Compression Plasma Flows Research Articles

Radiation Effects in Tungsten and Tungsten-Copper Alloys Treated with Compression Plasma Flows and Irradiated with He Ions.

The paper presents the results of studying the structure and phase state of tungsten and tungsten-copper alloy after pulsed action of compression plasma flows and irradiation with helium ions. The compression plasma flows were used to modify the surface layer of tungsten, as well as to create an alloy based on tungsten and copper. Using scanning electron microscopy and X-ray structural analysis, the formation of radiation defects on the tungsten surface was detected in the form of local areas of exfoliation and destruction, which begin to form at helium ion irradiation doses of 2 × 1017 cm-2. It is shown that preliminary plasma treatment of the surface in the melting mode leads to the complete disappearance of surface radiation defects up to a dose of 2 × 1017 cm-2, which may be associated with the formation of a fine-crystalline grain structure, the intergranular boundaries of which serve as effective sinks for primary radiation defects.

Oxidation of Zirconium Alloyed with Chromium Atoms by Means of Impact of Compression Plasma Flows

Oxidation of Zirconium Alloyed with Chromium Atoms by Means of Impact of Compression Plasma Flows

Thermal Stability of the Structural and Phase State of Aluminum and Alloys of the Al–Si System Doped with Zirconium Atoms under the Influence of Compression Plasma Flows

Thermal Stability of the Structural and Phase State of Aluminum and Alloys of the Al–Si System Doped with Zirconium Atoms under the Influence of Compression Plasma Flows

SCRATCH TESTING OF ZrN COATING ON TI-6AL-4V TITANIUM ALLOY SURFACE PRELIMINARY TREATED BY COMPRESSION PLASMA FLOWS IMPACT

Investigation of compression plasma flows preliminary impact influence on adhesion of ZrN coating deposited on Ti-6Al-4V titanium alloy was carried out. Profilometry, X-ray diffraction, and scratchtesting were used as investigation techniques. The findings showed that preliminary plasma impact led to the formation of developed surface relief and synthesis of titanium nitride on the surface of the alloy. Plasma processing provided a higher critical force Lc3 during scratch tests, which increases from 44 N (without processing) to 137 N (the density of absorbed energy 26 J/cm<sup>2</sup>, 6 pulses). With a decrease in the density of absorbed energy and a growth of the number of pulses, there was a tendency of the critical force Lc3 increase, that is mainly associated with the formation of an intermediate layer δ-TiN during plasma impact, the thickness of which increased with a growth of the number of pulses and a decrease in the density of absorbed energy.

MODIFICATION OF TI-6AL-4V TITANIUM ALLOY SURFACE RELIEF BY COMPRESSION PLASMA FLOWS IMPACT

Investigation of compression plasma flows impact on surface relief of Ti-6Al-4V titanium alloy was carried out in this work. Profilometry, x-ray diffraction, scanning electron microscopy, and sample weight measurements were used as investigation techniques. The findings showed that plasma impact led to the formation of developed surface relief (R<sub>a</sub> parameter was changed in the range of 0.7-2.7 μm) due to the action of hydrodynamic instabilities at the melt-plasma border. Increase in the number of pulses resulted in the growth of R<sub>a</sub> value. Numerical simulation of surface evolution under plasma impact was carried out on the basis of the model of incompressible fluid potential flow. Simulation data correlated with experimental data set. The hydrodynamic flow of the melt during plasma impact led to another process: surface erosion. Increase in both the absorbed energy density and the number of pulses resulted in erosion intensity increase. Formation of titanium nitride on the surface was observed as a result of the interaction of nitrogen (as a plasma generating gas) with the surface heated under plasma impact. Titanium nitride film prevented the development of the surface relief formed by the action of hydrodynamic instabilities.

Structure and Phase Composition of WNb Alloy Formed by the Impact of Compression Plasma Flows.

The results of a tungsten-niobium alloy synthesis by the impact of pulsed compression plasma flows are presented. Tungsten plates with a 2 μm thin niobium coating were treated with dense compression plasma flows generated by a quasi-stationary plasma accelerator. The plasma flow with an absorbed energy density of 35-70 J/cm2 and pulse duration of 100 μs melted the niobium coating and a part of the tungsten substrate, which caused liquid-phase mixing and WNb alloy synthesis. Simulation of the temperature distribution in the top layer of the tungsten after the plasma treatment proved the formation of the melted state. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to determine the structure and phase composition. The thickness of the WNb alloy was 10-20 μm and a W(Nb) bcc solid solution was found.

