The impact fretting wear has largely occurred at nuclear power device induced by the flow-induced vibra- tion, and it will take potential hazards to the service of the equipment. However, the present study focuses on ...The impact fretting wear has largely occurred at nuclear power device induced by the flow-induced vibra- tion, and it will take potential hazards to the service of the equipment. However, the present study focuses on the tangential fretting wear of alloy 690 tubes. Research on impact fretting wear of alloy 690 tubes is limited and the related research is imminent. Therefore, impact fretting wear behavior of alloy 690 tubes against 304 stainless steels is investigated. Deionized water is used to simulate the flow environment of the equipment, and the dry envi- ronment is used for comparison. Varied analytical tech- niques are employed to characterize the wear and tribochemical behavior during impact fretting wear. Char- acterization results indicate that cracks occur at high impact load in both water and dry equipment; however, the water as a medium can significantly delay the cracking time. The crack propagation behavior shows a jagged shape in the water, but crack extended disorderly in dry equip- ment because the water changed the stress distribution and retarded the friction heat during the wear process. The SEM and XPS analysis shows that the main failure mechanisms of the tube under impact fretting are fatiguewear and friction oxidation. The effect of medium(water) on fretting wear is revealed, which plays a potential and promising role in the service of nuclear power device and other flow equipments.展开更多
The worn scars on Alloy 690 after the fretting corrosion testing in simulated pressurized water reactor(PWR)secondary water have been comprehensively analyzed by scanning transmission electron microscopy(STEM)and tran...The worn scars on Alloy 690 after the fretting corrosion testing in simulated pressurized water reactor(PWR)secondary water have been comprehensively analyzed by scanning transmission electron microscopy(STEM)and transmission Kikuchi diffraction(TKD).The high-quality characterization results experimentally show that the fretting wear accelerates the corrosion of Alloy 690 in two approaches.The first one is to break the integrity of the oxide scale by introducing cavities at the oxide grain boundaries.The second one is to alter the microstructure of the underneath matrix,forming a nano-grained matrix layer.The increased grain boundary density in this layer can accelerate the consumption of Cr in the near-surface matrix.The loss of oxide scale integrity and the accelerated Cr consumption are believed to contribute to the deteriorated corrosion resistance of Alloy 690 during the fretting corrosion process.展开更多
The oxidation behavior of alloy 690 exposed to high-temperature and high-pressure steam and water at 280℃ for 1 h was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray ph...The oxidation behavior of alloy 690 exposed to high-temperature and high-pressure steam and water at 280℃ for 1 h was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). In high-temperature and high-pressure steam, the oxide film is composed of an outermost Ni-rich hydroxides layer, an intermediate layer of hydroxides and oxides enriched in Cr, an inner oxide layer. The film formed in high-temperature water is similar to that in steam, except for missing the Ni-rich hydroxides layer. Samples with different surface finishes (electropolished, mechanically polished, ground, and as-received) were prepared for comparison. A general increase of the oxide thickness with the degree of surface roughness is observed. The equivalent oxide thicknesses lie in the range of 100-200 nm for the as-received samples, 150-250 nm for the samples ground to 400# and 10-20 nm for the samples ground to 1500#, mechanically polished, and electropolished.展开更多
Alloy 690TT samples with four kinds of surface states were prepared: 1) ground to 400 grit; 2) ground to 1500 grit; 3) mechanically polished (MP) and 4) electro-polished (EP). The surface morphologies and the...Alloy 690TT samples with four kinds of surface states were prepared: 1) ground to 400 grit; 2) ground to 1500 grit; 3) mechanically polished (MP) and 4) electro-polished (EP). The surface morphologies and the surface skin layers' microstructures of these samples were characterized systematically using various methods and the effects of surface states on the oxidation behaviours of Alloy 690TT were also discussed. The results showed that surface roughness and micro-hardness decreased gradually from the ground to EP surfaces. The grains in the near-surface layers of the ground and MP surfaces had been refined and the residual strains were also very high. The dislocations on the ground surfaces were mainly parallel dislocation lines. The thickness of the superficial cold-worked layers decreased gradually from the ground surfaces to polished surfaces. The oxide morphologies and oxidation rate depended greatly on the surface states of samples. Cold-working by grinding treatments could benefit the outward diffusion of metallic atoms and the nucleation of surface oxides and then accelerate the growth of surface oxide films.展开更多
