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
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
Electric current heat treatment is an innovative technique to improve microstructures and mechanical properties of metallic materials.The microstructures and mechanical properties of a powder metallurgy high-speed ste...Electric current heat treatment is an innovative technique to improve microstructures and mechanical properties of metallic materials.The microstructures and mechanical properties of a powder metallurgy high-speed steel(PM-HSS)treated by electric current heat treatment and traditional heat treatment are comparatively investigated.Results showed that after austenitizing at 1130°C,the structure of PM-HSS sample composed of ferrite matrix,M6C,M23C6,and MC carbides,transformed into a martensite matrix accompanied by M6C and MC carbides.Compared to the traditional austenitizing at 1130℃ for 30 min,the electric current austenitizing at 1130℃ for 5 min dissolved more carbides,resulting in a greater solid solution of alloying elements in the matrix.Further traditional triple tempering led to carbide coarsening,whereas electric current triple tempering promoted the carbide dissolution.Notably,the dissolution of more carbides resulted in a higher C content in the martensite matrix of HSS treated by electric current,significantly promoting the formation of nanotwins(5-20 nm in width).The electric current triple tempering sample exhibited a yield strength of 3097 MPa,compressive strength of 5016 MPa,and a fracture strain of 30.0%,outperforming the traditional triple tempering sample by nearly 600 MPa in yield strength.Analysis revealed that this significant strengthening was primarily attributed to nanotwin formation and solid solution strengthening caused by carbide dissolution.展开更多
The impurity iron in silicon material will seriously affect the photoelectric conversion efficiency of silicon solar cells.However,the traditional silicon purification method has the disadvantages of long cycle,high e...The impurity iron in silicon material will seriously affect the photoelectric conversion efficiency of silicon solar cells.However,the traditional silicon purification method has the disadvantages of long cycle,high energy consumption and serious pollution.In this study,an efficient and green pulsed electric current purification technology is proposed.The electromigration effect of iron elements,the current density gradient driving of iron phase,and the gravity of iron phase all affect the migration behavior of iron phase in silicon melt under pulsed electric current.Regardless of the depth of electrode insertion into the silicon melt,the solubility of iron in silicon decreases under the pulsed electric current,which helps to form the iron phase.At the same time,the iron phase tends to sink toward the bottom under the influence of gravity.When the electrode is shallowly inserted,a non-uniform electric field is formed in the silicon melt,and the iron phase is mainly driven by the current density gradient to accelerate sink toward the bottom.When the electrode is fully inserted,an approximately uniform electric field is formed in the silicon melt,and iron elements are preferentially migrated to the cathode by electromigration,forming iron phase sinking at the cathode.The study of impurity iron migration behavior in silicon melt under pulsed electric current provides a new approach for the purification of polycrystalline silicon.展开更多
As the most important irradiation-induced defects,dislocation loop and copper-rich nanocluster are the major contributors to the embrittlement of the neutron-irradiated reactor pressure vessel steels.In this study,suc...As the most important irradiation-induced defects,dislocation loop and copper-rich nanocluster are the major contributors to the embrittlement of the neutron-irradiated reactor pressure vessel steels.In this study,such nano-defects were introduced into the material by 3 MeV Fe ions up to the dose of 1 dpa at high temperature(290℃)to simulate neutron irradiation.It was found that pulsed electric current can effectively reduce 95%of irradiation-induced hardening.Correspondingly,the characterization results showed that almost all the dislocation loops disappeared and the quantity of copper-rich nanoclusters also reduced greatly at relatively low temperature(450℃),and the process took only 20 min.Mean-while,it was qualitatively proved by positron annihilation spectroscopy that the number of irradiation-induced vacancy-type defects and solute-enriched clusters was significantly decreased after electropuls-ing.Furthermore,under the pulsed electric field,the rapid annihilation of the dislocation loops due to their accelerated collision with vacancies can remove the nucleation sites of the copper-rich nanoclusters and make them become dispersed,further promoting the nanoclusters that lack nucleation sites dissolv-ing faster.Therefore,this electropulsing treatment provides a practical“in-situ”performance repair tech-nology to extend the service life of reactor pressure vessel steels by regulating the interaction between vacancies,interstitial atoms and irradiation-induced defects.展开更多
