A. S. Tyuftyaev

• Joint Institute for High Temperatures, Russian Academy of Sciences

Low-temperature plasma is used in metallurgy for steel alloying by nitrogen, deoxidization of magnetic alloys, obtaining of steels with particularly low carbon content, metal cleaning of nonmetallic inclusions, desulfurization and other refining processes. The wide application of those technologies is restrained by absence of reliable generators of...

The analysis of the current state of the technological process and equipment for plasma coating of various powder materials has been carried out. To increase the processing efficiency during the deposition of ceramic materials and refractory alloys a novel technological scheme of plasma spraying with a powder feed axially to the cathode was propose...

A low-temperature plasma generator of a mixture of nitrogen and propane has been developed, with the possibility of supplying propane to the cathode region, to the arc burning zone, and also to the plasma stream below the arc binding zone. The maximum propane flow rate for a given plasmatron design and plasma-forming nitrogen flow rate, at which th...

In this work, the behavior of cathodes made from pure tungsten and pure hafnium in the direct current electric arc at 200 A and in atmospheric pressured argon medium was investigated. The research was focused on the processes happening with the cathodes during the arc initiation phase (first 100 ms after the power input). The processes of rapid cat...

In the present work, the structure of the discharge channels glow of a discharge with a liquid cathode at different pH values of the solution at a given concentration of alkali metal (Na) ions in the solution is investigated by the methods of emission spectroscopy and high-speed photography. The dependence of the atomic sodium line intensity in the...

In this work the destruction mechanism of a pure tungsten cathode during the initiation of direct current arc is studied. The experimental work shows that the cathode resides in liquid form during the initiation of the arc, and the process of its destruction happens by ejecting droplets from its surface with the following explosion. The average spe...

The results of studies of the influence of the electrophysical characteristics of a heterogeneous plasma flow on the properties of Al 2 O 3 coatings (phase composition, adhesion, porosity) during plasma arc thermal spraying on a steel grade 20 in dynamic vacuum, in the pressure range from 7 to 50 kPa and at 100 kPa are presented. As well as the res...

An efficient low-temperature plasma generator with direct arc for plasma remelting was developed and studied with direct and reverse polarity. It has an expanding nozzle channel and the remelted metal acts as a second electrode. An efficiency of ≈90% and a long service life with a current strength of up to 200 A were obtained. It is shown that the...

In recent years, gas–liquid media are of interest due to their damping properties, which may be sufficient to prevent the mechanical destruction of the oil-filled equipment in consequence of electrical breakdown. For this purpose, an experimental installation was created, where the classical method of electric explosion of a wire is used to study t...

Spraying processes for composite pseudo-alloy coatings by plasma and electric-arc methods are analyzed. During performance of the work the effect of interaction of components of mechanical mixtures of powders in a plasma jet and materials of dissimilar wires in the electric-arc method on properties of the coatings obtained is considered. The possib...

In this work the detailed structure of a direct current discharge with a liquid cathode was studied by high-speed imaging and emission spectroscopy. The movement of filaments into which the discharge channel is divided is studied. The processes of formation and destruction of filaments are investigated. Spectra were recorded at different distances...

We have studied the influence of a flow of high-enthalpy nitrogen plasma generated by a dc plasmatron on the morphology, electrical properties, and UV photoconductivity of ZnO films on sapphire substrates. It was found that the resistance of nitrogen-plasma-treated ZnO films increased (by a maximum factor of 10⁴) and the processed films exhibited c...

The paper presents the experimental results on plasma heating of fired periclase-carbonaceous refractory material. A high heating rate of more than 1000∘C/h was achieved. The thermophysical properties of the fired refractory were refined. It was shown that fired periclase-carbon has a lower thermal conductivity than unfired (9.5 and 25 W/(m·K), res...

Experiments on plasma heating of a burnt periclase–carbon refractory are performed. The heating rate is high, more than 1000 K/h. The thermophysical properties of the burnt refractory are refined using the experimental results. The burnt periclase–carbon refractory has a lower thermal conductivity than the green refractory (9.5 and 25 W/(m K), resp...

