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This paper reports on titanium carbide synthesis in an atmospheric-pressure arc plasma reactor by exposing a stoichiometric starting mixture (Ti : C ~ 1 : 1.05) to a plasma jet. The phase composition of the synthesized TiC powder has been determined as a function of the time during which the starting mixture was exposed to a thermal plasma flow and the current (40–120 A) through the electric arc plasma source. The powders obtained under optimal conditions consist of the cubic titanium carbide phase and have a broad particle size distribution, with distinct agglomerates on the order of 50–100 μm in size. It is worth noting that the surface of the agglomerates has the form of a densified perforated crust (with a pore diameter no greater that 2 μm). [ABSTRACT FROM AUTHOR]

A 100-W class low power arcjet thruster using a hollow cathode was proposed, with the goal of reducing cathode erosion. The hollow cathode's emitter was lanthanum hexaboride expecting its excellent thermionic emission performance. The experiment used argon as a propellant and compared two different emitter lengths. The estimated emitter temperature was almost the same regardless of the emitter length, however, due to of the efficient heat exchange with the longer arc plasma region, the longer emitter provided better performance with higher discharge voltage. Additionally, the hollow cathode was compared to the conventional rod cathode, and the hollow cathode was found to have some advantages. The specific impulse of the hollow cathodes was higher than that of the rod cathode at low flow rate. The results showed that the hollow cathode is best for high specific power and high specific impulse operation. The unstable transition between low- and high-voltage modes has been observed in the rod cathode, but not in the hollow cathode configurations. Helium was put to the test as a propellant and compared to argon for simulate the future use of hydrogen as a propellant. The thrust efficiency was lower due to the high discharge voltage and significant heat loss, but the specific impulse was higher as expected. No severe recession or erosion of the emitter was observed after the test campaign, but some surface color change was seen which may affect in the long-term operation. • Arcjet using LaB 6 hollow cathode was proposed to improve cathode erosion. • Long emitter provides high efficiency due to long arc length. • High Isp at low flow rate and stable discharge compared with rod cathode. • Operable with He with higher specific impulse but lower efficiency. • No sever erosion of emitter but surface color changes were observed. [ABSTRACT FROM AUTHOR]

A novel plasma-pulsed GMAW hybrid welding (plasma-GMAW-P) process is proposed for joining 6061 aluminum and zinc-coated steel. The results show that the change in welding heat input has little effect on the microstructure of the joint and the composition of the intermetallic compounds (IMCs) but only changes the thickness of the reaction layer (increased from 5 μm to 12 μm). when the plasma arc current is 20 A and the MIG current is 80 A, the welded joint obtained has the highest tensile-shear force. With the optimal process parameters, the weld strength obtained by filling ER4043 welding wire is the highest, accounting for 65% of the tensile-shear force of the base material. The effect of the plasma arc acting on the joint properties is studied through the microstructure and a tensile-shearing test. The action position of the plasma arc plays a significant role in the Al/steel interface, which directly influences the strength of the welded joints. Regardless of the plasma-GMAW-P style used to obtain the joints, Fe-Al IMCs appear at the interface. When the plasma arc is in front of the welding direction and the GMAW-P arc is in the rear, the tensile-shear force reaches the maximum of 3322 N. [ABSTRACT FROM AUTHOR]

The object of this study was the substances that could be used to generate arc plasma. Conventional and promising plasma media were analyzed in order to identify the most universal one in terms of a set of properties for efficient energy transfer of material. It is shown that the mean-enthalpy media have a harmonious ratio of temperature and enthalpy and could provide a change in the energy state of the processed material with maximum efficiency. It is established that the most universal set of properties is demonstrated by the medium enthalpy plasma of the N-O-C-H system. The use of mixtures of air with hydrocarbons for its generation makes it possible to reach the average mass temperature of (5...7)·10³ K and change the oxidative-reducing potential of the plasma medium over a wide range. Given this, heat treatment is possible with maximum preservation of the original composition of the material. Experimental studies of plasma flows of the N-O-C-H system confirmed the presence of reducing components capable of binding oxygen to air that is sucked into the jet. On rich mixtures, the oxygen content in the jet at a distance of 100 mm does not exceed 5 %. The positive effect of combined energy input into plasma-forming substance on the process of generation and formation of plasma jet has been proven. The use of energy of different physical nature makes it possible to maintain the local energy parameters of the plasma flow during material processing. This is due to the release of additional heat as a result of the interaction of plasma and plasma components with ambient air. The use of plasma of the N-O-C-H system in surface engineering technologies could expand the range of processed materials and reduce the operating costs of the process. [ABSTRACT FROM AUTHOR]

The corrosion of steel structures in coastal areas is a major issue. Therefore, in the present study, the protection against the corrosion of structural steel is carried out by depositing 100 μm thick Al and Al-5 Mg coatings using a plasma arc thermal spray process, immersing them in 3.5 wt.% NaCl solution for 41 days (d). To deposit such metals, one of the best known processes, arc thermal spray, is frequently used, but this process has severe defects and porosity. Thus, to minimize the porosity and defects of arc thermal spray, a plasma arc thermal spray process is developed. In this process, we used normal gas to create plasma instead of argon (Ar) and nitrogen (N2) with hydrogen (H) and helium (He). Al-5 Mg alloy coating exhibited uniform and dense morphology, where it reduced more than four times the porosity compared to Al, where Mg fills the voids of the coating, resulting in greater bond adhesion and hydrophobicity. The open circuit potential (OCP) of both coatings exhibited electropositive values due to the formation of native oxide in Al, while in the case of Al-5 Mg, the coating is dense and uniform. However, after 1 d of immersion, both coatings showed activation in OCP, owing to the dissolution of splat particles from the corner where the sharp edges are present in the Al coating, while Mg preferentially dissolved in the Al-5 Mg coating and made galvanic cells. Mg is galvanically more active than Al in the Al-5 Mg coating. Due to the capacity of the corrosion products to cover the pores and defects, both coatings stabilized the OCP after 13 d of immersion. The total impedance of the Al-5 Mg coating is gradually increased and is higher than the Al, which can be attributed to the uniform and dense coating morphology where Mg dissolves and agglomerates to form globular corrosion products and deposit over the surface, thereby causing barrier protection. The defect bearing corrosion products on Al coating led to the cause having a higher corrosion rate than the Al-5 Mg coating. A total of 5 wt.% mg in the Al coating improved the corrosion rate by a rate of 1.6 times compared to the pure Al in the 3.5 wt.% NaCl solution after 41 d of immersion. [ABSTRACT FROM AUTHOR]

