Localized Corrosion Behavior Research Articles

Study on localized corrosion behavior of hot extrusion deformed GW103K magnesium alloy

This study investigated the corrosion behavior in the core and at the edge of the cross-section of an extruded GW103K (Mg–10Gd–3Y–0.4Zr) alloy. Equivalent stress and strain were modeled using finite element simulations. The stress and strain in the core were lower than those at the edge. The microstructure, corrosion morphology, and grain orientation of the alloy were examined using optical microscopy, scanning electron microscopy, and electron backscatter diffraction, respectively. The results showed that most grains in the core exhibited a basal plane orientation and lower surface energy, whereas those at the edge exhibited cylindrical orientations. Hydrogen evolution experiments and electrochemical tests showed that the corrosion resistance in the core was higher than that at the edge. Scanning Kelvin probe force microscopy measurements of the surface potential distribution in the cross-section revealed a large potential difference between the second-phase particles at the edge and the matrix, with obvious galvanic corrosion. The alloy core exhibited low stress and a higher content of grains with basal plane orientation, along with a small potential difference between the second-phase particles and the matrix. Thus, the corrosion resistance in the core was higher than that at the edge.

Atomic-scale de-passivation mechanisms of anatase TiO2 induced by corrosive halides based on density-functional theory

By using density-functional theory calculations, we systematically investigated the localized corrosion behavior of anatase TiO2 by chloride (Cl)/fluoride (F) via different mechanisms. Energetics for adsorption and substitution pointed to a more aggressive influence of F over Cl, revealing that F was more likely to induce TiO2 de-passivation by “adsorption-thinning” mechanism, though surface hydroxylation can promote Cl etching via this mechanism. Whereas Cl accessed to TiO2 interior with nearly negligible diffusion energy barrier, facilitated by dramatic relaxations via mechanism of Cl residing at oxygen vacancies (VO), accompanied by a reduction in passivity. Moreover, the annihilation/creation of VO at the TiO2 (101) surface was dominated by competition of adsorbed species. While a subsurface VO can move towards the outermost surface by exchanging with lattice O, a surface VO can spontaneously re-combine with a surface O promoting re-passivation. Co-adsorption of Cl/F with O can significantly inhibit VO–O combination by directly occupying the VO site or by reducing the energy to create a VO. Our studies outlined the non-negligible interactions between corrosive species and defects in TiO2 and the mechanisms concerning Cl/F/O inducing re(de)-passivation, the understanding of which is meaningful in mitigating Ti corrosion in environments containing halides.

Effect of solution annealing temperature on the localised corrosion behaviour of a modified super austenitic steel produced in an open-air atmosphere

Two annealing heat treatments were investigated regarding localised corrosion behaviour on Nb and Mn-bearing super austenitic stainless steel. The material was designed based on physical metallurgical principles supported by Thermo-Calc modelling and was produced in an open-air atmosphere based on pre-sorted SS scrap plus ferroalloys elements. The production method aims for metal waste valorisation considering small foundries without an atmosphere-controlled process. Secondary phases at annealing temperatures were experimentally analysed by different microstructural characterisation methods and correlated by the Thermo-Calc modelling. In addition, electrochemical techniques and SKPFM were used to study the relationship between observed phases and localised corrosion performance. As the main results, a good correlation was observed between Thermo-Calc calculations and the microstructural characterisation. In particular, M23C6 carbides, σ phase, and Nb-MX were identified for the sample treated at 1120 °C, while for the sample treated at 1180 °C, σ phase and Nb-MX were identified, no M23C6 were detected. As regards localised corrosion behaviour, the M23C6 carbides and σ phase for sample 1120 °C generated Cr and Mo depletion zones and diminished the corrosion resistance in corrosive aqueous solutions. In the case of sample 1180 °C, the σ-phase with a smaller size and volume fraction than sample 1120 °C was observed, leading to a more uniform Cr and Mo distribution through the microstructure, obtaining high corrosion resistance and showing promising corrosion behaviour, similar to commercial SS 254smo considering its production in open-air.

