The hot deformation behaviours of 316LN-Mn austenitic stainless steel were investigated by uniaxial isothermal compression tests at different temperatures and strain rates.The microstructural evolutions were also stud...The hot deformation behaviours of 316LN-Mn austenitic stainless steel were investigated by uniaxial isothermal compression tests at different temperatures and strain rates.The microstructural evolutions were also studied using electron backscatter diffraction.The flow stress decreases with the increasing temperature and decreasing strain rate.A constitutive equation was established to characterize the relationship among the deformation parameters,and the deformation activation energy was calculated to be 497.92 k J/mol.Processing maps were constructed to describe the appropriate processing window,and the optimum processing parameters were determined at a temperature of 1107-1160℃ and a strain rate of 0.005-0.026 s^(-1).Experimental results showed that the main nucleation mechanism is discontinuous dynamic recrystallization(DDRX),followed by continuous dynamic recrystallization(CDRX).In addition,the formation of twin boundaries facilitated the nucleation of dynamic recrystallization.展开更多
Purpose:This paper aims to investigate the differences between conference papers and journal papers in the field of computer science based on Bayesian network.Design/methodology/approach:This paper investigated the di...Purpose:This paper aims to investigate the differences between conference papers and journal papers in the field of computer science based on Bayesian network.Design/methodology/approach:This paper investigated the differences between conference papers and journal papers in the field of computer science based on Bayesian network,a knowledge-representative framework that can model relationships among all variables in the network.We defined the variables required for Bayesian networks modeling,calculated the values of each variable based Aminer dataset(a literature data set in the field of computer science),learned the Bayesian network and derived some findings based on network inference.Findings:The study found that conferences are more attractive to senior scholars,the academic impact of conference papers is slightly higher than journal papers,and it is uncertain whether conference papers are more innovative than journal papers.Research limitations:The study was limited to the field of computer science and employed Aminer dataset as the sample.Further studies involving more diverse datasets and different fields could provide a more complete picture of the matter.Practical implications:By demonstrating that Bayesian networks can effectively analyze issues in Scientometrics,the study offers valuable insights that may enhance researchers’understanding of the differences between journal and conference in computer science.Originality/value:Academic conferences play a crucial role in facilitating scholarly exchange and knowledge dissemination within the field of computer science.Several studies have been conducted to examine the distinctions between conference papers and journal papers in terms of various factors,such as authors,citations,h-index and others.Those studies were carried out from different(independent)perspectives,lacking a systematic examination of the connections and interactions between multiple perspectives.This paper supplements this deficiency based on Bayesian network modeling.展开更多
Nuclear energy is a low-carbon,safe,efficient,and sustainable clean energy.The new generation of nuclear energy systems operate in harsher environments under higher working temperatures and irradiation doses,while tra...Nuclear energy is a low-carbon,safe,efficient,and sustainable clean energy.The new generation of nuclear energy systems operate in harsher environments under higher working temperatures and irradiation doses,while traditional nuclear power materials cannot meet the requirements.The development of high-performance nuclear power materials is a key factor for promoting the development of nuclear energy.Oxide dispersion strengthened(ODS)steel contains a high number density of dispersed nano-oxides and defect sinks and exhibits excellent high temperature creep performance and irradiation swelling resistance.Therefore,ODS steel has been considered as one of the most promising candidate materials for fourth-generation nuclear fission reactor cladding tubes and nuclear fusion reactor blankets.The preparation process significantly influences microstructure of ODS steel.This paper reviews the development and perspective of several preparation processes of ODS steel,including the powder metallurgy process,improved powder metallurgy process,liquid metal forming process,hybrid process,and additive forging.This paper also summarizes and analyzes the relationship between microstructures and the preparation process.After comprehensive consideration,the powder metallurgy process is still the best preparation process for ODS steel.Combining the advantages and disadvantages of the above preparation processes,the trend applied additive forging for extreme manufacturing of large ODS steel components is discussed with the goal of providing a reference for the application and development of ODS steel in nuclear energy.展开更多
The effect of cerium(Ce)on the solidification microstructure of Cr_(4)Mo_(4)V bearing steel was investigated via a combined experimental and theoretical method.With a trace amount(0.056 wt%)of Ce addition,the coarse c...The effect of cerium(Ce)on the solidification microstructure of Cr_(4)Mo_(4)V bearing steel was investigated via a combined experimental and theoretical method.With a trace amount(0.056 wt%)of Ce addition,the coarse columnar grains in as-cast microstructure transform into equiaxed ones,and the average diameter is reduced from 56 to 27μm.The network-like and bulky primary MC and M2C carbides at the interdendritic regions become disconnected and refined,and their volume percentage decreases from4.15 vol%to 2.1 vol%.Ce-inclusions acting as heterogeneous nucleation agents of prior-austenite grains and Ce atoms segregating at grain boundaries,both contribute to the refinement of grains.Thermodynamic calculations reveal that primary carbides are precipitated afterγ-austenite forms near the end of the solidification process.The modification of primary carbides in size and amount is mainly attributed to the isolated remaining melt separated by refinedγ-austenite grains in which the nucleation of carbides is promoted,while the growth is restrained owing to the less segregation of alloying elements.展开更多