The second phase dissolution and elements migration behavior of a nickel-based single crystal superalloy during solution heat treatment with direct current were investigated for simplifying and shortening the solution...The second phase dissolution and elements migration behavior of a nickel-based single crystal superalloy during solution heat treatment with direct current were investigated for simplifying and shortening the solution heat treatment of the Ni-based single crystal superalloy.The results showed that the electric current solution heat treatment improved microstructural homogenization as well as the distribution of alloying elements,especially for the refractory metal W and Mo.The microsegregation ratios for Mo and W after electric current solution heat treatment at 1230℃for 4 h are near those without electric current at 1250℃for 4 h.The electric current accelerated theγ′phase dissolution process,and theγ′phase could be completely dissolved at a lower treatment temperature or within a shorter treatment time under electric current solution heat treatment with direct current.A microcosmic current model was proposed to analyze the effect of the electric current on the solution heat treatment of the Ni-based single crystal superalloy.展开更多
The tribological behaviors of carbon block sliding against copper ring with and without electric current applied were investigated by using an advanced multifunctional friction and wear tester, and the electric-arc be...The tribological behaviors of carbon block sliding against copper ring with and without electric current applied were investigated by using an advanced multifunctional friction and wear tester, and the electric-arc behaviors were analyzed in detail. The results show that the normal load is one of the main controlling factors for generation of electric arc during friction process with electric current applied. The strength of electric arc is enhanced with the decrease of normal loads and the increase of electric currents. The unstable friction process and the fluctuated dynamic friction coefficients are strongly dependent upon the electric arc. The wear volumes and the wear mechanism of carbon brush were affected by the electric arc obviously. As no electric arc occurs, no clear discrepancy of the wear volumes of the carbon samples with and without electric current applied could be detected. While the wear mechanisms are mainly mechanical wear. However, under the condition of the electric arc appearance, the wear volume of carbon with electric current applied increases much more rapidly than that without electric current applied and also increases obviously with the increase of electric current strengths and the decrease of normal loads. The wear mechanisms of carbon block are mainly electric arc ablation accompanying with adhesive wear and material transferring.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 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
CNTs-Cu and graphite-Cu composites were separately prepared by powder metallurgy technique under the same consolidation processing. Tribological behavior of the composites with electric current was investigated by usi...CNTs-Cu and graphite-Cu composites were separately prepared by powder metallurgy technique under the same consolidation processing. Tribological behavior of the composites with electric current was investigated by using a pin-on-disk friction and wear tester. The results show that the friction coefficient and wear rate of the composites decrease with increasing the reinforcement content, and increase with increasing the electric current density; the effects of electric current are more obvious on tribological properties of graphite-Cu composites than on CNTs-Cu composites; for graphite-Cu composites the dominant wear mechanisms are electric arc erosion and adhesive wear, while for CNTs-Cu composites are adhesive wear.展开更多
A new approach to applying the electric current pulse （ECP） with parallel electrodes to the promotion of the transition from columnar crystal to equiaxed crystal and the improvement of macrosegregation was introduce...A new approach to applying the electric current pulse （ECP） with parallel electrodes to the promotion of the transition from columnar crystal to equiaxed crystal and the improvement of macrosegregation was introduced. The ECP was applied to different stages of the solidification. The results showed that the application of the ECP in both the initial stage （the thickness of solidified shell reached 2 mm approximately） and the late stage （the thickness of solidified shell reached 14 mm approximately） of solidification can promote the columnar to equiaxed transition （CET）. The analysis showed that during solidification, a large number of nuclei around the upper surface fell off due to ECP, which subsequently showered on the melt and impinged the growth front of the columnar crystal. Therefore, the CEToccurred. In addition, this method was also employed to influence the solidification process of bearing steel, and the results showed that the structure was changed from columnar crystal to equiaxed crystal, indicating that ECP can enhance the homogeneity of structure and composition of bearing steel.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
