In order to reveal the temperature dependence of anisotropic stress？rupture behavior of SRR99 single crystal superalloys under conditions of temperature ranging from 650 to 1 040 °C and typical stresses,fracture...In order to reveal the temperature dependence of anisotropic stress？rupture behavior of SRR99 single crystal superalloys under conditions of temperature ranging from 650 to 1 040 °C and typical stresses,fracture morphologies and microstructure evolution were investigated by SEM and TEM.From the Larson-Miller curves,it is found that single crystal with [001] orientation has the optimum stress rupture property in comparison with [011] and [111] orientations at lower and intermediate temperature.With increasing temperature to 1 040 °C,stress-rupture properties of single crystals with three principal orientations tend to be equivalent.Based on the fracture surface and microstructural observations,superior stress？rupture behavior of single crystal with [001] orientation was rationalized and the effect of misorientation of single crystal on stress rupture property was also discussed.展开更多
At temperatures ranging from 760 to 1100 °C, the tensile properties of a nickel-based third generation single crystal superalloy DD9 with [100],[120] and [110] orientations were studied. The microstructures and f...At temperatures ranging from 760 to 1100 °C, the tensile properties of a nickel-based third generation single crystal superalloy DD9 with [100],[120] and [110] orientations were studied. The microstructures and fracture surfaces were observed by OM, SEM and TEM. Results show that the tensile strength of [100] specimen is higher than that of [120] and [110] specimens at 760 and 850 °C;while at the temperatures higher than 980 °C, the tensile strength of all specimens has little difference. The fracture mechanisms of [100],[120] and [110] specimens are the same at 760 and 980 °C. At 1100 °C, the fracture surfaces of [100] and [120] specimens are characterized by dimple features;while [110] specimen shows mixed quasi-cleavage and dimple featured fracture surfaces. At 760 °C, obvious superlattice stacking faults (SSFs) are observed only in [100] specimen;while at 1100 °C, the dislocation configurations of all specimens are similar. The difference in the number of potential active slip systems in [100],[120] and [110] specimens during the tensile deformation process is the main reason for the transverse tensile anisotropy.展开更多
Using the devices of split Hopkinson tension bar(SHTB)and split Hopkinson pressure bar(SHPB),the dynamic tension and compression experiments in three typical forming directions(rolling direction(RD),transverse directi...Using the devices of split Hopkinson tension bar(SHTB)and split Hopkinson pressure bar(SHPB),the dynamic tension and compression experiments in three typical forming directions(rolling direction(RD),transverse direction(TD)and normal direction(ND))were carried out at strain rates of 1000,2000 and 4000 s-1,respectively.From the microscopic point of view,the effect of strain rate and anisotropy on tension compression asymmetry of aviation aluminum alloy 7050 was studied by scanning electron microscope(SEM),metallographic microscope and electron backscatter diffraction(EBSD).The results showed that there was obvious asymmetry between tension and compression,especially that the yield strength of the material in tension was higher than that in compression.The asymmetry in the elastic stage of tension-compression was weaker and the asymmetry in the strengthening stage was stronger with the increase of strain rate.At the same strain rate,the changing trend of the flow stress was distinct under different orientations of tension and compression,which was related to the stress direction of the grains.According to EBSD grain orientation analysis and raw material texture pole figure analysis,it was found that the larger the difference in the degree of grain refinement during tension and compression,the larger the macro-flow stress difference.展开更多
Let X^H = {X^H（8）,8∈ R^N1} and XK = {X^K（t）,t ∈R^2} be two independent anisotropic Gaussian random fields with values in R^d with indices H = （H1,... ,HN1） ∈ （0, 1）^N1, K = （K1,..., KN2）∈ （0, 1）^N2, r...Let X^H = {X^H（8）,8∈ R^N1} and XK = {X^K（t）,t ∈R^2} be two independent anisotropic Gaussian random fields with values in R^d with indices H = （H1,... ,HN1） ∈ （0, 1）^N1, K = （K1,..., KN2）∈ （0, 1）^N2, respectively. Existence of intersections of the sample paths of XH and XK is studied. More generally, let E1 R^N1, E2 R^N2 and F R^d be Borel sets. A necessary condition and a sufficient condition for P{（X^H（E1） ∩ X^K（E2）） ∩ F ≠ Ф} 〉 0 in terms of the Bessel-Riesz type capacity and Hausdorff measure of E1 x E2 x F in the metric space （R^N1＋N2＋d, ρ） are proved, whereρ is a metric defined in terms of H and K. These results are applicable to solutions of stochastic heat equations driven by space-time Gaussian noise and fractional Brownian sheets.展开更多
