Pulsed Current Mode Research Articles

Evaluating porosity formation in gas metal arc directed energy deposition of an aluminium alloy

Porosity formation in gas metal arc directed energy deposition of aluminium alloys is a critical challenge as it affects the structural integrity of build parts. An experimental investigation is reported here to examine the influence of energy input on pore size and area fraction in single- and multi-layer build samples of an aluminium alloy for short-circuiting and pulsed current gas metal arc. The energy input is estimated from real-time current and voltage transients. The porosity distribution in deposited samples is measured using an image segmentation approach. The pulsed current mode yielded 16–22% lower pore area fraction in comparison to short-circuiting mode. For the range of process conditions considered, an increase in energy input reduced pore area fraction significantly.

Pulse current stabilizer with digital control for the power supply system of the plasmatron

Purpose. Solution of theoretical and practical problems on providing digital control of a pulse converter using high-speed microprocessor tools in the output current stabilization mode with provision of a specified duration of transient processes caused by an increase in load voltage and output current astaticity, which allows to obtain significant advantages over analog versions. Methodology. Review of literary and patent sources on the subject, theory of pulse automatic control systems, mathematical modeling of processes in pulse current stabilizers in the MATLAB / Simulink software environment and physical prototyping. Findings. A simulation model of an autonomous power supply system based on a converter using soft switching technology of transistors and an arc load is presented. A control law is synthesized and a model of a pulse current stabilizer is developed. A method is proposed and ways are found to control a pulse current stabilizer that provide a given duration of transients and astatism of the output current. A model of a pulse stabilizer with digital control based on a single-crystal computing module is developed and manufactured. The results of the study confirm the achievement of a finite duration of transient processes caused by a step change in the load voltage, close to 3-4 periods of conversion and output current astaticism. It is shown that the use of a pulse stabilizer using a fully digital control circuit has undeniable advantages over analog systems. Originality. The problem of synthesizing a digital controller for a given control time by the method of desired transfer functions for a soft switching operating converter on an arc load is solved. In addition to the given control time, additional quality requirements in the steady state are provided. Practical value.The use of microprocessor technology makes it possible not only to implement complex and new highly efficient control algorithms for a converter operating in the pulse current stabilizer mode, but also to perform additional functions for overload protection, self-diagnostics and telemetry of pulse converters. The use of this same digital device simultaneously for the purpose of controlling a pulse converter will allow to abandon analog PWM controllers and thereby reduce its own energy consumption and weight and size characteristics, increase the reliability of the functioning of pulse converters in power supply systems as a whole.

Hardfacing of GX40CrNiSi25-20 cast stainless steel with an austenitic manganese steel electrode

Abstract To enhance the wear and corrosion resistance of engineering components, various surface modification techniques have been devised. Among these, arc welding processes employing specialized electrodes offer relatively straightforward methods with low production costs for hardfacing applications. This paper focuses on the hardfacing process using pulsed current arc welding to reinforce cast austenitic steel structural components, aiming to prolong their lifespan. Typically, hardfacing coatings utilize Fe, Ni, and Co-based alloys. Among these, Fe-based alloys, such as manganese austenitic alloys employed in our experiments, are favored for their robust mechanical work hardening capacity, resulting in significant hardness enhancements (from 186–219 HV5 in the as-deposited layer to 468–492 HV5 after mechanical work hardening) under intense wear and impact conditions. The innovation of the hardfacing process developed in this study lies in utilizing a universal TIG source adapted for manual welding with a covered electrode in pulsed current mode. This hardfacing technique can be applied to both worn components in operation and new ones before being put into service, thereby ensuring long-term durability and reducing maintenance costs.

Electrodeposition of Silicon in the Low-Temperature LiCl-KCl-CsCl-K2SiF6 Melt Under Direct and Pulse Current

In this work, the effect of electrolysis modes and their parameters on the morphology of the silicon deposits on glassy carbon were studied. In direct current mode it was found that an increase in current density and deposition time changes the morphology of the silicon from a coating to a deposit with a complex surface. Scanning electron microscopy showed that silicon films produced at low current densities and a short deposition time are represented by spherical particles with a diameter of less than 1 μm. The pulse current mode made it possible to increase the cathode density of the deposition current, and the pulse current density to an average of ≈250 mA cm−2 does not lead to the formation of a large amount of dendritic deposit. It was found that a low frequency makes it possible to obtain higher-quality silicon coatings, because when the frequency increases, the coating most often does not cover the entire electrode. The high value of the duty cycle, even at low pulse current densities, always leads to the formation of dendrites. An increase in the total deposition time also leads to an increase in the amount of deposit and the formation of dendrites.

