Vacuum Arc Discharge Research Articles

Mechanical and tribological behavior of W/WCN bilayers grown by pulsed vacuum arc discharge

This study investigates W/WCN coatings grown by means of a repetitive pulsed vacuum arc discharge while varying the substrate temperature from room temperature (RT) to 200°C. The coatings were grown using a cathode with W (6N) and WC (6N) targets for the W and WCN layers, respectively, and an anode that contains stainless-steel 304 as a substrate. The films grown at RT and at 150°C possessed a lower percentage of carbon obtained from energy dispersive spectroscopy. This characteristic was related to the hardness, the coefficient of friction and the adherence. These films also possessed the best mechanical and tribological properties. Several wear mechanisms were identified, such as delamination and plowing out of abrasive and adhesive particles.

Structural, mechanical, electrical and wetting properties of ZrNx films deposited by Ar/N2 vacuum arc discharge: Effect of nitrogen partial pressure

Non-stiochiometric zirconium nitride (ZrNx) thin films have been deposited on silicon substrates by vacuum arc discharge of (N2+Ar) gas mixtures at different N2 partial pressure ratio. The microstructure, mechanical, electrical and wetting properties of these films are studied by means of X-ray diffraction (XRD), micro-Raman spectroscopy, Rutherford back scattering (RBS) technique, conventional micro-hardness testing, electrical resistivity, atomic force microscopy (AFM) and contact angle (CA) measurements. RBS results and analysis show that the (N/Zr) ratio in the film increases with increasing the N2 partial pressure. A ZrNx film with (Zr/N) ratio in the vicinity of stoichiometric ZrN is obtained at N2 partial pressure of 10%. XRD and Raman results indicate that all deposited films have strained cubic crystal phase of ZrN, regardless of the N2 partial pressure. On increasing the N2 partial pressure, the relative intensity of (111) orientation with respect to (200) orientation is seen to decrease. The effect of N2 partial pressure on micro-hardness and the resistivity of the deposited film is revealed and correlated to the alteration of grain size, crystallographic texture, stoichiometry and residual stress developed in the film. In particular, it is found that residual stress and nitrogen incorporation in the film play crucial role in the alteration of micro-hardness and resistivity respectively. In addition, CA and AFM results demonstrate that as N2 partial pressure increases, both the surface hydrophobicity and roughness of the deposited film increase, leading to a significant decrease in the film surface free energy (SFE).

Theory of the negative anode drop in low-pressure discharges

A kinetic model of the anode region with a negative anode potential drop is proposed, which explicitly takes into account the ratio of the directed velocity of electrons in plasma v0 to their thermal speed vT as a parameter of the electron velocity distribution function. A transcendent equation is derived for determination of the negative anode drop as a function of the ratio v0/vT. It is shown that, unlike the known Langmuir formula, the anode drop remains negative for any value of v0/vT. In the case of small values (v0/vT ≪ 1), the derived expression asymptotically reduces to the Langmuir formula. It is shown that the dependence of electron concentration on the potential differs from the Boltzmann law. The anode regions of the short high-current vacuum-arc discharge and the classical low-pressure discharge are considered as examples. For the vacuum-arc discharge, the current density distribution and the anode drop distribution over the anode surface under strong current contraction are calculated. For the low-pressure discharge, potential drops are calculated across the region of the inhomogeneous near-anode plasma and the space charge layer.

Characterization of TiAlV Films Prepared by Vacuum Arc Deposition: Effect of Substrate Temperature

Three TiAlV lms have been prepared by vacuum arc discharge technique at di erent substrate temperatures (50, 300, and 400 ◦C). The depositions were carried out from aluminum, vanadium and titanium elemental targets. The temperature e ects on the crystalline quality and texture have been investigated by means of X-ray di raction. Two phases have been identi ed and the grain size has been found to increase with temperature. The composition of the lms has been determined by proton induced X-ray emission technique. The Ti ratio was found to increase with temperature. The microhardness, measured by the Vickers indentation method was found to decrease with temperature. X-ray photoelectron spectroscopy was used to study the chemical composition of the passive layer formed on the lms by analyzing high resolution spectra of Al 2p, Ti 2p and V 2p. This layer was mainly composed of TiO2 with a small participation of other oxidation and metallic states of Ti, Al and V.

