Microstructures and properties of the nitrided layers fabricated on titanium substrate by direct current nitrogen arc melting technique

The nitrided layers mainly containing TiN dendrites were fabricated by direct current nitrogen arc melting method. The test results show that the layers are harder and more resistant to wear than the titanium substrate. Arc traveling speeds and arc currents have an effect on both the microstructures and the properties of the layers. Decreasing the arc traveling speed or increasing the arc current can obviously enhance the hardness and the wear resistance of the nitrided layers.

Numerical Simulation of Low Current Vacuum Arc Supersonic Flow

Based on a two-dimensional axisymmetric magneto-hydrodynamic （MHD） model, low current vacuum arc （LCVA） characteristics are studied. The influence of cathode process under different axial magnetic fields and different anode radii on LCVA characteristics is also simulated. The results show that the influence of both cathode process and anode radii on LCVA is significant. The sign of anode sheath potentials can change from negative to positive with the decrease of anode radii. The simulation results are in part verified by experimental results. Especially, as the effect of ion kinetic energy is considered, ion temperature is improved significantly; which is in agreement with experimental results.

Influence of arc current and pressure on non-chemical equilibrium air arc behavior

The influence of arc current and pressure on the non-chemical equilibrium （non-CE） air arc behavior of a nozzle structure was investigated based on the self-consistent non-chemical equilibrium model. The arc behavior during both the arc burning and arc decay phases were discussed at different currents and different pressures. We also devised the concept of a non- equilibrium parameter for a better understanding of non-CE effects. During the arc burning phase, the increasing current leads to a decrease of the non-equilibrium parameter of the particles in the arc core, while the increasing pressure leads to an increase of the non-equilibrium parameter of the particles in the arc core. During the arc decay phase, the non-CE effect will decrease by increasing the arc burning current and the nozzle pressure. Three factors together-- convection, diffusion and chemical reactions--influence non-CE behavior.

The microstructural characterization of the nitrided layers prepared by direct current nitrogen arc

The characteristics of nitrided layers prepared on commercially pure titanium substrates by direct current nitrogen arc are presented by scanning electron microscopy （SEM） and transmission electron microscopy （TEM） micrographs as well as X-ray diffraction （ XRD ）. The titanium nitride （ TiN ） dendrites were fully developed with interconnected cellular morphologies at the top surface but grew almost perpendicular to the integrace with coarser arms in the middle area. Also less TiN was found near the interface. The energy inputs had an obvious effect on the microstructures and the hardness of the nitrided layers. The maximum micro-hardness was 2 500 HV at the top surface which was over 9 times higher than that of the substrate.

Influence of Jet Angle and Ion Density of Cathode Side on Low Current Vacuum Arc Characteristics

In this study, the influence of the initial jet angles （IJAs） and ion number densities （INDs） at the cathode side on the low current vacuum arc （LCVA） characteristics is simulated and analysed. The results show that the ion temperature, electron temperature, ion number density, axial current density and plasma pressure all decrease with the increase of the cathode IJAs. It is also shown that LCVA can cause a current constriction for lower cathode IND, and the anode sheath potential is more nonuniform, which is mainly related to the nonuniform distribution of the axial current density at the anode side.

Parameter Analysis for Arc Snubber of EAST Neutral Beam Injector

According to the B-H curve and structural dimensions of the snubber by the Fink- Baker Method, the inductive voltage and the eddy current of any core tape with the thickness of the saturated regions are derived when the accelerator breakdown occurs. Using the Ampere＇s law, in each core tape, the eddy current of the core lamination is equal to the arc current, and the relation of the thickness of the saturated regions for different laminations can be deduced. The total equivalent resistance of the snubber can be obtained. The transient eddy current model based on the stray capacitance and the equivalent resistance is analyzed, and the solving process is given in detail. The exponential time constant and the arc current are obtained. Then, the maximum width of the lamination and the minimum thickness of the core tape are determined. The experimental time constant of the eddy current obtained, with or without the bias current, is approximately the same as that by the analytical method, which proves the accuracy of the adopted assumptions and the analysis method.

A Design Model of Core Snubber for EAST NBI

A transformer type iron core snubber, as a protective device against the stray capacitance during the breakdown in EAST, is analyzed in detail. Three kinds of topology are presented. Then with the analysis for equivalent circuit, the ranges of three key parameters, i.e., secondary side resistance, leakage inductance and snubber inductance, are determined. By con- sidering the saturation of the magnetic material, a design principle is Mso presented. A nearly 1：10 core snubber is tested. It is proved that a high permeability core with secondary resistor can restrain the discharge current effectively.

