Galvanic Corrosion Prevention of Complex Assemblies through Modeling

Development of a galvanic monitoring probe to improve service life prediction of reinforced concrete structures with respect to reinforcement corrosion

Lightweight metals such as aluminum (Al) are being frequently coupled to polymer-matrix composites (PMCs) to reduce weight and improve performance in a multitude of applications in the defense, aerospace, automotive and civil-infrastructure industries. The intimate contact of carbon-fiber reinforced (CFR) PMCs with Al alloys can result in galvanic corrosion of the Al alloys. The electrically conductive carbon fibers in the CFR PMCs serve as cathodes and induce galvanic corrosion of the Al. The galvanic corrosion between 6061-T6 Al and CFR PMC can be effectively attenuated by decoupling Al from CFR PMC using an insulating skirt layer. The deposition of salts on the insulative skirt, however, can create a continuous ionically-conductive electrolyte film that can bridge the CFR PMC and Al, thus reducing the effectiveness of the skirt. The utilization of hydrophobic coatings on the skirt can help to attenuate galvanic corrosion by breaking up the continuous electrolyte film. In this study, the effect of hydrophobic coatings on insulative skirt materials was investigated to attenuate galvanic corrosion between mechanically coupled 6061-T6 Al and CFR PMC. Experiments were conducted in accelerated laboratory and outdoor conditions. The galvanic corrosion rates were monitored for coatings of different degrees of hydrophobicity, various skirt lengths, and exposure conditions and. Initially, the galvanic corrosion rates for couples with different insulating-skirt lengths coated with a silane-based ceramer (i.e., Siloxel) were monitored in a humidity chamber at 30o C and 90% RH over a period of up to 3 days using the zero resistance ammeter (ZRA) technique. The couples were sprayed with salt solutions of different concentrations. Results from this accelerated humidity ZRA experiment showed that a skirt length of only 0.5 inch was very effective in attenuating galvanic corrosion. To study the effectiveness of different coatings, specimens were fabricated with a 0.5-inch long skirt and coated with either Siloxel, epoxy, polyurethane or latex. The resulting galvanic corrosion rates were then compared. The two best coatings in attenuating galvanic corrosion (i.e., Siloxel and polyurethane) were selected for outdoor exposure. CFR PMC/Al galvanic couples with 0.5 inch insulating skirts (with either the Siloxel or polyurethane coatings, or no coatings) were exposed at rain forest (Manoa) and severe marine (MCBH) environments for 2 months. The CFR PMC/Al galvanic specimens at the severe marine site were exposed in two conditions: sheltered and unsheltered. The sheltered specimens were subjected to significant salt build up; whereas, the unsheltered specimens were subjected to cleansing effects of rain. The effect the salt deposition characteristics on galvanic corrosion between the sheltered and the unsheltered conditions was studied.

