The reactor pressure vessel(RPV)is susceptible to brittle fracture due to the influence of ion irradiation and high temperature,which presents a significant risk to the safe operation of nuclear reactors.It has been d...The reactor pressure vessel(RPV)is susceptible to brittle fracture due to the influence of ion irradiation and high temperature,which presents a significant risk to the safe operation of nuclear reactors.It has been demonstrated that pulsed electric current can effectively address the issue of embrittlement in RPV steel.However,the relationship between pulse parameters(duty ratio,frequency,current,and time)and the effectiveness of pulse current processing has not been systematically studied.The application of machine learning methods enables autonomous exploration and learning of the relationship between data.Consequently,this study proposes a machine learning method based on the random forest model to establish the relationship between the parameters of electrical pulses and the repair effect of RPV steel.A generative adversarial network is employed to enhance data diversity and scalability,while a particle swarm optimization algorithm is utilized to optimize the initialization weights and biases of the random forest model,aiming to improve the model’s fitting ability and training performance.The results indicate that the coefficient of determination R-square(R^(2)),root mean squared error and mean absolute error values are 0.934,0.045,and 0.036,respectively,suggesting that the model has the potential to predict the performance recovery of RPV steel after pulsed electric field treatment.The prediction of the impact of pulse current parameters on the repair effect will help to enhance and optimize the repair process,thereby providing a scientific basis for pulse current repair processing.展开更多
The anodic layer and oxygen evolution behavior of Pb-Ag-Nd alloy during pulse current polarization and constant current polarization in 160 g/L H2SO4 solution was comparatively investigated by chronopotentiometry, SEM...The anodic layer and oxygen evolution behavior of Pb-Ag-Nd alloy during pulse current polarization and constant current polarization in 160 g/L H2SO4 solution was comparatively investigated by chronopotentiometry, SEM, XRD, EIS and Tafel techniques. The results show that the anodic layer on Pb-Ag-Nd alloy formed through pulse current polarization is more intact and presents fewer micro-holes than that formed through constant current polarization. This could be attributed to the low current density period, which works as a ‘recovery period＇. During this period, the oxygen evolution reaction is less intense, which benefits the recovery of porous anodic layer. Pb-Ag-Nd anode also shows a lower anodic potential during pulse current polarization, which is in accordance with its smaller charge transfer resistance and smaller Tafel slope coefficient at high over-potential region. The lower anodic potential could be ascribed to the higher concentration of Pb O2 in the anodic layer, which promotes the formation of more reactive sites for the oxygen evolution reaction.展开更多
Previous studies have shown that transcranial pulse current stimulation(tPCS) can increase cerebral neural plasticity and improve patients' locomotor function.However, the precise mechanisms underlying this effect...Previous studies have shown that transcranial pulse current stimulation(tPCS) can increase cerebral neural plasticity and improve patients' locomotor function.However, the precise mechanisms underlying this effect remain unclear.In the present study, rat models of stroke established by occlusion of the right cerebral middle artery were subjected to tPCS, 20 minutes per day for 7 successive days.tPCS significantly reduced the Bederson score, increased the foot print area of the affected limbs, and reduced the standing time of affected limbs of rats with stroke compared with that before intervention.Immunofluorescence staining and western blot assay revealed that tPCS significantly increased the expression of microtubule-associated protein-2 and growth-associated protein-43 around the ischemic penumbra.This finding suggests that tPCS can improve the locomotor function of rats with stroke by regulating the expression of microtubule-associated protein-2 and growth-associated protein-43 around the ischemic penumbra.These findings may provide a new method for the clinical treatment of poststroke motor dysfunction and a theoretical basis for clinical application of tPCS.The study was approved by the Animal Use and Management Committee of Shanghai University of Traditional Chinese Medicine of China(approval No.PZSHUTCM190315003) on February 22, 2019.展开更多
The effect of rectangle wave pulse current on solidification structure of ZA27 alloy was studied. The restdts show that the wave pattern relies on the frequency range of harmonic wave and the energy of pulse current w...The effect of rectangle wave pulse current on solidification structure of ZA27 alloy was studied. The restdts show that the wave pattern relies on the frequency range of harmonic wave and the energy of pulse current within the frequency range of pulse current. Imposed pulse current could induce the solidification system to oscillate. The frequency range and the relevant energy distribution of pulse current exert an influence on the amount of atoms involved for forming critical nucleus, the surface states of dusters in melt, the oscillating state of melt on the surface of dusters, the active energy of atom diffusion , the frequnce response of the resonance of bulk melt and the absorbability of the solidification system to the external work. Rectangle wave pulse current involves rich harmonic waves ; the amplitudes of high order of harmonic waves are higher and reduce slowly, so it has a better effect on inoculation and modification.展开更多