Although it is well established that nitrogen(N)deficiency induces leaf senescence,the molecular mechanism of N deficiency-induced leaf senescence remains largely unknown.Here,we show that an abscisic acid(ABA)-respon...Although it is well established that nitrogen(N)deficiency induces leaf senescence,the molecular mechanism of N deficiency-induced leaf senescence remains largely unknown.Here,we show that an abscisic acid(ABA)-responsive NAC transcription factor(TF)is involved in N deficiency-induced leaf senescence.The overexpression of MdNAC4 led to increased ABA levels in apple calli by directly activating the transcription of the ABA biosynthesis gene MdNCED2.In addition,MdNAC4 overexpression promoted N deficiency-induced leaf senescence.Further investigation showed that MdNAC4 directly bound the promoter of the senescence-associated gene(SAG)MdSAG39 and upregulated its expression.Interestingly,the function of MdNAC4 in promoting N deficiency-induced leaf senescence was enhanced in the presence of ABA.Furthermore,we identified an interaction between the ABA receptor protein MdPYL4 and the MdNAC4 protein.Moreover,MdPYL4 showed a function similar to that of MdNAC4 in ABA-mediated N deficiencyinduced leaf senescence.These findings suggest that ABA plays a central role in N deficiency-induced leaf senescence and that MdPYL4 interacts with MdNAC4 to enhance the response of the latter to N deficiency,thus promoting N deficiency-induced leaf senescence.In conclusion,our results provide new insight into how MdNAC4 regulates N deficiency-induced leaf senescence.展开更多
The realization of long-range magnetic ordering in two-dimensional(2D)van der Waals systems significantly expands the scope of the 2D family as well as their possible spin-related phenomena and device applications.The...The realization of long-range magnetic ordering in two-dimensional(2D)van der Waals systems significantly expands the scope of the 2D family as well as their possible spin-related phenomena and device applications.The atomically thin nature of 2D materials makes their magnetically ordered states sensitive to local environments,and this necessitates advanced characterization at the atomic scale.Here,we briefly review several representative 2D magnetic systems,namely,iron chalcogenides,chromium chalcogenides,chromium trihalides,and their het-erostructures.With powerful scanning-probe microscopy,atomically resolved characterization of their crystalline configurations,electronic structures,and magnetization distributions has been achieved,and novel phenomena such as giant tunneling magnetoresistance and topological superconductivity have been observed.Finally,we discuss the challenges and new perspectives in this flourishing field.展开更多
Hot compression bonding was first used to join oxide-dispersion-strengthened ferrite steels(14 YWT)under temperatures of 750–1100℃ with a true strain range of 0.11–0.51. Subsequently, the microstructure evolution a...Hot compression bonding was first used to join oxide-dispersion-strengthened ferrite steels(14 YWT)under temperatures of 750–1100℃ with a true strain range of 0.11–0.51. Subsequently, the microstructure evolution and mechanical properties of the joints were characterized, revealing that the 14 YWT steels could be successfully bonded at a temperature of at least 950℃ with a true strain of 0.22, without degrading the fine grain and nanoparticle distribution, and the presence of inclusions or micro-voids along the bonding interface. Moreover, the joints had nearly the same tensile properties at room temperature and exhibited a similar fracture morphology with sufficient dimples compared to that of the base material. An electron backscattered diffraction technique and transmission electron microscopy were systematically employed to study the evolution of hot deformed microstructures. The results showed that continuous dynamic recrystallization characterized by progressive subgrain rotation occurred in this alloy, but discontinuous dynamic recrystallization characterized by strain-induced grain boundary bulging and subsequent bridging sub-boundary rotation was the dominant nucleation mechanism. The nuclei will grow with ongoing deformation, which will contribute to the healing of the original bonding interface.展开更多
As an advanced solid state bonding process,plastic deformation bonding(PDB)is a highly reliable metallurgical joining method that produces significant plastic deformation at the bonding interface of welded joints thro...As an advanced solid state bonding process,plastic deformation bonding(PDB)is a highly reliable metallurgical joining method that produces significant plastic deformation at the bonding interface of welded joints through thermo-mechanical coupling.In this study,PDB behavior of IN718 superalloy was systematically investigated by performing a series of isothermal compression tests at various processing conditions.It was revealed that new grains evolved in the bonding area through discontinuous dynamic recrystallization(DDRX)at 1000–1150℃.Electron backscattered diffraction(EBSD)and transmission electron microscopy(TEM)results revealed that the bonding of joints is related with interfacial grain boundary(IGB)bulging process,which is considered as a nucleation process of DRXed grain under different deformation environments.During recrystallization process,the bonded interface moved due to strain-induced boundary migration(SIBM)process.Stored energy difference(caused by accumulation of dislocations at the bonding interface)was the dominant factor for SIBM during DRX.The mechanical properties of the bonded joints were dependent upon the recrystallized microstructure and SIBM ensued during PDB.展开更多
