In the condition of the 3 mm gap, experiments for 360 Hz intermediate-frequency vacuum arc are carried out in interrupters with the diameters being 41 mm and with the contact materials being CuCr50 and Cu-W-WC alloy r...In the condition of the 3 mm gap, experiments for 360 Hz intermediate-frequency vacuum arc are carried out in interrupters with the diameters being 41 mm and with the contact materials being CuCr50 and Cu-W-WC alloy respectively. The results indicate that the contacts material is closely related to the breaking capacity of the vacuum interrupters and characteristics of an intermediate-frequency vacuum arc. For contacts with the same diameter, the breaking capacity of CuCr50 is better than that of Cu-W-WC. When the current fails to be interrupted, the arcs overflow the gap and present irregular performances in the first half wave. Consequently a voltage spike appears. More macroscopic metal droplets can be seen in the arc column between CuCr50 contacts because of the lower melting point. It is observed that the droplet emission is much more severe during arc reignition than that in the first half wave. It is much more conspicuous that the high frequency arc voltage noises appear in Cu-W-WC contacts when the vacuum arcs reignite, for higher temperature and stronger electronic emission ability of Cu-W-WC contacts.展开更多
In this report,two new contact structures of a vacuum interrupter with a sinusoidal curved surface are proposed to improve the capability by increasing the surface area.The experimental investigation of vacuum arc at ...In this report,two new contact structures of a vacuum interrupter with a sinusoidal curved surface are proposed to improve the capability by increasing the surface area.The experimental investigation of vacuum arc at intermediate frequency(360-800 Hz)was conducted and the results were compared with a butt contact with the same contact diameter(41 mm)and the same material.By analyzing the arc behavior,arc voltage characteristics,arc energy,current interrupting capacity,ablation of the anode contact and condensation of the arc products at a 3 mm gap,the differences in their vacuum arc characteristics were determined.The correlations of their arc energy with the amplitude and the frequency of the current were also achieved.Analysis suggests that the ruled curved contact has strong application potentiality because of its low arc energy,low arc voltage noise and arc voltage peak,light ablation on the surface of the anode contact and high interrupting capacity.展开更多
In this study, the changes of a vacuum arc＇s appearance were observed and the volt-ampere characteristics of the vacuum arc at intermediate frequency were analyzed under a transverse magnetic field （TMF）. The TMF a...In this study, the changes of a vacuum arc＇s appearance were observed and the volt-ampere characteristics of the vacuum arc at intermediate frequency were analyzed under a transverse magnetic field （TMF）. The TMF and phase shift time were calculated by using the TMF contact model and the large phase shift of the magnetic field at a higher frequency was conductive to the dispersion process of residual plasma. The arc velocity was higher at 800 Hz than at 400 Hz. It can be inferred that TMF will encourage arc movement at 800 Hz. Moreover, the arc movement has an impact on the arc voltage. Because of the increasing length of the arc column with a high arc velocity, the elongated arc causes the arc voltage to increase. Specifically, the volt-ampere characteristics of the vacuum arc are divided into three stages in this paper. The higher the frequency, the greater the initial rate of rise in the arc voltage and the larger the area surrounded by arc volt-ampere characteristics. The correlations between the arc voltage and the amplitude and frequency of the current are also presented.展开更多
One of the issues of plasma technologies is the design of a high-performance plasma source.Due to its properties,a diffuse vacuum arc discharge may be one of the promising options.In this study,the dependence of the c...One of the issues of plasma technologies is the design of a high-performance plasma source.Due to its properties,a diffuse vacuum arc discharge may be one of the promising options.In this study,the dependence of the charge composition of a diffuse vacuum arc plasma with a hot cathode on the value of the external axial magnetic field and discharge voltage was investigated.The study was conducted with a thermionic gadolinium(Gd)cathode.Monitoring the charge composition was done by analyzing the emission spectra of the plasma.Steady states of arc discharge were obtained for a range of parameters.The arc currents were 30 and 40 A,the arc voltage was up to 29 V and the external magnetic field was varied from 0 to 20 mT.It was found that in the presence of the eternal magnetic field the defining factor of the charge composition was the arc voltage.Moreover,for a fixed arc voltage,an increase in magnitude causes an increase in intensities of all atomic and ionic plasma components(Gd,Gd+,Gd++).The potential causes of this effect were discussed.It was established that in an axial magnetic field it is possible to implement discharge modes with predominance of single-charge ions by increasing the magnitude of the external magnetic field.Potentially,these discharge modes will be of use for the implementation of plasma methods for reprocessing spent nuclear fuel.展开更多
Large-sized titanium alloy ingots produced by vacuum arc remelting(VAR)technology are susceptible to metallurgical imperfections such as compositional segregation,inconsistent solidification microstructures,black spot...Large-sized titanium alloy ingots produced by vacuum arc remelting(VAR)technology are susceptible to metallurgical imperfections such as compositional segregation,inconsistent solidification microstructures,black spots,and inclusions.These defects are intricately linked to the electromagnetic effects,temperature distribution,and fluid dynamics during the melting process.The self-induced magnetic field created by the electric current,along with the axial magnetic field applied to stabilize the arc,significantly influences the solidification of titanium alloy ingots.A mathematical model optimized for the integrated analysis of multiple fields—electromagnetic,fluid,and thermal—was developed for the VAR solidification process of titanium alloys.The influence mechanism of electromagnetic field on the macroscopic solidification process of titanium alloy was investigated.The findings indicate the presence of two competing forces within the VAR molten pool,namely,thermal buoyancy and the Lorentz force.Introducing a coupled self-induced magnetic field and elevating the current to 15 kA led to an increase in the molten pool depth by 42.9%and a reduction in the thickness of the mushy zone by 25.2%.The application of a constant axial magnetic field enhances a unidirectional momentum buildup within the molten pool,thereby enhancing the flow velocity and cooling efficiency of melt.展开更多
