Cyclic Potentiodynamic Polarization Research Articles

Additive Manufacturing: Corrosion Proofing by Infusion of Interstitial Solute—Exemplified for Alloy 22

The corrosion resistance of Cr-containing alloy parts made by additive manufacturing can be significantly improved by a post-treatment of gas-phase-based infusion of concentrated interstitial solute (carbon and nitrogen). We demonstrate this universal approach for the example of low-temperature nitrocarburization by solid-reagent pyrolysis applied to Alloy 22 (UNS N06022) parts made by laser powderbed fusion. We show that the post-treatment improves the crevice-corrosion resistance of these parts, as well as the corrosion resistance of corresponding parts made from wrought Alloy 22 to surpass the maximum crevice corrosion test temperature specified in ASTM G48-D, whereas non-treated samples typically fail well below. Similarly, cyclic potentiodynamic polarization testing (ASTM G61-86) demonstrates that the post-treatment makes the additively manufactured alloy and the wrought alloy more corrosion-resistant than the non-treated wrought alloy.

Passivation of precipitation-hardened UNS N07718 in a shallow sour aqueous solution.

Passivation of precipitation-hardened UNS N07718 in 5 wt% NaCl + 0.5 wt% CH3COOH was investigated. Cyclic potentiodynamic polarisation revealed that the alloy surface was passivated without active-passive transition behaviour. The alloy surface was in a stable passive state during potentiostatic polarisation at 0.5 VSSE for 12 h. Bode and Mott-Schottky plots showed that the passive film became electrically resistive and less defective with n-type semiconductive properties during the polarisation. X-ray photoelectron spectra revealed that Cr- and Fe-enriched hydro/oxide layers were formed on the outer and inner layers of the passive film, respectively. The thickness of the film was almost constant with the increase of the polarisation time. The outer Cr-hydroxide layer changed into a Cr-oxide layer during the polarisation, resulting in a decreased donor density in the passive film. The film's composition change during the polarisation should be related to the corrosion resistance of the alloy in the shallow sour conditions.

Microstructure and corrosion investigation of FeCoCrNiMo0,5(MnAl)0,3 high entropy alloy produced by 316 L stainless steel scrap

FeCrCoNiMo 0,5 (MnAl) 0.3 high-entropy alloy (HEA) was manufactured via arc melting process by adding the related metal powders into scrap of 316L stainless steel for corrosion resistance tests under salt and acid conditions. Cyclic potentiodynamic polarization experiments performed under acidic conditions revealed pre-passivation due to abundance of network modifying metals in HEA composition which was further analyzed by electrochemical impedance spectroscopy. Elemental resolved analysis of leftover solutions was used to compare metal ions released during corrosion. X-ray diffraction analysis indicated the phase change in heat treated HEA samples. Non-heat treated HEA samples can be compared with stainless steel under moderate corrosion conditions and had better hardness results.

Protection of galvanized steel using benzotriazole as a corrosion inhibitor in simulated concrete pore solution and alkali-activated fly ash solution

In this study, the natural passivation ability and chloride-induced subsequent increased levels of corrosion behaviour of galvanized steel in simulated concrete pore (SCP) solution and alkali-activated fly ash (AAFA) solution, with and without benzotriazole (BTA), were evaluated using corrosion potential (Ecorr), linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and cyclic potentiodynamic polarization (CPP). In addition, scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM/EDS) were used to observe the morphologies of passive layers and corrosion products of galvanized steel. It was highlighted that the hydrogen evolution could be prevented by AAFA solution to some extent, thus providing a new insight on the inhibition of hydrogen evolution for galvanized steel in concrete. Moreover, due to the formation of a complex protective film, galvanized steel in AAFA solution exhibited significantly higher corrosion resistance to chloride attack than that exposed to SCP solution, which could be further enhanced by the addition of BTA.

