Applying Pulse Current Research Articles

Effect of Pulse Current on Interface Microstructure and Bonding Properties of TA1/304 Double-Layer Clad plates

It is difficult to effectively improve the low bonding strength of TA1/304 clad plates. This study proposes a new process for applying pulse current (1500 A, 500 Hz, 50% duty cycle) to TA1/304 clad plates during the rolling process, which changes the interface microstructure and effectively improves the bonding strength of the clad plates. The influence of the pulsed current on the interface microstructure and bonding strength was systematically studied. The results indicate that the clad plate is initially bonded at 750 °C and 35% reduction ratio under electrically-assisted rolling (EAR), and finally the higher bonding strength is obtained at 850 °C and 48% reduction ratio, reaching 395 MPa. The strengthening of the interface element diffusion and grain refinement under the action of the pulsed current are important reasons for the improvement in the bonding strength of the clad plate. This discovery provides new ideas for the preparation of clad plates with high bonding performance.

Surface and tribology characterization of diamond-like carbon flakes reinforced oxide film by pulse anodizing

Hard anodizing by using direct current (DC) is one of the conventional approaches to fabricate composite oxide film. However, the formation of high porosity and microcracks lead to significant surface defects that limit its usage in load-bearing application. The present study aims to fabricate composite oxide film by applying pulse current (PC) with incorporating Diamond-like carbon (DLC) flakes to improve surface quality. For the first phase, the growth mechanism was studied by different anodizing time at constant (1 g/L DLC) in the electrolyte. Meanwhile, the mechanical and tribological performance of DLC content in the electrolyte were determined at second phase. Oxide film has been successfully fabricated on the surface of Aluminum alloy AA2017-T4 by anodizing in diluted sulphuric acid (20 wt%) containing DLC flakes. Then, surface morphological and tribological properties were evaluated. Results showed the thickness and growth rate of (1 g/L) DLC flakes reinforced oxide film fabricated by pulse current and direct current, approximately measured at 34.41 μm (growth rate: 0.58 μm/min) and 118.08 μm (growth rate: 1.97 μm/min), respectively. By increasing the DLC content (0–20 g/L) in electrolyte, it enhanced the microhardness and durability of the composite oxide film. However, oxide film fabricated with 5 g/L DLC in electrolyte formed enough transfer layer to reduce friction during the sliding wear process.

Improving the high cycle fatigue property of Ti6Al4V ELI alloy by optimizing the surface integrity through electric pulse combined with ultrasonic surface rolling process

To improve the surface integrity and high cycle fatigue property of Ti6Al4V ELI alloy, the electric pulse has been introduced into the ultrasonic surface rolling process (USRP), which is called electric pulse-assisted ultrasonic surface rolling process (EUSRP). With the help of “electroplasticity” of the electric pulse, the thickness of the surface gradient deformation layer was about three times of the USRP specimens by adjusting the pulse current level. However, the surface hardness decreases due to the continuous effect of the pulse current and the “skin effect” during treatment. It is worth noting that the higher the applied pulse current, the more severe the softening. This paradox causes the fatigue performance of EUSRP specimens lower than that of USRP specimens. To break this paradox, the EUSRP treatment is followed by a USRP treatment. The EUSRP-2 (with a pulse current of 200 A) +USRP specimens exhibit excellent surface hardness, a gradient deformation layer thickness of about 400 µm, low surface roughness and high compressive residual compressive stress. Besides, the hardening mechanisms of the different surface strengthening specimens have been quantitatively analyzed in combination with microstructure analysis. The fatigue life of Ti6Al4V ELI alloy can be improved by about 25 times at 780 MPa using the EUSRP-2+USRP treatment, the main reason for the highest fatigue life is the deepest surface gradient layer and the deepest crack initiation site. The fatigue limit of the EUSRP-2+USRP specimens is not the highest because too much surface hardening causes compressive residual stress relaxation during cycling and the beneficial effect of compressive residual stress is eliminated.