To investigate the reason for Mn segregation in TC2 titanium alloy bars,a multiphysics-coupled mathematical model was established using the BMPS-VAR numerical simulation software,incorporating electro-magnetic,thermal...To investigate the reason for Mn segregation in TC2 titanium alloy bars,a multiphysics-coupled mathematical model was established using the BMPS-VAR numerical simulation software,incorporating electro-magnetic,thermal,and flow fields.Numerical simulation was performed to analyze the dynamic evolution of varying-mass electrode fragments during the vacuum arc remelting(VAR)of a∅508-mm TC2 titanium alloy in-got.The results indicate that Mn segregation caused by 15-kg electrode fragmentation during the VAR process of a TC2 titanium alloy ingot corresponds to the segregation observed in the TC2 titanium alloy bar.The numerical simulation of the VAR process provides effective result prediction and technical support for solving practical problems in smelting.展开更多
The use of an alternative magnetic field during vacuum arc remelting(VAR)can have significant effects on the primary carbide and mechanical properties of M50-bearing steel.The solidification structure and the primary ...The use of an alternative magnetic field during vacuum arc remelting(VAR)can have significant effects on the primary carbide and mechanical properties of M50-bearing steel.The solidification structure and the primary carbide morphology of the VAR ingot were analyzed by optical microscopy and scanning electron microscopy.Characterization and analysis of the growth direction of primary carbides were conducted using high-resolution rapid electron backscatter diffraction.Solute elements segregation was analyzed using an electron probe microanalyzer.FLUENT was utilized to conduct numerical simulations to validate the experimental findings and elucidate the underlying mechanism.Compared to traditional VAR,magnetic-controlled VAR generates a horizontal circulation,which makes a shallower and flatter molten pool and a more even temperature distribution.In the time dimension,the local solidification time is shortened,and the concentration of solute elements will be alleviated.In the spatial dimension,the secondary dendrite arm spacing decreases,alleviating the degree of inter-dendritic segregation.Consequently,the possibility of forming a segregation diminishes.Both aspects promote the even distribution of solute atoms,resulting in less segregation and hindering the development of primary carbide.This leads to the refinement of primary carbide size and its uniform distribution.The magnetic-controlled vacuum arc melting not only refines the dendritic structure in the M50 ingot,causing it to expand more axially along the ingot,but also refines primary carbides and improves tensile and wear-resistant mechanical properties.展开更多
Arc motion and splitting of vacuum arc at intermediate frequency（400-800 Hz） were investigated under transverse magnetic field（TMF）.The experiment was performed on cup-type TMF contacts with contact diameter of 40...Arc motion and splitting of vacuum arc at intermediate frequency（400-800 Hz） were investigated under transverse magnetic field（TMF）.The experiment was performed on cup-type TMF contacts with contact diameter of 40 mm and a contact gap of 4 mm in a single-frequency circuit.With high-speed photography we characterized the arc appearance at different arc currents from 3.3 kA-rms to 10 kA-rms at intermediate frequencies.As arc current increases from3.3 kA-rms to 10 kA-rms the arc appearance changes obviously.When current value is 3.3 kArms（current frequency 400-800 Hz）,there is almost no splitting arc;when the current exceeds5 kA-rms（current frequency 400-800 Hz）,the arc rotates at a speed above 20 m/s,accompanied by an observable splitting arc.The splitting arc could be observed at different frequencies and the arc-voltage had no noises when splitting occurred.The motion direction and the velocity of arc column were studied.Finally,the formation of a split arc was discussed.展开更多
CuCr alloys are important contact materials, but all conventional preparing methods have disadvantages and mismatch the requirements for mass production and high properties. The CuCr25 alloys were prepared by means of...CuCr alloys are important contact materials, but all conventional preparing methods have disadvantages and mismatch the requirements for mass production and high properties. The CuCr25 alloys were prepared by means of arc smelting in vacuum, and their microstructures, physical properties as well as dielectric strength were investigated. The experimental results show that vacuum arc smelting is an ideal method to produce CuCr25 contact alloys with fine microstructure, low gas content, high density and dielectric strength. Meanwhile, with the high productivity and low cost, CuCr25 contact materials can be produced with mass production through vacuum arc smelting method.展开更多
Cf/Cu composite was prepared by vacuum melting infiltration. Ti and Cr were doped to the Cu alloy to improve the wettability between Cu and carbon. The microstrueture was investigated by XRD, SEM and EDS. The arc eros...Cf/Cu composite was prepared by vacuum melting infiltration. Ti and Cr were doped to the Cu alloy to improve the wettability between Cu and carbon. The microstrueture was investigated by XRD, SEM and EDS. The arc erosion rate of Cf/Cu composite was investigated in vacuum. The results showed that the Ti and Cr could improve the wettability between Cu and C/C preform and the infiltration ability of Cu into C/ C preform greatly. A TiC interface formed between the fibers and matrix. The good bonding between the fiber and matrix guaranteed that part of the Cu matrix can still be bonded on the fibers even when the material was exposed to the plasma. Consequently, the carbon fibers were protected from the erosion. In comparison, Cu was completely consumed by the arc erosion. Hence, the graphite was eroded and presented a cauliflower-like morphology. Therefore, the prepared C/Cu bad better ability to resist the arc erosion, compared with common Cu-C material.展开更多
