves extract as a natural inhibitor for mild steel corrosion in 3 M H2SO4 solution. The corrosion inhibitory activity was analyzed by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The surface roughness and its properties through scanning electron microscopy (SEM). The obtained result from EIS divulges that the gradual increase in inhibitor concentration and time of immersion leads to progressive increase in inhibition efficiency. At the end of 8 hours immersion time and inhibitor concentration of 1000 mg/l the highest inhibition efficiency of (88%) was obtained. The potentiodynamic polarization results indicated that addition of B. eurycoma leaves extracts hindered the reaction rates of anodic and cathodic reactions thereby performing as mixed- type inhibitor. The corrosion current density also revealed that in the presence of B. eurycoma leaves extracts the value of corrosion density reduced considerably from 265.2 \(\mu\) A/cm2 for sample without inhibitor to 67.8 \(\mu\) A/cm2 for sample with inhibitor. Again, it was observed that in the presence B. eurycoma leaves extracts the mechanism of hydrogen (effervescence) evolution was unique whereas the anodic dissolution of iron mechanism experienced the impact of the inhibitor. SEM inspection revealed that the mild steel surface showed smoother and lower damage in the presence of inhibitor. Obvious correlations were found between corrosion inhibition efficiency and some quantum chemical parameters such as energy of highest occupied molecular orbital (EHOMO), energy of lowest unoccupied molecular orbital (ELUMO), energy gap (EL–H) and electronic density etc. The obtained results were further elucidated with frontier molecular orbital theory.

The effect of Al on the corrosion resistance of binary Mg-Al solid solutions: Combining in-situ electrochemistry with combinatorial thin films

The effect of varying Al concentrations on the electrochemical corrosion resistance of binary Mg-Al solid solutions thin films under alkaline immersion conditions was investigated via a combination of in-situ flow-cell, scanning vibrating electrode technique and microscopy analysis. These spatially resolving characterization techniques are employed along the Al concentration gradient of the combinatorically grown thin films enabling efficient screening of the Al concentration dependent electrochemical corrosion behaviour. The analysis revealed an increasing corrosion resistance with increasing Al concentration, as a consequence of Al induced hydroxide reinforcement. Specifically, the addition of >4 wt.% Al decreases the corrosion current density in the range of 70–90 % compared to pure Mg.

Microstructure and Phase Composition of Novel Crossover Al-Zn-Mg-Cu-Zr-Y(Er) Alloys with Equal Zn/Mg/Cu Ratio and Cr Addition

Microstructure and Phase Composition of Novel Crossover Al-Zn-Mg-Cu-Zr-Y(Er) Alloys with Equal Zn/Mg/Cu Ratio and Cr Addition

Dense Al2O3 sealing inhibited high hydrostatic pressure corrosion of Cr/GLC coating

The corrosion failure of amorphous carbon (a-C) coatings is commonly ascribed to the existence of growth microdefects, which serve as pathways for corrosive fluids to permeate the substrate. Atomic layer deposition (ALD) is renowned for its ability to augment the corrosion resistance of metallic materials. Graphite-like carbon (GLC) is one of the amorphous carbon materials dominated by hybridized sp2-C bonds. In this study, an ALD-deposited Al2O3 layer is specially introduced on the Cr/GLC multilayer coating to solve the aforementioned corrosion risk of a-C by taking the sealing conception for defects. Compared to the as-deposited Cr/GLC coating, the coating encapsulated with Al2O3 layer depicts the reduction of corrosion current density over two orders of magnitude under a wide pressure range of 0.1 ~ 15 MPa. Particularly, the presence of released Crn+ and Fen+ in the corrosion solution is significantly diminished, accompanying with a small quantity of Aln+ generated in sealed coating during corrosion. Microstructural analysis and electrochemical results identified that both the dense Al2O3 layer offered strong safeguard for Cr elements released from multilayers, whilst amorphous carbon network inhibited the likelihood chloride penetration induced by partially infiltrated Al2O3, which made the synergistic contributions to the enhancement of corrosion resistance for Cr/GLC coating for deep-sea applications.

Laser remelting of high-velocity arc-sprayed Fe-based amorphous coating for improving corrosion resistance in 3.5 % NaCl solution with varying Na2S concentrations

In this study, high-velocity arc-spraying (HVAS) was employed to produce Fe-based amorphous coatings, and subsequent to that, laser remelting (LR) technology was applied on the as-sprayed coatings (ASC) to prepare laser remelted coatings (LRC). The corrosion resistance of both coatings was tested in 3.5 wt% NaCl solutions containing varying Na2S concentrations (0, 20, 50, 100, and 200 ppm) to accurately simulate the corrosion environment of offshore components. The corrosion behavior was investigated using electrochemical workstation, scanning electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy. The experimental results revealed that LR resulted in the elimination of defects in Fe-based amorphous coatings, a substantial reduction in porosity, the disappearance of the laminar structure, and the achievement of a homogeneous composition. The corrosion tendency of ASC and LRC both exhibited a pattern of initially decreasing, then increasing and finally decreasing with increasing sulfide concentration. This was attributed to the deposition of corrosion products on the surface and the dissolution of the corrosion products. When the sulfide concentration exceeded 50 ppm, the corrosion current density of both coatings slowly and was lower than that at 20 ppm, indicating that both coatings possessed strong corrosion resistance at higher sulfide concentrations. Highly polarized anions in solution (e.g. HS−, S2−) occupied vacancies in the passivation film, destabilizing the coating's passivation film and consequently diminishing its corrosion resistance. From the electrochemical analysis, it was evident that LRC exhibited greater corrosion resistance than ASC at all sulfide-containing solution concentrations, which was attributed to its smoother surface, denser structure and more stable passivation film.

