The influence of different cryogenic sequences on the rolling contact fatigue(RCF)life of M50-bearing steel has been studied.The results show that direct cryogenic treatment after quenching can effectively improve RCF...The influence of different cryogenic sequences on the rolling contact fatigue(RCF)life of M50-bearing steel has been studied.The results show that direct cryogenic treatment after quenching can effectively improve RCF life.The L_(10)life is strikingly 5 times longer than that with cryogenic treatment after tem-pering.This is caused by the distinct lattice construction of martensite and the transformation of retained austenite.More secondary nanocarbides and fine twins are formed via cryogenic treatment before tem-pering compared with cryogenic treatment after tempering.The improvement in the RCF life of the steel is attributed to the joint effects of the secondary nanocarbides and twin boundaries with a width of 5-13 nm,which delays significantly crack initiation and propagation.This study highlights a common method to improve the service life of high-carbon and high-alloy steels by adjusting the cryogenic se-quence.展开更多
Effect of cerium(Ce)on creep strength and microstructure of 316LN austenitic stainless steel(316LN steel)at 700℃/150 MPa was investigated by scanning electron microscopy(SEM),scanning transmission electron microscopy...Effect of cerium(Ce)on creep strength and microstructure of 316LN austenitic stainless steel(316LN steel)at 700℃/150 MPa was investigated by scanning electron microscopy(SEM),scanning transmission electron microscopy(STEM)and thermodynamic calculations.Addition of 0.032 wt%Ce to 316LN steel results in a prominent increase in creep life from 313 to 556 h.Ce enriches in titanium nitride nanoparticles,increases slightly the activity and diffusion coefficient of Mo,and facilitates the formation of fine and dense intragranular Laves phase precipitates.Thus the creep strength is remarkably enhanced by Ce addition in 316LN steel through the intragranular Laves phase precipitation strengthening.It reveals a new insight into the improvement effect of rare earth(RE)elements such as Ce on creep strength of austenitic stainless steels,which inspired the design of RE-microalloying heat-resistant steels.展开更多
Seismic stratigraphy, core logging and the data from cores are used to identify the development and evolution of the east provenance-sedimentary system and to analyze its influence on the quality of reservoirs in the ...Seismic stratigraphy, core logging and the data from cores are used to identify the development and evolution of the east provenance-sedimentary system and to analyze its influence on the quality of reservoirs in the eastern depression of the North Yellow Sea Basin. The eastern provenance-sedimentary system is a fan delta (delta) and subaqueous fan sedimentary system with volcanic provenance. Its evolution is closely related to internal uplift and coeval volcanic activity. During faulting and volcanic activity, an internal uplift gradually formed and the eastern provenance-sedimentary system began to develop. Clastic materials from the weathered uplift and volcanic activity were the main sources of sediment and were deposited in the Middle Jurassic to the Early Cretaceous. A subaqueous fan sedimentary system developed in the Middle Jurassic, a deltaic to subaqueous fan sedimentary system developed in the Late Jurassic, and a fan delta to subaqueous fan sedimentary system developed in the Early Cretaceous. The volcaniclastic detritus was mainly composed of acidic materials with a small amount of intermediate materials. The reservoir in the eastern sedimentary system is a type of tight sandstone with ultra-low porosity and very low permeability due to the influence of volcanism and diagenesis. The reservoir quality is worse than those of the northern and the western sedimentary systems. However, the high volume of volcanic materials and deep-marine sedimentary conditions resulted in good-quality hydrocarbon source rocks that ensures the exploration potential in the eastern sedimentary system reservoir.展开更多
Main observation and conclusion Steric bulk plays a significantly paramount role in late transition metal promoted olefin(co)polymerization in terms of polymer molecular weight and catalyst thermal stability.Numerous ...Main observation and conclusion Steric bulk plays a significantly paramount role in late transition metal promoted olefin(co)polymerization in terms of polymer molecular weight and catalyst thermal stability.Numerous sterically encumbered nickel and palladium catalysts have been developed,but they are usually uni-directional.In this contribution,from a bi-directional side the distinctive horizontally and vertically concerted steric strategy was well-developed and applied toα-diimine nickel catalysts.In ethylene polymerization,the increase of vertically steric bulk(H,Ph,Biph)led to an enhanced polymer molecular weight,a slightly ascended branching density;likewise increasing horizontally steric bulk(Ph,Nap,Ant)further resulted in the increase of polymer molecular weight and branching density.As a result,in sharp contrast to Ni1(H)without steric bulk,Ni5(Ant)with horizontally and vertically concerted steric bulk was thermally stable,showed very high activities at a level of 107 g·mol–1·h^(–1),and produced polyethylenes with the highest molecular weight of 518.8×10^(4)g·mol^(-1)and the broader range of branching density from 2.4/1000C to 27.8/1000C.In the copolymerization of ethylene with methyl 10-undecenoate,Ni5(Ant)also provided the highest copolymer molecular weight but gave the lowest incorporation of co-monomer.This work sheds light on the steric effect on olefin(co)polymerization.展开更多