Cerium Compounds Coating as a Single Self-Healing Layer for Corrosion Inhibition on Aluminum 3003

The formation of cerium hydroxide was studied, and its capacity as a corrosion inhibitor on aluminum substrates was evaluated. These particles were deposited by immersing the substrate in a bath with cerium nitrate and hydrogen peroxide. Four different immersion times were used to determine the differences in behavior from low concentrations to an excess of particles on the surface. The coatings were analyzed morphologically by scanning electron microscope (SEM) and optical microscope, and chemically by energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Electrochemical corrosion analysis was studied using cyclic potentiodynamic polarization (CPP), electrochemical impedance spectroscopy (EIS), and electrochemical noise (EN). The results show that for 2 and 5 min of immersion, there was corrosion inhibition caused by the presence of cerium Ce3+ in the coating, but with excess cerium hydroxide particles, corrosion was favored. The presence of cerium particles favors corrosion at 30 s of immersion. This is the same case at 60 min, where corrosion was favored by the excess of Ce4+ particles on the surface.

Pitting corrosion resistance of additive manufactured alloy 718 in alkaline brines at elevated temperatures

AbstractThe feasibility of additive manufacturing (AM) to produce industrial components, also for the oil and gas industry, has been demonstrated in the past. Therefore, current research efforts focus on demonstrating the reliability of AM materials subjected to demanding service conditions. In this regard, special attention has been paid to its corrosion resistance in harsh environments as one of the most critical properties in these applications. The beneficial combination of high strength, excellent thermal stability, and outstanding corrosion resistance makes alloy 718 (UNS N07718) the most used wrought and AM nickel alloy in the oil and gas industry. Wrought 718 has an extensive record of field performance in demanding oil and gas applications including directional drilling tools that undergo extreme mechanical loads in corrosive drilling fluids. On the other hand, limited data regarding the corrosion behavior of AM718 in typical drilling environments has been collected so far. In this research work, the pitting susceptibility of selective laser melted alloy 718 in simulated drilling environments has been studied. Open circuit potential measurements as well as cyclic potentiodynamic and potentiostatic polarization tests were used to characterize the pitting corrosion resistance of AM718 in alkaline brines at elevated temperatures. In addition, microstructural particularities in alloy 718 were investigated to explain the observed differences in the electrochemical behaviors.

Advanced strategies for hydrogen generation by rhodium metal catalysts coated by the electrodeposition method

The theory and kinetics of the hydrogen evolution reaction (HER) on electrodeposited rhodium in acidic media (0.5 M H2SO4 solution) were looked into. An electrodeposition approach using direct current (DC) and pulse current (PC) was used to deposit rhodium on a stainless steel 304 (SS304) substrate. Several parameters, including rhodium concentrations, current densities, temperature, pH, and coating duration, were used to optimise the rhodium bath. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray (EDX) analyses were used to assess the change in surface shape and chemical composition. The best coating was demonstrated at PC 75% duty cycle with an optimised current density of 4.0 A/dm2, which was better than the remaining PC cycles and DC source coating, indicating the most productive activity for hydrogen production. The activity of Rh catalyst coatings resembled that of pure platinum metal. Cyclic voltammetry (CV), chronopotentiometry (CP), and potentiodynamic polarisation techniques were studied to determine the HER. The results obtained from the PC technique with a 75% duty cycle give more HER performance.

Electrochemical Behaviour and Direct Cell Viability Analysis of Hybrid Implants Made of Ti-6Al-4V Lattices Infiltrated with a Bioabsorbable Zn-Based Alloy

Biodegradable metals are being developed for biomedical implants or components of implants. Biodegradable zinc-based materials, in particular, have been shown to promote bone regeneration in orthopaedic applications. Here, we investigated the potential of a hybrid Ti-Zn system, comprising a Ti-6Al-4V biostable lattice produced by additive manufacturing (AM) infiltrated by a bioabsorbable Zn-2%Fe alloy, to serve as an osseointegrated implant for dental and orthopaedic applications. The osseointegration of implants can be enhanced by a porous implant structure that facilitates bone ingrowth to achieve superior bonding between the bone tissue and the implant. The hybrid material was evaluated in terms of microstructure and localized chemical composition using scanning and transmission electron microscopy with special attention to the interface between the Ti-based lattice and the biodegradable alloy. The electrochemical behaviour of the Ti-Zn system was analysed in a simulated physiological environment in terms of open circuit potential test and cyclic potentiodynamic polarization. Cytotoxicity was evaluated using direct cell viability tests. The results demonstrate desirable properties of the hybrid Ti-Zn system as a non-cytotoxic material with an acceptable corrosion rate.

