Formation Of Corrosion Pits Research Articles

Corrosion behavior of high manganese steel by iron-oxidizing bacteria in wastewater at the bottom of liquefied natural gas storage tanks

High manganese steel is a new generation of material for the fabrication of liquefied natural gas (LNG) storage tanks. The corrosion behavior of high manganese steel induced by iron-oxidizing bacteria (IOB) living in wastewater from LNG tanks bottom was investigated. The results revealed that IOB can induce a generation of a dense and thick biotransformation film on the steel. Interestingly, the biotransformation film could be able to reduce the corrosion rate of high manganese steel by 71% and alleviate the formation of corrosion pits. A corrosion inhibition mechanism is postulated, elucidating the protective role of the iron-manganese oxide composite biofilm.

Effects of dual-phase deformation behaviors on simultaneously enhanced tensile properties and stress corrosion resistance of 2Cr13 martensitic stainless steel treated by laser shock peening

Effects of changes in martensite and carbide induced by laser shock peening (LSP) on tensile properties and stress corrosion behaviors of 2Cr13 martensitic stainless steel (MSS) were investigated. Results indicated that LSP not only caused plastic deformation of the martensite and carbide but also brittle deformation of carbide. Based on fine/coarse grain heterostructure, carbide plastic and brittle deformation, carbide local decomposition, compressive residual stress and grain coarsening caused by tensile stress, 14.7 % and 44.5 % increase in the strength and ductility in NaCl solution are respectively achieved for MSS with a surface where the formation of corrosion pits is significantly suppressed.

Comparison of Performance of NiCr2O4 and Cr2O3 Formed on the Ni-Based Superalloy RR1000 Under Corrosive Conditions

AbstractSamples of the Ni-based superalloy, RR1000, were exposed to 98% Na2SO4/2% NaCl salts at 700 °C with a flux of 1.5 µg cm−2 h−1 in flowing air + 300 ppm SO2 for a total of 250 h. Three pre-exposure conditions were studied: a bare reference alloy; fast heating to the test temperature followed by a 100 h hold; heating at a rate of 5 °C min−1 to the test temperature following by a 100 h hold. The surface oxide formed under the latter two conditions were Cr2O3 or NiCr2O4, respectively. The results show corrosion pit formation on the surface of the base, reference sample, and no pits present on the sample with the preformed Cr2O3. Some protection was found for the sample heated at 5 °C min−1 with a delay in the progression to accelerated corrosion attack. Additional testing under moisture containing air was also conducted. This showed no obvious difference in surface oxide morphology under the two tested heating rates for the short-term exposures examined but a difference was noted to be dependent on the moisture content of the air.

Effect of Corrosion and Post-Weld Treatment on the Fatigue Behavior of Multipass Robot GMAW Welds of S700MC Steel

High-strength steel is a candidate material for offshore structures, which are currently being constructed with regular-strength steel. These structures are constantly exposed to harsh environmental conditions and experience cyclic loadings, which can lead to premature failure due to the synergistic effects of corrosion and fatigue. In this regard, the current study aims to investigate the effects of corrosion and High-Frequency Mechanical Impact (HFMI) treatment on the fatigue behavior of welded joints made of S700MC steel. Multipass butt-welded joints were fabricated via the Robot GMAW method at an optimally selected heat input of 0.7405 kJ/mm. The microstructure of the weldments was studied using light optical microscopy. Tensile and Vickers microhardness tests were performed to evaluate the mechanical properties of the welded joints. To simulate marine environment corrosion in the laboratory, the as-welded samples were exposed to salt fog spray for 720 h. Subsequently, specimens were subjected to cyclic loading to evaluate their fatigue strength, while SEM and stereomicroscopy were used to analyze the fractured surfaces, providing a comprehensive understanding of the fracture mode. The findings suggest that although corrosion led to increased surface roughness and the formation of corrosion pits, its influence on the fatigue behavior of the weldments might be less significant compared to other geometrical factors, at least for the exposure time employed in the study.