Oxidation of Alloy 690 TT samples either manually ground to 400 and 1500 grit, mechanically polished, or electropolished was performed in a solution of 1500 10 6B and 2.3 10 6Li with 2.5 10 6dissolved H2, at 325℃ and...Oxidation of Alloy 690 TT samples either manually ground to 400 and 1500 grit, mechanically polished, or electropolished was performed in a solution of 1500 10 6B and 2.3 10 6Li with 2.5 10 6dissolved H2, at 325℃ and 15.6 MPa for 60 days. The oxide films grown on samples with different surface states were analyzed using various techniques. Results show that a triple-layered structure was formed after immersion: an outermost layer with large scattered oxide particles rich in Fe and Ni, an intermediate layer with small compact oxide particles rich in Cr and Fe for the ground surfaces and loose needle-like oxides rich in Ni for the polished surfaces, and an inner layer with continuous Cr-rich oxides. The surface state was found to affect not only the surface morphology, but also the corrosion rate. Grinding accelerated the growth of protective oxide films such that the ground samples showed a lower oxidation rate than the polished ones.Samples of ground Alloy 690 TT showed superior resistance to intergranular attack(IGA).展开更多
The effects of surface state and applied stress on the stress corrosion cracking (SCC) behaviors of thermally treated (TT) Alloy 690 in 10 wt% NaOH solution with 100 mg/L litharge at 330 ℃ were investigated using...The effects of surface state and applied stress on the stress corrosion cracking (SCC) behaviors of thermally treated (TT) Alloy 690 in 10 wt% NaOH solution with 100 mg/L litharge at 330 ℃ were investigated using C-ring samples with four kinds of surface states and two different stress levels. Sample outer surfaces of the first three kinds were ground to 400 grit (ground), shot-peened (SP) and electro-polished (EP) and the last one was used as the as-received state. Two samples of every kind were stressed to 100% and 200% yield stress of Alloy 690TT, respectively. The results showed that the oxide film consisted of three layers whereas continuous layer rich in Cr was not found. The poor adhesive ability indicated that the oxide film could not protect the matrix from further corrosion. Lead was found in the oxide film and the oxides at the crack paths and accelerated the dissolution of thermodynamically unstable Cr in these locations and also in the matrix. The crack initiation and propagation on Alloy 690TT were effectively retarded by SP and EP treatments but were enhanced by grinding treatment, compared with the cracks on the as-received surface. The cracking severity was also enhanced by increasing the externally applied stress. The accelerated dissolution of Cr and the local tensile stress concentration in the near-surface layer caused by cold-working and higher applied stress reduced the SCC-resistance of Alloy 690TT in the studied solution.展开更多
The segregation and precipitation behavior of Alloy 690 containing 0.001-0.11 wt% nitrogen during isothermal solidification at 1370 and 1355 ℃ have been investigated using optical microscopy (OM),electron probe mic...The segregation and precipitation behavior of Alloy 690 containing 0.001-0.11 wt% nitrogen during isothermal solidification at 1370 and 1355 ℃ have been investigated using optical microscopy (OM),electron probe microanalysis (EPMA) and transmission electron microscopy (TEM).The results indicate that the volume fraction of TiN-type nitride formed during isothermal solidification increases with the nitrogen content of Alloy 690.Segregation of Ti and Cr exists in samples solidified at 1370 and 1355℃.The Ti content in the residual liquid markedly decreases and the concentration of Cr increases when the nitrogen content of Alloy 690 increases.Furthermore,N and S also show segregation to some extent in the residual liquids at 1355℃.Accompanying by the segregation of Cr,Ti,C,N and S,sulfides and chromium nitrides form.In a low nitrogen content Alloy 690,sulfur segregates and precipitates in the form of Ti 4 C 2 S 2 and (Cr,Ti)S,but in the form of (Cr,Ti)S or CrS in a high nitrogen content Alloy 690.(Cr,Ti)N-type nitrides with an fcc crystal structure have been identified in a sample with 0.11 wt% nitrogen.展开更多
Alloy 690TT tube samples with different scratch depths were repaired by grinding treatments using abra-sive papers of two different particle sizes.The microstructure and stress corrosion cracking(SCC)behavior were stu...Alloy 690TT tube samples with different scratch depths were repaired by grinding treatments using abra-sive papers of two different particle sizes.The microstructure and stress corrosion cracking(SCC)behavior were studied in detail.During grinding,the plastic accumulation zone vulnerable to SCC was removed.Meanwhile,some residual slip steps remained in the scratched area.Corrosion tests lasting 1000,2000,3000,and 4000 h show that the sensitivity and risk of SCC in the scratched area are decreased by grind-ing.Treatment using abrasive particles of a smaller size is more effective.Nevertheless,deep scratches remained hazardous even after the grinding.展开更多