(Digital Presentation) The Effect of Tartaric-Sulfuric Acid (TSA) Anodizing on the Corrosion Resistance of the AA7475-T761

The microstructure of the high strength aluminum alloy, AA7475–T761, in the as-received condition was characterized by optical microscopy, scanning electron microscopy and transmission electron microscopy, and statistical analyses of grain size and micrometer precipitates distribution and density were performed. An anodic aluminum oxide (AAO) film was potentiostatically grown on the alloy in tartaric sulfuric acid (TSA). The anodizing behavior of the alloy and the mechanisms of localized corrosion initiation and propagation in bare (not anodized) and anodized conditions were discussed. The alloy corrosion behavior was investigated in sodium chloride solutions using electrochemical techniques (cyclic potentiodynamic polarization) and the morphology and extent of corrosion propagation was investigated through optical microscopy, optical profilometry and scanning electron microscopy analyses. It was observed that the two alloy surface conditions (bare and anodized) play different roles in the propagation of the localized corrosion process. The bare alloy presented lower localized corrosion potentials and the propagation of the localized corrosion was shallower, but more heavily distributed, than in the anodized condition. However, the alloy in the anodized condition presented lower repassivation potentials due to the deeper pits formed. In addition, the variability of pitting potentials for the anodized condition was high, due to the heterogenous structure of the AAO film formed, and dependent on the time and drying storage conditions previous to electrochemical characterizations. The electrochemical results were correlated with the microstructural characteristics of the oxide surface film of the alloy in both conditions, bare (not anodized) and anodized.

Electrochemical Study of Pitting Corrosion of Corrosion Resistant Alloys in Supercritical CO2 Environment

Various types of corrosion resistance alloys such as 13 Cr, Super 13 Cr, and duplex stainless steels are typically used in oil and gas and CO2 capture and storage applications, especially the injection section, where the pipeline could be exposed to aqueous phase and the risk of localized corrosion is of high concern. The composition of these materials is engineered to provide high corrosion-resistant properties. The operating conditions in the above-mentioned applications can include high CO2 pressure and high temperature leading to the “so-called” supercritical CO2 condition. Under the supercritical CO2 conditions, the pH of the aqueous phase in the system can be as low as pH ~ 3 buffered by the dissolved CO2. The environment can also contain high salinity, and therefore, the passive layer on the stainless steel might be locally damaged resulting in pitting corrosion. While there are numerous studies available on the localized corrosion of different stainless steels in chloride-containing aqueous environment, the number of studies in supercritical CO2 conditions is limited. The objective of this work is to understand the effect of supercritical CO2 on the localized corrosion mechanism of corrosion resistant alloys.Three different types of corrosion resistant alloys (13 Cr, Super 13 Cr, and duplex stainless steel) are studied under CO2 pressure (0 to 14 MPa) and at high temperature (150˚C) in 5 wt.% NaCl solution. The experiments are conducted in a high-pressure autoclave system at a consistent initial pH for comparison. The electrochemical behavior and the pitting corrosion are studied using cyclic potentiodynamic polarization and potentiostatic measurements. The surface of each specimen is investigated using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) before and after the electrochemical experiments to characterize the microstructural and localized corrosion features, respectively. All the tested materials show passive behavior under the conditions of the current study, however the pitting potential decreased in this order: duplex, Super 13 Cr and 13 Cr stainless steel.

