High-temperature Pulsed Plasma Research Articles

Effect of High-Temperature Pulsed Deuterium Plasma on the Structure and Mechanical Properties of the Surface of Cu–Ga and Cu–Ga–Ni Alloys

Effect of High-Temperature Pulsed Deuterium Plasma on the Structure and Mechanical Properties of the Surface of Cu–Ga and Cu–Ga–Ni Alloys

Generation and Diagnostics of Pulse Plasma Flows

Pulsed plasma accelerators are widely used for the production of high-temperature pulsed plasma flows for fundamental and practical applications. The basic parameters of pulsed plasma accelerators are the characteristics of the external electric and magnetic circuits, as well as the structural and energy properties of the plasma flow. This work aims to characterize an IPU-30 pulsed plasma accelerator. The triple Langmuir probe method, calorimetric plasma energy density measurements, Rogowski coil, and high-speed visible imaging with a Phantom VEO710S fast camera are used to diagnose the pulsed plasma obtained in the IPU-30. The local plasma parameters such as electron temperature and density, the energy density of the pulsed plasma flow, pulsed plasma current, and also discharge current are experimentally obtained at different discharge voltages and air pressure in the chamber. The typical waveforms of the triple probe and Rogowski coil are presented in the form of oscillograms. The images of plasma formation in the discharge gap are obtained and the velocity of a pulsed plasma flow is measured.

Analysis of Thermal Physical Processes and Peculiarities of Modification of a Steel Surface by Pulsed Plasma Flows

The temperature gradient and melting depth of the surface of iron-based alloys under the action of high-temperature pulsed plasma beams have been estimated and compared with the experimental data. It has been shown that the steel surface melts under the action of a pulsed plasma flow at an energy density of 15–20 J/cm2; the heat front propagates to a depth of up to 20 μm, the thickness of the molten layer being less than 10 μm. The characteristic size of the microstructure formed as a result of thermal perturbation is estimated at 17 nm. The formation of new phases with crystallite sizes that vary in the range of 16–270 nm is demonstrated experimentally. It has been shown that the formation of nanosize crystalline structure and modified near-surface region are the main factors responsible for strengthening steels.

Treatment with a High-Temperature Pulsed Plasma and Laser Radiation for Die Steel Surface Layer Hardening

Comparative analysis is provided for features of structure and phase composition formation, hardness, roughness, and wear resistance of die steel 4Kh5MFS surface treated with a high-temperature pulsed plasma and laser radiation. It is established that after plasma treatment surface roughness Ra was 0.42–0.78 μm, and after laser treatment it was 1–1.17 μm. It is shown that after plasma treatment surface wear resistance is better than after laser treatment. Plasma treatment makes it possible to obtain surface hardness of the order of 840 HV that is 10% higher than after laser treatment. The data obtained indicate that pulsed sources of high-temperature plasma based on plasma accelerators may be considered as a promising tool for forming improved operating properties for a die steel 4Kh5MFS surface.

Influence of the pulsed plasma treatment on the corrosion resistance of the low-alloy steel plated by Ni-based alloy

This paper presents investigation results of the influence of high temperature pulsed plasma flows (HTPPF) treatment on the corrosion resistance of low-alloy steel 0.2C-Cr-Mn- Ni-Mo cladded by the rapidly quenched nickel-based alloy. A technique that allows obtaining a defect-free clad layer with a good adhesion to the substrate was developed. It is shown that the preliminary treatment of steel samples by nitrogen plasma flows significantly increases their corrosion resistance in the conditions of intergranular corrosion test in a water solution of sulfuric acid. A change of the corrosion mechanism of the clad layer from intergranular to uniform corrosion was observed as a result of sub-microcrystalline structure formation and homogeneous distribution of alloying elements in the plasma treated surface layer thus leading to the significant increase of the corrosion resistance.