Periodically changed current is called pulse current.It has been found that using the pulse current to charge/discharge lithium-ion batteries can improve the safety and cycle stability of the battery.In this short rev...Periodically changed current is called pulse current.It has been found that using the pulse current to charge/discharge lithium-ion batteries can improve the safety and cycle stability of the battery.In this short review,the mechanisms of pulse current improving the performance of lithium-ion batteries are summarized from four aspects:activation,warming up,fast charging and inhibition of lithium dendrites.Related content may help us use the pulse current to improve the performance of lithium-ion batteries and further optimize pulse current technology.展开更多
In recent research, a novel method combined with pulse current （PC） deposition and the ultrasonic （U） field was used to fabricate pure nickel and nickel-ceria composite coatings, respectively. Morphology, crack pr...In recent research, a novel method combined with pulse current （PC） deposition and the ultrasonic （U） field was used to fabricate pure nickel and nickel-ceria composite coatings, respectively. Morphology, crack propagation, and crystal texture were observed and analysed by using environment scanning electron microscopy （E-SEM） and transmission electron microscopy （TEM）. Orthogonal experiment [L16 （45）] was designed to optimize the parameters of pulsed power and the appropriate amount of RE addition based on microhardness. Effect of RE addition and pulsed current on the mechanism of co-electrodeposition was also investigated and compared. Experimental results indicated that it produced the alloying coatings, exhibiting compact grain and amorphous state. Nano-sized RE would preferentially occupy and pad at the edge of cracked gaps and micropore to limit the growing location and space for coarse Ni grain. Furthermore, during annealing at 480 ℃ for 2 h, a solid-solution precipitated phase named NiCexO1-x （0展开更多
In this work, the influence of pulse current parameters on springback and bending force of magnesium alloy duringelectropulse-assisted （EPA） V-bending was investigated. The experimental results showed that pulse cur...In this work, the influence of pulse current parameters on springback and bending force of magnesium alloy duringelectropulse-assisted （EPA） V-bending was investigated. The experimental results showed that pulse current can effec-tively reduce the springback and the bending force compared to the experiments without current. The frequency has a moresignificant influence on bending force and springback than electric current density. Electroplastic （EP） effect begins towork when pulse current parameters reach a threshold value. To explore the mechanism of EPA V-bending, themicrostructure evolution and fracture surface of the bending specimen were studied. It was found that pulse current canpromote the occurrence of dynamic recrystallization （DRX） of magnesium alloy compared to traditional hot formingprocess. The fracture mode of AZ31B under EPA V-bending evolves from brittle fracture to ductile fracture withincreasing pulse current parameters. Based on the discussion of athermal and thermal effects of EP effect, the mechanismof pulse current to promote DRX is studied and athermal effect is proved to exist.展开更多
Theoretical analysis is made on the temperature field at the time of pulse current discharge in a metal structure with an elliptical embedding crack. In finding the temperature field, analogy between the current flow ...Theoretical analysis is made on the temperature field at the time of pulse current discharge in a metal structure with an elliptical embedding crack. In finding the temperature field, analogy between the current flow through an elliptical embedding crack and the fluid flow through a barrier is made based on the similarity principle. Boundary conditions derived from this theory are introduced so that the distribution of current density and the temperature field expressions can be obtained. The study provides a theoretic basis to the applications of stopping spatial crack with electromagnetic heating.展开更多
A novel current feed style, alternating pulse current, was proposed in electrocoagulation aiming at preventing the passivation of electrode materials. The open circuit potential （OCP） measurements after anodic and c...A novel current feed style, alternating pulse current, was proposed in electrocoagulation aiming at preventing the passivation of electrode materials. The open circuit potential （OCP） measurements after anodic and cathodic potentiodynamic polarization showed that cathodic polarization could activate Al electrode. The surface of Al electrode after alternating pulse current electrocoagulation was investigated by scanning electron microscope （SEM） and X-ray photoelectron spectroscopy （XPS）, and the results indicate that passivation of Al is not observed. Furthermore, the simulated wastewater treatment tests show that alternating pulse current electrocoagulation has a visible energy saving effect and is worthy of generalization.展开更多
The effects of pulse current on the superplastic deformation of AZ31 magnesium alloy with different microstructures were examined. The results of TEM analysis showed that the dislocation movement was mainly glide, and...The effects of pulse current on the superplastic deformation of AZ31 magnesium alloy with different microstructures were examined. The results of TEM analysis showed that the dislocation movement was mainly glide, and the dislocation lines were approximate parallel with few dislocation tangles observed, which indicated that the dislocation movementwas promoted during the deformation, and therefore the formability of the coarse-grained AZ31 magnesium alloy was enhanced by the pulse current. This effect was also indicated by the asymmetrical contour of the free bulging sample, which was observed in the unidirectional pulses auxiliary equi-biaxial tensile test of coarse-grained alloy. In addition, the phenomenon of the restrained cavity growth caused by the thermoelectrical effect of the pulse current was discovered and studied.展开更多
