Vacuum Arc Discharge Research Articles

Properties of super-hard carbon films deposited by pulsed arc process

The pulsed vacuum arc discharge (pulsed arc) is the most efficient PVD-technology for the deposition of super-hard carbon films on tools and machinery parts. Using the pulsed arc discharge a stable evaporation process of carbon and an efficient deposition of hydrogen-free ta-C type films is possible. In this paper, important properties of such ta-C films and their process conditions are explained. The films were characterized by hardness measurements using nanoindentation, friction and wear properties using oscillating sliding tests, and structural analysis using Raman spectroscopy.

Study on tribological behavior and cutting performance of CVD diamond and DLC films on Co-cemented tungsten carbide substrates

The tribological behaviors of diamond and diamond-like carbon (DLC) films play a major role on their machining and mechanical applications. In this study, diamond and diamond-like carbon (DLC) films are deposited on the cobalt cemented tungsten carbide (WC–Co) substrate respectively adopting the hot filament chemical vapor deposition (HFCVD) technique and the vacuum arc discharge with a graphite cathode, and their friction properties are evaluated on a reciprocating ball-on-plate tribometer with counterfaces of silicon nitride (Si 3N 4) ceramic, cemented tungsten carbide (WC) and ball-bearing steel materials, under the ambient air without lubricating condition. Moreover, to evaluate their cutting performance, comparative turning tests are conducted using the uncoated WC–Co and as-fabricated CVD diamond and DLC coated inserts, with glass fiber reinforced plastics (GFRP) composite materials as the workpiece. The as-deposited HFCVD diamond and DLC films are characterized with energy-dispersive X-ray spectroscopy (EDX), scanning electron microscope (SEM), X-ray diffraction spectroscopy (XRD), Raman spectroscopy and 3D surface topography based on white-light interferometry. Furthermore, Rocwell C indentation tests are conducted to evaluate the adhesion of HFCVD diamond and DLC films grown onto WC–Co substrates. SEM and 3D surface topography based on white-light interferometry are also used to investigate the worn region on the surfaces of diamond and DLC films. The friction tests suggest that the obtained friction coefficient curves that of various contacts exhibit similar evolution tendency. For a given counterface, DLC films present lower stable friction coefficients than HFCVD diamond films under the same sliding conditions. The cutting tests results indicate that flank wear of the HFCVD diamond coated insert is lower than that of DLC coated insert before diamond films peeling off.

On the influence of a TiN interlayer on DLC coatings produced by pulsed vacuum arc discharge: Compositional and morphological study

The influence of a TiN interlayer on DLC coatings grown on silicon (1 0 0), 316 stainless steel and KCl by using the PAPVD pulsed arc discharge technique is presented in this paper. The structure of the coatings was determined by means of FTIR through observation of the absorption band modes of CH 2 between 3100 and 2800 cm −1 and representation of the sp 3 and sp 2 carbon bonds, respectively. The sp 3/sp 2 bonds ratio was calculated by using the base line method and producing a value greater than 1 which was a good prediction of high hardness. XPS analysis of the films was made; the wide spectrum showed the elemental composition of the films (Ti, N, C). A narrow spectrum of C1s at binding energy of 284.48 eV was obtained, and its deconvolution showed peaks of sp 3, sp 2 and Ti–C. Ti–C bonds were formed due to diffusion of carbon atoms into a TiN matrix. The concentration for the XPS spectra was calculated by using the area under the curve of sp 3 and sp 2 peaks. The morphology of the bilayer, including roughness, grain size and thickness was studied through SPM techniques.

The Effect of Boundary Conditions on the Distribution of Physical Parameters in a High-Current Vacuum Arc Discharge

Through the use of a 2-D model of a high-current vacuum arc discharge (VAD) in an axial magnetic field, the distribution of high-current VAD parameters in a plasma area was calculated for different boundary conditions on the cathode plasma boundary, the anode, and the side boundary of plasma. Calculations were made for different current and external magnetic field values. The cathode boundary of plasma was assumed as either equipotential or having specified current density distribution. The side boundary of plasma coincided with either the external ion trajectory or the boundary of the calculated area. In the case with a specified current density, potential distribution on the cathode plasma boundary was calculated. There is a significant difference in the distribution of high-current VAD parameters when calculations are made with the use of models having different boundary conditions. A possibility of different-boundary-condition application for the adequate description of a high-current VAD is discussed. A simple mathematical model has been used for a vivid interpretation of the obtained results.

