DC Vacuum Arc Research Articles

Stable DC vacuum arc plasma generation from a 100 mm TiB2 cathode

Titanium diboride exhibits outstanding properties for hard and wear resistant coatings. However, efficient physical vapor deposition (PVD) processing through DC vacuum arc, with a deposition rate unreachable for any other PVD technique, is comparatively unexplored for TiB2 thin films due to challenges associated with the film synthesis process. In this work, we used an industrial scale arc plasma source having a plane cathode of 100 mm in diameter and a permanent magnet on its back side. We present analysis of the cathode surface, plasma generation/composition, as well as analysis of collected macroparticles. The cathode weight loss and the amount of generated macroparticles were measured as a function of process parameters (arc current and pressure, in both Ar and N2 gas). Plasma analysis shows average ion energies around 120 and 25 eV for Ti and B, respectively, and plasma ion composition of approximately 50 % Ti and 50 % B. The cathode weight loss was around 0.3–0.5 g/min, of which at least 25 % is estimated to be macroparticles. Notably, the intensity of the macroparticle generation was reduced with an increase in N2 pressure. Altogether, the results show a stable and reproducible plasma generation process and a high potential for the use of the cathodic arc as an efficient and useful method for deposition of metal borides.

Determination of the critical contact separation length for DC interruption in a vacuum subject to an external transverse magnetic field

The objective of this work is to experimentally determine the critical contact separation length Lcritical for DC interruption in vacuum under an external transverse magnetic field (TMF), according the interruption behaviors and vacuum arc characteristics. L is defined as the separation length at the instant of TMF application. Lcritical is the critical and the minimal necessary separation length of the contacts for a successful DC interruption in vacuum. A pair of Helmholtz coils was used to generate the external TMF. A high-speed camera was used to record the vacuum arc appearance. The experimental results quantitatively determine Lcritical for DC vacuum interruption under a certain DC and the external TMF. When the DC ranged from 100 to 500 A under an external TMF of 30 mT, Lcritical ranged from 2.1 to 3.7 mm and did not show linear variation. Second, the extinguishing time of DC vacuum interruption te at various currents significantly increased in a similar pattern under decreasing L in the range of 0.3–1.6 ms. The decrease in L mainly increased the duration of the stable stage and had little apparent influence on the duration of the unstable stage of the DC vacuum arc. Third, the physical mechanism determining Lcritical in DC vacuum interruption under a TMF could be explained from two aspects: the expansion of the vacuum arc column and the diffusion of the metal plasma. In successful DC vacuum interruption, Lcritical should be large enough for the formation and expansion of the “C”-shaped arc column, and enough space should be available for the diffusion of the metal plasma.

A comparison of plasma generation, plasma transport, and film formation for a DC vacuum arc source with Ti–X compound cathodes (X = W, C, Al, and Si)

This investigation reports the influence of Ti–C and Ti–W cathode composition on an industrial-scale dc vacuum arc plasma source. Further, we analyze the influence of plasma generation and plasma properties on the resulting cathode surface after the operation and on basic film properties. The results are compared with previous work focused on Ti–Al and Ti–Si compound cathodes. For all Ti–X compound cathodes (X = W, C, Al, and Si), a direct correlation between plasma ion energy/charge and the cohesive energy of the cathode was demonstrated, with a small number of exceptions to a limited set of specific cathode compositions. Hence, the “velocity rule” and effects from different electron temperatures were suggested to be important for gaining a more detailed understanding of plasma properties. A discrepancy was found between the cathode and plasma ion composition, though the difference was reduced in a corresponding comparison between the cathode and the deposited film composition. A significant contribution of a flux of neutrals and/or macroparticles to the final film composition was, therefore, suggested. The effect of the melting point of the cathode phase composition on the intensity of macroparticle generation and the smoothness of the cathode surface operation was also investigated. The presented results contribute to the fundamental understanding of vacuum arc plasma generation and transport and are of importance for further development and applicability of Ti-based coatings from arc deposition.