On the Nature of Critical Potentials for Aluminum Repassivation

Repassivation (Erp) and pitting transition potential (Eptp)1,2 are considered critical parameters in aluminum pitting, because they have been associated with repassivation phenomena3,4. The physical meaning of Erp has long been well-established in the literature as the threshold between stable pitting and complete repassivation of the material5–7. The nature of Eptp, however, has not been thoroughly explained in the current literature apart from the primary assumption that it represents the commencement of repassivation4. Moreover, experimental investigation and evidence to expand this argument as well as to explore the relationship between these two potentials has been scarce4.The present work aims to address these open questions with cyclic potentiodynamic polarization (CPP) and potentiostatic experiments conducted on high purity Al in NaCl. Repassivation trends at and below Eptp were explained based on the assumption of actively corroding fractions which were dependent on the applied potential. Morphological transformation was also observed during polarization as evidenced by electron microscopy and X-ray microtomography after the electrochemical tests. The observation of a distinct Erp separate from the Eptp during slow CPP scans was related to the charge passed and was hypothesized to be the net effect of the gradually decreasing actively corroding area at potentials below Eptp, which resulted in morphology that restricted mass transport out of the pits, which delayed complete repassivation. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. References K. Nisancioglu and H. Holtan, Corrosion Science, 18, 1011–1023 (1978).K. L. Moore, J. M. Sykes, and P. S. Grant, Corrosion Science, 50, 3233–3240 (2008).S. T. Pride, J. R. Scully, and J. L. Hudson, J. Electrochem. Soc., 141, 3028 (1994).M. Yasuda, F. Weinberg, and D. Tromans, J. Electrochem. Soc., 137, 3708 (1990).A. Broli and H. Holtan, Corrosion Science, 13, 237–246 (1973).G. S. Frankel, J. R. Scully, and C. V. Jahnes, J. Electrochem. Soc., 143, 1834 (1996).G. S. Frankel, J. Electrochem. Soc., 145, 2186 (1998).

A Perspective on the Repassivation Potential and a Novel Calculation Thereof

Corrosion can occur on metallic surfaces in nearly any humid environment, leading to either early failure or costly repairs. Specifically, localized corrosion, such as pitting, can be difficult to identify at an early stage and can act as crack nucleation sites. Determining under which conditions pitting will take place is therefore important for maintenance and design, yet non-trivial from an electrochemical perspective.The pitting potential (Epit) and repassivation potential (Erp) have long been used in literature to determine a material’s susceptibility to pitting, with the latter acting as the lower threshold at which pitting can occur. A lower threshold of pitting can often be useful for conservative estimates, making Erp a popular parameter. However, a consensus on how to measure and define Erp has yet to be defined. Conventional cyclic potentiodynamic polarization (CPP) scans to measure Erp are shrouded in controversy, as values were found to be dependent on the scan rate and turn-around current density, unless sufficient charge densities had passed. Even once a plateau of Erp is reached at sufficient charge densities, there is debate as to if values are too conservative at that point. Two recent pitting frameworks have proposed alternative measurements of Erp, using both 1-D pit and 3-D bulk electrodes. Breakthroughs and limitations from both of these theories will be considered.In this work, the various methods of measuring and defining Erp will be discussed to provide clarity between different notation and to highlight possible paths going forward. In addition, an alternative calculation of Erp is proposed which is less conservative yet harmonized with the critical pit stability product (ix)crit, as both thresholds should represent the same lower limit of pitting. The proposed equation to calculate Erp includes dependencies on conventional parameters, such as the anodic Tafel behavior within a pit (ba), the transition potential (ET), and the critical percent saturation of metal salts (f). Validation is provided through both results found in literature and the use of Finite Element Method (FEM) modeling in conjunction with the maximum pit model.

Corrosion behavior of a bulk nanocrystalline Al-Fe alloy

Nanocrystalline Al-Fe alloy, with uniform microstructure and high solid solubility of Fe, has been produced by high-energy ball milling. Cyclic potentiodynamic polarization tests revealed high pitting potential. Hardness and corrosion resistance of the Al-Fe alloy were higher than any commercial Al alloy. High hardness and corrosion resistance were attributed to the nanocrystalline structure and formation of solid solution. X-ray photoelectron spectroscopy, secondary ion mass spectrometry, and scanning transmission electron microscopy indicated the incorporation of Fe to the surface film and Fe enrichment at the alloy/surface film interface, which were attributed to the enhanced corrosion performance.

Corrosion Resistance of Aluminum Alloy AA2024 with Hard Anodizing in Sulfuric Acid-Free Solution.