The microstructure and properties of the 93W-4Ni-2Co-1Fe(mass fraction,%) tungsten heavy alloys prepared by mechanical alloying and electric current activated sintering from mixed elemental powders were investigated.A...The microstructure and properties of the 93W-4Ni-2Co-1Fe(mass fraction,%) tungsten heavy alloys prepared by mechanical alloying and electric current activated sintering from mixed elemental powders were investigated.After 15 h milling,the average W grain size in the powders is decreased to 120 nm.For the powders milled for 15 h,the density,hardness and transverse rupture strength of the alloys sintered only by an intensive pulse electric current are the maximum.When the total sintering time keeps constant,the properties of the sintered alloys can be obviously improved by optimizing the sintering time of pulse-and constant-currents.A bulk ultrafine alloy with an average W grain size of about 340 nm can be obtained by sintering 15 h-milled powders in a total sintering time of 6 min.The corresponding sintered density,hardness and transverse rupture strength reach 16.78 g /cm3,HRA84.3 and 968 MPa,respectively.展开更多
Three kinds of AI-Si piston alloys were prepared and subjected to pulse electric current treatment （PECT） at different pouring temperatures. Some aspects of the solidification microstructures were examined including...Three kinds of AI-Si piston alloys were prepared and subjected to pulse electric current treatment （PECT） at different pouring temperatures. Some aspects of the solidification microstructures were examined including the morphology and the distribution of the matrix and the secondary phases by using of optical microscopy （OM）, SEM and EDS methods. Results indicate that PECT can refine the grains of α-AI in the alloys as effectively as chemical modification by sodium salt. The processing parameters of PECT on the multi-component AI-Si alloys were then optimized through the testing of tensile strength, elongation and microhardness of the prepared alloys. A new theory was put forward to explain the mechanism of PECT.展开更多
Continuous solidification experiments are carried out with Pb–Al alloys under the influence of the electric current pulses（ECPs）. The results demonstrate that the ECPs mainly affect the microstructure formation thr...Continuous solidification experiments are carried out with Pb–Al alloys under the influence of the electric current pulses（ECPs）. The results demonstrate that the ECPs mainly affect the microstructure formation through changing the energy barrier for the nucleation of the minority phase droplets（MPDs） and minority phase particles（MPPs） during cooling Pb–Al alloys in the liquid–liquid and liquid–solid phase transformation temperature ranges in advance of the solidification of the matrix liquid. For Pb–Al alloys with Al-rich droplets/particles as the minority phase, the ECPs lower the energy barriers for the nucleation of the MPDs/MPPs and cause a significant increase in the nucleation rate of the MPDs/MPPs and, thus,promote the formation of Pb–Al alloys with a well-dispersed or even nanoparticles dispersed microstructure. The ECPs parameters show an important influence on the microstructure formation of Pb–Al alloys. The refinement extent of the MPDs/MPPs increases with the increase in the peak current density. For a given peak current density, the refinement extent of the MPDs/MPPs increases with the increases in the pulse frequency and pulse width first, and then level off and become asymptotic.展开更多
Microstructure of reaction sintering of ZnAl2O4 at 1500℃ by hot-pressing(HP) and pulse electric current was investigated. The results indicated that the existed cracks in sintered body were caused by structure mismat...Microstructure of reaction sintering of ZnAl2O4 at 1500℃ by hot-pressing(HP) and pulse electric current was investigated. The results indicated that the existed cracks in sintered body were caused by structure mismatch. It is the evidence that periodical temperature field existed during pulse electric current sintering of nonconductive materials. The distance between high temperature areas was related to die diameter.展开更多
