Ab st ra ct Nanocrystalline materials exhibit unique properties due to their extremely high grain boundary(GB) density.However,this high-density characteristic induces grain coarsening at elevated temperatures,thereby...Ab st ra ct Nanocrystalline materials exhibit unique properties due to their extremely high grain boundary(GB) density.However,this high-density characteristic induces grain coarsening at elevated temperatures,thereby limiting the widespread application of nanocrystalline materials.Recent experimental observations revealed that GB segregation and second-phase pinning effectively hinder GB migration,thereby improving the stability of nanocry stalline materials.In this study,a mouified phase-field model that integrates mismatch strain,solute segregation and precipitation was developed to evaluate the influence of lattice misfit on the thermal stability of nanocrystalline alloys.The simulation results indicated that introducing a suitable mismatch strain can effectively enhance the microstructural stability of nanocrystalline alloys.By synergizing precipitation with an appropriate lattice misfit,the formation of second-phase particles in the bulk grains can be suppressed,thereby facilitating solute segregation/precipitation at the GBs.This concentrated solute segregation and precipitation at the GBs effectively hinders grain migration,thereby preventing grain coarsening.These findings provide a new perspective on the design and regulation of nanocrystalline alloys with enhanced thermal stability.展开更多
Hydride precipitation in zirconium cladding materials can damage their integrity and durability.Service temperature and material defects have a significant effect on the dynamic growth of hydrides.In this study,we hav...Hydride precipitation in zirconium cladding materials can damage their integrity and durability.Service temperature and material defects have a significant effect on the dynamic growth of hydrides.In this study,we have developed a phasefield model based on the assumption of elastic behaviour within a specific temperature range(613 K-653 K).This model allows us to study the influence of temperature and interfacial effects on the morphology,stress,and average growth rate of zirconium hydride.The results suggest that changes in temperature and interfacial energy influence the length-to-thickness ratio and average growth rate of the hydride morphology.The ultimate determinant of hydride orientation is the loss of interfacial coherency,primarily induced by interfacial dislocation defects and quantifiable by the mismatch degree q.An escalation in interfacial coherency loss leads to a transition of hydride growth from horizontal to vertical,accompanied by the onset of redirection behaviour.Interestingly,redirection occurs at a critical mismatch level,denoted as qc,and remains unaffected by variations in temperature and interfacial energy.However,this redirection leads to an increase in the maximum stress,which may influence the direction of hydride crack propagation.This research highlights the importance of interfacial coherency and provides valuable insights into the morphology and growth kinetics of hydrides in zirconium alloys.展开更多
A microscopic phase-field model was used to investigate a directional coarsening mechanism caused by the anisotropic growth of long period stacking and different effects of phases on precipitation in Ni-Al-V alloy.The...A microscopic phase-field model was used to investigate a directional coarsening mechanism caused by the anisotropic growth of long period stacking and different effects of phases on precipitation in Ni-Al-V alloy.The results show that DO22 mainly coarsens along its short axis,which may press the neighboring L12,leading to the interaction among atoms.Diffusion channels of Al are formed in the direction where the mismatch between γ＇ and γ reduces;the occupation probabilities are anisotropic in space;and direction coarsening of L12 occurs finally.With a rise of ageing temperature,phases appear later and DO22 is much later at a higher temperature,the average occupation probabilities of Al and V reduce,and Al changes more than V.展开更多
Effective charge separation and transfer is deemed to be the contributing factor to achieve high photoelectrochemical(PEC)water splitting performance on photoelectrodes.Building a phase junction structure with control...Effective charge separation and transfer is deemed to be the contributing factor to achieve high photoelectrochemical(PEC)water splitting performance on photoelectrodes.Building a phase junction structure with controllable phase transition of WO_(3) can further improve the photocatalytic performance.In this work,we realized the transition from orthorhombic to monoclinic by regulating the annealing temperatures,and constructed an orthorhombic–monoclinic WO_(3)(o-WO_(3)/m-WO_(3))phase junction.The formation of oxygen vacancies causes an imbalance of the charge distribution in the crystal structure,which changes the W–O bond length and bond angle,accelerating the phase transition.As expected,an optimum PEC activity was achieved over the o-WO_(3)/m-WO_(3) phase junction in WO_(3)-450 photoelectrode,yielding the maximum O_(2) evolution rate roughly 32 times higher than that of pure WO_(3)-250 without any sacrificial agents under visible light irradiation.The enhancement of catalytic activity is attributed to the atomically smooth interface with a highly matched lattice and robust built-in electric field around the phase junction,which leads to a less-defective and abrupt interface and provides a smooth interfacial charge separation and transfer path,leading to improved charge separation and transfer efficiency and a great enhancement in photocatalytic activity.This work strikes out on new paths in the formation of an oxygen vacancy-induced phase transition and provides new ideas for the design of catalysts.展开更多
