Aluminum alloy tubes were prepared by tube spinning.The intergranular and electrochemical corrosion tests were used to investigate the intergranular corrosion behavior of the 5A06 aluminum alloy blank sample and the s...Aluminum alloy tubes were prepared by tube spinning.The intergranular and electrochemical corrosion tests were used to investigate the intergranular corrosion behavior of the 5A06 aluminum alloy blank sample and the spinning sample.Results showed that the intergranular corrosion resistance of the spinning sample was higher than that of the blank sample.In addition,the electrochemical corrosion resistance of the spinning sample was higher than that of the blank sample.The EDS maps indicated a uniform element distribution pattern of aluminum and magnesium.Moreover,the phase composition and lattice constant of the samples were obtained by XRD analysis.The differences in microstructure between the aluminum alloy subjected to the spinning process and the untreated aluminum alloy were determined by EBSD.The differences were mainly attributed to the complex interactions among grain size,dislocations and grain boundaries.展开更多
The intergranular corrosion (IGC) behavior of high nitrogen austenitic stainless steel (HNSS) sensitization treated at 650-950℃ was investigated by the double loop electrochemical potentiodynamic reactivation (D...The intergranular corrosion (IGC) behavior of high nitrogen austenitic stainless steel (HNSS) sensitization treated at 650-950℃ was investigated by the double loop electrochemical potentiodynamic reactivation (DL-EPR) method. The effects of the electrolytes, scan rate, sensitizing temperature on the susceptibility to IGC of HNSS were examined. The results show that the addi-tion of NaCl is an effective way to improve the formation of the cracking of a passive film in chromium-depleted zones during the reactivation scan. Decreasing the scan rate exhibits an obvious effect on the breakdown of the passive film. A solution with 2 mol/L H2SO4+1 mol/L NaCl+0.01 mol/L KSCN is suitable to check the susceptibility to IGC of HNSS at a sensitizing temperature of 650-950℃ at a suitable scan rate of 1.667 mV/s. Chromium depletion of HNSS is attributed to the precipitation of Cr2N which results in the susceptibility to IGC. The synergistic effect of Mo and N is suggested to play an important role in stabilizing the passive film to prevent the attack of IGC.展开更多
In order to study the effects of aging treatment on the intergranular corrosion(IGC) and stress corrosion cracking(SCC) of 7003 aluminum alloy(AA7003), the intergranular corrosion test, electrochemical test and ...In order to study the effects of aging treatment on the intergranular corrosion(IGC) and stress corrosion cracking(SCC) of 7003 aluminum alloy(AA7003), the intergranular corrosion test, electrochemical test and slow strain rate test(SSRT), combined with optical microscopy(OM) and scanning electron microscopy(SEM) as well as transmission electron microscopy(TEM) observations have been carried out. The IGC and electrochemical test results showed that the IGC resistance of AA7003 for peak aged(PA) temper is the lowest, with double peak aged(DPA) the moderate, and retrogression and re-aging(RRA) the highest among three tempers, which is attributed to the continuous feature of precipitation on grain boundary of PA temper and the interrupted feature of precipitation on grain boundary of DPA and RRA tempers, as well as the wide precipitation free zones(PFZ) of RRA temper. In addition, the SSRT results indicated that all three tempers AA7003 are susceptible to SCC in IGC solution, and the change tendency of SCC susceptibility(ISCC) of AA7003 for three tempers follows the order: ISCC(RRA)展开更多
This study analyzes acoustic emission (AE) signals during the intergranular corrosion (IGC) process of 316L stainless steel welded joints under different welding currents in boiling nitric acid. IGC generates seve...This study analyzes acoustic emission (AE) signals during the intergranular corrosion (IGC) process of 316L stainless steel welded joints under different welding currents in boiling nitric acid. IGC generates several AE signals with high AE activity. The AE technique could hardly distinguish IGC in stainless steel welded joints with different welding heat inputs. However, AE signals can effectively distinguish IGC characteristics in different corrosion stages. The IGC resistance of a heat-affected zone is lower than that of a weld zone. The initiation and rapid corrosion stages can be distinguished using AE results and microstructural analysis. Moreover, energy count rate and amplitude are considered to be ideal parameters for characterizing different IGC processes. Two types of signals are detected in the rapid corrosion stage. It can be concluded that grain boundary corrosion and grain separation are the AE sources of type 1 and type 2, respectively.展开更多
The corrosion behaviour and mechanism of superpure austenitic stainless steel 00Cr25Ni22Mo2N in urea processing environment was studied using metallography,SEM, TEM,SIMS and AES techniques.The results show that the ga...The corrosion behaviour and mechanism of superpure austenitic stainless steel 00Cr25Ni22Mo2N in urea processing environment was studied using metallography,SEM, TEM,SIMS and AES techniques.The results show that the gas extraction tube made of non-sensitized 00Cr25Ni22Mo2N steel suffered intergranular corrosion.Corrosive media penetrated not only into the tube wall through grain boundaries but also expanded from the boundary towards the interior of the grain.Neither depletion of Cr nor precipitates were found at the grain boundaries.However,P(and Si)was segregated at the grain boundaries to a great extent.Semiquantitative calculation indicates that the P content at the grain boundaries is about 25 wt-%,three orders of magnitude higher than the content within the grain.Sugges- tion is made that the potential difference between the grain and its boundary due to the segre- gation results in the observed intergranular corrosion.展开更多