Influence of Plasma Temperature on the Concentration of NO Produced by Pulsed Arc Discharge

This study conducted experiments on producing inhaled medical nitric oxide （iNO） by pulsed arc discharge in dry and clean air under different discharge current. The concentration of NO and NO2 produced by air discharge, as well as the change of the ratio of NO2/NO under different discharge current were investigated. Through the analysis of plasma emission spectrum, the relationship between discharge current and arc plasma temperature was studied. The results indicate that, as discharge current increases, the arc plasma temperature increases, which then leads to the increase of NO concentration, the decrease of NO2 concentration, and the rapid decrease of the ratio of NO2/NO. When the plasma temperature is 9000 K, the ratio of NO2/NO is approximately 60%, while when the plasma temperature varies between 10550 K and 11300 K, the NO2/NO ratio is within the range of 4.2% to 4.6%.

Non-Intrusive Magneto-Optic Detecting System for Investigations of Air Switching Arcs

In current investigations of electric arc plasmas, experiments based on modern testing technology play an important role. To enrich the testing methods and contribute to the understanding and grasping of the inherent mechanism of air switching arcs, in this paper, a nonintrusive detecting system is described that combines the magneto-optic imaging（MOI） technique with the solution to inverse electromagnetic problems. The detecting system works in a sequence of main steps as follows： MOI of the variation of the arc flux density over a plane, magnetic field information extracted from the magneto-optic（MO） images, arc current density distribution and spatial pattern reconstruction by inverting the resulting field data. Correspondingly, in the system, an MOI set-up is designed based on the Faraday effect and the polarization properties of light, and an intelligent inversion algorithm is proposed that involves simulated annealing（SA）.Experiments were carried out for high current（2 kA RMS） discharge cases in a typical low-voltage switchgear. The results show that the MO detection system possesses the advantages of visualization, high resolution and response, and electrical insulation, which provides a novel diagnostics tool for further studies of the arc.

APPLICATION OF ARTIFICIAL NEURAL NETWORK MODELING TO PLASMA ARC WELDING OF ALUMINUM ALLOYS

By using alternating current plasma arc welding,the influences were studied of such parameters as welding curent,arc voltage,welding speed,wire feed rate,and magnitude of ion gas flow on front melting width,wdle reinforcement,and back melting width of LF6 aluminum alloy.Model of the formation of welding seam in alternating current plasma arc welding of aluminum was set up with the method of artificial neural neural network - BP algorithm. Qyakuty of formation was consequently predicted and evaluated.The experimental result shows that,compared with other modeling methods,artificial network model can be used to more accurately predict formation of weld,and to guide the production practice.

Analysis and Application of the Series Core Snubber

The transformer core snubber （CS）, as one of the most important components in the EAST （experimental advanced superconducting tokamak） NBI （neutral beam injector） system, is designed to limit grid damage and protect the ion source during periods of electrical breakdowns. A transformer core snubber is analyzed in detail in this paper. Several kinds of soft magnetic cores are presented and compared. With analysis and experiment on the basic characteristics of the cores, the most suitable materials are suggested. The circuit simulation code is established which could simulate faulty conditions with concentrated and distributed CS concepts. Based on the above work, an ion source CS is developed with series type of distributed topology. The CS has been subjected to experimental validation at 80 kV with a peak short-current of approximately 400 A in a real NBI system, which proves the accuracy of the adopted assumptions and the analysis method.

Design and characteristics of a new type laminar plasma torch for materials processing

Laminar plasma jet(LPJ)generated by laminar plasma torch(LPT)has a favorable temperature and velocity distribution.Thus,it is superior to the turbulent plasma jet in material processing.However,most of the reported LPTs usually operate at a relatively low output power with a relatively low arc voltage and thermal efficiency,which limits its capabilities.In this context,this paper attempts to design a new type of high-power LPT with a relatively low arc current and a high thermal efficiency.In the first section,the design principle of the main components is studied and discussed in detail,and a new high-power LPT is proposed.Then,the experimental characteristics of the proposed high-power LPT are examined.Experimental results reveal the following characteristics of the proposed LPT.(1)The max jet length of the proposed LPT reaches at 540 mm.(2)Its mean arc voltage is higher than 290 V when the LPT works with arc currents lower than 200 A.leading to an output power greater than 50 kW.(3)The mean thermal efficiency is higher than 509f.Lastly,the proposed LPT has been applied to spheroidize the aluminum oxide powers.The experiment results for the production of spherical powders show that the proposed LPT hits a good characteristic for material processing.

Research of Arc Chamber Optimization Techniques Based on Flow Field and Arc Joint Simulation

The preliminary design of an arc chamber in the 550 kV SF6 circuit breaker was proposed in accordance with the technicai requirements and design experience. The structural optimization was carried out according to the no-load flow field simulation results and verified by no-load pressure measurement. Based on load simulation results such as temperature field variation at the arc area and the tendency of post arc current under different recovery voltage, the second optimal design was completed and its correctness was certificated by a breaking test. Results demonstrate that the interrupting capacity of an arc chamber can be evaluated by the comparison of the gas medium recovery speed and post arc current growth rate.

