Designing alloys capable of withstanding irradiation is a crucial aspect of developing materials for nuclear reactors and aerospace applications.Local chemical order(LCO)has recently been recognized as a new microstru...Designing alloys capable of withstanding irradiation is a crucial aspect of developing materials for nuclear reactors and aerospace applications.Local chemical order(LCO)has recently been recognized as a new microstructural parameter to leverage,and its effect on the mechanical properties of body-centered cubic(BCC)multi-principal element alloys(MPEAs)has attracted much attention.However,the impact of LCO on the dynamic evolution of irradiation-induced defects in BCC MPEAs remains much less explored.In this study,we engineered varying degrees of LCO and local lattice distortion in NbZrTi BCC MPEAs by alloying them with different concentrations of interstitial oxygen solutes,and analyzed their effects on the evolution of radiation-induced defects during He irradiation at 673 K to 873 K,with a fluence of 5×10^(16) ions/cm^(2) and a peak dose of approximately 1 DPA.Using first-principles calculations and atomic-scale analysis of microstructures and chemical elements,we discovered that interstitial oxygen atoms enhance LCO and increase local lattice distortion.These heterogeneities increase the formation energy,and localize the diffusion,of vacancies,hence effectively reducing the transport of aggregating helium that causes bubble swelling.The initiation and growth of dislocation loops and precipitates are depressed as well.The manipulation of irradiation defects in BCC MPEAs,through orchestrating interstitial oxygen solutes and the LCO they provoke,adds a practical strategy for designing advanced alloys for nuclear applications.展开更多
C-N co-doped interstitial high entropy alloy(iHEA)was reported to have high strength and ductility.However,iHEA with fully recrystallized ultrafine grains(UFGs)and underlying thermally activated pro-cesses associated ...C-N co-doped interstitial high entropy alloy(iHEA)was reported to have high strength and ductility.However,iHEA with fully recrystallized ultrafine grains(UFGs)and underlying thermally activated pro-cesses associated with dislocation slip,twinning,and solute drag have not been reported yet.In this work,a C-N co-doped iHEA with nominal composition Fe_(48.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)N_(1.0)(at.%)was prepared,and the microstructures were tuned by cold-rolling and annealing treatments to improve mechanical properties.Upon cold-rolling with a strain of 1.74,the main microstructures in the iHEA are composed of nano-grains,nano-twins,HCP laminates,and high density of dislocations,leading to ultrahigh hardness of 466.7 HV and tensile strength of 1730 MPa at the expense of ductility(2.44%).Both the nanostructures and the high hardness of the iHEA can be maintained up to an annealing temperature of 600℃(462.5 HV).After annealing at 650℃ for 1 h,the UFG microstructures are obtained in the iHEA,containing re-crystallized grains with an average grain size of 0.91μm and nanoprecipitates with an average diameter of 90.8 nm.The combined strengthening and hardening effects of UFGs,nanoprecipitates,twinning,and solutes contribute to high strain hardening(n=0.81),gigapascal yield strength(984 MPa),and good duc-tility(20%).The C-N co-doping leads to a strong drag effect on dislocation slip,resulting in a nano-scale mean free path of dislocation slip λ(1.44 nm)and much small apparent activation volume V^(∗)(15.8 b^(3))of the UFG iHEA.展开更多
Interstitial atoms that commonly occupy the octahedral or tetrahedral interstices of face-centered cubic(FCC)lattice,can significantly affect the dislocation behaviors on deformation.Recently,interstitial doping has b...Interstitial atoms that commonly occupy the octahedral or tetrahedral interstices of face-centered cubic(FCC)lattice,can significantly affect the dislocation behaviors on deformation.Recently,interstitial doping has been applied to tune the mechanical properties of the emerging multicomponent,often termed high-entropy alloys(HEAs)or medium-entropy alloys(MEAs).However,the fundamental mechanisms of the dislocation nucleation and the onset of plasticity of interstitial multicomponent alloys governed by the concentration of interstitial atoms are still unclear.Therefore,in the present work,an instrumented nanoindentation was employed to investigate the interstitial concentration effects of carbon atoms on single FCC-phase equiatomic FeNiCr MEAs during loading.The results show that the pop-in events that denote the onset of incipient plasticity are triggered by the sudden heterogeneous dislocation nucleation via the primary atoms-vacancy exchange with the instant stress field,regardless of the interstitial concentration.Moreover,the measured activation volumes for dislocation nucleation of the FeNiCr MEAs are determined to be increased