DC vacuum arc deposition system with an anode generating magnetic field for preparation of TiN films

In this study, a coiled anode that generates a magnetic field using a DC arc was designed and employed in a cathodic vacuum-arc deposition system. Its performance was evaluated by the formation of TiN films with and without a magnetic field. When the magnetic field was applied by the coiled anode, the deposition rate was approximately 1.5 times faster than that without the magnetic field. In addition, a reduction in the number of droplets with films of the same thickness was expected. Furthermore, the hardness of the film was improved by approximately 10% with the magnetic field of the coiled anode, resulting in a very hard film of 43.7 GPa. These results suggest that the coiled anode is effective in reducing the number of droplets and is promising for the formation of super-hard films, which are preferred for cutting tools.

DC vacuum arc deposition with open winding-path anode assembled with C-ring plates

Vacuum arc deposition (VAD), which utilizes the vapored high energy metal ions from an electrode, is widely used in industry. Though VAD has many advantages, the reduction of droplets on deposited films is an essential issue to solve for its industrial application. In this study, we have developed a new type of filtered arc deposition (FAD) utilizing a winding coil with copper C-ring-shaped plates in a vacuum chamber. TiN films were deposited on substrates with a normal linear FAD and the new FAD. TiN films were analyzed, and it was found that the number of droplets was significantly reduced with the new FAD.

Development of a Graphite Coating and Its Transfer from Batch to Coil Process for Application in PEMFC for Hydrogen-Powered Vehicles

In the present paper, coating systems consisting of a metallic corrosion barrier and a conductive graphitic carbon layer were deposited by a DC vacuum arc process. The coatings were developed in a batch process for application in the polymer electrolyte membrane fuel cell (PEMFC), and transferred to a continuous coil process to facilitate industrial mass production. The coating samples in the coil process had to achieve comparable results to the samples produced in the batch process, to meet the requirements of the environment prevailing in the fuel cell.The transfer to roll-to-roll processes is a crucial factor for commercial upscaling of PEMFC production. The experimental results showed that the electrical conductivity and corrosion resistance of the samples in the coil process were significantly improved compared to the uncoated base material and showed comparable performance to batch coated samples. X-ray photoelectron spectroscopy (XPS) was performed to determine the depth profile and the surface composition. Additional measurements were recorded for the contact resistances using the four-wire sensing method as well as corrosion resistance using potentiodynamic methods.

Vacuum Arc Evolution Characteristics in Low-Voltage DC Current Interruption Under Composite Transverse Magnetic Fields

Based on our novel dc vacuum interruption technology under composite transverse magnetic fields (TMFs), the arc voltage of dc vacuum arc can be effectively improved to interrupt the dc current. The objective of this work is to experimentally investigate the vacuum arc characteristics and their evolution in dc current interruption under composite TMFs. The composite TMFs were generated by both multipole permanent magnets and cup-type TMF contacts. The vacuum arc photos were recorded by a high-speed camera. The experimental results indicate that under these composite TMFs, the dc current could be successfully interrupted, which was closely related to the dc vacuum arc characteristics and their evolution. The experimental dc current and voltage were less than 500 A and 500 V. First, the evolution of the dc vacuum arc could be divided into Stable and Unstable stages, according to the characteristics of the arc voltage waveform. In the Stable stage, the dc vacuum arc might be stagnated, constricted, and rotated with a stable arc voltage of 20 V. In the Unstable stage, the dc vacuum arc was transferred to the outer periphery of the contact in the form of a ``C''-shape, and the arc voltage significantly increased higher than the supply dc voltage. Second, there was an Extinction Area in the middle of Area 4 under the composite TMFs, which made the dc vacuum arc always extinguish at this position. Third, repeated fluctuations of the arc voltage are caused by the formation and extinction of the ``C''-shaped arc. Finally, when the distance between the igniting area and Extinction Area increased, the duration of the Stable stage increased, while the duration of the Unstable stage decreased.