Optimization of grain boundary engineering(GBE) process is explored in a Fe–20Cr–19Mn–2Mo–0.82N high-nitrogen and nickel-free austenitic stainless steel, and its intergranular corrosion(IGC) property after GBE tre...Optimization of grain boundary engineering(GBE) process is explored in a Fe–20Cr–19Mn–2Mo–0.82N high-nitrogen and nickel-free austenitic stainless steel, and its intergranular corrosion(IGC) property after GBE treatment is experimentally evaluated. The proportion of low Σ coincidence site lattice(CSL) boundaries reaches 79.4% in the sample processed with 5% cold rolling and annealing at 1423 K for 72 h;there is an increase of 32.1% compared with the solution-treated sample. After grain boundary character distribution optimization, IGC performance is noticeably improved. Only Σ3 boundaries in the special boundaries are resistant to IGC under the experimental condition. The size of grain cluster enlarges with increasing fraction of low ΣCSL boundaries, and the amount of Σ3 boundaries interrupting the random boundary network increases during growth of the clusters, which is the essential reason for the improvement of IGC resistance.展开更多
The data obtained by bending tests for intergranular embrittlement after 45 h and 450 h exposure to Strauss solution have been reported for 304 stainless steel. The results show that an embrittlement peak appears at ...The data obtained by bending tests for intergranular embrittlement after 45 h and 450 h exposure to Strauss solution have been reported for 304 stainless steel. The results show that an embrittlement peak appears at 650℃ for all samples quenched from 1260℃ and then sensitized for 150 h at 480, 565, 650, 730, 815 and 900℃ respectively. The temperature corresponding to the embrittlement peak is decreased to 565℃ when the sensitizing time is prolonged to 1 500 h. In this paper, these data are analyzed with an isothermal kinetic model of nonequilibrium grain boundary segregation, indicating that the embrittlement peak is related to the critical time for nonequilibrium grain boundary segregation of sulfur.展开更多
Heat treatment is an effective method to improve the intergranular corrosion resistance of the sensitized Al–Mg alloy due to dissolution of the grain boundary precipitates above the solvus temperature ofβ-phase.The ...Heat treatment is an effective method to improve the intergranular corrosion resistance of the sensitized Al–Mg alloy due to dissolution of the grain boundary precipitates above the solvus temperature ofβ-phase.The grain boundary precipitates will grow and coarsening below the solvus temperature.In this study,the in-situ intergranular corrosion performance regeneration of the sensitized Al–Mg alloy can be realized by low-density electro-pulsing treatment below the solvus temperature ofβ-phase.Our findings show that the dissolution of grain boundary precipitates by electro-pulsing treatment is accelerated at relatively low temperature in comparison to traditional heat treatment.The athermal effect produced by the interaction between atoms and electrons on the dissolution of grain boundary precipitates is the main reason for the improved corrosion resistance below the solvus temperature ofβ-phase.展开更多
With Nb-Ti-stabilized 430 ferritic stainless steel(NTS430FSS) and SUS 430 ferritic stainless steel(SUS430FSS) as experimental materials, the influence of precipitation on intergranular corrosion resistance was inv...With Nb-Ti-stabilized 430 ferritic stainless steel(NTS430FSS) and SUS 430 ferritic stainless steel(SUS430FSS) as experimental materials, the influence of precipitation on intergranular corrosion resistance was investigated. A series of aging treatment were carried out. The free-exposure corrosion test and double loop electrochemical potentiokinetic reactivation(DL-EPR) test with a scan rate of 1.67 m V/s at 26 °C were applied to evaluate the intergranular corrosion(IGC) resistance. Metallographic observation, scanning electron microscope(SEM), transmission electron microscope(TEM) with energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD) analysis were conducted. The results show that IGC occurred in SUS430 FSS aged above 700 °C, while it occurred in NTS430 FSS as the temperature was improved to 1 050 °C. The critical degree of sensitization Ir/Ia reaches 0.305 in SUS430 FSS, which is higher than that of NTS430 FSS, i.e. 0.010, aged at 950 °C for 2 h. The TEM, EDS and XRD results show that a large amount of Cr23C6 precipitates with size of 60 nm×22 nm are located at the SUS430 FSS grain boundaries as chains. With the addition of Nb and Ti and reduction of C, the amount of precipitates reduces significantly in NTS430 FSS. A majority of Cr23C6 were replaced by Ti C and Nb C. Only a small amount of spherical Ti C(R=186 nm) and square Ti N(312 nm×192 nm) with Nb and Cr adsorbed are left along grain boundaries. Due to the dual stabilization of Nb and Ti, the precipitation of Cr23C6 is restrained, the chromium depleted region is avoided and accordingly the resistance to the intergranular corrosion is improved.展开更多
The intergranular corrosion (IGC) character of tin-added B316LX and the influence of tin addition on IGC susceptibility were investigated by DL-EPR, oxalic acid etch test and transmission electron microscopy. IGC su...The intergranular corrosion (IGC) character of tin-added B316LX and the influence of tin addition on IGC susceptibility were investigated by DL-EPR, oxalic acid etch test and transmission electron microscopy. IGC susceptibility of B316LX is mainly caused by the precipitation of M23C6 carbide and intermetallic Laves phase. DL-EPR test is unsuitable to evaluate the IGC susceptibility of B316LX with long-time sensitization, because more carbides and inter- metallic phases are formed at grain boundaries and inside the grains, which induce more severe IGC and pits attacks. Tin addition increases the IGC susceptibility, maybe due to diffusion of tin toward grain boundaries.展开更多
