The effects of current pulsing on the microstructure, hardness and tensile properties at different temperatures of gas tungsten arc （GTA） weldments of titanium matrix composites were studied. Full-penetration butt j...The effects of current pulsing on the microstructure, hardness and tensile properties at different temperatures of gas tungsten arc （GTA） weldments of titanium matrix composites were studied. Full-penetration butt joints were made with or without current pulsing. Optical microscopy, hardness test and scanning electron microscopy were employed to evaluate the metallurgical characteristics of welded joints. Tensile properties of weldments at different temperatures were studied and correlated with the microstructure. The results exhibit that current pulsing leads to the refinement of the weld microstrucmre and TiB whisker and the redistribution of reinforcements resulting in higher hardness, tensile strength and ductility of weldments in the as-welded condition.展开更多
Superalloy C-276 is known to be prone to hot cracking during fusion welding by Gas Tungsten Arc method. Microsegregation occurring during cooling of fusion zone with consequent appearance of topologically close-packed...Superalloy C-276 is known to be prone to hot cracking during fusion welding by Gas Tungsten Arc method. Microsegregation occurring during cooling of fusion zone with consequent appearance of topologically close-packed phases P and IX has been held responsible for the observed hot cracking. The present work investigated the possibility of suppressing the microsegregation in weldments by resorting to current pulse. Weldments were made by continuous current gas tungsten arc welding and pulsed current gas tungsten arc welding using ERNiCrMo-4 filler wire. The weld joints were studied with respect to microstructure, microsegregation, and mechanical properties. Optical microscopy and scanning electron microscopy were employed to study the microstructure. Energy-Dispersive X-ray Spectroscopy was carried out to evaluate the extent of microsegregation. Tensile testing was carried out to determine the strength and ductility. The results show that the joints fabricated with pulsed current gave rise to narrower welds with practically no heat affected zone, a refined microstructure in the fusion zone, reduced microsegregation, and superior combination of mechanical properties.展开更多
Non-metallic inclusions in steel are a significant challenge,affecting material properties and leading to issues such as stress concentration,cracking,and accelerated corrosion.Current methods for removing inclusions,...Non-metallic inclusions in steel are a significant challenge,affecting material properties and leading to issues such as stress concentration,cracking,and accelerated corrosion.Current methods for removing inclusions,including bubble,electromagnetic stirring,filtration separation,fluid flow,and sedimentation,often struggle with the removal of fine inclusions.Apart from these known methods,pulsed electric current(PEC),as an emerging technology,has demonstrated immense potential and environmental advantages.PEC offers adjustable current parameters and simple equipment,making it an attractive alternative to traditional methods.Its green energy-saving features and excellent results in regulating inclusion morphology and migration,as well as inhibiting submerged entry nozzle(SEN)clogging,make it a promising technology.In comparison to continuous current technology,PEC has shown significant advantages in regulating inclusions,not only improving purification efficiency but also demonstrating outstanding performance in flow stability and energy consumption.The ability of PEC to efficiently reduce inclusion numbers enhances the purity and quality of molten steel,improving its mechanical properties.Currently,the theoretical basis for controlling the movement of inclusions by current is mainly composed of three major theories:the double electric layer theory,electromagnetic force reverse separation theory,and electric free energy drive theory.These theories together form an important framework for researchers to understand and optimize the behavior of impurity movement controlled by electric current.Looking ahead,PEC is expected to pave the way for new solutions in directional regulation of inclusion migration,efficient inclusion removal,SEN clogging prevention,and the purification of molten steel.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
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
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
The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental resul...The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% （mass fraction） Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.展开更多
A mathematical model considering free nuclei was developed to reveal the migration behavior of the free nuclei. Numerical simulation results show that most of the nuclei on the top surface of the melt move downwards a...A mathematical model considering free nuclei was developed to reveal the migration behavior of the free nuclei. Numerical simulation results show that most of the nuclei on the top surface of the melt move downwards and distribute randomly inside the Al melt, which induces more nucleation sites resulting in grain refinement. At the same time, the effect of nuclei size on the nuclei distribution and refinement employing electric current pulse （ECP） was also investigated. The smaller nuclei migrate a short distance with the Al melt at lower speed. But for the larger nuclei, the migration downwards with higher speed benefits the refinement of interior grains of the melt. The research results help to better understand the refinement process and provide a more reasonable explanation of the grain refinement mechanism using ECP.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