Features of the Formation of Ultralow Energy High-Intensity Metal and Gaseous Ion Beams

This article studies the features and patterns of the formation of high-intensity beams of metal and gaseous ions of low and ultralow energy from dc vacuum arc and gas-discharge plasma. It presents the results of repetitively pulsed plasma immersion extraction of aluminum, titanium, and nitrogen ions from the plasma followed by the formation and transport of ion beam under conditions of its ballistic focusing. This article presents the experimental data on the influence of the grid focusing electrode cell sizes of 150 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$500~\mu \text{m}$ </tex-math></inline-formula> , the bias potential amplitude from 0.1 to 2 kV, the conditions for neutralizing the space charge of the beam during preliminary plasma injection into drift space and when using an additional thermoelectron source on the transport and focusing of ion beams. Here, it discusses the effect of the characteristic dimensions of the fine-structured grid and plasma parameters at ultralow bias potential amplitudes and the presence of significant initial energy in ions on the ion beam focusing. It was found that at bias potential amplitudes of 0.6 kV, it is possible to form repetitively pulsed ion beams with high current density reaching 170 mA/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . The obtaining of such beams opens up the possibility of implementing the method of high-intensity ion implantation under conditions of multiple decreases in the irradiated surface sputtering.

Transient modelling and simulation of the forced arc extinguish period of the circuit breakers

Plasma transport during continuous extinction processes from high-current arcs to fully extinction is an important issue in the study of vacuum arcs. In this research a 3D hybrid plasma model has been developed to study the extinguish period of the DC vacuum arc. The model treats the electrons as a massless fluid and ions as macro particles. The ion-neutral collision processes including both charge exchange collisions and momentum exchange collisions are considered with Monte-Carlo method. By this approach, the vacuum arc model consists of plasma jets ejected from multiple cathode spots is established and the behaviours of ions under the collisions with neutral atoms are simulated. It is shown that a large number of low-speed ions are generated in the interelectrode region due to the chare exchange collisions between ions and neutrals. And as the arc current drops to zero, the proportion of low-speed ions to the total ions at each moment becomes higher and higher.

Enhanced discharge and surface properties of TiSiCN coatings deposited by pulse-enhanced vacuum arc evaporation

Pulse-enhanced vacuum arc evaporation (PEVAE), an advanced version of conventional DC vacuum arc evaporation, generates a high flux of electrons to ionize more gaseous and metallic atoms in the deposition system to facilitate coating deposition. Compared to the conventional DC mode, the highly ionized plasma improves the structure and properties of the coatings deposited by the PEVAE mode. To obtain a better understanding and evaluate the advantages and limitations of this technique, we conduct a comparative study on TiSiCN coatings deposited by the traditional DC mode and PEVAE mode for different target-to-substrate distances (Dt-s) in the reactive environment of HMDSN. The substrate current is determined by an oscilloscope and optical emission is monitored by a miniature fiber-optics spectrometer. The microstructure and properties of the coatings are characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, indentation test, nanoindentation, electrochemical measurement, and ball-on-disk wear test. The results demonstrate that the average substrate current increases by 53.8% as Dt-s increases from 200 mm to 300 mm. The pulsed current discharge in the HMDSN atmosphere increases the deposition rates by up to 36.4% and Ebi increases by 29% reflecting a denser microstructure. The PEVAE mode improves the microstructure of the TiSiCN coatings as well as resistance to corrosion and wear. Furthermore, it has good processing adaptability for different target-to-substrate distances.