Keyhole welding has an advantage in high efficiency, but the narrow process window for stable keyhole is a critical issue for application. Double-layer coaxial hybrid arcing technology is developed to decouple the heat and pressure properties in an arc source; this will improve the controllability of the weld pool thermal-force state. In this research, an arcing torch, designed by embedding an outer ring tungsten into the plasma arc nozzle to form a double-layer coaxial hybrid arc, was experimentally tested for its application possibility in the keyhole welding process. From the arc image and arc pressure results, stable hybrid arcing process was successfully achieved in the torch when the outer arc current is lower than 30 A. The arc pressure/current ratio in the outer arc current is about half to that in the center plasma arc current. Applying a 10-A outer arc current, keyhole welding can be achieved at a given center arc current of 110 A, which is lower than the threshold current for keyhole welding in an 8.3-mm thick 304 stainless steel plate. In the keyhole welding process in a 4.0-mm thick 304 stainless steel plate, keyhole behavior and the resultant weld have invisible change between the welding process with the hybrid arc torch and the ordinary plasma arc torch. The experimental test results give a promising method to improve the keyhole welding process window. [ABSTRACT FROM AUTHOR]

The keyhole arc welding technique has the advantage of improving welding efficiency by utilizing a stable keyhole mode. Accurate understanding of the keyhole effect is necessary to enhance the welding quality. Due to the high temperature and strong arc force involved, the complex gas–liquid–solid interactions in the complete keyhole process need to be explored. In order to fully demonstrate open keyhole mode welding, a three-tier sandwiched model based on multiphysics and multiphase effects was developed. The top layer of the model is filled with plasma arc, which gradually fuses and penetrates through the middle metal layer. Finally, it enters the third layer, resulting in an open keyhole mode. Multiphysics phenomena due to the plasma arc are fully included in the model, and the gas–liquid–solid interactions are calculated by combining the Volume of Fluid technique and the Enthalpy-porous technique. Arc ignition and dynamic open keyhole effect are demonstrated, and an arc discharge is shown from the open keyhole exit. The arc reflection phenomenon is observed as the arc is blocked by the weld pool frontier. The electric current path varies with the welding movement, and most of the current comes from the weld pool frontier. An experiment was conducted to obtain weld pool and keyhole images, which basically agree with the calculated results. Additionally, the calculated open keyhole time and electric potential drops also coincide well with experimental data. [ABSTRACT FROM AUTHOR]

A hybrid scheme integrating the current waste heat recovery system (WHRS) for a silicon arc furnace with plasma gasification for medical waste is proposed. Combustible syngas converted from medical waste is used to drive the gas turbine for power generation, and waste heat is recovered from the raw syngas and exhaust gas from the gas turbine for auxiliary heating of steam and feed water in the WHRS. Meanwhile, the plasma gasifier can also achieve a harmless disposal of the hazardous fine silica particles generated in polysilicon production. The performance of the proposed design is investigated by energy, exergy, and economic analysis. The results indicate that after the integration, medical waste gave rise to 4.17 MW net power at an efficiency of up to 33.99%. Meanwhile, 4320 t of the silica powder can be disposed conveniently by the plasma gasifier every year, as well as 23,040 t of medical waste. The proposed design of upgrading the current WHRS to the hybrid system requires an initial investment of 18,843.65 K$ and has a short dynamic payback period of 3.94 years. Therefore, the hybrid scheme is feasible and promising for commercial application. [ABSTRACT FROM AUTHOR]

The application of direct-current plasma arc furnace technology to the problem of coal gasification is investigated using computational multiphysics models of the plasma arc inside such units. An integrated modelling workflow for the study of DC plasma arc discharges in synthesis gas atmospheres is presented. The thermodynamic and transport properties of the plasma are estimated using statistical mechanics calculations and are shown to have highly non-linear dependencies on the gas composition and temperature. A computational magnetohydrodynamic solver for electromagnetically coupled flows is developed and implemented in the OpenFOAM® framework, and the behaviour of three-dimensional transient simulations of arc formation and dynamics is studied in response to different plasma gas compositions and furnace operating conditions. To demonstrate the utility of the methods presented, practical engineering results are obtained from an ensemble of simulation results for a pilot-scale furnace design. These include the stability of the arc under different operating conditions and the dependence of voltage–current relationships on the arc length, which are relevant in understanding the industrial operability of plasma arc furnaces used for waste coal gasification. [ABSTRACT FROM AUTHOR]

In developing a wire-arc directed energy deposition process for superalloys used in high-speed flight environments, Inconel 718 was deposited using a plasma arc process and tested for its high temperature performance. The deposited material was tested in both the as deposited condition and after an age-hardening industry standard heat-treatment for this alloy. Results showed a reduced performance in both deposited conditions, with heat-treated material significantly outperforming as deposited material up to 538 °C. The difference in performance was less significant from 760 to 1000 °C, owing to an in-test aging process which increased the performance of the as deposited material. The microstructure of deposited material showed significant cracking throughout the alloy and formation of secondary phases throughout the matrix, with significantly more precipitation after heat-treating. [ABSTRACT FROM AUTHOR]

In this letter, an annular anode is designed for producing arc plasmas with a large non-equilibrium region by using a counterflow cold gas through the annular anode. The coupled mass-momentum-energy exchange processes in an argon arc plasma are studied numerically and experimentally. The counter-injection of the cold argon gas from the center of the anode leads to a steep gradient of the heavy-particle temperature due to the formation of a thin stagnation layer resulting from the interaction of the high temperature plasma with the cold gas; and in particular, a large volume non-equilibrium 'dark' plasma region is obtained above the anode surface. The results show that, with the enhancement of the convective heat transfer process in the plasma core region, the fraction of the non-equilibrium region to the whole arc plasma region reaches 92.2% where the heavy-particle temperature can be reduced significantly, e.g. ∼2300 K, while simultaneously, the electron temperature and number density are remained at high levels greater than 8000 K and 2.4 × 1020 m−3, respectively, under the operating condition studied in this letter. This research not only deepens the understanding to the non-equilibrium synergistic transport mechanisms of arc plasmas, but also provides a method for producing a large volume non-equilibrium plasma region so as to promote various existing applications, or even creating new applications in the future. [ABSTRACT FROM AUTHOR]

Methods for controlling the electron beam power in a source based on a low-pressure arc discharge with layer stabilization of the emission plasma boundary are described. The control is carried out by the method of amplitude and latitude modulation within the duration of the submillisecond beam current pulse with a time resolution of 10 μs. Two ways to control the power of the electron beam are implemented: the first one is based on changing the concentration of the emission plasma by modulating the arc discharge current and the second method uses grid control (the mode of operation of the plasma triode) at the constant discharge current. Simplified diagrams of the power supply sources of the discharge and intergrid control voltage, typical oscillograms of the main currents of the discharge system, a graph of a quick-acting power change, and a control characteristic of a plasma triode are presented. [ABSTRACT FROM AUTHOR]

