Two-dimensional van der Waals ferromagnet Fe_(3)GeTe_(2)(FGT)holds a great potential for applications in spintronic devices due to its high Curie temperature,easy tunability,and excellent structural stability in air.T...Two-dimensional van der Waals ferromagnet Fe_(3)GeTe_(2)(FGT)holds a great potential for applications in spintronic devices due to its high Curie temperature,easy tunability,and excellent structural stability in air.Theoretical studies have shown that pressure,as an external parameter,significantly affects its ferromagnetic properties.In this study,we have performed comprehensive high-pressure neutron powder diffraction(NPD)experiments on FGT up to 5 GPa to investigate the evolution of its structural and magnetic properties with hydrostatic pressure.The NPD data clearly reveal the robustness of the ferromagnetism in FGT,despite of an apparent suppression by hydrostatic pressure.As the pressure increases from 0 to 5 GPa,the Curie temperature is found to decrease monotonically from 225(5)K to 175(5)K,together with a dramatically suppressed ordered moment of Fe,which is well supported by the first-principles calculations.Although no pressure-driven structural phase transition is observed up to 5 GPa,quantitative analysis on the changes of bond lengths and bond angles indicates a significant modification of the exchange interactions,which accounts for the pressure-induced suppression of the ferromagnetism in FGT.展开更多
Face-centered cubic(FCC)equi-atomic multi-principal element alloys(MPEAs)exhibit excellent mechan-ical properties over a broad temperature range from cryogenic temperatures(CTs)to room temperature(RT).Specifically,whi...Face-centered cubic(FCC)equi-atomic multi-principal element alloys(MPEAs)exhibit excellent mechan-ical properties over a broad temperature range from cryogenic temperatures(CTs)to room temperature(RT).Specifically,while the deformation mechanism is dominated solely by dislocation slip at RT,the re-duction in stacking fault energy(SFE)at CTs leads to enhanced strain hardening with deformation twin-ning.This study employs in-situ neutron diffraction to reveal the temperature-dependent deformation be-havior of the FCC/body-centered cubic(BCC)dual-phase(DP)Al7(CoNiV)93 medium-entropy alloy(MEA),which possesses a matrix exhibiting deformation behavior analogous to that of representative equi-atomic MPEAs.Alongside the increased lattice friction stress associated with reduced temperature as a thermal component,deformation twinning at liquid nitrogen temperature(LNT)facilitates dislocation activity in the FCC matrix,leading to additional strain hardening induced by the dynamic Hall-Petch effect.This would give the appearance that the improved strengthening/hardening behaviors at LNT,compared to RT,are primarily attributable to the FCC phase.In contrast,the BCC precipitates are governed solely by dislocation slip for plastic deformation at both 77 K and 298 K,exhibiting a similar trend in dislocation density evolution.Nevertheless,empirical and quantitative findings indicate that the intrinsically high Peierls-Nabarro barriers in the BCC precipitates exhibit pronounced temperature-dependent lattice fric-tion stress,suggesting that the BCC precipitates play a more significant role in the temperature-dependent strengthening/hardening behaviors for the DP-MEA.This study provides a comprehensive understanding of deformation behavior by thoroughly analyzing temperature-dependent strengthening/hardening mech-anisms across various DP-MPEA systems,offering valuable guidelines for future alloy design.展开更多
Dynamic transformation(DT)of austenite(γ)to ferrite(α)in the hot deformation of various carbon steels was widely investigated.However,the nature of DT remains unclear due to the lack of quantitative analysis of stre...Dynamic transformation(DT)of austenite(γ)to ferrite(α)in the hot deformation of various carbon steels was widely investigated.However,the nature of DT remains unclear due to the lack of quantitative analysis of stress partitioning between two phases and the uncertainty of local distribution of substitu-tional elements at the interface in multi-component carbon steels used in the previous studies.Therefore,in the present study,a binary Fe-Ni alloy withα+γduplex microstructure in equilibrium was prepared and isothermally compressed inα+γtwo-phase region to achieve a quantitative analysis of microstruc-ture evolution,stress partitioning,and thermodynamics during DT.γtoαDT during isothermal compres-sion andαtoγreverse transformation on isothermal annealing under unloaded condition after deforma-tion were accompanied by Ni partitioning.The lattice strains during thermomechanical processing were obtained via in-situ neutron diffraction measurement,based on which the stress partitioning behavior betweenγandαwas discussed by using the generalized Hooke’s law.A thermodynamic framework for the isothermal deformation in solids was established based on the basic laws of thermodynamics,and it was shown that the total Helmholtz free energy change in the deformable material during the isothermal process should be smaller than the work done to the deformable material.Under the present thermody-namic framework,the microstructure evolution in the isothermal compression of Fe-14Ni alloy was well explained by considering the changes in chemical free energy,plastic and elastic energies,and the work done to the material.In addition,the stabilization of the softαphase in Fe-14Ni alloy by deformation was rationalized since theγtoαtransformation decreased the total Helmholtz free energy by decreasing the elastic and dislocation energies.展开更多
