Repassivation Kinetics Research Articles

Selective Initiation of Corrosion Pits in Stainless Steel Using Scanning Electrochemical Cell Microscopy.

Scanning electrochemical cell microscopy is a useful technique for determining variations in corrosion behavior across a surface. However, the numerous options for experimental parameters and little understanding of their effect on the corroding system render comparisons of results between studies difficult. Herein, we explore changes in corrosion behavior of two martensitic stainless steels, a cast CA6NM and a wrought S41500, as a result of the chosen experimental parameters, including scan rate, approach potential, surface oil immersion, and tip aperture diameter. The study demonstrates that these experimental parameters can be controlled to probe oxide passivation kinetics and single pitting events by changing the surface state and cathodic currents. We measured the pitting and repassivation kinetics of a single pit and determined the compositional change of the Al2O3 inclusion site initiation point. Hundreds of data points were measured within 17 h of experimental time on the stainless steel samples, allowing statistical averages of corrosion and pitting values. This work will open new avenues for fine-tuning various corrosion aspects at the microscale, thereby contributing to a deeper understanding of the corrosion processes and mechanisms of diverse materials.

Assessing the tribo-corrosion resistance of surface nanostructured stainless-steel

In this work, surface mechanical rolling treatment (SMRT) was applied as a post-process nanostructuring technique to improve the tribo-corrosion degradation resistance of coarse grain (CG) 316L stainless steel (SS). The experimental findings reveal that when tribo-corrosion wear took place, the CG specimen experienced severe surface de-passivation, which increased wear-corrosion synergy and the rate of material loss. On the other hand, the SMRT specimen experienced enhanced re-passivation kinetics, which reduced wear-corrosion synergy and the rate of material loss. The wear mechanism for both the CG and SMRT specimens was abrasion-dominant, with the CG specimen having the presence of micro-pits within the wear track. In addition to these findings, the reduced surface roughness, improved hardness, formed compressive stresses, microstructural refinement, and martensite phase transformation induced by the SMRT process contributed to the enhanced tribo-corrosion resistance of the SMRT specimen. In total, SMRT was found to be a feasible technique to improve the tribo-corrosion resistance of CG 316L SS.

Visualization and Location Determination of Pit Initiation Sites in Martensitic Stainless Steel during Corrosion-Fatigue Cyclic Plastic Deformation

Low-carbon martensitic stainless steels, such as 13%Cr4%Ni, are widely used in manufacturing hydraulic turbine runners. High tensile strength steel, such as cast CA6NM or wrought S41500 martensitic stainless steel, has an acceptable resistance to corrosion and cavitation, and reduces the weight and cost while offering a more efficient design. During operation, the combined effect of cyclic loading (fatigue) and corrosion reduces the fatigue strength and can initiate cracks at localized corrosion surface defects.In this study, we determined the bulk and localized corrosion behavior of wrought (S41500) and cast (CA6NM) 13%Cr4%Ni stainless steel before and after plastic deformation.Susceptibility to pitting corrosion was studied using open circuit potential and potentiodynamic polarization measurements in 0.020 M NaCl. Localized corrosion behavior was studied using a scanning droplet cell (SDC) and oil immersed scanning electrochemical cell microscopy (OI-SECCM). The bulk and localized electrochemical measurements after different surface preparation methods (mechanical polishing, followed by etching or electro-etching in different media) were compared.The surface defects including micro-voids and inclusions of different types were characterized. The location of pit initiation was then determined using scanning electron microscopy and profilometry imaging. A three-electrode microcell with a working electrode of 1 mm² was designed and hyphenated with optical microscope to allow in situ tracking of pit initiation and growth. Chronopotentiometry and chronoamperometry controlled pit initiation, while optical microscopy demonstrated dynamic release of corrosion products and measured oxide repassivation kinetics.Finally, the in situ technique was developed further to include a microtensiometer fatigue apparatus to study the synergy effect between corrosion and fatigue. Location of pit initiation was compared with and without plastic deformation. Videos of pit initiation and growth will be presented.