The application of electric current pulse（ECP） to a solidification process refers to the immersion of electrodes into the liquid metal and the employment of thermal insulators on the upper surface of metal.In order ...The application of electric current pulse（ECP） to a solidification process refers to the immersion of electrodes into the liquid metal and the employment of thermal insulators on the upper surface of metal.In order to ascertain the effects of these two factors on the structure refinement by the ECP technique,three groups of experiments were performed with different types of electrodes or various thermal insulators.By the comparison between solidification structures under different conditions,it is followed that the electrode and the thermal insulator have an obvious influence on the grain refinement under an applied ECP,and further analysis demonstrates that the thermal conditions of the liquid surface play a vital role in the modification of solidification structure.Also,the results support the viewpoint that most of the equiaxed grains originate from the liquid surface subjected to an ECP.展开更多
A Cu-25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam （HCPEB） with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the allo...A Cu-25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam （HCPEB） with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the alloy before and after the treatment were investigated by scanning electron microscopy and X-ray diffraction. The results show that significant surface modification can be induced by HCPEB with the pulse number reaching 10. Craters with typical morphologies on the Cu-25Cr alloy surface are formed due to the dynamic thermal field induced by the HCPEB. Micro-cracks, as a unique feature, are well revealed in the irradiated Cu-25Cr specimens and attributed to quasi-static thermal stresses accumulated along the specimen surface. The amount of cracks is found to increase with the pulse number and a preference of these cracks to Cr phases rather than Cu phases is also noted. Another characteristic produced by the HCPEB is the fine Cr spheroids, which are determined to be due to occurrence of liquid phase separation in the Cu-25Cr alloy. In addition, an examination on surface roughness of all specimens reveals that more pulses will produce a roughened surface, as a result of compromising the above features.展开更多
The selection of process parameters for obtaining optimal tensile properties in the pulsed current gas tungsten arc welding is presented. The tensile properties include ultimate tensile strength, yield strength and no...The selection of process parameters for obtaining optimal tensile properties in the pulsed current gas tungsten arc welding is presented. The tensile properties include ultimate tensile strength, yield strength and notch tensile strength. All these characteristics are considered together in the selection of process parameters by modified taguchi method to analyse the effect of each welding process parameter on tensile properties. Experimental results are furnished to illustrate the approach.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 selection of process parameter in the gas tungsten arc （GTA） welding of titanium alloy was presented for obtaining optimum grain size and hardness. Titanium alloy （Ti-6Al-4V） is one of the most important non-f...The selection of process parameter in the gas tungsten arc （GTA） welding of titanium alloy was presented for obtaining optimum grain size and hardness. Titanium alloy （Ti-6Al-4V） is one of the most important non-ferrous metals which offers great potential application in aerospace, biomedical and chemical industries, because of its low density （4.5 g/cm^3）, excellent corrosion resistance, high strength, attractive fracture behaviour and high melting point （1678℃）. The preferred welding process for titanium alloy is frequent GTA welding due to its comparatively easier applicability and better economy. In the case of single pass （GTA） welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. Many considerations come into the picture and one needs to carefully balance various pulse current parameters to reach an optimum combination. Four factors, five level, central composite, rotatable design matrix were used to optimize the required number of experimental conditions. Mathematical models were developed to predict the fusion zone grain size using analysis of variance （ANOVA） and regression analysis. The developed models were optimized using the traditional Hooke and Jeeve＇s algorithm. Experimental results were provided to illustrate the proposed approach.展开更多
The effects of pulsing current parameters on weld pool geometry namely front height, back height, front width and back width of pulse current gas tungsten arc welded （GTAW） titanium alloy was analysed. Four factors,...The effects of pulsing current parameters on weld pool geometry namely front height, back height, front width and back width of pulse current gas tungsten arc welded （GTAW） titanium alloy was analysed. Four factors, five levels, central composite design were used to develop empirical relationships, incorporating pulsed current parameters and weld pool geometry.展开更多