Scaling the electrical current switching of exchange bias in fully epitaxial antiferromagnet/ferromagnet bilayers

While the electrical current manipulation of antiferromagnets (AFMs) has been demonstrated, the extent of the studied AFM materials has been limited with few systematic experiments and a poor understanding. We compare the electrical current switching of the exchange-bias field ($H_{ex}$) in AFM-Mn$_3A$N/ferromagnet-Co$_3$FeN bilayers. An applied pulse current can manipulate $H_{ex}$ with respect to the current density and FM layer magnetization, which shifts exponentially as a function of the current density. We found that the saturation current density and exponential decay constant $\tau$ increase with the local moment of AFM Mn atoms. Our results highlight the effect of the AFM local moment to electrical current switching of $H_{ex}$, although it has a near-zero net magnetization, and may provide a facile way to explore the electrical current manipulation of AFM materials.

Revisiting the Electroplating Process for Lithium-Metal Anodes for Lithium-Metal Batteries.

Electroplating has been studied for centuries, not only in the laboratory but also in industry for machinery, electronics, automobile, aviation, and other fields. The lithium-metal anode is the Holy Grail electrode because of its high energy density. But the recyclability of lithium-metal batteries remains quite challenging. The essence of both conventional electroplating and lithium plating is the same, reduction of metal cations. Thus, industrial electroplating knowledge can be applied to revisit the electroplating process for lithium-metal anodes. In conventional electroplating, some strategies like using additives, modifying substrates, applying pulse current, and agitating electrolyte have been explored to suppress dendrite growth. These methods are also effective in lithium-metal anodes. Inspired by that, we revisit the fundamental electroplating theory for lithium-metal anodes in this Minireview, mainly drawing attention to the theory of electroplating thermodynamics and kinetics. Analysis of essential differences between traditional electroplating and plating/stripping of lithium-metal anodes is also presented. Thus, industrial electroplating knowledge can be applied to the electroplating process of lithium-metal anodes to improve commercial lithium-metal batteries and the study of lithium plating/stripping can further enrich the classical electroplating technique.

Electrodeposition of Pd from a deep eutectic solvent system: effect of additives and hydrodynamic conditions

ABSTRACTElectrodeposition of palladium from a mixture of choline chloride/urea/palladium(II) chloride (deep eutectic solvent) has been carried out by direct and pulse current electrodeposition. The influence of five organic additives, current mode (direct current vs. pulsed current) and hydrodynamics on the surface morphology of the electrodeposited palladium films was investigated. The surface morphology and thickness of the palladium layers produced was determined by scanning electron microscope and energy dispersive X-ray fluorescence spectroscopy. The experimental results showed that the surface morphology of the palladium deposits could be affected significantly either by applying pulse current and/or addition of organic additives. Current mode, electrolyte agitation and surface effects of the selected additives mutually interfere with each other, causing changes in the microstructure of the deposits (coarse → nodular/smooth). It was possible to improve the palladium deposit quality and metal deposition rate by addition of appropriate additives and by applying pulsed current.

Structure and growth behavior of intermediate phase in Cu–Zr diffusion couple heated by pulse current

In this research, Cu–Zr diffusion couples were heated by pulse current and a conventional heating method, respectively. Comparative analyses on the diffusion behavior of Zr and Cu atoms, interfacial structure and growth behavior of diffusion reaction area were carried out. The results show that applying pulse current can accelerate the migration rate of atoms, promote the diffusion of Zr atoms to the copper substrate in a short holding time, achieve a metallurgical bonding and form a continuous, dense reaction layered structure with a two-layer interface. The pulse current heating can induce the formation of lamellar ZrCu phase in the copper substrate interface. After holding for a relatively short period of time, a large number of Zr atoms crossed through the ZrCu phase, formed ZrCu3 phase in the copper rich phase side and grew gradually along the depth direction of copper substrate. Meanwhile, the growth rate of ZrCu phase was relatively slow due to the weak diffusion ability of Cu atom to in zirconium matrix.

