Pulse Current Parameters Research Articles

Morphology of tellurium electrolytically deposited in a pulsed mode

Morphology of tellurium deposits produced by pulsed electrolysis of 0.005–0.05 M TeCl4 solutions in dimethyl sulfoxide was studied. The effect of the TeCl4 concentration and pulsed current parameters on the structure of electrolytically deposited tellurium films was examined.

Dynamic and temperature effects in spin-transfer switching

We have studied the dynamic switching triggered by spin angular momentum transfer in a pulsed current of a spin-valve-type trilayer structure, and its dependence on thermal effects. In order to determine the current pulse parameters, where fast and stable switching can be achieved, we have studied the magnetization’s dynamics properties as a function of applied current pulse amplitude and shape, waiting time, and initial orientation, and also as a function of the Gilbert damping constant. The magnetic layer is assumed to be single domain, ellipsoid shaped. In this paper also we present the thermal fluctuation effects on the switching behavior. The model is based on the Landau–Lifshitz–Gilbert equation and the stochastic Landau–Lifshitz–Gilbert equation with a spin-transfer term included, which are numerically integrated.

Nano-structural tailoring of manganese dioxide by using pulse current electrodeposition

A pulse current technique has been applied for the preparation of Manganese Dioxides (PCMD) in an additive-free MnSO 4–H 2SO 4 solution. The influence of pulse current parameters on surface characteristics has been studied by using scanning electron microscopy (SEM). Pore size distribution (PSD) of samples is determined from the desorption isotherm according to the Barrett–Joyner–Halenda (BJH) model. The subsequent effects on charge\\discharge cycle performance of deposited materials have been studied in laboratory designed RAM batteries. SEM images confirmed a decrease in PCMDs surface roughness showing more coherent and cracks-free deposits compares to a sample, which is deposited by direct current (DCMD). Results show that under optimized pulse condition, PSD data in PCMD is narrower and less than 3 nm, whereas DCMD exhibits a boarder pore size distribution and larger pore volume. Grain size, pore size distribution and pore volume were established to be important factors determining electrochemical behavior of deposited materials. Results of RAM batteries revealed that the cycle life of batteries made of PCMDs were rather higher than that made by conventional DCMD. Functional improvements are mainly attributed to enhanced current distribution as well as fewer amounts of incorporated water molecules into the PCMD crystal lattice. These could be considered as a result of lower accumulation of passive intermediates and a lower anodic overvoltage during electrodeposition of PCMD. Depending on the applied pulse parameters, nano-tailoring of PCMDs in different morphological varieties is possible.

Influence of high frequency pulse current on properties of electroformed nanocrystalline Ni–Mn alloys

The refinement of the grain size of electroformed deposits is an important way to improve the properties of the deposits. In the present study, Ni–Mn alloys in which the grain sizes approached ∼100 nm or below were electroformed by using a high frequency pulse power supply. The influence of the average deposition current density and pulse parameters on microhardness and tensile properties of the pulse electroformed Ni–Mn alloys was studied. The results show that the current parameters influence the properties of the alloys by changing their Mn content and grain size. With increase in average current density, microhardness and strength of the alloys increase and the elongation ratio decreases because of the increment of Mn content of the alloys and the decrement of grain size of the alloys. A shorter pulse on time and larger duty cycle contribute to higher microhardness and strength of the alloys.

Optimizing the Pulsed Current GTAW Parameters to Attain Maximum Impact Toughness

In this article, a procedure to select process parameters to obtain maximum impact toughness properties in the Pulsed Gas Tungsten Arc (PGTAW) welding of titanium alloy is presented. Titanium (Ti-6Al-4V) alloy has gathered wide acceptance in the fabrication of lightweight structures requiring a high strength-to-weight ratio, such as in road tankers and in space vehicles. The preferred welding process for titanium alloys is frequently Gas Tungsten Arc (GTA) welding due to its comparatively easier applicability and better economy. In the case of single pass gas tungsten arc welding of a thinner section of this alloy, the pulsed current has been found to be beneficial primarily due to its advantages over the conventional continuous current process. However, pulsed current welding is controlled by four important parameters, such as peak current, base current, pulse frequency, and pulse-on-time. To arrive at an optimum condition, one needs to carefully balance these four pulsed current parameters. The Design of Experiments concept has been used to optimize the experimental conditions. Regression analysis has been used to develop a mathematical model to predict impact toughness of titanium alloy joints incorporating pulsed current parameters. The model is optimized using the traditional Hooke and Jeeve's algorithm.