To improve the limiting current interruption capability and minimizing vacuum interrupter with axial magnetic field （AMF） electrodes, it is significant to investigate the vacuum arc behaviours between the contacts. ...To improve the limiting current interruption capability and minimizing vacuum interrupter with axial magnetic field （AMF） electrodes, it is significant to investigate the vacuum arc behaviours between the contacts. AMF distributions of the slot type electrodes were studied by both numerical analysis and experiments. Furthermore, the behaviours of vacuum arcs for different parameters of the slot type AMF electrodes were investigated by using high-speed CCD camera. The influences of gap distance, contact diameter and phase shift time between AMF and arc current on the vacuum arc were investigated. The results provide a reference for research and development of vacuum interrupters with slot type or other types of AMF electrode.展开更多
In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium a...In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium alloy ingots during VAR process.The results show that the temperature fields obtained by the simulation are well validated through the experiment results.The temperature distribution is different during the whole VAR process and the steady-state molten pool forms at 329 s for d100 mm × 180 mm ingots.At the initial stage of remelting,the heat dissipation of crucible bottom plays an important role in the whole heat dissipation system.At the middle of remelting,the crucible wall becomes a major heat dissipation way.The effect of cooling velocity on the solidification structure of ingots was investigated based on the temperature fields and the results can well explain the macrostructure of titanium alloy ingots.展开更多
ZrN/TiZrN multilayers are deposited by using the cathodic vacuum arc method with different substrate bias（from 0 to 800 V）,using Ti and Zr plasma flows in residual N 2 atmosphere,combined with ion bombardment of sam...ZrN/TiZrN multilayers are deposited by using the cathodic vacuum arc method with different substrate bias（from 0 to 800 V）,using Ti and Zr plasma flows in residual N 2 atmosphere,combined with ion bombardment of sample surfaces.The effect of pulsed bias on the structure and properties of films is investigated.Microstructure of the coating is analyzed by X-ray diffraction（XRD）,and scanning electron microscopy（SEM）.In addition,nanohardness,Young＇s modulus,and scratch tests are performed.The experimental results show that the films exhibit a nanoscale multilayer structure consisting of TiZrN and ZrN phases.Solid solutions are formed for component TiZrN films.The dominant preferred orientation of TiZrN films is（111） and（220）.At a pulsed bias of 200 V,the nanohardness and the adhesion strength of the ZrN/TiZrN multilayer reach a maximum of 38 GPa,and 78 N,respectively.The ZrN/TiZrN multilayer demonstrates an enhanced nanohardness compared with binary TiN and ZrN films deposited under equivalent conditions.展开更多
The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting(VAR)process have important effect on the subsequent mechanical p...The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting(VAR)process have important effect on the subsequent mechanical processes like forging,rolling and welding.In order to determine the fluid motion of molten pool,a 2D finite element model is established using ANSYS10.0 software,combined with the turbulent fluid flow and heat transfer.The fluid motion caused by thermo buoyancy forces is investigated at different VAR processes in the present study.The results indicate that the fluid flows symmetrically along the axis of the molten pool and clockwisely along the circle at the right pool’s profile.It is also shown that the maximum velocity increases with increasing melting rate and a direct proportional relationship exists.展开更多
A particle-in-cell simulation is conducted to investigate the plasma acceleration process in a micro-cathode vacuum arc thruster.A coaxial electrode structure thruster with an applied magnetic field configuration is u...A particle-in-cell simulation is conducted to investigate the plasma acceleration process in a micro-cathode vacuum arc thruster.A coaxial electrode structure thruster with an applied magnetic field configuration is used to investigate the effects of the distribution of the magnetic field on the acceleration process and the mechanism of electrons and ions.The modeling results show that due to the small Larmor radius of electrons,they are magnetized and bound by the magnetic field lines to form a narrow electron channel.Heavy ions with a large Larmor radius take a long time to keep up with the electron movement.The presence of a magnetic field strengthens the charge separation phenomenon.The electric field caused by the charge separation is mainly responsible for the ion acceleration downstream of the computation.The impact of variations in the distribution of the magnetic field on the acceleration of the plasma is also investigated in this study,and it is found that the position of the magnetic coil relative to the thruster exit has an important impact on the acceleration of ions.In order to increase the axial velocity of heavy ions,the design should be considered to reduce the confinement of the magnetic field on the electrons in the downstream divergent part of the applied magnetic field.展开更多
The greenhouse effect of SFe is a great concern today. The development of high voltage vacuum circuit breakers becomes more important. The vacuum circuit breaker has minimum pollution to the environment. The vacuum in...The greenhouse effect of SFe is a great concern today. The development of high voltage vacuum circuit breakers becomes more important. The vacuum circuit breaker has minimum pollution to the environment. The vacuum interrupter is the key part of a vacuum circuit breaker. The interrupting characteristics in vacuum and arc-controlling techniue are the main problems to be solved for a longer gap distance in developing high voltage vacuum interrupters. To understand the vacuum arc characteristics and provide effective technique to control vacuum arc in a long gap distance, the arc mode transition of a cup-type axial magnetic field electrode is observed by a high-speed charge coupled device （CGD） video camera under different gap distances while the arc voltage and arc current are recorded. The controlling ability of the axial magnetic field on vacuum arc obviously decreases when the gap distance is longer than 40 ram. The noise components and mean value of the arc voltage significantly increase. The effective method for controlling the vacuum arc characteristics is provided by long gap distances based on the test results. The test results can be used as a reference to develop high voltage and large capacity vacuum interrupters.展开更多
