Pit Initiation Research Articles

Effect of Surface Roughness on Pitting Corrosion of 2205 Duplex Stainless Steel Investigated by Electrochemical Noise Measurements.

The influence of surface roughness on the pitting corrosion behaviour of 2205 duplex stainless steel (DSS) in a chloride-containing environment was investigated using electrochemical noise (EN) techniques and morphology observation. A rougher surface condition increased the frequency of pit initiation because of the increase in more occluded pit sites. Rough surface finish also accelerated pit growth by increasing the actual dissolution rate in the pit. Metastable pits on rougher surfaces had longer lifetimes and grew to larger sizes, as their inner chemical environment was more easily maintained. However back-scatter images showed that pitting initiates on DSS 2205 regardless of the roughness condition.

Effect of crystallographic texture and microstructure on pitting corrosion behavior of low carbon steels: A Monte Carlo model

This work presents a model capable of describing the influence of the crystallographic texture and microstructure produced by Voronoi tessellation on the initial stage of pitting corrosion in API 5L steels. The proposed model takes into account several physical parameters of the material such as crystallographic orientation, gran size, grain boundary, number of inclusions, surface energy, and the Gibbs free energy change. The number of corrosion pits and their distribution associated with the initiation of pitting corrosion were determined using both Monte Carlo simulation and corrosion test. The good agreement between simulation results and the experimental observations verified the validity of the proposed model. The results showed that the pits initiation depends strongly on the change of surface energy due to the formation of new phases and the character of grain boundary and its distribution. The behaviour of nucleated pits is completely random, while their subsequent growth from a nucleation site has a strong influence from the crystallographic grains orientation.

Influence of filler material composition on the microstructural evolution, mechanical properties and corrosion behaviour of nickel-based super alloy C-276

The microstructural evolution, mechanical properties and corrosion resistance of nickel-based-Super Alloy C-276 joints were examined in the current investigation. Four different filler materials (ERNiCrMo-4, ERNiCrMo-10, ERNiCrMo-3 and ERNiCr-3) in combination with pulsed current gas tungsten arc welding were used to join 6 mm thick sheets of Alloy C-276. The better understanding of evolution of microstructures and their subsequent effect on the properties would be beneficial for employing such joints in practical applications. The microstructural analysis showed transition in the solidified structure for different filler materials. Furthermore, SEM-EDS analysis clearly revealed the precipitation of Mo or Nb-rich precipitates in the welds (or close to fusion boundary) for all the weldments. This situation caused a reduction in the mechanical properties and the initiation of corrosion pits (or cracking) during modified Huey test. However, the segregation of TCP phases (P or μ) was found to be in a lesser amount in the ERNiCrMo-4 weld followed by ERNiCrMo-10 weld (which needs further investigation) and hence resulted in a better mechanical properties and superior corrosion resistance as compared to the weld fabricated using ERNiCr-3 filler material. Therefore, the authors recommend the use of ERNiCrMo-4 filler material for joining of Alloy C-276 (followed by ERNiCrMo-10 filler material) in corrosive industrial applications.

Understanding the relation between pitting corrosion resistance and phase fraction of S32101 duplex stainless steel

The relation between phase fraction and pitting corrosion resistance of S32101 duplex stainless steel was interpreted by considering the stable and metastable pitting potential and galvanic corrosion rate of the duplex-phased matrix. As the ferrite fraction increased, the potential for the stable pitting corrosion was linearly decreased which was found to be closely related to the increase in the galvanic corrosion rate between the two constituent phases. It was also revealed that the pit propagation rate was more important than the pit initiation probability in determining the overall pitting corrosion resistance of the S32101 duplex stainless steel.

