Nitrogen Arc Research Articles

Microstructure and Mechanical Properties of High-Strength Steel 22SiMn2TiB by Pulsed Melt Inert-Gas Welding with Activated Nitrogen Arc

Microstructure and Mechanical Properties of High-Strength Steel 22SiMn2TiB by Pulsed Melt Inert-Gas Welding with Activated Nitrogen Arc

Characterization of Ultrahigh Pressure Nitrogen Arc Using Black Box Arc Model

In this paper, the effect of filling pressure on the black box arc parameters of nitrogen arc is reported using Mayr arc model. The arc current is approximately 130 A at 190 Hz. The filling pressure is varied at absolute pressure of 1, 20, and 40 bar. A phase transition from gas to supercritical state occurs when the pressure of nitrogen exceeds 33.5 bar at room temperature. To determine the effect of forced cooling, first, the free-burning arc is studied at different filling pressures. Afterwards, a self-blast arrangement is used where gas is blown into the arc near current zero. It has been observed that, without forced gas flow, both the time constant and the cooling power of the arc increase with the filling pressure. The forced cooling, however, reduces the time constant and further enhances the cooling power, thus facilitating the current interruption.

Effect of Nitrogen Arc Discharge Plasma Treatment on Physicochemical Properties and Biocompatibility of PLA-Based Scaffolds.

The effect of low-temperature arc discharge plasma treatment in a nitrogen atmosphere on the modification of the physicochemical properties of PLA-based scaffolds was studied. In addition, the cellular-mediated immune response when macrophages of three donors interact with the modified surfaces of PLA-based scaffolds was investigated. PLA surface carbonization, accompanied by a carbon atomic concentration increase, was revealed to occur because of plasma treatment. Nitrogen plasma significantly influenced the PLA wettability characteristics, namely, the hydrophilicity and lipophilicity were improved, as well as the surface energy being raised. The viability of cells in the presence of the plasma-modified PLA scaffolds was evaluated to be higher than that of the initial cells.

Black-box models for liquid nitrogen arc and its parameters optimization by PSO algorithm

Sulphur Hexafluoride (SF6) has been widely utilized in the Gas Insulated Switchgear (GIS) due to its great insulation ability. However, SF6 has great greenhouse effect. Liquid nitrogen (LN2) has been considered as a promising substitute for the SF6 gas because of its good insulation, arc quenching and cost effectiveness. To accurately simulate the LN2 switch, it is essential to establish a mathematical model for the LN2 arc. Black-box models have been commonly used in describing the dynamic characteristics of gas arc in circuit breaker simulations. There are numerous types of black-box models for gas arc, yet there is no literature available about the application of black-box model for the LN2 arc. This paper aims to establish the black-box model of LN2 arc. Based on the experimental data, several kinds of black-box models including Mayr, Cassie, Schwarz, Habedank and TP KEMA models were established, and their parameters were optimized by the Particle Swarm Optimization (PSO) algorithm. The performance of these black-box models was evaluated by the conductance error. The results indicated that black-box models can be employed for LN2 arc simulations, and the TP KEMA model exhibits the best performance with minimal conductance errors throughout the entire arcing process.

Optical observation of arcs in liquid nitrogen

Liquid Nitrogen (LN2) has good insulation and arc-quenching properties. It can minimize the switchgear losses to a low level due to its cryogenic nature. Optical observation of LN2-arcs is very important for the future design of the Liquid Nitrogen Insulated metal enclosed Switchgear (LNIS). It would help in determining the spacers sizing, and the clearance distances between the LN2 Switch and the other equipment inside the LNIS system. Until now, no one has ever done the optical analysis of high-luminance arcs in the LN2 environment. The objective of this work was to determine the shape, size and current-density effects of arc plasmas in LN2. One type of electrode geometry and three types of electrode materials were used to study the LN2-arc characteristics. The influence of cryogenic environment on the arcs were thoroughly studied. Results showed that the arcs in LN2 have a direct relationship with the applied voltages, interrupting currents and the magnetic fields. The higher the interrupting current, the larger is the size of the arc. It was also observed that different electrodes materials have different shapes of arc plasmas. Magnetic fields can significantly influence the LN2-arc by increasing its size, patterning its shape and reducing its arcing time.