Effect of Complex Inclusions on Localized Corrosion Behavior in Ferritic Steel

The localized corrosion behavior of different inclusions in a simulated solution of coastal industrial pollution is investigated in this study. It is indicated in the results that the Al2O3–MnS composite inclusions of ordinary carbon Q345B steel have microcracks and induce severe lattice distortions in the surrounding matrix. The MnS in the Al2O3–MnS composite inclusions dissolves preferentially to induce pitting corrosion. The microcracks and severe lattice distortion of the surrounding matrix accelerate the corrosion propagation. The preferential dissolution of CeAlO3–Ce2O2S inclusions induces pitting in No. 2 steel. The inherent physical and chemical properties of the inclusions and the chemical corrosion of the simulated fluid are vital in the initiation and expansion of pitting corrosion. The TiN in the test steel exhibits excellent resistance to pitting corrosion, and the double‐layer composite inclusions completely covered by TiN do not form corrosion pits in the simulated solution and do not cause the dissolution of the adjacent matrix. The coordinated addition of Ti–Ce can reduce the size of the inclusions and improve the probability of complete cladding of TiN.

Local Corrosion Behaviors in the Coarse-Grained Heat-Affected Zone in a Newly Developed Zr-Ti-Al-RE Deoxidized High-Strength Low-Alloy Steel.

Oxide metallurgy technology can improve the microstructure of a coarse-grained heat-affected zone (CGHAZ) but introduces extra inclusions. Local corrosion behavior of the CGHAZ of a Zr-Ti-Al-RE deoxidized steel was investigated in this work using theoretical calculations and experimental verification. The modified inclusions have a (Zr-Mg-Al-Ca-RE)Ox core claded by a CaS and TiN shell. CaS dissolves first, followed by the oxide core, leaving TiN parts. This confirms that the addition of rare earth can reduce lattice distortion and prevent a galvanic couple between the inclusions and the matrix, while the chemical dissolution of CaS causes localized acidification, resulting in the pitting corrosion initiation.

Bipolar electrochemistry for high throughput screening of localised corrosion in stainless steel rebars

The corrosion performance of stainless steel rebars is assessed by using bipolar electrochemistry. This method produces a quasi-linear potential gradient across the sample, with the technique providing rapid access to test for the nucleation and growth of pits across a wide range of applied potentials. The localised corrosion behaviour and resulting growth kinetics of Types 304L and 316L austenitic stainless steels (ASSs) are compared to Type 2101 and 2205 duplex stainless steels (DSSs). The difference in selective phase dissolution between pitting and trans-passive corrosion in DSSs is compared, with critical pitting potential, pit nucleation numbers, growth kinetics, volume loss, and aspect ratio of these four stainless steels discussed.

Galvanic corrosion of AA5052/304SS welded joint with Zn-based filler metal in marine engineering

Galvanic corrosion and localized corrosion behavior of AA5052/weld seam/304SS tri-metallic couples were examined by EIS, ZRE, SKP and SVET tests after tungsten inert gas (TIG) arc welding. The results showed that the weld seam had a relatively high corrosion susceptibility. The asymmetric corrosion of weld seam was attributed to the macro-galvanic effect between the weld seam/AA and the weld seam/SS. Localized corrosion of Zn in δ-FeZn10 induced the corrosion trenches and channels initiation. The deep corrosion propagation at the weld seam/SS interface was brought on by local acidity and micro-galvanic effect.

