Compression Plasma Flows Research Articles

The impact of a shock-compressed layer on the mass transfer of target material during processing compression plasma flows

The paper describes the results of experimental and numerical research of the thickness of the molten bath and the surface erosion of a substance under the influence of compression plasma flows. It has been demonstrated that the formation of the shock-compressed layer affects the melted depth and the mass erosion from the surface of the treated target.

Numerical study of mass transfer of a material under intense flows of high-speed electrons and plasma

The paper presents the mechanisms of mass transfer in a material under compressive plasma flows. The work contains numerical studies on mass loss from the surface of a sample treated by Compressive Plasma Flow, in the first case, and by High-Current Electron Beam, in the second case. The mass ablated from the material surface was computed with BETAIN software. The effects of plasma flow pressure on mass transfer of the material and processes of formation of the molten layer and erosion of mass from the material surface were investigated. It was revealed that plasma flow pressure formed a shock-compressed layer on the sample, and molten liquid was displaced from the center to peripheral regions. If sample size is less than the diameter of plasma spot, the melt is displaced out of the sample. This approach can explain experimental values of molten thickness and mass loss.

Study of parameters of a facility generating compressive plasma flows

The prosperity of plasma technologies stimulates making of a facility generating compressive plasma flows at the South Ural State University. The facility is a compact-geometry magnetoplasma compressor with the following parameters: stored energy up to 15 kJ, voltage of a bank from 3 to 5 kV; nitrogen, air, and other gases can serve as its operating gas. The investigation of parameters of the facility showed the following parameters of compressive plasma flows: impulse duration of up to 120 μs, discharge current of 50-120 kA, speed of plasma flow of 15-30 km/s. By contrast to the available facilities, the parameters of the developed facility can be adjusted in a wide range of voltage from 2 kV to 10 kV, its design permits generating CPF in horizontal and vertical positions.

Coating of a substrate with surface preliminarily treated with intensive flows of high-speed electrons and plasma using a magnetron

This paper presents results of the research in influence of preliminary surface treatment on adhesion of film to substrate (St8 or brass-target, CU, Ni-film). The preliminary treatment has been conducted by two methods: first, by compressive plasma flow with charge duration ∼100μs, plasma formation rate (15-20)×103 m/s; second, by low-energy high-current electron beams with pulse duration 2-3 μs and electron energy up to 30 keV. The investigation shows the strong influence of preliminary sample treatment and processing parameters on adhesion of film to substrate and final roughness. Experimental investigations have revealed the best adhesion of film to substrate, and the smoothest film is corresponding to the mode with preliminary LEHCEB irradiation with electron energy of 25, 30 keV. It was shown that the alternation of deposition with LEHCEB irradiation has resulted in large-scale surface smoothing: the surface has become glassy whereas craters of 10-20 μm have formed. It was shown that the magnetron-covered samples can withstand the saline mist for twice as long as samples with galvanic coatings.

Modification of the composite multi-layer oxide ceramic coating on meteoroid shielding element by compression plasma flow

The aim of this work is investigation of the influence of high-energy plasma impact on composite multi-layer coating (NiAl as a sublayer and Al2O3 as a top coat) on meteoroid shielding element. In order to reach this goal qausi-stationary plasma accelerator with impulse gas feeding was used. Experiments were conducted with use of helium and hydrogen gas mixture and nitrogen as plasma forming substance. Plasma accelerator generates plasma jet with electron temperature ≈ 150 kK and electron density (2.5-4) × 1016 cm-3. Visual examination, photography and spectral measurements were made through special vacuum chamber optical windows.

Surface nitriding and alloying of steels with Ti and Nb atoms by compression plasma flows treatment

Phase and element composition, microhardness of Ti/steel and Nb/steel systems treated by compression plasma flows have been investigated in this work. Auger electron spectroscopy, X-ray diffraction, scanning electron microscopy, energy-dispersion X-ray microanalysis and Vickers microhardness measurements were used for sample characterization. The findings showed that treatment of a “coating/steel” system by compression plasma flows generated in nitrogen atmosphere allowed alloying of the surface layer of steel by the coating element and nitriding it simultaneously. The variation of the pulses number (1–6) resulted in change of the alloying element concentration and formation of a number of phases in the alloyed layer: Fe2Ti, a supersaturated solid solution α-Fe(Ti,C) in the Ti alloyed layer and a supersaturated solid solution α-Fe(Nb,C) in the Nb alloyed layer. The formation of Ti(C,N) and Nb(C,N) carbonitrides with fcc crystal structure at the surface was also found. The change of phase composition and quenching effects resulted in substantial increase of microhardness.

Applying Compressive Plasma Flows to Improve Adhesion in a Film-Support System

The present paper is devoted to the influence of the support surface roughness on adhesion of a film-support system (a stainless steel (St3) support + a copper film). The film was deposited using a magnetron. The film was 7 μm thick. Prior to coating with the copper film the sample surface was treated with Low-Energry Power High-Current Electron Beams (LEHCEB) or Compressive Plasma Flows (CPF). An experimental facility similar to the magnetoplasma compressor was made. The surface was exposed to LEHCEB in modes that make it smoother or rougher. The sample surface gets rougher, if treated with CPF. As the profilometry data show, the contact area rises 4 times. And this, in its turn, strengthens the adhesion.