2024 aluminum alloys were consolidated by using spark plasma sintering(SPS) method,and then heat treated by solid solution treatment(SST) and aging treatment(AT) procedures.The average grain size of bulk samples sinte...2024 aluminum alloys were consolidated by using spark plasma sintering(SPS) method,and then heat treated by solid solution treatment(SST) and aging treatment(AT) procedures.The average grain size of bulk samples sintered with 5,20 and 50 μm powders was 3.72,4.73 and 8.11 μm,respectively.The difference between the average grain size and original powder size was attributed to the recrystallization during short sintering process.The number of the inclusion phases in these samples decreased after SST and increased after subsequent AT.Besides,it was observed that intergranular corrosion(IGC) cracks initiated from stable pits due to the electrochemical inhomogeneity between the intermetallic particles(IMPs) and the aluminum matrix(176.02,110.83 and 164.80 mV for as-SPS,as-SST and as-AT samples,respectively).Besides,the cracks would propagate along the grain boundaries(GBs) and bypass the IMPs at GBs during propagation.It was revealed that the sample after SST presented the best IGC resistance,and this was ascribed to the reduce of IMPs,both in size and number.展开更多
The effects of shot peening(SP) and plasma electrolytic oxidation(PEO) on the intergranular corrosion behavior of the novel high strength aluminum alloy 7A85(AA 7A85) were investigated by electrochemical polariz...The effects of shot peening(SP) and plasma electrolytic oxidation(PEO) on the intergranular corrosion behavior of the novel high strength aluminum alloy 7A85(AA 7A85) were investigated by electrochemical polarization and electrochemical impedance tests.The intergranular corrosion mechanism of SP,PEO and PEO combined with sealingtreated AA 7A85 was studied by the metallographic analysis,residual stress testing,X-ray diffractometer analysis and scanning electron microscopy.The results show that AA 7A85-T7452 is very sensitive to intergranular corrosion.SP would significantly improve its intergranular corrosion resistance.This is attributed to the combination action of residual compressive stress and grain refinement.PEO would reduce the largest corrosion depth by 41.6%.Moreover,PEO without sealing did not eliminate the intergranular corrosion due to the existence of the micropores and microcracks in the oxide coating.However,PEO combined with the SiO2sol–gel sealing treatment could effectively protect the AA 7A85-T7452 from intergranular corrosion because of the good corrosion resistance and barrier function of the sealed coating.展开更多
Additive manufacturing(AM)of Mg alloys has become a promising strategy for producing complex structures,but the corrosion performance of AM Mg components remains unexploited.In this study,wire and arc additive manufac...Additive manufacturing(AM)of Mg alloys has become a promising strategy for producing complex structures,but the corrosion performance of AM Mg components remains unexploited.In this study,wire and arc additive manufacturing(WAAM)was employed to produce single AZ31 layer.The results revealed that the WAAM AZ31 was characterized by significant grain refinement with non-textured crystallographic orientation,similar phase composition and stabilized corrosion performance comparing to the cast AZ31.These varied corrosion behaviors were principally ascribed to the size of grain,where cast AZ31 and WAAM AZ31 were featured by micro galvanic corrosion and intergranular corrosion,respectively.展开更多
The A1-2.79Li-1.3Cu-0.7Mg-0.12Zr(8090) alloy has excellent resistance to intergranular and exfoliation corrosion as naturally aged, worst as peak aged and rather better as underaged than as overaged. The corrosion beh...The A1-2.79Li-1.3Cu-0.7Mg-0.12Zr(8090) alloy has excellent resistance to intergranular and exfoliation corrosion as naturally aged, worst as peak aged and rather better as underaged than as overaged. The corrosion behaviour of the alloy is closely dependent on its microstructure. Under the peak aging condition, the coarse T_2 phase, which is continuously distributed along grain boundaries, has so low corrosion potential in comparison with the ma- trix, this makes the corrosion resistance of the alloy to be deteriorated by anodic dissolution along grain boundaries.展开更多
Temperature has an important impact on the corrosion resistance of mold with cooling channels prepared by casting method.The effect of preheating temperature of the mold and the carbon fiber core on the roughness and ...Temperature has an important impact on the corrosion resistance of mold with cooling channels prepared by casting method.The effect of preheating temperature of the mold and the carbon fiber core on the roughness and corrosion resistance of U-shaped cooling channels made of Al-12Si alloy was examined in depth.The experimental results suggest that as the preheating temperature increased from 273 K to 573 K,the roughness of the inner wall of the cooling channel reduced from 96.6μm to 77.0μm.When the preheating temperature continued to increase to 723 K,the roughness increased to 85.3μm.The wetting between the Al melt and the carbon fiber will reduce micro bubbles and waves on the channel wall as the preheating temperature rises,thereby reducing the roughness.However,with the further increase of preheating temperature,it will increase the solidification time of the Al melt.At this time,the carbon fiber and Al melt will take more time to react,which increases the roughness of the channel wall to a certain extent.The results of exfoliation corrosion show that the larger roughness will aggravate exfoliation corrosion.The prolongation of high temperature reaction time between the carbon fiber and the Al melt will lead to the segregation of Si,which is easy to cause intergranular corrosion.Therefore,reasonable preheating temperature has an important impact on the roughness and corrosion resistance of U-shaped cooling channels.展开更多