In the aeronautical industry, Al-Cu alloys are used as a structural material in the manufacturing of commercial aircraft due to their high mechanical properties and low density. One of the main issues with these Al-Cu alloy systems is their low corrosion resistance in aggressive substances; as a result, Al-Cu alloys are electrochemically treated by anodizing processes to increase their corrosion resistance. Hard anodizing realized on AA2024 was performed in citric and sulfuric acid solutions for 60 min with constant stirring using current densities 3 and 4.5 A/dm2. After anodizing, a 60 min sealing procedure in water at 95 °C was performed. Scanning electron microscopy (SEM) and Vickers microhardness (HV) measurements were used to characterize the microstructure and mechanical properties of the hard anodizing material. Electrochemical corrosion was carried out using cyclic potentiodynamic polarization curves (CPP) and electrochemical impedance spectroscopy (EIS) in a 3.5 wt. % NaCl solution. The results indicate that the corrosion resistance of Al-Cu alloys in citric acid solutions with a current density 4.5 A/dm2 was the best, with corrosion current densities of 2 × 10−8 and 2 × 10−9 A/cm2. Citric acid-anodized samples had a higher corrosion resistance than un-anodized materials, making citric acid a viable alternative for fabricating hard-anodized Al-Cu alloys.

Technical Note: Low-Cost Sample Holder with Flooded Gasket Prevents Crevice Corrosion in Pitting Corrosion Tests

This work describes an inexpensive holder for corrosion experiments, developed to avoid crevice corrosion during pitting corrosion tests of corrosion-resistant alloys. It is based on a flooded gasket, incorporated in a Stern-Makrides sample holder. Unlike the Avesta cell designed by Qvarfort, the proposed sample holder does not require a pump. The sample holder attaches to prismatic or cylindrical specimens cut from bars, plates, or any other component with a thickness greater than 10 mm. The sample holder is versatile and with no limitations on chloride concentration, solution composition, or temperature. The testing solution can be deaerated or saturated with any gas if needed. The sample holding method was validated by cyclic potentiodynamic polarization experiments on Types 304, 316 stainless steel, and C-22HS nickel-based alloy. Crevice corrosion was not evident in any of the specimens tested with the proposed method.

The Influence of Intralayer Porosity and Phase Transition on Corrosion Fatigue of Additively Manufactured 316L Stainless Steel Obtained by Direct Energy Deposition Process.

A direct energy deposition (DED) process using wires is considered an additive manufacturing technology that can produce large components at an affordable cost. However, the high deposition rate of the DED process is usually accompanied by poor surface quality and inherent printing defects. These imperfections can have a detrimental effect on fatigue endurance and corrosion fatigue resistance. The aim of this study was to evaluate the critical effect of phase transition and printing defects on the corrosion fatigue behavior of 316L stainless steel produced by a wire laser additive manufacturing (WLAM) process. For comparison, a standard AISI 316L stainless steel with a regular austenitic microstructure was studied as a counterpart alloy. The structural assessment of printing defects was performed using a three-dimensional non-destructive method in the form of X-ray microtomography (CT) analysis. The microstructure was evaluated by optical and scanning electron microscopy, while general electrochemical characteristics and corrosion performance were assessed by cyclic potentiodynamic polarization (CCP) analysis and immersion tests. The fatigue endurance in air and in a simulated corrosive environment was examined using a rotating fatigue setup. The obtained results clearly demonstrate the inferior corrosion fatigue endurance of the 316L alloy produced by the WLAM process compared to its AISI counterpart alloy. This was mainly related to the drawbacks of WLAM alloys in terms of having a duplex microstructure (austenitic matrix and secondary delta-ferrite phase), reduced passivity, and a significantly increased amount of intralayer porosity that acts as a stress intensifier of fatigue cracking.

Corrosion Resistance of 3D Printed Ti6Al4V Gyroid Lattices with Varying Porosity.