Nanoprecipitates and nanoscale retained austenite(RA)with suitable stability play crucial roles in deter-mining the yield strength(YS)and ductility of ultrahigh strength steels(UHSSs).However,owing to the kinetics inc...Nanoprecipitates and nanoscale retained austenite(RA)with suitable stability play crucial roles in deter-mining the yield strength(YS)and ductility of ultrahigh strength steels(UHSSs).However,owing to the kinetics incompatibility between nanoprecipitation and austenite reversion,it is highly challenging to si-multaneously introduce high-density nanoprecipitates and optimized RA in UHSSs.In this work,through the combination of austenite reversion treatment(ART)and subsequent flash austenitizing(FA),nanoscale chemical heterogeneity was successfully introduced into a low-cost UHSS prior to the aging process.This chemical heterogeneity involved the enrichment of Mn and Ni in the austenite phase.The resulting UHSS exhibited dual-nanoprecipitation of Ni(Al,Mn)and(Mo,Cr)_(2)C and nanoscale austenite stabilized via Mn and Ni enrichment.The hard martensitic matrix strengthened by high-density dual-nanoprecipitates con-strains the plastic deformation of soft RA with a relatively low fraction of-15%,and the presence of relatively stable nanoscale RA with adequate Mn and Ni enrichment leads to a marginal loss in YS but keeps a persistent transformation-induced plasticity(TRIP)effect.As a result,the newly-developed UHSS exhibits an ultrahigh YS of-1.7 GPa,an ultimate tensile strength(UTS)of-1.8 GPa,a large uniform elongation(UE)of-8.5%,and a total elongation(TE)of-13%.The strategy of presetting chemical heterogeneity to introduce proper metastable phases before aging can be extended to other UHSSs and precipitation-hardened alloys.展开更多
The yield stress of Fe-24Ni-0.3C(wt%)metastable austenitic steel increased 3.5 times(158→551 MPa)when the average grain size decreased from 35μm(coarse-grained[CG])to 0.5μm(ultrafine-grained[UFG]),whereas the tensi...The yield stress of Fe-24Ni-0.3C(wt%)metastable austenitic steel increased 3.5 times(158→551 MPa)when the average grain size decreased from 35μm(coarse-grained[CG])to 0.5μm(ultrafine-grained[UFG]),whereas the tensile elongation was kept large(0.87→0.82).In situ neutron diffraction measurements of the CG and UFG Fe-24Ni-0.3C steels were performed during tensile deformation at room temperature to quantitatively elucidate the influence of grain size on the mechanical properties and deformation mechanisms.The initial stages of plastic deformation in the CG and UFG specimens were dominated by dislocation slip,with deformation-induced martensitic transformation(DIMT)also occurring in the later stage of deformation.Results show that grain refinement increases the initiation stress of DIMT largely and suppresses the rate of DIMT concerning the strain,which is attributed to the following effects.(i)Grain refinement increased the stabilization of austenite and considerably delayed the initiation of DIMT in the<111>//LD(LD:loading direction)austenite grains,which were the most stable grains for DIMT.As a result,most of the<111>//LD austenite grains in the UFG specimen failed to transform into martensite.(ii)Grain refinement also suppressed the autocatalytic effect of the martensitic transformation.Nevertheless,the DIMT with the low transformation rate in the UFG specimen was more efficient in increasing the flow stress and more appropriate to maintain uniform deformation than that in the CG specimen during deformation.The above phenomena mutually contributed to the excellent combination of strength and ductility of the UFG metastable austenitic steel.展开更多
Antiferromagnetic spin fluctuation is regarded as the leading driving force for electron pairing in high-Tc superconductors.In iron-based superconductors,spin excitations at low energy range,especially the spin-resona...Antiferromagnetic spin fluctuation is regarded as the leading driving force for electron pairing in high-Tc superconductors.In iron-based superconductors,spin excitations at low energy range,especially the spin-resonance mode at ER~5kBTc,are important for understanding the superconductivity.Here,we use inelastic neutron scattering(INS)to investigate the symmetry and in-plane wave-vector dependence of low-energy spin excitations in uniaxial-strain detwinned Fe Se.The low-energy spin excitations(E<10 meV)appear mainly at Q=(±1,0)in the superconducting state(T9K)and the nematic state(T90 K),confirming the constant C_(2) rotational symmetry and ruling out the C_(4) mode at E≈3 meV reported in a prior INS study.Moreover,our results reveal an isotropic spin resonance in the superconducting state,which is consistent with the s±wave pairing symmetry.At slightly higher energy,low-energy spin excitations become highly anisotropic.The full width at half maximum of spin excitations is elongated along the transverse direction.The Q-space isotropic spin resonance and highly anisotropic low-energy spin excitations could arise from dyz intra-orbital selective Fermi surface nesting between the hole pocket aroundΓpoint and the electron pockets centered at MX point.展开更多
Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4%(±2%) was evaluated using the complementary techniques of in...Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4%(±2%) was evaluated using the complementary techniques of in-situ neutron diffraction, identical area electron backscatter diffraction, and transmission electron microscopy. In-situ neutron diffraction demonstrates that the compressive deformation was dominated by twin nucleation, twin growth, and basal slip, while detwinning dominated the unloading of compressive stresses and subsequent tension stage. With increasing number of cycles from one to eight: the volume fraction of twins at-2% strain gradually increased from 26.3% to 43.5%;the residual twins were present after 2% tension stage and their volume fraction increased from zero to 3.7% as well as a significant increase in their number;and the twinning spread from coarse grains to fine grains involving more grains for twinning. The increase in volume fraction and number of residual twins led to a transition from twin nucleation to twin growth, resulting in a decrease in yield strength of compression deformation with increasing cycles. A large number of-component dislocations observed in twins and the detwinned regions were attributed to the dislocation transmutation during the twinning and detwinning. The accumulation of barriers including twin boundaries and various types of dislocations enhanced the interactions of migrating twin boundary with these barriers during twinning and detwinning, which is considered to be the origin for increasing the work hardening rate in cyclic deformation of the AZ31 alloy.展开更多