EFFECT OF ARC CURRENT ON MECHANICAL PROPERTIES OF AlCrN COATINGS DEPOSITED USING CATHODIC ARC EVAPORATION

The AlCrN coatings were formed using cathodic arc evaporation at constant nitrogen pressure and arc current ranged from 50 to 120 A. Scanning electron microscopy, energy dispersive analysis, X-ray diffractometry, nanoindentation, adhesion tests and friction tests were used to investigate the effect of arc current on surface morphology, composition, structure, and mechanical and tribological properties of coatings. It was found that all coatings present cubic AlCrN with Al/(Al+Cr) ratio independent on arc current. Increase in the arc current results in increase in lattice parameter, crystallite size as well as deposition rate and coating surface roughness. A decrease in hardness with a simultaneous increase in Young's modulus is also observed. The adhesion of the coatings shows a non-linear character with the maximum (108 N) for the coating formed at an arc current of 80 A, which may explain the best wear resistance – the lowest wear rate 1.4·10-7 mm3/Nm.

Experimental study of the effect of argon on the restrike characteristics of nitrogen arc

The arc restrike process is a typical mode of operation within a direct current arc plasma torch. By using a transfer arc device with a planar anode parallel to the gas flow direction, the effect of argon addition on the disappearance of downstream old arc roots, the overall arc downstream movement process and the generation of upstream new arc roots of the nitrogen arc restrike process is experimentally investigated. The experimental results show that for pure nitrogen arc, the restrike frequency is very high and the old arc root disappears very quickly. The addition of argon will significantly decrease the temperature of the arc root and prolong the coexistence time of the old and new arc roots. This phenomenon is caused by the rapid decay of charged particle density in the nitrogen arc, because the recombination process of charged particles in the nitrogen arc is faster than that in the argon arc. The breakdown field strength at the upstream location where the new arc root occurs is calculated by combining the measurements of arc voltage, arc grayscale image and temperature. The results show that as the percentage of argon increases, the boundary layer thickness becomes thinner and the critical electric field strength required for arc breakdown decreases, leading to the generation of new arc roots more likely to occur toward the upstream location. This study improves the understanding of the effect of argon on the nitrogen arc restrike process.

Experimental study on the effect of argon shielding gas on the suppression of nitrogen arc anode ablation

The high heat flux density of the DC arc often leads to severe anode ablation, which is a key factor limiting the wider use of the DC plasma torches. In this study, a series of comparative experimental studies are conducted with the goal of suppressing nitrogen arc anode ablation by combining argon shielding flow and anode structure. It is found that for the planar electrode structure, the use of argon shielding gas can alleviate the ablation of the anode by nitrogen arc to some extent. If a boron nitride channel is installed on the anode surface to constrain the argon shielding flow, the electrode ablation can be significantly reduced. The experimental results show that there is no significant ablation on the anode surface after 1 h of operation of the nitrogen arc device with an arc current of 100 A. Further analysis reveals that, on the one hand, argon shielding gas can extend the range of motion of the nitrogen arc root along the anode surface and increase the speed of arc root motion, which has the effect of expanding the time-averaged arc anode attachment area. On the other hand, argon shielding gas can also increase the size of the nitrogen arc root and decrease the temperature of the arc root. The use of constraining channels can effectively control the range of motion of the arc root along the anode surface and strengthen the influence of argon shielding gas. The combination of these effects can substantially suppress the anode ablation of the DC arc device.