The influence of surface roughness on the interfacial dynamic recrystallization kinetics and mechanical properties of Ti-6 Al-3 Nb-2 Zr-1 Mo hot-compression bonding joints was systematically investigated.It is found t...The influence of surface roughness on the interfacial dynamic recrystallization kinetics and mechanical properties of Ti-6 Al-3 Nb-2 Zr-1 Mo hot-compression bonding joints was systematically investigated.It is found that for the bonding interface of rough surfaces,elongated fine grains are formed at the bonding interface due to shear deformation of the interfacial area.As the surface roughness increases,the proportion of elongated grains drastically decreases as they further reorient to form equiaxed grains along the bonding interface of rougher surfaces resulting from severe incompatible deformation of the interface area.Meanwhile,high-density geometrically necessary dislocations accumulate around the interfacial recrystallization area to accommodate the incompatible strain and lattice rotation.A rotational dynamic recrystallization mechanism is thereby proposed to rationalize the formation of fine interfacial recrystallization grains during bonding of rough surfaces.In contrast to that of rough surfaces,bonding interface of polished surfaces exists in the form of straight interface grain boundaries without fine grains under the same deformation conditions.While with the increase of deformation strain,small grain nuclei form along the bonding interface,which is associated with discontinuous dynamic recrystallization assisted by strain-induced boundary migration of interface grain boundaries.Moreover,the bonding joints of rough surfaces show lower elongation compared with that of polished surfaces.This is because the formation of heterogeneous fine grains with low Schmid factor along the bonding interface of rough surfaces,leading to worse compatible deformation capability and thereby poor ductility of bonding joints.展开更多
Semi-solid forging of iron-based alloys during solidification has unique characteristics distinct from those of the classical hot forging.With the aim of acquiring precise knowledge concerning the microstructural evol...Semi-solid forging of iron-based alloys during solidification has unique characteristics distinct from those of the classical hot forging.With the aim of acquiring precise knowledge concerning the microstructural evolution of bearing steel Cr4 Mo4 V in this process,a series of semi-solid forging experiments were carried out in which samples were wrapped in a designed pure iron sheath.The effects of forging temperature and forging reduction on the grain morphology and liquid flow behavior were investigated,respectively.By forging solidifying metal(FSM),bulky primary dendrites were broken and spheroidal grains with an average shape factor of 0.87 were obtained at 1360?C.With the decreasing forging temperature to 1340?C,the microstructural homogeneity can be improved.On the other hand,it shows that a higher forging reduction(50%)is essential for the spheroidization of grains and elimination of liquid segregation.Those microstructural characteristics are related to different motion mechanisms of solid and liquid phases at different forging temperatures.Additionally,the effect of semi-solid forging on the eutectic carbides was also investigated,and the results demonstrate that the higher diffusion capacity and less liquid segregation jointly lower the large eutectic carbides and consequently cause its uniform distribution during FSM.展开更多
Here,we report the leading manu facture of the large-scale integral weldless stainless steel forging ring(φ=15.6 m)by the multilayer additive hot-compression bonding technology.Moreover,the detailed interface healing...Here,we report the leading manu facture of the large-scale integral weldless stainless steel forging ring(φ=15.6 m)by the multilayer additive hot-compression bonding technology.Moreover,the detailed interface healing mecha nism involving interfacial oxide evolution is elucidated,which validates the feasibility and reliability of the technique we proposed.展开更多
The carbide precipitation behavior and mechanical properties of advanced high strength steel deformed at different temperatures are investigated by X-ray diffractometer(XRD),scanning electron microscope(SEM),transmiss...The carbide precipitation behavior and mechanical properties of advanced high strength steel deformed at different temperatures are investigated by X-ray diffractometer(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM) equipped with an energy dispersing spectroscopy(EDS),and tensile tests.The medium Mn steel was subjected to controlled deformation up to 70% at 750℃,850℃,950℃,and 1050℃,and then quenched with water to room temperature,followed by intercritical annealing at 630℃ for 10 min.In comparison with the undeformed and quenched specimen,it can be concluded that acicular cementite precipitates during the quenching and cooling process,while granular NbC is the deformation induced precipitate and grows during the following annealing process.As the deformation temperature increases from 750℃ to 1050℃,the product of strength and elongation increases at first and then decreases.The smallest average size of second phase particles(20 nm) and the best mechanical properties(32.5 GPa%) can be obtained at the deformation temperature of 950℃.展开更多
In this study, hot compression bonding was first applied to join 14Cr ferrite steel at temperatures of 950–1200°C and strains of 0.11–0.51 under strain rates of 0.01–30 s^(-1).Subsequently, tensile tests were ...In this study, hot compression bonding was first applied to join 14Cr ferrite steel at temperatures of 950–1200°C and strains of 0.11–0.51 under strain rates of 0.01–30 s^(-1).Subsequently, tensile tests were performed on the joints to evaluate the reliability of the joints formed.Detailed microstructural analyses suggest that two different competing dynamic recrystallization(DRX) mechanisms occur during the bonding process depending on the strain rate, and the joints obtained at different strain rate exhibits distinct healing effect.At a low strain rate(0.01 s^(-1)), continuous DRX occurs, as expected in high-stackingfault-energy materials, and is characterized by the progressive conversion of the sub-boundaries into larger-angle boundaries, which involves very limited grain boundaries migration.In addition, straininduced precipitation(SIP) is sufficient under this condition, further impeding the healing of bonding interface.Hence, the joints obtained at low strain rate fractured at the bonding interface easily.Whereas discontinuous DRX is activated at high strain rates(10 and 30 s^(-1)).Under this condition, the formation of sub-boundaries is severely suppressed, resulting in the piling-up of dislocations and hence the storage of a greater amount of stored energy for nucleation and subsequent nuclei growth via the long-distance grain boundaries migration.Meanwhile, the SIP process is sluggish, making the conditions much more favorable for grain boundaries migration which plays a key role in the healing of the original bonding interface.Thus, the joints can be successfully bonded when a high strain rate is applied, with the joints exhibiting tensile properties similar to that of the base material.展开更多