Intergranular stress corrosion crack susceptibility of austenite stainless steel was evaluated through threepoint bending test conducted in high temperature water. The experimental results showed that the frequent and...Intergranular stress corrosion crack susceptibility of austenite stainless steel was evaluated through threepoint bending test conducted in high temperature water. The experimental results showed that the frequent and efficient introduction of low energy coincidence site lattice boundaries through grain boundary engineering resulted in an apparent improvement of the intergranular stress corrosion crack resistance of austenite stainless steel.展开更多
The corrosion morphologies of aged magnesium alloy AZ80 were investigated by immersion corrosion tests, scanning electron microscopy (SEM), electrochemical measurement. The T5 heat treatment was carried out in a vac...The corrosion morphologies of aged magnesium alloy AZ80 were investigated by immersion corrosion tests, scanning electron microscopy (SEM), electrochemical measurement. The T5 heat treatment was carried out in a vacuum furnace, holding for 16 h at 177℃, and then cooling in air. The results showed intergranular corrosion (IGC) occurred as an aged AZ80 sample was immersed in 3.5 wt pct NaCI aqueous solution for 1 h and the narrow path attack progressed predominantly along the bulk β phase in the grain boundaries or took place in the eutectic areas. IGC was attributed to the network distribution of β phase along the grain boundaries, the depleted aluminium in the precipitation areas and the breakdown potential.展开更多
Variation and degradation of P-110 casing steel mechanical properties, due to sulfide stress cracking (SSC) in sour environments, was investigated using tensile and impact tests. These tests were carried out on spec...Variation and degradation of P-110 casing steel mechanical properties, due to sulfide stress cracking (SSC) in sour environments, was investigated using tensile and impact tests. These tests were carried out on specimens, which were pretreated under the following conditions for 168 hours: temperature, 60 ℃; pressure, 10 MPa; H2S partial pressure, 1 MPa and CO2 partial pressure, 1 MPa; preload stress, 80% of the yield strength (os); medium, simulated formation water. The reduction in tensile and impact strengths for P-110 casing specimens in corrosive environments were 28% and 54%, respectively. The surface morphology analysis indicated that surface damage and uniform plastic deformation occurred as a result of strain aging. Impact toughness of the casing decreased significantly and intergranular cracking occurred when specimens were maintained at a high stress level of 85% %.展开更多
The effect of chloride ion concentration, pH value, and grain size on the pitting corrosion resistance of a new ferritic stainless steel with 15wt% Cr was investigated using the anodic polarization method. The semicon...The effect of chloride ion concentration, pH value, and grain size on the pitting corrosion resistance of a new ferritic stainless steel with 15wt% Cr was investigated using the anodic polarization method. The semiconducting properties of passive films with different chloride ion concentrations were performed using capacitance measurement and Mott-Schottky analysis methods. The aging precipitation and intergranular corrosion behavior were evaluated at 400- 900℃. It is found that the pitting potential decreases when the grain size increases. With the increase in chloride ion concentration, the doping density and the flat-bland potential increase but the thickness of the space charge layer decreases. The pitting corrosion resistance increases rapidly with the decrease in pH value. Precipitants is identified as Nb(C,N) and NbC, rather than Cr-carbide. The intergranular corrosion is attributed to the synergistic effects of Nb(C,N) and NbC precipitates and Cr segregation adjacent to the precipitates.展开更多
The grain boundary structure of Cu alloy was observed and the characteristic of the boundaries was studied,including 70∶30 cupronickel and 70∶30 brass. The results show that in the case of the 70∶30 cupronickel thi...The grain boundary structure of Cu alloy was observed and the characteristic of the boundaries was studied,including 70∶30 cupronickel and 70∶30 brass. The results show that in the case of the 70∶30 cupronickel thin platelets with nickel and iron enrichment in it precipitate intergranular so that the alloy was sensitive to seawater corrosion. In the case of 70∶30 brass the situation of grain boundary segregation of different inclusions made the corrosion resistance of the alloy even worse. All of those were discovered through the corrosion behavior of the two different copper alloys served in various environments. The experimental methods used here were, scanning electron microscopy(SEM), transmission electron microscopy(TEM) and energy dispersive of X ray(EDX). The intergranular corrosion morphologies of those copper alloys served in engineering or exposed to seawater for a long term were given.展开更多
基金Funded by the National Natural Science Foundation of China(No.51802189)the Shanghai Lingang Innovation Program(No.SH-LG-GK-2020-28)。
文摘Aluminum alloy tubes were prepared by tube spinning.The intergranular and electrochemical corrosion tests were used to investigate the intergranular corrosion behavior of the 5A06 aluminum alloy blank sample and the spinning sample.Results showed that the intergranular corrosion resistance of the spinning sample was higher than that of the blank sample.In addition,the electrochemical corrosion resistance of the spinning sample was higher than that of the blank sample.The EDS maps indicated a uniform element distribution pattern of aluminum and magnesium.Moreover,the phase composition and lattice constant of the samples were obtained by XRD analysis.The differences in microstructure between the aluminum alloy subjected to the spinning process and the untreated aluminum alloy were determined by EBSD.The differences were mainly attributed to the complex interactions among grain size,dislocations and grain boundaries.