Spectroscopic Characterization of an Atmospheric Pressure Plasma Jet Used for Cold Plasma Spraying

Cold plasma spray, a powder deposition method by means of an atmospheric pressure plasma jet is a promising coating technology for use on temperature sensitive surfaces. For further improvement of this coating process, a deeper understanding of its thermokinetic properties is required. By means of optical emission spectroscopy, the plasma effluent of an atmospheric pressure nitrogen arc jet is characterized by different distances from the nozzle and different gas flow rates of 35 Lmin−1 and 45 Lmin−1. A Boltzmann plot of N2+(B-X) was used to determine rotational temperatures, which were found to be around 4000 K at the nozzle exit. Excitation temperatures, analyzed using atomic nitrogen lines, were around 6000 K for all distances. Stark broadening of the Hα-line was too weak for determination of electron density for both gas flow rates. Overall no influence on gas flow rate was found.

Simulation and Experimental Analysis of DC Arc Characteristics in Different Gas Conditions

The structures of high-voltage direct current (HVDC) relays are compact. In order to extinguish the arc, the external magnetic field is applied near the contact. HVDC relays with a large capacity are also filled with gas medium to enhance the ability of arc extinguishing. The research on the characteristics of the arc in different gases under different pressures is of great significance to improve the reliability and the lifetime of the HVDC relays. The characteristics of the arc in nitrogen, hydrogen, and nitrogen–hydrogen mixtures and that of the arc root motion in the magnetic field are simulated by means of magnetohydrodynamics (MHD). The arcing processes in N2 and air are tested by a high-speed camera, and the arc root coordinates are calculated by the image processing method, and the simulation models are verified. The result shows that under the same condition, the hydrogen arc voltage is the highest, and the moving speed of the arc root is the fastest, so that the arc extinguishing performance of the hydrogen is the best. Nitrogen–hydrogen mixture is also a superior arc extinguishing gas, and the higher the proportions of H2, the better the performance. With the increase of the pressure, arc voltage increases. Except H2, increasing the pressure of the gas is beneficial for arc motion.

Comparative Investigations of AlCrN Coatings Formed by Cathodic Arc Evaporation under Different Nitrogen Pressure or Arc Current.

Tools and machine surfaces are subjected to various types of damage caused by many different factors. Due to this, the protecting coatings characterized by the best properties for a given treatment or environment are used. AlCrN coatings with different compositions, synthesized by different methods, are often of interest to scientists. The aim of the presented work was the deposition and investigation of two sets of coatings: (1) formed in nitrogen pressure from 0.8 Pa to 5 Pa and (2) formed at arc current from 50 A to 100 A. We study relationships between the above technological parameters and discuss their properties. Coatings formed at nitrogen pressure (pN2) up to 3 Pa crystallize both in hexagonal AlN structure and the cubic CrN structure. For pN2 > 3 Pa, they crystallize in the CrN cubic structure. Crystallite size increases with nitrogen pressure. The coatings formed at different arc currents have a cubic CrN structure and the crystallite size is independent of the current. The adhesion of the coatings is very good, independent of nitrogen pressure and arc current.

Investigation of electrode erosion mechanism in Ar-N2 DC arc based on visualization of electrode phenomena

Cathode erosion is an important issue in the industrial applications of the direct-current arc. However, the mechanism of erosion under molecular gas has not been well clarified. The purpose of this study is to elucidate the erosion mechanism of tungsten-based cathodes in atmospheric pressure Ar-N2 DC arcs. Tungsten electrodes doped with various metal oxides as electron emitters were investigated. The metal vapor from the cathode was successfully visualized by an optical system that combined a high-speed camera with bandpass filters. The difference in the electrode temperature distribution due to the additives is explained with two factors. The first is the thermal factor that the high melting point additive is difficult to spread on the cathode surface. The second is the chemical factor that the emitter is reduced by nitrogen radicals. Advances in the understanding of such electrode phenomena are expected to lead to expanded applications of nitrogen arcs.