Mechanical and micro-structural studies of pulsed and constant current TIG weldments of super duplex stainless steels and Austenitic stainless steels

Abstract In the present research work, the influence of heat input rates on microstructures, hot tensile properties, and weld surface hardness number of Super Duplex Stainless Steel 2507 super duplex steels and austenitic steels 316L plates were investigated. Pulsed current and constant current modes were used in Tungsten Inert Gas (TIG) welding to join the dissimilar metals using ER2205 as filler. Microstructural studies were revealed at different zones of pulsed and constant current TIG weldments using optical microscopy. The tensile test was conducted at two different temperature conditions (i.e., 27 and 350°C) to investigate the strength of dissimilar weldments. Hardness measurements were made on the weld surface along the transverse direction using Vicker’s hardness tester. The microstructures revealed the formation of inter-granular austenite at the fusion zone with grain boundaries with austenite structures. Due to the constant heat input, a significant microstructural development with high austenite fractions was observed in constant current (CC)-TIG weldment. In comparison to CC-TIG weldments (UTS at 27°C = 600 MPa UTS at 350°C = 456 MPa), higher tensile characteristics were noted in Pulsed Current (PC)-TIG weldments (UTS at 27°C = 695 MPa UTS at 350°C = 475 MPa). The UTS of PC-TIG weldment is improved by 15.8% when compared to CC-TIG weldment due to the controlled heat input rates. PC-TIG weldments exhibited improved hardness numbers in various zones with smaller HAZ widths than CC-TIG weldments.

Plating Al coating on high-strength steel in chloroaluminate ionic liquid under pulse current modes

Aluminum coating is a potential candidate for cadmium coating replacement due to its excellent corrosion resistance and nontoxicity. Among the fabrication methods of Al coating, plating Al via ionic liquids has drawn major attention of researchers because of the superiority of controllability, stability and low energy consumption. However, the evolution rules of plating aluminum on high-strength steel via pulse current modes at room temperature requires deeper investigation. In this work, pulse current density and pulse duty factor are regulated to reveal the plating patterns of Al on 300M high-strength steel in AlCl3-EMIC (2:1 in mole) ionic liquid. It is found that higher current density can significantly facilitate the nucleation of Al grains and the compactness of morphology, while an enlarged pulse duty factor tends to result in more regular Al crystals. When the current density and the pulse duty factor are fixed at 20 mA cm−2 and 80 %, the densest and most uniform aluminum coating is obtained. The component of Al coating is verified to be pure Al crystals with good adhesion and the plating process achieves a high current efficiency of 97.27 %. Under the protection of Al coating, the impedance and galvanic corrosion current density of 300M steel substrate are optimized by two orders of magnitude, and the corrosion current density is markedly decreased from 5.58 μA cm−2 to 0.77 μA cm−2.

Lithium-Ion Battery Lifetime Extension With Positive Pulsed Current Charging

Some studies verified that the pulsed current charging technique could extend the battery lifetime and improve the charging performance of lithium-ion batteries. However, some researchers are skeptical of this opinion because their studies have not found any advantages of pulsed current charging over conventional Constant Current (CC) charging. Positive Pulsed Current (PPC), the most common pulsed current mode, was selected for the investigation in this work. The effect of the PPC with various parameters, including the duty cycle, amplitude, and frequency, on the performance and lifetime of lithium-ion batteries, are investigated by experiments. According to the experimental results, the charging speed, charging capacity, and maximum rising temperature are mainly determined by the duty cycle and amplitude of the PPC. The battery lifetime with PPC under the frequency range from 0.05 Hz to 2 kHz has been verified to be extendable. Moreover, the battery lifetime extension can even be over 100% under a specific frequency PPC compared with CC charging. This is the first work that summarizes the law of the pulse frequency on battery lifetime extension. In the future, the pulsed current is expected to be used in fast charging technologies without compromising battery lifetime.

