To advance the understanding of the corrosion behavior of stainless steel bellows in marine atmospheric environments and enhance the precision of service life predictions,this study employs finite element simulations ...To advance the understanding of the corrosion behavior of stainless steel bellows in marine atmospheric environments and enhance the precision of service life predictions,this study employs finite element simulations to investigate the pitting corrosion rates and pit morphologies of bellows peaks and troughs under varying electrolyte film thicknesses.The model incorporates localized electrochemical reactions,oxygen concentration,and homogeneous solution reactions.For improved computational accuracy,the fitted polarization curve data were directly applied as nonlinear boundary conditions on the electrode surface via interpolation functions.Simulation results reveal that the peak regions exhibit faster corrosion rates than the trough regions.With increasing electrolyte film thickness(from 10μm to 500μm),corrosion rates at both peaks and troughs decrease progressively,and after 120 hours of simulation,the maximum corrosion rate at the peaks declines from 0.720 mm/a to 0.130 mm/a,and at the troughs from 0.520 mm/a to 0.120 mm/a,with the disparity in corrosion rates diminishing over time.Furthermore,as corrosion progresses,pits propagate deeper into the substrate,exhibiting both vertical penetration and lateral expansion along the passive film interface,ultimately breaching the substrate.This research offers valuable insights into designing corrosion mitigation strategies for stainless steel bellows in marine environments.展开更多
The addition of vanadium substantially enhances the strength of the high-nitrogen austenitic stainless steel(HNASS),while maintaining excellent ductility and pitting corrosion resistance.The effects of vanadium microa...The addition of vanadium substantially enhances the strength of the high-nitrogen austenitic stainless steel(HNASS),while maintaining excellent ductility and pitting corrosion resistance.The effects of vanadium microalloying on the microstructure,mechanical properties,and pitting resistance of HNASS were systematically analyzed with a focus on the role of VN during the pitting process.The results suggest that vanadium promoted the precipitation of VN,contributing to grain boundary pinning and grain refinement.As vanadium content increased,the number of precipitates rose,and the average grain size decreased.At lower vanadium content(0-0.2 wt.%),the strength of the material was significantly reinforced with increasing vanadium content,while maintaining excellent ductility and pitting resistance.However,when the vanadium content reached 0.3-0.4 wt.%,precipitates demonstrated a substantially increased number and coarsened,accompanied by the formation of numerous dislocations around the precipitates.This brought about further strength reinforcement but a marked decline in ductility and pitting resistance.Additionally,pitting corrosion was initiated at the matrix-VN interface.Compared to the matrix,VN exhibited higher reactivity and preferentially reacted with Cl−ions,provoking dissolution.However,NH4+generated during the dissolution of VN facilitated repassivation of the material,suppressing further pitting propagation.展开更多
An effective approach to enhance the surface degradation characteristics of laser powder bed fusion(LPBF)type 420 stainless steel involves the incorporation of spherical cast WC/W_(2)C to create LPBF metal matrix comp...An effective approach to enhance the surface degradation characteristics of laser powder bed fusion(LPBF)type 420 stainless steel involves the incorporation of spherical cast WC/W_(2)C to create LPBF metal matrix composites(MMCs).However,the corrosion be-havior of stainless steel and cast WC/W_(2)C varies inversely across different pH levels,and the phenomenon of pitting corrosion in LPBF MMCs under varying pH conditions remains insufficiently explored.In LPBF 420+5wt%WC/W_(2)C MMCs,pits form adjacent to cast WC/W_(2)C in acidic and neutral environments,attributed to the presence of chromium-rich carbides and galvanic coupling effects.The dis-solution of the reinforced particles facilitates pit nucleation in alkaline conditions.Notably,in-situ reaction layers exhibit superior corro-sion resistance to the matrix or the reinforced particles across all pH levels.The distinct corrosion mechanisms influence the pitting corro-sion behavior,with the corrosion ranking based on critical pitting potential being neutral>alkaline>acidic,contrasting the observed kin-etics of pit growth(alkaline>acidic>neutral).展开更多
Pitting corrosion poses a significant challenge to 9Cr18 high-carbon chromium bearing steel in chloride-rich environments,severely compromising its structural integrity.The study systematically investigates the pittin...Pitting corrosion poses a significant challenge to 9Cr18 high-carbon chromium bearing steel in chloride-rich environments,severely compromising its structural integrity.The study systematically investigates the pitting behaviour of 9Cr18 bearing steel under salt spray conditions,focusing on the progressive evolution of surface morphology and cross-sectional characteristics of pits on finished bearings.Scanning electron microscopy,energy-dispersive spectroscopy and X-ray diffraction were employed to examine the surface morphology,elemental composition and phase structure of corrosion products over varying salt spray exposure durations.The results show that 9Cr18 steel exhibits localized pitting with“volcanic crater”-like pits in the early stage of salt spray corrosion.After 48 h,pitting develops into a“multi-point”pattern,marking the initial transition toward uniform corrosion.Until 240 h,corrosion products completely cover the surface,indicating the complete transformation from localized pitting to uniform corrosion.The high carbon and chromium content in 9Cr18 steel promotes carbide precipitation and uneven distribution in the matrix.Cr-depleted regions near the carbide/matrix interface serve as preferential sites for pitting initiation.The low effective utilization of chromium reduces the overall corrosion resistance of 9Cr18.展开更多