with the interstitial concentration,which definitely suggests the participation of interstitial atoms in the nucleation process.Besides,it is also found that the average value measured in statistics of the maximum shear stress corresponding to the first pop-in is enhanced with the interstitial concentration.Such scenario can be attributed to the improved local change transfer and lattice cohesion caused by the interstitial atoms with higher concentrations.Furthermore,the significant drag effect of interstitial carbon atoms hinders the mobile dislocations before exhaustion,which severely suppresses the subsequent occurrence of pop-in events in the carbon-doped specimens.The work gives a microscale view of interstitial effects on the mechanical properties of multicomponent alloys,which can further help to develop new interstitial strengthening strategies for structural materials with remarkable performance.展开更多
High-pressure electrides,characterized by the presence of interstitial quasi-atoms(ISQs),possess unique electronic structures and physical properties,such as diverse dimensions of electride states exhibiting different...High-pressure electrides,characterized by the presence of interstitial quasi-atoms(ISQs),possess unique electronic structures and physical properties,such as diverse dimensions of electride states exhibiting different superconductivity,which has attracted significant attention.Here,we report a new electron-deficient type of electride Li_(4)Al and identify its phase transition progress with pressurization,where the internal driving force behind phase transitions,bonding characteristics,and superconducting behaviors have been revealed based on first-principles density functional theory.Through analysis of the bonding properties of electride Li_(4)Al,we demonstrate that the ISQs exhibiting increasingly covalent characteristics between Al ions play a critical role in driving the phase transition.Our electron–phonon coupling calculations indicate that all phases exhibit superconducting behaviors.Importantly,we prove that the ISQs behave as free electrons and demonstrate that the factor governing T_(c) is primarily derived from Li-p-hybridized electronic states with ISQ compositions.These electronic states are scattered by low-frequency phonons arising from mixed vibrations of Li and Al affected by ISQs to enhance electron–phonon coupling.Our study largely expands the research scope of electrides,provides new insight for understanding phase transitions,and elucidates the effects of ISQs on superconducting behavior.展开更多
The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms i...The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms in a martensitic stainless steel with 0.3 wt%C and 0.5 wt%N after cryogenic treatment were investigated by the atom probe tomography.Carbon clusters begin to form after cryogenic treatment at-60℃and gradually increase with the decrease of cryogenic treatment temperature.While Mo–N and Cr–N pairs are homogeneously distributed in the matrix even after cryogenic treatment at-120℃,and then form enrichment phenomenon when the cryogenic temperature is deeply lowered to-190℃.It is found that the distinct redistributions of C and N atoms are associated with the different interaction energy between substitutional atoms and them.The stronger interaction between Cr,Mo atoms and N delays the segregation of N during the cryogenic treatment.Finally,the mechanical properties results confirmed that the deep lower cryogenic treatment is a promising method to improve the hardness and strength in the high nitrogen martensitic stainless steel.展开更多
It is urgent to establish a series of reasonable and general approaches to qualitatively and graphically characterize the four core effects of multi-principal element alloys(MPEAs)based on the inherent site preference...It is urgent to establish a series of reasonable and general approaches to qualitatively and graphically characterize the four core effects of multi-principal element alloys(MPEAs)based on the inherent site preference.In this contribution,a qualitatively and graphically characterizing approach to the diffusion behavior of interstitial nonmetallic atoms diffusing along the neighboring octahedra in MPEAs was explored intensively.For this purpose,the C atom diffusing along the neighboring octahedra in FCC_CoNiV MPEA with(V1.0000)1a(Co0.4445Ni0.4444V0.1111)3c,a constant ordered occupying configuration predicted in our previous paper,was demonstrated in detail.Six distinct diffusion paths along[110],[101],and[011]directions on XY,XZ,and YZ planes of FCC_CoNiV MPEA with forward and backward diffusion directions were explored one by one,respectively.The diffusion energy barrier,diffusion coefficient,diffusion constant,and activation energy were derived by employing first-principles calculations based on density functional theory alongside the Climbing Image Nudged Elastic Band method.Unlike diffusing behavior in pure metallic elements,the non-periodic diffusion energy barrier waves are revealed for the real FCC_CoNiV MPEA structure.The significant variations in the diffusion energy barriers are influenced by the atomic environment,particularly the interaction between V and C atoms,which enhances the localization of electrons and increases the overall diffusion energy barrier.The energy barriers show similar trends along six paths,but significant variations occur across different octahedral sites.展开更多
