Rescattering of stimulated Raman side scattering(SRSS)is observed for the first time via two-dimensional(2D)particle-in-cell(PIC)simulations.We construct a theoretical model for the rescattering process,which can pred...Rescattering of stimulated Raman side scattering(SRSS)is observed for the first time via two-dimensional(2D)particle-in-cell(PIC)simulations.We construct a theoretical model for the rescattering process,which can predict the region of occurrence of mth-order SRSS and estimate its threshold.The rescattering process is identified by the 2D PIC simulations under typical conditions of a direct-drive inertial confinement fusion scheme.Hot electrons produced by second-order SRSS propagate nearly perpendicular to the density gradient and gain nearly the same energy as in first-order SRSS,but there is no cascade acceleration to produce superhot electrons.Parametric studies for a wide range of ignition conditions show that SRSS and associated rescatterings are robust and important processes in inertial confinement fusion.展开更多
The strength-ductility trade-off has been the most challenging problem for structural metals for centuries.Nanoprecipitation strengthening is an ideal approach to enhance the strength without significantly sacrificing...The strength-ductility trade-off has been the most challenging problem for structural metals for centuries.Nanoprecipitation strengthening is an ideal approach to enhance the strength without significantly sacrificing the ductility.Stable nanoprecipitates have been successfully acquired by nanostructural design,but the number density of nanoprecipitates cannot be further increased.Researchers attempted to enhance number density by introducing highly potent nucleation sites(e.g.,dislocations).However,there remains controversy over the influence of dislocations on the nucleation and growth of coherent nanoprecipitates with minimized nucleation barrier.Here,Cu-rich nanoprecipitates in an HSLA steel,as a typical type of coherent nanoprecipitates,are investigated.By combining analytical calculation and experiments,we show that dislocations are harmful for the formation of large numbered Cu-rich nanoprecipitates in a certain density range.Insufficient dislocations deprive solute atoms which decrease homogenous precipitation that cannot be compensated by the increase in heterogeneous precipitation.Under such circumstance,Cu-rich nanoprecipitates have smaller number density but larger size and higher fraction of incoherent structures due to rapid Ostwald ripening.As a result,by controlling dislocation density,the yield strength is increased by 24%without obvious loss in ductility as compared with traditional solution-quench-age process.Our work would help to optimize composition and processing routes that fully exploit the nanoprecipitation strengthening effect.展开更多
Hierarchical Cr Co Ni medium entropy alloy(MEA)thin films with a dual-phase face-centred cubic(FCC)and hexagonal closed-packed(HCP)nanostructure were prepared on M2 steel substrates by closed field unbalanced magnetro...Hierarchical Cr Co Ni medium entropy alloy(MEA)thin films with a dual-phase face-centred cubic(FCC)and hexagonal closed-packed(HCP)nanostructure were prepared on M2 steel substrates by closed field unbalanced magnetron sputtering.Nanoindentation tests show an ultra-high hardness of 9.5 GPa,attributable to large amounts of innate planar defects(i.e.,growth twins and stacking faults)impeding dislocation motion in the coatings.A deep analysis of undeformed and post-mortem samples reveals grain refinement as the dominant deformation mechanism in FCC dominated regions,while phase transformation and shear banding played major roles in regions occupied by HCP phase.The grain refinement was facilitated by twin/matrix lamellae,with dislocations piling up and arranging into interconnecting grain boundaries.The shear banding was accelerated by innate planar defects in the HCP phase due to a lack of slip systems.Of particular interest is the observation of HCP→FCC phase transformation,which was catalysed by deformation-induced grain reorientation with innate stacking faults acting as embryos to grow the FCC phase.The results of this work suggest that multiple deformation pathways could be activated in Cr Co Ni coatings with assistance of growth defects,thereby imparting these technically important coatings appreciable ductility.展开更多