The feeding parameters in the final stage of vacuum arc remelting process obviously affect the solute segregation and shrinkage pore depth.Coupled with the electromagnetic field,fluid flow,and solute transport,a numer...The feeding parameters in the final stage of vacuum arc remelting process obviously affect the solute segregation and shrinkage pore depth.Coupled with the electromagnetic field,fluid flow,and solute transport,a numerical model was built to investigate the effect of feeding parameters on the ingot solidification phenomena.The Nb segregation and shrinkage pore depth in the solidified ingot were measured.The results show that the liquid moves along the solidification front and the vertex flow is formed in the liquid pool,which promotes solute transport.In the solidified ingot,the Nb segregation in the lower part is negative,while that in the upper part is positive.With the differential electrode applied,the positive segregation is slightly reduced but the segregation distribution remains unchanged.As the feeding current decreases,the positive segregation zone moves toward the ingot top surface,due to the final solidification position moving upward.With the feeding time extended,the positive segregation moves to the top surface and the shrinkage pore depth is reduced.As the feeding time is set at 12 min,the shrinkage pore depth can be reduced to 21 mm.展开更多
Vacuum arc ion sources are known for delivering high currents of ion beams in many technological applications. There is a great need in the present ion accelerator injection research for a titanium vacuum arc source t...Vacuum arc ion sources are known for delivering high currents of ion beams in many technological applications. There is a great need in the present ion accelerator injection research for a titanium vacuum arc source to produce high-ionized plasma, in which its parameter is extremely important to match the extractors geometry and the extraction voltage. In this paper, the radial and angular distributions of the titanium cathodic vacuum arc plasma parameters are measured by a cylindrical Langmuir probe and analyzed by the Druyvesteyn method from the I-V curves. The electron density ne is about 10^（17）m^（-3） and the effective electron temperature Tefr is in the range of 6.12-11.11 eV in the free expansion cup before the ion extraction. The measured distribution of ne over the expansion cross-section is non-uniform and axially unsymmetrical with its form similar to the Gaussian distribution, and most of the plasma is concentrated into an area whose radius is smaller than 5 mm. Teff has a nearly uniform distribution over the expansion cross-section during the discharge. The results of the plasma parameters＇ non-uniformity encourage the researchers to make some optimization designs to improve the parameter distributions, and then to facilitate ion extraction.展开更多
Experimental study of the long-gap distance vacuum arc distortion for three types of axial magnetic field （AMF） contacts, by using high-speed charge coupled device （CCD）, is presented. The arc current was of a hal...Experimental study of the long-gap distance vacuum arc distortion for three types of axial magnetic field （AMF） contacts, by using high-speed charge coupled device （CCD）, is presented. The arc current was of a half-cycle sine wave with a frequency of 50 Hz, produced by an L=C discharging circuit. The time of appearance and duration of vacuum arc distortion under three conditions were studied. It was found that the gap distance, current and diameter of the electrode affected the characteristics of vacuum distortion at a long-gap distance. Some characteristics of the vacuum arc at a long-gap distance were revealed and the experience and data for further investigation were provided.展开更多
A new method for the generation of high charged state metal ion beams is developed. This method is based on microwave heating of vacuum arc plasma in a magnetic trap under electron cyclotron resonance （ECR） conditio...A new method for the generation of high charged state metal ion beams is developed. This method is based on microwave heating of vacuum arc plasma in a magnetic trap under electron cyclotron resonance （ECR） conditions. Two gyrotrons for plasma heating were used, which were with the following parameters. The first is with a wave frequency of 37.5 GHz, a pulse duration of 1 ms and power of 100 kW, another is with 75 GHz, 0.15 ms and 400 kW. Two different magnetic traps were considered for vacuum arc plasma confinement. The first one is a simple mirror trap. Such system was already investigated and could provide high charge state ions. The second trap was with a cusp magnetic field configuration with native ＂minimum-B＂ field structure. Two different ways of metal plasma injection into the magnetic trap were used. The first one is an axial injection from an arc source located out of the trap, and the second is a radial injection from four arc sources mounted at the center of the trap. Both traps provide up to 200 eMA of ion beam current for platinum ions with highest charge state 10＋. Ion beams were successfully extracted from the plasma and accelerated by a voltage of up to 20 kV.展开更多
基金supported by National Natural Science Foundation of China (No.51377007)Specialized Research Fund for the Doctoral Program of Higher Education of China (No.20131102130006)Fundamental Research Funds for the Central Universities of China
文摘In the condition of the 3 mm gap, experiments for 360 Hz intermediate-frequency vacuum arc are carried out in interrupters with the diameters being 41 mm and with the contact materials being CuCr50 and Cu-W-WC alloy respectively. The results indicate that the contacts material is closely related to the breaking capacity of the vacuum interrupters and characteristics of an intermediate-frequency vacuum arc. For contacts with the same diameter, the breaking capacity of CuCr50 is better than that of Cu-W-WC. When the current fails to be interrupted, the arcs overflow the gap and present irregular performances in the first half wave. Consequently a voltage spike appears. More macroscopic metal droplets can be seen in the arc column between CuCr50 contacts because of the lower melting point. It is observed that the droplet emission is much more severe during arc reignition than that in the first half wave. It is much more conspicuous that the high frequency arc voltage noises appear in Cu-W-WC contacts when the vacuum arcs reignite, for higher temperature and stronger electronic emission ability of Cu-W-WC contacts.