A method is proposed for improving the performance properties of various materials, based on the synergy of high-intensity ion implantation and simultaneous energy impact on the surface, aimed at creating deep ionalloyed layers. Its implementation requires the use of repetitively-pulsed high-power density beams of metal and gas ions of submillisecond durations. This article presents the results of experimental studies on forming pulsed high-intensity titanium ion beams from vacuum arc plasma. The effect of the cell size of the grid electrode, shaped as a part of a sphere, on the focusing and transport efficiency is studied. A possibility of ballistic focusing of a titanium ion beam with a pulse duration from 150 to 500 μs and a power density of up to 100 kW/cm2 is experimentally shown. [ABSTRACT FROM AUTHOR]

The current study investigates the control effect of the pulsed arc discharge plasma on the impinging shock wave and boundary layer interaction (SWBLI) generated by a 14° wedge in a Mach 2.5 flow. The response characteristics of SWBLI on pulsed arc discharge actuation were illustrated, and the controlling mechanism of shock-induced flow separation under different plasma power settings was revealed. The results, which were well validated by the relative published experiment, showed that when setting the exciting power density ph as 1.0 × 1011 W/m3, the oblique shock wave obtained an obvious fluctuation, and the foot of the reattachment shock wave was partially removed. In addition, as the controlling gas bubble passed through the interaction region, the reverse flow zone was enlarged, and the separation shock wave was shifted upward. When ph was set to 4.8 × 109 W/m3, the flow separation induced by SWBLI was effectively suppressed and the size of the reverse flow zone was significantly reduced. Moreover, as the energy input was increased, the arc-induced blast wave (BW) velocity was obviously enhanced. Additionally, it is further found that the arc plasma energy deposition density in the discharge region was the determining factor for SWBLI control, even for a relatively small exciting energy input. Better drag reduction of the flow field would be achieved with the pulsed arc discharge plasma of higher power density, and a drag reduction rate of nearly 10.05% was obtained at ph = 1 × 1011 W/m3 control condition. [ABSTRACT FROM AUTHOR]

Wire arc additive manufacturing (WAAM) is a comparatively new wire-based technology used to produce complex products that cannot be made using traditional manufacturing methods. Selecting the best WAAM technique based on product specifications, manufacturability and functionality is a critical issue. In this paper, an attempt is made to evaluate different WAAM techniques using a hybrid multi-criteria decision-making technique. The objective of the proposed work is to demonstrate the weights and ranking of different WAAM techniques under the novel idea of integrated fuzzy CRITIC and fuzzy WASPAS. Gas metal arc welding (GMAW), double electrode GMAW (DE-GMAW), gas tungsten arc welding (GTAW), plasma arc welding-based WAAM (PAW-AM), and electron beam-based WAAM (EBM-AM) are considered as alternatives. Geometrical features, material supply, mechanical and thermal properties, operational characteristics, and economic challenges are considered as main criteria. Further, under each main criterion, sub-criteria are considered. The weights of the main criteria and sub-criteria are obtained by fuzzy CRITIC (criteria importance through inter-criteria correlation). With the help of these weights, the alternatives are ranked by fuzzy WASPAS (weighted aggregated sum-product assessment) for finding the most suitable technique. From the findings of this research, it is concluded that electron beam-based WAAM (EBM-AM) is preferable as per the chosen criteria type. Moreover, the consistency of the hybrid MCDM model has been verified using sensitivity analysis. [ABSTRACT FROM AUTHOR]

A gliding arc plasma source designed for high efficient ignition has been studied with the help of numerical simulation and experiments. A coupled 3D–0D approach has been proposed to model the gliding arc from ignition (the equilibrium stage) to extinguish (the non–equilibrium stage). The model takes the measured discharge morphology, voltage, current, and velocity as inputs, and has been validated by comparing the calculated temperature with experimental results from an independent group. The temporal evolution of the temperature as well as active species, and the effective penetration length of the gliding arc has been studied; the influence of the gliding arc-based plasma igniter on the ignition delay time of a premixed pentane-air gas has also been theoretically analyzed. [ABSTRACT FROM AUTHOR]

CoCrxFeMnNi (x represents the atomic percentage of Cr element, x = 20, 25, 30, and 35, denoted as Cr20, Cr25, Cr30, and Cr35 alloys) high-entropy alloy (HEA) coatings were cladded by plasma arc on the surface of 0Cr13Ni5Mo steel. The effects of Cr elements on the cavitation erosion mechanisms were studied by comparing the differences of microstructure, microhardness, cavitation erosion volume loss (CVL), cavitation erosion volume loss rate (CER), and eroded surface morphologies between the coatings. As the Cr content increased, the microhardness of the coatings increased continuously, and the microstructure transformed into fine dendrites. The microhardnesses of Cr20, Cr25, Cr30, and Cr35 were 223.9 HV, 250.5 HV, 265.2 HV, and 333.7 HV, respectively. With structural change, the slip pattern shifted from uniform distribution to distribution along the grain boundary, increasing slip resistance. Additionally, strain hardening capacity increased with reduced stacking fault energy (SFE). The resistance to cavitation erosion (CR) of the HEA increased with the increase in Cr content. The CVL of 20 h cavitation erosion of Cr35 coating was only 26.84% of that of 0Cr13Ni5Mo steel, and the peak CER was only 28.75% of that of 0Cr13Ni5Mo steel. The fracture damage mechanisms of the four HEA coatings were an obvious lamellar structure and fibrous fracture. [ABSTRACT FROM AUTHOR]

In metal additive manufacturing (AM), arc plasma is attracting attention as an alternative heat source to expensive lasers to enable the use of various metal wire materials with a high deposition efficiency. However, the stepwise material deposition and resulting limited number of degrees of freedom limit their potential for high‐throughput and large‐scale production for industrial applications. Herein, a high‐throughput metal 3D printing pen (M3DPen) strategy is proposed based on an arc plasma heat source by harnessing the surface tension of the molten metal for enabling continuous material deposition without a downward flow by gravity. The proposed approach differs from conventional arc‐based metal AM in that it controls the solidification and cooling time between interlayers of a point‐by‐point deposition path, thereby allowing for continuous metal 3D printing of freestanding and overhanging structures at once. The resulting mechanical properties and unique microstructures by continuous metal deposition that occur due to the difference in the thermal conditions of the molten metal under cooling are also investigated. This technology can be applied to a wide range of alloy systems and industrial manufacturing, thereby providing new possibilities for metal 3D printing. [ABSTRACT FROM AUTHOR]