Selective oxidation and nickel enrichment hinders the repassivation kinetics of multi-principal element alloy surfaces

Robust and sustained corrosion resistance in multi-principal element alloys (MPEA) requires rapid repassivation, i.e. regrowth of the passive layer once it is damaged or destroyed at the surface. In this study, we show that the repassivation of Al0.1CrCoFeNi MPEA in 0.6 M NaCl solution is hindered at pH of ∼ 2.4 - 6.8 due to the formation of a Ni-enriched subsurface layer as a result of selective oxidation and dissolution of several principal elements, which can be fully restored at pH of ∼ 14 from the oxidation of all principal elements. Specifically, surface characterization via X-ray photoelectron spectroscopy (XPS), high-angle annular dark-field (HAADF) imaging in scanning transmission electron microscopy (STEM), and atom probe tomography (APT), are coupled with density functional theory (DFT) calculations to determine surface composition, oxidation state, and electron work function to uncover the structural origin of the pH-dependent repassivation mechanisms. It was found that selective oxidation of Cr, Co, and Fe in the acidic to neutral solutions altered the surface composition to be significantly enriched in Ni as compared to the bulk. Once the original passive film is destroyed locally by either pitting or tribocorrosion, this altered surface composition exhibited a much poorer repassivation capability due to the increased electron work function and reduced surface reactivity at higher Ni concentration. These understandings could shed light on the future compositional design of non-equiatomic MPEAs towards sustained repassivation and corrosion resistance over a wide pH range.

Accelerated deterioration mechanism of 316L stainless steel in NaCl solution under the intermittent tribocorrosion process

In this research, the tribocorrosion behavior of 316L stainless steel in simulated seawater was investigated under continuous and intermittent sliding at open circuit potential. The tribocorrosion mechanism was discussed in terms of wear morphologies, mechanical property as well as chemical composition. Meanwhile, microstructure evolution inside the wear track and open circuit potential recorded after sliding were analyzed to quantify the repassivation kinetics and evaluate the impact of the regenerated passive film on wear. The results showed that the wear rate increased under intermittent sliding when the pause time is long enough to repassivate after sliding. Repeated sliding promoted the refinement of the grain inside the sliding area, which was beneficial to the generation of the thicker and more compact passive film inside the wear track. The ruptured passive film often acted as abrasives during subsequent sliding. Therefore, the accelerated material loss under intermittent sliding was attributed to the periodic mechanical removal of the thickened passive film and the enhanced abrasive wear inside the wear track.

Localized Corrosion Resistance on Additively Manufactured Ti Alloys by Means of Electrochemical Critical Localized Corrosion Potential in Biomedical Solution Environments.

This study proposes a new method, electrochemical critical localized corrosion potential (E-CLCP), in order to evaluate localized corrosion resistance of biomedical additive manufacturing (AM) titanium (Ti) alloys. The procedures for determining E-CLCP are completely different from that of the electrochemical critically localized corrosion temperature (E-CLCT) method (ISO 22910:2020). However, its application should be limited to pH and temperature of the human body because of the temperature scan. E-CLCP displays the localized corrosion resistance of AM Ti alloys based on the human body’s repassivation kinetics, whereas E-CLCT displays the localized corrosion resistance of the alloys based on passive film breakdown in much harsher corrosive environments.

(Invited) A High Throughput Screening Approach for Corrosion-Resistant Alloys

Additive manufacturing (AM) is an attractive process for alloy development with some techniques having the ability to print a standalone part that spans a wide composition range. Fabricating compositionally graded parts allows spatially sensitive characterization techniques to perform property measurements across the composition gradient, providing high throughput testing of composition and phase space. This study utilizes an AM technique to make incremental additions of a single alloying element to a high entropy alloy (HEA), exploring how these alloying additions impact the HEAs microstructure and corrosion behavior. Specimens were produced with an in-house laser engineered network shaping (LENS) system capable of in-situ mixing of up to 5 metal powders. The equiatomic CoCrFeMnNi HEA is used in this study and compositionally graded with pure elements (Ti, W, and Nb). The susceptibility of the compositionally graded specimens to local corrosion initiation are tested using a micro (100 μm)-electrochemical cell and a scratch tester designed to measure repassivation kinetics. The efficacy of using this high throughput screening approach to develop alloys with superior corrosion resistance will be discussed.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

