I. V. Lopatin

Surface modification of steels by complex diffusion saturation in low pressure arc discharge

A technique for surface hardening of type 4140 structural steel is proposed. The technique is based on the use of low pressure arc discharges. The complex treatment in one vacuum cycle involves a sequence of operations: ion cleaning of the surface and heating the sample, diffusion surface alloying with aluminum and nitriding. The sample temperature is not over 620 °C at all stages of the process. The structure, phase and element constitution, and microhardness of the surface layer have been investigated. It has been established that the significant increase in microhardness from 2.5 in the original state to 13 GPa in the modified layer after complex diffusion saturation in an arc discharge is due to the formation of iron nitride containing dispersed particles of aluminum nitride.

Generation of low-temperature gas discharge plasma in large vacuum volumes for plasma chemical processes

In the paper the principles of generation of low temperature capacitively coupled in a vacuum chamber of a large size with the use of original low-pressure arc discharges are considered. The designs of plasma sources and their main parameters are described. Examples of effective use of the generated plasma in plasma chemical modification of the surfaces of materials and products are presented.

Effect of thermionic cathode heating current self-magnetic field on gaseous plasma generator characteristics

The performance capabilities of the PINK, a plasma generator with a thermionic cathode mounted in the cavity of a hollow cathode, depending for its operation on a non-self-sustained low-pressure gas discharge have been investigated. It has been shown that when a single-filament tungsten cathode 2 mm in diameter is used and the peak filament current is equal to or higher than 100 A, the self-magnetic field of the filament current significantly affects the discharge current and voltage waveforms. This effect is due to changes in the time and space distributions of the emission current density from the hot cathode. When the electron mean free path is close to the characteristic dimensions of the thermionic cathode, the synthesized plasma density distribution is nonuniform and the cathode is etched nonuniformly. The cathode lifetime in this case is 8-12 h. Using a cathode consisting of several parallel-connected tungsten filaments ∼0.8 mm in diameter moderates the effect of the self-magnetic field of the filament current and nearly doubles the cathode lifetime. The use of this type of cathode together with a discharge igniting electrode reduces the minimum operating pressure in the plasma generator to about one third of that required for the generator operation with a single-filament cathode (to 0.04 Pa).

Influence of the composition of a plasma-forming gas on nitriding in a non-self-maintained glow discharge with a large hollow cathode

The article presents the results of an investigation into the influence of the composition of a plasma-forming gas (N2, Ar, He) on nitriding of VT1-0 grade titanium (0.25%-Fe; 0.1%-Si; 0.2%-O) and commercial 40X steel (0.4%-C; 1.0%-Cr) in the plasma of a non-self-maintained glow discharge with a large hollow cathode. It is shown that the efficiency of nitriding of 40X steel weakly depends on the composition of the plasma-forming gas mixture, whereas nitriding of VT1-0 titanium in a helium-nitrogen mixture leads to a noticeable increase in the microhardness of the specimen’s surface in comparison with nitriding in an argon-nitrogen gas mixture.

A plasma generator based on nonself-sustained low-pressure glow discharge with a large-volume hollow cathode

The results of studying nonself-sustained glow discharges in an electrode system with a hollow cathode with a volume of 0.25 m3 are presented. A high-current (up to 35 A) nonself-sustained glow discharge at low pressures (0.3–1.0 Pa) is initiated and sustained with the help of an auxiliary cold-hollow-cathode arc discharge. When the current of a nonself-sustained glow discharge increases from 2 to 35 A, its burning voltage changes from 40 to 300 V. These values are much lower than the voltage for a self-sustained glow discharge in the same electrode system. At a discharge current of 30 A, the electron concentration at the center of the hollow cathode is ne ∼ 1010–1011 cm−3 and the electron temperature is Te ≈ 2 eV. The discharge considered can be used in the system for modification of materials and products.

Generation of uniform low-temperature plasma in a pulsed non-self-sustained glow discharge with a large-area hollow cathode

Generation of plasma in a pulsed non-self-sustained glow discharge with a hollow cathode with an area of ≥2 m2 at gas pressures of 0.4–1 Pa was studied experimentally. At an auxiliary arc-discharge current of 100 A and a main discharge voltage of 240 V, a pulse-periodic glow discharge with a current amplitude of 370 A, pulse duration of 340 μs, and repetition rate of 1 kHz was obtained. The possibility of creating a uniform gas-discharge plasma with a density of up to 1012 cm−3 and an electron temperature of 1 eV in a volume of >0.2 m3 was demonstrated. Such plasma can be efficiently used to treat material surfaces and generate pulsed ion beams with a current density of up to 15 mA/cm2.

Structure, phase composition, and properties of the titanium surface modified by electron-ion-plasma methods

The results of studying the phase and elemental compositions, imperfect substructure, and mechanical and tribological properties of commercially pure VT1-0 titanium subjected to combined treatment, which involves nitriding in low-pressure gas-discharge plasma and nitride coating deposition, are presented. The regularities are analyzed, the physical mechanisms of structural modification are discussed, and the optimal impact modes allowing a multiple increase in the microhardness and wear resistance of the material are revealed.

Structure and properties of commercially pure titanium nitrided in the plasma of a low-pressure gas discharge produced by a PINK plasma generator

The paper analyzes the surface structure and properties of commercially pure VT1-0 titanium nitrided in the plasma of a low-pressure gas discharge produced by a PINK plasma generator. The analysis demonstrates that the friction coefficient of the nitrided material decreases more than four times and its wear resistance and microhardness increases more than eight and three times, respectively. The physical mechanisms responsible for the enhancement of strength and tribological properties of the material are discussed.

Combined surface modification of commercial aluminum

The paper analyzes research data on the structure and properties of surface layers of commercially pure A7-grade aluminum subjected to treatment that combines deposition of a thin metal film, intense pulsed electron beam irradiation, and nitriding in low-pressure arc plasma. The analysis shows that the combined method of surface modification provides the formation of a multilayer structure with submicro- and nano-sized phases in the material through a depth of up to 40 μm, allowing a manifold increase in its surface microhardness and wear resistance (up to 4 and 9 times, respectively) compared to the material core. The main factors responsible for the high surface strength are the saturation of the aluminum lattice with nitrogen atoms and the formation of nano-sized particles of aluminum nitride and iron aluminides.

A device and procedure for measurements of the effective secondary emission coefficient

The design of the device and procedure of measuring the effective secondary emission coefficient γeff in glow discharges with a large-area cathode are described. The values of γeff and the density of the ion current on the cathode in the self-sustained and nonself-sustained (under the additional external injection of electrons) discharge burning modes are determined. It is shown that for the self-sustained burning mode of the basic discharge with a current of 30 A, the value γeff ≈ 0.15, being in good agreement with both the theoretically calculated and known reference data. When the basic discharge occurs in the nonself-sustained mode, γeff = 0.08–0.12, depending on the discharge burning voltage, and the ion current density on the cathode surface is equal to 0.8–1.1 mA/cm2, being ≈10% lower than the value characteristic of the self-sustained discharge mode.