Herein, a combination of cold rolling (CR) and annealing treatment is used to investigate the evolution of the microstructure and mechanical properties of CoFeNiMnV high‐entropy alloys (HEAs) fabricated by powder plasma arc additive manufacturing (PPA‐AM). The deposited CoFeNiMnV HEAs exhibit a face‐centered cubic (FCC) structure with a small amount of σ phase precipitation. After 50% CR, the microstructure of CoFeNiMnV HEAs is severely deformed along the rolling direction, and the grain size is obviously refined. Therefore, the hardness and strength of the alloy are significantly improved. The rolled CoFeNiMnV HEAs are annealed at 500, 700 and 900 °C, for 60 min. The results show that annealing at 500 °C has little effect on the microstructure and dislocation density of the alloy, and the alloy still maintains high strength and hardness. With increasing of annealing temperature to 700 and 900 °C, the dislocation density of the CoFeNiMnV HEAs is significantly reduced. Meanwhile the σ phase is gradually dissolved, and the recrystallized grains and annealing twins are significantly coarsened. The analysis suggests that it decreases the strength of the CoFeNiMnV HEAs, but increases the elongation. CoFeNiMnV HEAs annealed at 700 °C for 60 min after CR exhibit an excellent high strength–toughness combination. [ABSTRACT FROM AUTHOR]

The formation process and some characteristics of a high-current electron beam in dependence on pressure and working gas (argon, air, helium) filling the diode as well as on induction of an external guide magnetic field are investigated. The explosive emission is initiated with the use of arc plasma sources built into a copper disc cathode. It is shown that both the beam current and its pulse energy increase monotonically with the magnetic field induction. The beam pulse energy dependence on the gas pressure is, on the contrary, nonmonotonic. At first, the beam pulse energy increases with the pressure and then falls down due to the development of a beam-plasma discharge, which decreases both the diode impedance and the beam pulse duration. [ABSTRACT FROM AUTHOR]

Arc discharge plasma nitriding (ADPN) of stainless steel was achieved using the thermionic electrons generated from column arc discharge to ionize the working gas to form a high-energy plasma. The column arc current is a key influential factor in the ADPN technique. AISI 420 martensite stainless steel (420 SS) was nitrided at a low temperature of ~ 440 °C to improve its mechanical properties and corrosion resistance using a highly efficient low-pressure ADPN technique. The arc plasma was generated by applying arc currents ranging from 100 to 130 A. The results of arc currents on the microstructure, mechanical characteristics, tribological properties, and corrosion performance of treated layers were investigated. The results revealed that the nitrided layers are primarily composed of expanded martensite (αN), Fe4N and Fe2-3 N, and a high arc current leads to the formation of a compound layer composed of Fe2-3 N and Fe4N. The surface microhardness and wear resistance of 420 SS were greatly improved following ADPN compared with conventional plasma nitriding. The samples treated at the higher arc current have a thicker nitrided layer and a tough surface with a higher fraction of Fe2-3 N, which shows the best wear and corrosion performance. [ABSTRACT FROM AUTHOR]

This study investigated the influence of the cutting feed rate on the hardness and microstructure of copper machined using a plasma arc (PA) to examine the resulting changes and their impact on the quality of the cut surface. Various constant cutting feed rates and amperage values were used as parameters to measure the cutting performance. Pre- and post-cut hardness measurements and scanning electron microscope (SEM) images were taken. The hardness of the copper surface was the same before and after plasma arc cutting (PAC). PAC did not affect the copper's hardness or the microstructure of the thermally affected cutting zone. The copper from the cut surface was melted by the PA operation near the edge of the cutting surface with no change in the microstructure. SEM imaging of the cut confirmed this. Thus, the quality of the cutting surface was not affected. In addition, the microstructure of the copper's thermally affected cutting zone did not alter the cutting surface's quality. Hardness measurements post-cutting yielded 69.28, 71.65, 70.15, and 60.09 HB for four tests at 500 mm/min and 30 A. The lowest cutting width was 1.504 mm at 12,000 mm/min, and the surface roughness was 2.5 µm at 500 mm/min. [ABSTRACT FROM AUTHOR]

Functionally graded material (FGM) is an appropriate response to high-performance and multi-functional applications. In this research, dual-wire plasma arc welding can be used to fabricate SS 316L-Inconel 625 FGM with a composition gradient of 50 wt.% by adjusting the volume fraction of welding wire delivered to the melt pool. The phase evolution, microstructure, composition, microhardness and tensile properties of different composition regions along the building direction were analyzed. The results show that good bonding in the bi-metallic interface region and defect-free microstructure. The microstructure along the deposition direction is mainly columnar and equiaxed dendritic structure, and the grain growth direction is mainly along the deposition direction. The existence of Laves phases is proved by EDS mapping and point detection. Due to remelting, an error is existed between the actual composition distribution and the designed discrete gradient. The microhardness value decreases first, and reaching a minimum at the bi-metallic interface of the 100–50 wt.% SS 316L, and then increase gradually (157 HV-208 HV). The ultimate tensile strength, yield strength and elongation are 554.12 ± 7.44 MPa, 340.79 ± 4.13 MPa and 26.65 ± 0.27%, respectively. From the feasibility study, the dual-wire plasma arc welding provides a novel additive manufacturing process for the FGMs. [ABSTRACT FROM AUTHOR]

Hydrogen is an energy carrier with a very high energy density (>119 MJ/kg). Pure hydrogen is barely available; thus, it requires extraction from its compounds. Steam reforming and water electrolysis are commercially viable technologies for hydrogen production from water, alcohols, methane, and other hydrocarbons; however, both processes are energy-intensive. Current study aims at understanding the methane and ethanol-water mixture pathway to generate hydrogen molecules. The various intermediate species (like CH X , CH 2 O, CH 3 CHO) are generated before decomposing methane/ethanol into hydrogen radicals, which later combine to form hydrogen molecules. The study further discusses the various operating parameters involved in plasma reforming reactors. All the reactors work on the same principle, generating plasma to excite electrons for collision. The dielectric barrier discharge reactor can be operated with or without a catalyst; however, feed flow rate and discharge power are the most influencing parameters. In a pulsed plasma reactor, feed flow rate, electrode velocity, and gap are the main factors that can raise methane conversion (40–60%). While the gliding arc plasma reactor can generate up to 50% hydrogen yield at optimized values of oxygen/carbon ratio and residence time, the hydrogen yield in the microwave plasma reactor is affected by flow rate and feed concentration. Therefore, all the reactors have the potential to generate hydrogen at lower energy demand. • Hydrogen production via the methane reforming pathway is discussed. • Ethanol decomposes into intermediate species that further splits into •H radical • Various plasma reforming reactors for H 2 production are discussed. • Influencing parameters in plasma reforming are identified. • Various process parameters affecting H 2 production are reviewed. [ABSTRACT FROM AUTHOR]

Twin-wire plasma arc additive manufacturing (TW-PAAM) is an innovative process for titanium aluminide manufacture which is low in equipment cost and high in efficiency. However, as an in situ alloying process, the composition homogeneity is typically a source of concern. The present work investigates this subject by observing the element input mode at various welding wire positions with a high-speed camera system and particle tracking method. It is found that when the welding wires are in a high position, the droplet enters the molten pool from the tip of the titanium wire, and the alloy element input interval is long, resulting in the formation of bands with high aluminium content at the edge of the deposition layer. When the welding wires are close to the workpiece surface, the droplet transfer mode switches to a mixture of dual wire-bridge transfer and Ti wire-bridge transfer. The diameter and transfer interval of the droplets decrease, as well as the heterogeneity of the deposition layer. The conclusion establishes a correlation between droplet transfer mode and composition homogeneity, which is beneficial for optimizing the TW-PAAM titanium aluminide fabrication process. [ABSTRACT FROM AUTHOR]