Effects of nanoscale chemical heterogeneity on the wear, corrosion, and tribocorrosion resistance of Zr-based thin film metallic glasses

The effects of nanoscale chemical heterogeneity on the wear, corrosion, and tribocorrosion resistance of ZrCuNiAl thin film metallic glasses were investigated by examining samples of similar global composition but with either homogenous or heterogeneous local composition. Unlike the homogenous sample, the heterogeneous sample exhibited local compositional fluctuations of Zr-rich (~52.8 at.%) and Zr-lean (~51.7 at.%) regions separated by ~413.0 ± 64.7 nm. Dry scratch wear study showed that the homogenous samples exhibited lower wear rates and friction coefficients than their heterogenous counterparts due to their higher hardness and lower stiffness, as measured from nanoindentation tests. Corrosion resistance of both samples was studied through potentiodynamic polarization and Mott-Schottky analysis in 0.6 M NaCl aqueous solution under room temperature. It was found that the heterogeneous samples exhibited higher pitting resistance than their homogenous counterparts by forming a protective passive layer with lower defect density. Finally, the effects of chemical heterogeneity on the tribocorrosion rate and repassivation kinetics of both samples were discussed based on their differences in mechanical and electrochemical properties measured.

In situ determinations of the wear surfaces, volumes and kinetics of repassivation: Contribution in the understanding of the tribocorrosion behaviour of a ferritic stainless steel in various pH

In tribocorrosion, the mechanic dominates the total wear. However, the corrosion wear should not be neglected for passive materials. As the film reactivity depends on pH, tribocorrosion experiments were performed on a ferritic stainless steel in sulphate solution (pH 1.5, 6.5 or 12.5). The passive film formation and degradation was evaluated through galvanic coupling tests while the degradation is quantified by image analysis. Wear results follows the Archard's law however, a non-linear dependence of the Archard's coefficient to the pH is found. The study of the worn surface reactivity highlights the role of the pH in the wear behaviour of the material as its influence on the film rebuilt kinetics and its contribution in the total wear.

Investigation of the Repassivation Process of CoCrMo in Simulated Biological Fluids

A thorough investigation into the repassivation process of CoCrMo in multiple simulated biological environments has been undertaken, looking in detail at both the kinetics and composition of the reformed oxide film. Specific focus of this research was aimed at determining the effect of bovine serum albumin (BSA) on these features. The kinetics of repassivation were obtained by using a variety of electrochemical techniques. The current transients formed were fitted to a second-order decay curve, which accouts for two separate phases: coverage and growth. The reformation of the passive film was fastest in a phosphate buffered saline environment, with the presence of BSA delaying this process because it inhibits the oxygen-reduction reaction as it obstructs the active sites of the alloy when adsorbed onto the surface. The composition of the newly formed film was analyzed with x-ray photoelectron spectroscopy. As expected, the film was primarily composed of chromium (III) oxide with small contributions from cobalt and molybdenum oxides. In the presence of BSA, the quantity of molybdenum within the film was drastically reduced; it was shown to be extracted into the bulk solution via inductively coupled mass spectroscopy. This is observed because BSA is able to complex preferentially to the molybdenum ions when the alloy is exposed, extracting them into solution and altering the composition and integrity of the film.

Activation and Repassivation of Stainless Steels in Artificial Brines as a Function of pH.