A cold-rolled 25Cr-7Ni-3Mo-0.2N duplex stainless steel(DSS) has been aged in two steps. Firstly, the aging treatment at interval of 50℃ in a temperature range from 900 to 1050℃ was carried out in order to obtain f...A cold-rolled 25Cr-7Ni-3Mo-0.2N duplex stainless steel(DSS) has been aged in two steps. Firstly, the aging treatment at interval of 50℃ in a temperature range from 900 to 1050℃ was carried out in order to obtain fine grains. Secondly, another aging treatment at 850℃ was performed to reveal the σ-phase precipitation behavior. A detailed microstructure evolution during those two aging steps was observed by the optical microscope(OM), the scanning electron microscope(SEM), the electron backscatter difraction(EBSD) and the transmission electron microscope(TEM). The results revealed that the micro-duplex structure with grain size of lower than 10 μm appeared after the first aging step. However, their grain size was rapidly increased with increasing aging temperature. Meanwhile, the δ → γ and/or δ → γ + σ transformations took place in association with the occurrence of the extensive recovery or a little recrystallization in δ-grains. During the second aging treatment, σ-phase mainly nucleated at δ/γ interfaces and further grew along those interfaces into various morphologies(e.g., butterfly and granule). A novel precipitation behavior was found in this study that the γ-grain boundaries bulged not only into the δ-grains as usual, but abnormally into the σ-phase precipitates without the prior precipitation of the isolated secondary austenite γ2or another phases.展开更多
Beyond the single ligand electronic and/or steric modifications, external stimuli are a useful tool for modulating catalytic polymerization reactions. Light stands out from external stimuli, but the corresponding phot...Beyond the single ligand electronic and/or steric modifications, external stimuli are a useful tool for modulating catalytic polymerization reactions. Light stands out from external stimuli, but the corresponding photoresponsive transition metal catalysts are significantly rare for olefin polymerization due to the difficult synthesis. In this contribution, in consideration of the key role of steric shielding on the axial sites, we installed four concerted azobenzene moieties into symmetrically terphenyl-based α-diimine Ni(II) complexes to prepare photoresponsive catalysts, which were applied to ethylene polymerization and copolymerization with polar monomer. Via the trans-cis isomerization of azobenzene-functionalized Ni(II) catalysts in dark or under UV light, catalytic activity, polymer molecular weight, branching density, incorporation of co-monomer, and even the ratio of branching pattern were significantly modulated in ethylene (co)polymerizations. This photo-controlled strategy behaved an opposite influence between ethylene polymerization and copolymerization, in terms of catalytic activity and polymer molecular weight. As a result, slightly branched ultrahigh molecular weight polyethylenes and high molecular weight functionalized polyethylenes were produced at ambient conditions.展开更多
The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms i...The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms in a martensitic stainless steel with 0.3 wt%C and 0.5 wt%N after cryogenic treatment were investigated by the atom probe tomography.Carbon clusters begin to form after cryogenic treatment at-60℃and gradually increase with the decrease of cryogenic treatment temperature.While Mo–N and Cr–N pairs are homogeneously distributed in the matrix even after cryogenic treatment at-120℃,and then form enrichment phenomenon when the cryogenic temperature is deeply lowered to-190℃.It is found that the distinct redistributions of C and N atoms are associated with the different interaction energy between substitutional atoms and them.The stronger interaction between Cr,Mo atoms and N delays the segregation of N during the cryogenic treatment.Finally,the mechanical properties results confirmed that the deep lower cryogenic treatment is a promising method to improve the hardness and strength in the high nitrogen martensitic stainless steel.展开更多