Modeling of Pitting Corrosion Damage Based on Electrochemical and Statistical Methods

A new prediction model for pitting corrosion damage considering both pit initiation and pit growth was presented. The pit initiation was modeled based on a combination of the Sridhar model and Macdonald model, and the critical potential was redefined at the same time. The pit initiation time can be divided into the time in which the open circuit potential (OCP) exceeds the repassivation potential (Erp), and the pit induction time, when OCP > Erp. The pit growth was modeled using the Markov process and extreme value statistics were used to describe the maximum pit depth distribution. If the time–consuming pit initiation process is neglected, it results in unacceptable errors in the pit growth kinetics parameters obtained. Thus, an acceleration method, the pre-initiated pits method, was developed to eliminate this negative effect. The proposed model was validated using experimental data on the pitting corrosion of 304 stainless steel (SS) and reproduces the experimental observations with high fidelity.

In Situ Monitoring of Pitting Corrosion on Stainless Steel with Digital Holographic Surface Imaging

A new approach – the digital holographic surface imaging (DHSI) – is proposed for in situ observation of the electrode surface during a typical localized corrosion process. The test results show that the experimental system is sensitive in detecting ions’ concentration changes in the vicinity of the electrode surface. The phase maps obtained with this method capture the dynamic concentration changes in front of the steel surface and exhibit the initiation, propagation or re-passivation processes of metastable pits. The proposed method can provide visual evidence of localized dissolution on the electrode surface and offer an in situ and simple means to monitor early-stage corrosion in real time, thereby exhibiting potential for extensive use in the study of electrochemical dynamic processes.

Photo-Enhanced Acid Chemical Etching of High-Quality Aluminum Nitride Grown by Metal-Organic Chemical Vapor Deposition

Photo-enhanced chemical (PEC) etch of wurtzite aluminum nitride (AlN) was investigated to overcome its low etch rate. Epitaxial AlN grown on Al2O3 substrate by metal-organic chemical vapor deposition method was immersed in phosphoric acid at different temperatures under 185 nm deep-UV excitation. An inverted pyramid structure with {10-1-1} faces initially appeared, after chemical etching, evolving into hexagonal columns with {1-100} m-planes. The PEC etch rate of m-plane AlN was six-fold higher than that of non-PEC one because the reaction was enhanced by the electron-hole pairs photo-generated by 185 nm wavelength. The decrease of the activation energy from 68.5 kJ/mol (non-PEC etch) to 48.1 kJ/mol (PEC etch) was extracted, implying a reaction-limited etching process. The PEC etch mechanism of wurtzite AlN in phosphoric acid was proposed, including the initiation and growth of the etch pit and the agglomeration of the hexagonal columns. Our results propose a facile method to control the surface morphology of AlN-based electronic and optoelectronic devices.

Corrosion resistance behavior of PVDF/ZrO2 composite in 3.5% NaCl

Abstract Marine structures come into contact with the seawater. Corrosion occurs on the walls of these structures and can quickly lead from surface damage to aesthetics impairment. The main cause of the corrosiveness are chloride ions which facilitate initiation and propagation of pits. Stainless steels provide a wide range of applications in seawater environments. They are used for the construction of heat exchangers, tanks and capacitors for electrical systems, refrigeration systems for power plants, tidal power, wind turbines localized at sea. Mild steel find its role in almost every product created from metal due to its low cost and easy availability. The polymeric materials are having multiple adsorption sites for bonding with metal surface and provides higher inhibition efficiency than the corresponding monomers. In the present work, the corrosion inhibition of mild steel in 3.5% NaCl by PVDF/ ZrO2 composites were studied. The composite samples were characterized by using XRD, FTIR and SEM. Potentiodynamic polarization and electrochemical impedance spectroscopic techniques were used to explore the enhanced corrosion inhibition of composites. The corrosion inhibition efficiency of PVDZr composites were found to increase with increase in concentration of ZrO2.