In order to study the effect of pulse current treatment on the mechanical properties,microstructure and cutting performance of YG8 cemented carbide,experiments were carried out by using self-made pulse current treatme...In order to study the effect of pulse current treatment on the mechanical properties,microstructure and cutting performance of YG8 cemented carbide,experiments were carried out by using self-made pulse current treatment device to treat cemented carbide samples with different current densities(J=5,10 and 15 A·mm^-2)After the treatment of pulse current,when the current density increased from 5 to 15 A·mm-2,the hardness of the sample was improved to HV 1605,HV 1629 and HV 1653from HV 1574;the transverse rupture strengths of the sample were 2136,2289 and 2364 MPa,which were all higher than that of the untreated sample(2062 MPa)increasing by 3.6%,11.0%and 14.6%,respectively;the corresponding cutting performance was increased by10.1%,13.9%and 19.4%,compared to that of the untreated tool.The tool’s life was also improved.After the treatmen of pulse current,pulse current provided the driving force for dislocation motion,making it more likely for the dislocation to multiply and slip,the dislocation density was increased,and the mechanical properties were significantly improved.展开更多
The variation in arc characteristics and behavior of metal transfer with the change in pulse parameters has been studied by high speed video camera during pulse current flux-cored arc weld deposition.A comparative stu...The variation in arc characteristics and behavior of metal transfer with the change in pulse parameters has been studied by high speed video camera during pulse current flux-cored arc weld deposition.A comparative study of similar nature has also been carried out during flux-cored arc weld deposition in globular and spray transfer modes.The effect of pulse parameters has been studied by considering their mean current and arc voltage.The arc characteristics studied by its root diameter,projected diameter and length,and the behavior of metal transfer noted by the metal transfer model and the droplet diameter have been found to vary significantly with the pulse parameters.The observation may help in understanding the arc characteristics with respect to the variation in pulse parameters which may be beneficial in using pulse current FCAW to produce desired weld quality.展开更多
The 1Cr18Ni9Ti specimens were treated respectively with pulse current under 520 V and 2 600 V during solidification and the solidification structure was observed.The results showed that pulse current can refine solidi...The 1Cr18Ni9Ti specimens were treated respectively with pulse current under 520 V and 2 600 V during solidification and the solidification structure was observed.The results showed that pulse current can refine solidification grains,cut primary dentrities remarkably and reduce second dentritic arm spacing.The mechanism and effect are changed with operation parameters.展开更多
Dense and submicron-grained NiAl-Al2O3 composite was fabricated by pulse current auxiliary sintering（PCAS）.Its microstructure was analyzed by XRD,SEM and TEM,and its mechanical behavior was evaluated through compres...Dense and submicron-grained NiAl-Al2O3 composite was fabricated by pulse current auxiliary sintering（PCAS）.Its microstructure was analyzed by XRD,SEM and TEM,and its mechanical behavior was evaluated through compression test and fracture toughness test.The average grain sizes of NiAl and Al2O3 are about 200 nm and 100 nm respectively.The Al2O3 particles dispersed in NiAl matrix,forming intergranular structure and intragranular structure.During sintering,Al2O3 particles were remarkably spherized due to the unique sintering mechanism of PCAS,which is beneficial to the improvement of toughness.The NiAl-Al2O3 composite exhibits high compressive yield strength,whether at room temperature or elevated temperature.Its room-temperature（23 ℃） and elevated-temperature（1 200 ℃） compressive yield strength are up to 2 050 MPa and 140 MPa,respectively.Meanwhile,its fracture toughness is significantly enhanced,which is up to 8.2 MPa？m1/2.It is suggested that the main strengthening-toughening mechanisms are grain refinement strengthening and Al2O3 dispersion strengthening.The fracture of larger NiAl grain is the transgranular cleavage and this is induced by crack tip deflection and grain boundary weakening which are caused by intergranular and intragranular Al2O3 particles,respectively.展开更多
To improve the formability of W-rare earth electrode, the influence of high-energy pulse on the plasticity property of W-CeOrods was investigated. The effects of current density(J), pulse width(tw), frequency(f), and ...To improve the formability of W-rare earth electrode, the influence of high-energy pulse on the plasticity property of W-CeOrods was investigated. The effects of current density(J), pulse width(tw), frequency(f), and strain rate on the plasticity of W-CeOrods were discussed in detail. Results of tensile tests show that the W-CeOrods applied with the electrical pulses obtain a maximum percentage total elongation at fracture(9.65 %), increased by118.7 % compared to that without pulses. This is owing to both the heat effect and the interaction of current between dislocations and rare earth additions. Electron back scattered diffraction(EBSD)-generated grain boundary(GB) maps suggest that the length of low-angle grain boundaries composed of high-density dislocations decreases after deformation while applying the pulse current. This demonstrates that the short-duration pulsed current enhances the mobility of dislocations. Scanning electron microscopy(SEM) images of the rods after deformation with the pulse current show that the long fiber-shaped additions become discontinuous,which could reduce the stress concentration and hinder the crack propagation.展开更多
