High-velocity Plasma Jet Research Articles

The structure and properties of a Cr3C2-Ni coating deposited by a high-velocity plasma jet onto a copper substrate

Chromium carbide-nickel coatings were deposited onto a technical grade copper substrate by means of a high-velocity plasma jet of a plasmatron operating in specially selected regimes. An analysis of the coatings showed evidence of the formation of a Ni-based solid solution, a complex chromium carbide (Cr7C3), and an fcc crystal phase with a lattice parameter of 3.614 A. The surface of the coatings exhibits a characteristic relief resulting from a dynamic interaction between melted and fused particles of the initial powder. The local hardness on some areas of the surface and in depth of the coating reaches 66±4.5 HRC, while the coating adhesion strength varies from 25 to 300 MPa.

Formation of boron carbide coating by electromagnetically accelerated plasma spraying

Boron carbide (B 4C) coating formation is investigated using an electromagnetically accelerated plasma spraying, which can generate a dense and a high velocity plasma jet of 1 MPa and 2.0–2.5 km/s by applying a pulsed high-current arc-discharge to accelerate and heat powders. Highly crystalline B 4C coatings with roughened coating-substrate interfaces were formed on mirror-polished stainless (SUS304) substrates without a binder material. The density and uniformity of the coating are improved by changing the source powder size from 30 to 10 μm, where the estimated porosity is decreased from 9 to 4%.

Laboratory and computer simulations of super-Alfvénic shocks in a weakly ionized medium

High Mach number shocks have been studied experimentally at the Kurchatov Institute in 2000 with the PF3 Plasma Focus [N. V. Filippov et al., Phys. Lett. A 211, 168 (1996)]. The main goal of these especially designed laboratory experiments was to provide data against which to test current numerical models, in order to better understand the interaction of a high-velocity plasma jet with a partially ionized gas in a strong transversal magnetic field. Observed magnetic field compression, plasma density profile evolution, and shock slowing down, are well reproduced by a two-dimensional hybrid code HAWAI2D [B. Lembege and F. Simonet, Phys. Plasmas 8, 3967 (2001)] with Monte Carlo collisions. Some of the code initial conditions are directly obtained from the numerous diagnostics installed in the experimental chamber. Others are derived from jet velocity and background density measurements, making use of a simplified model of jet propagation from the pinch. Ion-neutral collisions play a central role in the shock dynamics, as demonstrated in the simulations.

Optical measurements of plasma velocity and temperature in a low-rate, low-power LPPS system

Low-pressure plasma spraying (LPPS) is a promising method of applying coatings to surfaces for thermal, chemical, and mechanical protection. The deposition of coatings with superior properties requires an improved understanding of this complex spray process, including the detailed understanding of the time–temperature and chemical history to which an injected particle is exposed during its travel through the high-temperature and high-velocity plasma jet. In this paper, we report on measurements of the temperatures and velocities within the plasma in a low-pressure argon–hydrogen arcjet spray plasma being developed for mesoscale manufacturing of mechanical components. The measurements reported here make use of laser absorption, laser-induced fluorescence, and optical emission spectroscopy of the H α Balmer transition in atomic hydrogen. Both the absorption and fluorescence methods take advantage of the well-known spectral line broadening of atomic hydrogen, to extract the arcjet temperature and electron density. Jet axial velocities are measured via the time of flight, as detected by optical emission, of convected disturbances caused by intrinsic fluctuations in the arc voltage. Measurements made for various anode (nozzle) geometries indicate that relatively low (∼1 km s −1 mm −1) velocity gradients in the axial direction could be achieved with nozzles that include an expanding section of 10° half-angles. The measured temperatures and velocities suggest the presence of complex gas-dynamic shock structures in the arcjet plume, depending on the particular nozzle length and expansion section.

Airglow in the Visible and Infrared Spectral Ranges of the Disturbed Upper Atmosphere under Conditions of High-Velocity Plasma Jet Injection: I. Experimental data

The measurements of infrared emission from an artificial structure, which was generated during the Fluxus experiment with plasma jet injection into the atmosphere, are obtained and discussed for the first time. Additional experimental data on the airglow in the visible spectral band of the disturbed region of the atmosphere are presented. A generalized analysis of the data is given.