Oxygen-induced microstructural evolution critically governs the long-term reliability of refractory multi-principal element alloys(RMPEAs)in extreme environments,where oxygen ingress during prolonged high-temperature ...Oxygen-induced microstructural evolution critically governs the long-term reliability of refractory multi-principal element alloys(RMPEAs)in extreme environments,where oxygen ingress during prolonged high-temperature service can drastically alter micro structural stability and mechanical performance,yet its atomic-scale mechanisms remain poorly understood.Here,oxygen's dual role in NbZrTi-based RMPEAs is systematically revealed through aging experiments at 650℃for 48and 168 h,combined with multiscale characterization.High-oxygen alloys(3 at.%O)exhibited multi-phase precipitation,including Zr-O-enriched hexagonal close-packed and dual body-centered cubic phases(Zr+Ti-O-rich and Nb+Ti-rich),governed by oxygen redistribution and thermodynamic stabilization.Contrary to conventional precipitation hardening,oxygen segregation gradients at the grain boundaries induced lattice distortion mitigation in the matrix,leading to a twostage age-softening behavior:rapid initial hardness reduction(20%within 48 h)followed by a plateau regime.The interplay between oxygen-mediated phase separation and concentration-dependent solute partitioning highlights the delicate balance required to optimize RMPEAs for high-temperature applications.These findings establish oxygen concentration thresholds and grain boundary engineering as critical design parameters for RMPEAs,enabling simultaneous optimization of radiation resistance and century-scale stability in next-generation nuclear reactor structure materials.展开更多
Control of subsurface interstitial atoms in transition metals is an effective approach to modulate selec tivity in hydrogenation reactions.In this study,nickel was alloyed with gallium to form Ni_(3)Ga,thereby regulat...Control of subsurface interstitial atoms in transition metals is an effective approach to modulate selec tivity in hydrogenation reactions.In this study,nickel was alloyed with gallium to form Ni_(3)Ga,thereby regulating the octahedral interstitial sites.Subsequently,carbon atoms were introduced into the Ni_(3)Ga(forming Ni_(3)GaC_(0.5))via thermal treatment in an acetylene atmosphere,leading to a significant enhance ment in selectivity for acetylene hydrogenation reaction.The X-ray diffraction and transmission electron microscopy results demonstrate an increase in the lattice parameter due to the incorporation of carbon atoms and the uniform distribution of carbon in Ni_(3)GaC_(0.5)nanoparticles.The obtained Ni_(3)GaC_(0.5)/oCNT catalyst exhibits significantly improved selectivity in acetylene hydrogenation reaction,with approxi mately 82%ethylene selectivity at 98%conversion.Furthermore,it maintains good selectivity at variou hydrogen-to-alkyne ratios and displays good stability during long-term operation.The introduction of car bon suppresses the formation of the subsurface hydrogen structure under reaction conditions.Addition ally,the charge transfer between carbon and nickel results in the electron deficiency of nickel,effectively inhibiting the over-hydrogenation pathway and enhancing the selectivity.These results provide insight for the design of non-precious metal catalysts in selective hydrogenation reactions.展开更多
Theoretical and experimental investigations on the dependence of the intensity of infrared （IR） absorption of poly- crystalline cubic boron nitride thin films under the residual compressive stress conditions have be...Theoretical and experimental investigations on the dependence of the intensity of infrared （IR） absorption of poly- crystalline cubic boron nitride thin films under the residual compressive stress conditions have been performed. Our results indicate that the intensity of the IR absorption is proportional to the total degree of freedom of all the ions in the ordered regions. The reduction of interstitial Ar atom concentration, which causes the increase in the ordered regions of cubic boron nitride （cBN） crystallites, could be one cause for the increase in the intensity of IR absorption after residual compressive stress relaxation. Theoretical derivation is in good agreement with the experimental results concerning the IR absorption intensity and the Ar interstitial atom concentration in cubic boron nitride films measured by energy dispersion X-ray spec- troscopy. Our results also suggest that the interstitial Ar is the origin of residual compressive stress accumulation in plasma enhanced cBN film deposition.展开更多