A Type 1 niobium (Nb) part and a grade 5 titanium (Ti6Al4V) part were joined by laser weld, to form a component to be used in implantable medical devices for electrical stimulation therapies. This component could be exposed to body fluid or particularly water which could penetrate through the medical adhesive seal over the time of implantation. To meet the device reliability, performance, and patient safety goals, electrochemical immersion testing was conducted to study corrosion of the base metals and their galvanic couples and to evaluate corrosion resistance of the weld joints. Samples of as-manufactured Ti6Al4V parts, Nb parts, and weld joints were prepared, cleaned and inspected for testing (Figure 1, Table 1). A wire made of the same material and mostly sealed by medical adhesive, was welded to each sample for electrical connection. The surface areas of samples were calculated. They were divided into groups and tested at 37°C in glass jars containing de-ionized (DI) water or phosphate buffered saline (PBS), respectively. Electrochemical tests including open circuit potential (OCP); cathodic polarization (CP) or anodic polarization (AP); galvanic corrosion or zero resistance ammeter (ZRA) testing; anodic cyclic polarization (ACP) and potentiostatic polarization (PP) were performed at different times during immersion of the samples. The potentiodynamic scan rate for CP, AP and ACP scans was 0.2 mV/s. The tests used three-electrode configuration consisting of a working electrode (WE) which was the testing sample; a reference electrode (Ref.) which was a Ag/AgCl electrode in 3 M NaCl solution; and a counter electrode (CE) which was a piece of platinum sheet, or for galvanic corrosion testing, which was the secondary working electrode of the Nb/Ti6Al4V galvanic couple. Visual and stereomicroscopic examinations were made during and after the testing with a total of immersion time of about 100-130 days. After 3-4 days of immersion, OCP was stabilizing with an average of about 0.08, 0.05 and 0.07 V vs. Ref. in DI water and 0.11, -0.02 and 0.06 V vs. Ref. in PBS, for the Ti6Al4V, Nb and joint samples, respectively. Though the OCP difference was small, it indicated Nb would act as anode when joined or coupled to Ti6Al4V. Galvanic corrosion could occur in Nb of the joint, especially considering the anode (Nb) to cathode (Ti6Al4V) area ratio was as small as 0.01. A galvanic current was estimated to be about 9-13 nA/cm2 in DI water and 24-42 nA/cm2 in PBS based on anodic polarization of Nb and cathodic polarization of Ti6Al4V in potentiodynamic scans (Figure 2a). Further, galvanic corrosion potential and current (Figures 2b and 2c) of the Nb/Ti6Al4V couples was measured by ZRA testing. After ~48 days of testing, the galvanic current was stabilized with an average of about 1 nA/cm2 in both DI water and PBS, indicating a stable passive film formed on Nb surface. The average galvanic corrosion rate of Nb of the couples was about 0.008 μm/year in both DI water and PBS, calculated from the measured galvanic current which was considered more accurate (as obtained in a more steady state) and much lower than the estimation from potentiodynamic scans. ACP curves of the joint and base metal samples showed similar polarization behavior in both DI water and PBS (Figure 2d). All samples displayed stable passivation with low current from OCP to a potential of Ep ≅0.8 V vs. OCP. Beyond Ep, current increased markedly, and small hysteresis formed in ACP scans for the joint and Nb samples. Additional potentiostatic polarization was thus performed on the joint and Nb samples in PBS for ~4 days at potentials of 1.2 V and 1.4 V vs. Ref. which were above Ep and in the hysteresis range. The current would stabilize at the increased levels for both potentials. Neither localized pitting or crevice corrosion attack nor active gas bubbling was observed on the joints and parts. Corrosion rate estimated from the increased current at 1.4 V vs. Ref. for Nb could be as high as 66 μm/year. Depending on the type of device design, an electrochemical potential possibly applied to the joint component was assessed under simulated electrical signals for stimulation, which was measured to be under 0.3 V vs. Ref. and smaller than Ep. Therefore, the joint materials of Nb and Ti6Al4V are stable and suitable for the device application with no concern of corrosion. Figure 1

PurposeThe purpose of this paper is to evaluate the galvanic corrosion of nitinol orthodontic wires with six dental alloys in artificial saliva and consider the effect of initiated localized corrosion and real surfaces of anode and cathode on galvanic current.Design/methodology/approachLinear polarization and cyclic polarization curves for each alloy in de‐aerated Duffo and Castillo's artificial saliva are obtained. Galvanic corrosion investigation is conducted by polarization curve intersection and mixed potential theory methods. In order to verify the initiation of localized corrosion, scanning electron microscopy is used.FindingsInitiation of localized corrosion on the anode increases the galvanic current up to 45 times and therefore considering the effect of localized corrosion on galvanic corrosion is necessary. Placing stainless steel brackets or Aristaloy amalgam in direct contact to nitinol arch wire is not recommended.Originality/valueIn order not to underestimate the galvanic corrosion between two alloys, it is recommended to consider the effects of localized corrosion and anode/cathode surface area ratio. In this paper, an electrochemical method for estimating these factors is proposed.