Vacuum arc transient behaviors and voltage characteristics in low-current DC interruption under rotating TMF

The objective of this work is to determine the relationship between the vacuum arc transient behaviors and voltage characteristics in low-current DC interruption under a rotating transverse magnetic field (TMF). An external rotating TMF was generated by two pairs of Helmholtz coils, set at right angles. The phase angle of alternating currents in the two Helmholtz coils was shifted by 90°. The rotating frequency was 230 Hz, with a peak flux density of 32 mT. The contact material was CuCr25 (25% Cr), with a diameter of 18 mm. The DC vacuum arc appearance was recorded by using a high-speed CCD video camera. The experimental results indicate that the voltage characteristics were closely related to the DC vacuum arc transient behaviors. In low-current DC interruption under a rotating TMF, vacuum arcs experienced two main stages of evolution, a constriction and motion stage and an unstable stage. The increase in the arc voltage, caused by the unstable state of the cathode spot group located at the edge of the contacts and the stretched state of the DC vacuum arc column, was the key for DC vacuum successful interruption under the rotating TMF. Moreover, the interruption characteristics of the DC vacuum arc were quite sensitive to the contact separation length and the rotating TMF flux density. The duration of the total interruption process decreased with the increase in the rotating TMF flux density, which mainly affected the duration of the constriction and motion stage in the DC vacuum interruption.

Effects of Homopolar Magnetic Fields on Low-Current DC Vacuum Arcs

This article deals with the effects of homopolar magnetic fields on the lifetime of low-current dc vacuum arcs. A homopolar magnetic field is a distribution with the axially symmetric radially oriented field in the contact gap. It is produced when two dipole magnets are kept with the same poles facing each other. Switching experiments are conducted using an off-the-shelf ac vacuum contactor, and the ring magnets are used to set up a homopolar magnetic field in the contact gap. The arcing times are measured for currents varying from 1 to 30 A with voltages up to 100 V and magnetic surface strengths from 0.34 to 0.43 T. The tests are performed with the fixed contact of the vacuum contactor connected to positive as well as negative polarity. It is observed that the arcing time values are lesser in the presence of magnetic field with the fixed contact at the negative polarity due to asymmetry in the placement of the ring magnets. Finite element method (FEM) simulations are performed to examine the magnetic field distribution in the contact gap. The ratio of radial-to-axial magnetic field components in the contact gap decreases with increasing strength of magnets in the present experimental arrangement. It correlates well with the observed arcing time trends against the variation in the strength of magnets and the polarity of the fixed contact. The present article shows the potential of homopolar magnetic field in the development of dc vacuum contactors and interrupters without the need to create an artificial current zero using forced commutation.

Effect of Mo-Cu cathode composition on process stability, macroparticle formation, plasma generation, and thin-film deposition in DC arc synthesis

In this work, we present the correlation between cathode composition and features of the arcing process for Mo1 − xCux [x = 0.0, 0.07 (0.05), 0.14 (0.10), 0.21 (0.15), 0.40 (0.3), 0.73 (0.63), 0.97 (0.95), and 1.00, atomic fraction (weight fraction)] cathodes used in a DC vacuum-arc deposition system. It is found that the stability of the arcing process crucially depends on the cathode composition. The most stable arc spot and the lowest cathode potential (∼19 V) are detected for the Mo0.27Cu0.73 cathode, while the Mo0.93Cu0.07 cathode shows the most unstable arcing process with the highest cathode potential (∼28 V). The properties of the generated plasma are also strongly dependent on the relative ratio of the cathode elements. The metal ions from the Mo and Cu cathodes have peak kinetic energies around 136 and 62 eV, respectively, while for a Mo0.79Cu0.21 cathode, the corresponding energies are only 45 and 28 eV. The average charge states decreased from 2.1 to 1.6 for Mo ions and from 2 to 1.2 for Cu ions. The intensity of macroparticle generation and the size of the droplets correlate with the relative fraction of Cu. However, it is shown that, typically for the cathodes with a low amount of Cu, an increased abundance of visually observed macroparticles leads to droplet-free films. The film thicknesses and their compositions also demonstrate dependencies on the elemental composition of the cathode. These results are discussed in the light of no solubility between Mo and Cu and the high temperature of the cathode surface during the arcing process.