Owing to their attractive structure and mechanical properties,high-entropy alloys(HEAs) and mediumentropy alloys(MEAs) have attracted considerable research interest.The strength of HEAs/MEAs with a single face-centere...Owing to their attractive structure and mechanical properties,high-entropy alloys(HEAs) and mediumentropy alloys(MEAs) have attracted considerable research interest.The strength of HEAs/MEAs with a single face-centered cubic(FCC) phase,on the other hand,requires improvement.Therefore,in this study,we demonstrate a strategy for increasing the room-temperature strength of FCC-phase HEAs/MEAs by tuning cryo-pre-straining-induced crystal defects via the temperature-dependent stacking fault energyregulated plasticity mechanism.Through neutron diffraction line profile analysis and electron microscope observation,the effect of the tuned defects on the tensile strength was clarified.Due to the cryorolling-induced high dislocation density,mechanical twins,and stacking faults,the room-temperature yield strength of an equiatomic CoCrFeNi HEA was increased by ~290%,from 243 MPa(as-recrystallized)to 941.6 MPa(30% cryo-rolled),while maintaining a tensile elongation of 18%.After partial recovery via heat treatment,the yield strength and ultimate tensile strength decreased slightly to 869 and 936 MPa,respectively.Conversely,the elongation increased to 25.6%,The dislocation density and distribution of the dislocations were found to contribute to the strengthening caused by forest dislocations,which warrants further investigation.This study discussed the possibility of developing single-phase high-performance HEAs by tuning pre-straining-induced crystal defects.展开更多
High-entropy alloys are characteristic of extensive atomic occupational disorder on high-symmetric lattices,differing from traditional alloys.Here,we investigate the magnetic and thermal transport properties of the pr...High-entropy alloys are characteristic of extensive atomic occupational disorder on high-symmetric lattices,differing from traditional alloys.Here,we investigate the magnetic and thermal transport properties of the prototype face-centered-cubic high-entropy alloy CrMnFeCoNi by combining physical properties measurements and neutron scattering.Direct-current and alternating-current magnetizations measurements indicate a mictomagnetic behavior with coexisting antiferromagnetic and ferromagnetic interactions below room temperature and three anomalies are found at about 80,40,and 20 K,which are related to the paramagnetic to antiferromagnetic transition,the antiferromagnetic to ferromagnetic transition,and the spin freezing,respectively.The electrical and thermal conductivities are significantly reduced compared to Ni,and the temperature dependence of lattice thermal conductivity exhibits a glasslike plateau.Inelastic neutron scattering measurements suggest weak anharmonicity so that the thermal transport is expected to be dominated by the defect scattering.展开更多
In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, it ...In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, it is predicted that in the nonrelativistic limit of certain collinear antiferromagnets, there exists a type of chiral“Dirac-like” fermion, whose dispersion manifests four-fold degenerate crossing points formed by spin-degenerate linear bands, with topologically protected Fermi arcs. Such an unconventional chiral fermion, protected by a hidden SU(2) symmetry in the hierarchy of an enhanced crystallographic group, namely spin space group, is not experimentally verified yet. Here, by angle-resolved photoemission spectroscopy measurements, we reveal the surface origin of the electron pocket at the Fermi surface in collinear antiferromagnet CoNb3S6. Combining with neutron diffraction and first-principles calculations, we suggest a multidomain collinear antiferromagnetic configuration, rendering the the existence of the Fermi-arc surface states induced by chiral Dirac-like fermions.Our work provides spectral evidence of the chiral Dirac-like fermion caused by particular spin symmetry in CoNb_(3)S_(6), paving an avenue for exploring new emergent phenomena in antiferromagnets with unconventional quasiparticle excitations.展开更多
Precipitation-strengthened medium-entropy alloys(MEAs)often display an excellent balance of strength and ductility.However,the influence of temperature on their mechanical properties and plastic deformation mechanism ...Precipitation-strengthened medium-entropy alloys(MEAs)often display an excellent balance of strength and ductility.However,the influence of temperature on their mechanical properties and plastic deformation mechanism requires further exploration.This study examines the tensile behavior and plastic deformation mechanisms of the(CoCrNi)_(94)Ti_(3)Al_(3)alloy at 298,77,and 20 K using in-situ neutron diffraction and electron microscopy methods.The tensile property shows a clear temperature dependence.Lower temperatures result in improved mechanical performance,as indicated by an increase in yield strength,ultimate tensile strength(UTS),and elongation.Specifically,the yield strength increases from 844 to 1152 MPa at 20 K,while the UTS increases from 1306 to 1848 MPa.Similarly,elongation improves from 25.8%to 33.3%as temperature decreases.At lower temperatures,a larger number of dislocations and stacking faults form,enhancing the alloy’s strain hardening ability.Notably,dislocations exhibit wavy morphologies at 298 K,whereas planar behavior becomes predominant at 20 and 77 K.No FCC→HCP phase transformation is detected,a behavior that contrasts with the CoCrNi MEA under deformation at 20 K.Additionally,the interaction between dislocations and L12 nanoparticles exhibited temperature dependence,suggesting the need for future investigations.This study offers valuable insights for advancing the design of high-performance alloys suitable for cryogenic applications.展开更多