The chain-like prior particle boundaries(PPBs)as a kind of stubborn harmful precipitate will hinder atomic diffusion and particle connection.They can only be broken into nanoscale through thermal deformation(1160–120...The chain-like prior particle boundaries(PPBs)as a kind of stubborn harmful precipitate will hinder atomic diffusion and particle connection.They can only be broken into nanoscale through thermal deformation(1160–1200℃).Here,treated by the pulsed electric current at 800℃,PPBs were dissolved quickly as a result of the interaction between the pulsed electric current and the chain-like structure.According to the electromigration theory and the calculation results,the high current density regions will be mainly produced at the gaps due to the conductivity difference between the precipitates and the matrix.The atomic diffusion flux caused by the pulsed electric current is proportional to the current density.Therefore,the existence of a large number of gaps in the chain-like PPBs will make the high current density regions play a more positive role in fast-dissolution.展开更多
200-nm-thick Au interconnects on a quartz substrate were tested in-situ inside a dual-beam microscope by applying direct current, alternating current and alternating current with a small direct current component. The ...200-nm-thick Au interconnects on a quartz substrate were tested in-situ inside a dual-beam microscope by applying direct current, alternating current and alternating current with a small direct current component. The failure behavior of the Au interconnects under three kinds of electric currents were characterized in-situ by scanning electron microscopy. It is found that the formation of voids and subsequent growth perpendicular to the interconnect direction is the fatal failure mode for all the Au interconnects under three kinds of electric currents. The failure mechanism of the ultrathin metal lines induced by the electric currents was analyzed.展开更多
Gain refinement in metal alloy can be achieved by applying an electric current pulse(ECP)in solidification process.Forced flow inside the melt has been proved to be a key role in grain refinement.In this paper,the flu...Gain refinement in metal alloy can be achieved by applying an electric current pulse(ECP)in solidification process.Forced flow inside the melt has been proved to be a key role in grain refinement.In this paper,the fluid flow inside Ga 20 wt%-In 12 wt%-Sn alloy induced by a damping sinusoidal ECP flowing through two parallel electrodes into the cylindrical melt was investigated by both experimental measurements and numerical simulations.Experimental results showed that a strong descending jet was induced beneath the bottom of electrodes under the application of ECP.Besides,it was found that flow intensity increases with the increase of amplitude,frequency,and pulse width,respectively.In order to unlock the formation mechanism of flow pattern and the relevance of flow intensity varied with electrical parameters,a three-dimensional numerical model under the application of ECP was established.Meanwhile,a comparative study was conducted by numerical simulations to reveal the distributions of electromagnetic fields and forced flow.Numerical results showed that the downward Lorentz force induced by ECP was concentrated beneath the bottom of electrodes.This downward Lorentz force induces a descending jet and provokes a global forced flow.According to numerical simulations,the evolution of flow intensity with electrical parameters under the application of ECP can be understood by the time averaged impulse of Lorentz force.展开更多
The fracture of pipelines caused by corrosion cracks and the resulting oil and gas leakage can lead to great environmentalpollution and economic losses. These negative effects are due to serious corrosion of the plain...The fracture of pipelines caused by corrosion cracks and the resulting oil and gas leakage can lead to great environmentalpollution and economic losses. These negative effects are due to serious corrosion of the plain carbon steels used for armorof flexible pipe in oil and gas transmission medium. However, corrosion resistance of carbon steel armors has yet to beimproved. In this study, the relationship between corrosion resistance and pearlite fraction in the plain carbon steels hasbeen investigated through the application of pulsed electric current. Based on immersion test and electrochemical mea-surement, pulsed electric current increases the corrosion resistance of the plain carbon steels by reducing the fraction ofpearlite phase. Pitting corrosion, which tends to initiate by galvanic corrosion of ferrite and cementite, is therefore inhibiteddue to the decrease in pearlite fraction （mixture of ferrite and cementite） under electropulsing.展开更多
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(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financially supported by the National Natural Science Foundation of China(Nos.52271034,52301058 and 52471042)China Postdoctoral Science Foundation(No.2023M732183)Postdoctoral Fellowship Program of CPSF(No.GZB20230399).
