Galvanic Coupling Effect Research Articles

Corrosion mapping of intermetallic in a dissimilar weldment using in-situ alternating current scanning electrochemical microscopy

In the present work, in-situ corrosion activity mapping across explosively welded 304 L SS-Zr-4 dissimilar joint interfaces was performed using intermittent contact alternating current-scanning electrochemical microscopy (IC-AC-SECM). Two weld joint samples, one with a regular interface and another with an irregular interface, were examined for their local surface activities at an open circuit potential in tap water without using a redox mediator. The SEM micrographs showed the formation of intermetallics at localized regions of the irregular interface weld sample but not in the regular interface sample. The 304 L SS regions of the welds were relatively anodic, with current and impedance magnitude values of 270 ± 20 nA and 380 ± 20 kΩ respectively, when compared to the Zr-4 regions with the corresponding values of 160 ± 20 nA and 630 ± 20 kΩ, due to galvanic coupling effect. The IC-AC-SECM technique enabled the in-situ determination of corrosion activity of localized intermetallic region within the weldment. The current and impedance magnitude values of the intermetallic region were ∼ 240 nA and ∼ 450 kΩ, respectively, showing only a slightly lesser anodic activity as compared to the 304 L SS base metal. The results obtained from the IC-AC-SECM mapping showed a good correlation with the EDS elemental mapping of the dissimilar weldment with intermetallic. The findings indicate the effectiveness of the IC-AC-SECM technique for the in-situ localized corrosion mapping of dissimilar weld joints, showcasing its potential for various applications in assessing weld integrity.

Coupling effect of precipitates and hydrogen on pitting corrosion of stainless steel: Low potential region around precipitates

The coupling effect of hydrogen and NbCrN precipitate on pitting initiation and propagation of stainless steel were studied. After hydrogen charging, HMT results showed that more hydrogen was enriched on and around the precipitates. According to In-situ SKPFM and immersion results, the Volta potential of the precipitates is higher than that of the matrix before and after hydrogen charging. However, after hydrogen charging, a low Volta potential region appeared around the precipitates. The enrichment of hydrogen around the precipitates, the low potential around the precipitates, and consequent galvanic coupling effect lead to pits preferentially initiating and developing around the precipitates.

Effect of brazing and artificial aging on the corrosion and strengthening behavior of a quad-layer Al alloy composite

PurposeThis study aims to investigate the influence mechanism of brazing and aging on the strengthening and corrosion behavior of novel multilayer sheets (AA4045/AA7072/AA3003M/AA4045).Design/methodology/approachPolarization curve tests, immersion experiments and transmission electron microscopy analysis were used to study the corrosion behavior and tensile properties of the sheets before and after brazing and aging.FindingsThe strength of the sheet is weakened after brazing due to brittle eutectic phases, and recovered after aging due to enhanced precipitation strengthening in the AA7072 interlayer. The core of nonbrazed sheets cannot be protected due to the significant galvanic coupling effect between the intermetallic particles and the substrate. Brazing and aging treatments promote the redissolved of second phased and limit corrosion along the eutectic region in the clad, allowing the core to be protected.Originality/valueAA7xxx alloy was added to conventional brazed sheets to form a novel Al alloy composite sheet with AA4xxx/AA7xxx/AA3xxx structure. The strengthening and corrosion mechanism of the sheet was proposed. The added interlayer can sacrificially protect the core from corrosion and improves strength after aging treatment.

Mn oxide conversion coating on AZ31B Mg alloy with hexafluorozirconate as an inhibitor in the permanganate conversion bath

Surface modification is essential for Mg alloys, including conversion coating, plasma electrolytic oxidation, organic coating, and plasma spraying. Permanganate conversion coating is a potential alternative to chromate coating for Mg alloys. A continuous MnO2 coating on commercial Mg alloys, which generally contain micrometric secondary phase particles, is still challenging. A thin, continuous MnO2 conversion coating layer on AZ31B Mg alloy was successfully prepared by adding hexafluorozirconate anions (ZrF62−) to an acidic permanganate conversion bath. AZ31B Mg alloy comprised α-Mg matrix and micrometric Al8Mn5 particles. In addition to MnO2 and MgO/Mg(OH)2, MgF2 was present in the coating formed in the presence of ZrF62−, but the amount of ZrO2 was scarce. The average thickness of the coating was reduced from 665 to 66 nm when 0.02 M ZrF62− was added. As a result, the contact resistance was reduced from 367 to 8.59 mΩ. Meanwhile, the corrosion resistance was improved. The uniformity of MnO2 coating was discussed, focusing on the Al8Mn5/Mg galvanic coupling effect.