Optimization of the Anodic Dissolution of the Superalloy Inconel 718

Due to its particular mechanical and thermal properties, nickel-based superalloys such as Inconel 718 are widely used for aerospace industry. They are known to be the among the most difficult-to-cut- materials[1], so that conventional machining methods such as milling are inefficient and hard to proceed[2]. Because of its ability to generate high quality surfaces and to reproduce complex shapes. Pulse or Precise ElectroChemical Machining (PECM), an unconventional machining process (no cutting tools), can be useful to manufacture those alloys. This technic is based on the anodic oxidation of metals through a strong applied pulse current. The electrical signal is synchronized to the oscillation of the cathode corresponding to a rectilinear translational movement. Throughout the process, the electrolyte is continuously renewed that allows the removing of the solid residues of the dissolved metal and guarantees a good dissolution efficiency. The PECM is characterized by a very low inter-electrode distance (gap), from 0.01 to 0.2 mm, which ensures the dimensional accuracy. First step was to understand the physical-chemical phenomena related to the anodic dissolution of the Inconel 718 in the usual electrolyte NaNO3. Thus, polarization curves associated with current constant dissolution have been studied in 2,35 mol/L (20 % wt) NaNO3. Energy dispersive X-ray spectroscopy analysis of cross-sections were used to highlight the solid anodic products formed during anodization. They are mainly constituted of Ni and Nb oxides as well as γ '' (Ni3Nb) inclusions. From ICP analyses of the electrolyte, the dissolved elements in solution are mainly those of the austenitic matrix. Consequently, in order to optimize the dissolution process, the individual anodic behavior of both main components forming the superalloy, namely the matrix and the γ'' phase were studied in a mixture of NaNO3 and EDTA as a chelating agent. Linear Sweep Voltammetry (LSV) was performed to study the global behavior of each phase in the chelating medium. Chronopotentiometry was carried out to determine the dissolution yield. Finally, electrochemical impedance spectroscopy (EIS) measurements were performed to evaluate the electrochemical interface following the anodization process. It appears that, in presence of EDTA, the hydroxides formation in the electrolyte is limited, whereas the charge transfer resistance and the anodizing layer resistance decrease. As a final step, the electrolyte containing the chelating agent was subsequently tested for Inconel 718 in PECM configuration using a home – made experimental set up in order to determine the influence of the gap, the electrolyte flow and the pulse time on anodic dissolution. In addition, metallographic sections and dissolution products analysis were also made to identify the material integrity. [1] D. Dudzinski, A. Devillez, A. Moufki, D. Larrouquere, V. Zerrouki, et J. Vigneau, « A review of developments towards dry and high speed machining of Inconel 718 alloy », Int. J. Mach. Tools Manuf, vol. 44, no 4, p. 439-456, mars 2004. [2] M. Burger, L. Koll, E. A. Werner, et A. Platz, « Electrochemical machining characteristics and resulting surface quality of the nickel-base single-crystalline material LEK94 », J. Manuf. Process, vol. 14, no 1, p. 62-70, janv. 2012.

Electrodeposition of Nanotwin Cu by Pulse Current for Through-Si-Via (TSV) Process.

Recently, the through-Si-via (TSV) had been focused as an optimal solution for interconnecting the 3-dimensionaly stacked semiconductor devices. One of core processes in the TSV technology is the Cu filling process which electrochemically forms the Cu in the via with high aspect ratio. The nanotwin Cu is effective candidate for replacing the conventional electrodeposited Cu due to its ultrahigh mechanical strength and good electrical conductivity. In this work, the formation of the nanotwin Cu in the TSV by applying pulse current was systematically studied. Also, TSV filling behavior by electrodeposition with pulse current was compared with direct current. The variation of mechanical properties as well as the electrical resistivity of electrodeposited Cu by the pulse current also investigated.

Effect of additive and current mode on surface morphology of palladium films from a non-aqueous deep eutectic solution (DES)

Electrodeposition of palladium from a non-aqueous electrolyte solution [choline chloride/urea/palladium(II)chloride] has been carried out by direct and pulse current electroplating. In this study, the influence of an organic additive (nicotinic acid amide), current mode (direct current or pulse current deposition) and hydrodynamic on the surface morphology of electroplated palladium films was investigated. In order to determine the surface morphology and thickness of the electrodeposited palladium layers, a scanning electron microscope and an energy dispersive X-ray fluorescence spectroscope were used. In addition, the cell voltage during the different electrodeposition experiments was recorded and analysed. The experimental results showed that the surface morphology of the palladium deposits could be remarkably affected either by addition of the additive or by applying pulse current. Pulse plating and the selected inhibitor mutually interfere with each other, causing changes in the microstructure of the palladium deposits (e.g. smoothening or forming of micro-cracks). It was possible to optimise the palladium deposit quality by applying pulse current or by addition of the appropriate inhibitor.