Tensile and microstructural behavior of gas-tungsten-arc-welded electrolytic tough pitch copper joints

Electrolytic tough pitch (ETP) copper is extensively used in the manufacturing of electrical machines and automobiles. Compared with other pure coppers, ETP copper has lower weldability. Therefore, this study analyzes the weldability of ETP copper using the gas tungsten arc welding (GTAW) process. GTAW can be performed using constant-current (CC) and pulsed-current (PC) modes. Consequently, the properties of the joints fabricated using both modes are compared and analyzed in this study. The results show that the joint efficiencies of GTAW-CC and GTAW-PC joints are 81 and 89%, respectively. The optimal heat input and pulsating action in PC mode produce refined grains in the weld zone and heat-affected zone, resulting in a higher joint efficiency.

Optimizing the hydrothermal post-treatment process for a TiO2/WO3 hybrid coating to enhance the photocatalytic degradation of methylene blue under visible light

WO3 nanoparticles were grown hydrothermally on porous titania (TiO2) PEO-coated on Ti in an alkaline electrolyte using pulsed direct current mode. To achieve the best photodegradation of methylene blue (MB) mediated by the PEO/HT hybrid coatings under visible illumination, hydrothermal parameters including precursor concentration, temperature, and time were optimized. In this sense, increasing the Na2WO4 concentration resulted in a decrease in porosity percentage and an increase in average particle size. At an optimal precursor concentration of 0.005 M, the TiO2/WO3 hybrid coating exhibited 67% degradation compared to ∼47% degradation for a bare TiO2 coating. Based on the LaMer diagram, the growth mechanism of WO3 crystals under the hydrothermal process was described. The calculated band gap of the PEO/HT coatings reduced from 3.0 eV to 2.68 eV with an increase in W-based precursor content through the hydrothermal process. Consequently, the improvement in photocatalytic performance was attributed to the participation of more WO3 nanoparticles and the expansion of the light absorption range of TiO2 up to the visible light range. Increasing the hydrothermal temperature led to an increase in crystallinity and particle size due to growth, but a decrease in porosity. The optimal photocatalytic performance was achieved for the hybrid coatings at a concentration of 0.005 M, with a hydrothermal temperature of 120 °C and treatment time of 18 h, resulting in ∼88% degradation of methylene blue after 360 min of irradiation. The study of photoactivity on a pollutant model indicates that the resulting activity is primarily influenced by the morphology of hybrid coatings, followed by their specific surface area.

A Model Describing the Process of the Electrodeposition of Zinc Loose Deposits in Pulsed Current Modes

A phenomenological model describing the change in the structural characteristics of loose zinc deposits obtained in pulsed current modes is presented. Comparison of experimental data on the structural properties of deposits with the results of model calculations indicates the adequacy of the model. To describe the features of the dendritic deposit growth and to determine the duration of the homogeneous structure formation in pulsed modes, the concept of critical thickness is introduced, at which a sharp change in the loose deposit density occurs. The dependence of the zinc deposit critical thickness on the pulse duty ratio under pulsed current modes is determined. The increasing of the pulse duty ratio leads to denser deposits with rounded dendrite shapes and fewer growth points, as compared with the deposit obtained in galvanostatic mode.

Improved osteogenic activity of NiTi orthopedic implant by HAp-Nb2O5 composite coatings: Materials and biological points of view

The surface properties of NiTi, as an interface between the synthetic implant and living tissue, play a vital role in guaranteeing implantation success, especially during the initial stage. This contribution endeavors to enhance the surface features of NiTi orthopedic implants through the application of HAp-based coatings, placing emphasis on assessing the influence of Nb2O5 particles concentration in the electrolyte on resultant properties of HAp-Nb2O5 composite electrodeposits. The coatings were electrodeposited via pulse current mode under galvanostatic current control from an electrolyte containing 0–1 g/L of Nb2O5 particles. Surface morphology, topography, and phase composition were evaluated using FESEM, AFM, and XRD, respectively. EDS was employed to study surface chemistry. In vitro biomineralization and osteogenic activity of the samples were studied by immersing the samples in SBF and incubating them with osteoblastic SAOS-2 cells, respectively. The added Nb2O5 particles, at the optimum concentration, stimulated biomineralization, suppressed the Ni ion leaching, and improved SAOS-2 cell adhesion and proliferation. NiTi implant coated by HAp-0.50 g/L Nb2O5 layer showed tremendous osteogenic properties. Overall, the HAp-Nb2O5 composite layers bring forth fascinating coating in vitro biological performance, reducing Ni leaching, and promoting osteogenic activity, which are fundamental for the successful use of NiTi in vivo.