Detailed three-dimensional(3 D)microtomography characterizations of inclusions in electrode matrix,mushy zone(MZ)and liquid melt film(LMF)were performed to elucidate the motion and removal behavior of inclusions in el...Detailed three-dimensional(3 D)microtomography characterizations of inclusions in electrode matrix,mushy zone(MZ)and liquid melt film(LMF)were performed to elucidate the motion and removal behavior of inclusions in electrode tip during magnetically controlled electroslag remelting(MC-ESR)process.A transient 2 D numerical model was also built to verify the experimental results and proposed mechanisms.The number and size of inclusions exhibited an obvious increasing trend from edge to mid region in LMF,while remained almost the same in electrode matrix and MZ.The inclusions in LMF migrated from edge to mid region of LMF,accompanied with removal process.In addition,the kinetic conditions for inclusion migrating to LMF/slag interface(LSI)were enhanced during MC-ESR process,thereby improving the inclusion removal efficiency in LMF.This work highlights the 3 D characterization and motion/removal mechanisms of inclusions in electrode tip,as well as sheds new light on preparing high purity materials.展开更多
Dynamic strain-induced transformation of the low carbon steel Q(235) at 770℃ and 850℃ leads to fine ferrite grains. The microstructure characterization and mechanism of the fine ferrite grain were studied by scann...Dynamic strain-induced transformation of the low carbon steel Q(235) at 770℃ and 850℃ leads to fine ferrite grains. The microstructure characterization and mechanism of the fine ferrite grain were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) technique. The results show that strain-induced microstructure is the mixed microstructure of ferrite and pearlite, with cementite randomly distributed on ferrite grain boundaries and the grains interiors. EBSD images of grain boundaries demonstrate that high angle grain boundaries (HAGBs) are dominant in both of the deformation induced microstructures occurring below and above A(e3) , with only a few low angle grain boundaries (LAGBs) existing in the grain interiors. It implies that the dynamic strain-induced transformation (DSIT) happens above and below A(e3) temperature and has the same phase transition mechanisms. The refinement of ferrite is the cooperative effect of DSIT and continuous dynamic recrystallization (CDRX) of ferrite. Besides, DSIT is deemed as an incomplete carbon diffusion phase transition through the analysis of microstructure and the previous simulated results. The strengths of the Q(235) steel with refined ferrite and pearlite structure get doubled than the initial state without treated by DSIT and the residual stress in the refined structure is partly responsible for the ductility loss.展开更多
The interface healing mechanism of fine-grained Ni-Co-based superalloy during hot-compression bonding(HCB)is investigated.During HCB,the incompatibility of deformation between theγand the primary γ′leads to a large...The interface healing mechanism of fine-grained Ni-Co-based superalloy during hot-compression bonding(HCB)is investigated.During HCB,the incompatibility of deformation between theγand the primary γ′leads to a large number of dislocation pairs(DP),stacking faults(SF),and micro-twins(MT)in the primary γ′.These defects act as fast channels for elemental diffusion,leading to supersaturation of the primary γ′and promoting the growth of the γ-shell.On the one hand,the primary γ′with a γ-shell moves towards the bonding interface due to anomalous yielding phenomena of the primary γ′and plastic flow during HCB process.The increase in the number of defects leads to the growth of γ-γ′heterogeneous epitaxial recrystallization(HERX)grain with coherent structure at the bonding interface,which promotes the bulge of the interface grain boundaries(IGBs).On the other hand,the nucleation and growth of a necklace-like distribution of discontinuous dynamic recrystallization(DDRX)grain at the interface lead to the healing of IGBs.With the synergistic action of DDRX and HERX,the mechanical properties of Ni-Co-based superalloy joints through HCB achieve the same level as the base material.This finding further enriches the theory of interface healing in HCB.展开更多
基金financial support of the National Natural Science Foundation of China(Nos.52101105 and 51975263)。
文摘The hot deformation behaviours of 316LN-Mn austenitic stainless steel were investigated by uniaxial isothermal compression tests at different temperatures and strain rates.The microstructural evolutions were also studied using electron backscatter diffraction.The flow stress decreases with the increasing temperature and decreasing strain rate.A constitutive equation was established to characterize the relationship among the deformation parameters,and the deformation activation energy was calculated to be 497.92 k J/mol.Processing maps were constructed to describe the appropriate processing window,and the optimum processing parameters were determined at a temperature of 1107-1160℃ and a strain rate of 0.005-0.026 s^(-1).Experimental results showed that the main nucleation mechanism is discontinuous dynamic recrystallization(DDRX),followed by continuous dynamic recrystallization(CDRX).In addition,the formation of twin boundaries facilitated the nucleation of dynamic recrystallization.
基金The work of this paper is supported by the Chinese Academy of Sciences Literature and Information capacity building project,Youth Innovation Promotion Association of Chinese Academy of Sciences(No.2019176).