Synthesis of high-entropy carbides (HEC) requires high temperatures that can be provided by electric arc plasma method. However, the formation temperature of a single-phase sample remains unknown. Moreover, under some temperatures multi-phase structures can emerge. In this work, we developed an approach for a controllable synthesis of HEC TiZrNbHfTaC5 based on theoretical and experimental techniques. We used Canonical Monte Carlo (CMC) simulations with the machine learning interatomic potentials to determine the temperature conditions for the formation of single-phase and multi-phase samples. In full agreement with the theory, the single-phase sample, produced with electric arc discharge, was observed at 2000 K. Below 1200 K, the sample decomposed into (Ti-Nb-Ta)C, and a mixture of (Zr-Hf-Ta)C, (Zr-Nb-Hf)C, (Zr-Nb)C, and (Zr-Ta)C. Our results demonstrate the conditions for the formation of HEC and we anticipate that our approach can pave the way towards targeted synthesis of multicomponent materials. [ABSTRACT FROM AUTHOR]

The aim of this study was to optimize the cutting parameters such as cutting speed, standoff distance, cutting current and gas pressure of the CNC plasma arc cutting process that affected the material removal rate, surface roughness and nozzle diameter change after cutting performed on AISI 1020 mild steel plate. Three levels of variation were taken to the four cutting parameters that were chosen. Twenty-seven trial experiments were carried out using L27 orthogonal array of Taguchi design. In this experimental investigation, the highest material removal rate (MRR) of 8.96 g/s, Ra surface roughness (SR) of 15.734 mm and nozzle orifice diameter (ND) of 1.4637mm were achieved, whereas the lowest obtained values of MRR, SR and ND were 2.324 g/s, 5.98 mmand 1.2114 mm, respectively. For modeling the plasma arc cutting process experimental input parameters and responses' results, a hybrid ANN-GA model was constructed. This model was used to forecast and optimize MRR, SR and ND, as well as the control factors that go with it. The results indicated that the ANN-GA model could predict the output responses with a mean square error of 1.06885e-1. During optimization, a 4-9-3 network trained with neural network of back propagation by Levenberg-Marquardt algorithm was used to have the greatest prediction capability, with optimum values of MRR, SR and ND of 7.0032 g/s, 4.2062mmand 1.3142mm, respectively. Fromthe confirmation tests, the average results of 6.9247 g/s of MRR, 4.3429 mm of SR and 1.3703mm of ND were obtained. The percentage of errors between the ANN-GA predicted optimal responses' results and the confirmatory experimental results were found 1.121%, 3.250% and 4.269% for MRR, SR and ND, respectively. [ABSTRACT FROM AUTHOR]

The plasma pyrolysis and plasma catalysis of methane coupling were performed under room temperature and atmosphere. The coupling of methane through gliding arc plasma with different H 2 /CH 4 ratios and N 2 flow rates exhibited conversion from 25% to 40% and high selectivity of acetylene above 90%. Plasma emission spectra displayed lowest I Hβ /I Hα ratio at H 2 /CH 4 ratio of 3, while I Hβ /I Hα ratio decreased with increasing N 2 feed rate from 0 to 2 L/min, which had similar variation with selectivity of acetylene. X-ray photoelectron spectra for reduced catalysts demonstrated that metallic Pd species (335.4 eV) were transferred to electron-rich Pd species (334.8eV and 334.1 eV) with increasing Pd loading and Ag/Pd ratio, corresponding to red shift of linear adsorbed CO stretching frequency from 2060 to 2068 cm−1 to 2055-2015 cm−1. Superior plasma catalytic behavior over 0.1Pd0.5Ag/Al 2 O 3 catalyst has been reached with 86.5% selectivity of ethene and 36.2% conversion of methane. • Methane coupling to ethene can achieve high yield of 30.2% through plasma catalysis. • Gliding arc plasma made high gas temperature leading to more acetylene production. • Proper AgPd catalyst exhibited great suitability for plasma catalysis process. [ABSTRACT FROM AUTHOR]

A physical model and a mathematical approach were developed to describe ponderomotive acceleration a body pushed by plasma column of high-current arc in a railgun. In contrast to the previously published studies, the arc plasma generation was considered by taking into account kinetics of heavy particle fluxes in a non-equilibrium layer near the vaporizating (ablating) rails and the phenomena of heat and mass transfer and electric sheath at rail surfaces. The self-consistent numerical analysis has been conducted for a wide range of arc currents (up to 2MA). It has been shown that the electron temperature was determined mainly by the Joule energy dissipation supporting high degree of ionization. It has been determined that the arc voltage is about 102 V. The rails temperatures are relatively low (~ 3000 K) and therefore, the electron flux emitted from the cathode manly due to thermionic emission enhanced by Schottky effect is lower than the flux of ions from the plasma, which supported the current continuity at the cathode region. The calculated velocity vs of the plasma-solid body increased with the arc current (I) showing tendency to saturation. In range of I = 0.5–2 MA the vs slightly increased from 5 × 105 to 10 × 105 cm/s when the rail length increased from 1 to 3 m respectively. The dependence of the velocity on the arc current and the calculated plasma parameters are in range of those values observed experimentally. The nature of the velocity with arc current saturation is explained by presence of the dynamic pressure resulting in predicted velocity dependence on the arc current as 4-th root. [ABSTRACT FROM AUTHOR]

The development of a material modification method based on synergy of high-intensity ion implantation and simultaneous energy impact on the surface is aimed at creating deep ion-doped layers. To implement this method, the high power density of pulsed and repetitively-pulsed beams of metal and gas ions with micro-submillisecond duration are required. The paper presents the results of numerical simulation and experimental studies on the formation of pulsed high-intensity metal ion beams from vacuum arc plasma. The ballistic focusing of heavy ions at injection currents from 0.1 to 1 A has been studied. The influence of the ion current density, accelerating voltage, and conditions for neutralizing the beam space charge on the transport and focusing of a high power density ion beam has been studied. The possibility of ballistic formation of submillisecond titanium ion beams with a pulse power density of a hundred kilowatts per square centimeter has been experimentally shown. [ABSTRACT FROM AUTHOR]

