Introducing minor alloying elements is an effective strategy to improve the corrosion and mechanical properties of zirconium alloys for nuclear applications.During in-reactor service,external environment and stress ca...Introducing minor alloying elements is an effective strategy to improve the corrosion and mechanical properties of zirconium alloys for nuclear applications.During in-reactor service,external environment and stress can affect the distribution of alloying elements,substantially changing the degradation process of zirconium alloys.To date,there is a lack of in-depth understanding of the interaction between creep and microchemistry changes.Here,we conducted systematic transmission electron microscopy(TEM)and atom probe tomography(APT)investigations to address creep-induced redistribution of alloying elements in CZ1(Zr-Sn-Nb-Fe-Cr-Cu)zirconium alloy with different initial microstructures.Nb,Fe,Sn,and Cu are found to co-segregate at grain boundaries.The higher the intermediate annealing temperature,the larger the Gibbsian interfacial excesses of solute elements are.We further demonstrate that creep can reduce the excess value of Fe at grain boundaries due to the coarsening of Zr-Fe-Cr second phase particles via grain boundary and dislocation pipe diffusion.At the same time,the excess value of Sn is increased by diffusing from the matrix to grain boundaries.Moreover,Cu as a minor element in the concentration range of 0.05-0.3 wt.%is found to segregate at dislocations to form the Cottrell atmosphere and develop Cu-rich nanoclusters for suppressing dislocation motion.The new understanding of the segregation and clustering of minor alloying elements provides guidance for developing zirconium alloys with enhanced creep resistance.展开更多
L12-strengthened high entropy alloys(HEAs)with excellent room and high-temperature mechanical prop-erties have been proposed as promising candidates as structural materials for advanced nuclear systems.However,knowled...L12-strengthened high entropy alloys(HEAs)with excellent room and high-temperature mechanical prop-erties have been proposed as promising candidates as structural materials for advanced nuclear systems.However,knowledge about their radiation response is fairly limited.In the present work,a novel HEA with a high density of L12 nanoparticles was irradiated with He ion at 500°C.Transmission electron microscope(TEM)and atom probe tomography(APT)were employed to study the evolution of mi-crostructural stability and radiation-induced segregation.Similar to the single-phase FeCoNiCr HEA,the main microstructural features were numerous large faulted dislocation loops and helium bubbles.While the irradiation resistance of the present L12-strengthened HEA is much improved in terms of reduced bubble size,which could be attributed to the considerable He trapping efficiency of the coherent pre-cipitate/matrix interface and the enhanced capability of the interface for damage elimination when the matrix channel width is narrow.APT analysis revealed that an inverse-Kirkendall-mechanism-dominated radiation-induced segregation(RIS)occurs around bubbles,where a significant Co enrichment and Ni de-pletion can be clearly observed.In addition,the competing dynamics of ballistic mixing and elemental clustering that raised from the irradiation-enhanced diffusion in a highly supersaturated matrix,along with the low precipitation nucleation barrier due to the small lattice misfit,lead to a dynamical pre-cipitation dissolution and re-precipitation appears under irradiation.Such a promising phenomenon is expected to promote a potential self-healing effect and could in turn provide a sustainable irradiation tolerance over the operational lifetime of a reactor.展开更多
Radiation-induced segregation(RIS) is a typical non-equilibrium process that can dramatically alter the behavior of defect sinks and material properties under irradiation. However, RIS mechanisms have been rarely stud...Radiation-induced segregation(RIS) is a typical non-equilibrium process that can dramatically alter the behavior of defect sinks and material properties under irradiation. However, RIS mechanisms have been rarely studied around small He bubbles owing to the technical challenges involved in direct measurements of local chemistry. Here, using state-of-the-art atom probe tomography, we report the RIS behavior near He bubbles in the Fe Ni Co Cr high-entropy alloy that indicates Co segregates most strongly, followed by weaker Ni segregation, whereas Fe and Cr are depleted almost to the same degree. Exceptionally, the magnitude of Co segregation around He bubbles is higher than previously measured values at voids and dislocation loops. Electron energy-loss spectroscopy was used to measure the He density and pressure inside individual bubbles. We demonstrate that He bubbles are over-pressurized at the irradiation temperature that could result in the vacancy bias and the subsequent vacancy-dominated RIS mechanism.First-principles calculations further reveal that there are repulsive interactions between He and Co atoms that may reduce the frequency of Co-vacancy exchange. As a result, He atoms likely retard Co diffusion via the vacancy mechanism and enhance the heterogeneity of RIS in Co-containing multicomponent alloys. These insights could provide the basis for understanding He effects in nuclear materials and open an avenue for tailoring the local chemical order of medium-and high-entropy alloys.展开更多
Recent measurements of event-by-event elliptic flow in Au+Au collisions at S_(NN)^(1/2)=200GeV exhibit large relative fluctuations of about 40%—50%.The data are well described by fluctuations in the shape of the init...Recent measurements of event-by-event elliptic flow in Au+Au collisions at S_(NN)^(1/2)=200GeV exhibit large relative fluctuations of about 40%—50%.The data are well described by fluctuations in the shape of the initial collision region,as estimated event-by-event with the participant eccentricity using Glauber Monte Carlo.These results,combined with the demonstrated participant eccentricity scaling of the elliptic flow across nuclear species,constitute evidence of transverse granularity in the initial matter production in these collisions.展开更多
基金the funding support from the Young Elite Scientists Sponsorship Program by CSEE.
