Susceptibility To Localized Corrosion Research Articles

Corrosion Behavior of Austenitic Stainless Steel in High Sulphate Content

Austenitic stainless steels especially 316L has been used extensively in many sectors including construction, medical and household appliances due to their highly resistance to corrosion attack, reasonable cost and excel in mechanical properties. However, in corrosive media, 316L are susceptible to localised corrosion attack especially in seawater and high temperature. The corrosiveness of media increased as the anions contents increased. This paper presents the corrosion mechanism of 316L exposed to high concentration of sulphate in the salinity of seawater. The solution (media) was prepared according to the same composition as seawater including pH, salinity and dissolved oxygen. The corrosion mechanism were characterized to breakdown potential (Eb) of 316L which are the potential once reaches a sufficiently positive value and also known as pitting potential. This is the most point where localized corrosion susceptibility to evaluate and considered a potential, which could be an appropriate point according to any given combination of material/ambient/testing methods. The Eb value were identified at 4°C, 20°C, 50°C and 80°C and compared with Eb value of 316L in seawater. The Eb value of 316L in high sulphate are higher compared to seawater in every temperature which elucidate that some anions accelerate corrosion attack whereas some anions such as sulphate behaves as inhibiting effect to 316L.

Pitting Corrosion of Very Clean Type 304 Stainless Steel

The localized corrosion susceptibility of a clean grade of Type 304 (UNS S30400) stainless steel (SS304), which was processed with the intent of having fewer and smaller inclusions, was compared with regular grade SS304. Transmmission electron microscopy (TEM) analysis revealed that inclusions were composed of multiple phases that were either multi-element oxide or manganese sulfide (MnS). Oxide inclusions, which had only multi-oxide phases, were the dominant inclusion type in clean SS304, whereas MnS-containing inclusions, having both oxide and MnS phases together, were more frequent in regular SS304. The average size of inclusions was larger in regular SS304. Cyclic polarization tests showed that pitting potentials of clean SS304 were higher than regular grade SS304. Under exposure to strong oxidizing acid with Cl−, MnS-containing inclusions initiated pitting, whereas oxide inclusions did not, indicating that pit initiation is more frequent in regular SS304 because it has more MnS inclusions. The fewer pit initiation sites in clean SS304 was the reason for its higher pitting corrosion resistance.

A combined electron probe micro analysis and scanning Kelvin probe force microscopy study of a modified AA4xxx/AA3xxx aluminium brazing sheet

The electrochemical and microstructural properties of the clad and core from a modified AA3xxx/AA4xxx brazing sheet were investigated before and after brazing. For this, scanning Kelvin probe force microscopy (SKPFM) and field emission electron probe micro analysis (FE-EPMA) were used. The Volta potential difference (VPD) was measured as a function of depth for the brazed and non-brazed sheets. This was correlated with the cross-sectional variation of chemistry and microstructure that result from brazing. Furthermore, potentiodynamic polarization experiments and subsequent microscopic analysis of the corroded samples were used to explore the corrosion mechanism of the modified brazed sheet. The investigation revealed that the major consequences of brazing for the microstructure are: an increase in the Si content of the matrix in the heat affected zone (HAZ); a non-uniform distribution of Cu in the HAZ; an accumulation of Cu in Al–Si eutectics and around the grain boundaries, including α-Al(Mn,Fe)Si and Al2Cu intermetallics; the presence of some continuous grain boundaries in both the clad and core of the sheet; and the non-uniform precipitation of intermetallics at Al–Si eutectic phases. The impact of these microstructural changes on the corrosion behaviour of the brazed sheet was: to increase the VPD of the re-solidified clad matrix; to introduce localized corrosion susceptibility on the brazed clad and core structures; and to reduce the cathodic protection power of the re-solidified clad material. As a result of the correlation between microstructure and electrochemical behaviour, it was concluded that corrosion resistance of the modified aluminium brazing sheet could be improved by applying a post-braze heat treatment.