The structure and properties of a hard alloy coating deposited by high-velocity pulsed plasma jet onto a copper substrate

Using a plasmatron operating in specially calculated regimes, tungsten carbide (WC) based coatings were deposited onto a copper crystallizer plate. It was found that a local hardness of the WC-Co coating may reach up to 1.3×104 N/mm2 and the coating adhesion to substrate may be as high as 270 MPa. The elemental and phase compositions of coatings were studied by Rutherford backscattering spectroscopy, X-ray diffraction, and transmission electron microscopy with electron diffraction. The surface morphology and depth-composition profiles of the coatings were studied by optical and scanning electron microscopy. The coating is composed of WC crystal grains with hexagonal close packed (hcp) lattice, α-and β-Co grains, and cubic WC grains. The average size of the hcp WC grains is 0.15 μm and that of the cobalt particles is about 25 nm. In addition, the grain boundaries contain W3Co3C particles with an average size of 15 nm.

Neutralization of explosives by plasma jet impingement: feasibility study

Preliminary results of an experimental study to determine the feasibility of neutralizing explosives by impingement of a high-temperature, high-velocity pulsed plasma jet are presented. The pulsed plasma jet was created by an electrothermal gun, a device that relies upon vaporization of solid metal to produce a metal vapor plasma. The tests were conducted using an aluminum plasma with a pulse duration of 1 ms and peak energy of 100 kJ on 1-g specimens of PETN explosive. The specimens were placed inside a chamber at standoff distances of 15-30 cm from the 6.65-mm diameter muzzle of the electrothermal gun. The effectiveness of the plasma impingement was determined by comparing post-detonation experiments on the exposed and unexposed explosive specimens. High-speed imaging of the plasma jet impinging on the explosive and postmortem examination of the explosive specimens suggests that three distinct interactions occur. These interactions are: slow thermal decomposition (burning); rapid thermal decomposition (deflagration); and change in chemistry with negligible or no thermal decomposition. Initial results suggest that these three distinct interactions are a function of the mass flow rate and energy of the plasma.

Properties of electric arc plasma for metal cutting

The properties of plasmas generated for the air plasma cutting process have been investigated in this study. The plasma arc cutting process employs a plasma torch with a very narrow bore to produce a transferred arc to the workpiece at an average current density of within the bore of the torch. The energy and momentum of the high-velocity plasma jet generated by the plasma torch melts, vaporizes and removes the metal from the region of impingement of the jet. Measurements have been made of the total arc voltage, nozzle voltage, air flow rate and nozzle pressure over a range of arc currents of 40 - 160 A for a nozzle with a bore of 1.5 mm. Using high-resolution digital photography, the radius of the arc at the nozzle exit has been measured over the current range. Photographic observations indicate that an underexpanded supersonic plasma jet emanates from the nozzle. An approximate two-zone arc model has been developed to estimate the arc radius, voltage and pressure of the arc at the nozzle exit as a function of current and the predicted results have been compared with experiments. The study reveals that the nozzle of the plasma torch is heavily clogged because of the presence of an electric arc with a very high current density in the nozzle. The nozzle clogging effect increases the pressure in the chamber upstream of the nozzle as the arc current is increased for a constant mass flow rate of air. The nozzle clogging phenomenon is crucial to generate a plasma jet with the high momentum required to remove material from the molten workpiece and to maintain plasma stability.

Modeling of nonequilibrium effects in a high-velocity nitrogen-hydrogen plasma jet

A numerical simulation has been performed of a high-velocity nitrogen hydrogen plasma jet in air at atmospheric pressure including finite-rate chemical kinetics. Ions, electrons, and neutral atoms and molecules are treated as separate species in the plasma mixture. The chemical reactions considered are dissociation of molecular species, ionization of atomic species, charge exchange and dissociatioe recombination of nitrogen, and hydrogen-oxygen reactions. The calculational results show that strong departures from ionization and dissociation equilibrium develop in the downstream region as the chemical reactions freeze out at lower temperatures, in spite of the assumed chemical equilibrium at the nozzle exit. The calculations also show that ionized species are over-populated throughout the flow, while dissociated species in the core of the jet are underpopulated near the nozzle exit and become over-populated farther downstream. This initial underpopulation is due to diffusive depletion of dissociated species and enrichment of molecular species in the core of the jet.

Disintegration of carbon steel by high-velocity plasma jets

The disintegration of steel targets by high-velocity concentrated plasma jets is analyzed. The effects of carbon content, heat treatment, and specimen temperature on the disintegration pattern are revealed as a result.

A unipolar pulsed plasma generator in combination with a laser as a plasma jet source

A pulsed plasma generator ignited by plasma produced by laser radiation is described. The plasma generator can provide a relatively high-velocity plasma jet of specific chemical composition. The principal parameters of the plasma jet (its velocity, charged particle concentration, and temperature) have been measured and the properties of the plasma jet have been found to be independent of the polarity of the plasma generator ring electrode.