The pressure-induced structural evolution of apatite-type La9.33Si6026 was systematically studied using in situ syn- chrotron x-ray diffraction （XRD）. The XRD spectra indicated that a subtly reversible phase transit...The pressure-induced structural evolution of apatite-type La9.33Si6026 was systematically studied using in situ syn- chrotron x-ray diffraction （XRD）. The XRD spectra indicated that a subtly reversible phase transition from P63/m to P63 symmetry occurred at ~ 13.6 GPa because of the tilting of the SiO4 tetrahedra under compression. Furthermore, the La9.33Si6026 exhibited a higher axial compression ratio for the a-axis than the c-axis, owing to the different axial arrange- ment of the SiO4 tetrahedra. Interestingly, the high-pressure phase showed compressibility unusually higher than that of the initial phase, suggesting that the low P63 symmetry provided more degrees of freedom. Moreover, the La9.33Si6026 exhibited a lower phase transition pressure （PT） and a higher lattice compression than LaloSi6027. Comparisons between La9.33Si6026 and LaloSi6027 provided a deeper understanding of the effect of interstitial oxygen atoms on the structural evolution of apatite-type lanthanum silicates （ATLSs）.展开更多
In thermoelectrics,doping is essential to augment the figure of merit.Traditional strategy,predomina ntly heavy doping,aims to optimize carrier concentration and restrain lattice thermal conductivity.However,this tact...In thermoelectrics,doping is essential to augment the figure of merit.Traditional strategy,predomina ntly heavy doping,aims to optimize carrier concentration and restrain lattice thermal conductivity.However,this tactic can severely hamper carrier transport due to pronounced point defect scattering,particularly in materials with inherently low carrier mean-free-path.Conversely,dilute doping,although minimally affecting carrier mobility,frequently fails to optimize other vital thermoelectric parameters.Herein,we present a more nuanced dilute doping strategy in GeTe,leveraging the multifaceted roles of small-size metal atoms.A mere 4%CuPbSbTe_(3)introduction into GeTe swiftly suppresses rhombohedral distortion and optimizes carrier concentration through the aid of Cu interstitials.Additionally,the formation of multiscale microstructures,including zero-dimensional Cu interstitials,one-dimensional dislocations,two-dimensional planar defects,and three-dimensional nanoscale amorphous GeO_(2)and Cu_(2)GeTe_(3)precipitates,along with the ensuing lattice softening,contributes to an ultralow lattice thermal conductivity.Intriguingly,dilute CuPbSbTe_(3)doping incurs only a marginal decrease in carrier mobility.Subsequent trace Cd doping,employed to alleviate the bipolar effect and align the valence bands,yields an impressive figure-of-merit of 2.03 at 623 K in(Ge_(0.97)Cd_(0.03)Te)_(0.96)(CuPbSbTe_(3))_(0.04).This leads to a high energyconversion efficiency of 7.9%and a significant power density of 3.44 W cm^(-2)at a temperature difference of 500 K.These results underscore the invaluable insights gained into the constructive role of nuanced dilute doping in the concurrent tuning of carrier and phonon transport in GeTe and other thermoelectric materials.展开更多
The Pu-He pair potential fitted by ab initio data, and the Pu-Pu and He-He modified embedded atom method (MEAM) poten-tials have been implemented to perform multi-scale simulations for the interactions of fracture wit...The Pu-He pair potential fitted by ab initio data, and the Pu-Pu and He-He modified embedded atom method (MEAM) poten-tials have been implemented to perform multi-scale simulations for the interactions of fracture with the self-interstitial atom(SIA), He interstitial atom and He-vacancy clusters. The simulation results indicate that Pu atoms around the fracture agglom-erate into an elliptic self-interstitial loop. Interstitial He atoms evolve into separate interstitial atoms, small He atom clustersand some substitutional He atoms. The He-vacancy cluster forms a spheric structure with a 1:1 He-to-vacancy ratio. Finally,the existence of self-interstitial atoms will lead to the local change of Pu lattice and an increasing disorder, and the wholesimulation cell shows a melting state at about 10.0 ps.展开更多
基金financially supported by the National Key Research and Development Program of China(No.2019YFA0209900)the National Natural Science Foundation of China(Nos.12305290,12075179,52231001,and 12105219)+1 种基金the Postdoctoral Fellowship Program of CPSF(No.GZC20232089)the Innovative Scientific Program of China National Nuclear Corporation,and the Fundamental Research Funds for the Central Universities.