In the absence of any literature regarding the development of erosion resistance protective coatings on the aerospace engine parts using NiTi alloy, the current work has been focused on the detail investigation of the solid particle erosion resistance of the NiTi coating developed by atmospheric plasma spray technique. The coating has been prepared by considering an elemental mixture of equiatomic Ni and Ti powder as feedstock material with different plasma arc currents and primary gas flow rates. The quality of the coatings has been checked by different characterization techniques like x-ray diffraction, scanning electron microscopy and energy-dispersive spectroscopy. The defects observed from the microstructural investigation sometimes lead to more erosion and sometimes resulted in less erosion rate. The investigation of the effect of the porosity percentage on the erosion rate revealed that as the porosity percentage increases, the erosion rate increases at both 45° and 90° erodent impingement angles due to the lack in strength at the edges of the pores. Furthermore, the surface area of the roughness peaks, the stress concentration at the gap between the roughness peaks and height of the surface profile are mainly responsible for the erosion performance at both the erodent impact angles. The erosion rate is inversely proportional to the microhardness of the coatings. In addition to the above, according to the results disclosed by the erosion performance at different impingement angles, the coating is brittle in nature. The surface morphological study of the eroded coatings indicated various erosion mechanisms like plastic deformation, plowing, microcutting, lip formation, scratches, groove formation on the coatings impinged at 45° impact angle and groove formation, splat fracture, splat fragmentation, splat delamination, pit formation on the coatings impinged at 90° impingement angle. [ABSTRACT FROM AUTHOR]

In this research work, the severe double-shot peening (SDSP) and TiAlCr /AlCrSi plasma spray coating were performed on the commercial structural fabrication materials (Aluminium alloy) to improve the microstructure and surface properties. The materials were adapted to the shot peening process; compressive residual stress and microstrain were formed in the outer surface region as a grain size measurement of 25 µm. The oxygen reduction for Plasma spray TiAlCr/AlCrSi coating was implemented at the base materials; Al–Ti eutectic solid phase was directly converted into twin boundaries and Al lattice structure. Oxidation of micrographs revealed the fine grains boundaries, α′delta phase, porous titania (TiO2) surface, and lower surface roughness. Further, a higher hardness value for the oxidation sample was seen compared to base materials which were 36% augmented. Tensile results of SDSP and TiAlCr/AlCrSi coating were observed as the ultimate strength of 389 MPa and 420 MPa, 437 MPa. AlO2 surface and multiple bonding structures mainly contributed to the tensile strength of samples. Potential dynamic polarization studies were conducted on the three samples using 3.5% NaCl solution under natural environmental conditions to increase the corrosion resistance of the base materials. CrN and Cr2N did not observe on the outer surface. Further, dimples, voids, and cracks were not formed in the inner and outer surface layers. The plasma spray TiAlCr/AlCrSi coating method showed better results compared to shot peening process samples and increased the high tensile strength and elongation ratio of the fracture faces. [ABSTRACT FROM AUTHOR]

The composite Ni-Cr-Mo covering layers with excellent corrosion and wear resistance are deposited by plasma transferred arc (PTA), which can improve the service life of ships and solve the corrosion and wear problems of mechanized boats. The effects of Mo on the microstructure, hardness and corrosion resistance of covering layers were analyzed by OM, SEM, XRD, EDS, a micro hardness test, a friction test and a corrosion-resistance test. The results show that the structure of covering layers change and the austenite precipitates become granular with an increase of Mo content. In addition, the corrosion and wear resistance of covering layers are improved and the sample with 5% content of Mo has the best wear and corrosion resistance. [ABSTRACT FROM AUTHOR]

This work studied the sliding wear performance of TiAl-based nitride coatings synthesized on austempered ductile iron (ADI) by cathodic arc deposition (CAD) and plasma-based ion implantation and deposition (PBIID). Monolayer CAD TiAlN films and bilayer CAD and PBIID TiAl/TiAlN films deposited on an experimental device were analyzed and benchmarked against a commercial bilayer CAD film. Sliding wear was evaluated in a pin–on–disc tribometer. Two test conditions were employed, one intended to prevent damage (low load, short distance) and another intended to promote damage (higher load, longer distance). Regarding low load tests, all coated samples showed friction coefficients of 0.40–0.45 and negligible wear. Regarding high load tests, all coated variants exhibited lower or equal disc and pin wear rates with respect to uncoated ADI. In addition, coated samples displayed steady-state friction coefficients between 0.2 and 0.6 while uncoated ADI steady-state coefficients between 0.6 and 0.85. [ABSTRACT FROM AUTHOR]

The design and some characteristics of a source of radially converging low-energy (5–25 keV) high-current electron beams of microsecond pulse duration, which is aimed at surface modification of cylindrical parts and samples, are presented. The cathode unit of the source is a duralumin ring with an 8-cm inner diameter in which which 18 resistively decoupled arc plasma sources are built-in. The operability of the source electron gun in the vacuum-diode (with a residual-gas pressure of ~0.013 Pa) and gas-filled-diode modes at pressures of 0.05–0.09 Pa has been demonstrated. The beam energy density on the 1-cm-diameter anode is sufficient for surface melting of copper (the threshold of pulsed copper melting is 5–5.5 J/cm2 at a pulse duration of 2–3 µs) at a 17-kV charging voltage of the high-voltage pulse generator that powers the electron gun. [ABSTRACT FROM AUTHOR]

Atmospheric plasma spraying is an up-to-date and systematically developed technology. One of the crucial ideas is injecting the sprayed feedstock powder internally or externally into the plasma arc. The spraying parameters affect the microstructure and properties of the coating, which is decisive for the operation performance of coatings and specific machine components. This paper investigates the effect of atmospheric plasma spraying parameters, namely the feedstock injection mode and the spray distance, on cavitation erosion and wet environment tribological behaviour of Al2O3-13% TiO2 coatings. The internal and external injection spraying mode, constant spray velocity (500 mm/s), and two spray distances to the substrate, namely 80 mm and 100 mm, were employed. The microstructure, porosity and hardness of the deposited coatings were studied. Cavitation erosion resistance was estimated using the ASTM G32 method. The sliding wear resistance has been estimated in the distilled water environment using the ball-on-disc apparatus. The results indicate that the internal injection supports the cavitation erosion resistance and the aquatic sliding wear. The coating fabricated with the 80 mm spray distance using the internal method is characterized by the smallest wear and the highest anti-erosion performance. A shorter spraying distance indicates greater coatings uniformity, while the increasing distance reduces the hardness and porosity, which are beneficial for the performance of the coatings. The main wet sliding wear mechanism has been fatigue-induced material detachment, while the cavitation erosion mechanism depends on the brittle fracture resulting in material detachment and pitting. [ABSTRACT FROM AUTHOR]