The precipitation and evolution of secondary nitrides (S-nitrides) in the Alloy 690 electro-slag remelted (ESR) structure were investigated. Experimental results indicate that S-nitrides precipitated in the interd...The precipitation and evolution of secondary nitrides (S-nitrides) in the Alloy 690 electro-slag remelted (ESR) structure were investigated. Experimental results indicate that S-nitrides precipitated in the interdendritic region of the ESR structure at temperatures higher than 1100 ℃. S-nitrides could spread throughout the entire interdendritic area after sufficient exposure, and they were more numerous and much finer than primary nitrides. Furthermore, after studying the evolution of S-nitride particles at 1100, 1200 and 1300℃, it was determined that the precipitation of S-nitrides was controlled by the diffusion of nitrogen. In addition, by investigating the elemental segregation of ESR structure and calculating critical Ti concentrations, S-nitride precipitation was found to be thermodynamically inevitable in the Alloy 690 ESR structure.展开更多
Effect of ethanolamine (ETA) on Alloy 690 in simulated pressurized water reactor (PWR) secondary cooling water was studied by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, atomic fo...Effect of ethanolamine (ETA) on Alloy 690 in simulated pressurized water reactor (PWR) secondary cooling water was studied by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, atomic force microscopy (AFM), Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), X-ray photoelectron spectrometer (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). The results show that moderate addition of ETA can enhance the corrosion resistance of Alloy 690 in high-temperature pressurized water and the optimum additive value is 2 mg/L. The addition of ETA contributes to the formation of oxide rather than hydroxide in the film on the surface of Alloy 690. The corrosion resistance of Alloy 690 at 320 ℃ with the addition of ETA is better than that at 280 ℃.展开更多
The corrosion behaviors of alloy 690 in 1 wt pct sodium hydroxide aqueous solutions with and without PbO were characterized by electrochemical measurements, including potentiodynamic polarization, electrochemical impe...The corrosion behaviors of alloy 690 in 1 wt pct sodium hydroxide aqueous solutions with and without PbO were characterized by electrochemical measurements, including potentiodynamic polarization, electrochemical impedance spectroscopy and Mott-Schottky measurement. The results reveal that there is a great difference between the corrosion behaviors of alloy 690 in the two tested solutions. The corrosion current density in PbO-containing solution is higher than that in the solution without PbO, which may be attributed to the anodic dissolution of metallic lead deposited at the early stage of polarization. The electrochemical impedance of the specimen in PbO-free solution is higher than that in the solution containing PbO. The slope of the Mott-Schottky curve in Pb-containing solution decreases notably compared with that in the Pb-free solution, which can be interpreted by the chromium depletion in the duplex structure of passive films.展开更多
The surface oxidation and subsurface microstructure evolution of Alloy 690 TT can occur during partial slip fretting corrosion in high-temperature pure water.Detailed characterization methods such as laser scanning co...The surface oxidation and subsurface microstructure evolution of Alloy 690 TT can occur during partial slip fretting corrosion in high-temperature pure water.Detailed characterization methods such as laser scanning confocal microscopy,scanning electron microscopy,electron probe micro-analyzer,and transmission electron microscopy were used to reveal the related mechanism.The results showed that Cr_(2)O_(3) oxides together with a small number of spinel oxides were formed in sticking region since a small quantity of high-temperature water could pass through the gaps between the asperities to oxidize the materials.Widespread distribution of oxides in microslip region consisted of(Ni,Fe)Cr_(2)O_(4),because Ni^(2+)and Fe^(2+) ions could react with Cr_(2)O_(3) to generate a small amount of non-stoichiometric spinel oxides.The oxides around micropitting in microslip region consisted of double-layer structure.The outermost layer contained(Fe,Cr)-rich oxides due to the effect of fretting leading to mechanical mixing between Cr_(2)O_(3) and(Ni,Fe)(Fe,Cr)_(2)O_(4).The inner layer consisted of(Fe,Ni)-rich oxides owing to the consumption of Cr_(2)O_(3) by the reaction with Ni^(2+)and Fe^(2+) ions.The reciprocating motion of oxide particles in microslip region resulted in the stress-strain supporting the recrystallization for the formation and development of a tribologically transformed structure in subsurface and plowing effect by fretting in surface.展开更多