The pitting corrosion behaviors of 7A60 aluminum alloy in the retrogression and re-aging （RRA） temper were investigated by electrochemical impedance spectroscopy （EIS） and electrochemical noise （EN） techniques, ...The pitting corrosion behaviors of 7A60 aluminum alloy in the retrogression and re-aging （RRA） temper were investigated by electrochemical impedance spectroscopy （EIS） and electrochemical noise （EN） techniques, and the microstructure and the second phase content of the alloy were observed and determined by scanning electron microscopy （SEM） and energy dispersive spectrometer （EDS）. The results show that there exist two different corrosion stages for 7A60 alloy in 3.5%NaCl solution, and the corrosion process can be detected by the appearance of EIS spectrum with two capacitive time constants and the wavelet fractal dimension D extracted from EN. SEM and EDS results also demonstrate that severe pitting corrosion in 7A60 alloy is mainly caused by electrochemical active MgZn2 particles, secondly by Al2MgCu and Mg2Si. Al7Cu2Fe particles make little contribution to the pitting corrosion of 7A60 alloy.展开更多
In this study,the pitting corrosion behavior of 13Cr4Ni martensitic stainless steel(BASE)and that modified with rare earth(REM)in 0.1 mol/L Na Cl solution were characterized.Techniques such as automatic secondary elec...In this study,the pitting corrosion behavior of 13Cr4Ni martensitic stainless steel(BASE)and that modified with rare earth(REM)in 0.1 mol/L Na Cl solution were characterized.Techniques such as automatic secondary electron microscope(ASPEX PSEM detector),scanning electron microscope(SEM),transmission electron microscope(TEM),scanning Kelvin probe force microscope(SKP),potentiodynamic and potentiostatic polarizations were employed.The results obtained indicate that BASE steel contains Al_(2)O_(3)/Mn S,Al_(2)O_(3) and Mn S inclusions,while REM steels contain(La,Ce,Cr,Fe)-O and(La,Ce,Cr,Fe)-O-S inclusions.Compared with BASE steel,REM steel is more susceptible to induce the metastable pitting nucleation and repassivation,whereas it restrains the transition from metastable pitting to stable pitting.Adding 0.021%rare earth element to BASE steel can reduce the number and area of inclusions,while that of 0.058%can increase the number and enlarged the size of inclusions,which is also the reason that pitting corrosion resistance of 58 REM steel is slightly lower than that of 21 REM steel.In the process of pitting corrosion induced by Al_(2)O_(3)/Mn S inclusions,Mn S is preferentially anodic dissolved,and also the matrix contacted with Al_(2)O_(3) is subsequently anodic dissolved.For REM steels,anodic dissolution preferentially occurs at the boundary between inclusions and matrix,while(La,Ce,Cr,Fe)-O inclusions chemically dissolve in local acidic environment or are separated from steel matrix.The chemically dissolved substance(La^(3+) and Ce^(3+))of(La,Ce,Cr,Fe)-O inclusions are concentrated in pitting pits,which inhibits its continuous growth.展开更多
This study researched the relationship between the applied potential and the critical pitting temperature （CPT） of the 304 and new 200 series of stainless steels. The fluctuation about the potential dependent CPT fo...This study researched the relationship between the applied potential and the critical pitting temperature （CPT） of the 304 and new 200 series of stainless steels. The fluctuation about the potential dependent CPT for the stainless steels was investigated and the CPT range was obtained. The difference between the potential dependent CPTs of the 304 and 200 series of stainless steels with an applied potential of 100 mV （ vs SCE）, were presented, and by this means the pitting corrosion resistances of them were compared.展开更多
Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemic...Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum （XPS）. HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature （CPT） increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion （MARC）. The MARC can be expressed as an equation of CPT=2.55MARC-29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.展开更多
Pitting corrosion of 2Cr13 stainless steel was investigated by deep-sea exposure test at various depths of 500 m,800 m and 1200 m in the South China Sea for 4 months.With the aid of electrochemical measurements in sim...Pitting corrosion of 2Cr13 stainless steel was investigated by deep-sea exposure test at various depths of 500 m,800 m and 1200 m in the South China Sea for 4 months.With the aid of electrochemical measurements in simulated deep-sea environments and grey relational analysis,the influence of deepsea environments on passive film and the mechanism of pitting corrosion were discussed.The results indicated that with the increase of sea depth,pitting depth of 2Cr13 stainless steel increased,which can be attributed to the change of chemical composition and the degradation of pitting resistance of passive film.Film growth was greatly retarded in the condition of low seawater temperature and low dissolved oxygen content of deep sea,resulting in an unstable and vulnerable film.Pitting depth was most influenced by hydrostatic pressure,which can increase the adsorption and penetration of Cl-ion,and promote the proliferation of point defects in passive film,leading to rapid deconstruction of protective oxides of the film.Pitting sensitivity of 2Cr13 stainless steel increased eventually with the combination of accelerated dissolution and suppressed self-healing of passive film in deep sea.展开更多