When planning oil wells with stainless steel components, two possible reasons for depassivation have to be considered—chemical depassivation caused by acidizing jobs and mechanical depassivation caused by various tools and hard particles. The study explores conditions causing chemical activation of investigated steels and circumstances under which repassivation occurs after activation. The main focus of the study is to determine, how quickly various steels can repassivate under different conditions and to find pH values where repassivation will occur after depassivation. The investigated steels were ferritic (martensitic or bainitic) in the cases of 13Cr, 13Cr6Ni2Mo, and 17Cr4Ni2Mo, austenitic in the case of 17Cr12Ni2Mo, and duplex (austenitic and ferritic) in the case of 22Cr5Ni3Mo. Potentiodynamic experiments were employed to obtain electrochemical properties of investigated steels, followed by immersion tests to find ultimate conditions, where the steels still retain their passivity. After obtaining this information, scratch tests were performed to study the repassivation kinetics. It was found that repassivation times are similar for nearly all investigated steels independent of their chemical composition and microstructure.

Electrochemical studies on the effect of residual stress on the corrosion of 316L manufactured by selective laser melting

Selective Laser Melting (SLM) and various subsequent stress-relieving treatments were used to obtain 316 L specimens with compressive residual stresses, varying from 15 to 250 MPa. This enabled a study on the effect of residual stress on corrosion of 316 L using electrochemical methods, which is relevant for durability of additively manufactured materials. Overall, compressive stresses in SLM 316 L result in a measurable increase in the pitting potential, accompanied by a decrease in the passive film currents and donor densities. It is proposed that compressive stresses lower the film growth and repassivation kinetics but slightly enhances the pitting resistance of SLM 316 L.

Nanocrystalline Cermet Coatings for Erosion–Corrosion Protection

The processing techniques, microstructural characteristics, and erosion corrosion behaviour of Cr3C2–NiCr and tungsten carbide (WC)-based cermet coatings are reviewed in this work. Conventional and nanocrystalline Cr3C2–NiCr and WC-based cermet coatings are generally synthesized using thermal spray technique. The wear, erosion, and corrosion protection ability of conventional and nanocermet coatings are compared based on available literature. In Cr3C2–NiCr coatings, the corrosion resistance is offered by NiCr metal matrix while the wear resistance is provided by the carbide ceramic phase, making it suitable for erosion–corrosion protection. The nanocrystalline cermet coatings exhibits better erosion–corrosion resistance as compared to the conventional coatings. The nanocrystalline coatings reduces the erosion–corrosion rate significantly compared to conventional coatings. It is attributed to the presence of the protective NiCr metallic binder that allows easier and faster re-passivation when the coating is subjected to wear and the fine-grain structure with homogeneous distribution of the skeleton network of hard carbide phases. In addition, corrosion-accelerated erosion dominates the reaction mechanism of erosion–corrosion and, therefore, higher hardness, strength, and better wear resistance of nanocermet coating along with its faster repassivation kinetics accounts for improved corrosion resistance as compared to conventional coatings.

Electrode Scratching Technique As a Robust Way to Decouple Erosion-Corrosion Components

The substantial number of parameters and their interdependence makes the modelling and prediction of erosion-corrosion rates a rather challenging task, yet owing to increasing computational capacity one that is potentially solvable. To accurately estimate the rate of material loss, universally accepted explanations of the mechanisms of combined erosion and corrosion must be developed. The absence of reliable data can undermine safety and predictability of industrial processes, such as oil and gas transportation. The aim of this work is to demonstrate the application of an electrode scratching technique coupled with microstructural characterisation for improved understanding of synergy in erosion-corrosion. In this work, a rotating disc electrode scratching setup, with well-defined and controlled flow conditions, was developed to study individual contributions to erosion-corrosion. Linear potentiodynamic and potentiostatic polarization techniques were used to reproducibly monitor the kinetics of dissolution and repassivation of API X65 steel electrodes upon scratching. Samples characterized using high-resolution scanning electron microscopy (SEM) and white-light interferometry (WLI), confirm the synergy; the losses due to erosion-corrosion are larger than that of the summation of the separate contributions of erosion and corrosion. Focused Ion Beam (FIB) milling was implemented for in-situ lift-out of lamellae from scratched samples for Transmission Electron Microscopy (TEM) characterisation. We confirm distinct microstructural changes take place in the vicinity of scratches: with nanoscale grain refinement and orientation changes observed (See Figure 1). These results, coupled with electrochemical data and micro-hardness measurements, suggest time-dependent surface-hardening processes affect material loss rates during mechanical-electrochemical coupled corrosion. Figure 1