Black phosphorus （BP） is a good candidate for studying strain effects on two- dimensional （2D） materials beyond graphene and transition-metal dichalcogenides. This is because of its particular ability to sustain h...Black phosphorus （BP） is a good candidate for studying strain effects on two- dimensional （2D） materials beyond graphene and transition-metal dichalcogenides. This is because of its particular ability to sustain high strain and remarkably anisotropic mechanical properties resulting from its unique puckered structure. We here investigate the dependence of lattice vibrational frequencies on cry- stallographic orientations in uniaxially strained few-layer BP by in-situ strained Raman spectroscopy. The out-of-plane A1 mode is sensitive to uniaxial strain along the near-armchair direction whereas the in-plane B2g and A2 modes are sensitive to strain in the near-zigzag direction. For uniaxial strains applied away from these directions, all three phonon modes are linearly redshifted. Our experimental observation is explained by the anisotropic influence of uniaxial tensile strain on structural properties of BP using density functional theory. This study demonstrates the possibility of selective tuning of in-plane and out-of-plane phonon modes in BP by uniaxial strain and makes strain engineering a promising avenue for extensively modulating the optical and mechanical properties of 2D materials.展开更多
We analyze high-resolution anisotropy of magnetic susceptibility (AMS) of the loess-paleosol successions at Luochuan, central Chinese Loess Plateau, in order to investigate the AMS characteristics and their climatic i...We analyze high-resolution anisotropy of magnetic susceptibility (AMS) of the loess-paleosol successions at Luochuan, central Chinese Loess Plateau, in order to investigate the AMS characteristics and their climatic implications. Our results indicate a normal sedimentary magnetic fabric for almost of all samples, characterized by minimum susceptibility axes grouped in an almost vertical direction. Magnetic foliation and anisotropy degree show upwards decreasing trend due to decreasing post-depositional compaction. Magnetic lineations show no preferred directions and thus cannot indicate paleowind patterns. AMS parameters at Luochuan are controlled by particle size, pedogenesis, and sedimentary compaction. The high peaks of magnetic foliation and anisotropy degree of L2, L3, L6, L9, and L15 correspond to the coarse particle sizes of these loess beds, indicating the grain-size dependence of AMS.展开更多
The application of antimony sulfide(Sb_(2)S_(3))has been limited mainly to the energy storage and photoelectric conversion fields.However,in this work,the application of Sb_(2)S_(3) is extended to the field of electro...The application of antimony sulfide(Sb_(2)S_(3))has been limited mainly to the energy storage and photoelectric conversion fields.However,in this work,the application of Sb_(2)S_(3) is extended to the field of electromagnetic(EM)wave absorption for the first time.High-permittivity Sb_(2)S_(3) singlecrystal nanorods were prepared successfully and exhibited excellent performance,with a low reflection loss of -65.9 dB(13.0 GHz,3.8 mm)and an ultra-wide effective absorption bandwidth of 9.5 GHz(8.5-18.0 GHz,4.1 mm).After excluding the general absorption mechanisms,including conductive losses,interfacial polarization,and dipole polarization,the distinctive single-crystal volume polarization affected by shape anisotropy was proposed.This work not only meets the challenge of a single-component dielectric material design but also introduces a new concept for construction of efficient dielectric EM wave absorption material.展开更多
Harvesting the promising high energy density of advanced electrode materials in lithium-ion batteries is critically dependent on a mechanistic understanding on how the materials function and degrade along with the bat...Harvesting the promising high energy density of advanced electrode materials in lithium-ion batteries is critically dependent on a mechanistic understanding on how the materials function and degrade along with the battery cycling.Here,we tracked phase transformations during(de)lithiation of Sb_(2)Se_(3) single crystals using in situ high-resolution transmission electron microscopy(HRTEM)technique,and revealed electro-chemo-mechanical evolution at the reaction interface.The effect of this electro-chemo-mechanical coupling has a complicated interplay on the lithiation kinetics and causes various types of defects at the reaction front,including dislocation dipoles,antiphase boundaries,and cracks.In return,the formed cracks and related defects build a path for fast diffusion of lithium ions and trigger a highly anisotropic lithiation at the twisted reaction front,giving rise to the formation of presumably "dead" Sb_(2)Se_(3) nanodomains in amorphous Li_(x)Sb_(2)Se_(3).The detailed mechanistic understanding may facilitate the rational design of high-capacity electrode materials for battery applications.展开更多
基金Projects (2010CB631200,2010CB631206) supported by the National Basic Research Program of ChinaProject (50931004) supported by the National Natural Science Foundation of China
文摘In order to reveal the temperature dependence of anisotropic stress？rupture behavior of SRR99 single crystal superalloys under conditions of temperature ranging from 650 to 1 040 °C and typical stresses,fracture morphologies and microstructure evolution were investigated by SEM and TEM.From the Larson-Miller curves,it is found that single crystal with [001] orientation has the optimum stress rupture property in comparison with [011] and [111] orientations at lower and intermediate temperature.With increasing temperature to 1 040 °C,stress-rupture properties of single crystals with three principal orientations tend to be equivalent.Based on the fracture surface and microstructural observations,superior stress？rupture behavior of single crystal with [001] orientation was rationalized and the effect of misorientation of single crystal on stress rupture property was also discussed.