文摘Electric current heat treatment is an innovative technique to improve microstructures and mechanical properties of metallic materials.The microstructures and mechanical properties of a powder metallurgy high-speed steel(PM-HSS)treated by electric current heat treatment and traditional heat treatment are comparatively investigated.Results showed that after austenitizing at 1130°C,the structure of PM-HSS sample composed of ferrite matrix,M6C,M23C6,and MC carbides,transformed into a martensite matrix accompanied by M6C and MC carbides.Compared to the traditional austenitizing at 1130℃ for 30 min,the electric current austenitizing at 1130℃ for 5 min dissolved more carbides,resulting in a greater solid solution of alloying elements in the matrix.Further traditional triple tempering led to carbide coarsening,whereas electric current triple tempering promoted the carbide dissolution.Notably,the dissolution of more carbides resulted in a higher C content in the martensite matrix of HSS treated by electric current,significantly promoting the formation of nanotwins(5-20 nm in width).The electric current triple tempering sample exhibited a yield strength of 3097 MPa,compressive strength of 5016 MPa,and a fracture strain of 30.0%,outperforming the traditional triple tempering sample by nearly 600 MPa in yield strength.Analysis revealed that this significant strengthening was primarily attributed to nanotwin formation and solid solution strengthening caused by carbide dissolution.
基金financially supported by the National Natural Science Foundation of China(No.U21B2082)Natural Science Foundation of Beijing Municipality(No.2222065)and Fundamental Research Funds for the Central Universities(No.FRF-TP-22-02C2).
文摘The impurity iron in silicon material will seriously affect the photoelectric conversion efficiency of silicon solar cells.However,the traditional silicon purification method has the disadvantages of long cycle,high energy consumption and serious pollution.In this study,an efficient and green pulsed electric current purification technology is proposed.The electromigration effect of iron elements,the current density gradient driving of iron phase,and the gravity of iron phase all affect the migration behavior of iron phase in silicon melt under pulsed electric current.Regardless of the depth of electrode insertion into the silicon melt,the solubility of iron in silicon decreases under the pulsed electric current,which helps to form the iron phase.At the same time,the iron phase tends to sink toward the bottom under the influence of gravity.When the electrode is shallowly inserted,a non-uniform electric field is formed in the silicon melt,and the iron phase is mainly driven by the current density gradient to accelerate sink toward the bottom.When the electrode is fully inserted,an approximately uniform electric field is formed in the silicon melt,and iron elements are preferentially migrated to the cathode by electromigration,forming iron phase sinking at the cathode.The study of impurity iron migration behavior in silicon melt under pulsed electric current provides a new approach for the purification of polycrystalline silicon.
基金supported by the National Natural Science Foundation of China(No.U21B2082)the Beijing Municipal Natural Science Foundation(No.2222065)the Fundamental Research Funds for the Central Universities(No.FRF-TP-22-02C2).
文摘As the most important irradiation-induced defects,dislocation loop and copper-rich nanocluster are the major contributors to the embrittlement of the neutron-irradiated reactor pressure vessel steels.In this study,such nano-defects were introduced into the material by 3 MeV Fe ions up to the dose of 1 dpa at high temperature(290℃)to simulate neutron irradiation.It was found that pulsed electric current can effectively reduce 95%of irradiation-induced hardening.Correspondingly,the characterization results showed that almost all the dislocation loops disappeared and the quantity of copper-rich nanoclusters also reduced greatly at relatively low temperature(450℃),and the process took only 20 min.Mean-while,it was qualitatively proved by positron annihilation spectroscopy that the number of irradiation-induced vacancy-type defects and solute-enriched clusters was significantly decreased after electropuls-ing.Furthermore,under the pulsed electric field,the rapid annihilation of the dislocation loops due to their accelerated collision with vacancies can remove the nucleation sites of the copper-rich nanoclusters and make them become dispersed,further promoting the nanoclusters that lack nucleation sites dissolv-ing faster.Therefore,this electropulsing treatment provides a practical“in-situ”performance repair tech-nology to extend the service life of reactor pressure vessel steels by regulating the interaction between vacancies,interstitial atoms and irradiation-induced defects.