The high corrosion resistance of duplex stainless steel （DSS） is due to elements such as Cr, Mo and N, hut also depends on the microstructure. The best general properties are obtained with approximately equal amount...The high corrosion resistance of duplex stainless steel （DSS） is due to elements such as Cr, Mo and N, hut also depends on the microstructure. The best general properties are obtained with approximately equal amounts of austenite and ferrite and the absence of third phases such as σ（sigma） and Cr2N. In the present work the effect of heat input variations on the microstructure and corrosion resistance of a DSS UNS S32760 in artificial sea water media were studied. The corrosion resistance in 3.5 % of NaCl solution was evaluated by potentiostatic polarization tests at room temperature. It is found that the presence of sigma phase and Cr2N decreases the corrosion potential. The specimen with heat input of approximately 0.95 kJ/mm have the best corrosion characteristics, which is the result for the lack of deleterious phases such as sigma and Cr2 N and balanced ferrite austenite proportion.展开更多
Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardnes...Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardness profiles, microstructural features and residual stress distribution of aluminium alloy joints were reported. The use of pulsed current technique is found to improve the tensile properties of the weld compared with continuous current welding due to grain refinement occurring in the fusion zone.展开更多
In this work, low-density electric current pulse （ECP） has been applied to submerged entry nozzle （SEN） and its effect on the morphology of the inclusion buildup and the distribution of the inclusions in slab has ...In this work, low-density electric current pulse （ECP） has been applied to submerged entry nozzle （SEN） and its effect on the morphology of the inclusion buildup and the distribution of the inclusions in slab has been explored. The results reveal that under the unique effects of ECP, part of small inclusions less than 10 μm is expelled through the boundary layer along the current direction to form dense inclusion buildup. This method is of great potential to prolong the service life of SEN and improve the quality of the steel product.展开更多
An empirical relationship to predict tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy was developed. Incorporating process parameters such as peak current, base current, pulse frequency...An empirical relationship to predict tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy was developed. Incorporating process parameters such as peak current, base current, pulse frequency and pulse on time were studied. The experiments were conducted based on a four-factor, five-level, central composite design matrix. The developed empirical relationship can be effectively used to predict the tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy joints at 95% confidence level. The results indicate that pulse frequency has the greatest influence on tensile strength, followed by peak current, pulse on time and base current.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
基金Project(51371114)supported by the National Natural Science Foundation of ChinaProject(2012CB619600)supported by the National Basic Research Program of China+1 种基金Project(10SG15)supported by the Dawn Program of Shanghai Education Commission,ChinaProject(12XD1402800)supported by Shanghai Science and Technology Committee,China
文摘The effects of current pulsing on the microstructure, hardness and tensile properties at different temperatures of gas tungsten arc （GTA） weldments of titanium matrix composites were studied. Full-penetration butt joints were made with or without current pulsing. Optical microscopy, hardness test and scanning electron microscopy were employed to evaluate the metallurgical characteristics of welded joints. Tensile properties of weldments at different temperatures were studied and correlated with the microstructure. The results exhibit that current pulsing leads to the refinement of the weld microstrucmre and TiB whisker and the redistribution of reinforcements resulting in higher hardness, tensile strength and ductility of weldments in the as-welded condition.
基金supported by the Defence Research Development organization (DRDO) (No. ERIP/ ER/1103952/M/01/1403)Department of Science and Technology for the funding received from them under the FIST programme
文摘Superalloy C-276 is known to be prone to hot cracking during fusion welding by Gas Tungsten Arc method. Microsegregation occurring during cooling of fusion zone with consequent appearance of topologically close-packed phases P and IX has been held responsible for the observed hot cracking. The present work investigated the possibility of suppressing the microsegregation in weldments by resorting to current pulse. Weldments were made by continuous current gas tungsten arc welding and pulsed current gas tungsten arc welding using ERNiCrMo-4 filler wire. The weld joints were studied with respect to microstructure, microsegregation, and mechanical properties. Optical microscopy and scanning electron microscopy were employed to study the microstructure. Energy-Dispersive X-ray Spectroscopy was carried out to evaluate the extent of microsegregation. Tensile testing was carried out to determine the strength and ductility. The results show that the joints fabricated with pulsed current gave rise to narrower welds with practically no heat affected zone, a refined microstructure in the fusion zone, reduced microsegregation, and superior combination of mechanical properties.
基金supported by the Fundamental Research Funds for the Central Universities(No.FRF-BD-23-01).