文摘At temperatures ranging from 760 to 1100 °C, the tensile properties of a nickel-based third generation single crystal superalloy DD9 with [100],[120] and [110] orientations were studied. The microstructures and fracture surfaces were observed by OM, SEM and TEM. Results show that the tensile strength of [100] specimen is higher than that of [120] and [110] specimens at 760 and 850 °C;while at the temperatures higher than 980 °C, the tensile strength of all specimens has little difference. The fracture mechanisms of [100],[120] and [110] specimens are the same at 760 and 980 °C. At 1100 °C, the fracture surfaces of [100] and [120] specimens are characterized by dimple features;while [110] specimen shows mixed quasi-cleavage and dimple featured fracture surfaces. At 760 °C, obvious superlattice stacking faults (SSFs) are observed only in [100] specimen;while at 1100 °C, the dislocation configurations of all specimens are similar. The difference in the number of potential active slip systems in [100],[120] and [110] specimens during the tensile deformation process is the main reason for the transverse tensile anisotropy.
基金supported by the Natural Science Foundation of China(No.51675230)the Major Innovation Projects in Shandong Province (No. 2019JZZY010451)。
文摘Using the devices of split Hopkinson tension bar(SHTB)and split Hopkinson pressure bar(SHPB),the dynamic tension and compression experiments in three typical forming directions(rolling direction(RD),transverse direction(TD)and normal direction(ND))were carried out at strain rates of 1000,2000 and 4000 s-1,respectively.From the microscopic point of view,the effect of strain rate and anisotropy on tension compression asymmetry of aviation aluminum alloy 7050 was studied by scanning electron microscope(SEM),metallographic microscope and electron backscatter diffraction(EBSD).The results showed that there was obvious asymmetry between tension and compression,especially that the yield strength of the material in tension was higher than that in compression.The asymmetry in the elastic stage of tension-compression was weaker and the asymmetry in the strengthening stage was stronger with the increase of strain rate.At the same strain rate,the changing trend of the flow stress was distinct under different orientations of tension and compression,which was related to the stress direction of the grains.According to EBSD grain orientation analysis and raw material texture pole figure analysis,it was found that the larger the difference in the degree of grain refinement during tension and compression,the larger the macro-flow stress difference.
基金supported by Zhejiang Provincial Natural Science Foundation of China(Grant No. Y6100663)National Science Foundation of US (Grant No. DMS-1006903)
文摘Let X^H = {X^H（8）,8∈ R^N1} and XK = {X^K（t）,t ∈R^2} be two independent anisotropic Gaussian random fields with values in R^d with indices H = （H1,... ,HN1） ∈ （0, 1）^N1, K = （K1,..., KN2）∈ （0, 1）^N2, respectively. Existence of intersections of the sample paths of XH and XK is studied. More generally, let E1 R^N1, E2 R^N2 and F R^d be Borel sets. A necessary condition and a sufficient condition for P{（X^H（E1） ∩ X^K（E2）） ∩ F ≠ Ф} 〉 0 in terms of the Bessel-Riesz type capacity and Hausdorff measure of E1 x E2 x F in the metric space （R^N1＋N2＋d, ρ） are proved, whereρ is a metric defined in terms of H and K. These results are applicable to solutions of stochastic heat equations driven by space-time Gaussian noise and fractional Brownian sheets.