Based on multiphase flow and volume of fluid (VOF) methods, a 3D transient numerical model coupling arc, droplet, and molten pool for underwater wet self-shielded flux-cored arc welding (FCAW) was firstly developed. Multiple coupled physical fields including the temperature, velocity, and electromagnetic fields were numerically calculated. The simulation results indicate that the arc is always distributed at the bottom of the droplet and subject to it, and the temperature difference of the arc in a metal transfer period may reach up to 10,000 K. Meanwhile, the temperature of the liquid metal varies most significantly before and after the droplet necking, and the flow field of the droplet displays alternating patterns of convection and vortex, with the flow velocity varying from 0.3 to 1.4 m/s. After the droplet transferring into the molten pool, the liquid metal diffuses around firstly, and then flows back to the center due to the electromagnetic force and the central concave deformation. Besides, it is also found that as the welding goes on, the melt width does not increase constantly, which might even shrink in particular stage as a result of the cooling effect of surrounding environment and the metal backflow. In terms of the molten pool deformation, the results show that the latter droplet can bring a larger transient concave deformation than the former, while it does not accumulate to the stable deformation. In order to verify the reliability of the numerical model, underwater welding experiments and high-speed photography were carried out, the simulated arc and droplet are in good agreement with the experimental ones, and the molten pool morphologies also fit well, with a slight error of 0.4 mm in the melt width and 0.3 mm in the melt penetration. [ABSTRACT FROM AUTHOR]

The formation of pulsed and repetitively-pulsed high-intensity metal ion beams from vacuum arc plasma is numerically simulated and experimentally studied. The numerical simulation is performed using the KARAT code. The ballistic focusing of heavy ions at injection currents of 0.1–1 A is investigated. The influence of the ion current density, the accelerating voltage, and the conditions for neutralizing the space charge of a beam on the transport and focusing of a high-power-density ion beam has been studied. The conditions of appearance of a virtual anode are determined and studied. Multiple appearance and disappearance of a virtual anode are shown to occur at a long ion beam formation time and a low residual atmosphere pressure. The possibility of ballistic formation of submillisecond droplet-free titanium ion beams with a pulse power density of several hundreds of kilowatts per square centimeter has been experimentally shown. [ABSTRACT FROM AUTHOR]

In terms of the unified model of low-current arc discharge, which describes the processes occurring in the gas-discharge gap and in the electrodes, numerical calculations have been carried out to study the evaporation of carbon atoms and molecules from graphite electrodes into a nonequilibrium helium arc plasma. For different values of discharge current density, the distributions of atomic and molecular carbon and their ions are presented. [ABSTRACT FROM AUTHOR]

The control of Fe dilution and carbide dissolution plays a vital role on the performance of metal matrix composite hardfacings. In this paper, the NiCrBSi–WC composite hardfacing is deposited on 304 austenitic stainless steel by plasma transferred arc hardfacing at 120 A (specimen 1) and 140 A (specimen 2) transferred arc current values to obtain different levels of Fe dilution and W dissolution for comparative investigations. The Fe dilution examined by scanning electron microscopy for specimen 1 was 24.54% and for specimen 2 was 33.09%. The microstructural investigations revealed higher W dissolution for specimen 2 due to higher heat input which led to significant reduction in the amount of WC and W2C hard phases. The slurry abrasive wear test performed as per ASTM G105 showed two times reduction in abrasive wear resistance of specimen 2 as compared to specimen 1. The significant reduction in the performance of specimen 2 is mainly due to higher Fe dilution and higher W dissolution caused due to higher heat input. Hence, selection of appropriate process parameters is vital to control Fe dilution and carbide dissolution in order to achieve superior performance of composite hardfacings. [ABSTRACT FROM AUTHOR]

In this paper, physicochemical properties of pure Y2O3 and samarium (Sm)-doped Y2O3 transparent ceramics obtained via arc plasma melting are presented. Yttria powder with a selected molar fraction of Sm was first synthesized by a solid-state reaction method. High transparent yttria ceramics were obtained by arc plasma melting from both the pure and Sm oxide-doped powders. The morphological, chemical and physical properties were investigated by X-ray diffraction and scanning electron microscopy. The optical band gap was calculated from the absorption spectra so as to understand the electronic band structure of the studied materials. Samples indicate a series of luminescence bands in the visible region after excitation by laser light in the range from 210 to 250 nm. Magneto-optical measurements were carried out in the 300–800 nm range at room temperature. It can be seen that a maximum Verdet constant ca. 24.81 deg/T cm was observed for 405 nm and this value decreases with increasing wavelength. The potential usefulness of the polycrystalline material dedicated to optics devices is presented. [ABSTRACT FROM AUTHOR]

In this study, Al, Cu, Ni, Fe and Cr powders with equivalent molar ratio were taken and mechanically ball milled. Ball-milled AlCuNiFeCr was coated on the cleaned degreased Inconel-718 base material. Plasma Transferred Arc (PTA) method was adopted to get alloyed the coated particles on the base material. Phase formation, structural, elemental distribution in the alloyed region, enhancement of microhardness, wear behavior and wear mechanism of surface-modified Inconel-718 material were investigated. Result showed that the PTA treated sample possessed more BCC phases and large value of lattice distortion compared to the ball-milled powder. The top of the alloyed region mainly contained equiaxed crystals, inter-connected columnar dendrites, isolated inter-dendrites, secondary dendrite arm structure and Widmanstatten structure. The dendrites in the near interface region of the PTA alloyed region were gradually refined, became long and thin strips. The microhardness value of substrate, interface and alloyed surfaces were 348 ± 17.52 HV0.2, 643 ± 32.92 HV0.2 and 881 ± 44.64 HV0.2, respectively. The specific wear rate of PTA alloyed coatings was 0.0531 × 10–3 mm3/Nm which was less than that of Inconel-718 substrate (0.1711 ×10–3 mm3/Nm). The contact of the pin to the disc surface increased with the increase of the applied load from 40 N to 60 N. The COF of treated samples and Inconel-718 substrate at 40 N applied load with 1 m/s velocity were 0.28 and 0.46, respectively. Similarly, The COF at 60 N applied load with 0.8 m/s velocity were 0.42 and 0.81, respectively. Lower surface roughness was noticed on the treated worn-out samples due to less wear rate compared to the substrate material. [ABSTRACT FROM AUTHOR]

• A numerical model is established for rotating laser hybrid fillet welding with He-Ar shielding gas compositions. • Effects of rotating laser and He-Ar shielding gas compositions on arc physical properties are investigated. • With the He content increases, the arc temperature and distribution are more concentrated, the arc flow velocity and pressure decrease. • He-Ar shielding gas mixtures increase the arc heat flux density, suppress the shielding effect of laser-induced plume, and improve the weld penetration. To understand the influence mechanism of He-Ar shielding gas composition on arc physical properties in laser + GMAW hybrid welding, this study establishes an arc numerical analysis model in rotating laser + GMAW hybrid fillet welding by considering the geometric feature of joint configuration and the physical parameters of He-Ar shielding gas. The effects of He-Ar shielding gas mixtures in different ratios on arc plasma temperature, velocity, and pressure are investigated, respectively. The results show that with the increasing He content in the shielding gas, the overall shape of arc is compressed, the peak temperature decreases, the arc temperature distribution range is more concentrated, which is beneficial to increasing the weld penetration depth. The arc plasma flow velocity increases with the He content increases, but the plasma flow pattern becomes disordered when the He content reaches 50 %, which is not conducive to the stability of arc. The arc pressure value and the high-pressure distribution region near the workpiece surface increase significantly with an increasing He content ratio, due to the contraction effect of high He content mixed shielding gas on the arc. [ABSTRACT FROM AUTHOR]