Study on pitting corrosion behavior and semi in-situ pitting corrosion growth model of 304 L SS with elastic stress in NaCl corrosion environment

The passive film characterization and pitting corrosion behavior of 304 L SS with various elastic tensile and compressive stresses are investigated by electrochemical measurements, acoustic emission, X-ray photoelectron spectroscopy and scanning electron microscope. The elastic tensile stress could decrease the pitting corrosion sensitivity of 304 L SS at 16.63%σ0.2. As the elastic tensile stress further increases, the pitting corrosion sensitivity of 304 L SS increases. The compressive stress has the opposite effect on 304 L SS localized corrosion behavior. X-ray computed tomography is employed to construct the four-dimensional space-time model of pitting corrosion growth of 304 L SS under the 63.24%σ0.2 elastic tensile stress.

Influence of Metal Cation and Temperature on Localized Corrosion Behavior of Steels in Aqueous Environments

Steels are abundantly used in many areas because of their good formability and low price. Steels suffer from corrosion in aqueous environments with chloride ions. Corrosion of steels is also a serious problem for long-term usage of steel structures such as bridges and buildings. There are many studies focused on chloride ions. There are reports that metal cations have a tendency to inhibit the corrosion of steels in a chloride aqueous environment by forming a layer on the steel.The other important factor for corrosion of steels in an aqueous environment is temperature. The corrosion rate of metal in cold regions is expected to slow because of low temperature. A recent study on atmospheric exposure tests carried out in different places in Hokkaido, it has elucidated that the corrosion rate in the cold region is the same as in the warm region.However, it is not fully elucidated that temperature, especially below freezing point, and metal cations on corrosion behavior and distribution of active dissolution site. The purpose of this study is to investigate the influence of temperature and metal cations on thecorrosion behavior of steels.Steel sheets of 15 x 20 mm and 20 x 20 mm were used as specimens. Three solutions of 0.1 mM ZnCl2, 0.5 mM ZnCl2 and 1.0 mM ZnCl2 were used for examination of the effect of metal cations, and 20 mass % NaCl solution was used for examination of effect of temperature. After the tests, the morphology of specimens was examined by optical microscope and scanning electron microscope.After the wet/dry corrosion tests used 10 mL solutions droplets, corrosion products were formed on the specimens. The corrosion processes under NaCl and MgCl2 were similar. Yellow corrosion products were firstly observed in the solution during the wet period. In the case of under ZnCl2, after the formation of oxide layer on the specimens the corrosion proceeded in localized areas. The color of almost half area of the exposed surface was light, which might indicate less corrosion occurred in the area. The initial corrosion stage of steel preferred to form a brown area in the center of the droplet. There are no similar corrosion products thatcan be observed in comparison to the samples under MgCl2 and NaCl solutions.A lot of corrosion products and localized corroded areas were formed on specimens after being immersed at 273 K, while less corrosion products and homogenously corroded surface were observed on specimens after being immersed at 293K.The results indicated that corrosion morphology and preferentially corroded area were changed with the kind of metal cation and temperature.

Electrochemical Behavior of Additively Manufactured 7050 Aluminum Alloy in Chloride Environments

The benefits of additive manufacturing (AM) process combined with the high-strength, corrosion resistant and fracture toughness properties of the 7xxx series aluminum alloys make them promising candidates for the aerospace and defense industries. However, these alloys undergo unconventional thermal cycles during additive manufacturing process like laser powder bed fusion (LPBF) as well as during post-processing treatments like hot isostatic pressing, resulting in microstructures different from equivalent wrought alloys.In our work, we investigate how the effects of microstructural differences in a modified LPBF 7050 aluminum alloy compared to an equivalent wrought alloy, results in differences in electrochemical behavior. A series of AM 7050 aluminum alloy samples with different post-processing treatments and subsequent microstructures are tested for polarization and electrochemical impedance behavior in varying chloride ion concentrations. The effects of underaging and overaging treatment on the electrochemical behavior is also studied. Localized corrosion behavior of the alloys is investigated using immersion tests and scanning vibration electrode technique (SVET), which showed differences in pitting behavior and pit stability. The results indicate that AM 7050 alloy in general, showed less corrosion susceptibility compared to an equivalent wrought alloy.