文摘Black phosphorus （BP） is a good candidate for studying strain effects on two- dimensional （2D） materials beyond graphene and transition-metal dichalcogenides. This is because of its particular ability to sustain high strain and remarkably anisotropic mechanical properties resulting from its unique puckered structure. We here investigate the dependence of lattice vibrational frequencies on cry- stallographic orientations in uniaxially strained few-layer BP by in-situ strained Raman spectroscopy. The out-of-plane A1 mode is sensitive to uniaxial strain along the near-armchair direction whereas the in-plane B2g and A2 modes are sensitive to strain in the near-zigzag direction. For uniaxial strains applied away from these directions, all three phonon modes are linearly redshifted. Our experimental observation is explained by the anisotropic influence of uniaxial tensile strain on structural properties of BP using density functional theory. This study demonstrates the possibility of selective tuning of in-plane and out-of-plane phonon modes in BP by uniaxial strain and makes strain engineering a promising avenue for extensively modulating the optical and mechanical properties of 2D materials.
基金supported by the National Basic Research Program of China (Grant No. 2010CB833400)Chinese Academy of Sciences (Grant Nos.KZCX2-YW-Q09-06-04, KZCX2-YW-130)National Natural Science Foundation of China (Grant No. 40830104)
文摘We analyze high-resolution anisotropy of magnetic susceptibility (AMS) of the loess-paleosol successions at Luochuan, central Chinese Loess Plateau, in order to investigate the AMS characteristics and their climatic implications. Our results indicate a normal sedimentary magnetic fabric for almost of all samples, characterized by minimum susceptibility axes grouped in an almost vertical direction. Magnetic foliation and anisotropy degree show upwards decreasing trend due to decreasing post-depositional compaction. Magnetic lineations show no preferred directions and thus cannot indicate paleowind patterns. AMS parameters at Luochuan are controlled by particle size, pedogenesis, and sedimentary compaction. The high peaks of magnetic foliation and anisotropy degree of L2, L3, L6, L9, and L15 correspond to the coarse particle sizes of these loess beds, indicating the grain-size dependence of AMS.
基金supported by the National Natural Science Foundation of China(51572157,21902085,and 51702188)the Natural Science Foundation of Shandong Province(ZR2019QF012)+1 种基金the Fundamental Research Funds for the Central Universities(2018JC046)Young Scholars Program of Shandong University(2018WLJH25)。
文摘The application of antimony sulfide(Sb_(2)S_(3))has been limited mainly to the energy storage and photoelectric conversion fields.However,in this work,the application of Sb_(2)S_(3) is extended to the field of electromagnetic(EM)wave absorption for the first time.High-permittivity Sb_(2)S_(3) singlecrystal nanorods were prepared successfully and exhibited excellent performance,with a low reflection loss of -65.9 dB(13.0 GHz,3.8 mm)and an ultra-wide effective absorption bandwidth of 9.5 GHz(8.5-18.0 GHz,4.1 mm).After excluding the general absorption mechanisms,including conductive losses,interfacial polarization,and dipole polarization,the distinctive single-crystal volume polarization affected by shape anisotropy was proposed.This work not only meets the challenge of a single-component dielectric material design but also introduces a new concept for construction of efficient dielectric EM wave absorption material.
基金supported by the National Key R&D Program of China(2018YFB1304902)the National Natural Science Foundation of China(11904372,U1813211,and 12004034)+2 种基金Beijing Institute of Technology Research Fund Program for Young ScholarsBeijing Institute of Technology Laboratory Research Project(2019BITSYA03)China Postdoctoral Science Foundation Funded Project(2021M690386)。
文摘Harvesting the promising high energy density of advanced electrode materials in lithium-ion batteries is critically dependent on a mechanistic understanding on how the materials function and degrade along with the battery cycling.Here,we tracked phase transformations during(de)lithiation of Sb_(2)Se_(3) single crystals using in situ high-resolution transmission electron microscopy(HRTEM)technique,and revealed electro-chemo-mechanical evolution at the reaction interface.The effect of this electro-chemo-mechanical coupling has a complicated interplay on the lithiation kinetics and causes various types of defects at the reaction front,including dislocation dipoles,antiphase boundaries,and cracks.In return,the formed cracks and related defects build a path for fast diffusion of lithium ions and trigger a highly anisotropic lithiation at the twisted reaction front,giving rise to the formation of presumably "dead" Sb_(2)Se_(3) nanodomains in amorphous Li_(x)Sb_(2)Se_(3).The detailed mechanistic understanding may facilitate the rational design of high-capacity electrode materials for battery applications.