文摘Purpose:This paper aims to investigate the differences between conference papers and journal papers in the field of computer science based on Bayesian network.Design/methodology/approach:This paper investigated the differences between conference papers and journal papers in the field of computer science based on Bayesian network,a knowledge-representative framework that can model relationships among all variables in the network.We defined the variables required for Bayesian networks modeling,calculated the values of each variable based Aminer dataset(a literature data set in the field of computer science),learned the Bayesian network and derived some findings based on network inference.Findings:The study found that conferences are more attractive to senior scholars,the academic impact of conference papers is slightly higher than journal papers,and it is uncertain whether conference papers are more innovative than journal papers.Research limitations:The study was limited to the field of computer science and employed Aminer dataset as the sample.Further studies involving more diverse datasets and different fields could provide a more complete picture of the matter.Practical implications:By demonstrating that Bayesian networks can effectively analyze issues in Scientometrics,the study offers valuable insights that may enhance researchers’understanding of the differences between journal and conference in computer science.Originality/value:Academic conferences play a crucial role in facilitating scholarly exchange and knowledge dissemination within the field of computer science.Several studies have been conducted to examine the distinctions between conference papers and journal papers in terms of various factors,such as authors,citations,h-index and others.Those studies were carried out from different(independent)perspectives,lacking a systematic examination of the connections and interactions between multiple perspectives.This paper supplements this deficiency based on Bayesian network modeling.
基金supported by the National Key Research and Development Program[Grant No.2018YFA0702900]the National Natural Science Foundation of China[Grant No.51774265]+4 种基金the National Science and Technology Major Project of China[Grant No.2019ZX06004010]the Strategic Priority Research Program of the Chinese Academy of Sciences[Grant No.XDC04000000]Ling Chuang Research Project of China National Nuclear CorporationProgram of CAS Interdisciplinary Innovation TeamYouth Innovation Promotion Association,CAS。
文摘Nuclear energy is a low-carbon,safe,efficient,and sustainable clean energy.The new generation of nuclear energy systems operate in harsher environments under higher working temperatures and irradiation doses,while traditional nuclear power materials cannot meet the requirements.The development of high-performance nuclear power materials is a key factor for promoting the development of nuclear energy.Oxide dispersion strengthened(ODS)steel contains a high number density of dispersed nano-oxides and defect sinks and exhibits excellent high temperature creep performance and irradiation swelling resistance.Therefore,ODS steel has been considered as one of the most promising candidate materials for fourth-generation nuclear fission reactor cladding tubes and nuclear fusion reactor blankets.The preparation process significantly influences microstructure of ODS steel.This paper reviews the development and perspective of several preparation processes of ODS steel,including the powder metallurgy process,improved powder metallurgy process,liquid metal forming process,hybrid process,and additive forging.This paper also summarizes and analyzes the relationship between microstructures and the preparation process.After comprehensive consideration,the powder metallurgy process is still the best preparation process for ODS steel.Combining the advantages and disadvantages of the above preparation processes,the trend applied additive forging for extreme manufacturing of large ODS steel components is discussed with the goal of providing a reference for the application and development of ODS steel in nuclear energy.
基金Project supported by the National Natural Science Foundation of China(52031013,52173305,52233017)the National Key Research and Development Program(2018YFA0702900)。
文摘The effect of cerium(Ce)on the solidification microstructure of Cr_(4)Mo_(4)V bearing steel was investigated via a combined experimental and theoretical method.With a trace amount(0.056 wt%)of Ce addition,the coarse columnar grains in as-cast microstructure transform into equiaxed ones,and the average diameter is reduced from 56 to 27μm.The network-like and bulky primary MC and M2C carbides at the interdendritic regions become disconnected and refined,and their volume percentage decreases from4.15 vol%to 2.1 vol%.Ce-inclusions acting as heterogeneous nucleation agents of prior-austenite grains and Ce atoms segregating at grain boundaries,both contribute to the refinement of grains.Thermodynamic calculations reveal that primary carbides are precipitated afterγ-austenite forms near the end of the solidification process.The modification of primary carbides in size and amount is mainly attributed to the isolated remaining melt separated by refinedγ-austenite grains in which the nucleation of carbides is promoted,while the growth is restrained owing to the less segregation of alloying elements.
基金Open access funding provided by Shanghai Jiao Tong Universityfunded by Shandong Province Major Science and Technology Innovation Project(2018CXGC0209)+1 种基金Shandong Provincial Fruit Industry Technology System-Cultivation and Soil Fertilization Post(SDAIT-06-04)Natural Science Foundation of Shandong Provincial(ZR2020ZD18).