Humidity Effects on Pitting of Ground Stainless Steel Exposed to Sea Salt Particles

The effect of relative humidity (RH) on the corrosion of coarse-ground 304 stainless steel exposed for one year under sea salt particles was investigated. Total corrosion damage accumulation was higher at 40% RH than at 76% RH. At 40% RH, pits were numerous and irregularly shaped with a rough, cross-hatched structure. At 76% RH, pits were much fewer in number and ellipsoidal with crystallographically faceted surfaces. Higher Epit resulting from lower [Cl−] impeded initiation at 76% RH. Cathodic resource competition likely limited growth and resulted in lower total volume loss. At 40% RH, lower Epit due to higher [Cl−] led to initiation of multiple pits supported by discrete cathodes under individual droplets. Despite more cathodic current available at 76% RH, higher damage accumulation at 40% RH was due to lower anodic stability requirements resulting from higher [Cl−]. At 76% RH, pitting proceeded with increasing active area at conditions above critical stability, leading to ellipsoidal pits with facets. The cross-hatched morphology at 40% RH was ascribed to growth at the critical stability conditions, driven by constant current through a fixed active area. Small cracks at the 40% RH pits might have been caused by hydrogen environment assisted cracking.

Numerical analysis of pitting corrosion fatigue in floating offshore wind turbine foundations

The mooring system of offshore floating wind foundations, which anchors the floating foundations to the seabed, sustains large dynamic loads during operation. The mooring chains are connected to the floating foundation below the water level through fairleads and chain-stoppers. The corrosive marine environment and the cyclic loading make the mooring connection prone to corrosion pitting and fatigue crack initiation and propagation from the pits, particularly in the weld zones. In this study, a finite element analysis of the crack growth from corrosion pits has been performed and the results are presented in order to provide an estimate of the extent of damage after the crack is detected. A Python script have been developed which generates the pit profiles based on a non-uniform random distribution of pit dimensions. 3D pits and elliptical cracks are embedded at critical points of weldment on the mooring point and analysed using ABAQUS XFEM. The Walker’s model has been applied in the model to examine the effect of realistic R ratios in floating structures on pitting corrosion fatigue crack propagation along with direct cyclic solver. The numerical results obtained from this study are discussed in terms of the corrosion pitting effects on fatigue crack propagation behaviour in Spar-type floating offshore wind turbine foundations.

Liquid-Air Interface Corrosion of A537 Steel in High Level Liquid Radioactive Waste Simulant in a Sealed Container

Liquid-air interface (LAI) corrosion is regarded as a potential issue for interim storage tanks of high level liquid radioactive waste. Insightful studies have been carried out and several hypotheses have been proposed so far, while none has been directly confirmed experimentally. A sealed container has been developed to investigate the effect of atmosphere on LAI corrosion of partially immersed A537 steels, in which the composition and temperature of air can be changed accordingly, i.e. CO2 concentration varied between 0.05 wt% (natural air) and 1.97 wt%, and temperature varied between 25°C and 34°C. It has been found that the pitting initiation process under both anodic polarization and free immersion conditions can be largely accelerated by the increase of CO2 concentration. More importantly, a planar pH electrode has been applied to measure pH at the interface during anodic polarization and free immersion, and the occurrence of LAI corrosion can be correlated with the same interface pH at a certain temperature regardless of CO2 concentration, indicating a “critical pH” for LAI corrosion determined by this method. This finding suggests that LAI corrosion in high level liquid radioactive waste may be investigated through determination of a critical pH in certain circumstances.

Morphological Characteristics of Trenching around MnS Inclusions in Type 316 Stainless Steel: The Role of Molybdenum in Pitting Corrosion Resistance

The role of Mo alloying in the pit initiation process at MnS inclusions in stainless steels was investigated by measuring polarization curves, depassivation pH, and scanning electron microscopy. Molybdenum existed in the steel matrix but was not detected in the MnS inclusions in Type 316 stainless steel. While Mo alloying did not inhibit the dissolution of the MnS inclusions in a NaCl solution, neither a metastable nor a stable pit occurred in the small areas with the MnS inclusions in the Mo-added specimen. The MnS/steel matrix boundary preferentially dissolved in the Mo-free specimen, with deep trenches formed. However, no deep trench was observed in the Mo-added specimen at low potentials. The depassivation pH of the Mo-added specimen in a 0.1 M NaCl-1 mM Na2S2O3 solution was lower than that of the Mo-free specimen, suggesting that Mo alloying prevents the depassivation of the steel matrix at the boundary and inhibits the formation of trenches. In a 1 M HCl-1 mM Na2S2O3 solution, the active dissolution rate of the steel was suppressed by Mo alloying. This suggests that, even after trenching at high potentials, Mo alloying inhibits the initiation of pitting inside the trenches.

