Compression Plasma Flows Research Articles

Spectroscopic study of plasma flow created by a magnetoplasma compressor

Magnetoplasma compressor with a semi-transparent electrode system that operates in the ion current transfer regime is studied. The thermodynamic parameters of the discharge and the compression plasma flow generated in N2+5 % H2 mixture at 500 Pa pressure with input energy 4.9 kJ have been measured. Special construction of the accelerator electrode system enable the electrode shielding by the self-magnetic field resulting in protection from the erosion. Fully predominant N II spectrum is observed in the compression plasma flow. The plasma flow velocity, electron temperature and electron density maximum values are measured close to 35 km/s, 4 eV and 2 × 1016cm−3, respectively.

Numerical studies for the linear growth of resistive wall modes generated by plasma flows in a slab model

The resistive wall mode generated by plasma-wall relative rotations is studied numerically in a slab model with a compressible plasma flow parallel to the magnetic field. The linear growth of the mode is investigated with different parameters in numerical simulations. The critical plasma flow velocities for the instability are calculated as the wave number of the mode and other parameters vary. It is found that in the long wavelength regime, the critical velocity is in the range of the sound speed cs, as predicted in theory. In the short wavelength regime however, the critical velocity increases to a level of Alfvén velocity VA and a second stable region is found. This region eventually merges with the first stable region as the wave number increases and stabilizes the mode. The growth rate of the mode decreases with the wave number of the mode and the plasma viscosity. The critical wave number for the instability is also calculated as the plasma velocity changes.

Silicon surface periodic structures produced by plasma flow induced capillary waves

Silicon single crystal surface modification by the action of nitrogen quasistationary compression plasma flow generated by a magnetoplasma compressor is studied. It has been found that highly oriented silicon periodic cylindrical shape structures are produced during a single pulse surface treatment. The periodical structure formation can be related to the driven capillary waves quenched during fast cooling and resolidification phase of the plasma flow interaction with silicon surface. These waves are induced on the liquid silicon surface due to the compression plasma flow intrinsic oscillations.

Melting and crystallization dynamics of single-crystal silicon exposed to compression plasma flows

The melting and crystallization of single-crystal silicon wafers exposed to compression plasma flows generated by quasi-stationary plasma accelerators are studied by numerical simulation. The results include the phase transition kinetics described on the basis of the Kolmogorov equation. The space-time characteristics of the melting and crystallization processes for variously shaped plasma pulses are discussed. Based on the experimental data and estimates, it is concluded that thermoelectric instability plays an essential role in the formation of three-dimensional periodic structures.

Bulk periodic structures formation on monocrystalline silicon surface under the action of compression plasma flows

The results of numerical simulation of monocrystalline silicon melting and crystallization under the action of compression plasma flow generated by quasistationary plasma accelerators with regard to phase transformations based on Kolmogorov equation are presented. Temporal and spatial characteristics of melting and crystallization processes for pulses of various forms are discussed. Based on data received and estimates made, the conclusion on substantial role of thermoelectric instability in bulk periodic structures formation was made.

Diagnostics of silicon submicron cylindrical structures obtained by plasma flow action

Periodic submicron cylindrical structures (SCS) produced in a single pulse treatment of silicon single crystal by supersonic compression plasma flow have been studied. The nitrogen quasistationary plasma flow generated by magnetoplasma compressor is used for modification of Si (1 0 0) surface. SCS have been analyzed using optical microscopy, scanning electron microscopy and atomic force microscopy. Typical species of cylindrical structures formed at the silicon surface have been discussed. These structures are induced by the plasma flow action and then quenched from the molten state during fast cooling and resolidification. SCS have been compared to periodical silicon surface structures made by plasma, ion beams and laser interaction with silicon.

Modification of high-speed steels by nitrogen compression plasma flow: Structure, element composition, tribological properties

The influence of the nitrogen compression plasma flow impact on the phase and element composition and tribological properties of AISI M2 and AISI T1 high-speed steels was investigated in this work. The bank capacitor initial voltage, the number of pulses and nitrogen pressure in the vacuum chamber varied during experiments, providing the change of energy deposited in the surface layer within the limits of 5–13 J/cm 2 per pulse. X-ray diffraction analysis, Auger electron spectroscopy, Rutherford backscattering analysis, scanning electron microscopy, optical microscopy, friction coefficient and microhardness measurements were used for the characterization of the treated samples. It was found that the treatment of both types of steel resulted in austenite formation in the surface layer and carbide partial dissolution. The growth of energy deposited in the surface layer leads to the increase of thickness of the affected by treatment layer up to 24 μm and to the decrease of MC and M 6C carbides volume fraction in the analyzed layer. Treatment leads to nitrogen penetration into the steel up to the depth of 400 nm and the redistribution of the alloying elements in the surface layer. The decrease of hardness due to dissolution of carbides was observed almost in all range of treatment parameters, thus making unsuitable the usage of the compression plasma flow treatment for high-speed steels tribological properties improvement as a stand-alone technique.