Ultra high fluence implantation of aluminum ions into CP–Ti

This study describes the possibility of ultra-high fluence low ion energy aluminum implantation for surface modification of titanium. The DC vacuum arc source was used to produce dense metal plasma. Plasma immersion aluminum ions extraction and their ballistic focusing in equipotential space of negatively biased hemispherical electrode were used to obtain high-intensity aluminum ion beam with the maximum amplitude of 0.6 A at the ion current density up to 200 mA/cm2. The original filtration system was used to prevent the deposition of vacuum arc aluminum macroparticles onto the irradiated area of titanium sample. Aluminum low energy ions (mean ion energy 2.6 keV) were implanted into titanium with the fluences reaching 1021 ion/cm2. The effect of substrate temperature, ion current density on the phase composition, microstructure and elemental distribution was studied by X-ray diffraction, scanning electron microscopy, glow-discharge optical emission spectroscopy and transmission electron microscopy. The results show the appearance of Ti3Al intermetallic phase after Al implantation. The depth of aluminum penetration into titanium increases with the substrate temperature and multiply exceeds the projected ranges of ions of given energies and reaches several dozens of μm.

Investigations on the safe stroke of mechanical HVDC vacuum circuit breaker

Here, a DC vacuum arc interruption test based on the hybrid high-speed actuator and the method of commutation is carried out in the synthetic loop system. The safe stroke is one of the basic breaking parameters. The minimum safe stroke directly determines the commutation time and breaking property of the mechanical DC vacuum circuit breaker. The main circuit breaker is a high-speed vacuum switch driven by electromagnetic repulsion actuator. In order to simplify its control system, the commutation switch also adopts high-speed vacuum switch. The main current source for verification test of this DC breaker system is provided by a LC oscillator circuit with lower frequency. Simulations with some experiments were completed on breaking process of this system by PSCAD. The breaking current is 4 kA by the DC breaker system proposed here, the opening speed is about 2.417 m/s in this experimental system; From the results, the simulation and experimental waveforms are compared and analysed, and some effects on safe stroke of the DC vacuum circuit breaker is studied. The shortest arcing time is about 0.89 ms and the minimum safe stroke is about 2.15 mm under the lower voltages.

Process development for stabilization of vacuum arc plasma generation from a TiB2 cathode

Herein, we present stable and reproducible arc plasma generation from a TiB2 cathode. The process development contains three complimentary features: Use of a Mo cylinder around the TiB2 cathode improves arc ignition and stabilizes the process by keeping the arc spot at the cathode surface. The evolution of the cathode surface during erosion and the process stability is further improved by addition of 1wt% carbon in the cathode, with no resulting change in plasma characteristics (ion energy, ion charge states, macroparticles). Finally, an increased plasma density through use of a separate anode provides the last key point, which together with the other two contributes to highly controlled plasma generation from TiB2 using DC vacuum arc, and complete utilization of the cathode material. The combined results provide a novel and efficient route for synthesis of metal borides.

High intensity, macroparticle-free, aluminum ion beam formation

We describe a vacuum arc based system for the generation of repetitively pulsed metal ion beams with very high current density, and the results of experimental investigations of the performance of this new system, as well as the results of numerical simulations. Our approach uses a DC vacuum arc as a metal plasma source, and the beam-forming technique is a hybrid method using features of conventional gridded ion extraction together with some plasma immersion attributes. A hemispherical grid is located some distance from the plasma source so as to intercept part of the metal plasma flow and repetitively pulse-biased to the requisite ion beam energy. Ions are accelerated in the high voltage sheath that forms in front of the biased grid and focused into a converging beam that can be of a very high current density. Space charge neutralization is provided by cold plasma that streams through the grid during the bias-off part of the cycle. At the same time, macroparticles in the vacuum arc plasma are blocked from viewing the target by a metal disk positioned centrally on the hemispherical grid. In the work outlined here, we formed 5 keV aluminum ion beams with a current density up to 470 mA/cm2 at a negative bias amplitude of 3 kV and a pulse repetition rate of 105 pulse per second. The experiments and numerical simulations demonstrate the formation of high-intensity macroparticle-free aluminum ion beams for material surface modification and other possible applications.