Experimental and simulation studies on damage mechanisms of tungsten and molybdenum under compressed plasma flow irradiation

The failure mechanism of plasma-facing components (PFCs) under extreme plasma conditions relevant for fusion reactors were investigated. Here, edge-localized mode (ELM)-like transient thermal shock irradiation experiments were performed on tungsten and molybdenum using compressed plasma flow, and combined with thermal–mechanical analysis by means of finite element simulations to discuss the grain structure evolution, cracking behavior and variations of hardness. When ELM-like thermal shock irradiation was sufficient to melt tungsten and molybdenum, a submicron-sized cellular sub-grain structure was created on their surface due to the high temperature gradient of the molten layer under the effect of Bénard–Marangoni instability. Rapid directional solidification from the bottom of the molten layer to the surface induced the formation of columnar grains dominated by the <200> orientation. While the formation of cellular sub-grains increased hardness, the thermal effect of irradiation and the formation of columnar grains led to softening. The high thermal stress induced by the ELM-like thermal shock produced macro-cracks and micro-cracks on the surface of tungsten and only micro-cracks on the surface of molybdenum. Macro-cracks were generated due to the intrinsic brittleness of tungsten. As a result of stress evolution, longitudinal macro-cracks extending perpendicular to the surface experienced transverse transformation within the material. Micro-cracks formed due to the embrittlement of the re-solidification zone, and their width increased with the melting depth. These results help us to understand failure mechanisms in PFCs under extreme operating conditions and are valuable for developing future fusion reactors.

Окисление циркония, легированного хромом, при воздействии компрессионных плазменных потоков

The results of investigation of the zirconium structure on the first stage of oxidation at temperature 700 °C in the air atmosphere after 15 minutes are presented. The commercial pure zirconium alloy as well as zirconium alloyed with chromium atoms by means of compression plasma flows impact are investigated. The results showed the possibility to form the top layer in zirconium alloyed with chromium when a thin chromium coating (1 mm) was deposited on the surface and the compression plasma flow with the absorbed energy density 25 – 43 J/cm2 influenced. Due to alloying with chromium, the high-temperature β-phase of zirconium is stabilized at room temperature as β-Zr(Cr) solid solution and martensite α′-Zr phase is formed. The oxidation at temperature 700 °C demonstrated the higher oxidation resistance of the zirconium samples treated with compression plasma flows at the highest absorbed energy density 43 J/cm2. This regime modified the top layer of the zirconium sample without β-Zr(Cr) solid solution formation which enhances the oxygen diffusion.

Термическая стабильность структурно-фазового состояния алюминия и сплавов системы Al – Si, легированных атомами циркония при воздействии компрессионных плазменных потоков

The results of structural-phase state investigations of Аl, Al – 12,6 wt. % Si – 0,1 wt. % Fe and Al – 12,6 wt. % Si – 0,5 wt. % Cu – 2,7 wt. % Mg – 0,3 wt. % Ni – 0,3 wt. % Fe – 0,2 wt. % Mn alloys surface layers alloyed by zirconium atoms under action of compression plasma flows are presented. The formation of metastable compounds Al3Zr with L12 structure and (Al,Si)3Zr with D022 structure in the alloyed layers of aluminum and silumin samples, respectively, was found. Alloying with zirconium atoms makes it possible to increase the microhardness of surface layer in 1.4 – 3 times. Thermal stability of the structure and phase composition of alloyed layers at 550 °C was investigated. The transformation of Al3Zr – L12 into Al3Zr – D023 phase in aluminium and (Al,Si)3Zr disintegration with ZrSi2 in Al – Si alloys was observed during annealing. The formed surface layers had elevated temperature strength.

Chromium doped tungsten alloy for plasma-facing components of fusion reactors formed by compression plasma flows

Chromium doped tungsten (Cr-W) alloys are formed by compression plasma flows (CPFs) treatment at different absorbed energy densities (20 – 50 J/cm2), and are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray microanalysis (EDX), and the Vickers hardness test. XRD analysis betokens that the dominant crystal orientation changes from (110) to (200) after CPFs treatment, and the intensity ratio (I200/I110) between the diffraction lines corresponding to (200) and (110) planes increases with an increase in the absorbed energy density. SEM and EDX analyses betoken spatial inhomogeneity at 20 J/cm2, improved uniformity at 30 J/cm2, and cracks at higher energy density. The hardness of the Cr-W alloy varies with absorbed energy density and has a maximum value of 379 HV at 20 J/cm2.