Effect of pre-corrosion on crack initiation behavior of friction stir welded aluminum alloy 2024-T3 in high and low cycle fatigue regimes

The effect of microstructural inhomogeneity and pre-corrosion in 3.5% NaCl solution is investigated on the fatigue crack nucleation behavior of welded AA2024-T3. The localized corrosion affects the heat-affected zone more than the weld nugget zone. The formation of corrosion pits often occurs in the region between the adjacent Al-matrix and intermetallic particles due to the reverse polarity behavior of S-phase precipitates (Al2CuMg) in the saltwater environment. Further, the long-term stability of the welded joint is examined by immersing the specimens in 3.5% NaCl solution for different time intervals ranging from 10 hrs to 200 hrs. After 100 hrs of immersion in the salt water, high and low cycle fatigue behavior of the corroded samples has been examined. Long-term exposure to the saltwater environment results in intergranular corrosion due to localized pitting. The micro-mechanism of the pitting process under salt water and its effect on fatigue lives is studied.

Pioneering Enhanced Corrosion Resistance along the Normal Plane of an Ultra-Light Mg-Li Extruded Sheet.

The microstructure and corrosion anisotropy of the Mg-5Li extruded sheet were investigated in this work. Three distinct samples cut from the normal plane (A), longitudinal plane (B), and cross-sectional plane (C) of the as-extruded sheet were prepared. The microstructure was analyzed using optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The corrosion resistance and behaviors of the three samples in a 0.1 mol/L NaCl solution were evaluated by employing hydrogen evolution, mass loss testing, electrochemical assessments, and corrosion morphology analyses. The results revealed that sample A displayed a distinctive bimodal (0002) basal texture, along with clearly distinguishably larger grain sizes than the other samples. The effect of grain size and crystallographic orientation on the corrosion resistance was highlighted, indicating the pioneering corrosion resistance of sample A and the lowest corrosion resistance of sample C. Furthermore, all three samples exhibited the characteristic filiform corrosion during the initial stages of corrosion, progressing into the formation of corrosion pits, with sample C displaying pronounced susceptibility.

Corrosion behavior of Yb4Hf3O12 ceramics exposed to Calcium-Ferrum-Alumina-Silicate (CFAS) coupled with water vapor at 1400 °C

In this work, the corrosion behavior of Yb4Hf3O12 ceramics under CFAS coupled with water vapor environment at 1400 °C for 2–50 h was investigated. Results show that the CFAS were rapidly dissolved into ceramics under test environment, and then the Yb-Ca-Si apatite and Hf-rich fluorite phases were re-precipitated. Simultaneously, the water vapor corrosion mainly induced grain surface corrosion, resulting in the formation of corrosion pits and ridge-like structures. Moreover, the pores and microcracks caused by water vapor corrosion offer additional penetration path for CFAS melt.

Attempt to Optimize the Corrosion Resistance of HRB400 Steel Rebar with Cr and RE.

The corrosion resistance of the HRB400 steel rebar alloyed with Cr and rare earths (RE) was systematically studied from two aspects, including the properties of the passive film and the protectiveness of the rust layer. The results presented that Cr increased the corrosion resistance of the steel rebar through stabilizing the passive film and was not involved in the formation of corrosion pits, while the pitting corrosion was initiated by the dissolution of (RE)2O2S inclusion, resulting in the local acidification at the bottom of the corrosion pits, which decreased the stability of the passive film. As for the long-term corrosion process, both Cr and RE decreased the corrosion rate of the steel rebar, which was related to the promotion effect on the formation of α-FeOOH in the rust layer from Cr and RE.