Effect of scratching frequency on the tribocorrosion resistance of Al-Mn amorphous thin films

Amorphous metallic thin films show great promise for applications where mechanical and chemical attack coexist due to their excellent wear, corrosion, and tribocorrosion resistance. In this research, the effect of scratching frequency on amorphous Al-Mn thin film were studied in simulated seawater by varying the scratching frequency from 0.05 to 1 Hz in reciprocal motion. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied to characterize the microstructure before and after tribocorrosion testing. Post-tribocorrosion topography measurement was performed using non-contact optical 3D profilometer. It was found that the total tribocorrosion rate, including both mechanical and chemical wear, increased with increasing scratching frequency. Mechanical wear increased with scratching frequency, mostly related to an increment of coefficient of friction and real contact area. On the other hand, chemical wear tend to increase with scratching frequency, most likely due to faster repassivation kinetics at lower frequency. Cross-sectional TEM analysis shows that the disordered surface layer primarily consists of aluminum oxide where manganese is completely absent.

The effects of microstructures and repassivation kinetics on the tribocorrosion resistance of ferrite and ferrite-martensite stainless steels

The study addresses the tribocorrosion behavior of a ferritic stainless steel and a ferrite-martensite stainless steel under two passive potentials. The dual phase microstructure was produced by a specific heat treatment applied to the ferritic stainless steel. Since both materials have the same chemical composition, their tribocorrosion resistances are discussed in terms of microstructure benefit. This benefit concerns the determination of the wear rate, as well as the identification of the wear mechanism from surface and sub-surface observations. In parallel, current transients recorded during sliding are analyzed to quantify the kinetics of repassivation and evaluate the impact of the rebuilding of oxide film on wear.The results show that the hardness of the material is the main parameter that controls wear for the sliding conditions selected in this work. In a second order of magnitude, the nature of the oxide layer plays a role in the damage mechanism. Finally, if the oxide growth rate is affected by both the applied potential and the microstructure, it mainly affects the subsurface microstructure of the wear track with a thickening of the grain refined layer, as the repassivation is faster.

Corrosion inhibition of aluminium alloy by rhamnolipid biosurfactant derived from pseudomonas sp. PS-17

PurposeThe purpose of this paper is to study the influence of rhamnolipid biosurfactant complex on the corrosion and the repassivation of a freshly cut Al-Cu-Mg aluminium alloy surface.Design/methodology/approachThe electrochemical methods, supported by quantum-chemical calculations and scanning electron microscopy data, were used.FindingsIt was established that the rhamnolipid biosurfactant effectively inhibits corrosion of the alloy in synthetic acid rainwater. The efficiency of inhibition becomes stronger with the increase of biosurfactant concentration; however, above the critical micelle concentration, the further improvement in inhibition is minor. It is believed that the mechanism of corrosion inhibition is related to the adsorption of the biosurfactant molecule on the aluminium alloy surface and the formation of a barrier film; however, the formation of a complex compound (salt film) between aluminium ions and rhamnolipid on anodic sites of the alloy is not ruled out. In case of surface mechanical activation of the alloy, the biosurfactant molecule effectively prevents corrosion. Furthermore, addition of the biosurfactant to the corrosion environment increases the repassivation kinetics of the alloy by two to four times as compared with an uninhibited environment.Practical implicationsThe commercial impact of the study consists in the possibility of obtaining of environmentally safe corrosion inhibitors of aluminium alloys by biosynthesis from renewable agricultural raw materials.Originality/valueThe originality of this paper is to study the effectiveness of “green” corrosion inhibitor based on biogenic product on freshly generated surface of aluminium alloy.