The Feasibility of Using Bipolar Electrochemistry to Study Pitting and Crevice Corrosion of Stainless Steels in Cementitious Materials

The durability of carbon steel reinforced concrete infrastructure is often limited by rate of corrosion damage progression. Over the past couple of decades, corrosion-resistant alloys, such as stainless steels (SS), have garnered attention as a potential way to address the durability of reinforced concrete exposed to aggressive marine environments. However, there are currently no models available to accurately forecast corrosion of stainless-steel reinforced infrastructure and durability projections for carbon steel may not consider the necessary mechanistic steps.Traditional corrosion durability projections adopt the classic two stage model considering the time prior to and following corrosion initiation often distinguished by the point in time where enough chlorides have accumulated at the steel surface to exceed the chloride concentration required to initiate corrosion.[1] Such models do not consider the evolution of pitting or crevice corrosion and the potential for progression to more widespread corrosion. Therefore, research is required to first identify the expected corrosion damage morphology of stainless steels in concrete and then to formulate a theoretical framework that can be used to describe accurately its progression provided expected exposure conditions. This work attempts to develop an efficient yet informative method to study pitting corrosion evolution of steel in concrete with the objective of identifying the role of the cement pore structure on damage evolution and pit or crevice stability.Recently, bipolar electrochemistry has been used to identify potential-kinetic-corrosion damage mode relationships from single measurements on ferritic [2] and duplex stainless steels.[3] Bi-polar electrochemistry (BPE) comprises indirect dc polarization of a conductive element usually immersed in an electrolyte in cases where direct contact to the elements need to be avoided. In application to pitting corrosion studies, BPE followed by post exposure 3D surface metrology can provide pitting characteristics as a function of applied potential from a single experiment. In this work various BPE configurations including single and split electrodes are used to assess the feasible in applying a suitable potential distribution on steel plate specimens that have a thin cement overlay. A finite element model was developed to simulate the applied potential distribution considering the cell geometry and interfacial kinetics. The corrosion damage morphology and the pitting characteristics obtained will be compared to that of chloride-ponded SS reinforced concrete beams to uncover mechanistic insight on SS corrosion damage evolution. Tuutti, K: Corrosion of steel in concrete. 1982, Stockholm. Swedish Cement and Concrete Research Institute, ISSN 0346-6906. Royal Institute of Technology, Stockholm. Department of Building MaterialsZhou, Yiqi, and Dirk Lars Engelberg. "On the application of bipolar electrochemistry to characterise the localised corrosion behaviour of type 420 ferritic stainless steel." Metals10, no. 6 (2020): 794.Zhou, Yiqi, and Dirk Lars Engelberg. "Fast testing of ambient temperature pitting corrosion in type 2205 duplex stainless steel by bipolar electrochemistry experiments." Electrochemistry Communications117 (2020): 106779.

(Digital Presentation) On the Effect of Sizing on Electrochemical Response and Localized Corrosion Behavior of Alumix 123 P/M Alloy

Powder metallurgy (PM) as an additive technique for fabricating parts has been used by many industries such as automotive, aerospace, and medical. However, it has been centered mostly around automotive industry which has benefited from large volume production, low cost, and near-net-shape manufacturing that comes with PM. High demand for producing fuel-efficient and light vehicles in automotive industry provides a driving force for extensive research activity on PM of aluminum alloys. Among different aluminum alloys, PM of 2xxx series are among the best choices due to their good sinterability and mechanical response. But industrial PM parts need post processing treatments such as sizing to meet the real-world applications. While sizing is widely used in industry to provide tighter tolerance, it can also help improving density, fatigue behavior, yield strength, and hardness. But there were very few studies on the effect of sizing on electrochemical response. In this study we produced Alumix 123 PM alloy using a press-and-sinter process and then sizing was applied on some of the samples to compare their long-term electrochemical behavior. The changes in the surface profile and roughness of the samples were investigated using confocal laser scanning microscopy. Electrochemical impedance spectroscopy (EIS) as a powerful technique for investigating long-term electrochemical behavior has been used to find the effect of sizing on corrosion response of Alumix 123 PM. In addition, effect of sizing on localized corrosion and pitting tendency was thoroughly discussed using electrochemical polarization results, scanning electron microscope images, and EIS outcomes.