A hot-rolled deep drawing(HDD)steel with high r-value and uniformdistribution of{111}texture in thickness was developed by hot rolling in ferrite region withlubricating between the roller and the steel.The experimenta...A hot-rolled deep drawing(HDD)steel with high r-value and uniformdistribution of{111}texture in thickness was developed by hot rolling in ferrite region withlubricating between the roller and the steel.The experimental results show that the carbon contentand finish rolling temperature have significant effects on beneficial texture{111},and lubricatingduring hot rolling at low temperature in alpha-region makes the distribution of the textureuniform.Three basic requirements needed to meet for HDD steel were concluded by comparing differentcarbon contents and hot rolling processes.展开更多
Nickel-based superalloy IN738LC produced by selective laser melting(SLM)exhibits inferior hightemperature creep properties than its cast counterparts due to relatively smaller grain size,particularly for the plane nor...Nickel-based superalloy IN738LC produced by selective laser melting(SLM)exhibits inferior hightemperature creep properties than its cast counterparts due to relatively smaller grain size,particularly for the plane normal to the building direction.This work studied effects of post heating strategy on the microstructure and especially the grain size to improve the high temperature creep resistance.The asbuilt microstructure exhibited a fine grain size and large quantities of MC carbides that could effectively hinder grain growth.It was found that unconventional two-step heat treatments could lead to substantial grain growth,and the effect is particularly prominent at a specific temperature.The ease of grain growth was explained after classifying the microstructural evolution(boundary carbide transformation)during each heating step and related to the reduced grain boundary pinning force from MC carbides.Creep tests validated the effect of the new heat treatment scheme on the SLM-processed IN738LC at 850℃.An extended creep fracture life(1.5 to 4 times improvement)and lower secondary creep rates were achieved with samples subjected to the newly optimized two-step heat treatment.The complete creep curves are also firstly presented for SLM-IN738LC,confirming the effectiveness of grain growth and highlighting the importance of dedicated heat treatment for SLM superalloys.展开更多
Fe_(72.4)Co_(13.9)Cr_(10.4)Mn_(2.7)B_(0.34)high entropy steel was prepared by magnetron sputtering.The alloy exhibits a high yield strength of 2.92±0.36 GPa while achieving appreciable plasticity of 13.7±1.9...Fe_(72.4)Co_(13.9)Cr_(10.4)Mn_(2.7)B_(0.34)high entropy steel was prepared by magnetron sputtering.The alloy exhibits a high yield strength of 2.92±0.36 GPa while achieving appreciable plasticity of 13.7±1.9%at the ultimate compressive strength(3.37±0.36 GPa).The distribution of iron and chromium shows an un-usual,characteristic spinodal-like pattern at the nanometer scale,where compositions of Fe and Cr show strong anticorrelation and vary by as much as 20 at.%.The high strength is largely attributable to the compositional modulations,combined with fine grains with body-centered cubic(BCC)crystal structure,as well as grain boundary segregation of interstitial boron.The impressive plasticity is accommodated by the formation and operation of multiplanar,multicharacter dislocation slips,mediated by coherent in-terfaces,and controlled by shear bandings.The excellent strength-ductility combination is thus enabled by a range of distinctive strengthening mechanisms,rendering the new alloy a potential candidate for safety-critical,load-bearing structural applications.展开更多
Gradient structure is emerging as an effective strategy to fabricate metals with remarkable mechanical performance,but have not been verified in intermetallic compounds for high-temperature applications.Through experi...Gradient structure is emerging as an effective strategy to fabricate metals with remarkable mechanical performance,but have not been verified in intermetallic compounds for high-temperature applications.Through experiments and atomic simulations,we show that a typical intermetallic TiAl alloy with gra-dient structure has a significant strengthening effect both at room temperature and high temperatures.The room-temperature compressive strength of TiAl alloys with gradient grain obtained by additive man-ufacturing is 2.57 GPa,which is∼2.7 times as strong as that with equiaxed grain.The strengthening effect is attributed to more sessile dislocations in gradient structure caused by the intersections of mul-tiple slip systems in gradient grain.More importantly,the strengthening effect is still effective at high temperatures and the compressive strength is 1.28 GPa at 750°C.The simulation results show that this strengthening effect is due to the increased Hirth dislocation at high temperatures.This study expands the applications of TiAl alloys for load-bearing structures and provides a new strategy for improving the strength of intermetallic compounds at both room temperature and high temperatures.展开更多