文摘Although it is well established that nitrogen(N)deficiency induces leaf senescence,the molecular mechanism of N deficiency-induced leaf senescence remains largely unknown.Here,we show that an abscisic acid(ABA)-responsive NAC transcription factor(TF)is involved in N deficiency-induced leaf senescence.The overexpression of MdNAC4 led to increased ABA levels in apple calli by directly activating the transcription of the ABA biosynthesis gene MdNCED2.In addition,MdNAC4 overexpression promoted N deficiency-induced leaf senescence.Further investigation showed that MdNAC4 directly bound the promoter of the senescence-associated gene(SAG)MdSAG39 and upregulated its expression.Interestingly,the function of MdNAC4 in promoting N deficiency-induced leaf senescence was enhanced in the presence of ABA.Furthermore,we identified an interaction between the ABA receptor protein MdPYL4 and the MdNAC4 protein.Moreover,MdPYL4 showed a function similar to that of MdNAC4 in ABA-mediated N deficiencyinduced leaf senescence.These findings suggest that ABA plays a central role in N deficiency-induced leaf senescence and that MdPYL4 interacts with MdNAC4 to enhance the response of the latter to N deficiency,thus promoting N deficiency-induced leaf senescence.In conclusion,our results provide new insight into how MdNAC4 regulates N deficiency-induced leaf senescence.
基金The authors acknowledge financial support from the National Nat-ural Science Foundation of China(Grant No.12004278)the Natural Science Foundation of Fujian Province(2022J06035)the Ministry of Education,Singapore,under its ARC Tier 2 program(Award T2EP-50122-0007).
文摘The realization of long-range magnetic ordering in two-dimensional(2D)van der Waals systems significantly expands the scope of the 2D family as well as their possible spin-related phenomena and device applications.The atomically thin nature of 2D materials makes their magnetically ordered states sensitive to local environments,and this necessitates advanced characterization at the atomic scale.Here,we briefly review several representative 2D magnetic systems,namely,iron chalcogenides,chromium chalcogenides,chromium trihalides,and their het-erostructures.With powerful scanning-probe microscopy,atomically resolved characterization of their crystalline configurations,electronic structures,and magnetization distributions has been achieved,and novel phenomena such as giant tunneling magnetoresistance and topological superconductivity have been observed.Finally,we discuss the challenges and new perspectives in this flourishing field.
基金financial support from National Key Research and Development program (Grant No.2016YFB0300401)National Natural Science Foundation of China (Grant Nos. U1508215, 51774265)key Program of the Chinese Academy of Sciences (Grant No. ZDRW-CN-2017-1)
文摘Hot compression bonding was first used to join oxide-dispersion-strengthened ferrite steels(14 YWT)under temperatures of 750–1100℃ with a true strain range of 0.11–0.51. Subsequently, the microstructure evolution and mechanical properties of the joints were characterized, revealing that the 14 YWT steels could be successfully bonded at a temperature of at least 950℃ with a true strain of 0.22, without degrading the fine grain and nanoparticle distribution, and the presence of inclusions or micro-voids along the bonding interface. Moreover, the joints had nearly the same tensile properties at room temperature and exhibited a similar fracture morphology with sufficient dimples compared to that of the base material. An electron backscattered diffraction technique and transmission electron microscopy were systematically employed to study the evolution of hot deformed microstructures. The results showed that continuous dynamic recrystallization characterized by progressive subgrain rotation occurred in this alloy, but discontinuous dynamic recrystallization characterized by strain-induced grain boundary bulging and subsequent bridging sub-boundary rotation was the dominant nucleation mechanism. The nuclei will grow with ongoing deformation, which will contribute to the healing of the original bonding interface.
基金the National Key Research and Development Program[grant number 2018YFA0702900]the National Natural Science Foundation of China[grant numbers U1508215,51774265]+2 种基金the National Science and Technology Major Project of China[Grant No.2019ZX06004010]the Key Program of the Chinese Academy of Sciences[Grant No.ZDRW-CN-2017-1]the CAS Interdisciplinary Innovation Team。
文摘As an advanced solid state bonding process,plastic deformation bonding(PDB)is a highly reliable metallurgical joining method that produces significant plastic deformation at the bonding interface of welded joints through thermo-mechanical coupling.In this study,PDB behavior of IN718 superalloy was systematically investigated by performing a series of isothermal compression tests at various processing conditions.It was revealed that new grains evolved in the bonding area through discontinuous dynamic recrystallization(DDRX)at 1000–1150℃.Electron backscattered diffraction(EBSD)and transmission electron microscopy(TEM)results revealed that the bonding of joints is related with interfacial grain boundary(IGB)bulging process,which is considered as a nucleation process of DRXed grain under different deformation environments.During recrystallization process,the bonded interface moved due to strain-induced boundary migration(SIBM)process.Stored energy difference(caused by accumulation of dislocations at the bonding interface)was the dominant factor for SIBM during DRX.The mechanical properties of the bonded joints were dependent upon the recrystallized microstructure and SIBM ensued during PDB.