The most straightforward and potentially ideal route to produce polar-functionalized polyethylene is direct copolymerization of ethylene with polar monomers.However,access to high-molecular-weight polar copolymers rep...The most straightforward and potentially ideal route to produce polar-functionalized polyethylene is direct copolymerization of ethylene with polar monomers.However,access to high-molecular-weight polar copolymers represents one of the biggest challenges in the field of olefin polymerization.In this contribution,we report a family of well-designed nickel catalysts that readily address this issue under convenient and highly desired ambient conditions.Under 1 bar at 30℃,polar-functionalized ultrahigh number-average molecular weight polyethylenes(UHMWPEs,Mn=0.83-1.10×10^(6) g mol^(−1))are directly generated.The highest average number of incorporated polar units per polymer chain is 122.This enhances copolymer molecular weights by two orders of magnitude relative to previous reports.Notably,this nickel catalyst family also exceptionally produces the highest number-average molecular weight polyethylenes(Mn=6.04×10^(6) g mol^(−1))at 1 bar.The Sterimol B1 steric parameter of nickel catalyst quantitatively correlates to polymer molecular weight.Mechanistic insights from density functional theory(DFT)calculation reveal that the low barrier(10.4 kcal mol^(−1))of ethylene insertion as the rate-limiting step should be responsible for high activity and the formation of UHMWPE.This coordination-insertion approach is a striking contrast to the high energy free-radical approach.展开更多
AZ31B magnesium alloys are commonly used in lightweight structures of automobile and aerospace industry.In this work,the ultrasonic-induced transient liquid phase bonding technique is deployed to joint AZ31B magnesium...AZ31B magnesium alloys are commonly used in lightweight structures of automobile and aerospace industry.In this work,the ultrasonic-induced transient liquid phase bonding technique is deployed to joint AZ31B magnesium alloys at 490℃ with Ag interlayer in the atmosphere.The effect of ultrasonic vibration on microstructure and mechanical properties of welding seam is investigated.As vibration duration increases,the width of the welding seam increases firstly and then decreases.When the ultrasound vibration sustained for one second,the eutectic reaction occurred in the contacting interface between Ag interlayer and the base metal AZ31B,resulting in formation of liquid phase and metallurgical bonding.When the ultrasound vibration sustained for seven second,the width of the welding seam increased to a maximum of about 303.1μm and the average shear bond strength of the welding joint attained the peak value of about 66.87 MPa.When the ultrasound vibration sustained over seven seconds,the liquid phase is gradually squeezed out and the width of the welding seam decreases.α-Mg and AgMg_(3) can be observed in the welding seam.The analysis shows thatα-Mg has a certain strengthening effect.The whole process of appearance,growth and integration ofα-Mg is analyzed.展开更多
基金supported by the National Natural Science Foun-dation(Grant No.52031013)the National Key Research and Development Program(Grant No.2018YFA0702900).
文摘The influence of different cryogenic sequences on the rolling contact fatigue(RCF)life of M50-bearing steel has been studied.The results show that direct cryogenic treatment after quenching can effectively improve RCF life.The L_(10)life is strikingly 5 times longer than that with cryogenic treatment after tem-pering.This is caused by the distinct lattice construction of martensite and the transformation of retained austenite.More secondary nanocarbides and fine twins are formed via cryogenic treatment before tem-pering compared with cryogenic treatment after tempering.The improvement in the RCF life of the steel is attributed to the joint effects of the secondary nanocarbides and twin boundaries with a width of 5-13 nm,which delays significantly crack initiation and propagation.This study highlights a common method to improve the service life of high-carbon and high-alloy steels by adjusting the cryogenic se-quence.
基金financially supported by the National Natural Science Foundation of China(No.51871212)the National Key Research and Development Program of China(2020YFB2006800)+4 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC04010400)the Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.Y2021060)the Key Project for the Application of Advances in Science and Technology of the Chinese Academy of Sciences(KFJ-HGZX-032)the Project for the Application of Advances in Science and Technology of the Chinese Academy of Sciences in Henan Province(2022203)the K.C.Wong Education Foundation。
文摘Effect of cerium(Ce)on creep strength and microstructure of 316LN austenitic stainless steel(316LN steel)at 700℃/150 MPa was investigated by scanning electron microscopy(SEM),scanning transmission electron microscopy(STEM)and thermodynamic calculations.Addition of 0.032 wt%Ce to 316LN steel results in a prominent increase in creep life from 313 to 556 h.Ce enriches in titanium nitride nanoparticles,increases slightly the activity and diffusion coefficient of Mo,and facilitates the formation of fine and dense intragranular Laves phase precipitates.Thus the creep strength is remarkably enhanced by Ce addition in 316LN steel through the intragranular Laves phase precipitation strengthening.It reveals a new insight into the improvement effect of rare earth(RE)elements such as Ce on creep strength of austenitic stainless steels,which inspired the design of RE-microalloying heat-resistant steels.
