The conditions of a gas-discharge starting of the massive metal cathode with remote anode at small gas flows (Ar, 20-100 sccm) through the cathode cavity have been investigated. Optimization of ...geometry of the arc-discharge electrodes and the use of repetitively-pulsed power input mode (1 kW) during starting of the cathode provide reliable ignition of a glow discharge, accelerated starting of the cathode in distributed thermal emission mode (10 A, 15-20 s), reduction of energy and frequency of local cathode spots during starting process.
The results of studying the parameters of the plasma generated in an arc with a self-heating hollow cathode and a vaporizable anode placed in a magnetic field of two oppositely connected solenoids ...are presented. Compression of the discharge column in an inhomogeneous magnetic field provides an increase in power density on the surface of the crucible anode to ~1 kW/cm2 and an increase in the degree of ionization of the metal vapor to 50–80%. Using the method of reactive evaporation of aluminum in the Ar/О2 gas mixture we obtained Al2O3 coatings at the rate of 4–8 μm/h under an ion current density of 6–11 mA/cm2, a bias voltage of 50–200 V, and a temperature of 620 °С. It is shown that, with an increase in the ion current density and ion energy, the fraction of the α-phase in the Al2O3 coating increases to 100%. The single-phase α-Al2O3 coatings are characterized by the predominant orientation of crystallites (300).
•Nanocrystalline Al2O3 coatings deposited at 620 °C by reactive anodic thermal evaporation of Al•High deposition rate (8 μm/h) and Al ionization degree (0.8) achieved by discharge compression in magnetic field•α-Al2O3 content grows up to 100% with increasing of intensity of ion assistance.•Crystallization mechanism of α-Al2O3 depends on composition of accelerating ions on coating surface.•Domination of Al ion leads to γ-phase grow and following γ-α recrystallization under ion bombardment.
We propose a method for obtaining TiN coatings by reactive anodic evaporation of titanium using a high-current (30 A) discharge with a self-heated hollow cathode in an Ar + N
2
gas mixture. The ...optical spectral analysis shows that the gas-discharge plasma contains a large amount of activated titanium, while the fraction of singly charged metal ions supplied from the plasma to substrate reaches up to 70%. Titanium coatings with 2-μm thickness and up to 24-GPa hardness were obtained at a nitrogen flow rate of 5 cm
3
/min. The rate of TiN deposition at a distance of 7 cm from the vapor source amounted to ~4 μm/h.
We have studied the thermal regime of a self-heated hollow cathode in combined low-current (1–5 A) dc discharge and high-current (up to 100 A) pulsed-periodic discharge and the influence of the ...pulsed parameters on the current-voltage characteristic of the high-current discharge. It has been shown that, after the application of a voltage pulse (200–500 V), the discharge current attains its peak value and is stabilized over a time of ~100 μs. The discharge voltage in the quasi-stationary discharge stage exceeds the continuous discharge voltage at the same current by many times and depends on the mean value of the current in the discharge gap. The interpretation of the form of the
I–V
characteristics of the pulsed discharge is based on the dynamics of heating and cooling of the cathode surface layer and on the variations in the integral temperature of the cathode.
Method for low-temperature (<200°C) deposition of SiCN-based coatings in a large volume chamber (0.3 m3) by decomposition of organosilicon precursor in nitrogen-argon plasma of discharge with ...self-heated hollow cathode and remote anode (40 cm) at pressure of ~1 mTorr was investigated. The analysis of the composition of coatings by IR spectroscopy and the analysis of plasma composition are carried out by optical emission spectroscopy. The influence of discharge current (10-40 A) and the flow of gas mixture (5-15 sccm hexamethyldisilazane and 60 sccm Ar-N2 mixture) on plasma composition and elemental composition of coatings was investigated. It is shown that the degree of decomposition of precursor molecules is increased with growth of the current and with increase of Ar content in the gas mixture.
