Effect of electrodes and thermal insulators on grain refinement by electric current pulse

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.

Migration behavior of solidification nuclei in pure Al melt under effect of electric current pulse

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.

Influences of pulse electric current treatment on solidification microstructures and mechanical properties of Al-Si piston alloys

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.

Microstructure and Temperature Distribution in ZnAl_2O_4 Sintered Body by Pulse Electric Current

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.

EFFECT OF ELECTRIC CURRENT PULSE ON SUPERPLASTICITY OF ALUMINIUM ALLOY 7475

The superplastic deformation of aluminium alloy 7475 applied electric current pulse has been studied.The results presented that applying a high density current pulse raises both the elongation rate and the m value,and makes supperior superplastic properties at high strain rate of 10^(-2)s^(-1),the optimum deformation temperature could move from 530℃to 480~510℃,TEM observation showed the superplastic deformation of the alloy is the results of grain boundary slips and dislocation slips in grains under function of the electron wind;the intergranular tear is a main behavior of fracture of the alloy.

Effect of melt pulse electric current and thermal treatment on A356 alloy

Effects of the melt pulse electric current and thermal treatment on solidification structures of A356 alloy were investigated. In the experiments, the low temperature melt(953 K and 903 K) treated by pulse electric current was mixed with high temperature melt(1 223 K). By the control experiments, the results show that the solidification structure of A356 alloy is refined apparently by the pulse electric current together with melt thermal treatment process, and the mechanical properties, especially the elongation ratio of the specimen treated is improved greatly. The structure change of the melt by pulse electric current and melt thermal treatment is the main reason for the refinement of the solidification structure of A356 alloy.

Equivalent Resistance in Pulse Electric Current Sintering

The sintering resistance for conductive TiB2 and non-conductive A12O3 as well as empty die during pulse current sintering were investigated in this paper. Equivalent resistances were measured by current and valtage during sintering the conductive and non-conductive materials in the same conditions. It is found that the current paths for conductive are different from those for non-conductive materials. For non-conductive materials, sintering resistances are influenced by powder sizes and heating rates, which indicates that pulse current has some interaction with non-conductive powders. For conductive TiB2 , sintering resistances are influenced by heating rates and ball-milling time, which indicates the effect of powders activated by spark.

Evolution of melt convection in a liquid metal driven by a pulsed electric current

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.

Development of a high current short pulse electron gun

Dielectric wall accelerator(DWA), towards high gradient acceleration field(30 MeV/m–100 MeV/m), is under development at Institute of Modern Physics. A prototype was designed and constructed to prove the principle. This needs a short pulse high current electron source to match the acceleration field generated by the Blumlein-type pulse forming lines(PFLs). In this paper, we report the design and test of a new type short pulse high current electron gun based on principle of vacuum arc discharge. Electron beams of 100 mA with pulse width of 10 ns were obtained.

Effect of high density pulse electric current on solidification structure of low temperature melt of A356 alloy

The effect of high density pulse electric current (HDPEC) on the solidification structure of the low temperature melt(LTM) of commercial A356 alloy was investigated. In the experiments, the HDPEC was discharged in the LTM (953?K, 903?K and 873?K). By the control experiments, the results showed that the solidification structure of the LTM of A356 alloy is refined apparently when the HDPEC is discharged in low temperature melt. However, the holding time of melt treated has an adverse effect on the solidification structure. The longer the holding time of the melt treated with HDPEC, the coarser the microstructure. With the same discharge voltage, the lower the temperature of LTM, the more obscure the refinement of solidification structure. Finally, the mechanism of microstructure refining by HDPEC was analyzed.

Removal of phenol by activated alumina bed in pulsed high-voltage electric field

A new process for removing the pollutants in aqueous solution-activated alumina bed in pulsed high-voltage electric field was investigated for the removal of phenol under different conditions. The experimental results indicated the increase in removal rate with increasing applied voltage, increasing pH value of the solution, aeration, and adding Fe^2＋. The removal rate of phenol could reach 72.1% when air aeration flow rate was 1200 ml/min, and 88.2% when 0.05 mmol/L Fe^2＋ was added into the solution under the conditions of applied voltage 25 kV, initial phenol concentration of 5 mg/L, and initial pH value 5.5. The addition of sodium carbonate reduced the phenol removal rate. In the pulsed high-voltage electric field, local discharge occurred at the surface of activated alumina, which promoted phenol degradation in the thin water film. At the same time, the space-time distribution of gas-liquid phases was more uniform and the contact areas of the activated species generated from the discharge and the pollutant molecules were much wider due to the effect of the activated alumina bed. The synthetical effects of the pulsed high-voltage electric field and the activated alumina particles accelerated phenol degradation.