基金National Natural Science Foundation of China(Nos.51677002,51937004)Civil Aircraft Special Research and Technology Research Project(MJ-2017-S-46)+1 种基金State Key Laboratory of Reliability and Intelligence of Electrical Equipment(No.EERIKF004)Hebei University of Technology and selected from the 1st International Symposium on Insulation and Discharge Computation for Power Equipment.
文摘In this report,two new contact structures of a vacuum interrupter with a sinusoidal curved surface are proposed to improve the capability by increasing the surface area.The experimental investigation of vacuum arc at intermediate frequency(360-800 Hz)was conducted and the results were compared with a butt contact with the same contact diameter(41 mm)and the same material.By analyzing the arc behavior,arc voltage characteristics,arc energy,current interrupting capacity,ablation of the anode contact and condensation of the arc products at a 3 mm gap,the differences in their vacuum arc characteristics were determined.The correlations of their arc energy with the amplitude and the frequency of the current were also achieved.Analysis suggests that the ruled curved contact has strong application potentiality because of its low arc energy,low arc voltage noise and arc voltage peak,light ablation on the surface of the anode contact and high interrupting capacity.
基金supported by Special Scientific and Research Funds for Doctoral Specialty of Institution of Higher Learning (200800060004)National Natural Science Foundation of China (No. 51177004)by the Innovation foundation of BUAA for Ph.D Graduates
文摘In this study, the changes of a vacuum arc＇s appearance were observed and the volt-ampere characteristics of the vacuum arc at intermediate frequency were analyzed under a transverse magnetic field （TMF）. The TMF and phase shift time were calculated by using the TMF contact model and the large phase shift of the magnetic field at a higher frequency was conductive to the dispersion process of residual plasma. The arc velocity was higher at 800 Hz than at 400 Hz. It can be inferred that TMF will encourage arc movement at 800 Hz. Moreover, the arc movement has an impact on the arc voltage. Because of the increasing length of the arc column with a high arc velocity, the elongated arc causes the arc voltage to increase. Specifically, the volt-ampere characteristics of the vacuum arc are divided into three stages in this paper. The higher the frequency, the greater the initial rate of rise in the arc voltage and the larger the area surrounded by arc volt-ampere characteristics. The correlations between the arc voltage and the amplitude and frequency of the current are also presented.
基金supported by the Russian Science Foundation(No.23-72-10073)。
文摘One of the issues of plasma technologies is the design of a high-performance plasma source.Due to its properties,a diffuse vacuum arc discharge may be one of the promising options.In this study,the dependence of the charge composition of a diffuse vacuum arc plasma with a hot cathode on the value of the external axial magnetic field and discharge voltage was investigated.The study was conducted with a thermionic gadolinium(Gd)cathode.Monitoring the charge composition was done by analyzing the emission spectra of the plasma.Steady states of arc discharge were obtained for a range of parameters.The arc currents were 30 and 40 A,the arc voltage was up to 29 V and the external magnetic field was varied from 0 to 20 mT.It was found that in the presence of the eternal magnetic field the defining factor of the charge composition was the arc voltage.Moreover,for a fixed arc voltage,an increase in magnitude causes an increase in intensities of all atomic and ionic plasma components(Gd,Gd+,Gd++).The potential causes of this effect were discussed.It was established that in an axial magnetic field it is possible to implement discharge modes with predominance of single-charge ions by increasing the magnitude of the external magnetic field.Potentially,these discharge modes will be of use for the implementation of plasma methods for reprocessing spent nuclear fuel.
基金financially supported by the National Natural Science Foundation of China(Nos.52422408 and 52171031)the Excellent Youth Fund of Liaoning Natural Science Foundation(No.2023JH3/10200001)the Liaoning Xingliao Talents-Top-notch Young Talents Project(No.XLYC2203064).