It has been a central task of solidification research to predict solute microsegregation. Apart from the Lever rule and the Scheil-Gulliver equation, which concern two extreme cases, a long list of microsegregation mo...It has been a central task of solidification research to predict solute microsegregation. Apart from the Lever rule and the Scheil-Gulliver equation, which concern two extreme cases, a long list of microsegregation models has been proposed. However, the use of these models often requires essential experimental input information, e.g., the secondary dendrite arm spacing(λ), cooling rate( ˙T) or actual solidification range(△T). This requirement disables these models for alloy solidification with no measured values for λ,˙T and △T. Furthermore, not all of these required experimental data are easily obtainable. It is therefore highly desirable to have an easy-to-apply predictive model that is independent of experimental input,akin to the Lever rule or Scheil-Gulliver model. Gong, Chen, and co-workers have recently proposed such a model, referred to as the Gong-Chen model, by averaging the solid fractions(f_(s)) of the Lever rule and Scheil-Gulliver model as the actual solid fraction. We provide a systematic assessment of this model versus established solidification microsegregation models and address a latent deficiency of the model, i.e.,it allows the Lever rule solid fraction fsto be greater than one(f_(s)> 1). It is shown that the Gong-Chen model can serve as a generic model for alloy solidification until fsreaches about 0.9, beyond which(f_(s)> 0.9) its applicability is dictated by both the equilibrium solute partition coefcient(k) and the solute diffusion coefcient in the solid(Ds), which has been tabulated in detail.展开更多
The micro structure and mechanical properties of new kind of hot-rolled high strength and high elongation steels with retained austenite were studied by discussing the influence of different carbon content. The resear...The micro structure and mechanical properties of new kind of hot-rolled high strength and high elongation steels with retained austenite were studied by discussing the influence of different carbon content. The research results indicate that carbon content has a significant effect on retaining austenite and consequently resulting in high elongation. Besides, new findings about relationship between carbon content and retained austenite as well as properties were discussed in the paper.展开更多
The different chemical composition of silicon and manganese as well as different retained austenite fraction ranged from 4% to 10% of the high strength and high elongation steels were studied in the paper. The disloca...The different chemical composition of silicon and manganese as well as different retained austenite fraction ranged from 4% to 10% of the high strength and high elongation steels were studied in the paper. The dislocations and carbon concentration in retained austenite were observed by a transmission electron microscope and an electric probe analyzer, respectively. The experimental results showed that silicon and manganese are two fundamental alloying elements to stabilize austenite effectively but retaining austenite in different mechanisms. Meanwhile, the cooling processing played an important role in controlling the fraction of retained austenite of the hot-rolled high strength and high plasticity steels.展开更多
A central research topic in condensed matter physics is the understanding of the evolution of various phases and phase transitions under different tuning parameters such as temperature, magnetic field and pressure. To...A central research topic in condensed matter physics is the understanding of the evolution of various phases and phase transitions under different tuning parameters such as temperature, magnetic field and pressure. To explore the pressure-induced evolution of the magnetism and Fermi surface of the heavy fermion antiferromagnet Yb Pt Bi, we performed tunnel diode oscillator based measurements under pressure at low temperatures in high magnetic fields. Our results reveal that the magnetic order strengthens and the Fermi surface shrinks as the pressure increases, which are consistent with typical observations for Yb-based heavy fermion compounds. In addition, an anomalous change in the quantum oscillation amplitudes is observed above 1.5 GPa, and determining the origin requires further study.展开更多
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDA25050700)the Fund of the National Key Laboratory of Plasma Physics(Grant No.6142A04230103)+2 种基金the National Natural Science Foundation of China(Grant No.11805062)the China Postdoctoral Science Foundation(Grant No.2022M720513)the Anhui Provincial Natural Science Foundation(Grant No.2308085QA25).