A fully-differential charge pump（FDCP）with perfect current matching and low output current noise is realized for phase-locked loops（PLLs）.An easily stable common-mode feedback（CMFB）circuit which can handle high ...A fully-differential charge pump（FDCP）with perfect current matching and low output current noise is realized for phase-locked loops（PLLs）.An easily stable common-mode feedback（CMFB）circuit which can handle high input voltage swing is proposed.Current mismatch and current noise contribution from the CMFB circuit is minimized.In order to optimize PLL phase noise,the output current noise of the FDCP is analyzed in detail and calculated with the sampling principle.The calculation result agrees well with the simulation.Based on the noise analysis,many methods to lower output current noise of the FDCP are discussed.The fully-differential charge pump is integrated into a 1–2 GHz frequency synthesizer and fabricated in an SMIC CMOS 0.18μm process.The measured output reference spur is–64 dBc to–69 dBc.The in-band and out-band phase noise is–95 dBc/Hz at 3 kHz frequency offset and–123 dBc/Hz at 1 MHz frequency offset respectively.展开更多
针对当前电力系统中数据采集与监视控制系统(Supervisory Control And Date Acquisition,SCADA)和相量测量单元(Phasor Measurement Units,PMU)并存,以及不同规格的PMU之间不能实现完全同步的现状,引入了一种基于不完全同步PMU的电力系...针对当前电力系统中数据采集与监视控制系统(Supervisory Control And Date Acquisition,SCADA)和相量测量单元(Phasor Measurement Units,PMU)并存,以及不同规格的PMU之间不能实现完全同步的现状,引入了一种基于不完全同步PMU的电力系统动态状态估计模型,与SCADA组成混合量测系统,在此基础上提出了一种考虑相位失配量的线性动态状态估计算法.结合线性定常系统卡尔曼滤波原理,分别对相位失配量和系统状态进行滤波处理,实现对系统状态的估计.相比于传统方法,该算法的雅可比矩阵为常数阵,缩短了状态估计时间,减少了不必要的迭代.采用Matlab平台在IEEE 30节点系统上进行仿真实验,结果表明,在PMU不完全同步的情况下,提出的方法较传统的线性算法具有更好的性能,在很大程度上减小了状态估计产生的误差.展开更多
The precipitated phases in the WNZ,TMAZ,HAZ and BM of the friction stir welding(FSW)joint were observed using the transmission electron microscopy(TEM)and the lattice fringe spacing of the precipitated phases was meas...The precipitated phases in the WNZ,TMAZ,HAZ and BM of the friction stir welding(FSW)joint were observed using the transmission electron microscopy(TEM)and the lattice fringe spacing of the precipitated phases was measured.Combined with X-ray diffraction(XRD),the types of precipitated phases among the joint were confirmed and then the strength mismatch mechanism was revealed.The results show the precipitated phases of 7075 aluminum alloy FSW joint mainly consist of MgZn_(2),AlCuMg and Al_(2)CuMg.The microzone of the joint experienced different thermal cycles,the types and sizes of precipitated phases are different and the strengthening effect is different.The strengthening effect of the AlCuMg and Al_(2)CuMg are better than that of MgZn_(2).The precipitated phase in the WNZ mainly includes AlCuMg and Al_(2)CuMg,as well as the grain size is fine,the microhardness in this zone is pretty high.The number of precipitated phase AlCuMg and Al_(2)CuMg is smaller in the TMAZ and the MgZn_(2)is relatively more,which lead the microhardness decrease.The number of precipitated phase MgZn_(2)is relative larger in the HAZ,as well as the grain coarsening,the microhardness in this zone is lowest of the joint.At the same time,there are the precipitate free zones(PFZ)among the 7075 aluminum alloy FSW joint,which decreases the microhardness of the whole joint to some extent.展开更多
基金financially supported by the National Natural Science Foundation of China (Nos.52122408, 51901013,51971018,52101188,52225103,52071023 and U20B2025)the Funds for Creative Research Groups of NSFC (No.51921001)the financial support from the Fundamental Research Funds for the Central Universities (University of Science and Technology Beijing,Nos.FRF-TP-2021-04C1 and 06500135)。
文摘Ab st ra ct Nanocrystalline materials exhibit unique properties due to their extremely high grain boundary(GB) density.However,this high-density characteristic induces grain coarsening at elevated temperatures,thereby limiting the widespread application of nanocrystalline materials.Recent experimental observations revealed that GB segregation and second-phase pinning effectively hinder GB migration,thereby improving the stability of nanocry stalline materials.In this study,a mouified phase-field model that integrates mismatch strain,solute segregation and precipitation was developed to evaluate the influence of lattice misfit on the thermal stability of nanocrystalline alloys.The simulation results indicated that introducing a suitable mismatch strain can effectively enhance the microstructural stability of nanocrystalline alloys.By synergizing precipitation with an appropriate lattice misfit,the formation of second-phase particles in the bulk grains can be suppressed,thereby facilitating solute segregation/precipitation at the GBs.This concentrated solute segregation and precipitation at the GBs effectively hinders grain migration,thereby preventing grain coarsening.These findings provide a new perspective on the design and regulation of nanocrystalline alloys with enhanced thermal stability.