Low energy, high intensity metal ion implantation method for deep dopant containing layer formation

This study describes the first results of high intensity macroparticle-free aluminum ion beam formation and its application to low ion energy implantation. A DC vacuum arc was used to produce aluminum plasma flow. A repetitively pulsed macroparticle-free high intensity aluminum ion beam was formed using a plasma immersion ion extraction combined with ion beam focusing. A very high current ion beam with the current up to 0.475 A at bias pulse duration of 4 μs and the pulse repetition rate of 105 pulses per second was obtained. Nickel substrates were irradiated by aluminum ions with very high current densities up to 100 mA/cm2 and accelerating voltages up to 2.1 kV. The maximum fluence of implantation reached 1.2 × 1021 ion/сm2. The results of the element composition of the modified layer were also investigated.

Joint influence of steered vacuum arc and negative repetitively pulsed bias on titanium macroparticles suppression

This paper presents the results of an experimental study of titanium macroparticle accumulation on a negatively biased substrate immersed in DC vacuum arc plasma generated by an evaporator with an axial magnetic field and a steered arc evaporator. Using a steered arc with a tangential magnetic field strength of 200 Gs reduced the generation of macroparticles 5-fold compared to a plasma source with an axial magnetic field. The application of repetitively pulsed negative bias significantly decreased macroparticle assembly on the substrate surface for both evaporator designs. After 20 min of ion-plasma treatment with negatively pulsed bias (−2 kV, 7 μs, 105 p.p.s.) and steered arc, the observed macroparticle surface density appeared to be 2 orders of magnitude smaller than after vacuum arc plasma deposition at the anode potential using an evaporator with an axial magnetic field. The possibility of high–frequency short–pulse plasma immersion ion implantation by implementing DC vacuum arc plasma is discussed.

High-intensity low energy titanium ion implantation into zirconium alloy

This research describes the possibility of ultra-high dose deep titanium ion implantation for surface modification of zirconium alloy Zr-1Nb. The developed method based on repetitively pulsed high intensity low energy titanium ion implantation was used to modify the surface layer. The DC vacuum arc source was used to produce metal plasma. Plasma immersion titanium ions extraction and their ballistic focusing in equipotential space of biased electrode were used to produce high intensity titanium ion beam with the amplitude of 0.5 A at the ion current density 120 and 170 mA/cm2. The solar eclipse effect was used to prevent vacuum arc titanium macroparticles from appearing in the implantation area of Zr sample. Titanium low energy (mean ion energy E = 3 keV) ions were implanted into zirconium alloy with the dose in the range of (5.4–9.56) × 1020 ion/cm2. The effect of ion current density, implantation dose on the phase composition, microstructure and distribution of elements was studied by X-ray diffraction, scanning electron microscopy and glow-discharge optical emission spectroscopy, respectively. The results show the appearance of Zr-Ti intermetallic phases of different stoichiometry after Ti implantation. The intermetallic phases are transformed from both Zr0.7Ti0.3 and Zr0.5Ti0.5 to single Zr0.6Ti0.4 phase with the increase in the implantation dose. The changes in phase composition are attributed to Ti dissolution in zirconium lattice accompanied by the lattice distortions and appearance of macrostrains in intermetallic phases. The depth of Ti penetration into the bulk of Zr increases from 6 to 13 μm with the implantation dose. The hardness and wear resistance of the Ti-implanted zirconium alloy were increased by 1.5 and 1.4 times, respectively. The higher current density (170 mA/cm2) leads to the increase in the grain size and surface roughness negatively affecting the tribological properties of the alloy.