The repassivation behavior of Alloy 690 T T in simulated primary water at different temperatures was investigated by the rapid scratching electrode technique together with electrochemical measurements.The results show...The repassivation behavior of Alloy 690 T T in simulated primary water at different temperatures was investigated by the rapid scratching electrode technique together with electrochemical measurements.The results showed that the repassivation process had three stages: the initial stage conformed to the place exchange model, the final stage conformed to the high field ion conduction model and in between there was a transition stage. At the initial stage, when the repassivation process of alloys was controlled by the place exchange model, anodic dissolution of substrate was dominated;after the film coverage rate was more than 0.99, the repassivation process of alloys was controlled by high field ion conduction model. Increasing the temperature resulted in a reduction of the repassivation rate and protectiveness of the passive film. The correlations among several mechanisms describing the repassivation behavior of alloys were discussed.展开更多
In pressurized water reactor,fretting corrosion has become the main reason for the failure of 690TT heat exchanger tubes.The effect of temperature on the fretting corrosion behavior between 690TT tube and 405 stainles...In pressurized water reactor,fretting corrosion has become the main reason for the failure of 690TT heat exchanger tubes.The effect of temperature on the fretting corrosion behavior between 690TT tube and 405 stainless steel(SS)bar has been studied during 106 fretting cycles.The overall average coefficient of friction(COF)values descends with an increase in test temperature,while the width of worn scar becomes wider.The severest fretting corrosion happens when the test temperature is at 100℃.The wear mechanism differs at different test temperatures,from adhesive wear at room temperature to abrasive wear and delamination at 100℃,to abrasive wear at 200℃.Deformation slips,high residual strain concentration,and micro-cracks are found which are disadvantageous for the further service performance of the tubes.展开更多
The oxides formed on the surface of the alloy 690 in hydrogenated supercritical water at 400℃ for 1000 h were investigated using scanning electron microscopy,transmission electron microscopy,scanning transmission ele...The oxides formed on the surface of the alloy 690 in hydrogenated supercritical water at 400℃ for 1000 h were investigated using scanning electron microscopy,transmission electron microscopy,scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy.The oxides on me surface of the alloy 690 exhibited multi-layer structure:an outer layer consisted of granular crystallites(NiO and NiFe_2O_4) and a compact inner layer(spinel and Cr_2O_3).Chemical analysis indicated that the outer layer was enriched in nickel but depleted in chromium,whereas the inner layer was enriched in chromium and iron but depleted in nickel.The inner layer was also characterized as layered structure by Fe-rich spinel on top of continuous Cr_2O_3 layer.Besides,Cr_2O_3 nodules were readily observed at the oxides/alloy interface.展开更多
The finite element simulation software SYSWELD is used to numerically simulate the temperature field,residual stress field,and welding deformation of Q690D thick plate multi-layer and multi-pass welding under differen...The finite element simulation software SYSWELD is used to numerically simulate the temperature field,residual stress field,and welding deformation of Q690D thick plate multi-layer and multi-pass welding under different welding heat input and groove angles.The simulation results show that as the welding heat input increases,the peak temperature during the welding process is higher,and the residual stress increases,they are all between 330–340 MPa,and the residual stress is concentrated in the area near the weld.The hole-drilling method is used to measure the actual welding residual stress,and the measured data is in good agreement with the simulated value.The type of post-welding deformation is angular deformation,and as the welding heat input increases,the maximum deformation also increases.It shows smaller residual stress and deformation when the groove angle is 40°under the same heat input.In engineering applications,under the premise of guaranteeing welding quality,smaller heat input and 40°groove angle should be used.展开更多
Alloy 690 is a typical Ni-Cr-Fe alloy, which is widely used in nuclear power application. However, filler metal 52M (FM-52M) used in alloy 690 weldment is fimnd to be susceptible to ductility-dip cracking (DDC) , ...Alloy 690 is a typical Ni-Cr-Fe alloy, which is widely used in nuclear power application. However, filler metal 52M (FM-52M) used in alloy 690 weldment is fimnd to be susceptible to ductility-dip cracking (DDC) , which seriously affects safety and life extension in nuclear application. In this paper, the DDC susceptibility of FM-52M in welding process was investigated using finite element method. At first, Gleeble-based testing technique, strain to fracture ( STF ) test, was used to evaluate the DDC susceptibility and the formation mechanism of DDC was explained. The result shows that FM-52M is most susceptible at 1 050 ℃ and grain boundary weakness at high temperature induces crack initiation. Afterwards, in order to evaluate the DDC susceptibility under complex stress state, tube-plate welding model was built by means of ABAQUS software. Susceptible regions could be confirmed associated with STF results. The simulation result shows that HAZ is the most susceptible region in FM-52M joint.展开更多