文摘Non-metallic inclusions in steel are a significant challenge,affecting material properties and leading to issues such as stress concentration,cracking,and accelerated corrosion.Current methods for removing inclusions,including bubble,electromagnetic stirring,filtration separation,fluid flow,and sedimentation,often struggle with the removal of fine inclusions.Apart from these known methods,pulsed electric current(PEC),as an emerging technology,has demonstrated immense potential and environmental advantages.PEC offers adjustable current parameters and simple equipment,making it an attractive alternative to traditional methods.Its green energy-saving features and excellent results in regulating inclusion morphology and migration,as well as inhibiting submerged entry nozzle(SEN)clogging,make it a promising technology.In comparison to continuous current technology,PEC has shown significant advantages in regulating inclusions,not only improving purification efficiency but also demonstrating outstanding performance in flow stability and energy consumption.The ability of PEC to efficiently reduce inclusion numbers enhances the purity and quality of molten steel,improving its mechanical properties.Currently,the theoretical basis for controlling the movement of inclusions by current is mainly composed of three major theories:the double electric layer theory,electromagnetic force reverse separation theory,and electric free energy drive theory.These theories together form an important framework for researchers to understand and optimize the behavior of impurity movement controlled by electric current.Looking ahead,PEC is expected to pave the way for new solutions in directional regulation of inclusion migration,efficient inclusion removal,SEN clogging prevention,and the purification of molten steel.
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.
基金Projects(51074031,51271042,50874022)supported by the National Natural Science Foundation of ChinaProject(2013M530913)supported by the China Postdoctoral Science FoundationProject(DUT12RC(3)35)supported by the Fundamental Research Funds for the Central Universities of China
文摘The combined effects of direct current pulsed magnetic field （DC-PMF） and inoculation on pure aluminum were investigated, the grain refinement behavior of DC-PMF and inoculation was discussed. The experimental results indicate that the solidification micro structure of pure aluminum can be greatly refined under DC-PMF. Refinement of pure aluminum is attributed to electromagnetic undercooling and forced convection caused by DC-PMF. With single DC-PMF, the grain size in the equiaxed zone is uneven. However, under DC-PMF, by adding 0.05% （mass fraction） Al5Ti-B, the grain size of the sample is smaller, and the size distribution is more uniform than that of single DC-PMF. Furthermore, under the combination of DC-PMF and inoculation, with the increase of output current, the grain size is further reduced. When the output current increases to 100 A, the average grain size can decrease to 113 μn.
基金Project(SELF-2011-01)supported by the Open Project of Shanghai Key Laboratory of Modern Metallurgy and Materials Processing,ChinaProjects(51204109,51035004)supported by the National Natural Science Foundation of China
文摘A mathematical model considering free nuclei was developed to reveal the migration behavior of the free nuclei. Numerical simulation results show that most of the nuclei on the top surface of the melt move downwards and distribute randomly inside the Al melt, which induces more nucleation sites resulting in grain refinement. At the same time, the effect of nuclei size on the nuclei distribution and refinement employing electric current pulse （ECP） was also investigated. The smaller nuclei migrate a short distance with the Al melt at lower speed. But for the larger nuclei, the migration downwards with higher speed benefits the refinement of interior grains of the melt. The research results help to better understand the refinement process and provide a more reasonable explanation of the grain refinement mechanism using ECP.
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Project(2009AA03Z110) supported by the National High Technology Research and Development Program of ChinaProject (2011CB012902) supported by the National Basic Research Program of China
文摘The application of electric current pulse（ECP） to a solidification process refers to the immersion of electrodes into the liquid metal and the employment of thermal insulators on the upper surface of metal.In order to ascertain the effects of these two factors on the structure refinement by the ECP technique,three groups of experiments were performed with different types of electrodes or various thermal insulators.By the comparison between solidification structures under different conditions,it is followed that the electrode and the thermal insulator have an obvious influence on the grain refinement under an applied ECP,and further analysis demonstrates that the thermal conditions of the liquid surface play a vital role in the modification of solidification structure.Also,the results support the viewpoint that most of the equiaxed grains originate from the liquid surface subjected to an ECP.
基金Projects(51101177,51401040,51171146,51171216) supported by the National Natural Science Foundation of ChinaProject(CSTC2012JJA245) supported by the Natural Science Foundation of Chongqing,China
文摘A Cu-25Cr alloy prepared by vacuum induction melting method was treated by the high current pulsed electron beam （HCPEB） with pulse numbers ranging from 1 to 100. Surface morphologies and microstructures of the alloy before and after the treatment were investigated by scanning electron microscopy and X-ray diffraction. The results show that significant surface modification can be induced by HCPEB with the pulse number reaching 10. Craters with typical morphologies on the Cu-25Cr alloy surface are formed due to the dynamic thermal field induced by the HCPEB. Micro-cracks, as a unique feature, are well revealed in the irradiated Cu-25Cr specimens and attributed to quasi-static thermal stresses accumulated along the specimen surface. The amount of cracks is found to increase with the pulse number and a preference of these cracks to Cr phases rather than Cu phases is also noted. Another characteristic produced by the HCPEB is the fine Cr spheroids, which are determined to be due to occurrence of liquid phase separation in the Cu-25Cr alloy. In addition, an examination on surface roughness of all specimens reveals that more pulses will produce a roughened surface, as a result of compromising the above features.