基金financially supported by the National Key Research and Development Program(No.2018YFA0702900)the Postdoctoral Science Foundation of China(No.2020M681004)+2 种基金the National Natural Science Foundation of China(No.51774265)the National Science and Technology Major Project of China(No.2019ZX06004010)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC04000000)。
文摘The influence of surface roughness on the interfacial dynamic recrystallization kinetics and mechanical properties of Ti-6 Al-3 Nb-2 Zr-1 Mo hot-compression bonding joints was systematically investigated.It is found that for the bonding interface of rough surfaces,elongated fine grains are formed at the bonding interface due to shear deformation of the interfacial area.As the surface roughness increases,the proportion of elongated grains drastically decreases as they further reorient to form equiaxed grains along the bonding interface of rougher surfaces resulting from severe incompatible deformation of the interface area.Meanwhile,high-density geometrically necessary dislocations accumulate around the interfacial recrystallization area to accommodate the incompatible strain and lattice rotation.A rotational dynamic recrystallization mechanism is thereby proposed to rationalize the formation of fine interfacial recrystallization grains during bonding of rough surfaces.In contrast to that of rough surfaces,bonding interface of polished surfaces exists in the form of straight interface grain boundaries without fine grains under the same deformation conditions.While with the increase of deformation strain,small grain nuclei form along the bonding interface,which is associated with discontinuous dynamic recrystallization assisted by strain-induced boundary migration of interface grain boundaries.Moreover,the bonding joints of rough surfaces show lower elongation compared with that of polished surfaces.This is because the formation of heterogeneous fine grains with low Schmid factor along the bonding interface of rough surfaces,leading to worse compatible deformation capability and thereby poor ductility of bonding joints.
基金supported financially by the National Key Research and Development Program(No.2018YFA0702900)the National Natural Science Foundation of China(Nos.U1508215,51774265 and 51701225)+3 种基金the National Science and Technology Major Project of China(No.2019ZX06004010)the Key Program of the Chinese Academy of Sciences(No.ZDRW-CN-2017-1)the Program of CAS Interdisciplinary Innovation TeamGleeble engineer Jiajun He for her technical support in superhot experiments.
文摘Semi-solid forging of iron-based alloys during solidification has unique characteristics distinct from those of the classical hot forging.With the aim of acquiring precise knowledge concerning the microstructural evolution of bearing steel Cr4 Mo4 V in this process,a series of semi-solid forging experiments were carried out in which samples were wrapped in a designed pure iron sheath.The effects of forging temperature and forging reduction on the grain morphology and liquid flow behavior were investigated,respectively.By forging solidifying metal(FSM),bulky primary dendrites were broken and spheroidal grains with an average shape factor of 0.87 were obtained at 1360?C.With the decreasing forging temperature to 1340?C,the microstructural homogeneity can be improved.On the other hand,it shows that a higher forging reduction(50%)is essential for the spheroidization of grains and elimination of liquid segregation.Those microstructural characteristics are related to different motion mechanisms of solid and liquid phases at different forging temperatures.Additionally,the effect of semi-solid forging on the eutectic carbides was also investigated,and the results demonstrate that the higher diffusion capacity and less liquid segregation jointly lower the large eutectic carbides and consequently cause its uniform distribution during FSM.
基金supported by the National Key Research and Development Program[Grant No.2018YFA0702900]the National Natural Science Foundation of China[Grant No.51774265]+2 种基金the National Science and Technology Major Project of China[Grant No.2019ZX06004010]Program of CAS Interdisciplinary Innovation TeamYouth Innovation Promotion Association,CAS。
文摘Here,we report the leading manu facture of the large-scale integral weldless stainless steel forging ring(φ=15.6 m)by the multilayer additive hot-compression bonding technology.Moreover,the detailed interface healing mecha nism involving interfacial oxide evolution is elucidated,which validates the feasibility and reliability of the technique we proposed.
基金supported by the National Key Research and Development Program [Grant No.2018YFA0702900]the National Natural Science Foundation of China [Grant No.U1508215,51774265]+3 种基金the National Science and Technology Major Project of China [Grant No.2019ZX06004010]the Key Program of the Chinese Academy of Sciences [Grant No.ZDRW-CN-2017-1]the Key Program of Natural Science Foundation of Hebei Province of China[Grant No.E2017203161]the CAS Interdisciplinary Innovation Team。
文摘The carbide precipitation behavior and mechanical properties of advanced high strength steel deformed at different temperatures are investigated by X-ray diffractometer(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM) equipped with an energy dispersing spectroscopy(EDS),and tensile tests.The medium Mn steel was subjected to controlled deformation up to 70% at 750℃,850℃,950℃,and 1050℃,and then quenched with water to room temperature,followed by intercritical annealing at 630℃ for 10 min.In comparison with the undeformed and quenched specimen,it can be concluded that acicular cementite precipitates during the quenching and cooling process,while granular NbC is the deformation induced precipitate and grows during the following annealing process.As the deformation temperature increases from 750℃ to 1050℃,the product of strength and elongation increases at first and then decreases.The smallest average size of second phase particles(20 nm) and the best mechanical properties(32.5 GPa%) can be obtained at the deformation temperature of 950℃.