Long-Term Electrochemical Criteria for Crevice Corrosion in Concentrated Chloride Solutions

Crevice corrosion is the predominant mode of localized corrosion of Alloy 22 in concentrated chloride solutions at near-boiling temperatures. A literature review was performed to assess the electrochemical criteria for the long-term initiation of stable crevice corrosion of nickel-based or passive alloys, such as Alloy 22, in terms of likelihood, timing, and magnitude of potential damage due to crevice corrosion. The assessment in this study intends to predict the long-term performance of the waste package in nuclear waste management. Specifically, the areas of review included (a) environments (e.g., solution chemistry and electrochemical polarized condition) and crevice corrosion initiation criteria, (b) data and models for Alloy 22 crevice corrosion, and (c) induction times for crevice corrosion initiation. The assessment of the criteria for crevice corrosion initiation indicates that without externally applied current (i.e., at the open-circuit corrosion potential), initiation of crevice corrosion could be more difficult compared to the case when external current is applied. Without external current, crevice corrosion may not be initiated and sustained until the corrosion potential reaches the breakdown potential. Because the breakdown potential is typically more anodic than the repassivation potential, it is likely that the use of repassivation potential as the initiation criterion can overestimate a localized corrosion susceptibility. A short-term laboratory polarization test of Alloy 22 investigated whether any pits developed under the crevice were unstable for growth and if they could be stifled (i.e., suppressed). The long-term immersion tests of Alloy 22 exhibited a trend of continuous decrease of corrosion rate with time while the corrosion potential increased with time. An assessment of the theoretical models appeared to adequately scale induction time for crevice corrosion initiation to extrapolated long time periods.

Interactions between mechanically generated defects and corrosion phenomena of Zr-based bulk metallic glasses

Using the example of a Zr–Ti–Al–Cu–Ni bulk metallic glass with an ex situ approach, two aspects were studied: (i) the effects of pre-formed corrosion pits on the room temperature deformation behaviour, and (ii) the effect of mechanically generated defects on the local corrosion susceptibility. For the latter, Vickers micro-indents generated with different loads were also employed as model defects. It is revealed that pre-formed corrosion pits act as favourable surface sites to which shear bands are linked and most likely nucleate, which leads to a slight reduction in the maximum compression stress. Further, mechanically generated defects have to be considered as critical weak points at a glassy sample surface which can act as preferential sites for local corrosion initiation and propagation. Local chemical and structural changes due to the formation of shear bands as a response to mechanical load are discussed as possible reasons for this. For potential high-load applications of bulk metallic glasses this interaction must be considered as an important lifetime limiting aspect.

Effect of Temperature on the Crevice Corrosion Resistance of Ni-Cr-Mo Alloys as Engineered Barriers of Nuclear Repositories

Deep geological disposal is the strongest alternative to the disposal of high level nuclear waste. Alloys 625, C-22, C-22HS and HYBRID-BC1 are considered among candidates as engineered barriers of nuclear repositories. Localized corrosion, like crevice or pitting corrosion, is one of the most important degradation processes that will limit the lifetime of containers. The susceptibility to crevice corrosion is measured by the value of the repassivation potential (ECO). The objective of the present work is to assess the effect of temperature on the crevice corrosion resistance of these alloys.Alloy HYBRID-BC1 was the most resistant to chloride-induced crevice corrosion, followed by alloys C-22HS, C-22 and 625. ECO showed a linear decrease with temperature. There is a temperature above which ECO does not decrease anymore, reaching a minimum value. This ECO value is a strong parameter for assessing the localized corrosion susceptibility of a material in a long term timescale, since it is independent of temperature, chloride concentration, crevice mechanism, crevice gap and type of crevice formers.

Effect of temperature on the crevice corrosion resistance of Ni-Cr-Mo alloys as engineered barriers in nuclear waste repositories

ABSTRACTNi-Cr-Mo alloys offer an outstanding corrosion resistance in a wide variety of highly corrosive environments. Alloys 625, C-22, C-22HS and HYBRID-BC1 are considered among candidates as engineered barriers of nuclear repositories. The objective of the present work was to assess the effect of temperature on the crevice corrosion resistance of these alloys. The crevice corrosion repassivation potential (ER,CREV) of the tested alloys was determined by the Potentiodynamic-Galvanostatic-Potentiodynamic (PD-GS-PD) method. Alloy HYBRID-BC1 was the most resistant to chloride-induced crevice corrosion, followed by alloys C-22HS, C-22 and 625. ER,CREV showed a linear decrease with temperature. There is a temperature above which ER,CREV does not decrease anymore, reaching a minimum value. This ER,CREV value is a strong parameter for assessing the localized corrosion susceptibility of a material in a long term timescale, since it is independent of temperature, chloride concentration and geometrical variables such as crevicing mechanism, crevice gap and type of crevice former.