Chemical nonequilibrium modelling of a free-burning nitrogen arc

Thermal and chemical nonequilibrium modelling is performed to investigate the plasma characteristics of a nitrogen arc. The arc plasma is coupled with the electrodes self-consistently in the computational domain. The self-consistent effective binary diffusion coefficient approximation treatment of diffusion and a generalized form of Ohm’s law are incorporated in the model. It is found the electric field has to undergo a reversal in front of the anode to preserve current conservation due to the strong diffusion current density. No field reversal is found in front of the cathode. The detailed chemical reaction processes are analyzed to understand the species density behaviour. Along the cathode surface, the maximum values of current density and heat flux density occur at the intersection of the flat tip and the conical surface. The distributions of different components of the current density and heat flux density change with the arc current. On the anode side, the electric field and diffusion components contribute to the current density, and have opposite signs and similar magnitudes on the axis, leading to an off-axis maximum of the current density. The electron condensation heat makes the largest contribution to the total heat flux in the high current density region, and the heavy-species contribution from the plasma becomes important in the arc fringe. The high heat flux and current density at the anode show that the nitrogen arc possesses excellent energy source properties for arc welding and other processes that require workpiece melting.

Aluminium nitride layers prepared by nitrogen arc discharge on Al-Si alloy substrate

AlN strengthening layers were prepared on the surface of the Al-Si alloy substrate by nitrogen arc discharge at various currents. The strengthening layer is mainly composed of AlN, Al and a small amount of Si. In the nitriding process, the melt from the melting region transports upward to form the layer and Si works as the catalyst. In this method, the nitriding reaction is rapid and stable, which is virtually not affected by the oxygen partial pressure. The nitride layer can greatly improve the wear resistant of the sample. As the nitride current increases, the volume loss of the frictional wear test under lubricant condition decreases first and then increases. The volume loss reaches its lowest value at 90 A, which is only about 1/38 that of the substrate.

Directional control of arcs in liquid nitrogen using externally biased magnetic fields

Arc quenching process inside the liquid nitrogen (LN2) can be accelerated by controlling the shape, size and direction of arc plasma through the controlled magnetic fields. This paper demonstrates the experimental investigations of controlling the arcs in specific directions through NdFeB based permanent magnets. The electrodes were shorted by fuse wires to initiate arc plasmas in LN2. The effects of magnetic fields on the arcs inside LN2 were observed for the very first time. The results show that arc plasma can be stretched, lengthened and thinned in the upward and downward directions through the North-South and South-North magnetic fields approach. These findings are good news that arcs can be controlled inside the LN2 environment and several important achievements such as increasing the life time of electrodes, reduction in LN2 consumption, reduction in bubbles formation, reduction in arcing times and getting a regular cylindrical shape, can be obtained through magnetic fields.

Current interruption performance of ultrahigh-pressure nitrogen arc

In this paper, the influence of gas filling pressure on the current interruption performance of different switch configurations with electric arcs burning in nitrogen has been experimentally investigated. A synthetic circuit generating a current of 130 A at 190 Hz is used and the initial rate of rise of recovery voltage just after current zero is varied from 9.8 V/µs to 84.9 V/µs. To evaluate the effect of forced gas flow on current interruption performance, three different test arrangements are investigated: a simple contact configuration with a free-burning arc, a contact and a cylindrical nozzle setup (tube-constricted arc), and finally a self-blast arrangement where the arc is cooled by a gas flow near current zero. In each arrangement, three different filling pressures are mainly studied: 1, 20, and 40 bar, the latter being in the supercritical region. In all cases, the interelectrode gap is fixed at 50 mm. It is observed that the interruption performance deteriorates with increased filling pressure in the absence of forced gas flow. A higher post-arc current is observed for the arcs burning at high filling pressures (i.e. 20 and 40 bar) compared to at atmospheric pressure in cases with no or little forced cooling. On the other hand, a forced gas flow near the current zero reduces the post-arc current and improves the interruption performance also at high filling pressures. Little effect of the supercritical state on the interruption performance of nitrogen is observed. Under the above-mentioned test conditions, the majority of the failures at high filling pressure are observed to be of thermal re-ignition type.