基金supported by the National Natural Science Foundation of China (No.50534010) and Baosteel Group Corporation
文摘The intergranular corrosion (IGC) behavior of high nitrogen austenitic stainless steel (HNSS) sensitization treated at 650-950℃ was investigated by the double loop electrochemical potentiodynamic reactivation (DL-EPR) method. The effects of the electrolytes, scan rate, sensitizing temperature on the susceptibility to IGC of HNSS were examined. The results show that the addi-tion of NaCl is an effective way to improve the formation of the cracking of a passive film in chromium-depleted zones during the reactivation scan. Decreasing the scan rate exhibits an obvious effect on the breakdown of the passive film. A solution with 2 mol/L H2SO4+1 mol/L NaCl+0.01 mol/L KSCN is suitable to check the susceptibility to IGC of HNSS at a sensitizing temperature of 650-950℃ at a suitable scan rate of 1.667 mV/s. Chromium depletion of HNSS is attributed to the precipitation of Cr2N which results in the susceptibility to IGC. The synergistic effect of Mo and N is suggested to play an important role in stabilizing the passive film to prevent the attack of IGC.
基金Funded by the National Natural Science Foundation of China(No.51371039)
文摘In order to study the effects of aging treatment on the intergranular corrosion(IGC) and stress corrosion cracking(SCC) of 7003 aluminum alloy(AA7003), the intergranular corrosion test, electrochemical test and slow strain rate test(SSRT), combined with optical microscopy(OM) and scanning electron microscopy(SEM) as well as transmission electron microscopy(TEM) observations have been carried out. The IGC and electrochemical test results showed that the IGC resistance of AA7003 for peak aged(PA) temper is the lowest, with double peak aged(DPA) the moderate, and retrogression and re-aging(RRA) the highest among three tempers, which is attributed to the continuous feature of precipitation on grain boundary of PA temper and the interrupted feature of precipitation on grain boundary of DPA and RRA tempers, as well as the wide precipitation free zones(PFZ) of RRA temper. In addition, the SSRT results indicated that all three tempers AA7003 are susceptible to SCC in IGC solution, and the change tendency of SCC susceptibility(ISCC) of AA7003 for three tempers follows the order: ISCC(RRA)
基金supported by the National Basic Research Program of China (No. 2015CB057602)the Major Scientific and Technological Special Project of China (No. 2011ZX06004-009)
文摘This study analyzes acoustic emission (AE) signals during the intergranular corrosion (IGC) process of 316L stainless steel welded joints under different welding currents in boiling nitric acid. IGC generates several AE signals with high AE activity. The AE technique could hardly distinguish IGC in stainless steel welded joints with different welding heat inputs. However, AE signals can effectively distinguish IGC characteristics in different corrosion stages. The IGC resistance of a heat-affected zone is lower than that of a weld zone. The initiation and rapid corrosion stages can be distinguished using AE results and microstructural analysis. Moreover, energy count rate and amplitude are considered to be ideal parameters for characterizing different IGC processes. Two types of signals are detected in the rapid corrosion stage. It can be concluded that grain boundary corrosion and grain separation are the AE sources of type 1 and type 2, respectively.
文摘The corrosion behaviour and mechanism of superpure austenitic stainless steel 00Cr25Ni22Mo2N in urea processing environment was studied using metallography,SEM, TEM,SIMS and AES techniques.The results show that the gas extraction tube made of non-sensitized 00Cr25Ni22Mo2N steel suffered intergranular corrosion.Corrosive media penetrated not only into the tube wall through grain boundaries but also expanded from the boundary towards the interior of the grain.Neither depletion of Cr nor precipitates were found at the grain boundaries.However,P(and Si)was segregated at the grain boundaries to a great extent.Semiquantitative calculation indicates that the P content at the grain boundaries is about 25 wt-%,three orders of magnitude higher than the content within the grain.Sugges- tion is made that the potential difference between the grain and its boundary due to the segre- gation results in the observed intergranular corrosion.