The properties of a discharge with a self-heated hollow cathode and an evaporating anode placed in a cusp magnetic field created by two oppositely connected coils installed near the anode and cathode ...are studied. There is a negatively biased sample holder in the region of the annular magnetic slit. Compressing the discharge column at the anode with a magnetic field ensures effective evaporation of the metal (aluminum) loaded into the crucible anode; the density of the oxygen-containing plasma generated in the volume was controlled by changing the current of the cathode magnetic coil. The rate of depositing the aluminum oxide coating by reactive anodic evaporation, in contrast to reactive magnetron sputtering, is not limited by the oxidation of the sputtering target; the lifetime of the thermal emission cathode is hundreds of hours. The high ion-current density of the plasma (up to 10 mA/cm
2
) ensures a decrease in the crystallization temperature and the formation of nanocrystalline oxide coatings. The conditions are determined for a stable discharge operation with a current of up to 40 A at a pressure of 0.1 Pa in an oxygen-argon mixture. The results of probe diagnostics of the plasma discharge parameters, deposition rate measurements, and an analysis of the structure and properties of aluminum oxide coatings are given.
In the course of the long-term performance (during 5 years) of a high-power source of gas ions (25 keV, 0.2 A, 600 cm2) with a plasma emitter based on cold cathode discharge, the character and rate ...of key constructive elements faults were determined, which allowed to calculate the inter-repair time, complexity and cost of the repair. The peculiarities of the gas-discharge system and the ion beam forming system limiting the effectiveness of ion beam treatment were revealed as well. Conditions favorable for the decrease in the discharge voltage by 50-200 V and igniting voltage up to 1.5-2 times are determined. The possibilities of lowering the minimal flow of working gas are demonstrated. The design of the discharge system with reduced sputtering rate of local areas of the hollow cathode is offered. The changes added to ion source design aimed to enhance the lifetime of the plasma chamber that is exposed to cyclic heating by the back electron beam leading to the development of through cracks, and to enlarge the rupture life of glow discharge hollow cathode by optimizing its configuration and the conditions of discharge ignition and burning, are described. The upgraded design of a multislit ion-optical system with enhanced performance ensures uniform surface distribution of ion fluence.
The paper examines carbon 0.5-1µ thick coatings obtained through various physical vapour deposition and chemical vapour deposition methods on stainless steel and tool steel substrates. Their ...composition, morphology and physical properties have also been studied. The correlations of erosive wear resistance and H3/E2ratio (where H is hardness and E is elastic modulus) have been identified for carbon coatings in regards to the production method. Ta-C carbon coatings demonstrate high resistance to dynamic loads with erosive wear in a sand-blast machine.
The composition, structure, and properties of TiC/a-C:H coatings obtained by simultaneous vacuum-arc deposition of titanium and carbon in a low-pressure argon-acetylene medium additionally activated ...by a low-energy (a few hundreds of electron-volts) electron beam. The creation of conditions under which the decomposition of acetylene is provided by the ionization and dissociation of molecules due to electron impacts and by the recharging of molecules through titanium and argon ions with subsequent dissociation should favor the most complete decomposition of acetylene in a wide range of pressures. With increasing acetylene pressure, the structure of the nanocomposite coating changes: the size of TiC crystallites decreases, and the fraction of interfaces (or the fraction of regions with a disordered (amorphous) structure) increases. The application of a bias voltage leads to an increase in the sizes of TiC nanocrystallites. The coatings with a maximum microhardness (∼40 GPa) have been obtained without the action of an electron beam under an acetylene pressure of ∼0.05–0.08 Pa and the atomic ratio Ti: C ∼ 0.9: 1.1 in the coating.
Intense emission from a grid-stabilized plasma cathode based on a glow discharge with an expanded anode area is studied. In the electrode system of the ion source, the potential difference between a ...large-mesh grid electrode (a hole diameter of 4–6 mm) and cathode and anode plasma reaches 200 V and the glow discharge current is up to 1 A. The current distribution over the electrodes of the plasma cathode is taken, and the dependences of the electron extraction efficiency and electron-emitting-plasma potential on the gas pressure and discharge parameters are obtained. A relationship between the geometric parameters of the grid, cathode plasma potential, and efficiency of electron extraction from the plasma is derived. It is shown that stable intense emission from the plasma cathode can be provided in wide ranges of gas pressure and discharge current by varying the geometry and mesh size of the plasma cathode grid. Discharge contraction in the grid plane at elevated gas pressures is explained. It is assumed that the emitting plasma becomes inhomogeneous due to variation in the thickness of near-electrode layers in the holes of the grid, which makes the distribution of the emission current from the plasma more nonuniform.
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