Observations on Pit Initiation Behavior of Carbon Steel Using Microelectrochemical System with Confocal Laser Scanning Microscopy

Observations on Pit Initiation Behavior of Carbon Steel Using Microelectrochemical System with Confocal Laser Scanning Microscopy

The hydrogen-induced pitting corrosion mechanism in duplex stainless steel studied by current-sensing atomic force microscopy

Duplex stainless steels have excellent corrosion resistance due to their two-phase microstructure and electrically insulating passive film. Nevertheless, hydrogen charging causes deterioration of the corrosion protection mechanisms, resulting in increased pitting susceptibility. In this study, current-sensing atomic force microscopy was used to investigate the electrical properties of the passive film formed on 2507 duplex stainless steel before hydrogen charging. Results were compared with optical images of pitting corrosion initiation after hydrogen charging and FeCl3 exposure. Highest passive film conductivity and current density were seen at grain boundaries, indicating poor passive film development and high pitting probability. High conductivity was also observed on the passive film located at the adjacent austenite phase, alluding to favorable conditions for pitting corrosion propagation. Phases were identified by magnetic force microscopy, while pit initiation with subsequent propagation after hydrogen charging and FeCl3 exposure was observed using optical microscopy. Pitting corrosion initiated at grain boundaries and propagated into the austenite grains. This study identified the pitting initiation and propagation mechanisms in 2507 duplex stainless steel.

Influence of inclusions on initiation of pitting corrosion and stress corrosion cracking of X70 steel in near-neutral pH environment

In-situ 2D and 3D microscopic technologies are used to analyze the influence of inclusions on pitting and stress corrosion cracking initiation of X70 steel in near-neutral pH solution. The chemical dissolution of complex oxide inclusions or part of them induces corrosion pits. Circular protected region forms around Ds inclusions due to dissolution of CaS. The Si-enriched inclusions remain intact, but interstice forms at the inclusion/matrix interface due to the dissolution of the matrix. Both complex oxide inclusions and Si-enriched inclusions can induce initiation of SCC micro-cracks, but most of the micro-cracks are generated inside the ferrite grains.

Investigation of the Localized Corrosion and Passive Behavior of Type 304 Stainless Steels with 0.2⁻1.8 wt % B.

The pitting corrosion resistance and passive behavior of type 304 borated stainless steels (Febalance–18Cr–12Ni–1.5Mn–(0.19, 0.78, and 1.76 wt %)B) manufactured through conventional ingot metallurgy were investigated. The alloys were composed of an austenitic matrix and Cr2B phase, and the volume fraction of Cr2B increased from 1.68 to 22.66 vol % as the B content increased from 0.19 to 1.76 wt %. Potentiodynamic polarization tests measured in aqueous NaCl solutions revealed that the pitting corrosion resistance was reduced as the B content increased and the pits were initiated at the matrix adjacent to the Cr2B phase. It was found that the reduced resistance to pitting corrosion by B addition was due to the formation of more defective and thinner passive film and increased pit initiation sites in the matrix.

Effect of Mo and Cr additions on the microstructure, mechanical properties and pitting corrosion resistance of austenitic Fe-30Mn-10.5Al-1.1C lightweight steels