Experimental Study of Dynamics of Plasma Expansion in a Vacuum-Arc Discharge and Anode Temperature Calculations

The given work was aimed to experimental studies of a plasma channel expansion in a vacuum-arc discharge between the CuCr50 electrodes; with the anode temperature calculated in this stage. Time dependences of an arc channel diameter have been obtained using a high-speed multiframing image analog camera. In addition, plasma expansion velocities V have been determined for different discharge electric currents. It has been demonstrated that V under the experiment conditions does not depend on the current value, nor it does on the presence or absence of the external axial magnetic field. The experiments show that when the electrodes differ in size, the arc discharge initiated in the center of the cathode expands with time until it reaches the size of a smaller electrode while keeping a cylindrical form. The obtained data on V were used for calculation of the anode temperature. Variations of the power supply and of the heating zone sizes with time as well as evaporation loss have been taken into account in the adopted model. It was shown that in the high-speed expansion mode, an anode spot appeared by insignificant heating of the anode. In the low-speed expansion mode, high heating of the anode is possible, with anode intense evaporation taking place. The anode temperature in stage of discharge gap fill by plasma during electric current commutation has been calculated.

High-Current Pulsed Vacuum-Arc Evaporator for Surface-Alloying Technologies

Plasma sources based on vacuum-arc discharge have a big disadvantage due to the high fraction of droplets in plasma flow produced during the operation of cathode spots. To avoid droplets, various kinds of curved magnetic filters are used. We have suggested one more approach to reduce the droplet content in an arc-discharge plasma basing on the intense evaporation of droplets caused by the ignition of ldquodroplet spotsrdquo in a discharge cell. A Penning-type arc discharge provides favorable conditions for the ignition and operation of droplet spots. In such a cell, a uniform plasma column is formed, whose temperature and density are much higher than those of a usual vacuum arc at the same discharge current. A further increase in energy density in the plasma of a reflective-discharge cell could be achieved by means of both the increase in discharge current and B-field optimization. This paper presents the results of the development and characterization of the pulsed plasma-source model combining a well-known high-current vacuum-arc evaporator with a Penning discharge cell. It has been recognized that the ion-current amplitude at the source output is as high as 800 A, plasma density is as high as 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">14</sup> cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> , and electron temperature range is 6-8 eV. Those conditions lead to an intensive evaporation of droplets on the fly. The copper film-deposition rate was measured to be at 1.5 nm/pulse, which corresponds to an instantaneous deposition rate of 2000 nm/s. The first results of the use of the evaporator for surface alloying are also presented.

ZnO thin films growth by pulsed vacuum arc discharge

A study of structural and morphologic features of ZnO coatings grown by pulsed vacuum arc discharge is presented in this work. The characteristics of the plasma generated during the production process are determined by using the Optical Emission Spectroscopy technique. The system employed for growing the films consists of a vacuum chamber with two opposite electrodes (the cathode is the target of zinc and the anode is the substrate of glass). The gas used for filling the reactor was high purity oxygen. The discharge was generated at a pressure of 200 Pa and a voltage of 200 V. Coatings were characterized by using X-ray diffraction and scanning probe microscopy (SPM) techniques. XRD patterns showed a hexagonal crystalline structure with peaks produced by planes (002) and (103). The roughness observed was of 98.6 nm. No great quantity of nanodroppers was observed on the coatings surface. Plasma spectroscopic studies revealed many lines belonging to different species like Zn (328.2, 330.3, 334.5 nm), Zn + (491.3 and 492.5 nm), O (372 nm) and O + (336.1, 337.25 and 518 nm) and weak bands of ZnO (526.47, 531.2, 536.94 nm). The presence of ZnO is an important finding because, for coatings produced by arc techniques, authors have reported ZnO as being exclusively produced on the substrate surface and not generated into the plasma. The electron temperature ( T e ) and density ( n e ) were determined by means of spectroscopic methods such as the relation between lines of the same ionization state for T e and the calculation of Stark Broadening for n e .

Minimum voltage principle in the theory of a high-current vacuum-arc discharge

The effect of an inhomogeneous magnetic field with axial and radial components on the structure of a high-current vacuum-arc discharge (VAD) has been theoretically studied. The characteristic features of current passage in a short VAD are considered using analytical expressions for the slope of the total current lines (TCLs) relative to the discharge axis, the axial components of the electric and magnetic fields, and the effective conductivity of discharge plasma. A two-dimensional mathematical model has been used to calculate the TCL shapes and the discharge voltage for various dimensions of the region of cathode spots. Calculations showed that the voltage drop on the discharge gap as a function of the arc discharge radius on the cathode has a minimum. The shape of TCLs and the arc radius on the cathode at this minimum agree with the available experimental data.