基金supported by the China Geological Survey (No. GZH200700405)the National Natural Science Foundation of China (No. 41602106)
文摘Seismic stratigraphy, core logging and the data from cores are used to identify the development and evolution of the east provenance-sedimentary system and to analyze its influence on the quality of reservoirs in the eastern depression of the North Yellow Sea Basin. The eastern provenance-sedimentary system is a fan delta (delta) and subaqueous fan sedimentary system with volcanic provenance. Its evolution is closely related to internal uplift and coeval volcanic activity. During faulting and volcanic activity, an internal uplift gradually formed and the eastern provenance-sedimentary system began to develop. Clastic materials from the weathered uplift and volcanic activity were the main sources of sediment and were deposited in the Middle Jurassic to the Early Cretaceous. A subaqueous fan sedimentary system developed in the Middle Jurassic, a deltaic to subaqueous fan sedimentary system developed in the Late Jurassic, and a fan delta to subaqueous fan sedimentary system developed in the Early Cretaceous. The volcaniclastic detritus was mainly composed of acidic materials with a small amount of intermediate materials. The reservoir in the eastern sedimentary system is a type of tight sandstone with ultra-low porosity and very low permeability due to the influence of volcanism and diagenesis. The reservoir quality is worse than those of the northern and the western sedimentary systems. However, the high volume of volcanic materials and deep-marine sedimentary conditions resulted in good-quality hydrocarbon source rocks that ensures the exploration potential in the eastern sedimentary system reservoir.
基金support from the National Natural Science Foundation of China(Nos.21871250 for Z.Jian,22001244 for Y.Zhang)the Jilin Provincial Science and Technology Department Program(No.20200801009GH).
文摘Main observation and conclusion Steric bulk plays a significantly paramount role in late transition metal promoted olefin(co)polymerization in terms of polymer molecular weight and catalyst thermal stability.Numerous sterically encumbered nickel and palladium catalysts have been developed,but they are usually uni-directional.In this contribution,from a bi-directional side the distinctive horizontally and vertically concerted steric strategy was well-developed and applied toα-diimine nickel catalysts.In ethylene polymerization,the increase of vertically steric bulk(H,Ph,Biph)led to an enhanced polymer molecular weight,a slightly ascended branching density;likewise increasing horizontally steric bulk(Ph,Nap,Ant)further resulted in the increase of polymer molecular weight and branching density.As a result,in sharp contrast to Ni1(H)without steric bulk,Ni5(Ant)with horizontally and vertically concerted steric bulk was thermally stable,showed very high activities at a level of 107 g·mol–1·h^(–1),and produced polyethylenes with the highest molecular weight of 518.8×10^(4)g·mol^(-1)and the broader range of branching density from 2.4/1000C to 27.8/1000C.In the copolymerization of ethylene with methyl 10-undecenoate,Ni5(Ant)also provided the highest copolymer molecular weight but gave the lowest incorporation of co-monomer.This work sheds light on the steric effect on olefin(co)polymerization.
基金support by the Project of Investigation on Fundamental Issues of Stainless Steels from Shenyang National Laboratory for Materials Science(SYNL)Institute of Metal Research(IMR),Chinese Academy of Sciences(CAS)(No.KGCX2-YW-221)
文摘A cold-rolled 25Cr-7Ni-3Mo-0.2N duplex stainless steel(DSS) has been aged in two steps. Firstly, the aging treatment at interval of 50℃ in a temperature range from 900 to 1050℃ was carried out in order to obtain fine grains. Secondly, another aging treatment at 850℃ was performed to reveal the σ-phase precipitation behavior. A detailed microstructure evolution during those two aging steps was observed by the optical microscope(OM), the scanning electron microscope(SEM), the electron backscatter difraction(EBSD) and the transmission electron microscope(TEM). The results revealed that the micro-duplex structure with grain size of lower than 10 μm appeared after the first aging step. However, their grain size was rapidly increased with increasing aging temperature. Meanwhile, the δ → γ and/or δ → γ + σ transformations took place in association with the occurrence of the extensive recovery or a little recrystallization in δ-grains. During the second aging treatment, σ-phase mainly nucleated at δ/γ interfaces and further grew along those interfaces into various morphologies(e.g., butterfly and granule). A novel precipitation behavior was found in this study that the γ-grain boundaries bulged not only into the δ-grains as usual, but abnormally into the σ-phase precipitates without the prior precipitation of the isolated secondary austenite γ2or another phases.
基金support from the National Natu-ral Science Foundation of China(Nos.22122110 and 21871250).