A high-energy pulse power source applied for studying solidifieation of metals and a Rogowski coil for measuring strong pulse current were developed according to the requirement of the present experiment. The variatio...A high-energy pulse power source applied for studying solidifieation of metals and a Rogowski coil for measuring strong pulse current were developed according to the requirement of the present experiment. The variation of electrical current during the discharge of pulse power source was analyzed. Furthermore, the quantitative relation between peak current, pulse width and pulse frequency etc. versus voltage, capacitance and transmission line of discharging circuit was examined.展开更多
Structure of main air discharging switch and a crowbar TVS （triggered vacuum switch） are designed and their triggering characteristics are investigated. The experimental results showed that for TVS the operating vol...Structure of main air discharging switch and a crowbar TVS （triggered vacuum switch） are designed and their triggering characteristics are investigated. The experimental results showed that for TVS the operating voltage range is from 1.3 kV to 120 kV, its maximum delay time is 400 ns and its jitter is 4-10 ns. Based on these results the crowbar 10/350μs （i.e., with a front time of 10μs and a duration of 350 μs） pulse current circuit and its controlling circuit are designed. With a 10μF stored capacitor C and a 6 μF waveform forming induction, a pulse current is generated with a maximum of 100 kA, front time of 10 ns and duration of 350μs. This pulse waveform can be used for testing SPD （surge protective devices）.展开更多
To overcome the shortcomings of conventional plasma arc welding （ PAW）, the ＇ controlled pulse key-holing＇ strategy is proposed and the keyhole PAW experiment system is developed. ＇The efflux plasma voltage signa...To overcome the shortcomings of conventional plasma arc welding （ PAW）, the ＇ controlled pulse key-holing＇ strategy is proposed and the keyhole PAW experiment system is developed. ＇The efflux plasma voltage signal is detected in realtime to characterize the keyhole size and dimension. The welding current waveform for controlled pulse key-holing strategy is implemented, and two slow-decreasing slopes are added at the dropping point from peak current to base current to further reduce both heat input and arc force so that the controllability of keyhole dynamics is improved. Two kinds of PAW tests are conducted, anti the different parameters of the controlled pulse current and the relevant efflux plasma voltage are measured in real-time to investigate ihe effects of welding current waveform parameters on the key-holing condition.展开更多
The complicated structure of electronic devices makes the conventional annealing method,which involves placing the entire device in a furnace,insufficient for achieving the desired quality.This issue is currently addr...The complicated structure of electronic devices makes the conventional annealing method,which involves placing the entire device in a furnace,insufficient for achieving the desired quality.This issue is currently addressed through the use of pulsed laser annealing,where a specific target layer is heated,preventing the overheating of other layers or the substrate.However,this method is only applicable to a very limited range of materials and requires very expensive,powerful pulsed laser sources.Herein,a novel approach for the selective local thermal treatment of thin films is proposed;in this method,short,powerful current pulses are applied to the target conductive layer.The application of two current pulses with a length of 1.5 s induced the crystallization of a 160-nm thick indium tin oxide(ITO)film,resulting in a sheet resistance of 8.68Ω·sq^(-1),an average visible light transmittance of 86.69%,and a figure of merit(FoM)of 293.61.This FoM is an order of magnitude higher than that of the as-prepared ITO film,and to the best of our knowledge,is among the highest reported values for the polycrystalline ITO films.Simulations have shown that even faster and more localized crystallization could be achieved by increasing the power of pulsed current.This novel annealing method is applicable to most semi-conductive or metallic thin films and requires only a relatively inexpensive pulsed current source,making it potentially more attractive than pulsed laser annealing.展开更多
Traditional heat treatment methods require a significant amount of time and energy to affect atomic diffusion and enhance the spheroidization process of carbides in bearing steel,while pulsed current can accelerate at...Traditional heat treatment methods require a significant amount of time and energy to affect atomic diffusion and enhance the spheroidization process of carbides in bearing steel,while pulsed current can accelerate atomic diffusion to achieve ultra-fast spheroidization of carbides.However,the understanding of the mechanism by which different pulse current parameters regulate the dissolution behavior of carbides requires a large amount of experimental data to support,which limits the application of pulse current technology in the field of heat treatment.Based on this,quantify the obtained pulse current processing data to create an important dataset that could be applied to machine learning.Through machine learning,the mechanism of mutual influence between carbide regulation and various factors was elucidated,and the optimal spheroidization process parameters were determined.Compared to the 20 h required for traditional heat treatment,the application of pulsed electric current technology achieved ultra-fast spheroidization of GCr15 bearing steel within 90 min.展开更多
基金financially supported by the National Natural Science Foundation of China(U21B2082,52474410)the National Key R&D Program of China(2023YFB3709903,2020 YFA0714900)+5 种基金the Key R&D Program of Shandong Province,China(2023CXGC010406)the Scientific Research Special Project for First-Class Disciplines in Inner Mongolia Autonomous Region(YLXKZXNKD-001)the Natural Science Foundation of Inner Mongolia Autonomous Region of China(2024ZD06)the Technology Support Project for the Construction of Major Innovation Platforms in Inner Mongolia Autonomous Region(XM2024XTGXQ16)the Beijing Municipal Natural Science Foundation(2222065)the Fundamental Research Funds for the Central Universities(FRF-TP-22-02C2).