Spin excitation continua observed in neutron scattering studies are often considered to be strong evidence of quantum spin liquid formation.In a disorder-free magnetic compound with a quantum spin liquid ground state,...Spin excitation continua observed in neutron scattering studies are often considered to be strong evidence of quantum spin liquid formation.In a disorder-free magnetic compound with a quantum spin liquid ground state,the elementary excitation is no longer the conventional spin waves(magnons).Instead,the magnons fractionalize into spinons,producing a characteristic two-spinon continuum.However,it remained uncertain whether a clean,ordered antiferromagnet could exhibit a continuous spectrum similar to that of a quantum spin liquid.This paper presents evidence of a spin excitation continuum in the magnetically ordered state of Na_(2)BaCo(PO_(4))_(2),where free spinons are absent.This challenges the interpretation of such a continuum as a definitive signature of a quantum spin liquid in new material studies.展开更多
We report thermodynamic and neutron scattering measurements of the triangular-lattice quantum Ising magnet TmMgGaO_(4)in longitudinal magnetic fields.Our experiments reveal a quasi-plateau state induced by quantum flu...We report thermodynamic and neutron scattering measurements of the triangular-lattice quantum Ising magnet TmMgGaO_(4)in longitudinal magnetic fields.Our experiments reveal a quasi-plateau state induced by quantum fluctuations.This state exhibits an unconventional non-monotonic field and temperature dependence of the magnetic order and excitation gap.In the high field regime where the quantum fluctuations are largely suppressed,we observed a disordered state with coherent magnon-like excitations despite the suppression of the spin excitation intensity.Through detailed semi-classical calculations,we are able to understand these behaviors quantitatively from the subtle competition between quantum fluctuations and frustrated Ising interactions.展开更多
The design of crosslinking domains is a vital factor to create functional hydrogels with controlled physical,mechanical,and adhesive properties.This paper demonstrates versatile synthetic systems of micelle-crosslinke...The design of crosslinking domains is a vital factor to create functional hydrogels with controlled physical,mechanical,and adhesive properties.This paper demonstrates versatile synthetic systems of micelle-crosslinked hydrogels with highly stretchable,self-healing,and selectively adhesive properties.For this,methacrylate-bearing random copolymer micelles are designed as physical and covalent crosslink domains via the self-assembly of amphiphilic random copolymers carrying hydrophilic poly(ethylene glycol)(PEG),hydrophobic butyl or dodecyl groups,and methacrylate-terminal PEG in water.The size,aggregation number,and pendant methacrylate number of the micelles are controlled by the composition and degree of polymerization.Hydrogels are efficiently obtained from the free radical polymerization of hydrophilic monomers such as PEG acrylate and acrylamide in the presence of the micelle crosslinkers in water.Owing to the dynamic yet selective chain exchange properties of the micelle domains,the hydrogels are highly stretchable up to over 1000%and show self-healing and selectively adhesive properties.The self-healing of hydrogels is promoted upon heating due to the fast chain exchange of the micelle domains,whereas hydrogels consisting of micelles with different alkyl groups are never adhesive because of their self-sorting properties.展开更多
We report thermodynamic and neutron diffraction measurements on the magnetic ordering properties of the honeycomb lattice magnet YbCl_(3). We find YbCl_(3) exhibits a Ne′el type long-range magnetic order at the wavev...We report thermodynamic and neutron diffraction measurements on the magnetic ordering properties of the honeycomb lattice magnet YbCl_(3). We find YbCl_(3) exhibits a Ne′el type long-range magnetic order at the wavevector(0, 0, 0) below TN= 600 mK.This magnetic order is associated with a small sharp peak in heat capacity and most magnetic entropy release occurs above the magnetic ordering temperature. The magnetic moment lies in-plane, parallel to the monoclinic a-axis, whose magnitude mYb= 0.86(3) μBis considerably smaller than the expected fully ordered moment of 2.24 μBfor the doublet crystal-field ground state. The magnetic ordering moment gradually increases with increasing magnetic field perpendicular to the ab-plane, reaching a maximum value of 1.6(2) μBat 4 T, before it is completely suppressed above ~ 9 T. These results indicate the presence of strong quantum fluctuations in YbCl_(3).展开更多
基金Project supported by the National Natural Science Foundation of China(Grant No.12074023)the Large Scientific Facility Open Subject of Songshan Lake(Grant No.KFKT2022B05)+1 种基金the Fundamental Research Funds for the Central Universities in ChinaNeutron diffraction experiments at the Materials and Life Science Experimental Facility of the J-PARC were performed through the user program(Proposal No.2023A0185).
文摘Two-dimensional van der Waals ferromagnet Fe_(3)GeTe_(2)(FGT)holds a great potential for applications in spintronic devices due to its high Curie temperature,easy tunability,and excellent structural stability in air.Theoretical studies have shown that pressure,as an external parameter,significantly affects its ferromagnetic properties.In this study,we have performed comprehensive high-pressure neutron powder diffraction(NPD)experiments on FGT up to 5 GPa to investigate the evolution of its structural and magnetic properties with hydrostatic pressure.The NPD data clearly reveal the robustness of the ferromagnetism in FGT,despite of an apparent suppression by hydrostatic pressure.As the pressure increases from 0 to 5 GPa,the Curie temperature is found to decrease monotonically from 225(5)K to 175(5)K,together with a dramatically suppressed ordered moment of Fe,which is well supported by the first-principles calculations.Although no pressure-driven structural phase transition is observed up to 5 GPa,quantitative analysis on the changes of bond lengths and bond angles indicates a significant modification of the exchange interactions,which accounts for the pressure-induced suppression of the ferromagnetism in FGT.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIP)(Nos.NRF-2021R1A2C3006662,NRF-2022R1A5A1030054,and RS-2023-00281246)supported by the Basic Science Research Program‘Fostering the Next Generation of Researchers(Ph.D.Candidate)’through the NRF funded by the Ministry of Edu-cation(No.RS-2023-00275651).