Substitution of Zn for Cu in Mg–Y–Zn alloys designed for fracturing ball

The microstructure, mechanical properties and degradation behaviour of Mg95Y3Zn2 (MYZ), Mg95Y3Zn1Cu1 (MYZC), and Mg95Y3Cu2 (MYC) (at.-%) alloys have been studied. All the alloys mainly contain α-Mg matrix and LPSO phase. By substituting Zn for Cu, the composition of the LPSO phase transformed from Mg–Y–Zn to Mg–Y–Zn–Cu, and then to Mg–Y–Cu. The ultimate compressive strength is 227, 231 and 238 MPa, respectively. The MYC alloy exhibited much higher degradation rate than MYZC and MYZ alloys. The strong galvanic coupling effect between LPSO phase and the matrix, the grain size refinement and the weak protection from the corrosion product layer are responsible for the high degradation rate. It is suggested that the newly developed MYC alloy is promising for fracturing ball application.

Impact of residual cementite on inhibition of CO2 corrosion of mild steel

A thick cementite skeleton exposed on a ferritic-pearlitic C1018 steel surface after pre-corrosion significantly compromised inhibition efficiency. However, this detrimental effect was insignificant for a lower carbon X65 steel with dispersed cementite microstructure, due to the insignificant amount of cementite that remained on its surface after pre-corrosion. After normalizing the increased cathodic area in the presence of residual cementite back to original area, both anodic and cathodic reactions were inhibited to the same extent as on bare steel with a sufficient inhibitor concentration. However, the detrimental effect of cementite cannot be completely eliminated due to its galvanic coupling effect.

Correlation of microstructure and bio-tribocorrosion behavior of equal channel angular pressed pure titanium

The effect of equal channel angular pressing (ECAP) strain (i.e., 1st to 4th pass) on the grain size and eventual mechanical and bio-tribocorrosion properties of commercially pure titanium (cp-Ti) has been investigated. Ultra-fine grains (UFG) of 0.8 µm size (from 12 µm) and yield strength enhancement to 785 MPa (from 381 MPa) have been observed for the ECAP 4th pass sample as compared to the annealed condition of cp-Ti. In addition, the maximum hardness increased by 101 HV to 293 HV in the 4th pass samples due to grain refinement caused by the ECAP process. Further, the tribocorrosion behaviour as a function of cp-Ti sample conditions in the simulated body fluid (SBF) has been evaluated. The ultra-fine-grained 4th pass sample shows a lower coefficient of friction (CoF) of ∼0.35 (from ∼0.5) and wear loss due to its enhanced strength than the annealed sample. Moreover, the ECAP 4th pass sample, because of its UFG, exhibits a more negative potential shift (∼0.82 V) as compared to annealed sample (∼0.88 V). However, this shift is marginal due to its low wear scar width and depth, which eventually induced less galvanic coupling effect in it. Abrasion and adhesion are the primary wear mechanisms for all the sample conditions.

Welding and galvanic coupling effects on the electrochemical activity of dissimilar AA2050 and AA7050 aluminum alloys welded by Friction Stir Welding (FSW)

In this work, the effects of friction stir welding (FSW) on the microstructure and electrochemical activities of dissimilar AA2050 and AA7050 aluminum alloys have been investigated. Local electrochemical tests supported by surface analytical characterization were used to study the local electrochemical activities developed along the weld zones of the dissimilar alloys. The investigation was carried out on the cross-section of the welded Al alloys. The results showed that the friction stir welding (FSW) of the dissimilar alloys affected the microstructure and the electrochemical behavior of the different regions (HAZ, TMAZ, SZ) formed by the welding process. Scanning vibrating electrode technique (SVET) and micropotentiometry by using an ion-selective microelectrode showed that TMAZ was the zone with the highest electrochemical activity. This zone corresponded to the transition region between the two welded alloys. The high electrochemical activity observed in this region was associated with the effect of welding on the microstructure and, also, with the galvanic coupling between the two alloys, where the alloy AA7050 acted as an anode and the AA2050 as a cathode. Preferential corrosion attack on the AA7050 alloy was also evident.