Nozzle Wear and Pressure Rise in Heating Volume of Self-blast Type Ultra-high Pressure Nitrogen Arc

This paper reports on experiments with ultra-high pressure nitrogen arcs in a self-blast type switch design. The effect of filling pressure on nozzle mass loss and pressure-rise in the heating volume were investigated. An arc current peak of 130 A at 190 Hz and a fixed inter-electrode gap of 50 mm were used throughout the experiment. The arc burns inside a polytetrafluoroethylene nozzle with a gas outflow vent in the middle. Nitrogen filling pressure of 1 bar, 20 bar, and 40 bar was tested, which also covers the supercritical region. Moreover, to study the effect of vent size on blow pressure near current zero, three different vent dimensions were investigated. By increasing the filling pressure, the energy deposited in the arc increases as a result of increased arcing voltage. It was observed that the pressure-rise in the heating volume is linked to the filling pressure, while the vent size plays a crucial role in the blow pressure near current zero. The nozzle mass loss per unit energy deposited in the arc is found to be independent of the filling pressure.

Physical and Theoretical Modeling of the Nitrogen Content of Duplex Stainless Steel Weld Metal: Shielding Gas Composition and Heat Input Effects

Duplex stainless steels (DSSs) are gaining more and more attention in corrosion-resistant applications and also in the transport and automotive industry. The outstanding mechanical and corrosion properties of DSSs highly depends on the austenite-to-ferrite phase balance (A/F). This phase ratio can shift in a large scale during welding. Thus, the heat input and the shielding gas composition should be optimized. Nitrogen addition to argon shielding is frequently used in DSS welding, because it is a potent austenite former. The dissolved nitrogen content in the heat-affected zone and the weld metal (WM) predetermines the A/F. To determine the effect of heat input and nitrogen content in shielding gas, two different heat inputs and six different gas compositions were used in autogenous tungsten inert gas welding. An improved theoretical model was established in order to simulate the WM dissolved nitrogen content, which calculates it with less error than the initial models. The correlation between nitrogen content and arc voltage was also determined. This improved model delivers the basics for shielding gas selection and the subsequent weld design for optimal A/F for industrial applications.

Ultrahigh-Pressure Nitrogen Arcs Burning Inside Cylindrical Tubes

When the pressure and temperature of a fluid exceed a critical point, the fluid enters into the supercritical (SC) region. In this region, the physical properties are believed to be in favor of a good current interruption medium. This paper focuses on the arc voltage characteristics of nitrogen arcs burning inside cylindrical tubes at different filling pressures: 1, 20, 40, and 80 bar, thus covering the SC region. Two different tube materials have been used in the experiments, alumina and polytetrafluoroethylene. Arc voltages are measured for arcs burning inside tubes of 2, 4, 8, and 15 mm inner diameters. In addition, free-burning arcs have been investigated at the same filling pressures. The arc current was 150 A at 350 Hz throughout the study. The arc voltage is found to increase with decreasing inner diameter of the tube at atmospheric pressure. At higher filling pressures (i.e., 20, 40, and 80 bar), however, such a simple relationship is not observed. The arc temperature and radius have been calculated based on the “simple theory of free-burning arcs” and the “two-zone ablation arc model.” The calculated arc radius decreases with increasing gas pressure. Furthermore, due to increased absorption of radiation at high filling pressures, ablation is found less significant for ultrahigh-pressure nitrogen arcs compared to atmospheric pressure arcs. This is in line with the observations from optical micrographs of the inner surfaces of the tubes exposed to arcs at different filling pressures.

Calculation of hardening process parameters for locomotive parts

The existing theoretical models of heating by concentrated sources with a high energy density generally describe processes with deep penetration welding of part surfaces. The purpose of this study is to identify the factors that have a major effect on hardening of parts through heat treatment with a high-speed or pulsed scanning stationary heat source, which creates a uniform temperature field. Using methods of regression analysis, the authors derived equations for calculating the hardening depth in the proposed hardening process, the rate and time of steel cooling in a critical temperature range. The paper presents the calculated parameters of the hardening process in which parts, including wheel flanges of locomotives, are heated by a plasma arc in nitrogen. The findings can be used to reduce costs of complex experiments aimed at selecting surface heat hardening parameters to increase the service life of locomotive mechanical parts.