文摘Rescattering of stimulated Raman side scattering(SRSS)is observed for the first time via two-dimensional(2D)particle-in-cell(PIC)simulations.We construct a theoretical model for the rescattering process,which can predict the region of occurrence of mth-order SRSS and estimate its threshold.The rescattering process is identified by the 2D PIC simulations under typical conditions of a direct-drive inertial confinement fusion scheme.Hot electrons produced by second-order SRSS propagate nearly perpendicular to the density gradient and gain nearly the same energy as in first-order SRSS,but there is no cascade acceleration to produce superhot electrons.Parametric studies for a wide range of ignition conditions show that SRSS and associated rescatterings are robust and important processes in inertial confinement fusion.
基金the National Natural Science Foundation of China(nos.51571117,51731006,92163215 and 52174364)。
文摘The strength-ductility trade-off has been the most challenging problem for structural metals for centuries.Nanoprecipitation strengthening is an ideal approach to enhance the strength without significantly sacrificing the ductility.Stable nanoprecipitates have been successfully acquired by nanostructural design,but the number density of nanoprecipitates cannot be further increased.Researchers attempted to enhance number density by introducing highly potent nucleation sites(e.g.,dislocations).However,there remains controversy over the influence of dislocations on the nucleation and growth of coherent nanoprecipitates with minimized nucleation barrier.Here,Cu-rich nanoprecipitates in an HSLA steel,as a typical type of coherent nanoprecipitates,are investigated.By combining analytical calculation and experiments,we show that dislocations are harmful for the formation of large numbered Cu-rich nanoprecipitates in a certain density range.Insufficient dislocations deprive solute atoms which decrease homogenous precipitation that cannot be compensated by the increase in heterogeneous precipitation.Under such circumstance,Cu-rich nanoprecipitates have smaller number density but larger size and higher fraction of incoherent structures due to rapid Ostwald ripening.As a result,by controlling dislocation density,the yield strength is increased by 24%without obvious loss in ductility as compared with traditional solution-quench-age process.Our work would help to optimize composition and processing routes that fully exploit the nanoprecipitation strengthening effect.
基金financially supported by the Australian Research Council Discovery Projects Grant (DP160104632)by an Australian Government Research Training Program (RTP) Scholarship.
文摘Hierarchical Cr Co Ni medium entropy alloy(MEA)thin films with a dual-phase face-centred cubic(FCC)and hexagonal closed-packed(HCP)nanostructure were prepared on M2 steel substrates by closed field unbalanced magnetron sputtering.Nanoindentation tests show an ultra-high hardness of 9.5 GPa,attributable to large amounts of innate planar defects(i.e.,growth twins and stacking faults)impeding dislocation motion in the coatings.A deep analysis of undeformed and post-mortem samples reveals grain refinement as the dominant deformation mechanism in FCC dominated regions,while phase transformation and shear banding played major roles in regions occupied by HCP phase.The grain refinement was facilitated by twin/matrix lamellae,with dislocations piling up and arranging into interconnecting grain boundaries.The shear banding was accelerated by innate planar defects in the HCP phase due to a lack of slip systems.Of particular interest is the observation of HCP→FCC phase transformation,which was catalysed by deformation-induced grain reorientation with innate stacking faults acting as embryos to grow the FCC phase.The results of this work suggest that multiple deformation pathways could be activated in Cr Co Ni coatings with assistance of growth defects,thereby imparting these technically important coatings appreciable ductility.