文摘Face-centered cubic(FCC)equi-atomic multi-principal element alloys(MPEAs)exhibit excellent mechan-ical properties over a broad temperature range from cryogenic temperatures(CTs)to room temperature(RT).Specifically,while the deformation mechanism is dominated solely by dislocation slip at RT,the re-duction in stacking fault energy(SFE)at CTs leads to enhanced strain hardening with deformation twin-ning.This study employs in-situ neutron diffraction to reveal the temperature-dependent deformation be-havior of the FCC/body-centered cubic(BCC)dual-phase(DP)Al7(CoNiV)93 medium-entropy alloy(MEA),which possesses a matrix exhibiting deformation behavior analogous to that of representative equi-atomic MPEAs.Alongside the increased lattice friction stress associated with reduced temperature as a thermal component,deformation twinning at liquid nitrogen temperature(LNT)facilitates dislocation activity in the FCC matrix,leading to additional strain hardening induced by the dynamic Hall-Petch effect.This would give the appearance that the improved strengthening/hardening behaviors at LNT,compared to RT,are primarily attributable to the FCC phase.In contrast,the BCC precipitates are governed solely by dislocation slip for plastic deformation at both 77 K and 298 K,exhibiting a similar trend in dislocation density evolution.Nevertheless,empirical and quantitative findings indicate that the intrinsically high Peierls-Nabarro barriers in the BCC precipitates exhibit pronounced temperature-dependent lattice fric-tion stress,suggesting that the BCC precipitates play a more significant role in the temperature-dependent strengthening/hardening behaviors for the DP-MEA.This study provides a comprehensive understanding of deformation behavior by thoroughly analyzing temperature-dependent strengthening/hardening mech-anisms across various DP-MPEA systems,offering valuable guidelines for future alloy design.
基金by JST FOREST Program(Grant No.JPMJFR203W,Japan)MEXT through Grant-in-Aid for Scientific Research(B)(No.19H02473,2019-2021)+2 种基金Grant-in-Aid for Scientific Research on Innovative Areas(Research in a proposed research area)(No.18H05456,2018-2022)the partial support through the research grant funded by the Amada Foundation(2022-2023)the financial support from the Amada Foundation(AF-2022017-B2).L.L.gratefully acknowledges the financial support provided by China Scholarship Council(No.201806295030)and thanks Dr.Elango Chandiran。
文摘Dynamic transformation(DT)of austenite(γ)to ferrite(α)in the hot deformation of various carbon steels was widely investigated.However,the nature of DT remains unclear due to the lack of quantitative analysis of stress partitioning between two phases and the uncertainty of local distribution of substitu-tional elements at the interface in multi-component carbon steels used in the previous studies.Therefore,in the present study,a binary Fe-Ni alloy withα+γduplex microstructure in equilibrium was prepared and isothermally compressed inα+γtwo-phase region to achieve a quantitative analysis of microstruc-ture evolution,stress partitioning,and thermodynamics during DT.γtoαDT during isothermal compres-sion andαtoγreverse transformation on isothermal annealing under unloaded condition after deforma-tion were accompanied by Ni partitioning.The lattice strains during thermomechanical processing were obtained via in-situ neutron diffraction measurement,based on which the stress partitioning behavior betweenγandαwas discussed by using the generalized Hooke’s law.A thermodynamic framework for the isothermal deformation in solids was established based on the basic laws of thermodynamics,and it was shown that the total Helmholtz free energy change in the deformable material during the isothermal process should be smaller than the work done to the deformable material.Under the present thermody-namic framework,the microstructure evolution in the isothermal compression of Fe-14Ni alloy was well explained by considering the changes in chemical free energy,plastic and elastic energies,and the work done to the material.In addition,the stabilization of the softαphase in Fe-14Ni alloy by deformation was rationalized since theγtoαtransformation decreased the total Helmholtz free energy by decreasing the elastic and dislocation energies.
基金Z.G.Yang acknowledges financial support from the National Key R&D program of China(grant No.2022YFB3705200)National Natural Science Foundation of China(grant No.52171008)+2 种基金H.Chen acknowledges financial support from the National Natural Science Foundation of China(grant No.51922054)Tsinghua University Initiative Scientific Research Program(No.20233080002)the Mobility Programme from the Sino-German Center(Grant No.M-0319).
文摘Nanoprecipitates and nanoscale retained austenite(RA)with suitable stability play crucial roles in deter-mining the yield strength(YS)and ductility of ultrahigh strength steels(UHSSs).However,owing to the kinetics incompatibility between nanoprecipitation and austenite reversion,it is highly challenging to si-multaneously introduce high-density nanoprecipitates and optimized RA in UHSSs.In this work,through the combination of austenite reversion treatment(ART)and subsequent flash austenitizing(FA),nanoscale chemical heterogeneity was successfully introduced into a low-cost UHSS prior to the aging process.This chemical heterogeneity involved the enrichment of Mn and Ni in the austenite phase.The resulting UHSS exhibited dual-nanoprecipitation of Ni(Al,Mn)and(Mo,Cr)_(2)C and nanoscale austenite stabilized via Mn and Ni enrichment.The hard martensitic matrix strengthened by high-density dual-nanoprecipitates con-strains the plastic deformation of soft RA with a relatively low fraction of-15%,and the presence of relatively stable nanoscale RA with adequate Mn and Ni enrichment leads to a marginal loss in YS but keeps a persistent transformation-induced plasticity(TRIP)effect.As a result,the newly-developed UHSS exhibits an ultrahigh YS of-1.7 GPa,an ultimate tensile strength(UTS)of-1.8 GPa,a large uniform elongation(UE)of-8.5%,and a total elongation(TE)of-13%.The strategy of presetting chemical heterogeneity to introduce proper metastable phases before aging can be extended to other UHSSs and precipitation-hardened alloys.