Localised corrosion initiation and microstructural characterisation of an Al 2024 alloy with a higher Cu to Mg ratio

An Al 2024 (AA2024-T351) alloy having less Mg and a higher proportion of Cu to Mg (mass ratio ≈3.7) has been characterised to provide input data for microscale and macroscale corrosion models. The Al 2024 alloy microstructure has a significant presence of nanoscale dispersoid and microscale AlCuFeMnSi (2nd phase) intermetallic particles, but a smaller population of microscale S phase (Al2CuMg) and θ phase (Al2Cu) intermetallic particles. Microscale electrochemical data show that pitting potential (SCE) values for 2nd phase, S phase, or matrix overlap significantly. The localised corrosion susceptibility is affected by S and inhomogeneous 2nd phase particles.

Passivation and localised corrosion susceptibility of new Al–Cr–Fe complex metallic alloys in acidic NaCl electrolytes

Al-based complex metallic alloys (CMAs) are crystalline intermetallic phases characterised by very complex crystal lattices, showing intriguing surface properties such as low wetting, low friction and hardness which include, for the Al–Cr–Fe system, high corrosion resistance. However, their passivation mechanisms (nm-thick oxide layer formation) still need to be understood in relation with localised corrosion susceptibility. New single phases were therefore characterised by electrochemical Microcell technique. The chromium cations in the oxide proved to play a significant role in stabilising the passive layer at low pH. Corrosion resistance of single- and polycrystalline samples was first compared by means of inductively coupled plasma mass spectrometer (ICPMS) analysis during immersion. Higher dissolution rates have been measured for the low Cr containing (12.5 at%) polycrystals compared to the single crystals. The resistance to localised corrosion attack of the single crystals in an aggressive 0.01 M HCl + 1 M NaCl solution at pH 2 was high, with an anisotropic behaviour of the anodic breakdown potential related to the grain orientation. The orthorhombic (0 0 1) termination with higher Cr/Al atoms ratio formed a passive layer with increased resistance against pitting. Ageing of the samples and the formation of surface Al oxy-hydroxide appeared to decrease the pitting corrosion resistance.

Effect of alloyed Cu on localized corrosion susceptibility of Al–Cu solid solution alloys—Surface characterization by XPS and STEM

Cu additions to Al alloys decrease pitting susceptibility provided that the Cu is retained solid solution. In this study, a range of electrochemical, surface analytical and electron microscopy characterization experiments were carried out with Al–Cu solid solution alloys to understand the origins of this inhibiting effect. Potential-controlled electrochemical polarization experiments carried out in dilute chloride solutions show that stimulation of alloy dissolution without inducing passive film breakdown significantly ennobles a subsequently measured pitting potential. Similar effects are not observed with high-purity Al or Al–Zn solid solution samples. The ennobling effect is more difficult to detect in large area electrodes due to pit initiation triggered by defects and inclusions that are more regularly encountered in larger electrodes. X-ray photoelectron spectroscopy of Al–Cu solid solution samples reveals no Cu enrichment above detection limits. However, scanning transmission electron microscopy and spectral imaging of specially prepared Al–Cu needle-type samples shows that Cu is enriched at the alloy interface by a range of exposure regimens including those that induce pitting. These results suggest the possibility of local Cu enrichment at incipient pit sites by metastable pitting, which can contribute to an ennoblement of the critical pitting potential under certain circumstances.

Electrochemical behavior of two austenitic stainless steel biomaterials

Potentiodynamic and potentiostatic polarization measurements were conducted in 0.9% NaCl solution to investigate the localized corrosion susceptibility of two austenitic stainless steel biomaterials: a low nitrogen, according to ASTM F 138 - the metallic material most widely utilized today in orthopedic applications; and a nitrogen- and niobium-bearing stainless steel, according to ISO 5832-9, which has shown a promising potential as a substitute of the F 138 steel for more severe loading applications and longer times inside the human body. The polarization tests revealed that the ISO 5832-9 steel is more corrosion resistant than the F 138. The critical pitting potential of the ISO 5832-9 steel could not be observed in the cyclic polarization curve up to the value of potential corresponding to its transpassivity. The potentiostatic scratch test confirmed the superiority of the ISO 5832-9 steel, which heal the mechanically damaged passive film at applied potential as high as 800 mV (SCE). Scanning electron microscopy (SEM) examination confirmed the presence of corrosion pits - lacelike pits - in a stable growth stage on the surface of F 138 steel and the absence of such pits in the specimens of the ISO 5832-9 steel. The higher corrosion resistance of the latter is attributed to the increased stability of the passive film and the high tendency to repassivate, which, in turn, is favored by the presence of nitrogen in interstitial solid solution in the austenite of this type of steel.