Electrochemical polarization behavior and superelastic properties of a Fe–Mn–Al–Ni–Cr shape memory alloy

AbstractThe present study investigates the corrosion behavior of a Fe–Mn–Al–Ni–Cr shape memory alloy in a 5.0 wt% NaCl solution in combination with the functional properties. In a single crystalline condition, the investigated alloy shows a superior superelastic response with a maximum recovery strain of 5.2%. Furthermore, the results of the potentiodynamic polarization and impedance spectroscopy show that the addition of chromium generally improves corrosion resistance by increasing the resistance to localized corrosion. The single crystalline condition, which is characterized by an austenitic matrix and scattered martensite plates, shows an enhanced, however, still unstable passive behavior due to the formation of corrosion pits along the martensite plates.

An Experimental Analysis of the High-Cycle Fatigue Fracture of H13 Hot Forging Tool Steels.

In this study, the axial fatigue behaviour of hot forging tool steels at room temperature was investigated. Fatigue tests were performed on two steels within the same H13 specification. The fatigue tests were carried out in the high-cycle fatigue domain under normal conditions. These tests were also performed on specimens in contact with a corrosive medium, applying stress values that led to the high-cycle fatigue domain under normal conditions for the sake of comparison. Both materials showed similar fatigue strengths when they were tested under normal conditions. In contrast, corrosion fatigue lives were much lower than in normal tests and differed significantly between the two steels. Crack initiation was triggered by microstructural and surface defects in the normal tests, whereas the formation of corrosion pits caused crack initiation in the corrosion fatigue tests. Moreover, a fracture surface analysis revealed dissimilar crack propagation areas between both steels, which suggested that both steels had different fracture toughness. These results were in line with the differences observed between the carbide and grain sizes of both of the material microstructures.

Extracellular polymeric substances secreted by marine fungus Aspergillus terreus: Full characterization and detailed effects on aluminum alloy corrosion

In this work, extracellular polymeric substances (EPS) secreted by marine fungus were fully characterized, and corrosion behavior and mechanism of aluminum alloy (AA) caused by EPS were studied. Approximately sixty species of proteins, nine monosaccharides and seven organic acids were characterized. Electrochemical measurements indicated that EPS enable the acceleration of AA corrosion, hence promoting the formation of corrosion pits. The pitting corrosion is formed because of a big cathode and small anode created by EPS. Nevertheless, the formation of a complete EPS film on the specimen surface results in a decreasing acceleration of corrosion.

Effect of pre-hot salt corrosion on hot salt corrosion fatigue behavior of the TC11 titanium alloy at 500 °C

Pre-hot salt corrosion (PHSC) tests is the samples with 0.1, 0.5, 1 and 4 mg/cm2 salt coating are corroded at 500 °C for 100 h. The hot salt corrosion fatigue (HSCF) tests were conducted on PHSC specimens at a stress ratio, a maximum stress amplitudes and temperature of −1, 450 MPa and 500 °C, respectively. The effect of PHSC on HSCF behavior of TC11 alloy at 500 °C was studied by deposition of solid NaCl. The HSCF sensitivity of the TC11 alloy at 500 °C was further increased by PHSC, and increased gradually with the increase in solid NaCl content. When the salt content exceeded 1 mg/cm2, the HSCF life was reduced by more than 99% compared with the samples without salt coating. The mechanism of HSCF was that the local stress concentration of the corrosion pits accelerated the initiation of fatigue cracks, hydrogen and the hydride phase promoted fatigue crack propagation. The PHSC process promoted the formation of corrosion pits, and accelerated the infiltration of hydrogen into the matrix and hydride formation, so the fatigue resistance of pre hot salt corrosion samples was reduced further. A greater NaCl deposition resulted in more severe surface corrosion damage of the titanium alloy, a stronger coupling of corrosion factors and alternating load in the HSCF process, and a greater reduction in fatigue resistance.