文摘Designing alloys capable of withstanding irradiation is a crucial aspect of developing materials for nuclear reactors and aerospace applications.Local chemical order(LCO)has recently been recognized as a new microstructural parameter to leverage,and its effect on the mechanical properties of body-centered cubic(BCC)multi-principal element alloys(MPEAs)has attracted much attention.However,the impact of LCO on the dynamic evolution of irradiation-induced defects in BCC MPEAs remains much less explored.In this study,we engineered varying degrees of LCO and local lattice distortion in NbZrTi BCC MPEAs by alloying them with different concentrations of interstitial oxygen solutes,and analyzed their effects on the evolution of radiation-induced defects during He irradiation at 673 K to 873 K,with a fluence of 5×10^(16) ions/cm^(2) and a peak dose of approximately 1 DPA.Using first-principles calculations and atomic-scale analysis of microstructures and chemical elements,we discovered that interstitial oxygen atoms enhance LCO and increase local lattice distortion.These heterogeneities increase the formation energy,and localize the diffusion,of vacancies,hence effectively reducing the transport of aggregating helium that causes bubble swelling.The initiation and growth of dislocation loops and precipitates are depressed as well.The manipulation of irradiation defects in BCC MPEAs,through orchestrating interstitial oxygen solutes and the LCO they provoke,adds a practical strategy for designing advanced alloys for nuclear applications.
文摘C-N co-doped interstitial high entropy alloy(iHEA)was reported to have high strength and ductility.However,iHEA with fully recrystallized ultrafine grains(UFGs)and underlying thermally activated pro-cesses associated with dislocation slip,twinning,and solute drag have not been reported yet.In this work,a C-N co-doped iHEA with nominal composition Fe_(48.5)Mn_(30)Co_(10)Cr_(10)C_(0.5)N_(1.0)(at.%)was prepared,and the microstructures were tuned by cold-rolling and annealing treatments to improve mechanical properties.Upon cold-rolling with a strain of 1.74,the main microstructures in the iHEA are composed of nano-grains,nano-twins,HCP laminates,and high density of dislocations,leading to ultrahigh hardness of 466.7 HV and tensile strength of 1730 MPa at the expense of ductility(2.44%).Both the nanostructures and the high hardness of the iHEA can be maintained up to an annealing temperature of 600℃(462.5 HV).After annealing at 650℃ for 1 h,the UFG microstructures are obtained in the iHEA,containing re-crystallized grains with an average grain size of 0.91μm and nanoprecipitates with an average diameter of 90.8 nm.The combined strengthening and hardening effects of UFGs,nanoprecipitates,twinning,and solutes contribute to high strain hardening(n=0.81),gigapascal yield strength(984 MPa),and good duc-tility(20%).The C-N co-doping leads to a strong drag effect on dislocation slip,resulting in a nano-scale mean free path of dislocation slip λ(1.44 nm)and much small apparent activation volume V^(∗)(15.8 b^(3))of the UFG iHEA.
基金financially supported by the Natural Science Foundation of Hunan province(nos.2021JJ40736,2019JJ60062 and 2020JJ6090)。
文摘Interstitial atoms that commonly occupy the octahedral or tetrahedral interstices of face-centered cubic(FCC)lattice,can significantly affect the dislocation behaviors on deformation.Recently,interstitial doping has been applied to tune the mechanical properties of the emerging multicomponent,often termed high-entropy alloys(HEAs)or medium-entropy alloys(MEAs).However,the fundamental mechanisms of the dislocation nucleation and the onset of plasticity of interstitial multicomponent alloys governed by the concentration of interstitial atoms are still unclear.Therefore,in the present work,an instrumented nanoindentation was employed to investigate the interstitial concentration effects of carbon atoms on single FCC-phase equiatomic FeNiCr MEAs during loading.The results show that the pop-in events that denote the onset of incipient plasticity are triggered by the sudden heterogeneous dislocation nucleation via the primary atoms-vacancy exchange with the instant stress field,regardless of the interstitial concentration.Moreover,the measured activation volumes for dislocation nucleation of the FeNiCr MEAs are determined to be increased with the interstitial concentration,which definitely suggests the participation of interstitial atoms in the nucleation process.Besides,it is also found that the average value measured in statistics of the maximum shear stress corresponding to the first pop-in is enhanced with the interstitial concentration.Such scenario can be attributed to the improved local change transfer and lattice cohesion caused by the interstitial atoms with higher concentrations.Furthermore,the significant drag effect of interstitial carbon atoms hinders the mobile dislocations before exhaustion,which severely suppresses the subsequent occurrence of pop-in events in the carbon-doped specimens.The work gives a microscale view of interstitial effects on the mechanical properties of multicomponent alloys,which can further help to develop new interstitial strengthening strategies for structural materials with remarkable performance.