Synergistic effect of crevice corrosion and galvanic coupling on 304SS fasteners degradation in chloride environments

The synergistic effect of crevice corrosion and galvanic coupling on the degradation of 304 stainless steel fasteners exposed to a chloride environment was investigated using electrochemical and surface analysis techniques. Results obtained revealed that the crevice region of the fastener showed lower corrosion resistance due to decreased surface passivation induced by the crevice geometry and low oxygen conditions, while the exposed region with a higher oxygen supply exhibited improved corrosion resistance. Coupling of the exposed and crevice regions of the fastener demonstrated accelerated corrosion attributable to galvanic effect. The driving force for the galvanic effect on the fastener was linked to three (3) key factors: (I) the potential difference established between the different regions on the fastener surface due to uneven oxygen distribution, (II) the difference in the solution environment, and (III) the difference in surface properties (active-passive surface). Morphological studies showed localised corrosion occurring mainly in the crevice.

Effect of selective atomic clustering, surface texture and grain boundary constitution on the corrosion behaviour of electrodeposited Sn-xBi coatings

Sn-xBi (x = 4, 7, 10, 14, and 17 wt%) coatings were electrodeposited onto mild steel to elucidate their corrosion behaviour. The B14 (Sn-14 wt% Bi) and B7 (Sn-7 wt% Bi) coating exhibited the highest (Polarization resistance (Rp) = 12,810.2 Ω·cm2) and least corrosion resistance (Rp = 2843.2 Ω·cm2), respectively. B14 coating exhibited the lower energy near (301) plane orientation against B7 coating which showed higher energy (321) and (111) plane orientation along the exposed surface. The galvanic coupling effect alleviated in B14 coating due to Sn nanoclusters into Bi grains as revealed by the atom probe tomography analysis.

INVESTIGAÇÃO DA ATIVIDADE ELETROQUÍMICA DE LIGA Al-Cu-Li APÓS PROCESSO DE SOLDAGEM POR FRICÇÃO E MISTURA

INVESTIGATION OF THE ELECTROCHEMICAL ACTIVITY OF AN Al-Cu-Li ALLOY AFTER FRICTION STIR WELDING PROCESS. In this work, the local electrochemical activity of the zones coupled by Friction Stir Welding (FSW) of an Al-Cu-Li alloy was studied and the results were correlated to the microstructural characteristics of each zone. Electrochemical studies were carried out in the zones affected by welding using cyclic voltammetry (CV) and scanning electrochemical techniques (namely, SECM - Scanning Electrochemical Microscopy and LEIS – Local electrochemical impedance spectroscopy). The results showed that the welding joint (WJ) is predominantly cathodic relatively to the heat affected zones (HAZ). The HAZ was always anodic and showed the highest electrochemical activities among the tested ones. The high electrochemical activity of the HAZ was associated with the effect of galvanic coupling between the cathodic region (WJ) and the anodic region (HAZ). In addition, the advancing side (AS) presented increased electrochemical activity compared to the retreating one (RS).

Corrosion mechanism of Ti-6Al-4V morse taper dental implants connected to 316 L stainless steel prosthetic abutment

The aim of this work was to investigate the effect of galvanic coupling between stainless steel AISI 316 L abutment type Morse taper and implant made of ASTM F1108–14 Ti-6Al-4V alloy. The assembly of the two alloys was carried out using mechanical imbrication by means of successive strikes at 0.05 J force onto the abutment inserted in the implant along the centerline. Corrosion attack at the interface of the alloys was evaluated according to the number of strikes used for joining the parts. Corrosion resistance was evaluated for the samples by open circuit potential measurements as function of time and scanning vibrating electrode technique (SVET) and scanning ion selective electrode technique (SIET) in phosphate buffer solution with pH adjusted to 3.0, and into which hydrogen peroxide was added to simulate tissue inflammatory conditions. Samples were evaluated at the cross and longitudinal sections. Results indicated that the number of strikes used in assembling affected corrosion susceptibility. The lowest amount of corrosion products was associated to the highest number of strikes used. The corrosion resistance was related to the characteristics of the crevice between the implant and the abutment. • Galvanic corrosion between Ti grade V dental implants and AISI 316 L prosthetic abutment was investigated. • Localized attack susceptibility increased with the number of strikes to connect the Ti grade V dental implant and the AISI 316 L abutment. • Local electrochemical techniques were very useful in evaluating the corrosion of the coupled dental implant and prosthetic abutment.