基金financial support from the Japan Society for the Promotion of Science(No.JP18H05479)JST(Japan Science and Technology Agency)CREST(No.JPMJCR1994)+1 种基金the Grant-in-Aid for Scientific Research(Nos.JP20H00306 and JP22K18888)the Data Creation and Utilization Type Material Research and Development(No.JPMXP1122684766)。
文摘The yield stress of Fe-24Ni-0.3C(wt%)metastable austenitic steel increased 3.5 times(158→551 MPa)when the average grain size decreased from 35μm(coarse-grained[CG])to 0.5μm(ultrafine-grained[UFG]),whereas the tensile elongation was kept large(0.87→0.82).In situ neutron diffraction measurements of the CG and UFG Fe-24Ni-0.3C steels were performed during tensile deformation at room temperature to quantitatively elucidate the influence of grain size on the mechanical properties and deformation mechanisms.The initial stages of plastic deformation in the CG and UFG specimens were dominated by dislocation slip,with deformation-induced martensitic transformation(DIMT)also occurring in the later stage of deformation.Results show that grain refinement increases the initiation stress of DIMT largely and suppresses the rate of DIMT concerning the strain,which is attributed to the following effects.(i)Grain refinement increased the stabilization of austenite and considerably delayed the initiation of DIMT in the<111>//LD(LD:loading direction)austenite grains,which were the most stable grains for DIMT.As a result,most of the<111>//LD austenite grains in the UFG specimen failed to transform into martensite.(ii)Grain refinement also suppressed the autocatalytic effect of the martensitic transformation.Nevertheless,the DIMT with the low transformation rate in the UFG specimen was more efficient in increasing the flow stress and more appropriate to maintain uniform deformation than that in the CG specimen during deformation.The above phenomena mutually contributed to the excellent combination of strength and ductility of the UFG metastable austenitic steel.
基金Beijing Normal University was supported by the Fundamental Research Funds for the Central Universitiesthe National Key Projects for Research and Development of China(No.2021YFA1400400)+1 种基金the National Natural Science Foundation of China(Grant Nos.12174029 and 11922402)the neutron beamtimes from J-PARC(Proposal No.2019A0002)。
文摘Antiferromagnetic spin fluctuation is regarded as the leading driving force for electron pairing in high-Tc superconductors.In iron-based superconductors,spin excitations at low energy range,especially the spin-resonance mode at ER~5kBTc,are important for understanding the superconductivity.Here,we use inelastic neutron scattering(INS)to investigate the symmetry and in-plane wave-vector dependence of low-energy spin excitations in uniaxial-strain detwinned Fe Se.The low-energy spin excitations(E<10 meV)appear mainly at Q=(±1,0)in the superconducting state(T9K)and the nematic state(T90 K),confirming the constant C_(2) rotational symmetry and ruling out the C_(4) mode at E≈3 meV reported in a prior INS study.Moreover,our results reveal an isotropic spin resonance in the superconducting state,which is consistent with the s±wave pairing symmetry.At slightly higher energy,low-energy spin excitations become highly anisotropic.The full width at half maximum of spin excitations is elongated along the transverse direction.The Q-space isotropic spin resonance and highly anisotropic low-energy spin excitations could arise from dyz intra-orbital selective Fermi surface nesting between the hole pocket aroundΓpoint and the electron pockets centered at MX point.
基金financially supported by the Elements Strategy Initiative for Structural Materials (ESISM, grant No. JPMXP0112101000) in Kyoto UniversityRXZ was supported by National Natural Science Foundation of China (NSFC, No. 51901007)+1 种基金SH and KA were supported by JSPS KAKENHI Nos. JP18H05479 and JP18H05476The neutron diffraction experiments at the Materials and Life Science Experimental Facility of the J-PARC were performed under a project program (Project No. 2014P0102)。
文摘Twinning and detwinning behavior of a commercial AZ31 magnesium alloy during cyclic compression–tension deformation with a total strain amplitude of 4%(±2%) was evaluated using the complementary techniques of in-situ neutron diffraction, identical area electron backscatter diffraction, and transmission electron microscopy. In-situ neutron diffraction demonstrates that the compressive deformation was dominated by twin nucleation, twin growth, and basal slip, while detwinning dominated the unloading of compressive stresses and subsequent tension stage. With increasing number of cycles from one to eight: the volume fraction of twins at-2% strain gradually increased from 26.3% to 43.5%;the residual twins were present after 2% tension stage and their volume fraction increased from zero to 3.7% as well as a significant increase in their number;and the twinning spread from coarse grains to fine grains involving more grains for twinning. The increase in volume fraction and number of residual twins led to a transition from twin nucleation to twin growth, resulting in a decrease in yield strength of compression deformation with increasing cycles. A large number of-component dislocations observed in twins and the detwinned regions were attributed to the dislocation transmutation during the twinning and detwinning. The accumulation of barriers including twin boundaries and various types of dislocations enhanced the interactions of migrating twin boundary with these barriers during twinning and detwinning, which is considered to be the origin for increasing the work hardening rate in cyclic deformation of the AZ31 alloy.
基金supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science(JSPS)KAKENHI(Nos.19K14838 and 21K03766)the“Creation of Life Innovation Materials for Interdisciplinary and International Researcher Development”project。
文摘Owing to their attractive structure and mechanical properties,high-entropy alloys(HEAs) and mediumentropy alloys(MEAs) have attracted considerable research interest.The strength of HEAs/MEAs with a single face-centered cubic(FCC) phase,on the other hand,requires improvement.Therefore,in this study,we demonstrate a strategy for increasing the room-temperature strength of FCC-phase HEAs/MEAs by tuning cryo-pre-straining-induced crystal defects via the temperature-dependent stacking fault energyregulated plasticity mechanism.Through neutron diffraction line profile analysis and electron microscope observation,the effect of the tuned defects on the tensile strength was clarified.Due to the cryorolling-induced high dislocation density,mechanical twins,and stacking faults,the room-temperature yield strength of an equiatomic CoCrFeNi HEA was increased by ~290%,from 243 MPa(as-recrystallized)to 941.6 MPa(30% cryo-rolled),while maintaining a tensile elongation of 18%.After partial recovery via heat treatment,the yield strength and ultimate tensile strength decreased slightly to 869 and 936 MPa,respectively.Conversely,the elongation increased to 25.6%,The dislocation density and distribution of the dislocations were found to contribute to the strengthening caused by forest dislocations,which warrants further investigation.This study discussed the possibility of developing single-phase high-performance HEAs by tuning pre-straining-induced crystal defects.