Optimizing pulsed current parameters to minimize corrosion rate in gas tungsten arc welded titanium alloy

The preferred process for welding titanium alloy is frequently gas tungsten arc (GTA) welding due to its comparatively easier applicability and better economy. Weld fusion zones of this alloy typically exhibit coarse columnar grains and lead to inferior mechanical and metallurgical properties. In the case of single pass GTA welding of a thinner section of this alloy, the pulsed current has been found to be beneficial primarily due to grain refinement of the weld fusion zone over the conventional continuous current process. Fusion zone grain refinement is controlled by pulsed current parameters such as peak current, back ground current, pulse frequency and pulse-on-time. In this investigation, a mathematical model has been developed to predict corrosion rate of gas tungsten arc welded titanium alloy by incorporating pulsed current parameters. Four factors, five level, central composite, rotatable design matrix has been used to minimize the experimental conditions. A mathematical model has been developed by response surface method (RSM). The developed model has been optimized using genetic algorithm (GA) and contour plots to attain minimum corrosion rate in the weld fusion zone.

Effect of pulsed current GTA welding parameters on the fusion zone microstructure of AA 6061 aluminium alloy

AA6061 aluminium alloy (Al−Mg−Si alloy) has gathered wide acceptance in the fabrication of food processing equipment, chemical containers, passenger cars, road tankers, and railway transport systems. The preferred process for welding these aluminium alloys is frequently Gas Tungsten Arc (GTA) welding due to its comparatively easy applicability and lower cost. In the case of single pass GTA welding of thinner sections of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current processes. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. In this investigation, an attempt has been made to develop a mathematical model to predict the fusion zone grain diameter incorporating pulsed current welding parameters. Statistical tools such as design of experiments, analysis of variance, and regression analysis are used to develop the mathematical model. The developed model can be effectively used to predict the fusion grain diameter at a 95% confidence level for the given pulsed current parameters. The effect of pulsed current GTA welding parameters on the fusion zone grain diameter of AA 6061 aluminium alloy welds is reported in this paper.

Effect of current pulsing on tensile properties of titanium alloy

Titanium and its alloys have been considered as one of the best engineering metals for industrial applications. This is due to the excellent combination of properties such as elevated strength to weight ratio, high toughness, excellent resistance to corrosion and good fatigue properties make them attractive for many industrial applications. Recently, considerable research has been performed on pulsed current gas tungsten arc welding process and reported advantages include improved bead contour, lower heat input requirements, reduced residual stresses and distortion. Metallurgical advantages of pulsed current welding frequently reported in literature include refinement of fusion zone grain size, reduced width of heat affected zone, etc. All these factors will help in improving the mechanical properties. Hence, in this investigation an attempt has been made to study the effect of pulsed current gas tungsten arc welding parameters on Ti–6Al–4V titanium alloy.

Developing mathematical models to predict grain size and hardness of argon tungsten pulse current arc welded titanium alloy

Abstract Titanium (Ti–6Al–4V) alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The frequently preferred welding process of titanium alloy is argon tungsten arc welding due to its comparatively easier applicability and better economy. In case of single pass welding of thinner section of this alloy, pulse current was found beneficial due to its advantages over the conventional continuous current process. Many considerations have come into the picture and one need to carefully balance various pulse current parameters to arrive at an optimum combination. Hence, in this investigation an attempt has been made to develop mathematical models to predict grain size and hardness of argon tungsten pulse current arc welded titanium alloy weldments. Four factors, five level, central composite, rotatable design matrix is used to optimize the required number of experiments. The mathematical models were developed by response surface method (RSM). The adequacy of the models was checked by ANOVA technique. By using the developed mathematical models, grain size and hardness of the joints can be predicted with 99% confidence level.

A compact pulse generator for radiographic source supply

Radiography of short-living objects using X-pinch radiation is a new perspective direction in diagnostics developed at the P. N. Lebedev Institute of Physics. High spatial (up to a few tenth of a micrometer) and temporal resolutions (up to 0.1 ns) achieved with the use of the X pinch is extremely interesting to the researches of transient processes and substances in extreme states. The X pinch is produced by two or more crossed wires (with wire diameters up to 30 µm) exploded under the influence of current running through them. Scanning radiation is generated in a dense high-temperature plasma (up to several kiloelectron volts) arising in the region of wire crossing. Among the main requirements on the generator used to create the X pinch are current amplitudes of 150–300 kA and rates of current increase of 1–2 kA/ns. Up to now, these current pulse parameters have been provided only by bulky stationary generators weighing from 300 kg to several tons. In the present paper, a small-size (weighing 70 kg) high-current pulse generator (with current amplitude exceeding 300 kA and pulse rise time of 200 ns) of soft x-ray radiation from high-temperature X-pinch plasma is described.