Correlation between repassivation kinetics and pitting potential of 316L stainless steel in the presence of green inhibitors

PurposeThis paper aims to investigate the stability of passive oxide film formed on the surface of 316L stainless steel in 3.5 Wt.% NaCl in the presence of two environmentally non-toxic inhibitors, i.e. leaf extracts of Musa spp. (MS) and Jatropha curcas (JC).Design/methodology/approachCurrent transients and potentiodynamic polarization curves were used to explain the stability of the passive film on Current transients and potentiodynamic polarization curves were used to explain the stability of the passive film on 316L stainless steel at both ambient temperature (25 °C) and 70 °C. For the potentiostatic tests, the coupons underwent cathodic stripping to remove the native oxide on their surfaces at −850 mV for 600 s, and a potential of 50 mV was imposed to observe the repassivation for 200 s. For the potentiodynamic tests, the pitting potential measured at 100 μA/cm2, corrosion potential and cathodic current density were obtained for analysis.FindingsThe current transients perfectly fitted into the exponential decay curve; i = is + ipeak exp(−t/τ), where the decay constant, τ measures the repassivating speed and extent to which the newly formed film heals and stabilizes. The current transients showed that MS and JC help in the repassivating process, especially at 300 ppm and 200 ppm, respectively, both at the lower temperature. The potentiodynamic curves mostly correlated with the current transients except for the hybrid inhibitor. The inhibitors increased the pitting potentials at concentrations that are correlated to their scanning electron micrograph images.Research limitations/implicationsBecause they are cheap and environmentally friendly, plant extracts that are proven corrosion inhibitors could be used to aid the formation of passive film on passive alloys in not-so-aggressive environments.Practical implicationsBoth MS and JC improve the film stability mostly at intermediate concentrations of 200 and 300 ppm, respectively, at ambient temperature and 70° C.Social implicationsUsing leaf extracts of plants as green inhibitors is considered an environmentally friendly engineering solution.Originality/valueThe leaf extracts are a convenient resource of green inhibitors because their plants are readily available or could be easily naturalized, the processing technique to obtain the extracts is very cheap and the inhibitors are environmentally friendly. In addition, cathodic stripping exposes a relatively larger surface area than that obtained using the most common forms of depassivation; hence, the efficiency of the inhibitor in aiding the formation of the new oxide film to cover the bare surface would be better measured. There is very lean research data on the combined use of green inhibitors and cathodic stripping to study repassivating kinetics of passive alloys.

Stress Corrosion Behavior of Low-temperature Liquid-Nitrided 316 Austenitic Stainless Steel in a Sour Environment

Low-temperature nitridation is a widely used surface heat treatment. Low-temperature liquid nitridation was applied to 316 austenitic stainless steel and an S-phase (expanded austenite) layer was achieved on the alloy surface. The effect of the S-phase layer on corrosion resistance and stress corrosion cracking was investigated in a sour environment. When a bending stress of 164 MPa (80 pct yield stress, YS) was applied, no macroscopic corrosion cracking and pits were observed on the nitrided samples and the S-phase layer stayed intact. Although no macroscopic corrosion cracking was observed on the non-nitrided samples under 205 MPa (100 pct YS), some pits were formed on the alloy surface. This could be attributed to the high stresses and hardness, and the excellent corrosion resistance of the S-phase layer introduced by low-temperature nitridation. Supersaturated nitrogen atoms in the S-phase layer can effectively prevent the decrease in pH of the corrosive medium and accelerate the alloy repassivation kinetics. However, when the bending stress was increased to 205 and 246 MPa (100 pct YS, 120 pct YS), macroscopic cracks were observed in the presence of both tensile stress and a corrosive medium.