基金supported by the National Key Research and Development Program of China (Grant Nos.2023YFA1406200 and 2022YFA-1405500)the National Natural Science Foundation of China (Grant Nos.12304021 and 52072188)+3 种基金Zhejiang Provincial Natural Science Foundation of China (Grant Nos.LQ23A040004 and MS26A040028)Natural Science Foundation of Ningbo (Grant Nos.2022J091 and ZX2025001430)the Program for Science and Technology Innovation Team in Zhejiang (Grant No.2021R01004)the Program for Changjiang Scholars and Innovative Research Team in University (Grant No.IRT_15R23)。
文摘High-pressure electrides,characterized by the presence of interstitial quasi-atoms(ISQs),possess unique electronic structures and physical properties,such as diverse dimensions of electride states exhibiting different superconductivity,which has attracted significant attention.Here,we report a new electron-deficient type of electride Li_(4)Al and identify its phase transition progress with pressurization,where the internal driving force behind phase transitions,bonding characteristics,and superconducting behaviors have been revealed based on first-principles density functional theory.Through analysis of the bonding properties of electride Li_(4)Al,we demonstrate that the ISQs exhibiting increasingly covalent characteristics between Al ions play a critical role in driving the phase transition.Our electron–phonon coupling calculations indicate that all phases exhibit superconducting behaviors.Importantly,we prove that the ISQs behave as free electrons and demonstrate that the factor governing T_(c) is primarily derived from Li-p-hybridized electronic states with ISQ compositions.These electronic states are scattered by low-frequency phonons arising from mixed vibrations of Li and Al affected by ISQs to enhance electron–phonon coupling.Our study largely expands the research scope of electrides,provides new insight for understanding phase transitions,and elucidates the effects of ISQs on superconducting behavior.
基金supported by the National Natural Science Foundation of China(No.51871212)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDC04000000)+1 种基金the Major Scientific and Technological Projects of Jiangxi Province(No.20194ABC28011)the Project to Strengthen Industrial Development at the Grass-roots Level(TC190A4DA/35)。
文摘The redistribution of C and N atoms during cryogenic treatment is crucial for the microstructure evolution and properties of high nitrogen martensitic steel.Here,the distinct redistribution behavior of C and N atoms in a martensitic stainless steel with 0.3 wt%C and 0.5 wt%N after cryogenic treatment were investigated by the atom probe tomography.Carbon clusters begin to form after cryogenic treatment at-60℃and gradually increase with the decrease of cryogenic treatment temperature.While Mo–N and Cr–N pairs are homogeneously distributed in the matrix even after cryogenic treatment at-120℃,and then form enrichment phenomenon when the cryogenic temperature is deeply lowered to-190℃.It is found that the distinct redistributions of C and N atoms are associated with the different interaction energy between substitutional atoms and them.The stronger interaction between Cr,Mo atoms and N delays the segregation of N during the cryogenic treatment.Finally,the mechanical properties results confirmed that the deep lower cryogenic treatment is a promising method to improve the hardness and strength in the high nitrogen martensitic stainless steel.
基金supported by the National Natural Science Foundation of China(50971043 and 51171046)the Key Research and Development Program of China(CISRI-21T62450ZD)+1 种基金the Natural Science Foundation of Fujian Province(2014J01176,2018J01754,and 2021J01590)the Student Research and Training Program(SRTP)of Fuzhou University(27297).
文摘It is urgent to establish a series of reasonable and general approaches to qualitatively and graphically characterize the four core effects of multi-principal element alloys(MPEAs)based on the inherent site preference.In this contribution,a qualitatively and graphically characterizing approach to the diffusion behavior of interstitial nonmetallic atoms diffusing along the neighboring octahedra in MPEAs was explored intensively.For this purpose,the C atom diffusing along the neighboring octahedra in FCC_CoNiV MPEA with(V1.0000)1a(Co0.4445Ni0.4444V0.1111)3c,a constant ordered occupying configuration predicted in our previous paper,was demonstrated in detail.Six distinct diffusion paths along[110],[101],and[011]directions on XY,XZ,and YZ planes of FCC_CoNiV MPEA with forward and backward diffusion directions were explored one by one,respectively.The diffusion energy barrier,diffusion coefficient,diffusion constant,and activation energy were derived by employing first-principles calculations based on density functional theory alongside the Climbing Image Nudged Elastic Band method.Unlike diffusing behavior in pure metallic elements,the non-periodic diffusion energy barrier waves are revealed for the real FCC_CoNiV MPEA structure.The significant variations in the diffusion energy barriers are influenced by the atomic environment,particularly the interaction between V and C atoms,which enhances the localization of electrons and increases the overall diffusion energy barrier.The energy barriers show similar trends along six paths,but significant variations occur across different octahedral sites.