Numerical Modeling of Pulse MIG Welding

A new heat source model for pulse MIG welding is developed which enables estimation of weld bead width and central penetration obtained with industrially pure Argon, Argon+5%, 25% CO2. The heat source model takes into account effects of various pulse current parameters such as pulse peak time, base time and mean current. Finite difference method with explicit time stepping technique is used to solve the two dimension Fourier's equation on non-uniform meshes generated by K-Method. Enthalpy method is used along with Kirchhoff variable transformation to solve the moving boundary problem. Relationship between enthalpy and temperature is used to include non-linear thermal properties of the material. The computed values of weld bead width and central penetration are within 8% and 5% of the experimental values respectively.

Developing mathematical models to predict tensile properties of pulsed current gas tungsten arc welded Ti–6Al–4V alloy

Titanium (Ti–6Al–4V) alloy has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process of titanium alloy is frequently gas tungsten arc (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 need to carefully balance various pulse current parameters to arrive at an optimum combination. Hence, in this investigation an attempt has been made to develop mathematical models to predict tensile properties of pulsed current GTA welded titanium alloy weldments. Four factors, five level, central composite, rotatable design matrix is used to optimise the required number of experiments. The mathematical models have been developed by response surface method (RSM). The adequacy of the models has been checked by ANOVA technique. By using the developed mathematical models, the tensile properties of the joints can be predicted with 99% confidence level.

Cycle life improvement of alkaline batteries via optimization of pulse current deposition of manganese dioxide under low bath temperatures

Pulse current electrodeposition (PCD) method has been applied to the preparation of novel electrolytic manganese dioxide (EMD) in order to enhance the cycle life of rechargeable alkaline MnO 2–Zn batteries (RAM). The investigation was carried out under atmospheric pressure through a systematic variation of pulse current parameters using additive free sulfuric acid–MnSO 4 electrolyte solutions. On time ( t on) was varied from 0.1 to 98.5 ms, off time ( t off) from 0.25 to 19.5 ms, pulse frequencies ( f) from 10 to 1000 Hz and duty cycles ( θ) from 0.02 to 0.985. A constant pulse current density ( I p) of 0.8 A dm −2 and average current densities ( I a) in the range of 0.08–0.8 A dm −2 were applied in all experiments. Resultant materials were characterized by analyzing their chemical compositions, X-ray diffractions (XRD) and scanning electron microscopy (SEM). Electrochemical characterizations carried out by charge/discharge cycling of samples in laboratory designed RAM batteries and cyclic voltammetric experiments (CV). It has been proved that specific selection of duty cycle, in the order of 0.25, and a pulse frequency of 500 Hz, results in the production of pulse deposited samples (pcMDs) with more uniform distribution of particles and more compact structure than those obtained by direct current techniques (dcMDs). Results of the test batteries demonstrated that, in spite of reduction of bath temperature in the order of 40 °C, the cycle life of batteries made of pcMDs (bath temperature: 60 °C) was rather higher than those made of conventional dcMDs (boiling electrolyte solution). Under the same conditions of EMD synthesis temperature of 80 °C and battery testing, the maximum obtainable cycle life of optimized pcMD was nearly 230 cycles with approximately 30 mAh g −1 MnO 2, compared to that of dcMD, which did not exceed 20 cycles. In accordance to these results, CV has confirmed that the pulse duty cycle is the most influential parameter on the cycle life than the pulse frequency. Because of operating at lower bath temperatures, the presented synthetic mode could improve its competitiveness in economical aspects.

Multiwire$X$-Pinches at 1-MA Current on the COBRA Pulsed-Power Generator

The rebuilt COBRA pulsed-power generator, which has a variable current-pulse waveform and amplitude (95-150-ns rise time and ~1-MA peak current), has extended the range of the current-pulse parameters that can be used to study the X-pinches. X-pinches with 4-12 wires of several different wire materials (from Al to W) with diameters from 25 to 75 mum have been studied. The influence of the rate of the rise of current and the X-pinch wire mass on the X-pinch plasma formation and pinch implosion dynamics has been studied using a set of diagnostics with spatial and/or temporal resolution. Multiwire X-pinches were placed in the diode center, and/or two four-wire X-pinches were placed in one of the four parallel return-current circuits of the diode. The experiments showed that the most important factor determining the first X-ray burst timing is the linear mass density of the X-pinch wires, and an optimal value for obtaining a single high-energy X-ray burst was found. Radiographic images of the different test objects, wires in wire-array Z-pinches, and the X-pinches, themselves, were obtained using a micrometer-scale spatial resolution

Influences of pulsed current tungsten inert gas welding parameters on the tensile properties of AA 6061 aluminium alloy

Medium strength aluminium alloy (Al–Mg–Si alloy) has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to-weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. In any structural application of this alloy consideration its weldability is of utmost importance as welding is largely used for joining of structural components. The preferred welding process of aluminium alloy is frequently tungsten inert gas (TIG) welding due to its comparatively easier applicability and better economy. In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. Many considerations come into the picture and one need to carefully balance various pulse current parameters to arrive at an optimum combination. Hence, in this investigation an attempt has been made to study the influence of pulsed current TIG welding parameters on tensile properties of AA 6061 aluminium alloy weldments.

