Ion current-adapted control of the arc current in a pulsed cathodic arc process

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

A measurement method immune to radio frequency (RF) fluctuations is proposed for obtaining electron temperature and plasma density in RF discharges. The self-bias voltage formed by applying a square voltage to a floating planar probe and its fundamental frequency current are measured to obtain electron temperature and plasma density. To investigate the change in electron temperature due to RF distortion, the case with and without RF filters is compared, and our method is least affected by RF fluctuations compared to the conventional methods: electron energy probability function (EEPF) and floating harmonic method (FHM). When the RF powers and the gas pressures change, the electron temperature and the ion density measured from our method agree well with those measured from the FHM. Although our method and the EEPF are slightly different due to the depletion of the EEPF at high energy (near the floating potential), the trends of the three methods (our method, FHM, and EEPF) agree well under all conditions. In our method, the electron temperature was investigated with and without correction for the increase in the ion current at probe tip radii of 5 and 1 mm. When correcting the increase in ion current due to the sheath expansion, the electron temperature is not overestimated and does not change in the planar probe with a small radius. This can be useful in plasma monitoring system where an RF filter cannot be installed, or the probe tip must be made small.

Influences of arc current on composition and properties of MgO thin films prepared by cathodic vacuum arc deposition

XPS and XAES studies of as grown and nitrogen incorporated tetrahedral amorphous carbon films deposited by pulsed unfiltered cathodic vacuum arc process

The effects of various parameters on the ion currents to Langmuir-type cylindrical probes of Pt or Pt/Rh alloy were studied experimentally. First of all, in very low ion density flows of pure combustion gases, the effects of the potential and the dimensions of the probe on the ion current were examined. In the case, an apparent increase in ion current due to thermal emission of electrons occurred when the surface temperature of a probe containing Rh became higher than 1 900°K. The sheath thickness around a probe seemed to be larger than 0.5 mm. Furthermore, experiments were conducted in combustion gas flows, the ion densities of which were increased with the addition of potassium. Besides the effects of the potential and the dimensions of the probe, those of the flow velocity and the ion density of the gas on the ion current were examined, and an empirical equation for the ion current was obtained.

Widespread applications of direct current (dc) cathodic arc deposition are hampered by macroparticle (MP) contamination, although a cathodic arc offers many unique merits such as high ionization rate, high deposition rate, etc. In this work, a flexible curvilinear electromagnetic filter is described to eliminate MPs from a dc cathodic arc source. The filter which has a relatively large size with a minor radius of about 85 mm is suitable for large cathodes. The filter is open and so the MPs do not rebound inside the filter. The flexible design allows the ions to be transported from the cathode to the sample surface optimally. Our measurements with a saturated ion current probe show that the efficiency of this flexible filter reaches about 2.0% (aluminum cathode) when the filter current is about 250 A. The MP density measured from TiN films deposited using this filter is two to three orders of magnitude less than that from films deposited with a 90 degrees duct magnetic filter and three to four orders of magnitude smaller than those deposited without a filter. Furthermore, our experiments reveal that the potential of the filter coil and the magnetic field on the surface of the cathode are two important factors affecting the efficacy of the filter. Different biasing potentials can enhance the efficiency to up to 12-fold, and a magnetic field at about 4.0 mT can improve it by a factor of 2 compared to 5.4 mT.

The titanium nitride (TiN) thin films were fabricated by the cathodic arc deposition technique. The effect of titanium cathode arc current on structural, chemical, and morphological properties of thin films was investigated by X-ray diffraction(XRD), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscope (FESEM) and atomic force microscopy (AFM), respectively. The XRD results showed titanium nitride formation with a fcc phase structure for all samples and the preferred orientation changed from (111) to (200) plane with increasing the cathode arc current from 50 to 60 A. The crystallized sizes of the thin films increased as increasing the cathode arc current. In addition, the relationship between the size of the microdroplets on the coating surfaces and the arc current was examined.

The feasibility of using ionization sensor for the investigation and diagnosis of the fuel combustion process in piston power plants with spark ignition is substantiated. It is shown that in order to expand the functions and increase the reliability of operation and signal processing accuracy of the ionization sensor it is necessary to know the impact of the flame fluctuating velocity on the latter. Based on the analysis of published data and in-house research a mechanism of the effect of fluctuation velocity on the electrical conductivity of hydrocarbon flame is proposed, estimated by the value of ion current. A formula for calculating the ion current is proposed, which includes the fluctuation velocity, the flame temperature and the concentration of carbon particles in the fuel. For methane-air flame, it was revealed that for U' 8 m/s an increase of ion current is observed, which is due to increased flame temperature and concentration of carbonaceous fuel particles in the zone of chemical reactions of the flame. When U' 8 m/s the ion current decreases due to the growth of heat consumption for heating the incoming fuel in the flame front, directly proportional to the fluctuation velocity. The results can be used to predict and monitor characteristics of turbulence in the combustion chambers of power plants with the aid of the ionization sensor.