文摘Large-sized titanium alloy ingots produced by vacuum arc remelting(VAR)technology are susceptible to metallurgical imperfections such as compositional segregation,inconsistent solidification microstructures,black spots,and inclusions.These defects are intricately linked to the electromagnetic effects,temperature distribution,and fluid dynamics during the melting process.The self-induced magnetic field created by the electric current,along with the axial magnetic field applied to stabilize the arc,significantly influences the solidification of titanium alloy ingots.A mathematical model optimized for the integrated analysis of multiple fields—electromagnetic,fluid,and thermal—was developed for the VAR solidification process of titanium alloys.The influence mechanism of electromagnetic field on the macroscopic solidification process of titanium alloy was investigated.The findings indicate the presence of two competing forces within the VAR molten pool,namely,thermal buoyancy and the Lorentz force.Introducing a coupled self-induced magnetic field and elevating the current to 15 kA led to an increase in the molten pool depth by 42.9%and a reduction in the thickness of the mushy zone by 25.2%.The application of a constant axial magnetic field enhances a unidirectional momentum buildup within the molten pool,thereby enhancing the flow velocity and cooling efficiency of melt.
文摘To investigate the reason for Mn segregation in TC2 titanium alloy bars,a multiphysics-coupled mathematical model was established using the BMPS-VAR numerical simulation software,incorporating electro-magnetic,thermal,and flow fields.Numerical simulation was performed to analyze the dynamic evolution of varying-mass electrode fragments during the vacuum arc remelting(VAR)of a∅508-mm TC2 titanium alloy in-got.The results indicate that Mn segregation caused by 15-kg electrode fragmentation during the VAR process of a TC2 titanium alloy ingot corresponds to the segregation observed in the TC2 titanium alloy bar.The numerical simulation of the VAR process provides effective result prediction and technical support for solving practical problems in smelting.
基金supported by the National Natural Science Foundation of China(Grant numbers 52204347,52274385,52004156,51904184,and 52204392)the National Key Research and Development Program of China(Grant number 2022YFC2904900)+1 种基金the Science and Technology Commission of Shanghai Municipality(13JC14025000,15520711000)the Shi Changxu Innovation Center for Advanced Materials(SCXKFJJ202204).
文摘The use of an alternative magnetic field during vacuum arc remelting(VAR)can have significant effects on the primary carbide and mechanical properties of M50-bearing steel.The solidification structure and the primary carbide morphology of the VAR ingot were analyzed by optical microscopy and scanning electron microscopy.Characterization and analysis of the growth direction of primary carbides were conducted using high-resolution rapid electron backscatter diffraction.Solute elements segregation was analyzed using an electron probe microanalyzer.FLUENT was utilized to conduct numerical simulations to validate the experimental findings and elucidate the underlying mechanism.Compared to traditional VAR,magnetic-controlled VAR generates a horizontal circulation,which makes a shallower and flatter molten pool and a more even temperature distribution.In the time dimension,the local solidification time is shortened,and the concentration of solute elements will be alleviated.In the spatial dimension,the secondary dendrite arm spacing decreases,alleviating the degree of inter-dendritic segregation.Consequently,the possibility of forming a segregation diminishes.Both aspects promote the even distribution of solute atoms,resulting in less segregation and hindering the development of primary carbide.This leads to the refinement of primary carbide size and its uniform distribution.The magnetic-controlled vacuum arc melting not only refines the dendritic structure in the M50 ingot,causing it to expand more axially along the ingot,but also refines primary carbides and improves tensile and wear-resistant mechanical properties.
基金supported by Special Scientific and Research Funds for Doctoral Specialty of Institution of Higher Learning of China(No.200800060004)National Natural Science Foundation of China(No.50877002)the Innovation Foundation of BUAA for Ph.D Graduates of China
文摘Arc motion and splitting of vacuum arc at intermediate frequency（400-800 Hz） were investigated under transverse magnetic field（TMF）.The experiment was performed on cup-type TMF contacts with contact diameter of 40 mm and a contact gap of 4 mm in a single-frequency circuit.With high-speed photography we characterized the arc appearance at different arc currents from 3.3 kA-rms to 10 kA-rms at intermediate frequencies.As arc current increases from3.3 kA-rms to 10 kA-rms the arc appearance changes obviously.When current value is 3.3 kArms（current frequency 400-800 Hz）,there is almost no splitting arc;when the current exceeds5 kA-rms（current frequency 400-800 Hz）,the arc rotates at a speed above 20 m/s,accompanied by an observable splitting arc.The splitting arc could be observed at different frequencies and the arc-voltage had no noises when splitting occurred.The motion direction and the velocity of arc column were studied.Finally,the formation of a split arc was discussed.
文摘CuCr alloys are important contact materials, but all conventional preparing methods have disadvantages and mismatch the requirements for mass production and high properties. The CuCr25 alloys were prepared by means of arc smelting in vacuum, and their microstructures, physical properties as well as dielectric strength were investigated. The experimental results show that vacuum arc smelting is an ideal method to produce CuCr25 contact alloys with fine microstructure, low gas content, high density and dielectric strength. Meanwhile, with the high productivity and low cost, CuCr25 contact materials can be produced with mass production through vacuum arc smelting method.