Optimising pulsed current TIG welding parameters to refine the fusion zone

The use of pulsed current parameters has been found to improve the mechanical properties of high strength Al–Zn–Mg–Cu welds compared to those of continuous current welds. This is due to grain refinement occurring in the fusion zone. In this investigation an attempt has been made to optimise pulsed current TIG welding parameters to attain maximum grain refinement in high strength AA 7075 aluminium alloy using statistical tools such as design of experiments, response table, and analysis of variance techniques.

Microstructural investigations on CdTe thin films electrodeposited using high current pulses

CdTe thin films were electrochemically deposited over FTO-coated glass substrates by singular unipolar current pulses of high magnitude. A wide range of periodic current pulse parameters was investigated in CdTe thin film deposition and the growth properties of the deposited film were determined as a function of variables viz. applied current density, average current and ON/OFF pulse duration and the conditions were optimized for stoichiometric CdTe film growth. A detailed investigation has been carried out to understand the effect of pulse parameters on CdTe growth phases and film microstructure. As evidenced by the diffraction patterns of pulse electrodeposited CdTe films mean current density of 0.36 mA/cm 2 represents an upper limit to form crystalline—CdTe film without secondary phases. Increase in pulse current show inclusion of secondary growth phases. A highly oriented cubic phase was obtained at low current pulse, due to low nucleation rate and surface diffusion of adions on the substrate to growth sites. The crystalline structure and morphology of films were analyzed using powder X-ray diffraction and scanning electron microscopy suggest that OFF time contributes more on the grain size, whereas ON time affects the rate of deposition and grain morphology.

Reducing Mass-Transport Limitations by Application of Special Pulsed Current Modes

Current pulsing, unlike potential pulsing, is generally considered ineffective in enhancing mass transport. However, we show here, that by properly selecting the pulsed current parameters, the depletion of the reactant at the electrode during cathodic reduction, or its excess during anodic dissolution, can be reduced compared to the corresponding dc current application, while still passing the same amount of charge in an identical amount of time. The advantageous pulsed current modes include a sequence of decreasing current density amplitudes, or pulsing the current at the same amplitude, but with increasing relaxation intervals. By comparison, it is also shown that applying a sequence of constant-amplitude square current pulses at constant time intervals leads to an identical concentration profile as in dc. The application to the battery-charging process is briefly discussed.

Surface Integrity in Micro-Hole Drilling Using Micro-Electro Discharge Machining

This paper presents an investigation into the drilling of micro-holes of diameter 0.3 mm in tool steel H13 by means of the Micro-EDM process. Scanning Electron Microscopy (SEM) and Scanning White Light Interferometry (SWLI) techniques are used to determine the influence of the drilling process parameters upon the surface roughness. The results reveal a series of randomly overlapped craters upon the machined surface, which represent the position and chronological sequence of individual sparks during the machining process. As the voltage and current increases, the crater appearance changes from a conical to a cylindrical shape, and its depth and diameter both increase. It is shown that surface roughness deteriorates as the pulse voltage increases. Finally a regression equation is established between the diameter of the crater and the pulse voltage, pulse current and pulse-on duration parameters. This equation enables the diameters of the craters, and hence the surface integrity of the machined surface, to be predicted for a given set of process parameters, and is therefore a valuable tool in achieving the goal of precision machining.

X pinch plasma development as a function of wire material and current pulse parameters

An X pinch plasma is produced using two or more fine metal wires arranged so that they cross and touch at a single point, in the form of an X, as the load of a pulsed power generator (pulser). X pinches produce very bright, small, short-lived sources of X-rays in the 1-10 keV range. The X-ray source size, pulse duration and photon energy spectra depend upon the wire material and diameter, and the current waveform from the pulser. Those with /spl sim/1 /spl mu/m source size can be used as point sources of X-ray radiation for point-projection radiography with high spatial resolution. We report experiments with a variety of different wire materials, including Al, Ti, Mo, W, among others, all of which produced high resolution images, and all of which have subnanosecond X-ray pulses for X-rays /spl ges/3 keV. X pinches produced using all of these materials had common development stages. However, the wire material and the rate of rise of the current pulse influenced the details of the dynamics, leading to variation in the timing of the X-ray burst(s) relative to the start of the current pulse. For a given wire material, wire diameter had only a small effect on X-ray emission timing. Final X pinch neck implosion speeds as high as 66-75 /spl mu/m/ns were estimated.