Analysis and Design of ITER 1 MV Core Snubber

The core snubber, as a passive protection device, can suppress arc current and absorb stored energy in stray capacitance during the electrical breakdown in accelerating electrodes of ITER NBI. In order to design the core snubber of ITER, the control parameters of the arc peak current have been firstly analyzed by the Fink-Baker-Owren （FBO） method, which are used for designing the DIIID 100 kV snubber. The B-H curve can be derived from the measured voltage and current waveforms, and the hysteresis loss of the core snubber can be derived using the revised parallelogram method. The core snubber can be a simplified representation as an equivalent parallel resistance and inductance, which has been neglected by the FBO method. A simulation code including the parallel equivalent resistance and inductance has been set up. The simulation and experiments result in dramatically large arc shorting currents due to the parallel inductance effect. The case shows that the core snubber utilizing the FBO method gives more compact design.

Mechanical and corrosion properties of 445J2 ultra pure ferritic stainless steel joint

The microstracture, mechanical and corrosion resistance properties of 445J2 ultra pure ferritic stainless steel thin plate joints conducted by the pulsed current gas tungsten arc welding （PCGTAW） were discussed in this paper. In order to avoid weld defects, the appropriate welding process was adjusted. The joints were subjected to optical microscopy, transverse static tensile, plastic deformation, intergranular corrosion and electrochemistry corrosion tests. The results indicated that the weld zone （WZ） is characterized with columnar grains and equiaxed grains and the heat-affected zone （HAZ） shows coarse ferrite grains due to the rapid solidification of thin plate welding. The PCGTAW joint exhibited acceptable mechanical properties and equivalent corrosion resistance properties as the base metal.

Analysis of Effects of the Arc Voltage on Arc Discharges in a Cathode Ion Source of Neutral Beam Injector

A hot cathode bucket ion source is used for the EAST（experimental advanced superconducting tokamak）neutral beam injector.The thermal electrons emitted from the surface of the cathode are extracted and accelerated by the electric field formed by the arc voltage,which is applied between the arc chamber of the ion source and the cathode.This paper analyzes the effects of arc voltage on the arc discharge in a hot cathode high current ion source.

Improvement of Microstructure and Mechanical Behavior of Gas Tungsten Arc Weldments of Alloy C-276 by Current Pulsing

Superalloy C-276 is known to be prone to hot cracking during fusion welding by Gas Tungsten Arc method. Microsegregation occurring during cooling of fusion zone with consequent appearance of topologically close-packed phases P and IX has been held responsible for the observed hot cracking. The present work investigated the possibility of suppressing the microsegregation in weldments by resorting to current pulse. Weldments were made by continuous current gas tungsten arc welding and pulsed current gas tungsten arc welding using ERNiCrMo-4 filler wire. The weld joints were studied with respect to microstructure, microsegregation, and mechanical properties. Optical microscopy and scanning electron microscopy were employed to study the microstructure. Energy-Dispersive X-ray Spectroscopy was carried out to evaluate the extent of microsegregation. Tensile testing was carried out to determine the strength and ductility. The results show that the joints fabricated with pulsed current gave rise to narrower welds with practically no heat affected zone, a refined microstructure in the fusion zone, reduced microsegregation, and superior combination of mechanical properties.

Effect of Autogenous Arc Welding Processes on Tensile and Impact Properties of Ferritic Stainless Steel Joints

The effect of autogeneous arc welding processes on tensile and impact properties of ferritic stainless steel conformed to AISI 409M grade is studied. Rolled plates of 4 mm thickness have been used as the base material for preparing single pass butt welded joints. Tensile and impact properties, microhardness, microstructure, and fracture surface morphology of continuous current gas tungsten arc welding （CCGTAW）, pulsed current gas tungsten arc welding （PCGTAW）, and plasma arc welding （PAW） joints are evaluated and the results are compared. It is found that the PAW joints of ferritic stainless steel show superior tensile and impact properties when compared with CCG-TAW and PCGTAW joints, and this is mainly due to lower heat input, finer fusion zone grain diameter, and higher fusion zone hardness.

Influence of Filler Metals in the Control of Deleterious Phases During the Multi-pass Welding of Inconel 718 Plates

The present study reported the effect of filler metals on the microstructure and mechanical properties of pulsed current gas tungsten arc-welded Inconel 718 plates. Two different filler metals such as ERNiCr-3 and ERNiCrMo-4 were employed for welding Inconel 718. The primary objective of this study is to suppress or eradicate the deleterious phase such as Laves or δ （delta） which is considered to be detrimental to the weld properties. Microstructure examination corroborated the presence of unmixed zone at the HAZ for both the weldments. Tensile test trials envisaged that ERNiCrMo-4 weldments offered better tensile properties compared to ERNiCr-3 weldments, whereas the impact toughness was found to be better for ERNiCr-3 weldments. Line mapping analysis was carried out to study the elemental migration across the weldments. The structure-property relationships of the weldments were arrived at using the combined tech- niques of optical and scanning electron microscopy. Optical and SEM/EDAX analysis showed that there is no prominent occurrence of deleterious phases at the weld zone on employing these filler metals.