Microstructure and depositional mechanism of Ni–P coatings with nano-ceria particles by pulse electrodeposition

Nano-CeO2 (RE) particles were co-deposited into Ni–P binary composite coatings by applying pulse current (PC) under ultrasonic (U) field. Morphology, chemical content and crystal microstructure were characterized by environmental scanning electron microscopy (E-SEM) with energy dispersive X-ray analysis (EDXA), XRD diffractometry and transmission electron microscopy (TEM). Experimental results show that Ni–P coating reinforced with 15g/L nano-CeO2, in amorphous state and with compact structure, can be improved in the microhardness from HV0.2580 to HV0.2780 by annealing at 600 °C for 2 h. The highest content of codeposited Ce and deposition rate can reach 2.3% and 68 μm/h, respectively. Furthermore, the effect of RE adsorption and pulse overpotential on depositional mechanism was investigated. n-CeO2 particles or Ce4+ ions with strong adsorption capacity acted as the catalytic nucleus to improve densification effectively. During annealing at 600 °C for 2 h, n-CeO2 particles will uniformly adsorb on crystal grain to preferentially pad and heal up gaps of cracking Ni boundaries, promoting dispersion strengthening with refiner-grained structure.

MAGNETIC PROPERTIES OF NANOCRYSTALLINE Fe–Ni ALLOYS SYNTHESIZED BY DIRECT AND PULSE ELECTRODEPOSITION

Nanocrystalline iron–nickel alloys are electrodeposited by direct and pulse current densities with the grain sizes between 8–16 nm. XRD patterns showed a variety of structure in alloys from fcc, bcc and mixed (fcc+bcc) by variation of Fe content of alloy. The fcc structure was observed for lower Fe content, dual phase structure for Fe content between 60–70% and bcc structure for higher Fe content. By applying pulse current, an increase in Fe content of alloys was observed. Magnetic property measurements showed a high saturation magnetization for the alloys increased with increase in Fe content and a low coercivity decreased with decrease in grain size for alloys with iron content below 60%.

Application of constant current pulse to suppress bubble incorporation and control deposit morphology during aqueous electrophoretic deposition (EPD)

Electrophoretic deposition (EPD) from aqueous suspension generally forms deposits containing enormous pores because of evolution of hydrogen gas at cathode and oxygen at anode due to electrolysis of water on application of DC electric field. We have demonstrated through this investigation on aqueous EPD of alumina suspension as an example that application of pulsed DC instead of the conventionally used continuous DC is a convenient and effective way to control and suppress the amount of bubble incorporation in the deposit. Bubble-free deposits of reasonable yield were obtained at suitable pulse widths and/or duty cycle. The deposit yield and bubble incorporation decreased progressively with decrease in the pulse width and duty cycle of the applied pulse current. A characteristic deposition window was found in the current vs. pulse width plot within which smooth and bubble-free deposits are obtained. The window is wider at low-applied currents compared to that at higher currents implying that it is easier to control the pulsed EPD at lower applied currents. No deposition occurred below the window whereas deposits with incorporated bubbles formed above the window. Possible mechanisms involved in pulsed EPD have been advocated on the basis of amount of hydrogen evolved/pulse due to the electrolysis of water. The discrete amount of H 2 evolved/pulse was higher for larger pulse widths leading to incorporation of more bubbles and vice versa. This was verified by monitoring the gain in weight of palladium (Pd) electrode used as cathode for electrolysis experiment since it is known to absorb hydrogen.