Enhancement of oxidation resistance in titanium by plasma treatment for high temperature applications

Titanium metal has many uses in various industries and applications due to its unique and distinctive properties, making it an important and effective material in daily use in many fields. However, they cannot be used for high-temperature applications for a long time due to their poor oxidation resistance at high temperatures. This study used compression plasma flows (CPFs) treatment to enhance the oxidation resistance of pure titanium samples in high-temperature environment. X-ray diffraction (XRD) was used to characterize air-annealed pure titanium samples with and without CPFs treatment. Without CPFs treatment, the XRD spectra of the samples annealed at 700 °C for 10 minutes and above consist of additional diffraction lines of (110), (101), and (211), representing the rutile TiO2 phase, indicating the occurrence of oxidation. However, TiO2 phases were absent in the XRD spectra of the samples treated with CPFs and then annealed under similar conditions. This indicates the effectiveness of the treatment and its ability to prevent oxidation at high temperatures. Moreover, the XRD investigation showed insignificant changes in the crystal structure of the samples annealed after plasma treatment. Thus, titanium and its alloys with CPFs treatment show potential for high-temperature applications.

Multi-Layers Composite Plasma Coatings Based on Oxide Ceramics and M-Croll

The paper considers the influence of the parameters of the plasma spraying process on the technological characteristics of multilayer coatings based on nickel-chromium, nickel-chromium-aluminum-yttrium materials, oxide ceramics, intended for operation at high temperature and additional dynamic loads. The design of plasma coatings during their application (with subsequent high-energy processing) under such conditions requires a comprehensive solution – both the use of high-quality powder ingredients and the optimization of technological parameters. The plasma process of applying powder materials has been improved to obtain the maximum values of their utilization factors. The technological characteristics that affect the properties of plasma coatings are optimized, namely: the flow rates of the plasma-forming and materials-transporting gases, the flow rate of supplied powder materials, the current and voltage of the electric arc of the plasma torch, the distance from the plasma torch nozzle exit to the substrate. The paper presents the results of studies of the structure of coatings, performed using scanning electron microscopy. Their analysis has made it possible to form general regularities obtained by the action of radiation of compression plasma flows on coatings formed by air plasma. The considered structures are created using the processes of melting, compaction and high-speed cooling of plasma coatings. The main optimization indicators are the maximum local compaction and spillage of the obtained compositions with the absence of defects and destruction from the impact of compression plasma flows. The main effect during the action of radiation of a compression plasma flow on previously formed coatings is thermal. It contributes heating of the near-surface layer. When the coating is exposed to radiation of compression plasma flows, a remelted layer of oxides with a thickness of about 12–15 µm is created, smoothing the relief of the formed surface and creating a network of cracks on the surface, diverging into the depth of the coating. The liquid-phase processes occurring in the molten phase of the near-surface layers after exposure to compression plasma radiation change the structure of the layers and contribute to the modification of their mechanical properties. By smoothing the surface, increasing the density of the surface crystallized layer and minimizing macro-defects – pores or macrocracks – the mechanical characteristics of the coatings increase.

The distribution pattern of the electron density and the electron temperature in a weakly compressible argon plasma jet measured by a Langmuir triple probe

High-speed plasma plays an important role in diverse areas. Plasma flow with a sufficiently high speed to arouse compression is usually not in thermal equilibrium, and the plasma characteristics are closely coupled with the flow field. The relation between the flow and the plasma parameters, especially the distributions of electron density, i.e. n e, and the electron temperature, i.e. T e, are of ultimate importance; however, this is not yet completely understood. In this work, a weakly compressible plasma jet produced by an arc torch is diagnosed using a Langmuir triple probe. The two-dimensional distributions of n e and T e are obtained consisting of 80 spatial points under arc currents of 70–100 A. The spatial patterns of the distributions demonstrate alternative expansion–compression wave structures. As the arc power increases, the wave structures remain almost unchanged, while n e increases monotonically. Moreover, in some regions T e decreases with the arc power, which has seldom been reported in the literature. In addition, the peaks of the radial distributions of T e always deviate from the central axis. These results are compared with previous works of strongly compressible plasma flows. The phenomena are then analyzed and explained from the perspective of fluid wave-plasma interactions and the actions of the ambipolar field in the electrons.