文摘Beyond the single ligand electronic and/or steric modifications, external stimuli are a useful tool for modulating catalytic polymerization reactions. Light stands out from external stimuli, but the corresponding photoresponsive transition metal catalysts are significantly rare for olefin polymerization due to the difficult synthesis. In this contribution, in consideration of the key role of steric shielding on the axial sites, we installed four concerted azobenzene moieties into symmetrically terphenyl-based α-diimine Ni(II) complexes to prepare photoresponsive catalysts, which were applied to ethylene polymerization and copolymerization with polar monomer. Via the trans-cis isomerization of azobenzene-functionalized Ni(II) catalysts in dark or under UV light, catalytic activity, polymer molecular weight, branching density, incorporation of co-monomer, and even the ratio of branching pattern were significantly modulated in ethylene (co)polymerizations. This photo-controlled strategy behaved an opposite influence between ethylene polymerization and copolymerization, in terms of catalytic activity and polymer molecular weight. As a result, slightly branched ultrahigh molecular weight polyethylenes and high molecular weight functionalized polyethylenes were produced at ambient conditions.
基金supported by the National Natural Science Foundation of China(No.51871212)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC04000000)+1 种基金the Major Scientific and Technological Projects of Jiangxi Province(No.20194ABC28011)the Project to Strengthen Industrial Development at the Grass-roots Level(TC190A4DA/35)。
文摘The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms in a martensitic stainless steel with 0.3 wt%C and 0.5 wt%N after cryogenic treatment were investigated by the atom probe tomography.Carbon clusters begin to form after cryogenic treatment at-60℃and gradually increase with the decrease of cryogenic treatment temperature.While Mo–N and Cr–N pairs are homogeneously distributed in the matrix even after cryogenic treatment at-120℃,and then form enrichment phenomenon when the cryogenic temperature is deeply lowered to-190℃.It is found that the distinct redistributions of C and N atoms are associated with the different interaction energy between substitutional atoms and them.The stronger interaction between Cr,Mo atoms and N delays the segregation of N during the cryogenic treatment.Finally,the mechanical properties results confirmed that the deep lower cryogenic treatment is a promising method to improve the hardness and strength in the high nitrogen martensitic stainless steel.
基金financial support from the National Natural Science Foundation of China(nos.21871250,22001244,and 21704011)the Jilin Provincial Science and Technology Department Program(no.20200801009GH).
文摘The most straightforward and potentially ideal route to produce polar-functionalized polyethylene is direct copolymerization of ethylene with polar monomers.However,access to high-molecular-weight polar copolymers represents one of the biggest challenges in the field of olefin polymerization.In this contribution,we report a family of well-designed nickel catalysts that readily address this issue under convenient and highly desired ambient conditions.Under 1 bar at 30℃,polar-functionalized ultrahigh number-average molecular weight polyethylenes(UHMWPEs,Mn=0.83-1.10×10^(6) g mol^(−1))are directly generated.The highest average number of incorporated polar units per polymer chain is 122.This enhances copolymer molecular weights by two orders of magnitude relative to previous reports.Notably,this nickel catalyst family also exceptionally produces the highest number-average molecular weight polyethylenes(Mn=6.04×10^(6) g mol^(−1))at 1 bar.The Sterimol B1 steric parameter of nickel catalyst quantitatively correlates to polymer molecular weight.Mechanistic insights from density functional theory(DFT)calculation reveal that the low barrier(10.4 kcal mol^(−1))of ethylene insertion as the rate-limiting step should be responsible for high activity and the formation of UHMWPE.This coordination-insertion approach is a striking contrast to the high energy free-radical approach.
基金supported by the Self-deployed Projects of Ganjiang Innovation Academy,Chinese Academy of Sciences(Grant No.E355B0020)the LingChuang Research Project of China National Nuclear Corporation(CNNC-LCKY-202283,CNNC-LCKY-202284).
文摘AZ31B magnesium alloys are commonly used in lightweight structures of automobile and aerospace industry.In this work,the ultrasonic-induced transient liquid phase bonding technique is deployed to joint AZ31B magnesium alloys at 490℃ with Ag interlayer in the atmosphere.The effect of ultrasonic vibration on microstructure and mechanical properties of welding seam is investigated.As vibration duration increases,the width of the welding seam increases firstly and then decreases.When the ultrasound vibration sustained for one second,the eutectic reaction occurred in the contacting interface between Ag interlayer and the base metal AZ31B,resulting in formation of liquid phase and metallurgical bonding.When the ultrasound vibration sustained for seven second,the width of the welding seam increased to a maximum of about 303.1μm and the average shear bond strength of the welding joint attained the peak value of about 66.87 MPa.When the ultrasound vibration sustained over seven seconds,the liquid phase is gradually squeezed out and the width of the welding seam decreases.α-Mg and AgMg_(3) can be observed in the welding seam.The analysis shows thatα-Mg has a certain strengthening effect.The whole process of appearance,growth and integration ofα-Mg is analyzed.