Reduction of switching current distribution in spin transfer magnetic random access memories

In this paper, the switching current distribution by spin transfer torque is investigated for CoFeB∕MgO∕CoFeB magnetic tunnel junctions (MTJs). The distribution of the spin transfer switching current for a MTJ with junction size of 85×110nm2 is 16% when the duration of applied pulse current is 5ms. In the case of magnetization reversal with magnetic field induced by current with 5ms pulse duration, the distribution of the switching field is 8.3%. According to our micromagnetic simulation, it is found that the spin transfer current switching seems to exhibit a nonuniform magnetization reversal process, whereas the magnetization switching by the magnetic field exhibits a uniform magnetization reversal process. This leads to the broader distribution related to the repeatability.

Spark plasma sintering as advanced PM sintering method

A short overview of works on spark plasma sintering (SPS) is given in the present paper. SPS is a newly developed rapid sintering technique with a great potential for achieving fast densification results with minimal grain growth in a short sintering time. It is proven by obtained experimental data that enhanced sinterability of powders subjected to SPS mainly associated with particle surface activation and increased diffusion rates on the contact zones caused by applied pulse current. Application of rapid heating results in bypassing of low temperature regions where surface transport controlled sintering is dominant. This preserves the powder surface area to temperature levels where bulk transport is significant. However, the nature of activation effects, especially in its regards to acceleration of diffusion processes, is not clearly established. A lot of research work reports about the occurrence of plasma during the application of pulse current. However, the appearance of thermal plasma during SPS is a controversial issue and plasma-particle interaction is a complex phenomenon. Presently the industrial application of SPS processing is considered mainly in the areas where it is difficult or extremely difficult to obtain high performance materials and where normally HP or hipping processes are applied. Apparently significantly more work is required in this field for better understanding of the entire process and for making a stable ground for more extended industrial application of SPS.

Investigations of pulse current electrodeposition for damascene copper metals

The influence of current density, duty cycle, and frequency of the applied pulse current on film qualities of electroplated copper was discussed. With various filled damascene structures, the corresponding filling power was optimized in a range of pulse current frequency. The optimized pulse current plating in conjunction with a leveler-free electrolyte resulted in a defect-free filling in approximate 100 nm damascenes and reduced the resistivity of Cu deposits.

Flux trapping characteristics of YBCO bulks using pulse magnetization [superconducting magnets

The authors have studied the magnetization characteristics of an array of high Tc superconductor (HTS) bulks. Experiments using pulsed field magnetization were carried out at 77 K. In the experiment, the width of the applied pulse current was varied; i.e.: (1) the wave-front length of the pulse magnetization current; and (2) the wave-tail length of the pulse magnetization current were changed independently. The authors measured the magnetization pattern of single HTS bulks and that of arrayed HTS bulks. Furthermore, several HTS bulks were arranged in array and inserted into a pulse magnetization coil wound by copper wire. The measured trapped magnetic flux distribution in this experimental setup was compared with experimental results from "field cooling". The experimental result shows that the trapped magnetic flux density is lower in the pulse magnetization than in the "field cooling". Also, the flux density pattern of pulse magnetization shows a conspicuous sag in the center of the bulk. As for the effect of the width of the applied pulse wave, the wave-front length affects strongly the trapped magnetic flux density. Meanwhile, the effect of the wave-tail length was very mild.

A Theoretical Analysis of the Effect of Inert Blocking Agent on the Galvanostatic Pulse Plating

A theoretical study on the effect of inert blocking inhibitors on the pulse electrodeposition of metal is presented. The model can be used to evaluate the influence of inhibitors with various adsorption and inclusion characteristics under the current‐pulse operating condition. It is shown in the simulation that under normal plating condition of small additive concentration, the additive surface coverage is larger in the pulse operating mode than in direct current mode. The characteristics of potential response during pulse on‐time depends on the adsorption capability of the additive and the pulse current that is applied. For a small applied pulse current, the additive‐adsorption‐induced activation overpotential may overwhelm the concentration overpotential, and a negative potential derivative with respect to time may occur during on‐time For a large applied current or with an additive of minor adsorption capability, the normal positive potential derivative with respect to time is expected during on‐time because the concentration overpotential is more influential.