文摘The selection of process parameters for obtaining optimal tensile properties in the pulsed current gas tungsten arc welding is presented. The tensile properties include ultimate tensile strength, yield strength and notch tensile strength. All these characteristics are considered together in the selection of process parameters by modified taguchi method to analyse the effect of each welding process parameter on tensile properties. Experimental results are furnished to illustrate the approach.
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.
文摘The selection of process parameter in the gas tungsten arc （GTA） welding of titanium alloy was presented for obtaining optimum grain size and hardness. Titanium alloy （Ti-6Al-4V） is one of the most important non-ferrous metals which offers great potential application in aerospace, biomedical and chemical industries, because of its low density （4.5 g/cm^3）, excellent corrosion resistance, high strength, attractive fracture behaviour and high melting point （1678℃）. The preferred welding process for titanium alloy is frequent GTA welding due to its comparatively easier applicability and better economy. In the case of single pass （GTA） welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. Many considerations come into the picture and one needs to carefully balance various pulse current parameters to reach an optimum combination. Four factors, five level, central composite, rotatable design matrix were used to optimize the required number of experimental conditions. Mathematical models were developed to predict the fusion zone grain size using analysis of variance （ANOVA） and regression analysis. The developed models were optimized using the traditional Hooke and Jeeve＇s algorithm. Experimental results were provided to illustrate the proposed approach.
文摘The effects of pulsing current parameters on weld pool geometry namely front height, back height, front width and back width of pulse current gas tungsten arc welded （GTAW） titanium alloy was analysed. Four factors, five levels, central composite design were used to develop empirical relationships, incorporating pulsed current parameters and weld pool geometry.
文摘The high corrosion resistance of duplex stainless steel （DSS） is due to elements such as Cr, Mo and N, hut also depends on the microstructure. The best general properties are obtained with approximately equal amounts of austenite and ferrite and the absence of third phases such as σ（sigma） and Cr2N. In the present work the effect of heat input variations on the microstructure and corrosion resistance of a DSS UNS S32760 in artificial sea water media were studied. The corrosion resistance in 3.5 % of NaCl solution was evaluated by potentiostatic polarization tests at room temperature. It is found that the presence of sigma phase and Cr2N decreases the corrosion potential. The specimen with heat input of approximately 0.95 kJ/mm have the best corrosion characteristics, which is the result for the lack of deleterious phases such as sigma and Cr2 N and balanced ferrite austenite proportion.
文摘Temperature distribution and weld bead profiles of constant current and pulsed current gas tungsten arc welded aluminium alloy joints were compared. The effects of pulsed current welding on tensile properties, hardness profiles, microstructural features and residual stress distribution of aluminium alloy joints were reported. The use of pulsed current technique is found to improve the tensile properties of the weld compared with continuous current welding due to grain refinement occurring in the fusion zone.
基金financially supported by the National Natural Science Foundation of China(No.51304039)the Fundamental Research Funds for the Central Universities(Nos.N110402008 and N130402021)Meishan Steel Plant Research Fund
文摘In this work, low-density electric current pulse （ECP） has been applied to submerged entry nozzle （SEN） and its effect on the morphology of the inclusion buildup and the distribution of the inclusions in slab has been explored. The results reveal that under the unique effects of ECP, part of small inclusions less than 10 μm is expelled through the boundary layer along the current direction to form dense inclusion buildup. This method is of great potential to prolong the service life of SEN and improve the quality of the steel product.
文摘An empirical relationship to predict tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy was developed. Incorporating process parameters such as peak current, base current, pulse frequency and pulse on time were studied. The experiments were conducted based on a four-factor, five-level, central composite design matrix. The developed empirical relationship can be effectively used to predict the tensile strength of pulsed current gas tungsten arc welded AZ31B magnesium alloy joints at 95% confidence level. The results indicate that pulse frequency has the greatest influence on tensile strength, followed by peak current, pulse on time and base current.
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.