文摘The reactor pressure vessel(RPV)is susceptible to brittle fracture due to the influence of ion irradiation and high temperature,which presents a significant risk to the safe operation of nuclear reactors.It has been demonstrated that pulsed electric current can effectively address the issue of embrittlement in RPV steel.However,the relationship between pulse parameters(duty ratio,frequency,current,and time)and the effectiveness of pulse current processing has not been systematically studied.The application of machine learning methods enables autonomous exploration and learning of the relationship between data.Consequently,this study proposes a machine learning method based on the random forest model to establish the relationship between the parameters of electrical pulses and the repair effect of RPV steel.A generative adversarial network is employed to enhance data diversity and scalability,while a particle swarm optimization algorithm is utilized to optimize the initialization weights and biases of the random forest model,aiming to improve the model’s fitting ability and training performance.The results indicate that the coefficient of determination R-square(R^(2)),root mean squared error and mean absolute error values are 0.934,0.045,and 0.036,respectively,suggesting that the model has the potential to predict the performance recovery of RPV steel after pulsed electric field treatment.The prediction of the impact of pulse current parameters on the repair effect will help to enhance and optimize the repair process,thereby providing a scientific basis for pulse current repair processing.
基金Projects(51204208,51374240)supported by the National Natural Science Foundation of ChinaProject(2012BAA03B04)supported by the National Science and Technology Pillar Program of ChinaProject(2014zzts028)supported by the Fundamental Research Funds for the Central Universities of Central South University,China
文摘The anodic layer and oxygen evolution behavior of Pb-Ag-Nd alloy during pulse current polarization and constant current polarization in 160 g/L H2SO4 solution was comparatively investigated by chronopotentiometry, SEM, XRD, EIS and Tafel techniques. The results show that the anodic layer on Pb-Ag-Nd alloy formed through pulse current polarization is more intact and presents fewer micro-holes than that formed through constant current polarization. This could be attributed to the low current density period, which works as a ‘recovery period＇. During this period, the oxygen evolution reaction is less intense, which benefits the recovery of porous anodic layer. Pb-Ag-Nd anode also shows a lower anodic potential during pulse current polarization, which is in accordance with its smaller charge transfer resistance and smaller Tafel slope coefficient at high over-potential region. The lower anodic potential could be ascribed to the higher concentration of Pb O2 in the anodic layer, which promotes the formation of more reactive sites for the oxygen evolution reaction.
基金supported by the National Key R&D Program of China, No.2018 YFC2001600(to CLS)the Shanghai Health Commission Accelerated the Development of Traditional Chinese Medicine Three-Year Action Plan Project, No.ZY(2018-2020)-CCCX-2001-06/2004-05(to CLS)+1 种基金the Program of Shanghai Academic Research Leader, No.19 XD1403600(to CLS)the National Natural Science Foundation of China for the Youth Project, No.81704163(to JJZ)。
文摘Previous studies have shown that transcranial pulse current stimulation(tPCS) can increase cerebral neural plasticity and improve patients' locomotor function.However, the precise mechanisms underlying this effect remain unclear.In the present study, rat models of stroke established by occlusion of the right cerebral middle artery were subjected to tPCS, 20 minutes per day for 7 successive days.tPCS significantly reduced the Bederson score, increased the foot print area of the affected limbs, and reduced the standing time of affected limbs of rats with stroke compared with that before intervention.Immunofluorescence staining and western blot assay revealed that tPCS significantly increased the expression of microtubule-associated protein-2 and growth-associated protein-43 around the ischemic penumbra.This finding suggests that tPCS can improve the locomotor function of rats with stroke by regulating the expression of microtubule-associated protein-2 and growth-associated protein-43 around the ischemic penumbra.These findings may provide a new method for the clinical treatment of poststroke motor dysfunction and a theoretical basis for clinical application of tPCS.The study was approved by the Animal Use and Management Committee of Shanghai University of Traditional Chinese Medicine of China(approval No.PZSHUTCM190315003) on February 22, 2019.
基金Funded by the Natural Science Foundation of Gansu Province(No.ZS021-A25-027-C)
文摘The effect of rectangle wave pulse current on solidification structure of ZA27 alloy was studied. The restdts show that the wave pattern relies on the frequency range of harmonic wave and the energy of pulse current within the frequency range of pulse current. Imposed pulse current could induce the solidification system to oscillate. The frequency range and the relevant energy distribution of pulse current exert an influence on the amount of atoms involved for forming critical nucleus, the surface states of dusters in melt, the oscillating state of melt on the surface of dusters, the active energy of atom diffusion , the frequnce response of the resonance of bulk melt and the absorbability of the solidification system to the external work. Rectangle wave pulse current involves rich harmonic waves ; the amplitudes of high order of harmonic waves are higher and reduce slowly, so it has a better effect on inoculation and modification.