Electrochemical and localized corrosion behavior of 316 L SS/copper/316 L SS sandwich composite in chloride-containing environment

Electrochemical and localized corrosion behavior of a 316 L SS/copper/316 L SS composite in 0.5 wt. % NaCl solution was investigated from cross-sectional and plane directions by electrochemical measurements and high-resolution microscopic examination. The galvanic coupling accelerated the dissolution at the internal surface and pitting attack at the external surface of the 316 L layer. Polarization up to 1 V/SCE resulted in formation of a corrosion product layer (ca. 992 nm) composed of metal oxides/hydroxides on top of the passive film, which consisted of a Fe2O3-rich outer layer (3.3 nm) and a Cr2O3-rich inner layer (4.1 nm). The copper corrosion was quite uniform. Data availability statementThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

Study on the local corrosion behaviour and mechanism of bogie steel welded joints

The local corrosion behaviour and mechanism of welded joints were studied. The results show that the corrosion was caused by the distribution of microstructure defects in different areas of the weld. In the early stage, the potential difference between the base metal and the heat affected zone was less than 50 mV, so there would be no galvanic effect. As the corrosion progressed, the potential difference increased gradually, and the maximum value exceeded 160 mV. During this period, the corrosion rate was mainly affected by galvanic effect, and the order was weld seam > base metal > heat affected zone.

Correlation of microstructure with corrosion performance in high zinc 7068 aluminum alloy aged using different T6 conditions

High-strength 7068 aluminum alloy containing >7 wt% zinc deserves evaluation of its SCC performance in different ageing conditions, because of reported less effectiveness of over-ageing in newly developed high‑zinc 7xxx series alloys. Microstructural features resulting from different ageing treatments are correlated with mechanical properties, localised corrosion behaviour, and SCC susceptibility. Localised attack manifested in dissolution of second phase precipitates which occurs from selective leaching of magnesium and aluminum. The micro-galvanic effect of iron-containing precipitates on the matrix dissolution is less as compared to Al 2 MgCu phase. Peak and overaged alloy exhibited higher resistance to intergranular corrosion and SCC because of discontinuous grain boundary precipitates and fewer Al 2 MgCu/α-Al micro-galvanic couples. • Differently aged high-Zn 7068 alloy is characterized using DSC, XPS, SEM and TEM. • Peak aged condition showed intermittent distribution of GBPs. • Corrosion of 7068 alloy in different T6 temper conditions is compared. • Over-ageing is not necessary for satisfactory SCC performance in this alloy.

Long-term localized corrosion behaviors of 5A06 aluminum alloys exposed in the natural deep-sea environment of South China Sea

The deep-sea field exposure experiment of 5A06 aluminum alloy was carried out successfully in the South China Sea with the sea depths of 1200 m, 2000 m, and 3000 m for one year. Corrosion morphologies show that pitting corrosion and crevice corrosion as the main corrosion types occur on the specimen surface, and that the crevice corrosion makes more contributions. The corrosion data results show that average corrosion rate, maximum pitting depth and corrosion area ratio reduce with the sea depth increasing and that the highest values are 13.8 μm a−1, 87.2 μm and 18.32% for 1200 m specimen. XPS results show that the oxygen content decreases with the sea depth increasing while the magnesium content increases. Comparing with 1200 m specimen, 2000 m and 3000 m specimens display higher ratios of Al2O3: Al(OH)3 and MgO: Mg(OH)2, which may be ascribed to the slightly higher oxygen concentration. Mott–Schottky results show that donor densities and acceptor densities are 1.14 × 1024 cm−3 and 9.16 × 1023 cm−3 for 1200 m, 2.82 × 1023 cm−3 and 2.10 × 1023 cm−3 for 1200 m, and 3.11 × 1023 cm−3 and 4.05 × 1023 cm−3 for 3000 m, respectively.