Investigation of microstructure and thermal stability of pulsed plasma processed chromium ferritic-martensitic steels

This paper presents results of the microstructural evolution and thermal stability of the promising Russian ferritic-martensitic steels (EP 823, EP 900, EK 181 and ChS 139) for the nuclear and fusion application after surface modification by high temperature pulsed plasma flows (HTPPF) treatment. Investigations of microstructure, topography and elemental content changes associated with irradiation by nitrogen plasma with energy density 19-28 J/ cm2 and pulse duration 20 μs were carried out. Changes in microstructure and elemental content occurring in the modified surface layer were characterized by means of scanning electron microscopy (SEM) and X-ray microanalysis (EDS and WDS). It was shown that independently of initial microstructure and phase composition, HTPPF treatment of ferritic- martensitic steels leads to formation of ultrafine homogeneous structure in the near surface layers with typical grain size ∼100 nm. Results of microstructure investigations after annealing during 1 hour demonstrates significant thermal stability of nanostructure formed by HTPPF treatment.

Microstructure modification and surface hardening of 12% chromium steels by pulsed gas plasma flows

The changes in the microstructure and the surface hardening of chromium (12 wt % Cr) ferritic–martensitic steels in various initial states treated by high-temperature pulsed gas plasma flows (flux energy density Q = 17–78 J/cm2, pulse duration τp = 15–20 μs) have been studied experimentally. Treatment of fuel-element pipes and monolithic specimens of 12% chromium steel under melting of near-surface layers is found to form a gradient structure–phase state with a submicrocrystalline (~130 nm) surface layer up to 10 μm thick. The parameters of the formed cellular submicrostructure and the modified layer thickness are found to weakly depend on the composition and the thermomechanical treatment of the steels. It is shown that treatment of fuel-element pipes made of 12% chromium steels by plasma flows leads to their surface hardening by 40–60% and by a factor of 1.7–1.9 upon surface liquid-phase alloying with aluminum and chromium irrespective of steel composition.

Surface modification of low activation ferritic–martensitic steel EK-181 (Rusfer) by high temperature pulsed plasma flows

The changes due to pulsed plasma flow irradiation on the near-surface microstructure and mechanical properties of the high-chromium, ferritic–martensitic steel EK-181 (Fe16Cr12W2VTaB) have been quantified. Irradiation of EK-181 in this manner produces a microstructural gradient near the material surface, with a two dimensional nanostructured cellular surface. The microstructure and mechanical properties of the modified layer are independent of the initial microstructure and phase composition, and are strongly defined solely by parameters of the plasma flow. High thermal stability of the pulsed plasma-modified layer was explicitly demonstrated.

Mössbauer studies of the near-surface layers of 20KhGNM steel after high-temperature plasma treatment

The influence of treatment with streams of high-temperature pulsed plasma on the phase composition of 20KhGNM steel is investigated via scanning electron spectroscopy and Mossbauer spectroscopy. It is demonstrated that a submicrocrystalline cell structure is formed on surface under irradiation. A magnetic phase and a paramagnetic austenitic phase formed after plasma treatment are observed.

Hydrogen and deuterium distribution in tungsten foils irradiated with high-temperature deuterium plasma in H2O- or D2O-filled hermetic chambers

Processes of deuterium and hydrogen accumulation and redistribution are studied via the elastic recoil detection method with the help of a Plasma Focus (PF-4) setup. These processes proceed when high-temperature pulsed deuterium plasma acts on two external tungsten foils used as the main elements of hermetic chambers filled with distilled or heavy water and one internal tungsten foil inserted into an aqueous medium. It is established that, under the action of pulsed deuterium plasma on the heavy water-filled chamber, implanted deuterium atoms and those existing in the heavy water, as well as hydrogen contained in the tungsten foils, are redistributed over the entire thicknesses of the three foils. When the distilled water-filled chamber is irradiated with pulsed deuterium plasma, implanted hydrogen is observed across the whole thickness of the external tungsten foils with a depth distribution maximum. Hydrogen and deuterium reach their maxima on the foil surface immersed in liquid. The revealed phenomenon can be explained by the fact that chemical bonds in the heavy and distilled water are broken and, afterward, free hydrogen and deuterium atoms are transferred to tungsten foils under the action of intense shock waves excited in the chamber.