基金The authors gratefully acknowledge the financial support by the National Key Research and Development Program(No.2018YFA0702900)National Science and Technology Major Project(No.J2019-VII-0002-0142)the National Natural Science Foundation of China(No.51831007).
文摘The second phase dissolution and elements migration behavior of a nickel-based single crystal superalloy during solution heat treatment with direct current were investigated for simplifying and shortening the solution heat treatment of the Ni-based single crystal superalloy.The results showed that the electric current solution heat treatment improved microstructural homogenization as well as the distribution of alloying elements,especially for the refractory metal W and Mo.The microsegregation ratios for Mo and W after electric current solution heat treatment at 1230℃for 4 h are near those without electric current at 1250℃for 4 h.The electric current accelerated theγ′phase dissolution process,and theγ′phase could be completely dissolved at a lower treatment temperature or within a shorter treatment time under electric current solution heat treatment with direct current.A microcosmic current model was proposed to analyze the effect of the electric current on the solution heat treatment of the Ni-based single crystal superalloy.
基金Project (2007CB714703) supported by the National Basic Research Program of ChinaProject (50521503) supported by the National Natural Science Foundation of ChinaProject (20050613015) supported by Research Fund for Doctoral Program of Higher Education of China
文摘The tribological behaviors of carbon block sliding against copper ring with and without electric current applied were investigated by using an advanced multifunctional friction and wear tester, and the electric-arc behaviors were analyzed in detail. The results show that the normal load is one of the main controlling factors for generation of electric arc during friction process with electric current applied. The strength of electric arc is enhanced with the decrease of normal loads and the increase of electric currents. The unstable friction process and the fluctuated dynamic friction coefficients are strongly dependent upon the electric arc. The wear volumes and the wear mechanism of carbon brush were affected by the electric arc obviously. As no electric arc occurs, no clear discrepancy of the wear volumes of the carbon samples with and without electric current applied could be detected. While the wear mechanisms are mainly mechanical wear. However, under the condition of the electric arc appearance, the wear volume of carbon with electric current applied increases much more rapidly than that without electric current applied and also increases obviously with the increase of electric current strengths and the decrease of normal loads. The wear mechanisms of carbon block are mainly electric arc ablation accompanying with adhesive wear and material transferring.
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Project (2007CB607603) supported by the National Basic Research Program of China
文摘CNTs-Cu and graphite-Cu composites were separately prepared by powder metallurgy technique under the same consolidation processing. Tribological behavior of the composites with electric current was investigated by using a pin-on-disk friction and wear tester. The results show that the friction coefficient and wear rate of the composites decrease with increasing the reinforcement content, and increase with increasing the electric current density; the effects of electric current are more obvious on tribological properties of graphite-Cu composites than on CNTs-Cu composites; for graphite-Cu composites the dominant wear mechanisms are electric arc erosion and adhesive wear, while for CNTs-Cu composites are adhesive wear.
基金Item Sponsored by National Natural Science Foundation of China(50674064,50734008)
文摘A new approach to applying the electric current pulse （ECP） with parallel electrodes to the promotion of the transition from columnar crystal to equiaxed crystal and the improvement of macrosegregation was introduced. The ECP was applied to different stages of the solidification. The results showed that the application of the ECP in both the initial stage （the thickness of solidified shell reached 2 mm approximately） and the late stage （the thickness of solidified shell reached 14 mm approximately） of solidification can promote the columnar to equiaxed transition （CET）. The analysis showed that during solidification, a large number of nuclei around the upper surface fell off due to ECP, which subsequently showered on the melt and impinged the growth front of the columnar crystal. Therefore, the CEToccurred. In addition, this method was also employed to influence the solidification process of bearing steel, and the results showed that the structure was changed from columnar crystal to equiaxed crystal, indicating that ECP can enhance the homogeneity of structure and composition of bearing steel.