基金financially supported by the National Natural Science Foundation of China(Grant Nos.51871048 and 51571058)。
文摘Optimization of grain boundary engineering(GBE) process is explored in a Fe–20Cr–19Mn–2Mo–0.82N high-nitrogen and nickel-free austenitic stainless steel, and its intergranular corrosion(IGC) property after GBE treatment is experimentally evaluated. The proportion of low Σ coincidence site lattice(CSL) boundaries reaches 79.4% in the sample processed with 5% cold rolling and annealing at 1423 K for 72 h;there is an increase of 32.1% compared with the solution-treated sample. After grain boundary character distribution optimization, IGC performance is noticeably improved. Only Σ3 boundaries in the special boundaries are resistant to IGC under the experimental condition. The size of grain cluster enlarges with increasing fraction of low ΣCSL boundaries, and the amount of Σ3 boundaries interrupting the random boundary network increases during growth of the clusters, which is the essential reason for the improvement of IGC resistance.
基金Item Sponsored by National Natural Science Foundation of China(50771036,51001030)
文摘The data obtained by bending tests for intergranular embrittlement after 45 h and 450 h exposure to Strauss solution have been reported for 304 stainless steel. The results show that an embrittlement peak appears at 650℃ for all samples quenched from 1260℃ and then sensitized for 150 h at 480, 565, 650, 730, 815 and 900℃ respectively. The temperature corresponding to the embrittlement peak is decreased to 565℃ when the sensitizing time is prolonged to 1 500 h. In this paper, these data are analyzed with an isothermal kinetic model of nonequilibrium grain boundary segregation, indicating that the embrittlement peak is related to the critical time for nonequilibrium grain boundary segregation of sulfur.
基金financially supported by the National Natural Science Foundation of China(Nos.51601011,51571013 and 51971019)the Beijing Laboratory of Metallic Materials and Processing for Modern Transportation,China。
文摘Heat treatment is an effective method to improve the intergranular corrosion resistance of the sensitized Al–Mg alloy due to dissolution of the grain boundary precipitates above the solvus temperature ofβ-phase.The grain boundary precipitates will grow and coarsening below the solvus temperature.In this study,the in-situ intergranular corrosion performance regeneration of the sensitized Al–Mg alloy can be realized by low-density electro-pulsing treatment below the solvus temperature ofβ-phase.Our findings show that the dissolution of grain boundary precipitates by electro-pulsing treatment is accelerated at relatively low temperature in comparison to traditional heat treatment.The athermal effect produced by the interaction between atoms and electrons on the dissolution of grain boundary precipitates is the main reason for the improved corrosion resistance below the solvus temperature ofβ-phase.
文摘With Nb-Ti-stabilized 430 ferritic stainless steel(NTS430FSS) and SUS 430 ferritic stainless steel(SUS430FSS) as experimental materials, the influence of precipitation on intergranular corrosion resistance was investigated. A series of aging treatment were carried out. The free-exposure corrosion test and double loop electrochemical potentiokinetic reactivation(DL-EPR) test with a scan rate of 1.67 m V/s at 26 °C were applied to evaluate the intergranular corrosion(IGC) resistance. Metallographic observation, scanning electron microscope(SEM), transmission electron microscope(TEM) with energy dispersive spectroscopy(EDS) and X-ray diffraction(XRD) analysis were conducted. The results show that IGC occurred in SUS430 FSS aged above 700 °C, while it occurred in NTS430 FSS as the temperature was improved to 1 050 °C. The critical degree of sensitization Ir/Ia reaches 0.305 in SUS430 FSS, which is higher than that of NTS430 FSS, i.e. 0.010, aged at 950 °C for 2 h. The TEM, EDS and XRD results show that a large amount of Cr23C6 precipitates with size of 60 nm×22 nm are located at the SUS430 FSS grain boundaries as chains. With the addition of Nb and Ti and reduction of C, the amount of precipitates reduces significantly in NTS430 FSS. A majority of Cr23C6 were replaced by Ti C and Nb C. Only a small amount of spherical Ti C(R=186 nm) and square Ti N(312 nm×192 nm) with Nb and Cr adsorbed are left along grain boundaries. Due to the dual stabilization of Nb and Ti, the precipitation of Cr23C6 is restrained, the chromium depleted region is avoided and accordingly the resistance to the intergranular corrosion is improved.