文摘A hot-rolled deep drawing(HDD)steel with high r-value and uniformdistribution of{111}texture in thickness was developed by hot rolling in ferrite region withlubricating between the roller and the steel.The experimental results show that the carbon contentand finish rolling temperature have significant effects on beneficial texture{111},and lubricatingduring hot rolling at low temperature in alpha-region makes the distribution of the textureuniform.Three basic requirements needed to meet for HDD steel were concluded by comparing differentcarbon contents and hot rolling processes.
基金financially supported by"Industrial Transformation Research Hub for Transforming Australia’s Manufacturing Industry through High Value Additive Manufacturing"of the Australian Research Council(grant No.IH130100008)the use of instruments and scientific and technical assistance at the Monash Centre for Electron Microscopy,a Node of Microscopy Australiathe financial support from the Monash Graduate Research Scholarship(MGS)and International Monash Postgraduate Research Scholarship(IMPRS)from the Monash University。
文摘Nickel-based superalloy IN738LC produced by selective laser melting(SLM)exhibits inferior hightemperature creep properties than its cast counterparts due to relatively smaller grain size,particularly for the plane normal to the building direction.This work studied effects of post heating strategy on the microstructure and especially the grain size to improve the high temperature creep resistance.The asbuilt microstructure exhibited a fine grain size and large quantities of MC carbides that could effectively hinder grain growth.It was found that unconventional two-step heat treatments could lead to substantial grain growth,and the effect is particularly prominent at a specific temperature.The ease of grain growth was explained after classifying the microstructural evolution(boundary carbide transformation)during each heating step and related to the reduced grain boundary pinning force from MC carbides.Creep tests validated the effect of the new heat treatment scheme on the SLM-processed IN738LC at 850℃.An extended creep fracture life(1.5 to 4 times improvement)and lower secondary creep rates were achieved with samples subjected to the newly optimized two-step heat treatment.The complete creep curves are also firstly presented for SLM-IN738LC,confirming the effectiveness of grain growth and highlighting the importance of dedicated heat treatment for SLM superalloys.
基金supported by an Australian Research Council Discovery Project(Grant No.DP160104632)an Aus-tralian Government Research Training Program Scholarship.Y.J.Chen acknowledges the support provided by the Australian Re-search Council(Grant No.DE210101773).
文摘Fe_(72.4)Co_(13.9)Cr_(10.4)Mn_(2.7)B_(0.34)high entropy steel was prepared by magnetron sputtering.The alloy exhibits a high yield strength of 2.92±0.36 GPa while achieving appreciable plasticity of 13.7±1.9%at the ultimate compressive strength(3.37±0.36 GPa).The distribution of iron and chromium shows an un-usual,characteristic spinodal-like pattern at the nanometer scale,where compositions of Fe and Cr show strong anticorrelation and vary by as much as 20 at.%.The high strength is largely attributable to the compositional modulations,combined with fine grains with body-centered cubic(BCC)crystal structure,as well as grain boundary segregation of interstitial boron.The impressive plasticity is accommodated by the formation and operation of multiplanar,multicharacter dislocation slips,mediated by coherent in-terfaces,and controlled by shear bandings.The excellent strength-ductility combination is thus enabled by a range of distinctive strengthening mechanisms,rendering the new alloy a potential candidate for safety-critical,load-bearing structural applications.
基金This research was supported by the National Natural Science Foundation of China(Nos.52174364,12202201,92163215,52101143,and 91860104)Natural Science Foundation of Jiangsu Province(Nos.BK20220918,BK20212009)+3 种基金Science Center for Gas Turbine Project(P2022-A-IV-001-003)China Postdoctoral Science Foundation(No.2021M691582)the Fundamental Research Funds for the Central Universities(Nos.30922010711 and 30922010202)Open Project Program of Key Laboratory of China North Engine Research Institute(No.6142212210103).