An experimental unit is described for effective alloying of steel with nitrogen by plasma arc remelting. Production regimes are developed for unit operation making it possible to obtain a super-equilibrium content of nitrogen (up to 0.22%) in remelted metal with action of a plasma flow at a temperature of ≈ 7000 K in molten metal with the metal tem...

The problem of crack strength and wear resistance of metal products increase becomes particular significance in relation to continuously increasing requirement to their reliability and long service time. Traditional methods of volume strengthening of structure elements mainly exhausted their capacity. At the same time their resource, for example, u...

The possibility of enhancing heat exchanger efficiency by applying capillary-porous coatings onto the surface of a heating element using gas-thermal spray techniques is explored. Aluminum oxide porous coating was applied by electric-arc metallization using AMC wire of 1.6 mm diameter as the coating material. Aluminum oxide coatings were applied by...

Spectroscopic and thermometric measurements were performed on the hafnium cathode in argon plasma at atmospheric pressure in a stable burning mode of the arc. The distribution of temperatures on the cathode and distribution of electron temperatures in plasma near the cathode are presented. It was shown that the obtained theoretical range of values...

Results are given for a study of the corrosion resistance of a number of protective coatings for offshore structures and shelf zone constructions operating under conditions of total and periodic immersion in sea water.

When the transformer oil is exposed to low power ultrasonic waves (< 2 W/cm²) at initial moment the breakdown voltage of transformer oil is reduced relative to the breakdown voltage of pure oil due to degassing and the occurrence of cavitation bubbles. With the increase of sonication time the breakdown voltage also increases, nonlinearly. The exper...

A generator of low-temperature dc plasma with an expanding channel of an output electrode for gas-thermal spraying was designed and constructed. The delivery of the sprayed powder into the cathode and anode arc-binding zones or into the plasma jet below the anode binding was realized. The electrophysical characteristics of both the plasma torch and...

In the present paper we present the results on the iterative supersonic nozzle profiling method for a dc plasma torch possessing an output electrode expanding channel with a power of up to 50 kW, taking into account the nonmonotonic dependence of the adiabatic exponent on temperature on the basis of the gas flow rate in the critical section and the...

An experimental set-up with a unified system of synchronized control signals was constructed to study the interaction of high-enthalpy plasma jet with the surface of heat-resistant materials. The analysis of air—lasma stream interaction with technical (isotropic) graphite is performed. The air—lasma jet has a temperature of 7000-8000 K in the inter...

Low-temperature plasma is used in the plasma-arc remelting of 55Kh20G9N4 steel. The plasmaforming gases employed are nitrogen and argon. The influence of the remelting parameters on the structure, the mechanical properties, the flexural strength, and the corrosion and wear resistance of the stainless steel is studied. When using nitrogen to form th...

The influence of the electric field on a single air bubble in transformer oil has been studied. It has been shown that, depending on its size, the bubble may initiate breakdown. The sizes of air and sulfur hexafluoride bubbles at which breakdown will not be observed have been estimated based on the condition for the avalanche-to-streamer transition...

Features are considered for the structure and formation of a heat-affected zone with surface plasma hardening based on high-carbon steel of type 60G. Original procedures are developed for determining tribological properties with dry friction and abrasive wear. Test results are given for the wear resistance of hardened layers with optimum treatment...

Plasma-arc heating of periclase-carbonaceous refractory was experimentally tested. A high heating rate of 600°C/h was achieved. The experimental results were used to correct the thermal characteristics of raw refractory and to determine the energy characteristics of the arc discharge. Raw periclase-carbonaceous refractory has high heat conductivity...

To increase the stability of the discharge arc, experimental studies of a plasma generator with a divergent channel of the output electrode are carried out. It is shown that the optimum opening angle of flow of 6° between the inside wall of the channel and the channel axis leads to increased stability of the arc compared to a cylindrical channel of...

We have developed and studied a new effective megawatt double-unit generator of low-temperature argon plasma, which belongs to the class of dc plasmatrons and comprises the cathode and anode units with divergent gas-discharge channels. The generator has an efficiency of about 80–85% and ensures a long working life at operating currents up to 4000 A...