Optimizing the Pulsed Current Gas Tungsten Arc Welding Parameters

The selection of process parameter in the gas tungsten arc （GTA） welding of titanium alloy was presented for obtaining optimum grain size and hardness. Titanium alloy （Ti-6Al-4V） is one of the most important non-ferrous metals which offers great potential application in aerospace, biomedical and chemical industries, because of its low density （4.5 g/cm^3）, excellent corrosion resistance, high strength, attractive fracture behaviour and high melting point （1678℃）. The preferred welding process for titanium alloy is frequent GTA welding due to its comparatively easier applicability and better economy. In the case of single pass （GTA） welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. Many considerations come into the picture and one needs to carefully balance various pulse current parameters to reach an optimum combination. Four factors, five level, central composite, rotatable design matrix were used to optimize the required number of experimental conditions. Mathematical models were developed to predict the fusion zone grain size using analysis of variance （ANOVA） and regression analysis. The developed models were optimized using the traditional Hooke and Jeeve＇s algorithm. Experimental results were provided to illustrate the proposed approach.

Investigation on 10/350 Crowbar Pulse Current Circuit

Structure of main air discharging switch and a crowbar TVS （triggered vacuum switch） are designed and their triggering characteristics are investigated. The experimental results showed that for TVS the operating voltage range is from 1.3 kV to 120 kV, its maximum delay time is 400 ns and its jitter is 4-10 ns. Based on these results the crowbar 10/350μs （i.e., with a front time of 10μs and a duration of 350 μs） pulse current circuit and its controlling circuit are designed. With a 10μF stored capacitor C and a 6 μF waveform forming induction, a pulse current is generated with a maximum of 100 kA, front time of 10 ns and duration of 350μs. This pulse waveform can be used for testing SPD （surge protective devices）.

A Pulsed Electromagnet for Laser Wakefield Electron Acceleration Experiments

Laser Wakefield plasma acceleration of electrons to energies above 10 GeV, may be possible in the new high power Laser beam facilities. The design of an Electron Spectrometer with an electro-magnet with adjustable magnetic field is proposed for the characterization of electron energy spectrum with a precision better than 10% for the entire energy range from 0.5 GeV to 38 GeV. The expected precision in the measurement of the electron energy is calculated as a function of the magnetic field, of the electron energy and of the magnet length. To outline the advantages offered by a pulsed electromagnet with high magnetic fields, the mass and the electric power lost in the coils of a 4 m long electromagnet with continuous current and Iron yoke are calculated.

Migration Behavior of Impurity Iron in Silicon Melt Under Pulsed Electric Current

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.

不同电学参数和水流条件下电栅对鲤(Cyprinus carpio)的阻拦效果

脉冲直流电导阻鱼技术已被广泛应用于阻止入侵物种扩散、驱赶鱼类远离危险区域并将其引导至有利区域,如鱼道。但是脉冲直流电的有效性受多方面因素的影响,其主导因素目前尚未定论。以鲤为研究对象,在静水条件下采用4因素3水平正交实验方法分析了脉冲电压、脉冲宽度、脉冲频率和电极摆放方式的电栅拦鱼效果及其对鱼类受伤尾数的主次影响,然后选择最优组合开展不同流速下(0,0.3,0.5 m/s)的驱鱼实验,分析流速对拦鱼效果的影响。结果表明:在静水工况下,影响拦鱼电栅效率的主要因素为电极布置方式>脉冲宽度>脉冲频率>脉冲电压,电极布置为方式1(垂直水流间距80 cm)、脉冲电压140 V、脉冲频率10 Hz、脉冲宽度10 ms是拦鱼效果最佳的组合。电学参数对鲤的伤害无显著性,平均受伤尾数不超过实验鱼总数的15%。流水条件下,三种流速工况下拦鱼电栅的阻拦率无显著差异,但是随着流速的增高阻拦率呈现先降低后增加的趋势。该研究将为保护鱼类资源和防止入侵鱼类跨区域传播提供依据。

Cementite Decomposition in Spherical Graphite Iron by Electropulsing

The influence of electropulsing on cementite decomposition in the spherical graphite iron has been studied. The results indicated that the cementite was decomposed in a short time by high current density electropulsing. With increasing electropulsing time, the in situ nucleation of graphite in cementite was accompanied with the quick decomposition of cementite. The dislocation accumulation adjacent to the cementite and the quick diffusion of carbon atom by electropulsing were main reasons for the quick decomposition of cementite. The in situ nucleation of graphite in the cementite resulted from the dislocation climbing crossing the cementite lamellae.