Mechanical properties and corrosion resistance characterization of a novel Co36Fe36Cr18Ni10 high-entropy alloy for bioimplants compared to 316L alloy

The high strength, ductility, and corrosion resistance of alloys are highly desirable functional materials for biomedical applications. Multi-component alloys with a single face-centered-cubic (fcc) phase structure can provide superior ductility, while microstructures such as twins and stacking faults (SF) can be incorporated into the matrix to improve the strength of the alloy without damaging plasticity. Here, we have developed a single-fcc phase alloy Co36Fe36Cr18Ni10 with low stacking faults energy, which can effectively produce annealed twins by recrystallization annealing after cold rolling. The microstructure and mechanical properties of Co36Fe36Cr18Ni10 compared to commercial 316L alloy was methodically investigated by EBSD, TEM, and tensile testing. The results reveal that the Co36Fe36Cr18Ni10 alloy contains more twin boundaries and a high density of nano-twins and SFs in the microstructure, which effectively improve the strength of Co36Fe36Cr18Ni10 alloy meanwhile maintaining a similar ductility to commercial 316L. The corrosion behavior of Co36Fe36Cr18Ni10 and 316L in simulated body fluids has been investigated using electrochemical characterization, indicated that compared to 316L ss, pitting in Co36Fe36Cr18Ni10 alloys is easily inhibited and rapid re-passivation, meanwhile the twin boundaries were effective in weakening the formation of corrosion pits and impeded the expansion of corrosion crack. Compare the surfaces of the two alloys after passivation, apart from the Cr2O3/Cr(OH)3 contained in the passive film, the interactions between Co and other components in the passivation film produce more indissoluble substances with a lower enthalpy of formation that will enhance the passive film stability of Co36Fe36Cr18Ni10 alloy.

Effect of Zn content on corrosion behavior of Mg-Y-Zn alloys

The microstructure, corrosion behavior, and electrochemical behavior of as-cast Mg-4Y-xZn (x=1,2,3,4 wt.%) are studied by SEM, weight loss and electrochemical tests. Mg12YZn (X), Mg3Y2Zn3 (W) and Mg24Y5 constitute the phase composition system of the alloy. When Zn content is 1 wt.%, all tests reveal that alloy has the optimal corrosion performance. The second phase in these alloys, due to their nobler nature than ?-Mg, exists as a cathode during the corrosion process, so that ?-Mg preferentially occurs corrosion to accelerate the formation of corrosion pits. After soaking in 3.5 wt.% NaCl solution for some time, the stability of the W phase changed, and gradually dissolved, which was finally removed by chromic acid used for removal of corrosion products. In addition, X phase can be used as an anode in the micro-galvanic cells formed with W phase to reduce the corrosion rate of ?-Mg and thus improve the corrosion performance of the alloy.

Focusing on the relationship between the precipitated phases and the pitting corrosion of ZL101A aluminum alloy

The pitting corrosion behavior of ZL101A aluminum alloy in simulated marine environment was investigated for guiding the composition design. The Volta potential of the precipitated phases was mainly characterized via the in situ SKPFM technique. The obtained results indicated that the precipitated phases of ZL101A were composed of Al–Si phase, Si–Mg–Fe phase and Si-rich/Al-poor phase, accelerating the formation of corrosion pits during immersion test. Both Al–Si phase and Si–Mg–Fe phase accelerated the corrosion process through the self-dissolution and the galvanic effect, respectively, which can be contributed to the high corrosion sensitivity of the two phases. Si-rich/Al-poor phase presented high corrosion resistance, which should be related to the deficiency of impure elements such as Mg and Fe.

Investigation on the SCC behavior of ZL101A aluminum alloy in simulated marine environments

Stress corrosion cracking (SCC) behavior of ZL101A aluminum alloy in solution and thin electrolyte layer (TEL) with different pH was investigated in detail. The results indicated that the precipitated phases of ZL101A were composed of α-Al/Si eutectic crystal phase and Si–Mg–Fe precipitated phase, which accelerated the formation of corrosion pits. ZL101A presented the highest SCC susceptibility in pH = 4 solution compared with pH = 7 and 10 solutions, which was mainly attributed to the enhanced synergistic effect of anodic dissolution, stress and hydrogen embrittlement. The basically similar SCC susceptibilities in TEL environments were mainly controlled by the anodic dissolution, which was attributed to the high diffusion rate of O2 in the thin electrolyte film.