The effects of phase transformation on mechanical properties and pitting corrosion of 2205 duplex stainless steel were investigated. The amount of a phase in the test specimen varied up to a maximum of 6 % by thermal ...The effects of phase transformation on mechanical properties and pitting corrosion of 2205 duplex stainless steel were investigated. The amount of a phase in the test specimen varied up to a maximum of 6 % by thermal treatment at 850 ℃ for up to 60 min. The results showed that ~ phase markedly increased the hardness and decreased the impact toughness of the test steel. But the increasing tendency of the ultimate tensile strength and the yield strength was not obvious, while the total elongation abruptly decreased with the aging time from 5 to 60 min. SEM impact microfractograph analysis revealed that the types of impact fracture changed from ductile mode to transcrystalline mode when the specimens were aged for 5-60 min. Furthermore, the extent of pitting potential reducing was found to be strongly temperature dependent, more pronounced at the higher temperature. During the incubation period of σ phase nucleation, the pitting corrosion test temperature and the aging time had collaborative effects on evidently displacing the pitting potential towards less noble values. After 15 min, the higher temperature contributed more to decreasing the pitting potential than the aging time.展开更多
Pitting corrosion of magnesium(Mg) alloys is greatly associated with their microstructure, especially second phases. The second phases in traditional Mg alloys such as AZ91 are electrochemically nobler than Mg matrix,...Pitting corrosion of magnesium(Mg) alloys is greatly associated with their microstructure, especially second phases. The second phases in traditional Mg alloys such as AZ91 are electrochemically nobler than Mg matrix, while the second phases in Rare earth(RE) Mg alloy GW93 are more active than Mg matrix. As a result, the pitting corrosion mechanism of Mg alloy GW93 is different from the traditional ones. This paper aims to clarify the pitting corrosion mechanism of Mg alloy GW93 through the studies of Volta potential by Scanning Kelvin Probe Force Microscopy(SKPFM), corrosion morphology by Scanning Electron Microscope(SEM), and corrosion resistance by electrochemical tests. Results reveal that the pitting corrosion of GW93 includes three stages, first, dissolution of the second phases, followed by corrosion of Mg matrix adjacent to the dissolved second phases, and finally, propagation of corrosion pits along the depth direction of the dissolved second phases. Anodic second phases and enrichment of Clin the thick corrosion product films dominate the propagation of pitting corrosion.展开更多
The effect of friction stir processing （FSP） on the pitting corrosion and the intergranular attack of 7075 aluminum alloy was investigated. Three friction stir processed samples were produced by employing a constant...The effect of friction stir processing （FSP） on the pitting corrosion and the intergranular attack of 7075 aluminum alloy was investigated. Three friction stir processed samples were produced by employing a constant tool travel speed of 100 mm/min at the rotating speeds of 630, 1000 and 1600 rpm. It was dem- onstrated that the processed samples suffered from both pitting and intergranular corrosion. Also, the sample processed at 1600 rpm exhibited the best pitting corrosion resistance. For all FS processed samples, the corrosion attack in the heat affected zone was pitting corrosion, whereas no intergranular corrosion was detected in this area.展开更多
A series of high nitrogen austenitic stainless steels were successfully developed with a pressurized electroslag remelting furnace. Nitride additives and deoxidizer were packed into the stainless steel pipes, and then...A series of high nitrogen austenitic stainless steels were successfully developed with a pressurized electroslag remelting furnace. Nitride additives and deoxidizer were packed into the stainless steel pipes, and then the stainless steel pipes were welded on the surface of an electrode with low nitrogen content to prepare a compound electrode. Using Si3N4 as a nitrogen alloying source, the silicon contents in the ingots were prone to be out of the specification range, the electric current fluctuated greatly and the surface qualities of the ingots were poor. The surface qualities of the ingots were improved with FeCrN as a nitrogen alloying source. The sound and compact macrostructure ingot with the maximum nitrogen content of 1.21wt% can be obtained. The 18Cr18Mn2Mo0.9N high nitrogen austenitic stainless steel exhibits high strength and good ductility at room temperature. The steel shows typical ductile-brittle transition behavior and excellent pitting corrosion resistance properties.展开更多
The thorough-thickness inhomogeneity of precipitate distribution and pitting corrosion behavior of 95 mm-thick 2297 Al-Li alloy rolled plate was investigated using scanning electron microscopy, transmission electron m...The thorough-thickness inhomogeneity of precipitate distribution and pitting corrosion behavior of 95 mm-thick 2297 Al-Li alloy rolled plate was investigated using scanning electron microscopy, transmission electron microscopy and electrochemistry method. Precipitate distribution and pit size were statistically analyzed to obtain quantitative information and corresponding correlation. The population density and the size fraction of precipitate on different sections in the thick plate are ranked from high to low in the following order: quarter-section(QS) > surface section(SS) > mid-section(MS). After 300 min potentiostatic polarization, the number and the total volume of pits are ranked from high to low as QS>SS>MS, indicating a higher pitting susceptibility of the plate in QS with more precipitates. The through-thickness inhomogeneity of pitting corrosion in 2297 Al-Li alloy thick plate is mainly ascribed to inhomogeneous precipitate distribution.展开更多
A set of evaluation indicators based on corrosion ratio in theory for assessing the extent of pitting corrosion and performance reduction are proposed. In order to quantify the morphology of pitting corrosion and extr...A set of evaluation indicators based on corrosion ratio in theory for assessing the extent of pitting corrosion and performance reduction are proposed. In order to quantify the morphology of pitting corrosion and extract the evaluation indicators,the 3D profile data obtained by pitting morphology measurement are imported into a special written program to automatically determine the location of each corrosion pit and distill any desired data pertinent to the pitting morphology. The results show that this method seems to be effective to analyze the corroded surface and characterize the pitting morphology.展开更多
Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military v...Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is frequently TIG （tungsten inert gas） welding due to its comparatively easier applicability and better economy.In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance technique has been used to find out the significant pulsed current parameters. Regression analysis has been used to develop the model. Using the developed model pitting corrosion potential values have been estimated for different combinations of pulsed current parameters and the results are analyzed in detail.展开更多
The pitting corrosion behavior of AZ91 alloy before and after micro-oxidation treatment in 3.5%Na Cl solution was investigated by cyclic potentiodynamic polarization(CPDP)and optical and SEM observations of corroded s...The pitting corrosion behavior of AZ91 alloy before and after micro-oxidation treatment in 3.5%Na Cl solution was investigated by cyclic potentiodynamic polarization(CPDP)and optical and SEM observations of corroded surfaces at different polarization potentials.The CPDP results show that both the alloy and the MAO-coated alloy suffer from pitting corrosion and it is difficult for pits to stop growth once the pits initiates.It is revealed that the air-formed Mg O film on AZ91 alloy,the MAO coating along with corrosion products(mainly Mg(OH))formed during CPDP can significantly influence the kinetics of the redox reactions of Mg,and further influence the propagation behavior of pitting corrosion.The optical and SEM images show that the corrosion products on AZ91 alloy are dense and protective but on the MAO-coated corrosion products are very loose.Such observations support the analyses of CPDP results that pits on AZ91 alloy spread to the width whereas pits on MAO-coated alloy propagate to the depth.Overall,pitting corrosion on the MAO-coated alloy can be very severe once the coating ruptures and post-treatments are necessary to provide a promising corrosion protection for the Mg alloys.展开更多
In this study,the relationship between spinodal decomposition and the formation of Ni-rich clusters and G-phase in the ferrite on hardening and pitting corrosion of two thermally aged duplex stainless steels(DSSs)at ...In this study,the relationship between spinodal decomposition and the formation of Ni-rich clusters and G-phase in the ferrite on hardening and pitting corrosion of two thermally aged duplex stainless steels(DSSs)at 475℃was investigated.Results indicate that,for 2205 DSS,pitting corrosion behavior is influenced by the presence and size of G-phase precipitates for longer aging times,but this contribution is masked by the advanced stage of spinodal decomposition in the ferritic structure.On the other hand,for 2101 DSS,the formation of Cr-richer nitrides impairs pitting corrosion resistance more than spinodal decomposition.展开更多
In this paper,the origin mechanism of pitting corrosion induced by Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions in a microalloyed steel was investigated by field emission scanning electron microscopy with energy ...In this paper,the origin mechanism of pitting corrosion induced by Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions in a microalloyed steel was investigated by field emission scanning electron microscopy with energy dispersive spectroscopy and electron backscattered diffraction,conductivity atomic force microscopy,immersion test,and first-principles calculation.The results show that the Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions are non-conductive,which are impossible to form corrosion couples with the steel matrix.There are no obvious lattice distortion zones in the steel matrix around the Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions,so it is difficult to form micro-galvanic corrosion near the Ce inclusion.The order of work functions of the Ce inclusions and the steel matrix from small to large is Ce_(2)O_(2)S<Ce_(2)O_(3)<CeAlO_(3)<steel matrix,which is consistent with their dissolution sequence in the immersion test in _(3).5 wt%NaCl solution.Consequently,it is effective and reliable to use work function to predict or judge the dissolution behaviors of the Ce inclusions or steel matrix in corrosive solution.The Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions have the tendency of self-dissolution and dissolve preferentially to the steel matrix in the solution by the salt effect,which lead to pitting corrosion of Ce-containing microalloyed steel.展开更多
Pitting corrosion behaviour of Monel-400 alloy in 3.5 wt pct NaCl sodium chloride solution has been investigated using the cyclic potentiodynamic anodic polarization technique. The effect of chloride ion concentration...Pitting corrosion behaviour of Monel-400 alloy in 3.5 wt pct NaCl sodium chloride solution has been investigated using the cyclic potentiodynamic anodic polarization technique. The effect of chloride ion concentration, pH values and difFerent temperatures on the pitting parameters were determined. The morphology of the pits produced after anodic polarization treatments was inspected by scanning electron microscope (SEM). The results indicated that, the increase in chloride ion concentration shifts Epit and Eprot of the alloy toward negative values and the pitting potential is much more dependent on pH value in the basic region. The breakdown of passivity with increasing temperature may be due to kinetic changes of passivating films and dissolution rate of the alloy in its passive state展开更多
基金supported by the National Natural Science Foundation of China(No.52074130)Engineering Research Center of Resource Utilization of Carbon-containing Waste with Carbon Neutrality,Ministry of Education,200237 Shanghai,PR China.