Lithium-sulfur (Li-S) batteries are promising next-generation rechargeable batteries due to their ultrahigh theoretical energy density. However, their cycling lifespan is hindered by the poor stability of Li metal anodes. The main challenge lies in the severe Li polysulfide (LiPS) corrosion on Li metal anodes. Herein, galvanic corrosion induced by LiPSs is identified as the main cause of nonuniform Li deposition and dissolution in working Li-S batteries. Concretely, LiPSs continuously corrode the Li metal anode and thereby increase its electrode potential to different extents according to the corrosion kinetics. The electrical connection of the Li metals with different corrosion kinetics causes galvanic corrosion and consequent selective Li deposition in severely corroded locations. Consequently, spatially heterogeneous LiPS corrosion eventually induces localized Li utilization, uneven Li distribution, and accelerated cell failure. To alleviate the galvanic corrosion, a Li fluoride-rich solid electrolyte interphase is preconstructed to passivate Li metal, suppress LiPS corrosion, and extend the cycling lifespan of Li-S batteries by 57% under harsh working conditions. This work identifies the chemical nature of nonuniform Li deposition following the galvanic corrosion mechanism and highlights the importance of passivating Li metal anodes to realize long-cycling Li-S batteries.

Galvanic corrosion generally occurred on Al/Cu bond pads post wafer saw resulted in pitting but no pitting was observed at wafer incoming. There is significant interest in the corrosion behavior of Cu-containing Al alloy, such as PL455, which remain of importance for automotive application due to bondability and reliability safety concern. All of pitting existed Cu precipitation on central of pit holes. A simple experiment simplifies galvanic corrosion condition and reveals its mechanism for definition root cause of pitting. Incoming wafer immerse into di-water in various temperature and air/nitrogen dissolved for 40 and 60 minutes. The experiment results conducted that low temperature and nitrogen dissolved into di-water can suppressed galvanic corrosion however it can't be fully suppressed due to halogen residual on bond pad post CF 4 plasma descum (accelerated corrosion rate) and copper precipitation on Al grain boundary during anneal. Copper precipitated in the Al grain boundary that created Al/Cu galvanic potential and interface, which was galvanic corrosion staring point and then galvanic reaction occurred while Al/Cu couple immersed into electrolyte environment which trigger galvanic corrosion. It interprets galvanic corrosion is observed post wafer saw.

Iron carbonate (FeCO3), magnetite (Fe3O4) and iron carbide (Fe3C) layers are able to form on carbon steel surfaces in aqueous carbon dioxide (CO2) environments, and suspected to play a critical role in uniform and localized corrosion of the underlying steel. Fe3C and Fe3O4 are known to establish micro-galvanic cells with uncovered regions of the steel surface, due to their conductive and semi-conductive nature respectively, enhancing corrosion rates. To evaluate the significance of the layers’ galvanic corrosion in an aqueous CO2 environment, layers of Fe3C, Fe3O4 and FeCO3 were formed on X65 carbon steel surfaces. The coupons were then galvanically coupled to a bare X65 carbon steel coupon at different area ratios (AR = 1 and 10) in a pH 5, 1 wt.% NaCl, CO2-saturated solution at 50°C. Galvanic currents were measured using zero resistance ammetry over 24 h, with similarly high galvanic currents measured for the Fe3C-bare steel and Fe3O4-bare steel couples, enhancing the bare steel corrosion rates. The galvanic current was significantly smaller and reversed for the FeCO3-bare steel couple, enhancing rather the corrosion rate of the FeCO3-covered coupon.