Corrosion of medical implants is a possible failure mode via induced local inflammatory effects, systemic deposition and corrosion related mechanical failure. Cyclic potentiodynamic polarisation (CPP) testing was utilized to evaluate the effect of increased porosity (60% and 80%) and decreased wall thickness in gyroid lattice structures on the electrochemical behaviour of LPBF Ti6Al4V structures. The use of CPP allowed for the landmarks of breakdown potential, resting potential and vertex potential to be analysed, as well as facilitating the construction of Tafel plots and qualitative Goldberg analysis. The results indicated that 60% gyroid samples were most susceptible to the onset of pitting corrosion when compared to 80% gyroid and solid samples. This was shown through decreased breakdown and vertex potentials and were found to correlate to increased lattice surface area to void volume ratio. Tafel plots indicated that despite the earlier onset of pitting corrosion, both gyroid test groups displayed lower rates of corrosion per year, indicating a lower severity of corrosion. This study highlighted inherent tradeoffs between lattice optimisation and corrosion behaviour with a potential parabolic link between void volume, surface area and corrosion being identified. This potential link is supported by 60% gyroid samples having the lowest breakdown potentials, but investigation into other porosity ranges is suggested to support the hypothesis. All 3D printed materials studied here showed breakdown potentials higher than ASTM F2129′s suggestion of 800 mV for evaluation within the physiological environment, indicating that under static conditions pitting and crevice corrosion should not initiate within the body.

Localized Corrosion of Chromium-Containing Conventional and Multiprincipal Element Alloys in Methanol and Aqueous Chloride Environments

The localized corrosion behavior of Type 304L stainless steel (UNS S30400), Alloy 625 (UNS N06625), and three experimental NiCoCrMo multiprincipal element alloys (MPEA), exposed to methanol/lithium chloride solutions with different water contents, is examined in this paper. Cyclic potentiodynamic polarization tests indicated that water increased the pitting and repassivation potentials and the critical temperature at which localized corrosion occurred in chloride solutions. The effect of water on repassivation potential in methanol-chloride solution depended on the chloride concentration and alloy content. At lower chloride concentration and higher alloy content, water had a greater inhibiting effect on repassivation potential, suggesting a competitive reaction between chloride and water on the metal surface in the pit. The localized corrosion resistance of the MPEAs followed the same trend as that of commercial stainless steels and Ni-base alloys in terms of the effect of alloying elements. The implications of these results on the mechanisms of localized corrosion are discussed.

Capacitor lifetime prolonged by addition of organic ammonium salt with cyclohexyl substituent and 2,5-dihydroxybenzenesulfonic anion

It is well known that the electrochemical corrosion negatively affects the functional properties of metal and steel materials that constitute a part of systems conducting electric charge. On the other hand, the phenomenon of corrosion is rarely associated with the degradation of chemical power sources and energy storage devices. This article is aimed to fill this gap by describing the effect demonstrated by a substituted ammonium salt with cyclohexyl substituent and 2,5-dihydroxybenzenesulfonate anion used as a corrosion inhibitor in symmetrical electrochemical capacitor system. The accelerated ageing test of capacitor systems has shown that the addition of substituted ammonium salt to capacitor electrolyte allows to extend the service lifetime of the entire system by inhibiting the corrosion of 316L stainless steel current collectors. The inhibitory effect of substituted ammonium salt additives on the electrochemical corrosion of 316L stainless steel surface has been also confirmed by cyclic potentiodynamic polarization (CPP) tests and X-ray photoelectron spectroscopy (XPS) measurements.

Evaluation of corrosion resistant, antimicrobial and cytocompatible behaviour of cobalt based metallosurfactants self-assembled monolayers on 316L stainless steel surface

The present research is aimed at developing a more economic and ecological way to improve the biocompatibility of medical-grade stainless steel. In order to accomplish the purpose, the 316L stainless steel has been functionalized by depositing self-assembled monolayers (SAMs) of cost-effective Cobalt-based metallosurfactants (CoMS). The fabrication of well-defined SAMs on the surfaces was characterised using FTIR-ATR, spectroscopic ellipsometry and water contact angle measurements. The corrosion stability of functionalized surfaces in simulated body fluid was accessed by various electrochemical and spectroscopic techniques like cyclic potentiodynamic polarisation (CPP), chronoamperometry, electrochemical impedance spectroscopy, FE-SEM, XPS and ICP-MS studies. The metallosurfactant SAMs provided superior corrosion and bacterial protection especially against Gram-negative E. coli bacteria. The cytotoxicity of the SAMs against mouse embryonic fibroblast cell line (NIH-3T3) was assessed by MTT and fluorescent assays. The experimental results reveals that the metallosurfactant SAMs are multifunctional i.e., they enhanced the anticorrosive and anti-bacterial properties of the SS 316L without compromising the cytocompatibility of the surface which make them promising candidates for biomedical applications.