Photoluminescence properties of porous silicon formed on plasma-processed substrates

Measurements have been made of the photoluminescence spectra of samples of porous silicon after they were processed with a compression plasma flow in a nitrogen atmosphere. A significant increase of the photoluminescence of the test samples is detected by comparison with porous silicon obtained by the usual technique.

Structure and Optical Properties of Porous Silicon Formed on Silicon Substrates Treated with Compression Plasma Flow

Porous silicon layers were formed on the silicon substrates treated with compression plasma flow. Pores density and lateral size on substrates treated with plasma is by 25% more than that on untreated substrates. The intensity of the PL of the PS layers, formed on the plasma treated substrates (PT PS), is twice more than that of the PS layers, formed on untreated substrates. Three month exposure of normal PS and PT PS layers to the air leads to the PL intensity increase by 3 and 5.7 times, respectively, as well as to the peak position shifting towards long wavelength region by 3.1 nm, in the case of PT PS layer. The PL intensity increase is attributable to the reduction of the dangling bond density as a result of passivation by oxygen.

Structure and phase composition of Nb/Ti system subjected to compression plasma flow impact

The results of structure, phase composition and mechanical properties of titanium alloyed with niobium atoms by means of compression plasma flow (CPF) impact on the “Nb coating (2.5μm)/Ti substrate” system are presented. The CPF treatment with the pulse duration of 100μs was carried out at the absorbed energy density of 13J/cm2 which is sufficient for melting of both niobium coating and some part of titanium substrate. The cross-section analysis by means of scanning electron microscopy revealed the formation of the alloyed layer with the thickness of 14μm and relatively uniform distribution of Nb along the depth (Nb concentration obtained by means of the EDX analysis was about 17at.%). Alloying of titanium with Nb atoms resulted in stabilization of a high-temperature β-Ti phase as a β-Ti(Nb) solid solution. In the near surface layer the niobium interacted with impurity atoms (N and C) providing carbonitride (Nb(C,N) and carbide and Nb2C) possible formation. Phase transformation in the surface layer of titanium led to microhardness increase up to 4.7GPa.

Microstructure, heat transfer, and melting of the layers of hard alloy containing titanium and tungsten carbides in conditions of high-power pulsed treatment

The influence of energy density and pulse count under the effect by compression plasma flows (CPFs) and high-current electron beams (HCEBs) on the melting depth and microstructure of modified layers of T15K6 alloy is investigated. A method of computer modeling of heat transfer under such high-power effects on the hard alloy taking into account the bulk ratio of alloy components, variations in their thermal characteristics with an increase in temperature, difference in the pulse shape, and corresponding spatial energy release is proposed. The comparison of calculated melting depths of alloy components for HCEBs and CPFs with the experimental data in a range of energy densities of 30–50 J/cm2 showed their good agreement. The interrelation of the features of the thermal effect of HCEBs and CPFs with the melting depth and microstructure of modified layers of T15K6 alloy is revealed.

Thermal stability of silicon photovoltaic structures produced using compression plasma flows

Thermal stability investigations of photovoltaic structures synthesized by the compression-plasma-flow treatment of doped silicon are performed. The samples are annealed in an atmosphere of nitrogen, in air or in vacuum in a temperature range of 100–900°C for 30 min or 3 h. The photovoltaic effect does not change after annealing at temperatures up to 600–700°C. It decreases 1.3–1.7 times after thermal annealing at a temperature of 900°C. The structure-phase changes of silicon treated with compression plasma flows are studied using X-ray diffraction and scanning electron microscopy methods. It is established that a recrystallized pre-surface layer with a thickness of 10–20 μm and modified (but not melted) layer with a thickness of up to 50–60 μm localized below the recrystallized layer are formed.

Erosion of materials under the effect of compression plasma flows

Erosion of the surface of St3-type steel and BrB2-type bronze samples as well as bronze and copper samples with zirconium coating under the effect of compression plasma flows is studied. The results show the increase in mass removed from the surface of samples with the growth of energy absorbed by the surface layer and with the growth of the number of pulses. Probable mechanisms of erosion have been discussed. Erosion leads to the decrease in the coating element concentration in the alloyed layer in the case of the coating/substrate system treatment. This effect depends on thermal characteristics of the treated material.