文摘To advance the understanding of the corrosion behavior of stainless steel bellows in marine atmospheric environments and enhance the precision of service life predictions,this study employs finite element simulations to investigate the pitting corrosion rates and pit morphologies of bellows peaks and troughs under varying electrolyte film thicknesses.The model incorporates localized electrochemical reactions,oxygen concentration,and homogeneous solution reactions.For improved computational accuracy,the fitted polarization curve data were directly applied as nonlinear boundary conditions on the electrode surface via interpolation functions.Simulation results reveal that the peak regions exhibit faster corrosion rates than the trough regions.With increasing electrolyte film thickness(from 10μm to 500μm),corrosion rates at both peaks and troughs decrease progressively,and after 120 hours of simulation,the maximum corrosion rate at the peaks declines from 0.720 mm/a to 0.130 mm/a,and at the troughs from 0.520 mm/a to 0.120 mm/a,with the disparity in corrosion rates diminishing over time.Furthermore,as corrosion progresses,pits propagate deeper into the substrate,exhibiting both vertical penetration and lateral expansion along the passive film interface,ultimately breaching the substrate.This research offers valuable insights into designing corrosion mitigation strategies for stainless steel bellows in marine environments.
基金founded by National Natural Science Foundations of China(Nos.52231003,52201084,and U21A20113)Major Program(JD)of Hubei Province(No.2023BAA019)+1 种基金Natural Science Foundation of Guangdong Province(No.2024A1515011022)Guangdong Province Basic and Applied Basic Research Fund Offshore Wind Power Joint Fund(No.2023B1515250006).
文摘The addition of vanadium substantially enhances the strength of the high-nitrogen austenitic stainless steel(HNASS),while maintaining excellent ductility and pitting corrosion resistance.The effects of vanadium microalloying on the microstructure,mechanical properties,and pitting resistance of HNASS were systematically analyzed with a focus on the role of VN during the pitting process.The results suggest that vanadium promoted the precipitation of VN,contributing to grain boundary pinning and grain refinement.As vanadium content increased,the number of precipitates rose,and the average grain size decreased.At lower vanadium content(0-0.2 wt.%),the strength of the material was significantly reinforced with increasing vanadium content,while maintaining excellent ductility and pitting resistance.However,when the vanadium content reached 0.3-0.4 wt.%,precipitates demonstrated a substantially increased number and coarsened,accompanied by the formation of numerous dislocations around the precipitates.This brought about further strength reinforcement but a marked decline in ductility and pitting resistance.Additionally,pitting corrosion was initiated at the matrix-VN interface.Compared to the matrix,VN exhibited higher reactivity and preferentially reacted with Cl−ions,provoking dissolution.However,NH4+generated during the dissolution of VN facilitated repassivation of the material,suppressing further pitting propagation.
基金support from the National Natural Science Foundation of China(No.U22B2065)the Science&Technology Fundamental Resources Investigation Program(No.2022FY101300)+1 种基金the Guangdong Basic and Applied Basic Research Foundation,China(No.2023A1515110926)Fundamental Research Funds for Central Universities(No.FRF-TP-25-082).
文摘An effective approach to enhance the surface degradation characteristics of laser powder bed fusion(LPBF)type 420 stainless steel involves the incorporation of spherical cast WC/W_(2)C to create LPBF metal matrix composites(MMCs).However,the corrosion be-havior of stainless steel and cast WC/W_(2)C varies inversely across different pH levels,and the phenomenon of pitting corrosion in LPBF MMCs under varying pH conditions remains insufficiently explored.In LPBF 420+5wt%WC/W_(2)C MMCs,pits form adjacent to cast WC/W_(2)C in acidic and neutral environments,attributed to the presence of chromium-rich carbides and galvanic coupling effects.The dis-solution of the reinforced particles facilitates pit nucleation in alkaline conditions.Notably,in-situ reaction layers exhibit superior corro-sion resistance to the matrix or the reinforced particles across all pH levels.The distinct corrosion mechanisms influence the pitting corro-sion behavior,with the corrosion ranking based on critical pitting potential being neutral>alkaline>acidic,contrasting the observed kin-etics of pit growth(alkaline>acidic>neutral).
基金supported by the National Natural Science Foundation of China(No.52404354).
文摘Pitting corrosion poses a significant challenge to 9Cr18 high-carbon chromium bearing steel in chloride-rich environments,severely compromising its structural integrity.The study systematically investigates the pitting behaviour of 9Cr18 bearing steel under salt spray conditions,focusing on the progressive evolution of surface morphology and cross-sectional characteristics of pits on finished bearings.Scanning electron microscopy,energy-dispersive spectroscopy and X-ray diffraction were employed to examine the surface morphology,elemental composition and phase structure of corrosion products over varying salt spray exposure durations.The results show that 9Cr18 steel exhibits localized pitting with“volcanic crater”-like pits in the early stage of salt spray corrosion.After 48 h,pitting develops into a“multi-point”pattern,marking the initial transition toward uniform corrosion.Until 240 h,corrosion products completely cover the surface,indicating the complete transformation from localized pitting to uniform corrosion.The high carbon and chromium content in 9Cr18 steel promotes carbide precipitation and uneven distribution in the matrix.Cr-depleted regions near the carbide/matrix interface serve as preferential sites for pitting initiation.The low effective utilization of chromium reduces the overall corrosion resistance of 9Cr18.