Characterization and evaluation of stable localized corrosion in a 7075-T6 aluminum alloy FSW joint before and after anodizing treatment

The microstructure and corrosion processes of a friction stir welded (FSW) 7075-T6 aluminum alloy joint, before and after anodizing surface treatment, have been characterized by advanced techniques, and the feasibility of anodizing treatment as a corrosion mitigation method has been evaluated. The results showed that different zones of the FSW joint had distinctly different microstructure and consequently different corrosion behavior in NaCl solution. Stable localized corrosion occurred in the transitional regions between the thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ), and was characterized by intergranular corrosion. The intergranular corrosion was ascribed to the galvanic coupling effect between Cu-rich grain boundary precipitates and the precipitates free zones (PFZs). Although anodizing and the subsequent sealing treatments could greatly improve the corrosion resistance of the base metal, the TMAZ/HAZ transition regions still showed much higher corrosion susceptibility than other regions. The high corrosion susceptibility of the FSW joint after anodizing treatment is not ascribed to the difference of the anodic oxide film in the regions, but the heterogeneous microstructure of the alloy beneath the anodic film. The present paper has shown that the stable localized corrosion in the FSW joint is intrinsically stemmed from the welding process itself and traditional mitigation method such as anodizing treatment cannot solve the problem; more effective corrosion mitigation methods are still awaited.

New insights into the mechanism of localised corrosion induced by TiN-containing inclusions in high strength low alloy steel

This work investigated the chemical and electrochemical mechanisms of localised corrosion triggered by CaS·xMgO·yAl2O3·TiN complex inclusions in high strength low alloy steel (HSLAS) under a simulated marine environment. Special focus was given to the role of the TiN portion of the inclusion on the initiation and growth of the corrosion pits. The thermodynamic process of pitting initiation was investigated by Gibbs free energy, Pourbaix diagram and first principle calculation. Localised corrosion is mainly induced by inclusions and triggered by dissolution of adjacent distorted matrix. Chemical dissolution of CaS portion in CaS·xMgO·yAl2O3·TiN complex inclusion creates an acidic aggressive environment that accelerates the further dissolution of inclusion and matrix. Galvanic coupling effect between TiN inclusion and matrix is directly verified. TiN covered with a TiO2 film acts as the cathodic phase in galvanic corrosion, although it has a lower Volta potential than the matrix. This is an unusual correlation with the scanning Kelvin probe force microscopy result, which has been explained for this special system.

Effect of hydrostatic pressure on galvanic corrosion of low-alloy steel in simulated deep-sea environments

ABSTRACT In order to study the effect of high hydrostatic pressure on the corrosion of low-alloy steels in deep-sea environments. The electrochemical corrosion behavior of single-metal system and triple-metal coupled system of 907A steel, 921A steel and 1# steel under different hydrostatic pressures were studied by electrochemical, weight loss and morphology observation methods. The results show that the high hydrostatic pressure promotes the corrosion of low-alloy steel by changing the composition and morphology of corrosion products. In addition, there was also severe galvanic corrosion between the couples with a low potential difference (< 60 mV),907A steel was used as the anode of the three-metal coupled system, and 921A steel and 1# steel as the cathode. The galvanic coupling effect accelerates the pitting corrosion of 907A steel as an anode metal. When using multi-metal couplers with low potential differences, they should be protected by both coating protection and cathodic protection.

Flash butt welding corrosion of mooring chains

ABSTRACT Flash butt welding is a resistance welding process that offers great advantages due to its high thermal efficiency, simplicity and high speed, makes it ideal for welding mooring chains. Despite its advantages, numerous corrosion problems are still being found in practice, both in the heat-affected zone and the weld line. Literature is scarce about it, limiting mostly to state the problem. The majority of the studies attribute this preferential corrosion to local changes in the microstructure that induce a galvanic coupling effect. Mooring chain R3 grade steel with preferential corrosion along the weld line has been studied from both metallographic examinations and electrochemical methods. Small differences were found in the microstructure of the heat-affected zone and base material (mainly composed of tempered martensite) but nevertheless, significant with respect to its corrosion behaviour. The corrosion mechanisms are discussed with particular attention to the electrochemical differences around the welding line.