Properties of ta‐C Films for Tools and Machinery Parts

AbstractThe pulsed vacuum arc discharge is an effective technology for the deposition of ta‐C coatings on tools and machinery parts. The properties of these carbon coatings differ substantially from conventional hard nitride films particularly with regard to hardness and wear‐resistance. The paper shows analytical results of ta‐C films in comparison to such hard coatings. Thereby different methods are applied for determination of adhesion, friction, wear‐resistance, and indentation hardness. A simple correlation was found between indentation hardness and wear‐resistance over a wide range of hard materials. Furthermore, all investigated films have a strong adhesion on steel in conventional Rockwell tests. But in scratch tests with increasing normal forces brittle ta‐C films delaminate at lower forces from the surface compared to nitride coatings.

Gas Phase Modification of Superhard Carbon Coatings Deposited by Pulsed DC‐Arc‐Process

AbstractThe pulsed vacuum arc discharge (pulsed arc) is the most efficient PVD technology for deposition of hard amorphous carbon coatings on tools and machinery parts. Due to the pulsed arc discharge a stable evaporation process and the efficient deposition of hydrogen‐free a‐C type coatings is possible. This paper shows that the pulsed arc enables the deposition of ta‐C and modified a‐C coatings with interesting coating properties in a wide pressure range of argon, acetylene and ammonia gas atmosphere. Coatings with different gas flow rates of these gases were deposited on steel substrates. The coating properties were characterized by using different analytical methods for determination of structure, hardness, friction and wear behaviour. The changes of film properties in dependence of the kind and the rate of gas flow are compared and discussed.

An experimental study of the dynamics of formation of plasma in a vacuum-arc discharge

An experimental study is made of the dynamics of formation of plasma in a vacuum-arc discharge (VAD) at different currents and different transverse dimensions of CuCr50 electrodes. High-speed multipleframe photography is used to obtain the time dependence of the current channel diameter and determine the rate of plasma expansion. It is demonstrated that the rate of expansion under the experimental conditions is independent of the discharge current, as well as of the presence or absence of external axial magnetic field. Two modes are identified, which differ from one another by the rate of expansion. Experiments are performed with anodes and cathodes of different diameters in the range of currents from 2 to 15 kA. It is demonstrated that, with electrodes of different sizes, a discharge initiated at the cathode center expands with time to the size of the smaller electrode while retaining the cylindrical shape. The anode temperature is calculated for two modes in view of the variation of the source power and of the transverse dimension of the zone of heating. It is demonstrated that the anode spot in the mode of rapid expansion is formed under insignificant heating of the anode. In the case of slow expansion, a strong heating of the anode is possible, under which its intense evaporation occurs. The anode temperature is calculated in view of the evaporation losses for modes with different numbers of jumpers arising as a result of the breaking of vacuum switch contacts.

Defect reduction of multi-walled carbon nanotubes by rapid vacuum arc annealing

A rapid thermal annealing process using a DC vacuum arc discharge system was shown to reduce defects in carbon nanotubes (CNTs). Multi-walled CNTs (MWCNTs) exhibit high-density structural imperfections when deposited via chemical vapour deposition at relatively low temperatures (∼650°C). These defects can be thermally annealed to reconstruct the graphitic structure. A vacuum arc discharge system was used to anneal the MWCNTs through several cycles at high temperatures (∼1800°C) followed by rapid cooling. The annealed MWCNTs were characterised by Raman spectroscopy and transmission electron microscopy. Rapid heating rearranged the imperfect graphitic structure and removed the weakly bonded defects. After eliminating a defect segment, the graphene shell was reconstructed during the cooling process to produce multi-shell perfection. This method effectively reduced MWCNT defects.

Characterization of arcs in ICRF transmission lines

Too high voltages can cause arcs to develop within coaxial transmission lines of ICRF antennas. To avoid damage, arcing must be detected and the RF power switched off. To ensure a high level of safety, the specifications of the detectors have to be based on a fine characterization of arcs. A test bench comprising a coaxial resonator and a fast acquisition system makes it possible to analyze the effects of breakdowns on power, voltage, pressure and DC current in the electrodes. For different types of breakdowns (multipactor, vacuum arc and gas discharge) and different configurations (presence or not of magnetic field, level of injected power), we investigate the processes involved in the specific development of an arc inside a RF coaxial line. The resulting classification of phenomena and the impact on the operational system requirements are discussed.

Modification of a metallic surface in a vacuum arc discharge plasma using thermally stimulated ion diffusion

A new process for modifying a metallic surface in a vacuum arc discharge plasma using thermally stimulated ion diffusion is considered. The effect of the bias voltage (negative substrate potential) on the processes that occur on the surface of a treated part is studied when the substrate material interacts with an accelerated metallic-ion flow. The phase and elemental compositions of the modified layer are studied for substrates made of nickel-based superalloys, austenitic and martensitic steels, and titanium-based alloys. The heat resistance, the salt corrosion resistance, and the corrosion cracking resistance of steels and titanium-based alloys are investigated after their modification in vacuum arc plasmas of pure metals (Ti, Zr, Al, Cr, Y) and related alloys. The surface modification caused by the thermally stimulated ion saturation of the surfaces of parts made from structural materials is shown to change the structural-phase states of their surfaces and, correspondingly, the properties of these materials in relation to the state of the surface.