基金Project supported by the National Natural Science Foundation of China (Grant Nos.U2230401,U1930401,and 12004048)the National Key Research and Development Program of China (Grant No.2021YFB3501503)+1 种基金the Science Challenge Project (Grant No.TZ2018002)the Foundation of LCP。
文摘Hydride precipitation in zirconium cladding materials can damage their integrity and durability.Service temperature and material defects have a significant effect on the dynamic growth of hydrides.In this study,we have developed a phasefield model based on the assumption of elastic behaviour within a specific temperature range(613 K-653 K).This model allows us to study the influence of temperature and interfacial effects on the morphology,stress,and average growth rate of zirconium hydride.The results suggest that changes in temperature and interfacial energy influence the length-to-thickness ratio and average growth rate of the hydride morphology.The ultimate determinant of hydride orientation is the loss of interfacial coherency,primarily induced by interfacial dislocation defects and quantifiable by the mismatch degree q.An escalation in interfacial coherency loss leads to a transition of hydride growth from horizontal to vertical,accompanied by the onset of redirection behaviour.Interestingly,redirection occurs at a critical mismatch level,denoted as qc,and remains unaffected by variations in temperature and interfacial energy.However,this redirection leads to an increase in the maximum stress,which may influence the direction of hydride crack propagation.This research highlights the importance of interfacial coherency and provides valuable insights into the morphology and growth kinetics of hydrides in zirconium alloys.
基金Projects(51075335,10902086,50875217) supported by the National Natural Science Foundation of ChinaProject(JC201005) supported by the Northwestern Polytechnical University Foundation for Fundamental Research,ChinaProject(CX201007) supported by the Doctorate Foundation of Northwestern Polytechnical University,China
文摘A microscopic phase-field model was used to investigate a directional coarsening mechanism caused by the anisotropic growth of long period stacking and different effects of phases on precipitation in Ni-Al-V alloy.The results show that DO22 mainly coarsens along its short axis,which may press the neighboring L12,leading to the interaction among atoms.Diffusion channels of Al are formed in the direction where the mismatch between γ＇ and γ reduces;the occupation probabilities are anisotropic in space;and direction coarsening of L12 occurs finally.With a rise of ageing temperature,phases appear later and DO22 is much later at a higher temperature,the average occupation probabilities of Al and V reduce,and Al changes more than V.
基金The financial support is gratefully acknowledged from the National Natural Science Foundation of China(Grant Nos.62004137,21878257,and 21978196)Natural Science Foundation of Shanxi Province(Grant No.20210302123102)+4 种基金Key Research and Development Program of Shanxi Province(Grant No.201803D421079)Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi(Grant No.2019L0156)Shanxi-Zheda Institute of Advanced Materials and Chemical Engineering(Grant No.2022SX-TD002)Shanxi Provincial Key Innovative Research Team in Science and Technology(Grant No.201605D13104510)Research Project Supported by Shanxi Scholarship Council of China(Grant No.2020-050).