基金Funded by the National Natural Science Foundation of China(No.51002121)Postgraduate Technology Innovation Project of Taiyuan University of Science and Technology(No.20134008)
文摘Cf/Cu composite was prepared by vacuum melting infiltration. Ti and Cr were doped to the Cu alloy to improve the wettability between Cu and carbon. The microstrueture was investigated by XRD, SEM and EDS. The arc erosion rate of Cf/Cu composite was investigated in vacuum. The results showed that the Ti and Cr could improve the wettability between Cu and C/C preform and the infiltration ability of Cu into C/ C preform greatly. A TiC interface formed between the fibers and matrix. The good bonding between the fiber and matrix guaranteed that part of the Cu matrix can still be bonded on the fibers even when the material was exposed to the plasma. Consequently, the carbon fibers were protected from the erosion. In comparison, Cu was completely consumed by the arc erosion. Hence, the graphite was eroded and presented a cauliflower-like morphology. Therefore, the prepared C/Cu bad better ability to resist the arc erosion, compared with common Cu-C material.
文摘To improve the limiting current interruption capability and minimizing vacuum interrupter with axial magnetic field （AMF） electrodes, it is significant to investigate the vacuum arc behaviours between the contacts. AMF distributions of the slot type electrodes were studied by both numerical analysis and experiments. Furthermore, the behaviours of vacuum arcs for different parameters of the slot type AMF electrodes were investigated by using high-speed CCD camera. The influences of gap distance, contact diameter and phase shift time between AMF and arc current on the vacuum arc were investigated. The results provide a reference for research and development of vacuum interrupters with slot type or other types of AMF electrode.
基金Project(2007CB613802) supported by the National Basic Research Program of China
文摘In order to get a better understanding of the vacuum consumable arc remelting(VAR) processes and thus to optimize them,a 3D finite element model was developed for the temperature fields and heat transfer of titanium alloy ingots during VAR process.The results show that the temperature fields obtained by the simulation are well validated through the experiment results.The temperature distribution is different during the whole VAR process and the steady-state molten pool forms at 329 s for d100 mm × 180 mm ingots.At the initial stage of remelting,the heat dissipation of crucible bottom plays an important role in the whole heat dissipation system.At the middle of remelting,the crucible wall becomes a major heat dissipation way.The effect of cooling velocity on the solidification structure of ingots was investigated based on the temperature fields and the results can well explain the macrostructure of titanium alloy ingots.
基金Project supported by the National Magnetic Confinement Fusion Science Program of China (Grant No. 2009GB106004)
文摘ZrN/TiZrN multilayers are deposited by using the cathodic vacuum arc method with different substrate bias（from 0 to 800 V）,using Ti and Zr plasma flows in residual N 2 atmosphere,combined with ion bombardment of sample surfaces.The effect of pulsed bias on the structure and properties of films is investigated.Microstructure of the coating is analyzed by X-ray diffraction（XRD）,and scanning electron microscopy（SEM）.In addition,nanohardness,Young＇s modulus,and scratch tests are performed.The experimental results show that the films exhibit a nanoscale multilayer structure consisting of TiZrN and ZrN phases.Solid solutions are formed for component TiZrN films.The dominant preferred orientation of TiZrN films is（111） and（220）.At a pulsed bias of 200 V,the nanohardness and the adhesion strength of the ZrN/TiZrN multilayer reach a maximum of 38 GPa,and 78 N,respectively.The ZrN/TiZrN multilayer demonstrates an enhanced nanohardness compared with binary TiN and ZrN films deposited under equivalent conditions.
基金the National Basic Research Program (973) of China(No.2007CB613802)
文摘The metallurgical structure and composition of ingots which depend critically on the fluid motion within the molten pool during the vacuum arc remelting(VAR)process have important effect on the subsequent mechanical processes like forging,rolling and welding.In order to determine the fluid motion of molten pool,a 2D finite element model is established using ANSYS10.0 software,combined with the turbulent fluid flow and heat transfer.The fluid motion caused by thermo buoyancy forces is investigated at different VAR processes in the present study.The results indicate that the fluid flows symmetrically along the axis of the molten pool and clockwisely along the circle at the right pool’s profile.It is also shown that the maximum velocity increases with increasing melting rate and a direct proportional relationship exists.
基金supported by National Natural Science Foundation of China(Nos.11735004,11575019,and 11702021)National Postdoctoral Program for Innovative Talents(BX20180029)Defense Industrial Technology Development Program(JCKY2018203B029)。
文摘A particle-in-cell simulation is conducted to investigate the plasma acceleration process in a micro-cathode vacuum arc thruster.A coaxial electrode structure thruster with an applied magnetic field configuration is used to investigate the effects of the distribution of the magnetic field on the acceleration process and the mechanism of electrons and ions.The modeling results show that due to the small Larmor radius of electrons,they are magnetized and bound by the magnetic field lines to form a narrow electron channel.Heavy ions with a large Larmor radius take a long time to keep up with the electron movement.The presence of a magnetic field strengthens the charge separation phenomenon.The electric field caused by the charge separation is mainly responsible for the ion acceleration downstream of the computation.The impact of variations in the distribution of the magnetic field on the acceleration of the plasma is also investigated in this study,and it is found that the position of the magnetic coil relative to the thruster exit has an important impact on the acceleration of ions.In order to increase the axial velocity of heavy ions,the design should be considered to reduce the confinement of the magnetic field on the electrons in the downstream divergent part of the applied magnetic field.