文摘Gradient structure is emerging as an effective strategy to fabricate metals with remarkable mechanical performance,but have not been verified in intermetallic compounds for high-temperature applications.Through experiments and atomic simulations,we show that a typical intermetallic TiAl alloy with gra-dient structure has a significant strengthening effect both at room temperature and high temperatures.The room-temperature compressive strength of TiAl alloys with gradient grain obtained by additive man-ufacturing is 2.57 GPa,which is∼2.7 times as strong as that with equiaxed grain.The strengthening effect is attributed to more sessile dislocations in gradient structure caused by the intersections of mul-tiple slip systems in gradient grain.More importantly,the strengthening effect is still effective at high temperatures and the compressive strength is 1.28 GPa at 750°C.The simulation results show that this strengthening effect is due to the increased Hirth dislocation at high temperatures.This study expands the applications of TiAl alloys for load-bearing structures and provides a new strategy for improving the strength of intermetallic compounds at both room temperature and high temperatures.
基金funding from the Australian Research Council(ARC) via DP180103205。
文摘It has been a central task of solidification research to predict solute microsegregation. Apart from the Lever rule and the Scheil-Gulliver equation, which concern two extreme cases, a long list of microsegregation models has been proposed. However, the use of these models often requires essential experimental input information, e.g., the secondary dendrite arm spacing(λ), cooling rate( ˙T) or actual solidification range(△T). This requirement disables these models for alloy solidification with no measured values for λ,˙T and △T. Furthermore, not all of these required experimental data are easily obtainable. It is therefore highly desirable to have an easy-to-apply predictive model that is independent of experimental input,akin to the Lever rule or Scheil-Gulliver model. Gong, Chen, and co-workers have recently proposed such a model, referred to as the Gong-Chen model, by averaging the solid fractions(f_(s)) of the Lever rule and Scheil-Gulliver model as the actual solid fraction. We provide a systematic assessment of this model versus established solidification microsegregation models and address a latent deficiency of the model, i.e.,it allows the Lever rule solid fraction fsto be greater than one(f_(s)> 1). It is shown that the Gong-Chen model can serve as a generic model for alloy solidification until fsreaches about 0.9, beyond which(f_(s)> 0.9) its applicability is dictated by both the equilibrium solute partition coefcient(k) and the solute diffusion coefcient in the solid(Ds), which has been tabulated in detail.
文摘The micro structure and mechanical properties of new kind of hot-rolled high strength and high elongation steels with retained austenite were studied by discussing the influence of different carbon content. The research results indicate that carbon content has a significant effect on retaining austenite and consequently resulting in high elongation. Besides, new findings about relationship between carbon content and retained austenite as well as properties were discussed in the paper.
文摘The different chemical composition of silicon and manganese as well as different retained austenite fraction ranged from 4% to 10% of the high strength and high elongation steels were studied in the paper. The dislocations and carbon concentration in retained austenite were observed by a transmission electron microscope and an electric probe analyzer, respectively. The experimental results showed that silicon and manganese are two fundamental alloying elements to stabilize austenite effectively but retaining austenite in different mechanisms. Meanwhile, the cooling processing played an important role in controlling the fraction of retained austenite of the hot-rolled high strength and high plasticity steels.
基金supported by the National Key Research and Development Program of China(Grant No.2017YFA0303100)the National Natural Science Foundation of China(Grant Nos.11974306 and 12034017)the Natural Science Foundation of Zhejiang Province(Grant No.2021C01002)。
文摘A central research topic in condensed matter physics is the understanding of the evolution of various phases and phase transitions under different tuning parameters such as temperature, magnetic field and pressure. To explore the pressure-induced evolution of the magnetism and Fermi surface of the heavy fermion antiferromagnet Yb Pt Bi, we performed tunnel diode oscillator based measurements under pressure at low temperatures in high magnetic fields. Our results reveal that the magnetic order strengthens and the Fermi surface shrinks as the pressure increases, which are consistent with typical observations for Yb-based heavy fermion compounds. In addition, an anomalous change in the quantum oscillation amplitudes is observed above 1.5 GPa, and determining the origin requires further study.