Deuterium and hydrogen distribution in a stack of Ta|(CD2) n |Ta foils under the action of high-temperature pulsed nitrogen plasma

Using the method of the elastic recoil detection (ERD) of hydrogen nuclei and a Plasma Focus setup (PF-4), we study the processes of the storage and redistribution of hydrogen and deuterium atoms in a stack of two tantalum foils and a deuterated polyethylene film sandwiched between them under pulsed irradiation with hot nitrogen plasma. It is established that the redistribution of implanted deuterium and hydrogen occurs at greater depths in both tantalum foils after 30 pulses of nitrogen plasma. The maximum concentrations of hydrogen and deuterium, namely 7 and 45 at % are observed on the surface of the second tantalum foil which is more distant from the PF-4 setup. The redistribution of deuterium from deuterated polyethylene onto the surface and volume of both Ta foils is observed. The observed phenomenon can be explained by the breaking of chemical bonds in the deuterated polyethylene and the transfer of freed deuterium into the Ta foils under the action of strong shock waves formed in the structure, as well as the accelerated diffusion of hydrogen and deuterium in the stress field caused by the shock wave.

Surface alloying of thin-walled metallic tube fragments using pulsed gas plasma flows

A technique is developed and conditions are determined for the surface liquid-phase alloying with aluminum and chromium of thin-walled tubes made of 12% Cr type steels with the use of high-temperature pulsed gas plasma flows. The surface morphology of the samples subjected to alloying is shown to depend on the type and thickness of a deposited film and the plasma treatment conditions. The optimum plasma treatment conditions are determined; as a result, alloying elements are rather uniformly distributed in a 10-μmthick near-surface layer at a preliminarily deposited film thickness of ∼0.5 μm. In this case, the average aluminum content in the surface layer changes in the range 6–18 wt % and the chromium content increases from ∼12 to ∼25–40 wt %.

Erosion of tungsten and its brazed joints with bronze irradiated by pulsed deuterium plasma flows

This work presents results on erosion of mono- and polycrystalline tungsten and its brazed joints with bronze substrates under irradiation by high-temperature pulsed (τp∼20μs) deuterium plasma flows, with a power density q=19–66GW/m2 and pulses numbering from 2 to 10, simulating the expected plasma disruptions and ELMs in fusion reactors. The surface erosion and heat resistance of tungsten and brazed joints were investigated by scanning electron microscopy, and erosion coefficients were determined by target mass loss.It is found that for both types of tungsten the surface starts to significantly crack even under relatively weak irradiation regimes (q=19GW/m2, N=2), at which point surface melting is not observed. Local melting becomes visible with an increase of q up to 25GW/m2. In addition, there is formation of blisters with a typical size of 1–2μm on the surface of monocrystalline samples and craters up to 2μm in diameter on polycrystalline samples. In addition, craters ∼10–30μm in diameter are formed on defects similar to those observed under unipolar arcs. At that point, the erosion coefficients change to within ranges of 0.2–0.7×10−5kg/Jm2.It is found that at q=50GW/m2, the brazed joints of monocrystalline tungsten with bronze of Cu-0.6% Cr-0.08% Zr have the highest heat resistance.

Corrosion and electrochemical behavior of aluminium treated with high-temperature pulsed plasma in CsCl–NaCl–NaNO 3 melt

Dense protective layers of aluminium corrosion products, whose composition depends on the oxidation temperature, are formed on the surface of aluminium treated with high-temperature pulsed plasma (HTPP) without visible remelting and then held in a chloride–nitrate melt in conditions of anodic polarization. Modification of aluminium treated with HTPP changes the properties of 20 μm layer under its surface and the oxide layer formed by such treatment has different morphology: it consists of smaller crystals and so has the other protective properties as compared with aluminium untreated by plasma.