Alloying of austenitic steel surface with zirconium using nitrogen compression plasma flow

In this study, the effect of a nitrogen compression plasma flow on the microstructural and mechanical properties, as well as on the elemental and phase compositions of a Zr/chromium–nickel steel system has been investigated. The Zr/steel system was exposed to a single pulse of the compression plasma flow or to a series of pulses. The samples were characterized by scanning electron microscopy, Auger electron spectroscopy, X-ray diffraction, and energy dispersive X-ray analyses, and subjected to a Vickers microhardness test. The findings showed the formation of a surface modified layer alloyed by Zr with the thickness of up to ∼12 μm. The modified layer contains α- and γ-iron-based solid solutions, the Fe23Zr6 intermetallic compound, and ZrN and Cr2N nitrides due to nitrogen diffusion. The microhardness of the modified layer increased by a factor of ∼2.

Microstructure, heat-transfer, and melting of hard alloy layers containing titanium and tungsten carbides under the conditions of power pulse treatment

The effect of energy density and pulse number of compression plasma flow (CPF) and high-current electron beams (HCEB) treatments on melting depth and microstructure of modified layer of T15K6 hard alloy has been investigated. The method of computerized modeling of heat transmis- sion during such high-powered impacts on hard alloy considering the volume ratio of alloy components, change of their thermophysical proper- ties with a rise in temperature, difference in pulse form, and corresponding spatial energy-release is proposed. The comparison of calculated depth of alloy components fusion for HCEB and CPF with experimental data in the energy density interval of 30–50 J/cm 2 shows their good correction. The interrelationship of HCEB and CPF heat effect peculiarities with melting depth and microstructure of modified T15K6 hard alloy layer is found.

Modification of structure and phase composition of eutectic silumin in affecting by high-intensive electron streams and compression plasma flows

The results of investigation of the structural-phase condition and microhardness of eutectic silumin exposed to low-energy high-intensity electron streams and compression plasma flows are presented. As a result of such treatment the near-surface layer up to 55 μm thick with dispersed cellular- dendrite structure and improved mechanical characteristics is formed. The comparative analysis of the effect of the parameters and treatment type on the surface layer structure is carried out.

Current Status of the Magnetoplasma Compressor Device in Belgrade - Study of Plasma Facing Materials Important for Fusion Reactors

The magnetoplasma compressor, a quasi stationary plasma accelerator, is a source of supersonic compression plasma flow. High plasma parameters of compression flow, large flow velocity and discharge duration enable their efficient usage for development of new plasma technologies, including material surface modification, creation of sub microstructures and nanostructures. In this paper spatial and temporal distribution of emissivity was studied using inverse Abel transform. This has been realized in LabVIEW environment. The plasma flow generated by quasi stationary plasma accelerators can be used for simulation of high energy plasma interaction with different materials of interest for fusion experiments. Surface phenomena are results of specific conditions during plasma flow interaction with target surface. As the next step in our research, spectral analysis of the plasma area around targets surface, after interaction between target and plasma, generated by magnetoplasma compressor, is planned. The first material which will be subjected to interaction with plasma will be a carbon fiber - material of big importance for divertor region in fusion devices.

Numerical Calculation of the Dynamics of Temperature Fields That Determine the Phase Composition of Polycrystalline Iron During Its Exposure to a Compression Plasma Flow

The results of Stefan problem-based calculations of the distribution of nonstationary temperature fields in the surface layer of iron samples exposed to compression plasma flows at the given initial and boundary conditions are presented with account for the temperature dependence of the heat capacity and thermal conductivity of a sample. It is shown that on ultrafast heating and cooling (~107 K/s), an iron sample exhibits a modified layer having a nonequilibrium microstructure and containing amorphous and nanocrystalline phases that increase its strength and wear resistance.

Structural and phase changes in single-crystalline silicon treated with compression plasma flows

The structural-phase changes in p-type single-crystalline silicon treated with compression plasma flows (CPFs) with an energy density of 5–12 J/cm2 are investigated by the X-ray diffraction method depending on the crystallographic orientation of the silicon and the plasma energy density. In addition, the conductivity type on the treated silicon surface is determined by means of measuring the sign of the thermopower.; the surface morphology, by scanning electron microscopy; and the open-circuit voltage, upon illumination of the treated silicon surface (AM1.5 spectrum). It is found that treatment with CPFs results in the occurrence of the photovoltaic effect conditioned by the formation of an n-type modified surface layer. Depending on the crystallographic orientation, the modified layer either remains single crystalline (for the initial orientation (111)) or is subjected to amorphization (for the initial orientation (100)). At an energy density of ∼8–9 J/cm2 the action of CPFs leads to texture formation on the silicon surface.

Cleaning of steel surface from scale by compression plasma flows

The investigation of compression plasma flow treatment parameter effect (the number of pulses and the energy absorbed by the surface layer) on cleaning efficiency of the steel surface from scale (Fe2O3/Fe3O4/FeO) is the main aim of the research carried out in this work. The results of the phase and element composition, cross-section morphology investigations are presented. The findings showed that efficiency of plasma cleaning increased with the growth of the pulses number (1–3) and the energy absorbed by the surface layer (10–20J/cm2 per pulse). Evaporation and cracking of scale due to the difference in coefficients of linear expansion of Fe2O3, Fe3O4, FeO and steel are supposed to be the main reasons for scale removal by plasma flow impact.