基金Supported by National Natural Science Foundation of China(Grant Nos.51375407,U1530136,51627806)Shanghai Municipal Science and Technology Talent Program of China(Grant No.14R21421500)Young Scientific Innovation Team of Science and Technology of Sichuan(Grant No.2017TD0017)
文摘The impact fretting wear has largely occurred at nuclear power device induced by the flow-induced vibra- tion, and it will take potential hazards to the service of the equipment. However, the present study focuses on the tangential fretting wear of alloy 690 tubes. Research on impact fretting wear of alloy 690 tubes is limited and the related research is imminent. Therefore, impact fretting wear behavior of alloy 690 tubes against 304 stainless steels is investigated. Deionized water is used to simulate the flow environment of the equipment, and the dry envi- ronment is used for comparison. Varied analytical tech- niques are employed to characterize the wear and tribochemical behavior during impact fretting wear. Char- acterization results indicate that cracks occur at high impact load in both water and dry equipment; however, the water as a medium can significantly delay the cracking time. The crack propagation behavior shows a jagged shape in the water, but crack extended disorderly in dry equip- ment because the water changed the stress distribution and retarded the friction heat during the wear process. The SEM and XPS analysis shows that the main failure mechanisms of the tube under impact fretting are fatiguewear and friction oxidation. The effect of medium(water) on fretting wear is revealed, which plays a potential and promising role in the service of nuclear power device and other flow equipments.
基金Shanghai Pujiang Program(No.21PJ1406400)is acknowledged for funding this research.
文摘The worn scars on Alloy 690 after the fretting corrosion testing in simulated pressurized water reactor(PWR)secondary water have been comprehensively analyzed by scanning transmission electron microscopy(STEM)and transmission Kikuchi diffraction(TKD).The high-quality characterization results experimentally show that the fretting wear accelerates the corrosion of Alloy 690 in two approaches.The first one is to break the integrity of the oxide scale by introducing cavities at the oxide grain boundaries.The second one is to alter the microstructure of the underneath matrix,forming a nano-grained matrix layer.The increased grain boundary density in this layer can accelerate the consumption of Cr in the near-surface matrix.The loss of oxide scale integrity and the accelerated Cr consumption are believed to contribute to the deteriorated corrosion resistance of Alloy 690 during the fretting corrosion process.
基金supported by the Special Funds for the Major State Basic Research Projects(G2011CB610502)the National Natural Science Foundation of China (No.51025104)
文摘The oxidation behavior of alloy 690 exposed to high-temperature and high-pressure steam and water at 280℃ for 1 h was investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). In high-temperature and high-pressure steam, the oxide film is composed of an outermost Ni-rich hydroxides layer, an intermediate layer of hydroxides and oxides enriched in Cr, an inner oxide layer. The film formed in high-temperature water is similar to that in steam, except for missing the Ni-rich hydroxides layer. Samples with different surface finishes (electropolished, mechanically polished, ground, and as-received) were prepared for comparison. A general increase of the oxide thickness with the degree of surface roughness is observed. The equivalent oxide thicknesses lie in the range of 100-200 nm for the as-received samples, 150-250 nm for the samples ground to 400# and 10-20 nm for the samples ground to 1500#, mechanically polished, and electropolished.
基金supported by the Special Funds for the Major State Basic ResearchProjects under grant No. G2011CB610502the National Natural Science Foundation of China under grant No. 51025104.
文摘Alloy 690TT samples with four kinds of surface states were prepared: 1) ground to 400 grit; 2) ground to 1500 grit; 3) mechanically polished (MP) and 4) electro-polished (EP). The surface morphologies and the surface skin layers' microstructures of these samples were characterized systematically using various methods and the effects of surface states on the oxidation behaviours of Alloy 690TT were also discussed. The results showed that surface roughness and micro-hardness decreased gradually from the ground to EP surfaces. The grains in the near-surface layers of the ground and MP surfaces had been refined and the residual strains were also very high. The dislocations on the ground surfaces were mainly parallel dislocation lines. The thickness of the superficial cold-worked layers decreased gradually from the ground surfaces to polished surfaces. The oxide morphologies and oxidation rate depended greatly on the surface states of samples. Cold-working by grinding treatments could benefit the outward diffusion of metallic atoms and the nucleation of surface oxides and then accelerate the growth of surface oxide films.