基金financially supported by the National Natural Science Foundation of China (Nos. 51501041, 51131008 and 51371053)China Postdoctoral Science Foundation (No. 2013M541463)+1 种基金National Key Technology R&D Program (No. 2012BAE04B00)Doctoral Fund of Ministry of Education of China (No. 20120071110013)
文摘The intergranular corrosion (IGC) character of tin-added B316LX and the influence of tin addition on IGC susceptibility were investigated by DL-EPR, oxalic acid etch test and transmission electron microscopy. IGC susceptibility of B316LX is mainly caused by the precipitation of M23C6 carbide and intermetallic Laves phase. DL-EPR test is unsuitable to evaluate the IGC susceptibility of B316LX with long-time sensitization, because more carbides and inter- metallic phases are formed at grain boundaries and inside the grains, which induce more severe IGC and pits attacks. Tin addition increases the IGC susceptibility, maybe due to diffusion of tin toward grain boundaries.
基金financially supported by the National Nature Science Foundations of China (Nos.51271012 and 51671013)。
文摘2024 aluminum alloys were consolidated by using spark plasma sintering(SPS) method,and then heat treated by solid solution treatment(SST) and aging treatment(AT) procedures.The average grain size of bulk samples sintered with 5,20 and 50 μm powders was 3.72,4.73 and 8.11 μm,respectively.The difference between the average grain size and original powder size was attributed to the recrystallization during short sintering process.The number of the inclusion phases in these samples decreased after SST and increased after subsequent AT.Besides,it was observed that intergranular corrosion(IGC) cracks initiated from stable pits due to the electrochemical inhomogeneity between the intermetallic particles(IMPs) and the aluminum matrix(176.02,110.83 and 164.80 mV for as-SPS,as-SST and as-AT samples,respectively).Besides,the cracks would propagate along the grain boundaries(GBs) and bypass the IMPs at GBs during propagation.It was revealed that the sample after SST presented the best IGC resistance,and this was ascribed to the reduce of IMPs,both in size and number.
基金financially supported by the National Natural Science Foundation of China (No.51171154)
文摘The effects of shot peening(SP) and plasma electrolytic oxidation(PEO) on the intergranular corrosion behavior of the novel high strength aluminum alloy 7A85(AA 7A85) were investigated by electrochemical polarization and electrochemical impedance tests.The intergranular corrosion mechanism of SP,PEO and PEO combined with sealingtreated AA 7A85 was studied by the metallographic analysis,residual stress testing,X-ray diffractometer analysis and scanning electron microscopy.The results show that AA 7A85-T7452 is very sensitive to intergranular corrosion.SP would significantly improve its intergranular corrosion resistance.This is attributed to the combination action of residual compressive stress and grain refinement.PEO would reduce the largest corrosion depth by 41.6%.Moreover,PEO without sealing did not eliminate the intergranular corrosion due to the existence of the micropores and microcracks in the oxide coating.However,PEO combined with the SiO2sol–gel sealing treatment could effectively protect the AA 7A85-T7452 from intergranular corrosion because of the good corrosion resistance and barrier function of the sealed coating.
基金the financial support by National Key Research and Development Project(Grand No.2020YFC1107202)Guangdong Basic and Applied Basic Research Foundation(Grand No.2020A1515110754)+3 种基金MOE Key Lab of Disaster Forest and Control in Engineering,Jinan University(Grand No.20200904008)Educational Commission of Guangdong Province(Grand No.2020KTSCX012)the Fundamental Research Funds for Central Universities(Grand No.21620342)the support from National Natural Science Foundation of China,NSFC(Grand No.51775556)。
文摘Additive manufacturing(AM)of Mg alloys has become a promising strategy for producing complex structures,but the corrosion performance of AM Mg components remains unexploited.In this study,wire and arc additive manufacturing(WAAM)was employed to produce single AZ31 layer.The results revealed that the WAAM AZ31 was characterized by significant grain refinement with non-textured crystallographic orientation,similar phase composition and stabilized corrosion performance comparing to the cast AZ31.These varied corrosion behaviors were principally ascribed to the size of grain,where cast AZ31 and WAAM AZ31 were featured by micro galvanic corrosion and intergranular corrosion,respectively.
文摘The A1-2.79Li-1.3Cu-0.7Mg-0.12Zr(8090) alloy has excellent resistance to intergranular and exfoliation corrosion as naturally aged, worst as peak aged and rather better as underaged than as overaged. The corrosion behaviour of the alloy is closely dependent on its microstructure. Under the peak aging condition, the coarse T_2 phase, which is continuously distributed along grain boundaries, has so low corrosion potential in comparison with the ma- trix, this makes the corrosion resistance of the alloy to be deteriorated by anodic dissolution along grain boundaries.