Energy-efficient electrochemical degradation of ciprofloxacin by a Ti-foam/PbO2-GN composite electrode: Electrode characteristics, parameter optimization, and reaction mechanism

Reducing energy comsuption is crucial to commercialize electrochemical oxidation technologies. In this study, a novel PbO2 composite electrode (Ti-foam/PbO2-GN) was successfully fabricated based on a porous titanium (Ti) foam substrate and a β-PbO2 active layer embedded with multiple graphene (GN) interlayers, and applied as an anode for energy-efficient pulse electrochemical oxidation of ciprofloxacin (CIP). In contrast to PbO2 and Ti-foam/PbO2 electrodes, the Ti-foam/PbO2-GN electrode surface exhibited a more compact structure, smaller crystal grain size, and greater electrochemical active surface area. CIP removal of 89.7% was obtained with a low energy consumption (EE/O) of 6.17 kWh m−3 under pulse electrolysis conditions with a current density of 25.00 mA cm−2, pulse frequency of 5000 Hz, and pulse duty cycle of 50.0%. Up to 70.7% of the energy was saved in the pulse current mode compared to the direct current mode. Narrowing the electrode spacing to 2 cm facilitated the mass transfer process and enhanced oxidation efficiency. According to the intermediates identified, the pulse electrolysis of CIP primarily involved hydroxylation of the quinolone ring, breaking of the piperazine ring, defluorination, and decarboxylation processes, and a possible degradation mechanism of CIP was proposed. The continuous oxidation performance of CIP and the relatively low leaching of Pb2+ suggested that the Ti-foam/PbO2-GN electrode exhibited excellent stability, repeatability, and safety. The degradation results of CIP in real water also exhibits the great potential of environmental application. As a result, pulse electrochemical oxidation using a Ti-foam/PbO2-GN electrode has proven to be an energy-efficient and promising alternative for antibiotic wastewater treatment.

The electroplastic effect in titanium alloys under tension

The electroplastic effect (EPE) is a phenomenon which consists in a decrease in the strain resistance and enhancing of the plasticity of metals under the effect of the electric current of a sufficiently high density [1]. The goal of the study is to compare the deformation behavior of single-phase commercially pure tita­nium Grade 4 and two-phase VT6 alloy under tension and external heating with introduction of a pulsed current. Current of various pulse ratio and density was supplied to the grips of the tensile testing machine from a pulse generator. To estimate the relative contribution of the electroplastic effect during passage of current to the reduction of flow stresses, the materials were also exposed to external heating. The microstructure of the samples in the sample head and in the vicinity of the fracture region in the longitu­dinal section was studied using optical microscopy. The electroplastic effect in the studied materials is manifested on the tensile curve through individual jumps in the downward flow stress at a high pulse ra­tio, whereas at a low current pulse ratio a decrease in the flow stress and strain hardening and increase in the plasticity are observed. It is shown that tension of the sample under the effect of current results in a greater decrease in the flow stresses than that observed under external heating at the same temperature for both materials. This confirms the athermal nature of the pulsed current effect. The critical density of the high pulse ratio current (q - 5000) capable of providing manifestation of the electroplastic effect is two times lower for a VT6 alloy than for pure titanium Grade 4. Under the same pulsed current modes, the flow stresses for VT6 decrease more than for Grade 4. Pulsed current of high pulse ratio caused an anomalous hardening effect in a VT6 alloy, but the physical nature of this effect requires an additional study. The pulsed current modes used in the study did not lead to any structural changes noticeable under optical magnification in the samples under tension, except for the disappearance of twins and separation of the impurity particles in Grade 4 and spheroidization of grains in VT6.