基金supported by the National Natural Science Foundation of China(Nos.12305290,U2441258,52231001)the Postdoctoral Fellowship Program of CPSF(No.GZC20232089)+1 种基金the Innovative Scientific Program of China National Nuclear Corporationthe Fundamental Research Funds for the Central Universities。
文摘Oxygen-induced microstructural evolution critically governs the long-term reliability of refractory multi-principal element alloys(RMPEAs)in extreme environments,where oxygen ingress during prolonged high-temperature service can drastically alter micro structural stability and mechanical performance,yet its atomic-scale mechanisms remain poorly understood.Here,oxygen's dual role in NbZrTi-based RMPEAs is systematically revealed through aging experiments at 650℃for 48and 168 h,combined with multiscale characterization.High-oxygen alloys(3 at.%O)exhibited multi-phase precipitation,including Zr-O-enriched hexagonal close-packed and dual body-centered cubic phases(Zr+Ti-O-rich and Nb+Ti-rich),governed by oxygen redistribution and thermodynamic stabilization.Contrary to conventional precipitation hardening,oxygen segregation gradients at the grain boundaries induced lattice distortion mitigation in the matrix,leading to a twostage age-softening behavior:rapid initial hardness reduction(20%within 48 h)followed by a plateau regime.The interplay between oxygen-mediated phase separation and concentration-dependent solute partitioning highlights the delicate balance required to optimize RMPEAs for high-temperature applications.These findings establish oxygen concentration thresholds and grain boundary engineering as critical design parameters for RMPEAs,enabling simultaneous optimization of radiation resistance and century-scale stability in next-generation nuclear reactor structure materials.
基金financial support provided by the National Natural Science Foundation of China(Nos.22002173,22072164,52161145403)Natural Science Foundation of Liaoning Province(No.2022-MS-004)+2 种基金China Postdoctoral Science Foundation(No.2020M680999)LiaoNing Revitalization Talents Program(No.XLYC1807175)the foundations of Shenyang National Laboratory for Materials Science。
文摘Control of subsurface interstitial atoms in transition metals is an effective approach to modulate selec tivity in hydrogenation reactions.In this study,nickel was alloyed with gallium to form Ni_(3)Ga,thereby regulating the octahedral interstitial sites.Subsequently,carbon atoms were introduced into the Ni_(3)Ga(forming Ni_(3)GaC_(0.5))via thermal treatment in an acetylene atmosphere,leading to a significant enhance ment in selectivity for acetylene hydrogenation reaction.The X-ray diffraction and transmission electron microscopy results demonstrate an increase in the lattice parameter due to the incorporation of carbon atoms and the uniform distribution of carbon in Ni_(3)GaC_(0.5)nanoparticles.The obtained Ni_(3)GaC_(0.5)/oCNT catalyst exhibits significantly improved selectivity in acetylene hydrogenation reaction,with approxi mately 82%ethylene selectivity at 98%conversion.Furthermore,it maintains good selectivity at variou hydrogen-to-alkyne ratios and displays good stability during long-term operation.The introduction of car bon suppresses the formation of the subsurface hydrogen structure under reaction conditions.Addition ally,the charge transfer between carbon and nickel results in the electron deficiency of nickel,effectively inhibiting the over-hydrogenation pathway and enhancing the selectivity.These results provide insight for the design of non-precious metal catalysts in selective hydrogenation reactions.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.50772096 and 61176051)
文摘Theoretical and experimental investigations on the dependence of the intensity of infrared （IR） absorption of poly- crystalline cubic boron nitride thin films under the residual compressive stress conditions have been performed. Our results indicate that the intensity of the IR absorption is proportional to the total degree of freedom of all the ions in the ordered regions. The reduction of interstitial Ar atom concentration, which causes the increase in the ordered regions of cubic boron nitride （cBN） crystallites, could be one cause for the increase in the intensity of IR absorption after residual compressive stress relaxation. Theoretical derivation is in good agreement with the experimental results concerning the IR absorption intensity and the Ar interstitial atom concentration in cubic boron nitride films measured by energy dispersion X-ray spec- troscopy. Our results also suggest that the interstitial Ar is the origin of residual compressive stress accumulation in plasma enhanced cBN film deposition.