Galvanic corrosion of metal/ceramic coupling

Chapter C.13 - Galvanic corrosion

The galvanic corrosion of magnesium alloy AZ91D coupled to a steel fastener was studied using a boundary element method (BEM) model and experimental measurements. The BEM model used the measured polarization curves as boundary conditions. The experimental program involved measuring the total corrosion rate as a function of distance from the interface of the magnesium in the form of a sheet containing a mild steel circular insert (5 to 30 mm in diameter). The measured total corrosion rate was interpreted as due to galvanic corrosion plus self corrosion. For a typical case, the self corrosion was estimated typically to be ∼ 230 mm/y for an area surrounding the interface and to a distance of about 1 cm from the interface. Scanning Kelvin Probe Force Microscopy (SKPFM) revealed microgalvanic cells with potential differences of approximately 100 mV across the AZ91D surface. These microgalvanic cells may influence the relative contributions of galvanic and self corrosion to the total corrosion of AZ91D.

The demand for the use of carbon-fiber-reinforced plastics (CFRP) in rehabilitation of deteriorating infrastructure is increasing worldwide. The design characteristics of reinforced concrete or steel members can be enhanced significantly by epoxy bonding CFRP laminates to the critically stressed tension areas. There is, however, a concern regarding possible galvanic corrosion when carbon and steel are bonded together. This paper presents the result of a study on the galvanic corrosion between CFRP laminates and steel. A total of 38 specimens made of steel and carbon fibers were prepared and tested. Two simulated aggressive environments and three different amounts of epoxy coating were used in addition to samples with no coating at all. Furthermore, the effect of the sizing agent on the galvanic corrosion rate was investigated, and three different solvents were used to remove the sizing agents from the surface of the carbon fibers. Potentiodynamic polarization and galvanic corrosion tests were conducted. T...

Electrochemical polarization methods were utilized to study the galvanic corrosion of steel coupled to brass. Polarization of a 70Cu-30Zn brass cathode controlled galvanic corrosion rate (galvanic current) of the steel anode in the couple. The effect of cathode/anode surface area ratio was predicted successfully from a single pair of polarization curves on cathode and anode. Above 40% copper, copper-zinc alloys behave essentially like pure copper. Below this critical composition, the alloys behaved like pure zinc. Dichromate inhibitor decreased galvanic current by increasing cathodic polarization on 70 Cu-30Zn brass; nitrite did the same by increasing anodic polarization on the steel. Tolytriazole (TTA) increased polarization on both brass and steel, but the resultant decrease (inhibition) of the galvanic current was not as great as that of either dichromate or nitrite at the same concentration.

Examining amino acids as environmentally friendly corrosion inhibitors for Cu and Co chemical mechanical planarization

The effect of sulfate-reducing bacteria (SRB) on electrochemical corrosion behavior of 16Mn steel, and galvanic corrosion behavior of the steels in the juncture area between bacterial and bacteria-free sea mud was studied in laboratory under simulated conditions. Sea mud dense with SRB was taken from the Qingdao beach. Part of the sea mud was sterilized and the rest was kept in the original condition. The sterilized and original sea mud was put respectively into two plastic testing troughs electrically-connected by an agar potassium chloride salt bridge. Galvanic and non-galvanic 16Mn steel samples were put into the trough at the same intervals. The SRB number measured by the MPN tri-tube method was about 2.4×105 per 100 g mud and was kept basically the same during the experimental period. Thep, pH, eH, T, S (salinity) were measured simultaneously. The galvanic current was measured with zero-resistance galvanometer and the corrosion rate was measured with the weight loss method. The results showed that (1) the corrosion rate of 16Mn steel in bacterial sea mud was 4.0 times that in bacteria-free sea mud; (2) galvanic corrosion occurs between steel samples buried in different (bacterial and bacteriafree) sea mud. The steel sample in the bacterial sea mud was the anode of a galvanic couple and had higher corrosion rate than that of the non-galvanic sample. The existence of the galvanic couple increased the corrosion rate of the sample in bacterial sea mud by 4.1%.

Comparison of the short and long-term degradation behaviors of as-cast pure Mg, AZ91 and WE43 alloys