文摘Introducing minor alloying elements is an effective strategy to improve the corrosion and mechanical properties of zirconium alloys for nuclear applications.During in-reactor service,external environment and stress can affect the distribution of alloying elements,substantially changing the degradation process of zirconium alloys.To date,there is a lack of in-depth understanding of the interaction between creep and microchemistry changes.Here,we conducted systematic transmission electron microscopy(TEM)and atom probe tomography(APT)investigations to address creep-induced redistribution of alloying elements in CZ1(Zr-Sn-Nb-Fe-Cr-Cu)zirconium alloy with different initial microstructures.Nb,Fe,Sn,and Cu are found to co-segregate at grain boundaries.The higher the intermediate annealing temperature,the larger the Gibbsian interfacial excesses of solute elements are.We further demonstrate that creep can reduce the excess value of Fe at grain boundaries due to the coarsening of Zr-Fe-Cr second phase particles via grain boundary and dislocation pipe diffusion.At the same time,the excess value of Sn is increased by diffusing from the matrix to grain boundaries.Moreover,Cu as a minor element in the concentration range of 0.05-0.3 wt.%is found to segregate at dislocations to form the Cottrell atmosphere and develop Cu-rich nanoclusters for suppressing dislocation motion.The new understanding of the segregation and clustering of minor alloying elements provides guidance for developing zirconium alloys with enhanced creep resistance.
文摘L12-strengthened high entropy alloys(HEAs)with excellent room and high-temperature mechanical prop-erties have been proposed as promising candidates as structural materials for advanced nuclear systems.However,knowledge about their radiation response is fairly limited.In the present work,a novel HEA with a high density of L12 nanoparticles was irradiated with He ion at 500°C.Transmission electron microscope(TEM)and atom probe tomography(APT)were employed to study the evolution of mi-crostructural stability and radiation-induced segregation.Similar to the single-phase FeCoNiCr HEA,the main microstructural features were numerous large faulted dislocation loops and helium bubbles.While the irradiation resistance of the present L12-strengthened HEA is much improved in terms of reduced bubble size,which could be attributed to the considerable He trapping efficiency of the coherent pre-cipitate/matrix interface and the enhanced capability of the interface for damage elimination when the matrix channel width is narrow.APT analysis revealed that an inverse-Kirkendall-mechanism-dominated radiation-induced segregation(RIS)occurs around bubbles,where a significant Co enrichment and Ni de-pletion can be clearly observed.In addition,the competing dynamics of ballistic mixing and elemental clustering that raised from the irradiation-enhanced diffusion in a highly supersaturated matrix,along with the low precipitation nucleation barrier due to the small lattice misfit,lead to a dynamical pre-cipitation dissolution and re-precipitation appears under irradiation.Such a promising phenomenon is expected to promote a potential self-healing effect and could in turn provide a sustainable irradiation tolerance over the operational lifetime of a reactor.
基金the funding support from the Hong Kong Research Grant Council (Grant Nos. City U11214820 and City U11205018)the funding support from the National Natural Science Foundation of China (NSFC) under project 11922215+2 种基金the funding support from the Natural Science Foundation of Guangdong Province in China (Grant No. 2019A1515011836)the support from National Natural Science Foundation of China (Grant No. 11974156)Guangdong International Science Collaboration Project (Grant No. 2019A050510001)。
文摘Radiation-induced segregation(RIS) is a typical non-equilibrium process that can dramatically alter the behavior of defect sinks and material properties under irradiation. However, RIS mechanisms have been rarely studied around small He bubbles owing to the technical challenges involved in direct measurements of local chemistry. Here, using state-of-the-art atom probe tomography, we report the RIS behavior near He bubbles in the Fe Ni Co Cr high-entropy alloy that indicates Co segregates most strongly, followed by weaker Ni segregation, whereas Fe and Cr are depleted almost to the same degree. Exceptionally, the magnitude of Co segregation around He bubbles is higher than previously measured values at voids and dislocation loops. Electron energy-loss spectroscopy was used to measure the He density and pressure inside individual bubbles. We demonstrate that He bubbles are over-pressurized at the irradiation temperature that could result in the vacancy bias and the subsequent vacancy-dominated RIS mechanism.First-principles calculations further reveal that there are repulsive interactions between He and Co atoms that may reduce the frequency of Co-vacancy exchange. As a result, He atoms likely retard Co diffusion via the vacancy mechanism and enhance the heterogeneity of RIS in Co-containing multicomponent alloys. These insights could provide the basis for understanding He effects in nuclear materials and open an avenue for tailoring the local chemical order of medium-and high-entropy alloys.
基金Supported by U.S.DOE Grants DE-AC02-98CH10886,DE-FG02-93ER40802,DE-FG02-94ER40818,DE-FG02-94ER40865,DE-FG02-99ER41099,and DE-AC02-06CH11357by U.S.NSF Grants 9603486,0072204,and 0245011+2 种基金by Polish KBN Grant 1-P03B-062-27 (2004-2007)by NSC of Taiwan Contract NSC 89-2112-M-008-024by Hungarian OTKA Grant F049823
文摘Recent measurements of event-by-event elliptic flow in Au+Au collisions at S_(NN)^(1/2)=200GeV exhibit large relative fluctuations of about 40%—50%.The data are well described by fluctuations in the shape of the initial collision region,as estimated event-by-event with the participant eccentricity using Glauber Monte Carlo.These results,combined with the demonstrated participant eccentricity scaling of the elliptic flow across nuclear species,constitute evidence of transverse granularity in the initial matter production in these collisions.
