Gas Plasma Source Research Articles

THE INFLUENCE OF PLASMA ASSISTANCE MODES ON CHARACTERISTICS AND COMPOSITION OF PVD ZIRCONIUM NITRIDE COATINGS

Zirconium nitride coatings are deposited by a vacuum-arc method at a low (0.01-0.04 Pa) nitrogen partial pressure in the modes without and with plasma assistance. The plasma assistance is provided by the operation of a gas plasma source based on a non-self-sustained arc discharge with thermionic and hollow cathodes. This new low-inertia method has not been practically studied in terms of formation of nitride coatings with different architecture (single-layer, multi-layer, gradient coatings). We note that the effect of plasma assistance (an increase of the nitrogen concentration in the nitride coating with the increasing nitrogen ion fraction in the gas-metal plasma) is practically unobservable in the ZrN coatings formed under the selected conditions. Furthermore, their phase compositions do not noticeably change and their physical, mechanical and tribological properties are not significantly improved.

Preface

Analytical Review of the Reports Presented at the 15th International Conference on Films and Coatings (ICFC2021)

Composition, structure and properties of Mo-N coatings formed by the method of vacuum-arc plasma-assisted deposition

Abstract A possibility in principle is shown for varying the elemental and phase compositions of nanocrystalline Mo-N coatings, synthesized using vacuum-arc plasma-assisted method, by changing the discharge parameters of the assisting gas plasma source at the constant pressure and composition of an Ar/N2 gas mixture. It is found out that an increase in the gas-to-metal ion current density ratio from 0 to 3 gives rise to a nearly twofold increase of nitrogen concentration in the coating of the Mo-N system. It is determined that as the discharge current is increased, the main metal (Mo) phase in the coating is replaced by a nitride phase with a nitrogen deficit (Mo2N), and then by a stoichiometric MoN phase. It is shown that the coatings formed in the plasma-assisted modes do not practically contain any metallic phase. With an increase in the nitrogen concentration the coating hardness increases by up to a factor of 1.3 (up to 36 GPa) and the wear resistance increases by about a factor of 2.4 (wear rate up to 2.1·10−7 mm3N−1 m−1) compared to the parameters of the coatings deposited in the regimes without plasma assistance. All coatings of the Mo-N system, synthesized in the plasma-assisted regimes, possess multiphase compositions: β-Mo2N, γ-Мо2N, δ-MoN. As the nitrogen concentration is increased, the volume fraction of δ-MoN phase increases to 67%. At the maximum nitrogen concentration, the Mo-N coating structure becomes columnar (plate-like) in the entire coating volume. The MoN and Mo2N plates have nanometric sizes, they are parallel to each other and combined into alternating packs. All Mo-N coatings are nanostructured, with the average Mo2N(β + γ) and MoN crystallite sizes being 3–4 and 3–5 nm, respectively.

Low-inertia method of control over nitrogen concentration in the PVD nitride coatings by non-self-sustained arc discharge with thermionic and hollow cathodes

Using the probe technique, a comparative analysis of parameters of the gas-metal plasma generated by low-pressure discharges is performed during variation of their main characteristics. It is shown that by varying the discharge current of the gas plasma source it is possible to readily change the fraction of gas ions in the gas-metal plasma generated by the arc evaporator and the gas plasma source with thermionic and hollow cathodes. In the case of nitride coatings, it is found out that the concentration of nitrogen in the coatings formed by the vacuum-arc plasma-assisted deposition increases, without any changes in the nitrogen working pressure. Using the coatings based on the Mo–N and Ti–N systems as examples, a twofold increase in the nitrogen concentration is shown as the ion current density of the gas plasma source increases by a factor of three in comparison with the modes without using this source. The method discussed in this study exhibits lower inertia compared to the traditional gas pressure variation.

Influence of nitrogen concentration on structure, composition and properties of nitride coatings deposited by vacuum arc plasma-assisted method

The coatings based on molybdenum nitride have been obtained by vacuum arc plasma-assisted method and have been investigated in a complex. For generation of gas-metal plasma two types of plazmagenerator were used: arc evaporator based on self-sustained arc discharge with cathode spot and a source of gas plasma on the basis of the non-self-sustained arc discharge with the combined hot and hollow cathode. The influence of the modes of plasma assistance on characteristics, composition and structure of MoN coatings was studied. It is revealed that the increase of arc current of a gas plasma source leads to increase in a share of nitrogen in gas-metal plasma, to increase the concentration of nitrogen in a coating, to increase in a share of molybdenum nitrides in coating and significant improvement of characteristics: to increase of hardness and wear resistance.