Photoluminescent Plasma Electrolytic Oxidation Coatings Containing YAG: Ce Produced on 1050 Aluminum Alloy

In this work, we investigated the possible incorporation of YAG (yttrium aluminum garnet)-Ce particles into plasma electrolytic oxidation (PEO) coatings on 1050AA (aluminum alloy) in order to endow the surface with photoluminescent properties. Different treatment times and current modes (direct or pulsed) were tested as PEO process parameters using as electrolyte a silicates-containing solution. The microstructure of the samples was characterized by SEM and XRD measurements, the corrosion properties were determined by EIS tests, whereas the photoluminescence was evaluated with a proper spectrometer. The concentration of the YAG-Ce particles incorporated in the PEO coating was strongly influenced by the current mode, and in particular, it was higher with pulsed current mode. A higher content of YAG-Ce particles results in a better corrosion resistance and photoluminescent effect. PEO process in pulsed unipolar mode using an electrolyte containing YAG-Ce particles resulted an effective way to produce samples of 1050AA with a surface characterized by photoluminescent properties.

Effect of Pulsed Current on Charging Performance of Lithium-Ion Batteries

The pulsed current has been proposed as a promising battery charging technique to improve the charging performance and maximize the lifetime for lithium-ion (Li-ion) batteries. However, the effect of the pulsed current charging is inconclusive due to the changeable current mode and conditions. This article systematically investigates the effect of various pulsed current charging modes, i.e., positive pulsed current mode, pulsed current-constant current mode, negative pulsed current mode, alternating pulsed current mode, sinusoidal-ripple current mode, and alternating sinusoidal-ripple current mode on battery performance. Moreover, a comprehensive analysis of the frequency impact on the quality of the current mode is performed. The current modes in this work are evaluated considering the maximum rising temperature, discharging capacity, and charging speed according to experimental results. Furthermore, this work provides guidance for developing pulsed current charging strategies to satisfy future charging requirements.

Investigation of hydroxyapatite (HAP) containing coating on grade 2 titanium alloy prepared by plasma electrolytic oxidation (PEO) at low voltage

In this work, plasma electrolytic oxidation (PEO) process was used to produce bioactive coatings, mainly composed by hydroxyapatite (Hap) and titanium oxide, on grade 2 titanium alloy. All PEO treatments were carried out using a maximum voltage of 315 V, a lower value in comparison with the works present in literature, thus resulting a more environmentally friendly process. The effects on the PEO coatings of KOH addition to electrolyte and of working in direct or pulsed current mode, were also investigated. The morphology and elemental composition of the coatings were characterised by scanning electron microscopy (SEM), whereas the phase analysis was carried out with X-ray diffraction (XRD). The corrosion resistance properties were investigated by open circuit potential measuraments, potentiodynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests. Moreover, cell-adhesion biological tests were performed. SEM analysis evidenced the presence of needle-shape crystals of hydroxyapatite, as confirmed by XRD, that totally or partially filled the pores of PEO layer. The corrosion test showed an improvement in the corrosion behaviour of the PEO coated samples in comparison with the untreated sample. Cell-Adhesion biological tests evidenced excellent cytocompatibility of the coatings with human cells and an improvement in the cell adhesion in comparison with the untreated sample.

Effects of Matrix Silicon Content on the Plasma Electrolytic Oxidation of Al-Si Alloys Using Different Power Modes

The plasma electrolytic oxidation (PEO) of pure Al and Al alloys containing 4, 9, 12, or 15 wt.% Si were investigated under pulsed bipolar current and pulsed bipolar voltage modes, respectively. It was determined that the discharge sparks preferentially occurred on the SiO2 relative to the Al2O3 during the initial stage of PEO processing regardless of the power mode. Following 30 min of PEO treatment under the two modes, the thicknesses of the layers decreased, whereas their specific energy consumption increased with increasing Si content in the matrix. The presence of primary Si in the alloy with 15 wt.% Si had a significantly negative effect on the PEO process in the pulsed bipolar current mode: The layer thickness decreased by 45%, and its specific energy consumption increased by 52%, compared with those on pure Al. However, in the pulsed bipolar voltage mode, the layer thickness on the evaluated samples only decreased slightly, and it became much more similar after treatment.

Removal behavior and mechanisms of cadmium and lead by coupled ethylenediaminetetraacetic acid washing and electrochemical reduction: influence of current conditions.