Effect of plasma treatment on corrosion-electrochemical interaction between titanium and chloride-nitrate melt

The corrosion-electrochemical behavior of titanium in a chloride melt containing 1–30 wt % sodium nitrate at a temperature of 790–900 K in an argon atmosphere is studied. Depending on the sodium nitrate content, either oxide layers of various structures can appear on the titanium surface or titanium dioxide nanopowder can form in the bulk of the melt. Treating VT-1 titanium with hydrogen or helium high-temperature pulsed plasma substantially changes the morphology and protective properties of the oxide films produced on titanium.

Effect of plasma treatment on corrosion-electrochemical behavior of titanium in molten mixture of cesium and sodium chlorides

The effect of high-temperature pulsed plasma (HTPP) on the corrosion-electrochemical behavior of titanium in a molten eutectic mixture of cesium and sodium chlorides in an argon atmosphere at temperatures of 790–810 K is studied. Upon the HTPP treatment in an oxygen or helium environment, a modified corrosion-resistant layer with a thickness up to 20 µm is formed on the titanium surface and decreases the corrosion rate of titanium in a chloride melt by a factor of 10–16.

Erosion of a TiAl intermetallic alloy under conditions simulating plasma disruptions

Radiation erosion and thermal stability of TiAl-based intermetallic alloys produced by vacuum-arc melting, compacting of microcrystal powders with binder and impregnantion by melt, and their brazed joints with bronze have been investigated under irradiation by high-temperature pulsed hydrogen plasma flows (the flow energy density Q = 0.2−0.9 MJ/m 2, the pulse duration 15 μs, the number of pulses 1–21) which simulate the expected plasma disruptions in a fusion reactor. It has been found that the erosion coefficients and thermal stability of alloys are determined by the way of their fabrication, and compacted intermetallides have a higher thermal stability in comparison with the cast ones. The brazed joints of the intermetallic compound with bronze under irradiation by pulsed hydrogen plasma up to the energy density Q = 0.75 MJ/m 2 have a high thermal stability and formation of cracks was not observed.

Laser facility using nonlinear optical effects and its application for probing high-temperature pulsed plasmas

A laser diagnostic complex is described, which uses the second harmonic of a Nd : YAG laser to probe an imploding plasma on the high-current S-300 generator. The complex allows a five-frame shadow photographing of the high-temperature pulsed plasma with an exposure of 1 ns and an interval of 10 ns. The laser pulse is shortened due to stimulated Brillouin scattering in carbon tetrachloride. Series of shadow photographs of different short-lived plasma objects are obtained. The plasma density and the velocity of plasma motion are estimated.

A high-temperature pulsed corona plasma system for fuel gas cleaning

Tars in fuel gases create serious obstacles for gasification. This paper describes a pulsed corona plasma system for tar removal from the fuel gas. Experiments were performed under gaseous temperatures of up to 500°C. Effects of the gaseous temperature on the electrical matching and tar removal are reported.

Use of high temperature pulsed plasma fluxes in modification of metal materials

The results of the modification of metal materials treated by high temperature pulsed plasma fluxes (HTPPF) with a specific power of incident flux changing in the (3–100) × 10 9 W m −2 range and a pulse duration lying from 15 to 50 μs have been presented. Results of HTPPF action were studied on the stainless steels of 18Cr-10Ni, 16Cr-15Ni, 13Cr-2Mo types; on the structural steels of 13Cr, St. 3, St. 45 types; on the tool steels of U8, 65G types, and others; on nickel and high nickel alloy of 20Cr-45Ni type; on zirconium-base alloys and other metals. The microstructure and properties of modified materiais (mechanical, tribological, erosion and other properties) and surface alloying of metals exposed to HTPPF action have been investigated. It was found that the material modification by HTPPF resulted in a simultaneous increase of several properties of the units treated: microhardness of the surface and layers of 40–60 μm in depth, tribological characteristics (friction coefficient, wear resistance), mechanical properties ( σ y σ 0.2, σ r) on retention of the initial plasticity, corrosion resistance, radiation erosion under ion irradiation and others. The determining factor of the changes observed is the formation of the fine cellular structure in the near-surface layers at a depth of 20 μm with dimensions of the cells changing in the range from 0.1 to 1.5 μm depending on the kind of material, its preliminary treatment and the parameters of plasma fluxes.