A small-scale plasma source based on a low-current vacuum arc is described. Temporal and spatial evolution of the ion current is measured. The plasma plume circular motion follows the cathode spot motion in the retrograde direction and is guided along the magnetic field line. It is observed that the applied magnetic field efficiently guide the plasma leading to an increase in the output ion current by a factor of 50 in comparison with that without the magnetic field.

Plasma technology is actively used for nanoparticle synthesis and modification. All plasma techniques share the ambition of providing high quality, nanostructured materials with full control over their crystalline state and functional properties. Pulsed-DC physical/chemical vapour deposition, high power impulse magnetron sputtering, and pulsed cathodic arc are consolidated low-temperature plasma processes for the synthesis of high-quality nanocomposite films in vacuum environment. However, atmospheric arc discharge stands out thanks to the high throughput, wide variety, and excellent quality of obtained stand-alone nanomaterials, mainly core–shell nanoparticles, transition metal dichalcogenide monolayers, and carbon-based nanostructures, like graphene and carbon nanotubes. Unique capabilities of this arc technique are due to its flexibility and wide range of plasma parameters achievable by modulation of the frequency, duty cycle, and amplitude of pulse waveform. The many possibilities offered by pulsed arc discharges applied on synthesis of low-dimensional materials are reviewed here. Periodical variations in temperature and density of the pulsing arc plasma enable nanosynthesis with a more rational use of the supplied power. Parameters such as plasma composition, consumed power, process stability, material properties, and economical aspects, are discussed. Finally, a brief outlook towards future tendencies of nanomaterial preparation is proposed. Atmospheric pulsed arcs constitute promising, clean processes providing ecological and sustainable development in the production of nanomaterials both in industry and research laboratories.

The 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.

Modified 9Cr-1Mo steels are commonly welded using gas tungsten arc welding process for its superior control over the rate of heat input and vaporization loss of the key alloying elements although the rate electrode deposition remains restricted. Recent developments in pulsed current gas metal arc welding have significantly improved its ability to enhance the rate of electrode deposition with a controlled heat input rate while its application for welding of modified 9Cr-1Mo steels is scarce. The present work reports a detailed experimental study on the pulsed current gas metal arc welding of modified 9Cr-1Mo steels. The effect of the shielding gas, welding current, and speed on the weld bead profile, microstructure and mechanical properties are examined. The results show that the pulsed current gas metal arc welding with appropriate welding conditions can provide acceptable bead profile and mechanical properties in welds of modified 9Cr-1Mo steels.

Characterization of diamond-like carbon coatings prepared by pulsed bias cathodic vacuum arc deposition

The work is dedicated to the development of an electromagnetic system for deflecting the primary electron beam in a plasma-beam installation (PBI). The system, consisting of two pairs of mutually perpendicular coils, enables two-dimensional control of the beam position, which allows for a reduction in specific thermal power, an increase in the total power of the beam-plasma discharge (BPD), and the implementation of heating and recrystallization annealing with a minimal temperature gradient. The coil parameters were calculated to generate a magnetic induction of up to 62.66 mT. The deflection of the electron beam on the surface of a metal plate was visually confirmed, demonstrating the operability and functional flexibility of the electromagnetic control system. Experiments in BPD mode using the differential collector method (aperture probe) showed an increase in ion current from 9 mA to 12 mA at an electron beam accelerating voltage of 5000 V, a deuterium pressure of 1 mTorr, and a deflection amplitude of 27.95 dB.

CrAISiN coatings have been used for wear applications, such as cutting tools due to their unique mechanical properties and oxidation resistance. The wear behavior of the diamond like carbon (DLC) layer is known to have low friction coefficient. Therefore, CrAISiN + DLC double layers were investigated in order to further improve the properties of CrAISiN coating. Both coatings were synthesized by using pulsed current cathodic arc deposition technique with series processes including CrAISiN layer and DLC layer, respectively. The properties such as thickness and hardness of both coatings were compared. CrAISiN + DLC coating with the high hardness of Hv5000 as compared to the CrAISiN coating with hardness up HV3100. The corrosion properties of the both coatings were evaluated in sulfuric acid by polarization test. The result shows the excellent corrosion resistance of the coated samples as compared to the blank stainless steel.