A Theoretical Analysis of Vacuum Arc Thruster and Vacuum Arc Ion Thruster Performance

Thrusters that exploit vacuum arc discharges to produce high-velocity plasma jets directly or as sources of plasma that is subsequently accelerated electrostatically have been proposed or are currently under development. Vacuum arc discharges exhibit certain regularities in their behavior that allow the performance of these thrusters to be described by simple semiempirical models. Empirical data on the current density distribution, charge state and velocity of ions created in vacuum arc discharges, and the total cathode mass loss rate are used to develop expressions for the expected thrust and specific impulse as a function of thruster geometry. Thruster electrical efficiency and thrust-to-power ratio are calculated based on measurements of the burning voltage for given thruster operating parameters. Estimates of achievable thruster performance for a wide range of cathode materials are presented. This analysis suggests that thrusters using vacuum arc sources can be operated efficiently with a range of propellant options that gives great flexibility in specific impulse. In addition, the efficiency of plasma production in these devices appears to be largely independent of scale because the metal vapor is ionized within tens of micrometers of the cathode electron emission sites, so this approach is well suited for micropropulsion.

Charging of Macroparticles in a Pulsed Vacuum Arc Discharge

A pulsed vacuum arc discharge emits a plasma as well as macroparticles (MPs) in the form of micrometer-sized molten droplets of cathode material. Due to their direction of flight and submicrometer to 100-mum diameter, these MPs often pose a contamination threat for both spacecraft-based thrusters and thin-film deposition systems. The velocity, mass, and charge of copper MPs emitted by a 100-A arc was experimentally measured and compared to a model based on thermionic electron emission. The MP velocity was determined by using a time-of-flight velocity filter. The charge was calculated by measuring particle deflection in a transverse electric field. The model predicts, and the experimental results verify, that the charge on the MPs becomes positive once the plasma is extinguished, and the MP travels in a vacuum, as would occur in a pulsed vacuum arc, versus a dc arc. Experimental results show a roughly quadratic dependence of particle charge on the particle diameter (q ~ D2), with a 1-mum particle having a positive charge of ~1000 electronic charges (1.6 times 10-16 C), and a 5-mum particle having a charge of ~25 000 electronic charges. The model is particle temperature dependent, and gives q ~ D2 at 1750 K and q ~ D1.7 at 2200 K. Arguments are also made for limitations on particle temperature due to radiative and evaporative cooling.

Plasmachemical synthesis of carbide compounds in metal-containing plasma jet from vacuum arc discharge

Features of the synthesis of metal carbides in metal-containing plasma jet from vacuum arc discharge have been studied. Factors determining the quality of coatings obtained using this plasmachemical method are revealed.

Extreme-ultraviolet source based on the electron-cyclotron-resonance discharge

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. Multiply 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 in a wavelength range of 13.5 nm ± 1% and an efficiency of about 1% for the conversion of the micro-wave radiation absorbed in the plasma to the extreme ultraviolet radiation were achieved in the preliminary experiments.

Influence of Highly Energetic Electrons on Probe Measurements in A Hot Cathode Arc Discharge Plasma

AbstractInfluences of highly energetic electrons on probe measurements has been investigated in a vacuum arc discharge plasma. Double and triple probe measurements clearly show these probe method is very sensitive for the small amount of hot electron component. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A novel process for plasma immersion ion implantation and deposition with ions from vaporization of solid targets

AbstractA novel source for plasma immersion ion implantation and deposition (PIII&amp;D) was developed in order to perform surface treatment of materials with ions from vaporization of solid targets. Usually this is obtained by means of beamline ion implanters, in which three dimensional implantation requires target manipulation, or by vacuum arc discharges, in which the presence of macroparticles is the main problem to be overcame. Samples of silicon wafers immersed in a lithium plasma produced by this source were submitted to low negative high frequency pulses (3‐4 kV/6 μs/3 kHz), causing lithium implantation and deposition. A very high strain and photoluminescence measured by high resolution X‐ray diffraction and Raman spectroscopy, respectively, were observed in the analyzed layers of the samples that were immersed in this plasma. XPS measurements revealed thick Li deposition for samples treated under conditions of high lithium vaporization rate. This novel process was effective for Li implantation/deposition and shows potential for PIII or PIII&amp;D of many different elements from solid targets as Ca, K, Mg and Al. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)