基金supported by National Natural Science Foundation of China(No.50477024)
文摘The greenhouse effect of SFe is a great concern today. The development of high voltage vacuum circuit breakers becomes more important. The vacuum circuit breaker has minimum pollution to the environment. The vacuum interrupter is the key part of a vacuum circuit breaker. The interrupting characteristics in vacuum and arc-controlling techniue are the main problems to be solved for a longer gap distance in developing high voltage vacuum interrupters. To understand the vacuum arc characteristics and provide effective technique to control vacuum arc in a long gap distance, the arc mode transition of a cup-type axial magnetic field electrode is observed by a high-speed charge coupled device （CGD） video camera under different gap distances while the arc voltage and arc current are recorded. The controlling ability of the axial magnetic field on vacuum arc obviously decreases when the gap distance is longer than 40 ram. The noise components and mean value of the arc voltage significantly increase. The effective method for controlling the vacuum arc characteristics is provided by long gap distances based on the test results. The test results can be used as a reference to develop high voltage and large capacity vacuum interrupters.
基金the support from Science and Technology Program of Hebei(Nos.20311004D and 20591001D)National Natural Science Foundation of China(No.51904024).
文摘The feeding parameters in the final stage of vacuum arc remelting process obviously affect the solute segregation and shrinkage pore depth.Coupled with the electromagnetic field,fluid flow,and solute transport,a numerical model was built to investigate the effect of feeding parameters on the ingot solidification phenomena.The Nb segregation and shrinkage pore depth in the solidified ingot were measured.The results show that the liquid moves along the solidification front and the vertex flow is formed in the liquid pool,which promotes solute transport.In the solidified ingot,the Nb segregation in the lower part is negative,while that in the upper part is positive.With the differential electrode applied,the positive segregation is slightly reduced but the segregation distribution remains unchanged.As the feeding current decreases,the positive segregation zone moves toward the ingot top surface,due to the final solidification position moving upward.With the feeding time extended,the positive segregation moves to the top surface and the shrinkage pore depth is reduced.As the feeding time is set at 12 min,the shrinkage pore depth can be reduced to 21 mm.
文摘Vacuum arc ion sources are known for delivering high currents of ion beams in many technological applications. There is a great need in the present ion accelerator injection research for a titanium vacuum arc source to produce high-ionized plasma, in which its parameter is extremely important to match the extractors geometry and the extraction voltage. In this paper, the radial and angular distributions of the titanium cathodic vacuum arc plasma parameters are measured by a cylindrical Langmuir probe and analyzed by the Druyvesteyn method from the I-V curves. The electron density ne is about 10^（17）m^（-3） and the effective electron temperature Tefr is in the range of 6.12-11.11 eV in the free expansion cup before the ion extraction. The measured distribution of ne over the expansion cross-section is non-uniform and axially unsymmetrical with its form similar to the Gaussian distribution, and most of the plasma is concentrated into an area whose radius is smaller than 5 mm. Teff has a nearly uniform distribution over the expansion cross-section during the discharge. The results of the plasma parameters＇ non-uniformity encourage the researchers to make some optimization designs to improve the parameter distributions, and then to facilitate ion extraction.
基金supported by National Natural Science Foundation of China (No.50477024)
文摘Experimental study of the long-gap distance vacuum arc distortion for three types of axial magnetic field （AMF） contacts, by using high-speed charge coupled device （CCD）, is presented. The arc current was of a half-cycle sine wave with a frequency of 50 Hz, produced by an L=C discharging circuit. The time of appearance and duration of vacuum arc distortion under three conditions were studied. It was found that the gap distance, current and diameter of the electrode affected the characteristics of vacuum distortion at a long-gap distance. Some characteristics of the vacuum arc at a long-gap distance were revealed and the experience and data for further investigation were provided.
基金supported by the Russian Foundation for Basic Research (grant #11-08-00259)by the Ministry of Education and Science of theRussian Federation (state contract No. 14.740.11.1333)
文摘A new method for the generation of high charged state metal ion beams is developed. This method is based on microwave heating of vacuum arc plasma in a magnetic trap under electron cyclotron resonance （ECR） conditions. Two gyrotrons for plasma heating were used, which were with the following parameters. The first is with a wave frequency of 37.5 GHz, a pulse duration of 1 ms and power of 100 kW, another is with 75 GHz, 0.15 ms and 400 kW. Two different magnetic traps were considered for vacuum arc plasma confinement. The first one is a simple mirror trap. Such system was already investigated and could provide high charge state ions. The second trap was with a cusp magnetic field configuration with native ＂minimum-B＂ field structure. Two different ways of metal plasma injection into the magnetic trap were used. The first one is an axial injection from an arc source located out of the trap, and the second is a radial injection from four arc sources mounted at the center of the trap. Both traps provide up to 200 eMA of ion beam current for platinum ions with highest charge state 10＋. Ion beams were successfully extracted from the plasma and accelerated by a voltage of up to 20 kV.