Ethylenediaminetetraacetic acid (EDTA) washing has been used extensively to remediate heavy metal-contaminated soils. Electrochemical reduction treatment of spent washing solution is an effective method of EDTA regeneration. However, at present, these two technologies are usually regarded as two independent treatment processes. This research raised a new heavy metal-contaminated soil treatment strategy-a combination technique of coupled EDTA washing and electrochemical reduction. We speculated that the combination of EDTA washing and electroreduction treatment could improve the efficiency of Cd and Pb removal from contaminated soil. In this study, the removal performance and mechanisms of Cd and Pb under different current conditions were investigated based on a coupling of EDTA washing and electrochemical reduction. The combination technique can increase Cd and Pb removal efficiencies by 13.37-15.24% and 14.91-27.05%, respectively, compared with EDTA washing alone. Sequential extraction analysis showed that the reducible fraction improved metal removal efficiency. The percentage of metal removed increased with an increased current value and EDTA concentration. In addition, pulse current mode removed more Cd and Pb than continuous current, although the difference was not significant (p > 0.05). However, pulse current could effectively eliminate the cathodic hydrogen evolution reaction, resulting in a further heavy metal deposition at the cathode. The combination technique exhibited enhanced removal efficiency due to EDTA regeneration in the suspension and the cathodic reduction reaction. The most cost-effective treatment in 48h was a pulse current mode of 32min on/16min off-32mA-EDTA-10mM, where 47.56% of Cd and 77.00% of Pb were removed from the soil with an electric energy consumption of 8.24 Wh.

The influence of saccharin adsorption on NiFe alloy film growth mechanisms during electrodeposition.

This article deals with the effects of current modes on saccharin adsorption during NiFe electrodeposition, and, as a consequence, its effect on chemical composition, crystal structure, and microstructure of deposited films. For this purpose, we obtained NiFe films using direct, pulse, and pulse-reverse electrodeposition modes. The deposit composition, crystal structure, and surface microstructure are studied. Direct current (DC) and pulse current (PC) films have a smooth surface, while a pulse-reverse current (PRC) film surface is covered by a volumetric cauliflower-like microstructure. The mechanism of the film surface development was considered from the point of view of saccharin adsorption and its action as an inhibitor of vertical grain growth during different current modes. During the DC and PC modes, saccharin is freely adsorbed on the growth centers and restrains their vertical growth. Whereas in the case of the PRC electrodeposition, saccharin adsorbs during cathodic pulses and desorbs during anodic pulses. Therefore, its inhibiting action decreases, vertical grain growth rises, and a rougher surface develops.

Energy-efficient pulse electrochemical oxidation of Acid Blue 9 using a Ti/SnO2-Sb/α,β-Polytetrafluoroethylene-Fe-PbO2 electrode: Kinetics, mass transfer and mechanism

This study focused on the electrochemical oxidation of Acid Blue 9 (AB 9) under direct and pulse current modes using a Ti/SnO2-Sb/α,β-Polytetrafluoroethylene-Fe-PbO2 (PTFE-Fe-PbO2) anode. The results showed that 99.0% of AB 9 and 68.9% of COD could be eliminated at initial pH of 5, initial AB 9 concentration of 100 mg L-1, pulse frequency of 4000 Hz, current density of 20 mA cm−2 and pulse duty cycle of 50% after 120 min of electrolysis. The pulse electrochemical oxidation of AB 9 at the investigated conditions followed pseudo-first-order kinetics. Compared with the direct current mode, 76.0% of energy consumption could be saved at pulse current mode. The effect of mass transfer and electrode distance on the pulse electrochemical oxidation of AB 9 was also investigated in terms of mass transfer coefficient and effectiveness factor, the results showed that the reduced electrode distance was beneficial to improve the mass transfer and oxidation efficiency, as well as the energy efficiency. LC-MS analysis revealed that benzenesulfonate group, C-N and C-S bonds in AB 9 molecule were initially cleaved under the attack of ⋅OH, then some carboxylic acids were formed and eventually mineralized to CO2 and H2O. Therefore, pulse electrochemical oxidation with a PTFE-Fe-PbO2 electrode might be a promising alternative to enhance the practicability of electrochemical treatment for dye wastewater.