Effect of Aging Treatments on the Repassivation Potential of Duplex Stainless Steel S32205

Abstract The effect of isothermal heat treatments at 475, 700, and 870°C on the localized corrosion susceptibility of 2205 duplex stainless steel (UNS S32205) was assessed in chloride-containing en...

Stress corrosion cracking of gas-tungsten arc welds in continuous-cast AZ31 Mg alloy sheet

AZ31 Mg alloy sheet was welded using a gas-tungsten arc (GTA) process over inserts containing 2.3–9.3 wt.% Al. The welded specimens were susceptible to SCC in distilled water, with susceptibility increasing with decreasing weld metal Al (or β particle) concentration. Primary stress corrosion cracks initiated at the weld metal–HAZ interface by stress-assisted localised dissolution and propagated through the weld and base metals by transgranular and intergranular H-assisted fracture (TG-HAF and IG-HAF) respectively. The IG fracture mode may be intrinsic to the texture imparted upon the base metal by rolling. The increase in SCC susceptibility with decreasing weld metal Al concentration is contrary to the purported roles of β particles in promoting localised corrosion and as crack nucleation sites, but corresponds with increases in weld – base metal galvanic current density and weld metal localised corrosion susceptibility.

Effect of Heat Treatment on Corrosion and Stress Corrosion Cracking of S32205 Duplex Stainless Steel in Caustic Solution

Duplex stainless steels (DSSs) have generally performed very well in caustic environments. However, some corrosion and stress corrosion cracking (SCC) of DSSs have been reported in different pulp mill environments employing caustic solutions. Studies have shown that the corrosion and SCC susceptibility of DSSs depend on the alloy composition and microstructure of the steel. In this study, the effect of a sulfide-containing caustic environment (pulping liquor) and material properties (DSS alloy composition and microstructure) on the corrosion and SCC of DSSs was evaluated. During metal fabrication processes, localized areas of DSSs may be exposed to different temperatures and cooling rates, which may lead to changes in the microstructure in these regions. This change in microstructure, in turn, may affect the general and localized corrosion or SCC susceptibility of the affected area as compared to the rest of the metal. Hence, the effect of different annealing and aging temperatures as well as cooling rates on the microstructure and corrosion behavior of S32205 DSSs in caustic environment was evaluated. The results showed that changes in the microstructure of S32205 DSSs due to selected heat treatments did not have a significant effect on the general corrosion susceptibility of the steel in caustic environment, but its SCC susceptibility varied with changes in microstructures.

In situ monitoring of corrosion processes within the bulk of AlMgSi alloys using X-ray microtomography

Susceptibility to localized corrosion of AlMgSi (AA6016 and AA6111) alloys in certain aggressive environments is high. In this study, synchrotron X-ray microtomography was used to monitor non-destructively corrosion processes within bulk materials. In the selected aggressive solutions, surface–deformed layers showed high localized corrosion susceptibility, but are more stable than the bulk of the alloy during corrosion propagation. In addition, exfoliation-like attack was observed as a transition from intergranular attack. This directed corrosion is not related to grain or crystallographic structure. Finally, intermetallic particles dissolution inside the materials after contact with aggressive solution of the intergranular corrosion path was evidenced.