基金Project(13JCZDJC29500)supported by the Key Project of Tianjin Natural Science Foundation,ChinaProjects(2011CB610505,2014CB046801)supported by the National Basic Research Program of ChinaProject(20120032110029)supported by the Specialized Research Fund for the Doctoral Program of Higher Education,China
文摘The pitting corrosion behaviors of 7A60 aluminum alloy in the retrogression and re-aging （RRA） temper were investigated by electrochemical impedance spectroscopy （EIS） and electrochemical noise （EN） techniques, and the microstructure and the second phase content of the alloy were observed and determined by scanning electron microscopy （SEM） and energy dispersive spectrometer （EDS）. The results show that there exist two different corrosion stages for 7A60 alloy in 3.5%NaCl solution, and the corrosion process can be detected by the appearance of EIS spectrum with two capacitive time constants and the wavelet fractal dimension D extracted from EN. SEM and EDS results also demonstrate that severe pitting corrosion in 7A60 alloy is mainly caused by electrochemical active MgZn2 particles, secondly by Al2MgCu and Mg2Si. Al7Cu2Fe particles make little contribution to the pitting corrosion of 7A60 alloy.
基金supported by the National Natural Science Foundation of China(No.51801219)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2019193)+1 种基金the Scientific Research Project of China Three Gorges Corporation(No.JD-YJ-05006)the National Key Research and Development Program of China(No.2017YFB0702302)。
文摘In this study,the pitting corrosion behavior of 13Cr4Ni martensitic stainless steel(BASE)and that modified with rare earth(REM)in 0.1 mol/L Na Cl solution were characterized.Techniques such as automatic secondary electron microscope(ASPEX PSEM detector),scanning electron microscope(SEM),transmission electron microscope(TEM),scanning Kelvin probe force microscope(SKP),potentiodynamic and potentiostatic polarizations were employed.The results obtained indicate that BASE steel contains Al_(2)O_(3)/Mn S,Al_(2)O_(3) and Mn S inclusions,while REM steels contain(La,Ce,Cr,Fe)-O and(La,Ce,Cr,Fe)-O-S inclusions.Compared with BASE steel,REM steel is more susceptible to induce the metastable pitting nucleation and repassivation,whereas it restrains the transition from metastable pitting to stable pitting.Adding 0.021%rare earth element to BASE steel can reduce the number and area of inclusions,while that of 0.058%can increase the number and enlarged the size of inclusions,which is also the reason that pitting corrosion resistance of 58 REM steel is slightly lower than that of 21 REM steel.In the process of pitting corrosion induced by Al_(2)O_(3)/Mn S inclusions,Mn S is preferentially anodic dissolved,and also the matrix contacted with Al_(2)O_(3) is subsequently anodic dissolved.For REM steels,anodic dissolution preferentially occurs at the boundary between inclusions and matrix,while(La,Ce,Cr,Fe)-O inclusions chemically dissolve in local acidic environment or are separated from steel matrix.The chemically dissolved substance(La^(3+) and Ce^(3+))of(La,Ce,Cr,Fe)-O inclusions are concentrated in pitting pits,which inhibits its continuous growth.
文摘This study researched the relationship between the applied potential and the critical pitting temperature （CPT） of the 304 and new 200 series of stainless steels. The fluctuation about the potential dependent CPT for the stainless steels was investigated and the CPT range was obtained. The difference between the potential dependent CPTs of the 304 and 200 series of stainless steels with an applied potential of 100 mV （ vs SCE）, were presented, and by this means the pitting corrosion resistances of them were compared.
基金supported by the National Natural Science Foundation of China and Baosteel Group Corporation (No.50534010)
文摘Pitting corrosion and crevice corrosion behaviors of high nitrogen austenitic stainless steels （HNSS） were investigated by electrochemical and immersion testing methods in chloride solution, respectively. The chemical constitution and composition in the depth of passive films formed on HNSS were analyzed by X-ray photoelectron spectrum （XPS）. HNSS has excellent pitting and crevice corrosion resistance compared to 316L stainless steel. With increasing the nitrogen content in steels, pitting potentials and critical pitting temperature （CPT） increase, and the maximum, average pit depths and average weight loss decrease. The CPT of HNSS is correlated with the alloying element content through the measure of alloying for resistance to corrosion （MARC）. The MARC can be expressed as an equation of CPT=2.55MARC-29. XPS results show that HNSS exhibiting excellent corrosion resistance is attributed to the enrichment of nitrogen on the surface of passive films, which forms ammonium ions increasing the local pH value and facilitating repassivation, and the synergistic effects of molybdenum and nitrogen.
基金finically supported by the National Natural Science Foundation of China(No.51931008)the Basic Technology Research Project for National Defense of China(No.JSHS2017207C001)。
文摘Pitting corrosion of 2Cr13 stainless steel was investigated by deep-sea exposure test at various depths of 500 m,800 m and 1200 m in the South China Sea for 4 months.With the aid of electrochemical measurements in simulated deep-sea environments and grey relational analysis,the influence of deepsea environments on passive film and the mechanism of pitting corrosion were discussed.The results indicated that with the increase of sea depth,pitting depth of 2Cr13 stainless steel increased,which can be attributed to the change of chemical composition and the degradation of pitting resistance of passive film.Film growth was greatly retarded in the condition of low seawater temperature and low dissolved oxygen content of deep sea,resulting in an unstable and vulnerable film.Pitting depth was most influenced by hydrostatic pressure,which can increase the adsorption and penetration of Cl-ion,and promote the proliferation of point defects in passive film,leading to rapid deconstruction of protective oxides of the film.Pitting sensitivity of 2Cr13 stainless steel increased eventually with the combination of accelerated dissolution and suppressed self-healing of passive film in deep sea.