文摘Effective charge separation and transfer is deemed to be the contributing factor to achieve high photoelectrochemical(PEC)water splitting performance on photoelectrodes.Building a phase junction structure with controllable phase transition of WO_(3) can further improve the photocatalytic performance.In this work,we realized the transition from orthorhombic to monoclinic by regulating the annealing temperatures,and constructed an orthorhombic–monoclinic WO_(3)(o-WO_(3)/m-WO_(3))phase junction.The formation of oxygen vacancies causes an imbalance of the charge distribution in the crystal structure,which changes the W–O bond length and bond angle,accelerating the phase transition.As expected,an optimum PEC activity was achieved over the o-WO_(3)/m-WO_(3) phase junction in WO_(3)-450 photoelectrode,yielding the maximum O_(2) evolution rate roughly 32 times higher than that of pure WO_(3)-250 without any sacrificial agents under visible light irradiation.The enhancement of catalytic activity is attributed to the atomically smooth interface with a highly matched lattice and robust built-in electric field around the phase junction,which leads to a less-defective and abrupt interface and provides a smooth interfacial charge separation and transfer path,leading to improved charge separation and transfer efficiency and a great enhancement in photocatalytic activity.This work strikes out on new paths in the formation of an oxygen vacancy-induced phase transition and provides new ideas for the design of catalysts.
基金supported by the National High Technology Research and Development Program of China(No.2007AA01Z282)the National Natural Science Foundation of China(No.60876019)
文摘A fully-differential charge pump（FDCP）with perfect current matching and low output current noise is realized for phase-locked loops（PLLs）.An easily stable common-mode feedback（CMFB）circuit which can handle high input voltage swing is proposed.Current mismatch and current noise contribution from the CMFB circuit is minimized.In order to optimize PLL phase noise,the output current noise of the FDCP is analyzed in detail and calculated with the sampling principle.The calculation result agrees well with the simulation.Based on the noise analysis,many methods to lower output current noise of the FDCP are discussed.The fully-differential charge pump is integrated into a 1–2 GHz frequency synthesizer and fabricated in an SMIC CMOS 0.18μm process.The measured output reference spur is–64 dBc to–69 dBc.The in-band and out-band phase noise is–95 dBc/Hz at 3 kHz frequency offset and–123 dBc/Hz at 1 MHz frequency offset respectively.
文摘针对当前电力系统中数据采集与监视控制系统(Supervisory Control And Date Acquisition,SCADA)和相量测量单元(Phasor Measurement Units,PMU)并存,以及不同规格的PMU之间不能实现完全同步的现状,引入了一种基于不完全同步PMU的电力系统动态状态估计模型,与SCADA组成混合量测系统,在此基础上提出了一种考虑相位失配量的线性动态状态估计算法.结合线性定常系统卡尔曼滤波原理,分别对相位失配量和系统状态进行滤波处理,实现对系统状态的估计.相比于传统方法,该算法的雅可比矩阵为常数阵,缩短了状态估计时间,减少了不必要的迭代.采用Matlab平台在IEEE 30节点系统上进行仿真实验,结果表明,在PMU不完全同步的情况下,提出的方法较传统的线性算法具有更好的性能,在很大程度上减小了状态估计产生的误差.
基金supported by the Natural Science Foundation of Hebei(Grant No.E2012210001)Natural Science Foundation of Jiangsu(Grant No.BK20141181)。
文摘The precipitated phases in the WNZ,TMAZ,HAZ and BM of the friction stir welding(FSW)joint were observed using the transmission electron microscopy(TEM)and the lattice fringe spacing of the precipitated phases was measured.Combined with X-ray diffraction(XRD),the types of precipitated phases among the joint were confirmed and then the strength mismatch mechanism was revealed.The results show the precipitated phases of 7075 aluminum alloy FSW joint mainly consist of MgZn_(2),AlCuMg and Al_(2)CuMg.The microzone of the joint experienced different thermal cycles,the types and sizes of precipitated phases are different and the strengthening effect is different.The strengthening effect of the AlCuMg and Al_(2)CuMg are better than that of MgZn_(2).The precipitated phase in the WNZ mainly includes AlCuMg and Al_(2)CuMg,as well as the grain size is fine,the microhardness in this zone is pretty high.The number of precipitated phase AlCuMg and Al_(2)CuMg is smaller in the TMAZ and the MgZn_(2)is relatively more,which lead the microhardness decrease.The number of precipitated phase MgZn_(2)is relative larger in the HAZ,as well as the grain coarsening,the microhardness in this zone is lowest of the joint.At the same time,there are the precipitate free zones(PFZ)among the 7075 aluminum alloy FSW joint,which decreases the microhardness of the whole joint to some extent.