基金supported by the Special Funds for the National Basic Research Program of China (No. 2011CB610502)the National Science and Technology Major Project (No. 2011ZX06004-009)the National Natural Science Foundation of China (No. 51025104)
文摘Oxidation of Alloy 690 TT samples either manually ground to 400 and 1500 grit, mechanically polished, or electropolished was performed in a solution of 1500 10 6B and 2.3 10 6Li with 2.5 10 6dissolved H2, at 325℃ and 15.6 MPa for 60 days. The oxide films grown on samples with different surface states were analyzed using various techniques. Results show that a triple-layered structure was formed after immersion: an outermost layer with large scattered oxide particles rich in Fe and Ni, an intermediate layer with small compact oxide particles rich in Cr and Fe for the ground surfaces and loose needle-like oxides rich in Ni for the polished surfaces, and an inner layer with continuous Cr-rich oxides. The surface state was found to affect not only the surface morphology, but also the corrosion rate. Grinding accelerated the growth of protective oxide films such that the ground samples showed a lower oxidation rate than the polished ones.Samples of ground Alloy 690 TT showed superior resistance to intergranular attack(IGA).
基金supported by the National Science and Technology Major Project(No. 20112x06004–009)the National Natural Science Foundation of China (No. 51025104)
文摘The effects of surface state and applied stress on the stress corrosion cracking (SCC) behaviors of thermally treated (TT) Alloy 690 in 10 wt% NaOH solution with 100 mg/L litharge at 330 ℃ were investigated using C-ring samples with four kinds of surface states and two different stress levels. Sample outer surfaces of the first three kinds were ground to 400 grit (ground), shot-peened (SP) and electro-polished (EP) and the last one was used as the as-received state. Two samples of every kind were stressed to 100% and 200% yield stress of Alloy 690TT, respectively. The results showed that the oxide film consisted of three layers whereas continuous layer rich in Cr was not found. The poor adhesive ability indicated that the oxide film could not protect the matrix from further corrosion. Lead was found in the oxide film and the oxides at the crack paths and accelerated the dissolution of thermodynamically unstable Cr in these locations and also in the matrix. The crack initiation and propagation on Alloy 690TT were effectively retarded by SP and EP treatments but were enhanced by grinding treatment, compared with the cracks on the as-received surface. The cracking severity was also enhanced by increasing the externally applied stress. The accelerated dissolution of Cr and the local tensile stress concentration in the near-surface layer caused by cold-working and higher applied stress reduced the SCC-resistance of Alloy 690TT in the studied solution.
基金supported by the National Natural Science Foundation of China (No. 50901076)
文摘The segregation and precipitation behavior of Alloy 690 containing 0.001-0.11 wt% nitrogen during isothermal solidification at 1370 and 1355 ℃ have been investigated using optical microscopy (OM),electron probe microanalysis (EPMA) and transmission electron microscopy (TEM).The results indicate that the volume fraction of TiN-type nitride formed during isothermal solidification increases with the nitrogen content of Alloy 690.Segregation of Ti and Cr exists in samples solidified at 1370 and 1355℃.The Ti content in the residual liquid markedly decreases and the concentration of Cr increases when the nitrogen content of Alloy 690 increases.Furthermore,N and S also show segregation to some extent in the residual liquids at 1355℃.Accompanying by the segregation of Cr,Ti,C,N and S,sulfides and chromium nitrides form.In a low nitrogen content Alloy 690,sulfur segregates and precipitates in the form of Ti 4 C 2 S 2 and (Cr,Ti)S,but in the form of (Cr,Ti)S or CrS in a high nitrogen content Alloy 690.(Cr,Ti)N-type nitrides with an fcc crystal structure have been identified in a sample with 0.11 wt% nitrogen.
基金jointly supported by National Natural Science Foundation of China (No. 51771211)National Key R&D Program(2019YFB1900904)the open-ended fund of the CAS Key laboratory of Nuclear Materials and Safety Assessment (Institute of Metal Research, Chinese Academy of Sciences, China)(No.2021NMSAKF01)
文摘Alloy 690TT tube samples with different scratch depths were repaired by grinding treatments using abra-sive papers of two different particle sizes.The microstructure and stress corrosion cracking(SCC)behavior were studied in detail.During grinding,the plastic accumulation zone vulnerable to SCC was removed.Meanwhile,some residual slip steps remained in the scratched area.Corrosion tests lasting 1000,2000,3000,and 4000 h show that the sensitivity and risk of SCC in the scratched area are decreased by grind-ing.Treatment using abrasive particles of a smaller size is more effective.Nevertheless,deep scratches remained hazardous even after the grinding.