To study the breakdown of transformer oil with gas bubbles an experimental setup was created that allows to determine electrical and optical properties of the discharge. Oil was sparged with air and sulfur hexafluoride gas. It was found that sparging oil with gas lowers the breakdown voltage of the oil. When a gas bubble is present between the elec...

The present paper discusses the issues of implementation of high-pressure ignition plasma torch in terms of discharge phenomena in compressed gases, dense nitrogen plasma properties and stable arcing power requirements. Contact ignition has been tested in a pressure range p = 1-25 bar and has proved to be a reliable solution for pilot arc burning.

A new generator of high enthalpy (H 0 > 40 kJ/g), chemically active nitrogen and air plasmas was designed and constructed. Main feature of the generator is an expanding channel of an output electrode; the generator belongs to the class of DC plasma torches with thermionic cathode with an efficiency of 80%. The generator ensures the formation of a s...

An experimental automated system was designed and constructed for studying the parameters and characteristics of non-stationary interacting system high-enthalpy-plasma stream-investigated sample: enthalpy of plasma in the incident stream; speed and temperature of plasma stream; temperature of electrons and heavy particles, ionic composition and the...

To protect deposited metal against oxidation in plasma powder surfacing, test was carried out with the process of combined supply of the powder and gas-forming additions. The effect of the parameters and the amount of sodium fluoride on the geometrical dimensions of the layers in surfacing chromium–nickel and chromium–manganese alloys is determined...

Pyrometric and spectroscopic investigations of pure tungsten cathode in argon arc plasma discharge at atmospheric pressure are reported. The distribution of surface cathode temperature and the radial distribution of plasma temperature at different distance from the cathode tip were measured. We conducted a comparison between our work and other stud...

A method is described for the plasma heating of steel in the tundish of a continuous caster. Results are presented from studies of the mechanical properties of rolled products made of steel that was cast after being heated above the liquidus temperature by different amounts. The degree of superheating of the steel was stabilized by having it underg...

Features of the formation and structure of plasma ceramic coatings sprayed with composite powders based on alumina and zirconia plated with nickel and aluminum are studied. The porosity and thermal conductivity of the coatings and the microhardness of the phase components are measured. It is found that a decrease in the thermal conductivity of the...

We have developed and studied a powerful high-enthalpy (H ≥ 20 kJ/g) air plasma jet generator with a divergent channel of the output electrode, which belongs to the class of dc plasmatrons with a thermionic cathode. The plasma generator possesses an efficiency of about 80% and ensures the formation of slightly divergent (2± = 12°) plasma jet with d...

In our work, the diffuse mode of the argon atmospheric arc binding to the conical tungsten cathode with a top angle of 60° is investigated. Results of our experiment have been compared with the results of other authors where cathode is made from lanthanated tungsten (W-2% La20j) and thoriated tungsten (W-2% ThOd. Using the pure tungsten cathode ope...

Study of the low temperature plasma generator’s gas-discharge track opening angle revealed that the expansion on the upstream channel between the generatrix and the channel axis increases the stability of the arc when compared to a cylindrical channel with a constant cross section and the optimum opening angle is 6 °.

The impact of high-enthalpy air plasma stream (H≥20 kJ/g) with a diameter of 60÷80 mm created by a powerful plasma torch (up to 1 MW) on isotropic graphite sample that is located at a distance of 200 mm from the nozzle outlet (jet velocity of 50÷150 m/s, temperature 6500÷7500 K and the electron concentration (2÷3)•1015 cm-3), leads to heating of th...

The installation for the investigation of the electric breakdown in the two-phase mixture of transformer oil and gas bubbles using the power supply with voltage doubler is described. Electrical, optical and spectral characteristics of the discharge are investigated. Periodical discharges with the frequency up to 1 kHz are detected in the gap. Maxim...

Megawatt generator of high-enthalpy air plasma jet (H ≥ 30 kJ/g) is constructed. Plasmatron belongs to the class of plasma torches with thermionic cathode, tangential swirl flow and divergent channel of an output electrode-anode. Plasma torch ensures the formation of the slightly divergent (2α = 12°) air plasma jet with the diameter D = 50 mm. The...