基金Project supported by the Natural Science Foundation of Shandong Province,China(Grant Nos.ZR2015AQ010 and ZR2016FB16)the Open Project Fund of State Key Laboratory of Superhard Materials of China(Grant No.201509)
文摘The pressure-induced structural evolution of apatite-type La9.33Si6026 was systematically studied using in situ syn- chrotron x-ray diffraction （XRD）. The XRD spectra indicated that a subtly reversible phase transition from P63/m to P63 symmetry occurred at ~ 13.6 GPa because of the tilting of the SiO4 tetrahedra under compression. Furthermore, the La9.33Si6026 exhibited a higher axial compression ratio for the a-axis than the c-axis, owing to the different axial arrange- ment of the SiO4 tetrahedra. Interestingly, the high-pressure phase showed compressibility unusually higher than that of the initial phase, suggesting that the low P63 symmetry provided more degrees of freedom. Moreover, the La9.33Si6026 exhibited a lower phase transition pressure （PT） and a higher lattice compression than LaloSi6027. Comparisons between La9.33Si6026 and LaloSi6027 provided a deeper understanding of the effect of interstitial oxygen atoms on the structural evolution of apatite-type lanthanum silicates （ATLSs）.
基金supported by the National Key R&D Program of China(2021YFB1507403)the National Natural Science Foundation of China(52071218,and 11874394)+1 种基金the Shenzhen University 2035 Program for Excellent Research(00000218)The University Synergy Innovation Program of Anhui Province(GXXT-2020-003)。
文摘In thermoelectrics,doping is essential to augment the figure of merit.Traditional strategy,predomina ntly heavy doping,aims to optimize carrier concentration and restrain lattice thermal conductivity.However,this tactic can severely hamper carrier transport due to pronounced point defect scattering,particularly in materials with inherently low carrier mean-free-path.Conversely,dilute doping,although minimally affecting carrier mobility,frequently fails to optimize other vital thermoelectric parameters.Herein,we present a more nuanced dilute doping strategy in GeTe,leveraging the multifaceted roles of small-size metal atoms.A mere 4%CuPbSbTe_(3)introduction into GeTe swiftly suppresses rhombohedral distortion and optimizes carrier concentration through the aid of Cu interstitials.Additionally,the formation of multiscale microstructures,including zero-dimensional Cu interstitials,one-dimensional dislocations,two-dimensional planar defects,and three-dimensional nanoscale amorphous GeO_(2)and Cu_(2)GeTe_(3)precipitates,along with the ensuing lattice softening,contributes to an ultralow lattice thermal conductivity.Intriguingly,dilute CuPbSbTe_(3)doping incurs only a marginal decrease in carrier mobility.Subsequent trace Cd doping,employed to alleviate the bipolar effect and align the valence bands,yields an impressive figure-of-merit of 2.03 at 623 K in(Ge_(0.97)Cd_(0.03)Te)_(0.96)(CuPbSbTe_(3))_(0.04).This leads to a high energyconversion efficiency of 7.9%and a significant power density of 3.44 W cm^(-2)at a temperature difference of 500 K.These results underscore the invaluable insights gained into the constructive role of nuanced dilute doping in the concurrent tuning of carrier and phonon transport in GeTe and other thermoelectric materials.
文摘The Pu-He pair potential fitted by ab initio data, and the Pu-Pu and He-He modified embedded atom method (MEAM) poten-tials have been implemented to perform multi-scale simulations for the interactions of fracture with the self-interstitial atom(SIA), He interstitial atom and He-vacancy clusters. The simulation results indicate that Pu atoms around the fracture agglom-erate into an elliptic self-interstitial loop. Interstitial He atoms evolve into separate interstitial atoms, small He atom clustersand some substitutional He atoms. The He-vacancy cluster forms a spheric structure with a 1:1 He-to-vacancy ratio. Finally,the existence of self-interstitial atoms will lead to the local change of Pu lattice and an increasing disorder, and the wholesimulation cell shows a melting state at about 10.0 ps.