基于改良UPOINT(S)系统的个体化治疗对CP/CPPS合并SD患者的疗效分析

目的基于改良UPOINT(S)临床表现分型系统,对慢性前列腺炎/慢性盆腔疼痛综合征(CP/CPPS)合并以勃起功能障碍(ED)、早泄(PE)为代表的性功能障碍(SD)患者采用以临床症状为导向的标准化诊断和个体化治疗,验证其临床疗效,并为选择临床治疗方案提供依据。方法选取2018年1月至2021年12月中国人民解放军联勤保障部队第九四○医院门诊治疗的160例CP/CPPS合并以ED和/或PE为代表的SD患者作为研究对象,随机分为常规药物治疗的对照组(n=53)、基于传统UPOINT临床表现分型系统指导治疗的传统组(n=49)和基于改良UPOINT(S)临床表现分型系统指导治疗的改良组(n=58)。根据各组治疗前后美国国立卫生研究院慢性前列腺炎症状指数(NIH-CPSI)评分、最大尿流率(Qmax)、视觉模拟评分法(VAS)评分、国际勃起功能指数5(IIEF-5)评分、中国早泄患者性功能评分表(C-ISFPE)评分、前列腺液中白细胞(EPS-WBC)计数的变化,评价三组临床疗效差异。结果治疗前三组临床资料差异均无统计学意义(P>0.05)。治疗后,与对照组比较,传统组和改良组在所有指标上均改善显著,差异均具有统计学意义(P<0.05);与传统组比较,改良组在治疗ED[IIEF-5评分(22.0±1.2)分vs.(19.8±2.0)分,P=0.006]和PE[C-ISFPE评分(25.5±1.8)分vs.(19.5±2.2)分,P=0.005]方面改善更加显著,差异均具有统计学意义(P<0.05)。结论基于改良UPOINT(S)临床表现分型系统指导的个体化治疗,可显著改善CP/CPPS合并SD患者的性功能异常状况,相较于常规治疗和基于传统UPOINT临床表现分型系统指导治疗的疗效更好。

ZERO-CURRENT AND ZERO-VOLTAGE SWITCHING PWM BOOST FULL-BRIDGE CON VERTER

This paper proposes a zer o current and zero voltage switching (ZCZVS) PWM Boost full bridge (FB) conve rter. With series inductors, the leading switches can realize zero current swit ching (ZCS) in a wide load range using the energy of the output capacitor. Ma king use of parasitic capacitors of the lagging switches and parallel auxiliary i nductance with the primary winding of the transformer, the lagging switches can realize zero voltage switching (ZVS) under any load. Compared with the ZCS PWM Boost FB converter, the new converter has no current duty cycle loss. Operat ional principle and parameter design are analyzed. Experimental results verify the effectiveness of the proposed converter.

Altering the Residual Stress in High-Carbon Steel through Promoted Dislocation Movement and Accelerated Carbon Diffusion by Pulsed Electric Current

Residual stress in high-carbon steel affects the dimensional accuracy, structural stability, and integrity of components. Although the evolution of residual stress under an electric field has received extensive attention, its elimination mechanism has not been fully clarified. In this study, it was found that the residual stress of high-carbon steel could be effectively relieved within a few minutes through the application of a low density pulse current. The difference between the current pulse treatment and traditional heat treatment in reducing residual stress is that the electric pulse provides additional Gibbs free energy for the system, which promotes dislocation annihilation and carbon atom diffusion to form carbides, thus reducing the free energy of the system. The electroplastic and thermal effects of the pulse current promoted the movement of dislocations under the electric field, thus eliminating the internal stress caused by dislocation entanglement. The precipitation of carbides reduced the carbon content of the steel matrix and lattice shrinkage, thereby reducing the residual tensile stress. Considering that a pulsed current has the advantages of small size, small power requirement, continuous output, and continuously controllable parameters, it has broad application prospects for eliminating residual stress.