Controlling the compactness and sp2 clusters to reduce interfacial damage of amorphous carbon/316L bipolar plates in PEMFCs

In proton exchange-membrane fuel cells, the compactness and composition of amorphous carbon (a-C) films directly affect the interface-induced degradation of a-C-coated metallic bipolar plates, but their roles and synergistic effects are ambiguous. In this study, by changing the working pressure, the compactness and composition of a-C are adjusted, and the relationship among the plasma state, microstructure, and performance of coated 316L stainless steel are studied. Results show that, at 2 mTorr, a high ionization degree of the plasma causes high compactness (highest density 2.52 g/cm3) and large sp2 cluster size in a-C films, resulting in their best performance. At 11 mTorr, the low ionization degree causes their loose structure and large sp2 cluster size. The possible galvanic coupling effect can result in serious interface damage and the highest Fe ions concentration of 13.05 ppm after a potentiostatic test. Thus, high compactness and large sp2 cluster sizes should be obtained simultaneously to improve their performance.

Antibacterial Efficacy of Cold-Sprayed Copper Coatings against Gram-Positive Staphylococcus aureus and Gram-Negative Escherichia coli

Contact surfaces have been identified as one of the main routes for pathogen transmission. The efficacy to kill both viruses and bacteria on touch surfaces is critical to reducing the rampant spread of harmful pathogens. Copper is one such material that has been traditionally used for its antimicrobial properties. However, most contact/touch surfaces are made up of steel or aluminum due to their structural properties. Therefore, coating high-touch components with copper is one possible solution to improve antibacterial efficacy. In this study, copper was coated on both stainless steel and aluminum substrates using a cold spray process which is a fast and economic coating technique. The coated samples in both as-deposited and heat-treated states were exposed to Escherichia coli and Staphylococcus aureus bacteria, and their efficacy was compared with bulk copper plate. It was found that both bacterial cells responded differently to the different coating properties such as coating thickness, porosity, hardness, surface roughness, oxide content, and galvanic coupling effect. These correlations were elucidated in light of various results obtained from antibacterial and bacterial attachment tests, and materials characterizations of the coatings. It is possible to tailor copper coating characteristics to render them more effective against targeted bacteria.

Local enhancement of hydrogen production by the hydrolysis of Mg17Al12 with Mg “model” material

The effect of galvanic coupling on the corrosion behavior of Mg and Mg17Al12 in Mg-Al alloys was studied by Scanning ElectroChemical Microscopy (SECM). The effect of galvanic coupling between Mg and Mg17Al12 was investigated using a “model” Mg+Mg17Al12 material with a controlled microstructure to evaluate the hydrogen evolution at a micrometric scale. SECM maps revealed that galvanic coupling between Mg and Mg17Al12 accelerates the corrosion rate (formation of a thicker passive layer) of both components. Mg17Al12 acts controversially to a conventional cathode in galvanic system since hydrogen production by its hydrolysis reaction was found to increase due to the electron transfer with the anode (Mg).

Salivary pH Effect on Orthodontic Appliances: In Vitro Study of the SS/DLC System

Stainless steels (SS) are the most-used alloys for manufacturing fixed orthodontic appliances due to their attractive set of mechanical properties, biocompatibility, and high corrosion resistance. Nevertheless, during regular orthodontic treatments–taking at least around 2 years–the intraoral environment inevitably degrades these bioalloys, releasing metallic ions into the oral cavity. In the first part of this in vitro study, the corrosion resistance of commercial SS appliances (brackets, tubes, and bands) was evaluated in Fusayama-Meyer artificial saliva at pH values of 2.3 and 6.8 over the course of 30 days. As expected, the results corroborated that salivary pH highly influences corrosion behaviour. Released Ni, Cr, and Fe were within dietary intake values. In the second part, a novel approach for oral corrosion prevention based on the chemical inertness of DLC materials is presented. SS surfaces were functionalized with biocompatible a-C:H-sputtered coatings and submitted to the same experimental conditions. The anticorrosion ability of this system was demonstrated, preventing the pitting corrosion that occurred on the SS substrates. Despite the galvanic coupling effect due to the presence of the Cr-based interlayer, this study enhanced the potential use of the reactive sputter-deposited a-C:H coatings in orthodontics.