Five Fe-30 wt%Mn-10.5 wt%Al-1.1 wt%C steels containing different Mo and Cr contents were prepared to investigate the effect of Mo and Cr addition on the microstructure, mechanical properties and pitting corrosion resistance of austenitic lightweight steels. The microstructures of all samples after solution treatment at 1050 °C consisted of austenite and κ-carbide, while DO3 ordered phases were additionally formed in samples containing 3 wt%Mo-3wt%Cr or 5 wt%Cr. The results of Nanoindentation tests indicated that the intrinsic strength of the austenite matrix decreased with the addition of Mo and Cr due to the suppression of κ-carbide precipitation and then the strength of the DO3 phase is equal or higher as compared to the austenite matrix. The tensile tests also showed that the yield strength decreased when 3 wt%Mo or 3 wt%Cr was added due to the suppression of κ-carbide precipitation, whereas it increased with further additions of Mo and Cr in both cases due to the formation of a DO3 ordered phases and grain refinement. Electrochemical tests showed that the resistance to pitting corrosion was improved by the addition of Mo and Cr due to the formation of a protective passive film; however, the excessive additions of Mo or Cr adversely deteriorated the resistance to pitting corrosion as the DO3 ordered phase which acted as pit initiation sites.

Combination of Electrochemical Noise and Acoustic Emission for Analysis of the Pitting Corrosion Behavior of an Austenitic Stainless Cast Steel

The pitting corrosion behavior of a high alloy cast steel is analyzed in a sodium chloride solution by combination of the electrochemical noise technique and the acoustic emission (AE) method. Four corrosion states are identified on the steel surface after the 70 h noise measurement test. The simultaneously monitored AE exhibits two types of acoustic signals. The first type of AE events is attributed to the local passive oxide breakdown and the pit initiation process and the second type of AE events is related to the subsequent associated hydrogen gas bubble evolution.

Pitting Corrosion of 10Ni8CrMoV High-Strength Steel Induced by a Potential Perturbation

Pitting corrosion of high-strength steel 10Ni8CrMoV under square wave polarization (SWP) in simulated deep-sea environment is investigated and the possible mechanism is proposed. The results show that potential perturbation generates periodic intensification effect on both anodic and cathodic processes by frequently breaking the electrode equilibrium state. The intensity of periodic intensification effect essentially depends on the concentration gradient of Fe2+ cations at the steel/solution interface which acts as the forced electrochemical oscillator. The concentration gradient and the resulting concentration polarization effect increase periodically with the increase in SWP potential range. The morphology observation of the pitting and electric charge calculation indicate that the periodic intensification effect can promote the initiation and growth of pits by enhancing the anodic dissolution even under cathodic protection, but it is ineffective below the hydrogen evolution potential. The decrease in either upper or lower potential can mitigate anodic dissolution. Through the statistical analysis of pitting size, it is found that the wide potential range tends to activate the metastable pitting formed under hydrostatic pressure, forming densely distributed pitting. Meanwhile, it is more favorable to the formation of fully grown pits with high size dispersion degree when the proportion of electric charge in the anodic process is higher.

Role for ERK1/2-dependent activation of FCHSD2 in cancer cell-selective regulation of clathrin-mediated endocytosis

Clathrin-mediated endocytosis (CME) regulates the uptake of cell-surface receptors as well as their downstream signaling activities. We recently reported that signaling can reciprocally regulate CME in cancer cells and that this crosstalk can contribute to cancer progression. To further explore the nature and extent of the crosstalk between signaling and CME in cancer cell biology, we analyzed a panel of oncogenic signaling kinase inhibitors for their effects on CME across a panel of normal and cancerous cells. Inhibition of several kinases selectively affected CME in cancer cells, including inhibition of ERK1/2, which selectively inhibited CME by decreasing the rate of clathrin-coated pit (CCP) initiation. We identified an ERK1/2 substrate, the FCH/F-BAR and SH3 domain-containing protein FCHSD2, as being essential for the ERK1/2-dependent effects on CME and CCP initiation. Our data suggest that ERK1/2 phosphorylation activates FCHSD2 and regulates EGF receptor (EGFR) endocytic trafficking as well as downstream signaling activities. Loss of FCHSD2 activity in nonsmall cell lung cancer (NSCLC) cells leads to increased cell-surface expression and altered signaling downstream of EGFR, resulting in enhanced cell proliferation and migration. The expression level of FCHSD2 is positively correlated with higher NSCLC patient survival rates, suggesting that FCHSD2 can negatively affect cancer progression. These findings provide insight into the mechanisms and consequences of the reciprocal regulation of signaling and CME in cancer cells.