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.
基金Project(2007CB616905) supported by the National Basic Research Program of ChinaProject(2007AA03Z112) supported by the National High-tech Research and Development Program of China+1 种基金Project(x2jqB6080210) supported by the Natural Science Foundation of Guangdong Province,ChinaProject(9140A18040709JW1601) supported by the Advanced Research Fund of Department of Defense,China
文摘The microstructure and properties of the 93W-4Ni-2Co-1Fe(mass fraction,%) tungsten heavy alloys prepared by mechanical alloying and electric current activated sintering from mixed elemental powders were investigated.After 15 h milling,the average W grain size in the powders is decreased to 120 nm.For the powders milled for 15 h,the density,hardness and transverse rupture strength of the alloys sintered only by an intensive pulse electric current are the maximum.When the total sintering time keeps constant,the properties of the sintered alloys can be obviously improved by optimizing the sintering time of pulse-and constant-currents.A bulk ultrafine alloy with an average W grain size of about 340 nm can be obtained by sintering 15 h-milled powders in a total sintering time of 6 min.The corresponding sintered density,hardness and transverse rupture strength reach 16.78 g /cm3,HRA84.3 and 968 MPa,respectively.
基金supported by Heilongjiang Provincial Natural Science Foundation(Grant No.E200504)in China and the Harbin Institute of Technology Inter-disciplines Foundation(Grant No.HIT.MD2002.14).
文摘Three kinds of AI-Si piston alloys were prepared and subjected to pulse electric current treatment （PECT） at different pouring temperatures. Some aspects of the solidification microstructures were examined including the morphology and the distribution of the matrix and the secondary phases by using of optical microscopy （OM）, SEM and EDS methods. Results indicate that PECT can refine the grains of α-AI in the alloys as effectively as chemical modification by sodium salt. The processing parameters of PECT on the multi-component AI-Si alloys were then optimized through the testing of tensile strength, elongation and microhardness of the prepared alloys. A new theory was put forward to explain the mechanism of PECT.
基金supported by the National Natural Science Foundation of China(Grant Nos.51771210,51501207,51471173 and 51271185)the China’s Manned Space Station Project(Grant No.TGJZ800-2-RW024)the Natural Science Foundation of Liaoning Province(Grant No.201501043)
文摘Continuous solidification experiments are carried out with Pb–Al alloys under the influence of the electric current pulses（ECPs）. The results demonstrate that the ECPs mainly affect the microstructure formation through changing the energy barrier for the nucleation of the minority phase droplets（MPDs） and minority phase particles（MPPs） during cooling Pb–Al alloys in the liquid–liquid and liquid–solid phase transformation temperature ranges in advance of the solidification of the matrix liquid. For Pb–Al alloys with Al-rich droplets/particles as the minority phase, the ECPs lower the energy barriers for the nucleation of the MPDs/MPPs and cause a significant increase in the nucleation rate of the MPDs/MPPs and, thus,promote the formation of Pb–Al alloys with a well-dispersed or even nanoparticles dispersed microstructure. The ECPs parameters show an important influence on the microstructure formation of Pb–Al alloys. The refinement extent of the MPDs/MPPs increases with the increase in the peak current density. For a given peak current density, the refinement extent of the MPDs/MPPs increases with the increases in the pulse frequency and pulse width first, and then level off and become asymptotic.
基金This work was supported by the National Natural Science Foundation of China under grant No.50232020 and 50220160657.
文摘Microstructure of reaction sintering of ZnAl2O4 at 1500℃ by hot-pressing(HP) and pulse electric current was investigated. The results indicated that the existed cracks in sintered body were caused by structure mismatch. It is the evidence that periodical temperature field existed during pulse electric current sintering of nonconductive materials. The distance between high temperature areas was related to die diameter.