Modification of WC hard alloy by compressive plasma flow

The effect of compressive plasma flows of nitrogen on the mechanical properties, phase and element composition of a WC hard alloy (6 wt.% of Co) has been investigated in this work. Compression plasma flows were obtained using a quasistationary plasma accelerator. X-ray diffraction analysis, Auger electron spectroscopy, scanning electron microscopy and X-ray microanalysis were used as investigation techniques.It was found that the whole depth of the modified layer amounted to 15 μm. The phase composition analysis showed that plasma treatment resulted in the transformation of a WC phase into a W2C one. The formation of a graphite phase was also found in the surface layer. The element composition analysis revealed surface segregation of carbon and cobalt. The findings also showed that microhardness of the hard alloy increased 1.7 times after treatment.

Mixing of chromium/carbon steel by compressive plasma flows

The microstructure, phase and element composition as well as mechanical properties of plasma mixed chromium/carbon steel have been investigated. Surface alloying of carbon steel with chromium has been performed with the use of the compressive plasma flow (CPF). In this technique, the action of relatively short, intense (∼100 μs and 13–18 J/cm 2) plasma pulses leads to a melting of the near-surface layer (∼15 μm) of the steel substrate together with the Cr film (∼2.5 μm) predeposited on it. A rapid liquid-phase mixing in the molten state occurs, leading to the formation of new phases during fast resolidification. It is observed that plasma treatment of the system results in the formation of doped austenite stabilized by chromium. There is an increase in the austenite content with the growth of both the energy density and the number of pulses. Moreover, a change of the preferred orientation of austenite, from (1 1 1) to (2 0 0), occurs with the increase of the number of pulses. Phase and structural changes result in improvement of mechanical properties.

Mössbauer investigations of iron under the action of hydrogen and nitrogen compressive plasma flows

Investigation of phase and element composition of iron modified by compression plasma flows generated by quasi-stationary plasma accelerator has been performed. The energy density absorbed by the sample surface was about 15 J/sm 2 per pulse that under the test conditions corresponds to the flow power density of 1.5×10 5 W/cm 2. According to Auger spectroscopy data, concentration of nitrogen in the surface layer reached to ∼20 at%. Modified layer with the thickness of tens of micrometers containing ε-Fe 2+ x N phase and nitrogen austenite ( γ N) has been formed.

The formation of low-dimensional structures by compressive plasma flows

The process of the deposition of low-dimensional structures on the silicon surface exposed to the compression plasma flow has been studied. Scanning electron microscopy, transmission electron microscopy and Rutherford backscattering spectroscopy have been used to analyze the morphology, microstructure and elemental composition of the near-surface layer. The deposited coating consists of a spherical metal containing particles with a size of 50–200 nm. Possible mechanism of the coating formation is discussed.

Deposition of nanostructured metal coatings on the modified silicon surfaces in the magnetoplasma compressor

The process of formation of nanostructured metal coatings on silicon and sodium chloride surfaces exposed to compression plasma flow has been studied. To analyze microstructure, morphology, elemental and phase composition of near-surface layer, methods of scanning electron microscopy (SEM), energy dispersive X-ray (EDX) microanalysis, and transmission electron microscopy (TEM) were used. The coating obtained looks like a monolayer consisting of spherical particles, a few to 200 nm in size, bonded to each other. These particles cover both plane surface areas and cylindrical structures formed in the course of plasma treatment. The coating thickness correlates with sizes of particles.

Structure-phase transformations in high-speed steel treated by compression plasma flow

The changes in the phase and element composition in the near-surface layer of high-speed AISI T1 steel after treatment with a nitrogen compression plasma flow are studied in this work. It was found that the treatment resulted in the partial dissolution of hardening carbides and the formation of γ -Fe phase. The nitrogen concentration is strongly dependent on the treatment parameters: the nitrogen pressure in the vacuum chamber and the number of impulses. The change in the phase composition led to a decrease in the friction coefficient and the microhardness.

On some mathematical modelling of self‐field MPD thrusters

AbstractWe are concerned with the mathematical modelling of high‐enthalpy compressible plasma flows of magnetoplasmadynamic (MPD) rocket thrusters. A closed system of partial differential equations is associated with corresponding two‐fluid flows which are subjected to strong electromagnetic fields. The numerical solution of the full original model requires nowadays huge computational costs. Therefore we use a heterogeneous domain decomposition where the corresponding coupled model is based on simplified conservation laws in a large subdomain. We establish new transmission conditions for the coupled MPD model, which appear as a byproduct of a detailed asymptotic analysis of the artificial interfaces that arise by domain decomposition. Moreover, a complete coupled mathematical MPD model is formulated, including appropriate outer boundary conditions. The well‐posedness of this model is discussed by using mathematical as well as physical arguments.