The Effects of B on the Microstructure and Corrosion Resistance of Zn–6Al–3Mg Alloy Coating

Hot dip galvanized zinc‐aluminum‐magnesium steel plates are widely used in fields such as power communication, automotive manufacturing, and marine engineering due to their excellent corrosion resistance. The use of microalloying can further improve their corrosion resistance. The effects of B on the microstructure and corrosion resistance of Zn–6Al–3Mg (ZAM) alloy coatings are systematically examined. Data indicates that the eutectic structure of the coating progressively refines as B content increases, concomitant with a reduction in the thickness of the Fe2Al5 inhibition layer owing to the augmented formation of an Al‐rich phase at the surface. When the addition of B reaches 0.12%, the microstructure of the alloy coating is minimized, and there is no further reduction in the thickness of the Fe2Al5 inhibition layer. Moreover, the presence of B diminishes the corrosion current density and bolsters corrosion resistance. Optimal corrosion performance, indicated by maximal density and uniformity of surface corrosion products and the lowest corrosion current density, is achieved at a B addition of 0.12%. The judicious selection of B content is pivotal for enhancing the microstructural and anti‐corrosive properties of ZAM alloy coatings. Therefore, adding 0.12% B to ZAM alloy can effectively improve the microstructure and corrosion resistance of the alloy coating.

Predicting the impact of water transport on carbonation-induced corrosion in variably saturated reinforced concrete

A modelling framework for predicting carbonation-induced corrosion in reinforced concrete is presented. The framework constituents include a new model for water transport in cracked concrete, a link between corrosion current density and water saturation, and a theory for characterising concrete carbonation. The theoretical framework is numerically implemented using the finite element method and model predictions are extensively benchmarked against experimental data. The results show that the model is capable of accurately predicting carbonation progress, as well as wetting and drying of cracked and uncracked concrete, revealing a very good agreement with independent experiments from a set of consistent parameters. In addition, insight is gained into the evolution of carbonation penetration and corrosion current density under periodic wetting and drying conditions. Among others, we find that cyclic wetting periods significantly speed up the carbonation progress and that the induced corrosion current density is very sensitive to concrete saturation.

Study on corrosion characteristics and mechanism of laser powder bed fusion of Mg–Zn–Zr alloy

Laser Powder Bed Fusion (LPBF) presents novel opportunities for the processing and manufacturing of magnesium (Mg) alloys. However, Mg alloys consistently face challenges with poor corrosion resistance. Consequently, it becomes imperative to delve into the corrosion behavior and mechanisms of Mg alloys formed through LPBF. This paper investigated the electrochemical corrosion behavior, the distribution of corrosion products, and the corrosion mechanism of LPBF ZK60 Mg alloy. The results show that the corrosion current density (Icorr) value of LPBF ZK60 Mg alloy is 3.76 μA∙cm−2. The hydrogen evolution in Hank's solution steadily increases with immersion time and reaches a stable state after 24 h. The corrosion rates calculated based on hydrogen evolution and weight loss are 2.1 mm/y and 2.4 mm/y, respectively. The corrosion resistance of LPBF ZK60 Mg alloy is predominantly affected by three factors: uneven microstructure, internal crack defects, and precipitate phases. The melt pool boundary is identified as a corrosion-vulnerable zone, which extends into the columnar crystal zone after corrosion. Crevice corrosion occurs at microcracks, and the precipitate phases within the grains and matrix induces galvanic corrosion. These findings suggest that the corrosion resistance of LPBF ZK60 Mg alloy may be regulated through targeted measures, such as eliminating cracks, achieving microstructure homogenization, and controlling the precipitate phases (including quantity, composition, and distribution).

Release of lead, copper, zinc from the initial corrosion of brass water meter in drinking water: Influences of solution composition and electrochemical characterization

Corrosion of brass plumbing materials may lead to metal release and deteriorate the drinking water quality. In this study, the initial corrosion of brass coupon cut from commercially available water meter was investigated. High rates of Pb, Cu and Zn release from the brass coupon were found during the early stage of corrosion (0-5 d) due to general corrosion and galvanic corrosion. The corrosion current density (Icorr) increased and resistance (RF) decreased during this period indicating that severe corrosion had occurred. In a later stage (5-30 d), a decreased Icorr and an increased RF were observed due to the development of a denser layer of Pb and Cu corrosion products which regulated the release of soluble Pb and Cu. The release of Zn continued and no significant Zn precipitation was found. Overall, particulate Pb, particulate Cu and soluble Zn dominated in the metal release during the initial corrosion of brass. The release of Pb, Cu and Zn was enhanced by a lower pH. Free chlorine was found to slightly reduce the release of Pb but promote the release of Cu and Zn. The presence of Pb on the brass surfaces was found to alleviate the dezincification process. A conceptual model based on metal release profile and electrochemical characterization was proposed to describe the initial corrosion of brass in typical drinking water.