基金Item Sponsored by Special Project of Education Depart ment of Shaanxi Province of China (07JK309)Project of Science andTechnology Research and Development Program of Shaanxi Province of China (2010K10-13)
文摘The effects of phase transformation on mechanical properties and pitting corrosion of 2205 duplex stainless steel were investigated. The amount of a phase in the test specimen varied up to a maximum of 6 % by thermal treatment at 850 ℃ for up to 60 min. The results showed that ~ phase markedly increased the hardness and decreased the impact toughness of the test steel. But the increasing tendency of the ultimate tensile strength and the yield strength was not obvious, while the total elongation abruptly decreased with the aging time from 5 to 60 min. SEM impact microfractograph analysis revealed that the types of impact fracture changed from ductile mode to transcrystalline mode when the specimens were aged for 5-60 min. Furthermore, the extent of pitting potential reducing was found to be strongly temperature dependent, more pronounced at the higher temperature. During the incubation period of σ phase nucleation, the pitting corrosion test temperature and the aging time had collaborative effects on evidently displacing the pitting potential towards less noble values. After 15 min, the higher temperature contributed more to decreasing the pitting potential than the aging time.
基金supported by the National Natural Science Foundation of China (No. 51471174)the National Key Basic Research Program of China (No. 2013CB632205)the National Key Research and Development Program of China (No. 2016 YFB0301105)
文摘Pitting corrosion of magnesium(Mg) alloys is greatly associated with their microstructure, especially second phases. The second phases in traditional Mg alloys such as AZ91 are electrochemically nobler than Mg matrix, while the second phases in Rare earth(RE) Mg alloy GW93 are more active than Mg matrix. As a result, the pitting corrosion mechanism of Mg alloy GW93 is different from the traditional ones. This paper aims to clarify the pitting corrosion mechanism of Mg alloy GW93 through the studies of Volta potential by Scanning Kelvin Probe Force Microscopy(SKPFM), corrosion morphology by Scanning Electron Microscope(SEM), and corrosion resistance by electrochemical tests. Results reveal that the pitting corrosion of GW93 includes three stages, first, dissolution of the second phases, followed by corrosion of Mg matrix adjacent to the dissolved second phases, and finally, propagation of corrosion pits along the depth direction of the dissolved second phases. Anodic second phases and enrichment of Clin the thick corrosion product films dominate the propagation of pitting corrosion.
基金the Department of Materials Engineering at Isfahan University of Technology for the technical support
文摘The effect of friction stir processing （FSP） on the pitting corrosion and the intergranular attack of 7075 aluminum alloy was investigated. Three friction stir processed samples were produced by employing a constant tool travel speed of 100 mm/min at the rotating speeds of 630, 1000 and 1600 rpm. It was dem- onstrated that the processed samples suffered from both pitting and intergranular corrosion. Also, the sample processed at 1600 rpm exhibited the best pitting corrosion resistance. For all FS processed samples, the corrosion attack in the heat affected zone was pitting corrosion, whereas no intergranular corrosion was detected in this area.
基金supported by the National Natural Science Foundation of China(No.50534010)
文摘A series of high nitrogen austenitic stainless steels were successfully developed with a pressurized electroslag remelting furnace. Nitride additives and deoxidizer were packed into the stainless steel pipes, and then the stainless steel pipes were welded on the surface of an electrode with low nitrogen content to prepare a compound electrode. Using Si3N4 as a nitrogen alloying source, the silicon contents in the ingots were prone to be out of the specification range, the electric current fluctuated greatly and the surface qualities of the ingots were poor. The surface qualities of the ingots were improved with FeCrN as a nitrogen alloying source. The sound and compact macrostructure ingot with the maximum nitrogen content of 1.21wt% can be obtained. The 18Cr18Mn2Mo0.9N high nitrogen austenitic stainless steel exhibits high strength and good ductility at room temperature. The steel shows typical ductile-brittle transition behavior and excellent pitting corrosion resistance properties.
基金Project(51671013)supported by the National Natural Science Foundation of ChinaProject(Z161100004916061)supported by the Beijing Nova Program,China
文摘The thorough-thickness inhomogeneity of precipitate distribution and pitting corrosion behavior of 95 mm-thick 2297 Al-Li alloy rolled plate was investigated using scanning electron microscopy, transmission electron microscopy and electrochemistry method. Precipitate distribution and pit size were statistically analyzed to obtain quantitative information and corresponding correlation. The population density and the size fraction of precipitate on different sections in the thick plate are ranked from high to low in the following order: quarter-section(QS) > surface section(SS) > mid-section(MS). After 300 min potentiostatic polarization, the number and the total volume of pits are ranked from high to low as QS>SS>MS, indicating a higher pitting susceptibility of the plate in QS with more precipitates. The through-thickness inhomogeneity of pitting corrosion in 2297 Al-Li alloy thick plate is mainly ascribed to inhomogeneous precipitate distribution.