• A 3D multiphase flow model has been established for the plasma transferred arc (PTA) cladding of composite powder (NiCrBSi/50 wt% WC) on a 40CrNi2MoA substrate. • The multiphase flow model simulates both the discrete phase (WC particles) and continuous phase in the melt pool, including the behaviors of heat transfer and particle distribution. • The influences of welding currents and preheating temperatures on the temperature field, the dimensions, and the HAZ depth of the cladding layers have been predicted by the model. • This is the first work of modeling 3D multiphase flow in PTA cladding process of particle-reinforced metal matrix composite (MMCs). In this paper, a 3D multiphase flow model has been established for the plasma transferred arc (PTA) cladding of composite powder (NiCrBSi/50 wt% WC) on a 40CrNi2MoA substrate. The multiphase flow model simulates both the discrete phase (WC particles) and continuous phase in the melt pool, including the behaviors of heat transfer and particle distribution. The buoyancy, arc pressure, surface tension, and electromagnetic force are calculated. The model is then used to predict the influences of welding currents and preheating temperatures on the depth of heat-affected zone (HAZ), the temperature field, and the dimensions of the cladding layers. To validate this model, the dimensions and the HAZ depth are analyzed and compared to experimental data. The results show that the dimensions and HAZ depth obtained by the model simulation are in good agreement with the experiment. The HAZ depth, the melt pool length, and the dimensions of cladding layer would increase with the increasing welding current or preheating temperature. Driven by the inward convection in the melt pool, WC particles tend to distribute around the center line of cladding layers. This is the first work of modeling 3D multiphase flow in PTA cladding process of particle-reinforced metal matrix composite (MMCs). The work can provide theoretical guidance for adjusting process parameters to control HAZ depth and cladding quality in actual production. [ABSTRACT FROM AUTHOR]

Plasma beam polishing has emerged as an innovative alternative to conventional metal finishing techniques. However, the precision machining ability of plasma arc encounters challenges due to the formation of surface undulations, while previous research has predominantly focused on parameter adjustments. In this paper, the feasibility of optimizing the plasma beam polishing process was validated through magnetic field regulation, as the surface topography and subsurface structure were obviously flattened. Given this, a micro plasma arc model under inhomogeneous axial magnetic field was established to explore the regulating mechanisms of the external axial magnetic field on the flow and heat transfer behavior of the plasma arc. Through this model, the plasma characteristics (magnetic induction intensity, electric potential, arc current, Lorentz force, plasma velocity and electron temperature) were comprehensively discussed. The results indicate that the external shape of the plasma arc is determined by the self-induced magnetic field, while the externally applied axial magnetic field significantly influences the internal flow of the plasma arc. The axial and radial magnetic fields generated by the excitation coil can induce circumferential rotation by dragging the plasma arc with Lorentz force, creating a more suitable energy beam for the polishing process. To verify the model, the arc temperature was measured using spectroscopic diagnostics, and the arc shape was captured using a high-speed camera, both of which were basically consistent with the simulation results. [Display omitted] • A method for optimizing the plasma beam metal polishing process is proposed. • A model of plasma beam under inhomogeneous axial magnetic field is established. • Factors affecting flow and heat behavior are studied to improve polishing ability. • Predicted arc temperature and shape are consistent with experimental measurements. [ABSTRACT FROM AUTHOR]

[Display omitted] • Arc discharge plasma nitriding (ADPN) demonstrated high nitriding kinetics of H13 steel. • ADPN treatment enhanced the corrosion resistance against molten Al-Si and tribological performance of H13 steel effectively. • A passivation layer that ultimately blocks the diffusion of Al-Si was observed in H13 steel after molten Al-Si corrosion. • An attempt was made to understand the molten Al-Si corrosion behavior of H13 steel before and after ADPN treatment. AISI H13 steels were nitrided via arc discharge plasma nitriding (ADPN) with various arc currents (55, 70, 85, and 100 A) at 400 °C. The surface microhardness, wear resistance, and molten Al-Si corrosion resistance of nitrided H13 steel exhibited significant enhancements. The surface microhardness and wear resistance of nitrided H13 steel were significantly improved due to the lubricity property of the ɛ-Fe 3 N phase formed on the surface and the solid solution strengthening of the α N. Meanwhile, the nitrided layer led to a change in the corrosion mechanism from dissolution to pitting. Compressive internal stresses in the nitrided layer inhibited crack formation and promoted passivation layer formation. The high-efficiency ADPN process not only yields a wear-resistant surface but also provides a potential solution for improving the corrosion resistance against molten alloys. [ABSTRACT FROM AUTHOR]

• Effects of high-frequency arc plasma energy deposition (APED) on shock wave interactions induced by blunt-headed protuberance on a flat plate were experimentally investigated by time-resolved schlieren. • The visualization results reveal that the pulsation of the separation shock was also affected by average discharge power, while the pulsation of boundary layer and shear layer was linked to both the discharge power and frequency. • The control of the thermal bubble structures on STBLI was very effective in terms of reducing the intensity of the low-frequency separation shock, and augmenting the high frequency component in the boundary layer. This paper presents experimental results of flow control method using plasma energy deposition on shock wave interactions induced by blunt-headed protuberance on a flat plate at Mach 2.0. Upstream of the leading edge of the protuberance, plasma energy deposition was generated by high-frequency pulsed discharge at three streamwise locations on the flat plate. High-speed Schlieren technique was utilized to investigate the unsteadiness characteristics of shock wave/turbulent boundary layer interaction (STBLI). The visualization results reveal that thermal bubble structures formed by the pulsed discharge could attenuate the separation shock continuously, resulting in a 12.8% decrease in the maximum pressure in the interaction wall. Experimental findings disclosed the dependency of this mitigation efficacy on the average discharge power. The pulsation of the separation shock was also affected by average discharge power, while the pulsation of boundary layer and shear layer was linked to both the discharge power and frequency. The numerical results predicted flow topology under control well with experiment results, low-density plasma layer was formed by high-frequency discharge, which weakening the separation shock substantially, the "λ" shock intensity was also decreased. The flow field of numerical simulation and experiments are in good agreement. Additionally, the control of the thermal bubble structures on STBLI was very effective in terms of reducing the motion and weakening the intensity of the low-frequency separation shock, and augmenting the high frequency component in the turbulent boundary layer and shear layer. [ABSTRACT FROM AUTHOR]