Comparing the corrosion behaviour of Zr 66/Ti 66–Nb 13Cu 8Ni 6.8Al 6.2 bulk nanostructure-dendrite composites

Bulk samples with 3 mm diameter of the Zr 66Nb 13Cu 8Ni 6.8Al 6.2 and Ti 66Nb 13Cu 8Ni 6.8Al 6.2 alloys with in situ formed nanostructured matrix and dendritic bcc phase were prepared by copper mould casting and characterized regarding their microstructure. The passivation ability and the localized corrosion susceptibility were determined from electrochemical dynamic and static polarization tests. Both alloys show excellent passivity in acidic as well as in alkaline chloride-free solutions due to the formation of very protective passive films. But the Zr 66Nb 13Cu 8Ni 6.8Al 6.2 alloy exhibits a low resistance to chloride-induced localized corrosion already at conditions 0.5 M H 2SO 4 (pH = 0.3) + ≥0.15 M KCl, whereas Ti 66Nb 13Cu 8Ni 6.8Al 6.2 is very stable up to 2 M HCl solution. This large difference in the pitting resistance is mainly explained by the diverse electrochemical behaviour of the main alloy components Zr and Ti. For both alloys preferential dissolution of the Cu-enriched and Nb-depleted nanostructured matrix takes place. In conclusion, it was found that by substituting the main element Zr in Zr 66Nb 13Cu 8Ni 6.8Al 6.2 alloy with Ti the environmental stability is greatly improved – another beneficial effect besides the achievement of exceptional mechanical properties.

The influence of copper content on intergranular corrosion of model AlMgSi(Cu) alloys

AbstractApplication prospects in automotive and aerospace industry have led to extensive studies on AA6xxx alloys in recent years. Varying amounts of Mg, Si and Cu and heat treatments are used to achieve the desired mechanical properties in these alloys. In this investigation, a series of tests have been designed and carried out on model AlMgSi(Cu) alloys to investigate the effects of Cu, Mg and Si composition and heat treatments on the corrosion properties for a range of Cu content levels (0.03, 0.15 and 0.80 wt%, respectively). The results indicate that the localized corrosion susceptibility of the model alloys primarily increased with Cu content. The Si and Mg content and ratio do not appear to have a significant effect on the local corrosion behaviour. Heat treatment can improve the corrosion resistance. However, this effect is small compared to that of the Cu content for the range of model alloys investigated. Intergranular corrosion will occur by micro‐galvanic coupling between the cathodic AlMgSi(Cu) (Q) phase precipitates and the aluminum matrix adjacent to the particles. The increasing susceptibility to intergranular corrosion with Cu content can be attributed to an increased formation of Q phase particles.

Role of Microstructure on the Corrosion Susceptibility of UNS S32101 Duplex Stainless Steel

Abstract Effect of heat treatments and resulting changes in microstructure on general and localized corrosion susceptibility of lean duplex stainless steel UNS S32101 in caustic and chloride solutions was investigated. Results show that changes in the microstructure (ferrite phase/austenite phase ratio and inter-metallic precipitation) of the duplex stainless steel (DSS), due to different annealing and aging treatments, affect its general and pitting corrosion resistance. The role of DSS microstructure in localized corrosion susceptibility was found to be significantly different in the chloride environments as compared to caustic environments.

Effect of Weak Acid Additions on the General and Localized Corrosion Susceptibility of Alloy 22 in Chloride Solutions

AbstractElectrochemical studies such as cyclic potentiodynamic polarization (CPP) and electrochemical impedance spectroscopy (EIS) were performed to determine the corrosion behavior of Alloy 22 (N06022) in 1M NaCl solutions at various pH values from acidic to neutral at 90°C. All the tested material was wrought Mill Annealed (MA). Tests were also performed in NaCl solutions containing weak organic acids such as oxalic, acetic, citric and picric acids.Results show that the CR of Alloy 22 was significantly higher in solutions containing oxalic acid than in solutions of pure NaCl at the same pH. Citric and Picric acids showed a slightly higher CR, and Acetic acid maintained the CR of pure chloride solutions at the same pH. Organic acids revealed to be weak inhibitors for crevice corrosion. Higher concentration ratios, compared to nitrate ions, were needed to completely inhibit crevice corrosion in chloride solutions.Results are discussed considering acid dissociation constants, buffer capacity and complex formation constants of the different weak acids.

Localized Corrosion Susceptibility of Supermartensitic Stainless Steel in Welded Joints

Abstract Supermartensitic stainless steels is known for its better weld-ability and corrosion resistance compared to the conventional martensitic, mainly due to its lower carbon content. This enables the production of welded joints with superior resistance to hydrogen embrittlement and to sensitization, particularly in the heat-affected zone. These characteristics can be optimized with the production of weldments using high-power density processes, such as electron beam welding. This process creates a narrow heat-affected zone with a high thermal gradient, which makes it less susceptible to precipitation, particularly to chromium carbides. Thus, its pitting potential is improved.