基金Sponsored by the National Natural Science Foundation of China(Grant No.51378417)Program for Changjiang Scholars and Innovative Research Team in University(IRT13089)PhD Innovation Fund of Xi'an University of Architecture and Technology
文摘A set of evaluation indicators based on corrosion ratio in theory for assessing the extent of pitting corrosion and performance reduction are proposed. In order to quantify the morphology of pitting corrosion and extract the evaluation indicators,the 3D profile data obtained by pitting morphology measurement are imported into a special written program to automatically determine the location of each corrosion pit and distill any desired data pertinent to the pitting morphology. The results show that this method seems to be effective to analyze the corroded surface and characterize the pitting morphology.
文摘Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is frequently TIG （tungsten inert gas） welding due to its comparatively easier applicability and better economy.In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance technique has been used to find out the significant pulsed current parameters. Regression analysis has been used to develop the model. Using the developed model pitting corrosion potential values have been estimated for different combinations of pulsed current parameters and the results are analyzed in detail.
基金the Fund of National Key Laboratory of Remanufacturing[Grant 614005180101]。
文摘The pitting corrosion behavior of AZ91 alloy before and after micro-oxidation treatment in 3.5%Na Cl solution was investigated by cyclic potentiodynamic polarization(CPDP)and optical and SEM observations of corroded surfaces at different polarization potentials.The CPDP results show that both the alloy and the MAO-coated alloy suffer from pitting corrosion and it is difficult for pits to stop growth once the pits initiates.It is revealed that the air-formed Mg O film on AZ91 alloy,the MAO coating along with corrosion products(mainly Mg(OH))formed during CPDP can significantly influence the kinetics of the redox reactions of Mg,and further influence the propagation behavior of pitting corrosion.The optical and SEM images show that the corrosion products on AZ91 alloy are dense and protective but on the MAO-coated corrosion products are very loose.Such observations support the analyses of CPDP results that pits on AZ91 alloy spread to the width whereas pits on MAO-coated alloy propagate to the depth.Overall,pitting corrosion on the MAO-coated alloy can be very severe once the coating ruptures and post-treatments are necessary to provide a promising corrosion protection for the Mg alloys.
基金PPGCEM/UFSCar(Materials Science and Engineering Postgraduate Program at the Federal University of São Carlos)CNPq(National Council for Scientific and Technological Development,Brazil-grant no.311163/2017-3 and 312614/2020-9)FAPESP(São Paulo Research Foundation,Brazil–grant no.2020/03205-6)
文摘In this study,the relationship between spinodal decomposition and the formation of Ni-rich clusters and G-phase in the ferrite on hardening and pitting corrosion of two thermally aged duplex stainless steels(DSSs)at 475℃was investigated.Results indicate that,for 2205 DSS,pitting corrosion behavior is influenced by the presence and size of G-phase precipitates for longer aging times,but this contribution is masked by the advanced stage of spinodal decomposition in the ferritic structure.On the other hand,for 2101 DSS,the formation of Cr-richer nitrides impairs pitting corrosion resistance more than spinodal decomposition.
基金supported by the National Natural Science Foundation of China (51774190,51961032)China Postdoctoral Science Foundation(2021MD703850)Natural Science Foundation of Inner Mongolia,China(2020MS05072)。
文摘In this paper,the origin mechanism of pitting corrosion induced by Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions in a microalloyed steel was investigated by field emission scanning electron microscopy with energy dispersive spectroscopy and electron backscattered diffraction,conductivity atomic force microscopy,immersion test,and first-principles calculation.The results show that the Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions are non-conductive,which are impossible to form corrosion couples with the steel matrix.There are no obvious lattice distortion zones in the steel matrix around the Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions,so it is difficult to form micro-galvanic corrosion near the Ce inclusion.The order of work functions of the Ce inclusions and the steel matrix from small to large is Ce_(2)O_(2)S<Ce_(2)O_(3)<CeAlO_(3)<steel matrix,which is consistent with their dissolution sequence in the immersion test in _(3).5 wt%NaCl solution.Consequently,it is effective and reliable to use work function to predict or judge the dissolution behaviors of the Ce inclusions or steel matrix in corrosive solution.The Ce_(2)O_(3),Ce_(2)O_(2)S,and CeAlO_(3) inclusions have the tendency of self-dissolution and dissolve preferentially to the steel matrix in the solution by the salt effect,which lead to pitting corrosion of Ce-containing microalloyed steel.
文摘Pitting corrosion behaviour of Monel-400 alloy in 3.5 wt pct NaCl sodium chloride solution has been investigated using the cyclic potentiodynamic anodic polarization technique. The effect of chloride ion concentration, pH values and difFerent temperatures on the pitting parameters were determined. The morphology of the pits produced after anodic polarization treatments was inspected by scanning electron microscope (SEM). The results indicated that, the increase in chloride ion concentration shifts Epit and Eprot of the alloy toward negative values and the pitting potential is much more dependent on pH value in the basic region. The breakdown of passivity with increasing temperature may be due to kinetic changes of passivating films and dissolution rate of the alloy in its passive state