Plasmachemical synthesis of aluminum-based nitride compounds in vacuum-arc discharge plasma

A vacuum-arc plasmachemical synthesis of aluminum-based nitride compounds (AlN and Ti-Al-N) is described. The compositions and structures of the obtained coatings have been studied. It is shown that the composition and structure of a coating can be effectively controlled by varying the discharge current, ion current density distribution, and gas pressure, provided that the plasma flow is free of droplets.

Deposition and Tribological Properties of CVD Diamond/Diamond-Like Carbon Composite Films

The CVD diamond/diamond-like carbon composite film is fabricated on the WC-Co substrate by depositing a layer of Diamond-like Carbon film on the surface of conventional Micro- or Nano-crystalline diamond film. The hot filament chemical vapor deposition (HFCVD) method and vacuum arc discharge with a graphite cathode are adopted respectively to deposit the MCD/NCD and DLC films. A variety of characterization techniques, including filed emission scanning electron microscope (FE-SEM) and Raman spectroscopy are employed to investigate the surface morphology and atomic bonding state of as-deposited MCD/DLC and NCD/DLC composite film. The results show that both MCD/DLC and NCD/DLC composite films present similar surface morphology with the MCD and NCD films, except for scattering a considerable amount of small-sized diamond crystallites among the grain boundary area. The atomic-bonding state of as-deposited MCD/DLC and NCD/DLC composite films is determined by the top-layered DLC film, which is mainly consisted of amorphous carbon phase and no discernible sp3 characteristic peak can be observed from their Raman spectrum. Furthermore, the tribological properties of as-deposited MCD/DLC and NCD/DLC composite films is examined using a ball-on-plate reciprocating friction tester under both dry sliding and water-lubricating conditions, comparing with conventional DLC, MCD and NCD films. Silicon nitride balls are used as counterpart materials. For the CVD diamond/DLC composite films, the self-lubricating effect of top-layered DLC film is beneficial for suppressing the initial friction peak, as well as shortening the run-in period. The average friction coefficients of MCD/DLC and NCD/DLC composite films during stable sliding period are 0.07 and 0.10 respectively in dry sliding; while under water-lubricating condition, they further decreases to 0.03 and 0.07.

Ion-beam formation of the active surface of methanol oxidation electrocatalysts on the tantalum substrates

The active surfaces of electrocatalysts are formed by the ion-beam-assisted deposition of one of the rare-earth metals and platinum onto tantalum substrates from a neutral vapor fraction and the vacuum-arc discharge plasma of a pulsed ion source. Deposited metal ions are used as agents to aid deposition. The composition and microstructure of the formed surface layers are investigated via scanning electron microscopy, electron probe microanalysis, electron backscatter diffraction, and Rutherford backscattering spectrometry. Electrocatalytic activity in the electrochemical oxidation of methanol, which underlies the operation of low-temperature fuel cells, is investigated via cyclic voltamperometry.

Multichannel vacuum arc discharge used for Z-pinch formation

Results are presented from experimental studies of the implosion dynamics and radiative characteristics of an aluminum Z-pinch formed from a plasma shell (PS). The PS with an initial diameter of 4 cm was produced with the help of a multichannel vacuum arc discharge and formed due to the evaporation of the electrode material in ten parallel arc discharges. The PS composition depended on the electrode material in the arc discharge. The described experiments were performed with aluminum electrodes. The total arc current was 80 kA. The PS implosion was provided by an IMRI-5 high-current generator with a current amplitude of 450 kA and rise time of 500 ns. The PS implosion resulted in the formation of a 0.2-cm-diameter plasma column with an electron temperature of 700–900 eV and average ion density of (5–8) × 1017 cm−3. The maximum radiation power per unit length in aluminum K-lines reached 300 MW/cm, the duration of the radiation pulse being 20 ns.

Stability of a vacuum arc discharge on surfaces of hot-rolled steels and its frequency characteristics

The stability of a vacuum arc discharge (VAD) with allowance made for the parameters of an external circuit and a deduced equation of the heterogeneous kinetics of elementary cathode spots (ECSs) in the group cathode spot with one-dimensional configuration is analyzed. It is theoretically and experimentally shown that a VAD with a rising voltage-current characteristic (VCC) is stable independently of the parameters of the external circuit. Stability conditions for a VAD with falling VCC are found.