基金financially supported by the Science and Technology Program of State Grid Corporation of China(Program Title:Research on Health Improvement Technology of Lithium Iron Phosphate Battery)。
文摘Periodically changed current is called pulse current.It has been found that using the pulse current to charge/discharge lithium-ion batteries can improve the safety and cycle stability of the battery.In this short review,the mechanisms of pulse current improving the performance of lithium-ion batteries are summarized from four aspects:activation,warming up,fast charging and inhibition of lithium dendrites.Related content may help us use the pulse current to improve the performance of lithium-ion batteries and further optimize pulse current technology.
基金Project supported by National Natural Science Foundation of China (50775113)Natural Science Foundation of Jiangsu Province (BK2007201)
文摘In recent research, a novel method combined with pulse current （PC） deposition and the ultrasonic （U） field was used to fabricate pure nickel and nickel-ceria composite coatings, respectively. Morphology, crack propagation, and crystal texture were observed and analysed by using environment scanning electron microscopy （E-SEM） and transmission electron microscopy （TEM）. Orthogonal experiment [L16 （45）] was designed to optimize the parameters of pulsed power and the appropriate amount of RE addition based on microhardness. Effect of RE addition and pulsed current on the mechanism of co-electrodeposition was also investigated and compared. Experimental results indicated that it produced the alloying coatings, exhibiting compact grain and amorphous state. Nano-sized RE would preferentially occupy and pad at the edge of cracked gaps and micropore to limit the growing location and space for coarse Ni grain. Furthermore, during annealing at 480 ℃ for 2 h, a solid-solution precipitated phase named NiCexO1-x （0
基金financial support from the Natural Science Foundation of Shandong Province (No. ZR2016EEM25)
文摘In this work, the influence of pulse current parameters on springback and bending force of magnesium alloy duringelectropulse-assisted （EPA） V-bending was investigated. The experimental results showed that pulse current can effec-tively reduce the springback and the bending force compared to the experiments without current. The frequency has a moresignificant influence on bending force and springback than electric current density. Electroplastic （EP） effect begins towork when pulse current parameters reach a threshold value. To explore the mechanism of EPA V-bending, themicrostructure evolution and fracture surface of the bending specimen were studied. It was found that pulse current canpromote the occurrence of dynamic recrystallization （DRX） of magnesium alloy compared to traditional hot formingprocess. The fracture mode of AZ31B under EPA V-bending evolves from brittle fracture to ductile fracture withincreasing pulse current parameters. Based on the discussion of athermal and thermal effects of EP effect, the mechanismof pulse current to promote DRX is studied and athermal effect is proved to exist.
基金Project supported by the National Natural Science Foundation of China (No.50675190)
文摘Theoretical analysis is made on the temperature field at the time of pulse current discharge in a metal structure with an elliptical embedding crack. In finding the temperature field, analogy between the current flow through an elliptical embedding crack and the fluid flow through a barrier is made based on the similarity principle. Boundary conditions derived from this theory are introduced so that the distribution of current density and the temperature field expressions can be obtained. The study provides a theoretic basis to the applications of stopping spatial crack with electromagnetic heating.
基金National 863 Plan(No.2005AA601010-02-2)Water Environment Research & Data Sharing Platform in the Middle Reaches of the Yangtse River(Wuhan University)(No.WERDSPMYR-0602)
文摘A novel current feed style, alternating pulse current, was proposed in electrocoagulation aiming at preventing the passivation of electrode materials. The open circuit potential （OCP） measurements after anodic and cathodic potentiodynamic polarization showed that cathodic polarization could activate Al electrode. The surface of Al electrode after alternating pulse current electrocoagulation was investigated by scanning electron microscope （SEM） and X-ray photoelectron spectroscopy （XPS）, and the results indicate that passivation of Al is not observed. Furthermore, the simulated wastewater treatment tests show that alternating pulse current electrocoagulation has a visible energy saving effect and is worthy of generalization.
基金supported by the National Natural Science Foundation of China(No. 51175112)Fundamental Research Funds for the Central Universities (Grant No. HIT.KLOF.2010039)
文摘The effects of pulse current on the superplastic deformation of AZ31 magnesium alloy with different microstructures were examined. The results of TEM analysis showed that the dislocation movement was mainly glide, and the dislocation lines were approximate parallel with few dislocation tangles observed, which indicated that the dislocation movementwas promoted during the deformation, and therefore the formability of the coarse-grained AZ31 magnesium alloy was enhanced by the pulse current. This effect was also indicated by the asymmetrical contour of the free bulging sample, which was observed in the unidirectional pulses auxiliary equi-biaxial tensile test of coarse-grained alloy. In addition, the phenomenon of the restrained cavity growth caused by the thermoelectrical effect of the pulse current was discovered and studied.