基金financially supported by the Liaoning Revitalization Talents Program(No.XLYC1807122)the National Natural Science Foundation of China(Nos.11804346,12005243,and 51771197)+1 种基金the Key Research Program of Frontier Sciences of Chinese Academy of Sciences(No.ZDBS-LY-JSC002)the Ministry of Science and Technology of China(No.2020YFA0406002)
文摘High-entropy alloys are characteristic of extensive atomic occupational disorder on high-symmetric lattices,differing from traditional alloys.Here,we investigate the magnetic and thermal transport properties of the prototype face-centered-cubic high-entropy alloy CrMnFeCoNi by combining physical properties measurements and neutron scattering.Direct-current and alternating-current magnetizations measurements indicate a mictomagnetic behavior with coexisting antiferromagnetic and ferromagnetic interactions below room temperature and three anomalies are found at about 80,40,and 20 K,which are related to the paramagnetic to antiferromagnetic transition,the antiferromagnetic to ferromagnetic transition,and the spin freezing,respectively.The electrical and thermal conductivities are significantly reduced compared to Ni,and the temperature dependence of lattice thermal conductivity exhibits a glasslike plateau.Inelastic neutron scattering measurements suggest weak anharmonicity so that the thermal transport is expected to be dominated by the defect scattering.
基金supported by the National Key R&D Program of China (Grant Nos. 2020YFA0308900 and 2022YFA1403700)the National Natural Science Foundation of China (Grant Nos. 12074163, 12134020, 11974157, 12104255, 12004159, and 12374146)+8 种基金Guangdong Provincial Key Laboratory for Computational Science and Material Design (Grant No. 2019B030301001)the Science, Technology and Innovation Commission of Shenzhen Municipality (Grant Nos. ZDSYS20190902092905285 and KQTD20190929173815000)Guangdong Basic and Applied Basic Research Foundation (Grant Nos. 2022B1515020046, 2021B1515130007, 2022A1515011915, 2019A1515110712, and 2022B1515130005)Shenzhen Science and Technology Program (Grant Nos. RCJC20221008092722009 and RCBS20210706092218039)the Guangdong Innovative and Entrepreneurial Research Team Program (Grant No. 2019ZT08C044)the beam time awarded by Australia’s Nuclear Science and Technology Organisation (ANSTO) (Grant No. P8130)the Materials and Life Science Experimental Facility of the Japan Proton Accelerator Research Complex (J-PARC) was performed under a user program (Proposal No. 2019B0140)performed at the Hiroshima Synchrotron Radiation Center (HiSOR) of Japan (Grant Nos. 22BG023 and 22BG029)Shanghai Synchrotron Radiation Facility (SSRF) BL03U (Grant No. 2022-SSRF-PT-020848)。
文摘In a Dirac semimetal, the massless Dirac fermion has zero chirality, leading to surface states connected adiabatically to a topologically trivial surface state as well as vanishing anomalous Hall effect. Recently, it is predicted that in the nonrelativistic limit of certain collinear antiferromagnets, there exists a type of chiral“Dirac-like” fermion, whose dispersion manifests four-fold degenerate crossing points formed by spin-degenerate linear bands, with topologically protected Fermi arcs. Such an unconventional chiral fermion, protected by a hidden SU(2) symmetry in the hierarchy of an enhanced crystallographic group, namely spin space group, is not experimentally verified yet. Here, by angle-resolved photoemission spectroscopy measurements, we reveal the surface origin of the electron pocket at the Fermi surface in collinear antiferromagnet CoNb3S6. Combining with neutron diffraction and first-principles calculations, we suggest a multidomain collinear antiferromagnetic configuration, rendering the the existence of the Fermi-arc surface states induced by chiral Dirac-like fermions.Our work provides spectral evidence of the chiral Dirac-like fermion caused by particular spin symmetry in CoNb_(3)S_(6), paving an avenue for exploring new emergent phenomena in antiferromagnets with unconventional quasiparticle excitations.
基金supported by the National Natural Science Foundation of China(Grant Nos.52305379,92163215,52174364,52101143)the Fundamental Research Funds for the Central Universities(Grant Nos.30922010711,30922010202)+2 种基金the Jiangsu Province Innovation Support Plan(Soft Science Research)(Grant No.BE2023024)the Natural Science Foundation of Jiangsu Province Major Project(Grant No.BK20243066)the Inner Mongolia Program of Grassland&Talents.The neutron-diffraction experiments were performed at BL19 in J-PARC with the proposals of 2022A0308,2023A0079,and 2023B0339.
文摘Precipitation-strengthened medium-entropy alloys(MEAs)often display an excellent balance of strength and ductility.However,the influence of temperature on their mechanical properties and plastic deformation mechanism requires further exploration.This study examines the tensile behavior and plastic deformation mechanisms of the(CoCrNi)_(94)Ti_(3)Al_(3)alloy at 298,77,and 20 K using in-situ neutron diffraction and electron microscopy methods.The tensile property shows a clear temperature dependence.Lower temperatures result in improved mechanical performance,as indicated by an increase in yield strength,ultimate tensile strength(UTS),and elongation.Specifically,the yield strength increases from 844 to 1152 MPa at 20 K,while the UTS increases from 1306 to 1848 MPa.Similarly,elongation improves from 25.8%to 33.3%as temperature decreases.At lower temperatures,a larger number of dislocations and stacking faults form,enhancing the alloy’s strain hardening ability.Notably,dislocations exhibit wavy morphologies at 298 K,whereas planar behavior becomes predominant at 20 and 77 K.No FCC→HCP phase transformation is detected,a behavior that contrasts with the CoCrNi MEA under deformation at 20 K.Additionally,the interaction between dislocations and L12 nanoparticles exhibited temperature dependence,suggesting the need for future investigations.This study offers valuable insights for advancing the design of high-performance alloys suitable for cryogenic applications.