Source for extreme ultraviolet lithography based on plasma sustained by millimeter-wave gyrotron radiation

An extreme-ultraviolet (EUV) source based on a low-pressure discharge sustained in a magnetic trap by the high-power millimeter-wave radiation under electron-cyclotron-resonance (ECR) conditions is discussed. Multiple charged ions are efficiently generated and excited in such a discharge (tin ions injected into the trap from a vacuum-arc discharge were used) and emit line radiation in the desired wavelength range. A radiation power of 50 W into a solid angle of 4π sr in a wavelength range of 13.5 nm±1% and an efficiency of about 1% for the conversion of the microwave radiation absorbed in the plasma to the extreme ultraviolet radiation were achieved in the preliminary experiments. The article describes in detail the method of measuring EUV light emission power and background radiation. The emissivity of the plasma heated by gyrotron radiation with frequencies of 170 and 300 GHz is calculated. The proposed scheme can reduce the size of the emitting region up to ∼ 1 mm. The source can operate in both continuous and in pulsed mode.

Why Perform Code‐to‐Code Comparisons: A Vacuum Arc Discharge Simulation Case Study

AbstractNumerical modeling is increasingly becoming an indispensable tool for investigations in many fields of physics. Such modeling is especially useful in today's big science projects as a tool that can provide predictions and design parameters. The reliability of simulation results is thus essential. Code‐to‐code comparisons can help increase our confidence in simulation results, especially when other verification methods – such as comparison to theoretical models or experimental results – are limited or unavailable. In this paper, we describe a code‐to‐code comparison exercise wherein we compare one‐dimensional vacuum arc discharge simulation results from two independent particle‐in‐cell (PIC) codes. As part of our case study, we define a vacuum arc discharge test problem that can be used by other research groups for further comparison. Early disagreement between the two sets of our results motivated us to re‐examine the underlying methods in our codes. After remedying discrepancies, we observe good agreement in vacuum arc discharge time‐to‐breakdown, as well as in the time evolution of particle and current densities. This exercise demonstrates the usefulness of code‐to‐code comparisons and provides an example case study for the benefit of other research groups who may wish to carry out similar code‐to‐code comparisons (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Modification of the structure and properties of high-speed steel by combined vacuum-plasma treatment

Modification of the surface of a cutting tool from steel R6M5 by the method of vacuum-plasma treatment including ion nitriding in gas plasma and deposition of a wear-resistant (Ti, Al)N coating in the metal-gas plasma of vacuum-arc discharge is studied. Regular features of formation of nitrided layer are determined and optimization of its structure for various operating conditions of the cutting tool is performed. Modes of vacuum- arc treatment providing the lowest intensity of wear of the tool in the process of cutting are determined.

Charge separation of plasma flow in curvilinear magnetic field

The energy spectra of ions occurring in various charged states in a flow of titanium plasma in a steady-state vacuum arc discharge have been studied. It is established that, during the motion of this flow through a plasma transport system based on a curvilinear magnetic field, ions with different charges are spatially separated. As a result, at the system output, ions with greater charges are concentrated in the inner part of the plasma flow, so that the average charge of ions in this region is higher than that in the outer part of the flow.

Substrate temperature influence on W/WCNx bilayers grown by pulsed vacuum arc discharge

W/WCNx coatings were produced by using a repetitive pulsed vacuum arc discharge on stainless-steel 304 substrates, varying the substrate temperature from room temperature to 200°C. Energy dispersive spectroscopy (EDS) was used for determining W, C and N concentrations dependence on the substrate temperature. A competition between C and N can be observed. Atomic force microscopy was employed for obtaining the thickness and grain size that present similar tendencies as a function of the temperature. X-ray diffraction characterization showed phases of W and α-WCN (hexagonal). Raman spectra for all substrate temperatures were obtained, presenting two peaks corresponding to D (disorder) and G (graphite) bands in the region of 1100–1700cm−1 due to the amorphous carbon. As an important conclusion, it was stated that substrate temperature has strong influence on the structure, chemical composition and morphology of W/WCNx bilayers, caused by the competition between carbon and nitrogen.

Angular distribution of plasma in the vacuum arc ion source

This paper presents measurements of the angular distribution of the plasma components and different charge states of metal ions generated by a MEVVA-type ion source and measured by a time-of-flight mass-spectrometer. The experiments were performed for different cathode materials (Al, Cu, and Ti) and for different parameters of the vacuum arc discharge. The results are compared with prior results reported by other authors. The influence of different discharge parameters on the angular distribution in a vacuum arc source is discussed.