Effect of Ce on the localized corrosion behavior of non-equiatomic high-entropy alloy Fe40Mn20Cr20Ni20 in 0.5 M H2SO4 solution

The effect of rare earth cerium (Ce) on the localized corrosion behavior of the non-equiatomic Fe40Mn20Cr20Ni20 high-entropy alloys were investigated in 0.5 M H2SO4 solution. The corrosion resistance of the alloys increased with addition of Ce, which owing to the protectiveness and compactness of passive film was enhanced. The composition and shape of inclusions were modified by Ce, which resulted in the alteration of the localized corrosion behavior. A linear relationship between the doping density and thickness of the passive film was identified. The discussion based on the point defect model (PDM) was carried out and give a qualitative analysis. Data and code availabilityThe raw/processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study.

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.

(Digital Presentation) Effect of Zirconium Addition on the Corrosion Behavior of Binary Magnesium-Zirconium Alloys

Magnesium (Mg) has the characteristics of low density and high specific strength, but its poor corrosion resistance is a fatal disadvantage. Therefore, various alloying elements are often added to Mg alloys to improve their properties. Among them, zirconium (Zr) is commonly added as a grain refiner for Mg alloys. However, in most cases, Zr was added as a secondary additive, by which the effect on the corrosion properties would be shadowed by other alloying elements. Therefore, this research aims to elucidate the effect of Zr addition on magnesium corrosion with two binary Mg-Zr alloys with different Zr concentrations (0.037wt% and 0.208wt%).In this study, scanning electron microscope (SEM) with X-ray energy dispersive spectroscopy (EDS) was used to study the Zr distribution and compositional difference in the alloys. Scanning Kelvin probe force microscope (SKPFM) was used to reveal the Volta potential difference between the Zr particles and the Mg matrix. In situ optical microscopic (OM) observation combined with open circuit potential (OCP) monitor was used to record the alloy corrosion morphology evolution. And through electrochemical impedance spectroscopy (EIS) analysis, the difference in the alloy corrosion properties was investigated. Hydrogen evolution tests were used to quantify the corrosion rates.Through SEM/EDS analysis, the size, distribution, and Fe content of the zirconium particles in the alloy are the most important differences between the two samples. For the sample with 0.208wt%Zr, the Zr particles are larger and contain more Fe. From SKPFM analysis, we also found that the Volta potential difference between the Zr particles and the Mg matrix is larger for the sample with higher Zr addition. Hydrogen evolution tests show that the corrosion rate of the 0.208wt%Zr sample is about 5 times compared to the 0.037wt%Zr sample, which is consistent with the EIS analysis results. The driving force of corrosion mainly comes from the microgalvanic effect provided by the Zr particles. The relationship between the Zr particles and localized corrosion behavior will also be discussed. Figure 1

Localized corrosion behavior studies by SVET of 1010 steel in different concentrations of sodium chloride containing [m-2HEA][Ol] ionic liquid as corrosion inhibitor

The anticorrosive performance and the inhibition mechanism of N-methyl-2-hydroxyethylammonium oleate,[m-2HEA][Ol], in electrolytes with different concentrations of NaCl, was studied using the scanning vibrating electrode technique (SVET), open circuit potential (OCP), polarization curve measurements, complemented by physicochemical analysis by Scanning Electron Microscopy coupled with Energy Dispersive X-ray (SEM-EDS) and Fourier transform infrared spectrometry (FTIR) in attenuated total reflection (ATR). [m-2HEA][Ol] was found to act immediately after immersion due to adsorption on the steel surface competing with chloride ions. SVET and physicochemical analysis revealed the nucleation of metastable pits that were inhibited by the formation of iron complexes with moieties of ionic liquid.