The paper presents the modified method for the supersonic nozzle profiling with respect to non-monotonic dependence of adiabatic index on temperature, as well as the results of nozzle profile calculation for two sets of input parameters, based on independently determined specific heat curve for molecular nitrogen N2 and products of its thermal deco...

The effects of real gases (excitation of vibrational degrees of freedom, dissociation and ionization) taken into account for supersonic nozzle profiling. The paper presents the method of the supersonic nozzle profiling for non-monotonic dependence of adiabatic index on temperature. The results of nozzle profile calculation for two sets of input par...

Assessment of the wear resistance in wheel–rail contact by determining the tribological characteristics of high-carbon steel in dry friction is proposed. Comparative test results are presented for such steel, as well as for hardened layers of wheel steel with optimal plasma surface hardening and different carbon and chromium contents. The wear resi...

Porous multilayer graphenes have been synthesized by decomposition of hydrocarbons in a thermal plasma jet. Products of synthesis were characterized by electron microscopy, thermogravimetry, Raman spectroscopy, and X-ray diffraction. Possibility of producing a wide range of graphene materials with different morphology and structure has been shown....

Pyrometric and spectroscopic investigations of lanthanated tungsten cathode in argon arc plasma discharge at atmospheric pressure are reported. The distribution of the surface cathode temperature was measured. Calculations and estimates of the emission current density are performed. Experimental data of the total current density are compared with t...

The influence of gas bubbles on the breakdown voltage of transformer oil is experimentally studied. The influence of the oil flow on the electrical characteristics of breakdown is analyzed. It is shown that sulfur hexafluoride and air bubbles decrease the breakdown voltage.

The influence of solitary gas bubbles on the breakdown voltage of transformer oil is studied experimentally. It is shown that discharges periodically arise in bubbles at fields lower than the oil breakdown field.

A technique of determination of the thermal conductivity of structural materials in a wide range of temperatures has been developed and verified. A three-dimensional simulation of the process of heat propagation into the body from the surface heated by a nonstationary source of heat has been performed based on the data obtained on thermal conductiv...

An improved design of tundish which has chambers for the plasma heating of liquid steel has been developed and tested. The design of the tundish improves heat and mass transfer processes inside it. The new design elements of the tundish accelerate the entry of the metal into zone occupied by the high-temperature plasma in order to improve the condi...

The macrostructure, mechanical properties, and defect distribution in steel are investigated as a function of its temperature in the tundish of the continuous-casting machine. In casting, the steel temperature in the tundish is regulated by plasma heating. Quality analysis of the steel indicates that such plasma heating is expedient.

Electrical breakdown strength of liquid-gas micro bubble mixtures of transformer oil with sulfur hexafluoride and air for the case of quasi homogeneous gas inclusions distribution and 10% volumetric gas content was experimentally investigated. DC voltage up to 140 kV was applied to a 8 mm gap between hemispherical electrodes. It is shown that trans...

The combination of forging with plasma-powder hardfacing is a further development of the method applied in the reconditioning of railway junctions. The process, equipment and the effect of impact energy on the properties of layers are investigated. The technology is promising for the hardening (reconditioning) of long components and eliminates the...

Measurement data obtained by the hydrostatic weighing method by means of sample impregnation in kerosene and weighing are given. Coating porosity estimation method by a new laser optical–acoustic method is developed.

The effect of technology for steel plasma heating in a CBCM tundish developed and assimilated for the first time within Russia on macrostructure and mechanical properties of a CCB is considered. It is shown that the technology provides a reduction in the degree of steel overheating above the liquidus temperature during casting. There is an increase...

Mobile equipment for melting the ice crust on the conductors and lightning-protection cables of overhead electric power lines is described, as one of the most promising methods of combating the destruction of the supports and of the electric power lines themselves due to ice-wind loads.

Plasma powder surfacing is improved if it is followed by high-temperature hammer impact on the coating. The structure and physicomechanical properties of a 65Kh25G13N3 alloy coating on 76Φ rail steel are assessed. This technology for the application of a wear-resistant coating on carbon steel may prove useful in the production and restoration of ra...