基金financially supported by the National Natural Science Foundation of China(Nos.51575369 and 51675357)。
文摘In order to study the effect of pulse current treatment on the mechanical properties,microstructure and cutting performance of YG8 cemented carbide,experiments were carried out by using self-made pulse current treatment device to treat cemented carbide samples with different current densities(J=5,10 and 15 A·mm^-2)After the treatment of pulse current,when the current density increased from 5 to 15 A·mm-2,the hardness of the sample was improved to HV 1605,HV 1629 and HV 1653from HV 1574;the transverse rupture strengths of the sample were 2136,2289 and 2364 MPa,which were all higher than that of the untreated sample(2062 MPa)increasing by 3.6%,11.0%and 14.6%,respectively;the corresponding cutting performance was increased by10.1%,13.9%and 19.4%,compared to that of the untreated tool.The tool’s life was also improved.After the treatmen of pulse current,pulse current provided the driving force for dislocation motion,making it more likely for the dislocation to multiply and slip,the dislocation density was increased,and the mechanical properties were significantly improved.
文摘The variation in arc characteristics and behavior of metal transfer with the change in pulse parameters has been studied by high speed video camera during pulse current flux-cored arc weld deposition.A comparative study of similar nature has also been carried out during flux-cored arc weld deposition in globular and spray transfer modes.The effect of pulse parameters has been studied by considering their mean current and arc voltage.The arc characteristics studied by its root diameter,projected diameter and length,and the behavior of metal transfer noted by the metal transfer model and the droplet diameter have been found to vary significantly with the pulse parameters.The observation may help in understanding the arc characteristics with respect to the variation in pulse parameters which may be beneficial in using pulse current FCAW to produce desired weld quality.
基金Sponsored by National Natural Science Foundation of China(50273873)Science and Technology Development Funds of Shanghai(01JC14001)
文摘The 1Cr18Ni9Ti specimens were treated respectively with pulse current under 520 V and 2 600 V during solidification and the solidification structure was observed.The results showed that pulse current can refine solidification grains,cut primary dentrities remarkably and reduce second dentritic arm spacing.The mechanism and effect are changed with operation parameters.
文摘Dense and submicron-grained NiAl-Al2O3 composite was fabricated by pulse current auxiliary sintering（PCAS）.Its microstructure was analyzed by XRD,SEM and TEM,and its mechanical behavior was evaluated through compression test and fracture toughness test.The average grain sizes of NiAl and Al2O3 are about 200 nm and 100 nm respectively.The Al2O3 particles dispersed in NiAl matrix,forming intergranular structure and intragranular structure.During sintering,Al2O3 particles were remarkably spherized due to the unique sintering mechanism of PCAS,which is beneficial to the improvement of toughness.The NiAl-Al2O3 composite exhibits high compressive yield strength,whether at room temperature or elevated temperature.Its room-temperature（23 ℃） and elevated-temperature（1 200 ℃） compressive yield strength are up to 2 050 MPa and 140 MPa,respectively.Meanwhile,its fracture toughness is significantly enhanced,which is up to 8.2 MPa？m1/2.It is suggested that the main strengthening-toughening mechanisms are grain refinement strengthening and Al2O3 dispersion strengthening.The fracture of larger NiAl grain is the transgranular cleavage and this is induced by crack tip deflection and grain boundary weakening which are caused by intergranular and intragranular Al2O3 particles,respectively.
基金financially supported by the National Key Technology R&D Program of China (No. 2012BAE06 B02)the Beijing Municipal Science and Technology Project (No. Z141100003814008)
文摘To improve the formability of W-rare earth electrode, the influence of high-energy pulse on the plasticity property of W-CeOrods was investigated. The effects of current density(J), pulse width(tw), frequency(f), and strain rate on the plasticity of W-CeOrods were discussed in detail. Results of tensile tests show that the W-CeOrods applied with the electrical pulses obtain a maximum percentage total elongation at fracture(9.65 %), increased by118.7 % compared to that without pulses. This is owing to both the heat effect and the interaction of current between dislocations and rare earth additions. Electron back scattered diffraction(EBSD)-generated grain boundary(GB) maps suggest that the length of low-angle grain boundaries composed of high-density dislocations decreases after deformation while applying the pulse current. This demonstrates that the short-duration pulsed current enhances the mobility of dislocations. Scanning electron microscopy(SEM) images of the rods after deformation with the pulse current show that the long fiber-shaped additions become discontinuous,which could reduce the stress concentration and hinder the crack propagation.