基金financially supported by the National Natural Science Foundation of China(No.51775353)the National Key Research and Development Program of China(No.2019YFB2006501)+2 种基金the Program for Natural Science Foundation of Liaoning Province(No.2021-BS-150)Science and Technology Program of Liaoning Provincial Department of Education(LJKZ0116)Hebei Key Laboratory of Dielectric and Electrolyte Functional Material,Northeastern University at Qinhuangdao(HKDEFM2021204)。
文摘Temperature has an important impact on the corrosion resistance of mold with cooling channels prepared by casting method.The effect of preheating temperature of the mold and the carbon fiber core on the roughness and corrosion resistance of U-shaped cooling channels made of Al-12Si alloy was examined in depth.The experimental results suggest that as the preheating temperature increased from 273 K to 573 K,the roughness of the inner wall of the cooling channel reduced from 96.6μm to 77.0μm.When the preheating temperature continued to increase to 723 K,the roughness increased to 85.3μm.The wetting between the Al melt and the carbon fiber will reduce micro bubbles and waves on the channel wall as the preheating temperature rises,thereby reducing the roughness.However,with the further increase of preheating temperature,it will increase the solidification time of the Al melt.At this time,the carbon fiber and Al melt will take more time to react,which increases the roughness of the channel wall to a certain extent.The results of exfoliation corrosion show that the larger roughness will aggravate exfoliation corrosion.The prolongation of high temperature reaction time between the carbon fiber and the Al melt will lead to the segregation of Si,which is easy to cause intergranular corrosion.Therefore,reasonable preheating temperature has an important impact on the roughness and corrosion resistance of U-shaped cooling channels.
文摘Intergranular stress corrosion crack susceptibility of austenite stainless steel was evaluated through threepoint bending test conducted in high temperature water. The experimental results showed that the frequent and efficient introduction of low energy coincidence site lattice boundaries through grain boundary engineering resulted in an apparent improvement of the intergranular stress corrosion crack resistance of austenite stainless steel.
基金the National HiTech R. & D. Program under grant No. 2001AA331050 Key Natural Science Foundation of Chongqing Science and Technology Commission under grant No. 200413A4002 Science & Technology Research Project of Chongqing Education Commission under grant No. KJ050604.
文摘The corrosion morphologies of aged magnesium alloy AZ80 were investigated by immersion corrosion tests, scanning electron microscopy (SEM), electrochemical measurement. The T5 heat treatment was carried out in a vacuum furnace, holding for 16 h at 177℃, and then cooling in air. The results showed intergranular corrosion (IGC) occurred as an aged AZ80 sample was immersed in 3.5 wt pct NaCI aqueous solution for 1 h and the narrow path attack progressed predominantly along the bulk β phase in the grain boundaries or took place in the eutectic areas. IGC was attributed to the network distribution of β phase along the grain boundaries, the depleted aluminium in the precipitation areas and the breakdown potential.
基金support of the State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University in Chinathe National Natural Science Foundation of China (Grant No.51004084)
文摘Variation and degradation of P-110 casing steel mechanical properties, due to sulfide stress cracking (SSC) in sour environments, was investigated using tensile and impact tests. These tests were carried out on specimens, which were pretreated under the following conditions for 168 hours: temperature, 60 ℃; pressure, 10 MPa; H2S partial pressure, 1 MPa and CO2 partial pressure, 1 MPa; preload stress, 80% of the yield strength (os); medium, simulated formation water. The reduction in tensile and impact strengths for P-110 casing specimens in corrosive environments were 28% and 54%, respectively. The surface morphology analysis indicated that surface damage and uniform plastic deformation occurred as a result of strain aging. Impact toughness of the casing decreased significantly and intergranular cracking occurred when specimens were maintained at a high stress level of 85% %.
基金financially supported by the Program for Liaoning Innovative Research Team in University(No.LT20120008)the Fundamental Research Funds for the Central Universities(No.N100402015)the General Scientifc Research Project of the Department of Education of Liaoning Province,China(No.L2012077)
文摘The effect of chloride ion concentration, pH value, and grain size on the pitting corrosion resistance of a new ferritic stainless steel with 15wt% Cr was investigated using the anodic polarization method. The semiconducting properties of passive films with different chloride ion concentrations were performed using capacitance measurement and Mott-Schottky analysis methods. The aging precipitation and intergranular corrosion behavior were evaluated at 400- 900℃. It is found that the pitting potential decreases when the grain size increases. With the increase in chloride ion concentration, the doping density and the flat-bland potential increase but the thickness of the space charge layer decreases. The pitting corrosion resistance increases rapidly with the decrease in pH value. Precipitants is identified as Nb(C,N) and NbC, rather than Cr-carbide. The intergranular corrosion is attributed to the synergistic effects of Nb(C,N) and NbC precipitates and Cr segregation adjacent to the precipitates.
文摘The grain boundary structure of Cu alloy was observed and the characteristic of the boundaries was studied,including 70∶30 cupronickel and 70∶30 brass. The results show that in the case of the 70∶30 cupronickel thin platelets with nickel and iron enrichment in it precipitate intergranular so that the alloy was sensitive to seawater corrosion. In the case of 70∶30 brass the situation of grain boundary segregation of different inclusions made the corrosion resistance of the alloy even worse. All of those were discovered through the corrosion behavior of the two different copper alloys served in various environments. The experimental methods used here were, scanning electron microscopy(SEM), transmission electron microscopy(TEM) and energy dispersive of X ray(EDX). The intergranular corrosion morphologies of those copper alloys served in engineering or exposed to seawater for a long term were given.