Structure and phase transformations of AISI M2 high-speed tool steel treated by PIII and subsequent compression plasma flows of nitrogen

The effect of ‘double’ treatment (plasma immersion ion implantation and subsequent compression plasma flows) on microstructure, element and phase composition, as well as on microhardness properties of AISI M2 high-speed tool steel has been studied. Such methods as Auger electron spectrometry (AES), X-ray diffraction (XRD), energy-dispersive X-ray (EDX) microanalysis and scanning electron microscopy (SEM) allowed us to obtain the data suggesting that under such treatment a martensite-austenite conversion and the formation of a deep (approx. 35 μm) three-layered structure take place. It has been established that transformations of near-surface regions are associated with the complete dissolution of the initial (Fe, Cr) 3(W, Mo) 3C carbide (≤5–10 μm) and the formation of γ N,M expanded austenite doped with atoms of nitrogen, carbon and alloying metals M=W, Mo, Cr.

Materials surface modification using quasi-stationary plasma accelerators

Quasi-stationary plasma accelerators of a new generation were studied for the capability to modify surface properties of materials widely applied in engineering (carbon steels) and in microelectronics (silicon). The action of high-energy plasma flow was shown to result in hardening the samples from carbon steels, the depth (∼0.1–0.3 mm) and microhardness (more than 10 000 MPa) of the modified surface layer being sufficient for practical purposes. Exposure of silicon wafer to medium-power compression plasma flow results in the formation of periodic sub-micron spatial structures on its surface. The main factors ensuring efficient modification of various materials under the compression plasma flow action are shown to be the rapid heating of surface due to kinetic energy thermalization of compression plasma flow during its deceleration, keeping temperature and pressure at necessary levels until the completion of physico-chemical transformations in the surface layer, and the fast crystallization of the molten layer in the presence of magnetic fields induced by the currents ‘swept-away’ from the discharge device with the compression flow.

Structure-phase transformation of high speed steel by various high intensity ion-plasma treatments

The influence of compressive plasma flow (CPF) treatment on structure and mechanical properties of AISI M2 steel was investigated and was compared with the influences of other known high intensive techniques such as high current ion implantation (HCII) and plasma immersion ion implantation (PIII) of nitrogen. The formation of structure-phase state of steel during HCII takes place under more equilibrium condition than during PIII and CPF treatments. So the structure of steel forming during HCII is more stable and is a superposition of martensite, hardening carbides, carbonitrides and small quantity of austenite. The condition of CPF treatment process is essentially more unequilibrium. It is similar to PIII but is more intensive. So the structure of thick (approx. 30 μm) surface layer of steel undergoes great changes—decay of main hardening M6C carbide and formation of expanded austenite doped by nitrogen and alloying elements of steel. The presence of this austenite improves wear resistance of steel while the decay of hardening carbides leads to microhardness decrease.

Materials surface modification using quasi-stationary plasma accelerators

Quasi-stationary plasma accelerators of a new generation were studied for the capability to modify surface properties of materials widely applied in engineering (carbon steels) and in microelectronics (silicon). The action of high-energy plasma flow was shown to result in hardening the samples from carbon steels, the depth (∼0.1–0.3 mm) and microhardness (more than 10 000 MPa) of the modified surface layer being sufficient for practical purposes. Exposure of silicon wafer to medium-power compression plasma flow results in the formation of periodic sub-micron spatial structures on its surface. The main factors ensuring efficient modification of various materials under the compression plasma flow action are shown to be the rapid heating of surface due to kinetic energy thermalization of compression plasma flow during its deceleration, keeping temperature and pressure at necessary levels until the completion of physico-chemical transformations in the surface layer, and the fast crystallization of the molten layer in the presence of magnetic fields induced by the currents ‘swept-away’ from the discharge device with the compression flow.

Structure and phase transformation of iron surface layer treated by compression nitrogen plasma flows

Investigation on a surface structure of iron modified by the action of compression plasma flows and determination of element and phase composition was carried out using X-ray diffraction analysis, Auger-electron spectroscopy, optical microscopy and scanning electron microscopy, along with studies on mechanical properties of the material. As a result, a layered structure of total depth up to 60 μm with nitrogen concentration up to 20 at.% develops at a sample surface. The final structure of near-surface area in the processed iron was shown to be formed from the ε-domain due to eutectoid decomposition on cooling, whereas an increase in both hardness and wear resistance results from dispergation of phase components.

Creation of silicon submicron structures by compression plasma flow action

Oriented submicron cylindrical structures obtained in a single pulse treatment of silicon monocrystal by compression plasma flow are described. The nitrogen plasma flow generated by magnetoplasma compressor is used for modification of Si (1 1 1) monocrystal surface. The speed of plasma flow was up to 40 km/s depending on input energy and gas used and its pressure. The electron density and temperature within the region of plasma flow maximal compression was up to 2×10 17 cm −3 and 20,000 K, respectively. Silicon samples placed perpendicular to the flow were exposed to a single 100 μs plasma pulse driven by the discharge current of 70 kA. Typical dimensions of cylindrical structures formed at the crystal surface are 0.1–2 μm in diameter and up to 200 μm in length. The influence of external magnetic field on the dimensions of the cylindrical structures was also investigated. The large diameter cylindrical structures have been noticed to exhibit the hollow features. The catalyst was not used in the process of silicon surface modification.