The results of processing the data on high-speed recording of tracks of plasma heated particles of Al2O3, Ti and Mo are used to determine the local and mean (in the cross section) values of the speed and temperature of the particles, and also the variation of the speed of these particles along the axis of the plasma jet in relation to different tec...

The results are presented of studies of the electrical characteristics of the discharge in plasmatrons with cylindrical and expanding channels of the output electrode. To obtain more complete information, investigations are performed with plasmatrons with solid and sectioned output electrodes. The comparative investigations revealed the particulari...

A short review is presented of experimental results concerning distribution of heat fluxes over the length of a generator of low temperature plasma (plasmatron). Comparative analysis is given of the operation of plasma generators with a divergent channel of the outlet electrode against plasma generators with a cylindrical channel of constant cross...

The results of experimental and theoretical investigations of low-temperature plasma generators with an expanding channel of the output electrode are presented. Experimental equipment with a sectioned output electrode has been constructed. The distribution of electric current in the section for different values of the consumption of gas and current...

The promising methods of hardening rapidly wearing friction pairs of mud pumps are analysed, and the efficiency of using plasma powder surfacing for increasing the service life of sleeves of cylindrical and valve sections is indicated. The results of laboratory and industrial tests carried out to determine the possibility of application of plasma w...

Plasma surface strengthening plant and processing of the rail rolling stock wheel pairs are described here. Following on from starting the equipment design up to hardened wheel pairs' acceptance, accurate adherence of the process-dependent parameters at plasma treatment, and automated control ensure hardened surface structure and properties stabili...

Results of experimental studies of a plasma generator with a divergent output electrode channel are presented, and a comparative analysis is performed of operation of this plasma generator and plasma generator with cylindrical channel of constant cross section. Studies of sectioned output electrodes are performed along with plasma generators with s...

A review is made of experimental and theoretical investigations of processes occurring in low-temperature plasma generators (LTPG) with divergent channel of the output electrode, and the possibilities of utilizing these generators in new plasma technologies are analyzed. Comparison is made of the characteristics of discharge (including the current-...

An experimental plant intended for high-temperature investigations of the thermal conductivity of structural materials is described. Results of investigations of the thermal conductivity of 12X18H10T stain-less steel in a 480- to 1200-K temperature range are given.

Promising methods of strengthening fast-wearing friction couples of drilling pumps are described. Advantage of application of plasma-jet powder hard-facing for extending the service life of cylindrical bushings and valve systems is shown. The results of laboratory and industrial tests of plasma-jet wearresistant coats (powders PN 50T45 and PG-SR4)...

Successful use of plasma hardening technology requires a search for optimum plasma treatment methods, especially when there is a change in the chemical composition of the metal in the products. In order to study the impact of the chemical composition of steel on the structure and properties after plasma hardening, various steel alloying options we...

The possibility of the plasma treatment application for increase of the operation life of railroad wheel ridges, rolls of the transport roller conveyer for hot cutting part, and worn out railroad frogs. The microstructure and phase composition of Hadfield steel (60G) have been investigated under nitrogen saturation in the process of plasma treatmen...

Improvement in fatigue resistance and wear resistance of steels should be provided under modern conditions. Plasma technologies make it possible to solve this problem. Quality of mill rollers, railroad wheels etc. can be improved with the use of plasma technology of surface hardening. Low-temperature plasma is utilized in this case. Plasma technolo...

A computer-controlled plasma technology was developed for the treatment of rolling stock wheels, providing the thermal hardening of tread and flange working surfaces. As a result of the plasma treatment the surface hardness of the wheel grows from 255 up to 420-450 HB. Herewith, the wear capability of the wheel metal grows 2-3 times and its resista...

Presents the design features and basic parameters of an industrially important plasma jets source developed from a high-current arc pasmatron (I

Dependences between the voltage of the arc and gas consumption have been obtained for the 300 A current and different values of the bulb angle. It is assumed that there are three mechanisms for the burning of the electric arc in the plasmatron. The first mechanism for small values of the angle is well known. The second mechanism is valid for the an...