Tensile strength of corroded steel bars

Among the pathological manifestations associated with reinforced concrete, corrosion of the reinforcement is one of the most serious issues since it is related to the durability of the structures and the safety of the users. Although the reinforcement in the structural components is protected by a covering layer, carbonation or the presence of chlorides in the concrete generates necessary conditions for corrosion of the reinforcement. This causes a reduction in the cross section and the generation of products that, due to their volumetric expansion, cause cracks in the interior of the concrete. This work evaluates the effects of corrosion on mechanical properties of corroded reinforcements through accelerated conditions in the laboratory. Steel bars installed inside cylindrical concrete specimens are subjected to accelerated corrosion, immersed in a saline solution with the application of an electric current for periods of 1, 3, 5 and 7 d. After corrosion, the steel bars are removed and their weight loss, degree of corrosion and tensile strength are evaluated. The results demonstrate an increased degree of corrosion with exposure time to the saline solution and the non-uniform reduction of the tensile strength of the bars due to the formation of corrosion pits with varying depth along the bar.

Corrosion fatigue life prediction of crude oil storage tank via improved equivalent initial flaw size

Corrosion fatigue is identified as the main failure mechanism for structures working in severe corrosive medium subjected to cyclic rotating bending fatigue, for example crude oil storage tank (COST). Emphasis is placed on the study of corrosion pit formation and the development of cracks from pits. An improved equivalent initial flaw size (I-EIFS) is proposed for corrosion fatigue life prediction. Based on the concept of equivalent initial flaw size (EIFS), pitting corrosion and small crack growth are equivalent to a part of long crack growth process in corrosion fatigue process. Pitting and crack propagation are quantified throughout the fatigue loading thereby allowing a model to be developed that included the stages of pit development, pit-to-crack transition and crack growth in order to predict the fatigue life. A corrosion fatigue life prediction case is adopted to demonstrate the effectiveness of the proposed model. Based on the proposed model, failure analysis and stress calculation are performed to predict the corrosion fatigue life of COST, which provides a method for the life prediction of COST. The validity of proposed method is verified by comparing the service life of COST.

Mechanical response of aluminum 7075 with heat treatment and exfoliation corrosion

The present investigation was focussed to evaluate the mechanical properties of AA7075 subjected to corrosion and heat treatment. Exfoliation corrosion has been used to infuse rapid corrosion on the material coupled with high temperature and subsequent low-temperature aging (HLA). It has been found that the localized corrosion pit formation occurs with HLA and corrosion exposure durations with substantial inter-granular changes and formation of cracks. Significant reduction in mechanical properties was observed with HLA-treated samples subjected to corrosion. The material’s stiffness was increased due to HLA, and again within the corrosive environment, a decreasing trend was observed with immersion durations. A series of simple one-dimensional linear and polynomial equations were developed to determine the properties of AA7075 samples subjected to HLA and corrosion.

Analysis of Zr55Al10Cu30Ni5 bulk metallic glass pitting behavior in distilled water environment leading to fatigue-corrosion rupture

Even though formation of corrosion pits is reported on Zr-based BMGs prone to fatigue loading immersed in corrosive environments, the characterizations of the pit growth and its transition to the fatigue crack are still particularly vague. To enhance the comprehension on this critical issue, the present work examines the fatigue behavior of Zr55Al10Cu30Ni5 (at%) BMG under four-point bending loading configuration in air and in distilled water. Specimens exposed to water environment emphasized presence of corrosion pits, leading to a decrease of the fatigue resistance in comparison with air. Furthermore, the pit-to-crack transition phenomenon emphasizes strong similarities with the Kondo's mechanism.