System for deposition of diamond like a-C:H films in Ar-C2H2 plasma with ion beam assistance

The paper presents a system which comprises a gas plasma source and an ion source and allows surface treatment of dielectrics due to ion charge compensation by plasma electrons. The ion energy corresponds to the discharge voltage of the ion source. The hardness of a-C:H coatings deposited by the method is up to 40–45 GPa.

Generation of low-temperature plasma by low-pressure arcs for synthesis of nitride coatings

Experiments were performed to study gas, metal, and mixed metal-gas plasmas. The plasmas were generated with the use of an arc evaporator and a gas-plasma source with a hot filament and hollow cathode that were operated independently or simultaneously. It has been revealed that the arc current of gas-plasma source affects the parameters of the metal-gas plasma and the element concentrations in the coatings. It has been demonstrated that the characteristics of the nitride coatings produced by plasma-assisted vacuum-arc deposition can be controlled by varying the parameters of the arc in the gas-plasma source.

Reduction in surface resistivity of polymers by plasma source ion implantation

The surface resistivity of several polymers such as poly(styrene/butadiene copolymer), modified poly(phenyleneoxide), poly(ethylene terephthalate), and polyimide was improved by the argon gas plasma source ion implantation (Ar-PSII) technique equipped with a mesh-type conducting grid. With the grid, the surface resistivities of the modified polymers decreased up to 11 orders of magnitudes at a high ion dose, and remained nearly at the same values after 3 months. The PSII treated polymer sample with the grid provided more uniformly modified surface and lower surface resistivity than that treated without the grid. The extent of the decrease in surface resistivity depended on the polymer structures and physical properties. However, the surface resistivity was independent of the sample thickness, the grid size, and the grid height. Surface analyses using scanning electron microscopy, time-of-flight secondary ion mass spectrometry, and Raman spectroscopy provided the useful information on modified surfaces.

Rf gas plasma source development for heavy ion fusion

Presently the Heavy Ion Fusion Virtual National Laboratory is researching ion sources and injector concepts to understand how to optimize beam brightness over a range of currents (50–2000 mA argon equivalent). One concept initially accelerates millimeter size, milliamp beamlets to 1 MeV before merging them into centimeter size, ampere beams. Computer simulations have shown the final brightness of the merged beams is dominated by the emittance growth of the merging process, as long as the beamlets’ ion temperature is below a few electron volts. Thus, a radio frequency multicusp source capable of high current density can produce beams with better brightness compared to ones extracted from a colder source with a large aperture and lower current density. Initial experiments with such a source have successfully demonstrated simultaneously high current density, ∼100 mA/cm2, and fast turn on, ∼1 μs. Results from these experiments are presented as well as progress and plans for the next set of experiments for these sources.

Ion Nitriding of Steels in a System with a Thermionic Gas Plasma Source

A study has been made into the method of ion nitriding of tool steels in the nitrogen plasma of arc discharge with a thermionic cathode. It is found that ion nitriding with a thermionic source of nitrogen plasma causes a considerably lower hydrogenation of steels than in the cases of gas nitriding in the presence of ammonia or ion nitriding in nitrogen-hydrogen mixtures in a glow discharge. The nitrogen concentration in subsurface layers of nitrided steels is 21 to 27 at.%. The process of ion nitriding lasted for 2 to 4 hours. After the process, the microhardness of carbon steel and alloyed steel surfaces increases by factors of 2 to 5. The greatest thickness of the hardened layer reaches 150 μm.

Ion Sputtering of Metals in a System with a Thermionic Inert Gas Plasma Source

A high-efficiency sputtering system with a thermionic source of inert gas plasma is described. Characteristics of the sputtering system were studied. Sputtering coefficients, etching rates and energy expenditure coefficients were investigated as functions of argon ion energy for Cr, At, Mo, Ti and steel 3. It is shown that the sputtering system under study has a high productive capacity; the etching rate ofthe steel substrate reaches 30 μm/h. The sputtering system provides for an easy control over the process of ion etching with an aid of several easily measurable and controllable parameters (negative potential of the substrate, magnetic intensity, cathode filament current and pressure), which are practically independent of each other in the operating pressure range employed. The sputtering system offers the advantage of using various operating gases such as Ar, Xe, He, N 2 , H 2 .