基金supported by the National Key Research and Development Program of China(grant nos.2021YFA1400400,2022YFA1402204,and 2024YFA1408303)the National Natural Science Foundation of China(grant nos.12134020,12104255,12204223,12374124,and 12374146)+2 种基金the Open Fund of the China Spallation Neutron Source Songshan Lake Science City(grant no.KFKT2023A06)the Fundamental Research Funds for the Central Universities(grant no.226-2024-00068)the Guangdong Provincial Quantum Science Strategic Initiative(grant nos.GDZX2401006 and GDZX2401007).
文摘Spin excitation continua observed in neutron scattering studies are often considered to be strong evidence of quantum spin liquid formation.In a disorder-free magnetic compound with a quantum spin liquid ground state,the elementary excitation is no longer the conventional spin waves(magnons).Instead,the magnons fractionalize into spinons,producing a characteristic two-spinon continuum.However,it remained uncertain whether a clean,ordered antiferromagnet could exhibit a continuous spectrum similar to that of a quantum spin liquid.This paper presents evidence of a spin excitation continuum in the magnetically ordered state of Na_(2)BaCo(PO_(4))_(2),where free spinons are absent.This challenges the interpretation of such a continuum as a definitive signature of a quantum spin liquid in new material studies.
基金supported by the Innovation Program of Shanghai Municipal Education Commission(2017–01-07–00-07-E00018)the National Key R&D Program of the MOST of China(2016YFA0300203,2016YFA0300500,2016YFA0301001,and 2018YFE0103200)+6 种基金the National Natural Science Foundation of China(11874119)Shanghai Municipal Science and Technology Major Project(2019SHZDZX04)the Hong Kong Research Grants Council(17303819 and 17306520)supported by the National Natural Science Foundation of China(11875265)the Scientific Instrument Developing Project of the Chinese Academy of Sciences(3He based neutron polarization devices)the Institute of High Energy Physicsthe Chinese Academy of Sciences。
文摘We report thermodynamic and neutron scattering measurements of the triangular-lattice quantum Ising magnet TmMgGaO_(4)in longitudinal magnetic fields.Our experiments reveal a quasi-plateau state induced by quantum fluctuations.This state exhibits an unconventional non-monotonic field and temperature dependence of the magnetic order and excitation gap.In the high field regime where the quantum fluctuations are largely suppressed,we observed a disordered state with coherent magnon-like excitations despite the suppression of the spin excitation intensity.Through detailed semi-classical calculations,we are able to understand these behaviors quantitatively from the subtle competition between quantum fluctuations and frustrated Ising interactions.
基金Japan Society for the Promotion of Science KAKENHI,Grant/Award Numbers:JP19K22218,JP20H02787,JP20H05219,JP22H04539The Ogasawara Foundation for the Promotion of Science&Engineering+1 种基金Noguchi InstituteIketani Science and Technology Foundation。
文摘The design of crosslinking domains is a vital factor to create functional hydrogels with controlled physical,mechanical,and adhesive properties.This paper demonstrates versatile synthetic systems of micelle-crosslinked hydrogels with highly stretchable,self-healing,and selectively adhesive properties.For this,methacrylate-bearing random copolymer micelles are designed as physical and covalent crosslink domains via the self-assembly of amphiphilic random copolymers carrying hydrophilic poly(ethylene glycol)(PEG),hydrophobic butyl or dodecyl groups,and methacrylate-terminal PEG in water.The size,aggregation number,and pendant methacrylate number of the micelles are controlled by the composition and degree of polymerization.Hydrogels are efficiently obtained from the free radical polymerization of hydrophilic monomers such as PEG acrylate and acrylamide in the presence of the micelle crosslinkers in water.Owing to the dynamic yet selective chain exchange properties of the micelle domains,the hydrogels are highly stretchable up to over 1000%and show self-healing and selectively adhesive properties.The self-healing of hydrogels is promoted upon heating due to the fast chain exchange of the micelle domains,whereas hydrogels consisting of micelles with different alkyl groups are never adhesive because of their self-sorting properties.
基金supported by the National Key R&D Program of the Ministry of Science and Technology of China (Grant No. 2016YFA0300203)the Innovation Program of Shanghai Municipal Education Commission (Grant No. 2017-01-07-00-07-E00018)+1 种基金the Shanghai Municipal Science and Technology Major Project (Grant No. 2019SHZDZX01)the National Natural Science Foundation of China (Grant No. 11874119)。
文摘We report thermodynamic and neutron diffraction measurements on the magnetic ordering properties of the honeycomb lattice magnet YbCl_(3). We find YbCl_(3) exhibits a Ne′el type long-range magnetic order at the wavevector(0, 0, 0) below TN= 600 mK.This magnetic order is associated with a small sharp peak in heat capacity and most magnetic entropy release occurs above the magnetic ordering temperature. The magnetic moment lies in-plane, parallel to the monoclinic a-axis, whose magnitude mYb= 0.86(3) μBis considerably smaller than the expected fully ordered moment of 2.24 μBfor the doublet crystal-field ground state. The magnetic ordering moment gradually increases with increasing magnetic field perpendicular to the ab-plane, reaching a maximum value of 1.6(2) μBat 4 T, before it is completely suppressed above ~ 9 T. These results indicate the presence of strong quantum fluctuations in YbCl_(3).