基金financial support from the National Key Research and Development Program of China(Grant No.2018YFA0702900)the National Natural Science Foundation of China(Grant Nos.U1508215,51774265)+2 种基金the Key Program of the Chinese Academy of Sciences(Grant No.ZDRW-CN-2017-1)the National Science and Technology Major Project of China(Grant No.2019ZX06004010)the CAS Interdisciplinary Innovation Team。
文摘In this study, hot compression bonding was first applied to join 14Cr ferrite steel at temperatures of 950–1200°C and strains of 0.11–0.51 under strain rates of 0.01–30 s^(-1).Subsequently, tensile tests were performed on the joints to evaluate the reliability of the joints formed.Detailed microstructural analyses suggest that two different competing dynamic recrystallization(DRX) mechanisms occur during the bonding process depending on the strain rate, and the joints obtained at different strain rate exhibits distinct healing effect.At a low strain rate(0.01 s^(-1)), continuous DRX occurs, as expected in high-stackingfault-energy materials, and is characterized by the progressive conversion of the sub-boundaries into larger-angle boundaries, which involves very limited grain boundaries migration.In addition, straininduced precipitation(SIP) is sufficient under this condition, further impeding the healing of bonding interface.Hence, the joints obtained at low strain rate fractured at the bonding interface easily.Whereas discontinuous DRX is activated at high strain rates(10 and 30 s^(-1)).Under this condition, the formation of sub-boundaries is severely suppressed, resulting in the piling-up of dislocations and hence the storage of a greater amount of stored energy for nucleation and subsequent nuclei growth via the long-distance grain boundaries migration.Meanwhile, the SIP process is sluggish, making the conditions much more favorable for grain boundaries migration which plays a key role in the healing of the original bonding interface.Thus, the joints can be successfully bonded when a high strain rate is applied, with the joints exhibiting tensile properties similar to that of the base material.
基金the financial support of the National Key Research and Development Program of China(Nos.2016YFB0300401,2018YFF0109404 and 2016YFB0301401)the National Natural Science Foundation of China(Nos.U1860202,U1732276,50134010,51704193,51904184 and 52004156)+1 种基金the Science and Technology Commission of Shanghai Municipality(Nos.13JC14025000 and 15520711000)the China Postdoctoral Science Foundation(No.2020M671072)。
文摘Detailed three-dimensional(3 D)microtomography characterizations of inclusions in electrode matrix,mushy zone(MZ)and liquid melt film(LMF)were performed to elucidate the motion and removal behavior of inclusions in electrode tip during magnetically controlled electroslag remelting(MC-ESR)process.A transient 2 D numerical model was also built to verify the experimental results and proposed mechanisms.The number and size of inclusions exhibited an obvious increasing trend from edge to mid region in LMF,while remained almost the same in electrode matrix and MZ.The inclusions in LMF migrated from edge to mid region of LMF,accompanied with removal process.In addition,the kinetic conditions for inclusion migrating to LMF/slag interface(LSI)were enhanced during MC-ESR process,thereby improving the inclusion removal efficiency in LMF.This work highlights the 3 D characterization and motion/removal mechanisms of inclusions in electrode tip,as well as sheds new light on preparing high purity materials.
基金support from the National Natural Science Foundation of China (NSFC) under Grantb No. 50871109
文摘Dynamic strain-induced transformation of the low carbon steel Q(235) at 770℃ and 850℃ leads to fine ferrite grains. The microstructure characterization and mechanism of the fine ferrite grain were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) technique. The results show that strain-induced microstructure is the mixed microstructure of ferrite and pearlite, with cementite randomly distributed on ferrite grain boundaries and the grains interiors. EBSD images of grain boundaries demonstrate that high angle grain boundaries (HAGBs) are dominant in both of the deformation induced microstructures occurring below and above A(e3) , with only a few low angle grain boundaries (LAGBs) existing in the grain interiors. It implies that the dynamic strain-induced transformation (DSIT) happens above and below A(e3) temperature and has the same phase transition mechanisms. The refinement of ferrite is the cooperative effect of DSIT and continuous dynamic recrystallization (CDRX) of ferrite. Besides, DSIT is deemed as an incomplete carbon diffusion phase transition through the analysis of microstructure and the previous simulated results. The strengths of the Q(235) steel with refined ferrite and pearlite structure get doubled than the initial state without treated by DSIT and the residual stress in the refined structure is partly responsible for the ductility loss.
基金financially supported by the National Key Research and Development Program(No.2018YFA0702900)the National Natural Science Foundation of China(Nos.52173305,52101061,52233017 and52203384)+6 种基金the National Science and Technology Major Project of China(No.2019ZX06004010)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC04000000)the China Postdoctoral Science Foundation(Nos.2020M681004 and 2021M703276)the IMR Innovation Foundation(No.2022-PY12)the Ling Chuang Research Project of China National Nuclear CorporationCNNC Science Fund for Talented Young ScholarsYouth Innovation Promotion Association,CAS.
文摘The interface healing mechanism of fine-grained Ni-Co-based superalloy during hot-compression bonding(HCB)is investigated.During HCB,the incompatibility of deformation between theγand the primary γ′leads to a large number of dislocation pairs(DP),stacking faults(SF),and micro-twins(MT)in the primary γ′.These defects act as fast channels for elemental diffusion,leading to supersaturation of the primary γ′and promoting the growth of the γ-shell.On the one hand,the primary γ′with a γ-shell moves towards the bonding interface due to anomalous yielding phenomena of the primary γ′and plastic flow during HCB process.The increase in the number of defects leads to the growth of γ-γ′heterogeneous epitaxial recrystallization(HERX)grain with coherent structure at the bonding interface,which promotes the bulge of the interface grain boundaries(IGBs).On the other hand,the nucleation and growth of a necklace-like distribution of discontinuous dynamic recrystallization(DDRX)grain at the interface lead to the healing of IGBs.With the synergistic action of DDRX and HERX,the mechanical properties of Ni-Co-based superalloy joints through HCB achieve the same level as the base material.This finding further enriches the theory of interface healing in HCB.