基金supported by the Chinese Academy of Sciences Innovation Foundation under Grant No. CXJJ14-M44
文摘The precipitation and evolution of secondary nitrides (S-nitrides) in the Alloy 690 electro-slag remelted (ESR) structure were investigated. Experimental results indicate that S-nitrides precipitated in the interdendritic region of the ESR structure at temperatures higher than 1100 ℃. S-nitrides could spread throughout the entire interdendritic area after sufficient exposure, and they were more numerous and much finer than primary nitrides. Furthermore, after studying the evolution of S-nitride particles at 1100, 1200 and 1300℃, it was determined that the precipitation of S-nitrides was controlled by the diffusion of nitrogen. In addition, by investigating the elemental segregation of ESR structure and calculating critical Ti concentrations, S-nitride precipitation was found to be thermodynamically inevitable in the Alloy 690 ESR structure.
基金supported by the National Key Science and Technology Project of China (No. 2011ZX06004-017)the National Natural Science Foundation of China (No. 51025104)
文摘Effect of ethanolamine (ETA) on Alloy 690 in simulated pressurized water reactor (PWR) secondary cooling water was studied by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, atomic force microscopy (AFM), Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), X-ray photoelectron spectrometer (XPS) and time of flight secondary ion mass spectrometry (ToF-SIMS). The results show that moderate addition of ETA can enhance the corrosion resistance of Alloy 690 in high-temperature pressurized water and the optimum additive value is 2 mg/L. The addition of ETA contributes to the formation of oxide rather than hydroxide in the film on the surface of Alloy 690. The corrosion resistance of Alloy 690 at 320 ℃ with the addition of ETA is better than that at 280 ℃.
基金supported by the National Natural Science Foundation of China(No.50871020)National Science and Technology Infrastructure Platforms Construction Projects (No.2005DKA10400)
文摘The corrosion behaviors of alloy 690 in 1 wt pct sodium hydroxide aqueous solutions with and without PbO were characterized by electrochemical measurements, including potentiodynamic polarization, electrochemical impedance spectroscopy and Mott-Schottky measurement. The results reveal that there is a great difference between the corrosion behaviors of alloy 690 in the two tested solutions. The corrosion current density in PbO-containing solution is higher than that in the solution without PbO, which may be attributed to the anodic dissolution of metallic lead deposited at the early stage of polarization. The electrochemical impedance of the specimen in PbO-free solution is higher than that in the solution containing PbO. The slope of the Mott-Schottky curve in Pb-containing solution decreases notably compared with that in the Pb-free solution, which can be interpreted by the chromium depletion in the duplex structure of passive films.
基金financial supports of the Beijing Natural Science Foundation(Grant No.2194081)the Project funded by China Postdoctoral Science Foundation(Grant No.2018M641187)the Fundamental Research Funds for the Central Universities(Grant No.FRF-TP-18-047A1)。
文摘The surface oxidation and subsurface microstructure evolution of Alloy 690 TT can occur during partial slip fretting corrosion in high-temperature pure water.Detailed characterization methods such as laser scanning confocal microscopy,scanning electron microscopy,electron probe micro-analyzer,and transmission electron microscopy were used to reveal the related mechanism.The results showed that Cr_(2)O_(3) oxides together with a small number of spinel oxides were formed in sticking region since a small quantity of high-temperature water could pass through the gaps between the asperities to oxidize the materials.Widespread distribution of oxides in microslip region consisted of(Ni,Fe)Cr_(2)O_(4),because Ni^(2+)and Fe^(2+) ions could react with Cr_(2)O_(3) to generate a small amount of non-stoichiometric spinel oxides.The oxides around micropitting in microslip region consisted of double-layer structure.The outermost layer contained(Fe,Cr)-rich oxides due to the effect of fretting leading to mechanical mixing between Cr_(2)O_(3) and(Ni,Fe)(Fe,Cr)_(2)O_(4).The inner layer consisted of(Fe,Ni)-rich oxides owing to the consumption of Cr_(2)O_(3) by the reaction with Ni^(2+)and Fe^(2+) ions.The reciprocating motion of oxide particles in microslip region resulted in the stress-strain supporting the recrystallization for the formation and development of a tribologically transformed structure in subsurface and plowing effect by fretting in surface.