Connection between Atomic Scale Characterization and Electrochemical Behavior during Passivation of Polycrystalline and Single Crystal Ni-Cr and Ni-Cr-Mo Alloys

Ni-Cr and Ni-Cr-Mo alloys owe their superior corrosion resistance to the surface enrichment of passivating Cr-rich oxides or hydroxides and the synergistic effect of Mo in the film1–3. However, the specific role of alloying elements such as Mo are not well-understood, especially with respect to their position relative to the oxide/metal interface and atomistic influence on film growth, localized breakdown, and repassivation processes. The composition, structure, and thickness of the passivating oxide films are additionally challenging to characterize in-situ due to their nanoscale dimensions and the high electric field imposed by aqueous growth. The key processes which take place in oxide films and regulate their behavior in aqueous environments are atomic, ionic, and electronic in nature and currently poorly understood, often requiring study at the resolution and detection limits of characterization methods4. The main goal of this work is to integrate bulk polycrystalline and single crystal electrochemical measurements with nanoscale characterization to advance the fundamental understanding of the structure, molecular, and electronic properties of oxides formed during aqueous passivation and uncover the role of Mo on surface stability in corrosive environments. The alloys under study are Ni-11Cr, Ni-11Cr-6Mo, Ni-22Cr, and Ni-22Cr-6Mo, wt%, polycrystalline solid solutions with additional focus on individual grain orientations in isolation from grain or twin boundaries. DC and AC electrochemical techniques were utilized for exploring the controlled growth of passive oxide films on these materials in aqueous chloride and chloride-free solutions of various acidity. The repassivation kinetics of polycrystalline and single grain crystal surfaces were determined potentiostatically and galvanostatically after previously formed air oxides were reduced. A major challenge to analysis of the oxidation rate from electrochemical data is that film thickening rate must be assessed independently from the total oxidation rate. Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) results indicate that a significant portion of the applied anodic charge during oxidation is associated with direct cation ejection and/or dissolution rather than film thickening. Single frequency electrochemical impedance spectroscopy (SF-EIS) and ICP-MS were thus applied as novel characterization methods to model the electrochemically grown oxides and measure in-situ changes in oxide thickness and elementary dissolution reaction rates during passivation and film dissolution and/or cation emission. The oxide thicknesses calculated using these methods were related to the charge that goes toward oxide film growth and the related oxidation current density. Atomic force microscopy (AFM) topography images and profiles across single grain surfaces at intermediate stages of potentiostatically and galvanostatically controlled oxide growth were obtained to give insight on the nucleation and morphology of oxides formed. The surface roughness was derived from these images in order to quantify the influence of the minor alloying elements, and chloride presence on the morphology and degree of film breakdown during the stages of passivation. 3D atom probe tomography and X-ray photoelectron spectroscopy analysis of the oxides following potentiostatic and galvanostatic growth provided additional information regarding the location and chemical identity of elements across the films. This pairing of operando mesoscale electrochemical techniques with ex-situ microscopy describes the competitive oxidation and dissolution processes in aqueous environments and achieves an atomic-scale understanding of the oxide surface morphology along with the influence of minor alloying elements. The fate of all elements during fast repassivation was tracked operando for analysis of the significant impact of dissolution and cation ejection during passivation using ICP-MS, SF-EIS, and AFM measurements. The role of kinetics on passivation was found to play a crucial role over thermodynamics, resulting in non-conformal and unexpected oxide growth dictated by the minimization of interfacial energy and stresses. Finally, Mo was found to serve a number of roles during passivation and collects at the film/solution interface as well as throughout oxides. ACKNOWLEDGEMENTS This work was funded by the U.S. Office of Naval Research Multi-University Research Initiative under a subcontract from Northwestern University SP0028970-PROJ0007990 with Dr. David A. Shifler. REFERENCES 1. F. Bocher, R. Huang, and J. R. Scully, Corrosion, 66, 1–15 (2010). 2. A. C. Lloyd, J. J. Noël, S. McIntyre, and D. W. Shoesmith, Electrochim. Acta, 49, 3015–3027 (2004). 3. A. C. Lloyd, J. J. Noël, N. S. McIntyre, and D. W. Shoesmith, JOM, 57, 31–35 (2005). 4. P. Jakupi, D. Zagidulin, J. J. Noël, and D. W. Shoesmith, Electrochim. Acta, 56, 6251–6259 (2011).