基金financially supported by the National Natural Science Foundation of China(Nos.51874023 and U1860206)the Fundamental Research Funds for the Central Universities(FRF-TP20-02B)the Recruitment Program of Global Experts。
文摘The chain-like prior particle boundaries(PPBs)as a kind of stubborn harmful precipitate will hinder atomic diffusion and particle connection.They can only be broken into nanoscale through thermal deformation(1160–1200℃).Here,treated by the pulsed electric current at 800℃,PPBs were dissolved quickly as a result of the interaction between the pulsed electric current and the chain-like structure.According to the electromigration theory and the calculation results,the high current density regions will be mainly produced at the gaps due to the conductivity difference between the precipitates and the matrix.The atomic diffusion flux caused by the pulsed electric current is proportional to the current density.Therefore,the existence of a large number of gaps in the chain-like PPBs will make the high current density regions play a more positive role in fast-dissolution.
基金supported by the National Basic Research Program of China (No.2004CB619303)"The Hundred Talent Plan"of Chinese Academy of Sciencespartially by the National Natural Science Foundation of China (No.50571103).
文摘200-nm-thick Au interconnects on a quartz substrate were tested in-situ inside a dual-beam microscope by applying direct current, alternating current and alternating current with a small direct current component. The failure behavior of the Au interconnects under three kinds of electric currents were characterized in-situ by scanning electron microscopy. It is found that the formation of voids and subsequent growth perpendicular to the interconnect direction is the fatal failure mode for all the Au interconnects under three kinds of electric currents. The failure mechanism of the ultrathin metal lines induced by the electric currents was analyzed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.U1760204,51974183,52071194,and 52074180).
文摘Gain refinement in metal alloy can be achieved by applying an electric current pulse(ECP)in solidification process.Forced flow inside the melt has been proved to be a key role in grain refinement.In this paper,the fluid flow inside Ga 20 wt%-In 12 wt%-Sn alloy induced by a damping sinusoidal ECP flowing through two parallel electrodes into the cylindrical melt was investigated by both experimental measurements and numerical simulations.Experimental results showed that a strong descending jet was induced beneath the bottom of electrodes under the application of ECP.Besides,it was found that flow intensity increases with the increase of amplitude,frequency,and pulse width,respectively.In order to unlock the formation mechanism of flow pattern and the relevance of flow intensity varied with electrical parameters,a three-dimensional numerical model under the application of ECP was established.Meanwhile,a comparative study was conducted by numerical simulations to reveal the distributions of electromagnetic fields and forced flow.Numerical results showed that the downward Lorentz force induced by ECP was concentrated beneath the bottom of electrodes.This downward Lorentz force induces a descending jet and provokes a global forced flow.According to numerical simulations,the evolution of flow intensity with electrical parameters under the application of ECP can be understood by the time averaged impulse of Lorentz force.
基金financially supported by the National Natural Science Foundation of China(No.51601011)the Fundamental Research Funds for the Central Universities+2 种基金the Recruitment Program of Global Expertsthe State Grid Scientific and Technological Research Program of China(No.5211DS17001X)the Zhejiang Electric Power Corporation Scientific and Technological Research Program of China(No.5211DS5002 M).
文摘The fracture of pipelines caused by corrosion cracks and the resulting oil and gas leakage can lead to great environmentalpollution and economic losses. These negative effects are due to serious corrosion of the plain carbon steels used for armorof flexible pipe in oil and gas transmission medium. However, corrosion resistance of carbon steel armors has yet to beimproved. In this study, the relationship between corrosion resistance and pearlite fraction in the plain carbon steels hasbeen investigated through the application of pulsed electric current. Based on immersion test and electrochemical mea-surement, pulsed electric current increases the corrosion resistance of the plain carbon steels by reducing the fraction ofpearlite phase. Pitting corrosion, which tends to initiate by galvanic corrosion of ferrite and cementite, is therefore inhibiteddue to the decrease in pearlite fraction （mixture of ferrite and cementite） under electropulsing.