文摘A high-energy pulse power source applied for studying solidifieation of metals and a Rogowski coil for measuring strong pulse current were developed according to the requirement of the present experiment. The variation of electrical current during the discharge of pulse power source was analyzed. Furthermore, the quantitative relation between peak current, pulse width and pulse frequency etc. versus voltage, capacitance and transmission line of discharging circuit was examined.
基金supported by the New Century Talent Foundation of Ministry of Education of China (NCET-08-0438)
文摘Structure of main air discharging switch and a crowbar TVS （triggered vacuum switch） are designed and their triggering characteristics are investigated. The experimental results showed that for TVS the operating voltage range is from 1.3 kV to 120 kV, its maximum delay time is 400 ns and its jitter is 4-10 ns. Based on these results the crowbar 10/350μs （i.e., with a front time of 10μs and a duration of 350 μs） pulse current circuit and its controlling circuit are designed. With a 10μF stored capacitor C and a 6 μF waveform forming induction, a pulse current is generated with a maximum of 100 kA, front time of 10 ns and duration of 350μs. This pulse waveform can be used for testing SPD （surge protective devices）.
基金Acknowledgement The authors are grateful to the financial support for this research from the National Natural Science Foundation of China （Key Program Grant No. 50936003）.
文摘To overcome the shortcomings of conventional plasma arc welding （ PAW）, the ＇ controlled pulse key-holing＇ strategy is proposed and the keyhole PAW experiment system is developed. ＇The efflux plasma voltage signal is detected in realtime to characterize the keyhole size and dimension. The welding current waveform for controlled pulse key-holing strategy is implemented, and two slow-decreasing slopes are added at the dropping point from peak current to base current to further reduce both heat input and arc force so that the controllability of keyhole dynamics is improved. Two kinds of PAW tests are conducted, anti the different parameters of the controlled pulse current and the relevant efflux plasma voltage are measured in real-time to investigate ihe effects of welding current waveform parameters on the key-holing condition.
基金supported by the National Key R&D Program of China(No.2021YFB2801600)the National Natural Science Foundation of China(Nos.52072060,52202164 and 52021001)the Natural Science Foundation of Sichuan(Nos.2023NSFSC1950 and 2022NSFSC1990).
文摘The complicated structure of electronic devices makes the conventional annealing method,which involves placing the entire device in a furnace,insufficient for achieving the desired quality.This issue is currently addressed through the use of pulsed laser annealing,where a specific target layer is heated,preventing the overheating of other layers or the substrate.However,this method is only applicable to a very limited range of materials and requires very expensive,powerful pulsed laser sources.Herein,a novel approach for the selective local thermal treatment of thin films is proposed;in this method,short,powerful current pulses are applied to the target conductive layer.The application of two current pulses with a length of 1.5 s induced the crystallization of a 160-nm thick indium tin oxide(ITO)film,resulting in a sheet resistance of 8.68Ω·sq^(-1),an average visible light transmittance of 86.69%,and a figure of merit(FoM)of 293.61.This FoM is an order of magnitude higher than that of the as-prepared ITO film,and to the best of our knowledge,is among the highest reported values for the polycrystalline ITO films.Simulations have shown that even faster and more localized crystallization could be achieved by increasing the power of pulsed current.This novel annealing method is applicable to most semi-conductive or metallic thin films and requires only a relatively inexpensive pulsed current source,making it potentially more attractive than pulsed laser annealing.
基金supported by the National Key R&D Program of China(2020YFA0714900,2023YFB3709903)the National Natural Science Foundation of China(U21B2082,52474410)+6 种基金the Key R&D Program of Shandong Province,China(2023CXGC010406)the Scientific Research Special Project for First-Class Disciplines in Inner Mongolia Autonomous Region(YLXKZX-NKD-001)the International Science and Technology Cooperation Project of Higher Education Institutions in Inner Mongolia Autonomous Region(GHXM-002)the Natural Science Foundation of Inner Mongolia Autonomous Region of China(2024ZD06)the Technology Support Project for the Construction of Major Innovation Platforms in Inner Mongolia Autonomous Region(XM2024XTGXQ16)the Beijing Municipal Natural Science Foundation(2222065)the Fundamental Research Funds for the Central Universities(FRF-TP-22-02C2).
文摘Traditional heat treatment methods require a significant amount of time and energy to affect atomic diffusion and enhance the spheroidization process of carbides in bearing steel,while pulsed current can accelerate atomic diffusion to achieve ultra-fast spheroidization of carbides.However,the understanding of the mechanism by which different pulse current parameters regulate the dissolution behavior of carbides requires a large amount of experimental data to support,which limits the application of pulse current technology in the field of heat treatment.Based on this,quantify the obtained pulse current processing data to create an important dataset that could be applied to machine learning.Through machine learning,the mechanism of mutual influence between carbide regulation and various factors was elucidated,and the optimal spheroidization process parameters were determined.Compared to the 20 h required for traditional heat treatment,the application of pulsed electric current technology achieved ultra-fast spheroidization of GCr15 bearing steel within 90 min.