基金financially supported by the National Natural Science Foundation of China (No. 51771211)the Key Research Program of Frontier Sciences+2 种基金the Chinese Academy of Sciences(No. QYZDY-SSWJSC012)the Key Program of the Chinese Academy of Sciences (No. ZDRW-CN-2017-1)the National Science and Technology Major Project (No. 2015ZX06002005)。
文摘The repassivation behavior of Alloy 690 T T in simulated primary water at different temperatures was investigated by the rapid scratching electrode technique together with electrochemical measurements.The results showed that the repassivation process had three stages: the initial stage conformed to the place exchange model, the final stage conformed to the high field ion conduction model and in between there was a transition stage. At the initial stage, when the repassivation process of alloys was controlled by the place exchange model, anodic dissolution of substrate was dominated;after the film coverage rate was more than 0.99, the repassivation process of alloys was controlled by high field ion conduction model. Increasing the temperature resulted in a reduction of the repassivation rate and protectiveness of the passive film. The correlations among several mechanisms describing the repassivation behavior of alloys were discussed.
基金supported by the National Natural Science Foundation of China (No.51771211)the Large-scale advanced PWR major projects (No.2017ZX06002006)+1 种基金the Liaoning Provincial Natural Science Foundation of China (No.20180540076)the open-ended fund of the CAS Key laboratory of Nuclear Materials and Safety Assessment (Institute of Metal Research,Chinese Academy of Sciences,China) (Nos.2019NMSAKF02 and 2017NMSAKF04)
文摘In pressurized water reactor,fretting corrosion has become the main reason for the failure of 690TT heat exchanger tubes.The effect of temperature on the fretting corrosion behavior between 690TT tube and 405 stainless steel(SS)bar has been studied during 106 fretting cycles.The overall average coefficient of friction(COF)values descends with an increase in test temperature,while the width of worn scar becomes wider.The severest fretting corrosion happens when the test temperature is at 100℃.The wear mechanism differs at different test temperatures,from adhesive wear at room temperature to abrasive wear and delamination at 100℃,to abrasive wear at 200℃.Deformation slips,high residual strain concentration,and micro-cracks are found which are disadvantageous for the further service performance of the tubes.
文摘The oxides formed on the surface of the alloy 690 in hydrogenated supercritical water at 400℃ for 1000 h were investigated using scanning electron microscopy,transmission electron microscopy,scanning transmission electron microscopy and energy-dispersive X-ray spectroscopy.The oxides on me surface of the alloy 690 exhibited multi-layer structure:an outer layer consisted of granular crystallites(NiO and NiFe_2O_4) and a compact inner layer(spinel and Cr_2O_3).Chemical analysis indicated that the outer layer was enriched in nickel but depleted in chromium,whereas the inner layer was enriched in chromium and iron but depleted in nickel.The inner layer was also characterized as layered structure by Fe-rich spinel on top of continuous Cr_2O_3 layer.Besides,Cr_2O_3 nodules were readily observed at the oxides/alloy interface.
文摘The finite element simulation software SYSWELD is used to numerically simulate the temperature field,residual stress field,and welding deformation of Q690D thick plate multi-layer and multi-pass welding under different welding heat input and groove angles.The simulation results show that as the welding heat input increases,the peak temperature during the welding process is higher,and the residual stress increases,they are all between 330–340 MPa,and the residual stress is concentrated in the area near the weld.The hole-drilling method is used to measure the actual welding residual stress,and the measured data is in good agreement with the simulated value.The type of post-welding deformation is angular deformation,and as the welding heat input increases,the maximum deformation also increases.It shows smaller residual stress and deformation when the groove angle is 40°under the same heat input.In engineering applications,under the premise of guaranteeing welding quality,smaller heat input and 40°groove angle should be used.
文摘Alloy 690 is a typical Ni-Cr-Fe alloy, which is widely used in nuclear power application. However, filler metal 52M (FM-52M) used in alloy 690 weldment is fimnd to be susceptible to ductility-dip cracking (DDC) , which seriously affects safety and life extension in nuclear application. In this paper, the DDC susceptibility of FM-52M in welding process was investigated using finite element method. At first, Gleeble-based testing technique, strain to fracture ( STF ) test, was used to evaluate the DDC susceptibility and the formation mechanism of DDC was explained. The result shows that FM-52M is most susceptible at 1 050 ℃ and grain boundary weakness at high temperature induces crack initiation. Afterwards, in order to evaluate the DDC susceptibility under complex stress state, tube-plate welding model was built by means of ABAQUS software. Susceptible regions could be confirmed associated with STF results. The simulation result shows that HAZ is the most susceptible region in FM-52M joint.