Development of high current Bi and Au beams for the synchrotron operation at the GSI accelerator facility

In this work, the latest results of developing high current ion beams of Au and Bi at GSI facility are described. The difficulties in the production of required charge state in vacuum arc discharge ion sources using the pure materials in the cathodes are discussed. As a possible solution, admix of a small amount of more refractory metal to the cathode material is considered. As a significant result, a dramatic improvement in the production of high charge state Bi ions using the mixed Bi-Cu cathodes (with 8%-15% of Cu admixed) compared to pure Bi cathodes is presented. The preliminary results of investigation of the material structure of Bi-Cu cathodes are discussed. As a next step, it is planned to test the composition of Au with Pd, Zr, and Fe as cathode materials.

Effect of annealing process on TiN/TiC bilayers grown by pulsed arc discharge

In this work, a study of annealing process effect on TiN/TiC bilayer is presented. The annealing temperature was varied between room temperature and 500°C. Materials were produced by the plasma-assisted pulsed vacuum arc discharge technique. In order to grow the films, a target of Ti with 99.9999% purity and stainless-steel 304 substrate were used. For the production of TiN layer, the reaction chamber was filled up with nitrogen gas until reaching 25Pa and the discharge was performed at 310V. The TiC layer was grown in a methane atmosphere at 30Pa and 270V. X-ray diffraction and X photoelectron spectroscopy were employed for studying the structure and chemical composition evolution during the annealing process. At 400°C, TiO2 phase begun to appear and it was well observed at 500°C. Crystallite size and microstrain was obtained as a function of the annealing temperature. XPS technique was employed for analyzing the bilayers before and after the annealing process. Narrow spectra of Ti2p, N1s and O1s were obtained, presenting TiO phases.

Formation of plasma technological influence of vacuum arc on the internal surfaces of metal pipes and putting of the protecting coatings

In many cases of industrial applications it is economically profitable or technically necessary to combine bulk features of one material with surface features of another one in a single material. Vacuum-arc treatment of products from inexpensive materials to form new required features of surface layers is more perspective owing to its unlimited feasibility in process efficiency. Pipes are in great demand in oil-gas industries and power engineering. But there are no effective methods for pipe inner surface treatment and pipe coating deposition, which makes it impossible to use inexpensive steel pipes under conditions of aggressive liquids, high temperature, high pressure and other parameters leading to oxidation, erosion and pipe life. Therefore, development of plasma-arc technologies of pipe inner surface treatment and pipe coating deposition is very topical and actual. A specific effect of vacuum-arc discharge on material surface is due to high concentration of energy in a chaotically rapidly moving cathode spot, short-term local heating of surface and its rapid cooling. The technological effect of cathode plasma on surface is based on cathode spot movement. The effect of a plasma flow of cathode spots formed on the outer surface of a pipe cathode and controlled by a system of vacuum-arc cathode spot fixation with magnets placed inside an electrode has been considered. A great number of studies have been devoted to explaining and investigating “anomalous” movement of the cathode spots. It has been shown that the cathode spot moves in the direction of the greatest action of discharge’s own magnetic field and outer magnetic field. The magnets initiate an arc magnetic field that confines the cathode spots and makes it possible to scan (control) them on the electrode-cathode surface and act with a plasma flow and deposit coats on inner surface of a coaxially placed pipe-product. The high efficiency of the plasma vacuum-arc method for pipe inner surface treatment and coat deposition has been found.

Hybrid Method for the Formation of Biocomposites on the Surface of Stainless Steel Implants

This study reports a hybrid method which allows the formation of biocomposites on stainless steel implants. The main idea of the method is to create multilayer coatings consisting of titanium primer layer and a microarc calcium-phosphate coating. The titanium layer is deposited from plasma of continuous vacuum-arc discharge, and calcium-phosphate coating is formed by the microarc oxidation technique. The purpose of the hybrid method is to combine the properties of good strength stainless steel with high bioactivity of calcium-phosphate coating. This paper describes the chemical composition, morphology characteristics, adhesion and the ability of the formed biocomposites to stimulate the processes of osteoinduction. It is expedient to use such biocomposites for implants which carry heavy loads and are intended for long-term use, e.g. total knee endoprosthesis.

Vacuum Arc Discharge on Integrally Cold Cathode

Initial researches of the existence of a cathode spot on the working surface were conducted in vacuum arc plasma sources of the coaxial design. The moving of the cathode spots on the limited sizes working surface does not give full picture of the development of the arc discharge. This article describes the vacuum arc plasma source of extended design generating the directed belt plasma stream and operating in pulse mode. The researches carried out give additional information about development of the cathode spots of the vacuum arc discharge. It is found that the speed of the cathode spots' motion depends on the cathode temperature.