ELEMENTAL AND PHASE COMPOSITIONS AND MECHANICAL PROPERTIES OF TITANIUM SURFACE LAYER ALLOYED BY Zr, Nb, AND Al UNDER THE ACTION OF COMPRESSION PLASMA FLOWS

ELEMENTAL AND PHASE COMPOSITIONS AND MECHANICAL PROPERTIES OF TITANIUM SURFACE LAYER ALLOYED BY Zr, Nb, AND Al UNDER THE ACTION OF COMPRESSION PLASMA FLOWS

Oxidation of Zirconium Alloy Processed with Compression Plasma Flows

Oxidation of Zirconium Alloy Processed with Compression Plasma Flows

Structure and phase composition of hypereutectic silumin alloy Al – 20Si after compression plasma flows impact

The results of structure and phase composition investigation in hypereutectic silumin alloy with 25 at. % Si content after high-energy pulsed compression plasma flows impact are presented in the work. The compression plasma flows impact with an absorbed energy density 25 – 40 J/cm2 allows to modify the sub-surface layer with a thickness up to 30 – 32 µm due to its melting and high rate solidification. By means of X-ray diffraction method, it was found the formation of two silicon phases with different grain sizes. The high-dispersed structure of silicon is presented in the Al-Si eutectic while the silicon phase with coarse grains exists in the primary crystals. The obtained results are the basis for a new method development for nanostructuring of the surface layers of hypereutectic silumin alloys increasing its wear resistance.

Dispersion relations for waves in visco-gravitating anisotropic magnetoplasmas

The effect of Braginskii's full viscosity tensor on an infinite non-conducting, gravitating anisotropic plasma in which the medium is trapped in a strong magnetic field is discussed in the context of Braginskii's magnetohydrodynamic model with Chew–Goldberger–Low double adiabatic approximation and finite Larmor radius (FLR) correction. Through linearization of the perturbed equations, the general dispersion relation is derived for the separate compression, shear, and drift viscosity components as well as the FLR corrections. We investigate the stability for parallel and transverse perturbations with respect to the direction of the magnetic field, and both gravitational and fire-hose instabilities are found. The role of each viscous term is to suppress instability, but each component works in different ways. The FLR acts in a way that is very similar to the drift viscosity. The instability threshold is found to be independent of viscosity for compression and shear viscosity, but both the drift viscosity and FLR corrections can change the critical wavenumber for the instability. The compression viscosity is most effective at reducing the growth rate of the gravitational instability, whereas the shear viscosity works to suppress the fire-hose instability. The result of the present study may be useful for the study of large scale compression, shear, and drift plasma flow in and around clusters of galaxies and galactic disks and for the solar and stellar wind.

Модификация структуры заэвтектического силуминового сплава Al-44Si при воздействии компрессионных плазменных потоков

Effects of the high-energy compression plasma flows on the structure, elemental composition, and phase state of Al-44 at.% Si hypereutectic silumin alloy have been investigated. Using scanning electron and optical microscopy it was found decreasing in grain size of both primary silicon particles and Al-Si eutectic parts with increase of absorbed energy density of compression plasma flows. The primary silicon crystals were dispersed down to 300 nm in the result of high cooling rate of the melted layer after its homogenization by means of hydrodynamic mixing. It was found that increase in the absorbed energy density, homogenization of elemental composition in the modifies layer occurs due to increase in lifetime of the melted state and more efficiency mixing process.

Wave Processes in Rotating Compressible Astrophysical Plasma Flows with Stable Stratification

The wave processes in a rotating layer of compressible astrophysical plasma with a stable stratification and a linear entropy profile are studied theoretically. The compressibility is taken into account in the anelastic approximation. In this approximation the acoustic waves are filtered out, the system contains terms with a potential temperature (entropy), and the continuity equation contains an initial stratified density profile. The Coriolis force in the magnetohydrodynamic equations for a compressible astrophysical plasma is considered in four different approximations: a traditional f-plane, a nontraditional f-plane (given the horizontal component of the Coriolis force), a traditional β-plane, and a nontraditional β-plane. Linear and nonlinear theories of wave processes have been developed for each Coriolis force approximation under consideration. New types of waves have been found, with the rotation, magnetic field, gravity, and compressibility serving as their restoring mechanisms. The compressibility effects are represented in the new dispersion equations by the Brunt–Vaisala frequency for compressible stratified flows dependent on both initial density and pressure profiles. All of the realizable types of three-wave interactions have been revealed through a qualitative analysis of the dispersion curves. A system of equations for the amplitudes of interacting waves and the growth rates of parametric instabilities have been derived by the multiscale expansion method.

Study of MHD dynamo effect at the outlet from plasma accelerator in the presence of longitudinal magnetic field

AbstractProperties of compressible flows in the quasi‐stationary plasma accelerator have been studied in the presence of an additional longitudinal magnetic field and the arising rotation of plasma flow. Numerical study was carried out within the framework of two‐dimensional magnetic hydrodynamics (MHD) model of the axisymmetric plasma flows taking into account the finite conductivity of medium and radiation transport. Dynamics of compressible plasma flows is accompanied by the MHD dynamo effect or generation of magnetic field on a conical shock wave forming at the outlet from the accelerator.