Direct Arc Research Articles

Insight into phase stability and thermoelectric properties of semiconducting iron silicides with manganese substitution: β-Fe1−xMnxSi2 (0≤x≤0.05)

Metal-doped iron silicides (β-FeSi2) are promising thermoelectric materials for high-temperature applications. However, the addition of metal dopants usually causes the formation of secondary metallic phases, resulting in the degradation of thermopower. Here we report the stability of semiconducting β-phase (higher than 95 %) of Mn-doped β-FeSi2 obtained at Mn concentration from 1 % to 5 %, where the samples were prepared through direct arc melting and heat treatment process. The carrier density remarkably increases with Mn content, but the mobility decreases. The electrical resistivity significantly decreases with Mn content. The Seebeck coefficient of Mn-doped samples is improved and stable at high-temperature regions because of the reduction of the bipolar effect and β-phase stability. The thermal conductivity slightly increases with Mn. As a result, the maximum thermoelectric power factor PF = 970 μWm−1K−2 and dimensionless figure of merit ZT = 0.12 at 800 K are obtained in a 3 % Mn-doped sample. The stability of β-phase and the improved carrier density are the origins of enhanced thermoelectric properties, where the Seebeck coefficient is improved, and the electrical resistivity is reduced. Our study provides insight into the importance of phase stability for enhancing thermoelectric transport in Mn-doped β-FeSi2.

Two-temperature modeling of lamellar cathode arc

A three-dimensional, two-temperature (2T) model of a lamellar cathode arc is constructed, drawing upon the conservation equations for mass, momentum, electron energy, and heavy particle energy, in addition to Maxwell’s equations. The model aims to elucidate how the physical properties of electrons and heavy particles affect heat transfer and fluid flow in a lamellar cathode arc. This is achieved by solving and comparing the fields of electron temperature, heavy particle temperature, fluid flow, current density, and Lorentz force distribution under varying welding currents. The results show that the guiding effect of the lamellar cathode on current density, the inertial drag effect of moving arc, and the attraction effect of Lorentz force at the lamellar cathode tip primarily govern the distribution of the arc’s physical fields. The guiding effect localizes the current density to the front end of the lamellar cathode, particularly where the discharge gap is minimal. Both the inertial drag effect and the attraction effect of Lorentz force direct arc flow toward its periphery. Under the influence of the aforementioned factors, the physical fields of the lamellar cathode arc undergo expansion and shift counter to the arc’s direction of motion. A reduction in welding current substantially weakens the guiding effect, causing the arc’s physical fields to deviate further in the direction opposite to the arc motion. In comparison with a cylindrical cathode arc, the physical fields of the lamellar cathode arc are markedly expanded, leading to a reduction in current density, electron temperature, heavy particle temperature, cathode jet flow velocity, and Lorentz force.

Structure relations with transport properties in p-type thermoelectric materials: Iron silicides

Understanding the structure and its relations with the transport properties is important for designing a good thermoelectric (TE) material. In this work, we investigate the relationship between those properties of the low-cost and eco-friendly materials, β-Fe1-xMnxSi2 (0≤x≤0.10), prepared by direct arc melting and heat treatment process. The metallic phases (tetragonal α-Fe2Si5 and cubic ε-FeSi) are transformed into the semiconductor phase (orthorhombic β-FeSi2) through heat treatment. The amount of β-FeSi2 significantly decreases at x ≥ 0.09. Mn atoms act as an acceptor and improve the carrier density (nH of holes) but decrease the mobility (μH). By substituting Mn to β-FeSi2, the Seebeck coefficient (S) is more uniform at high temperatures and the electrical resistivity (ρ) effectively decreases, leading to an improvement in the power factor. The thermal conductivity (κ) slightly increases with Mn doping. However, with increasing Mn content, the formation of secondary phases increases, resulting in the reduction of solid solution of Mn in β-phase; therefore, the electrical transport deteriorates. As a result, the optimum doping level for improving TE performance is obtained at x = 0.05 sample, verifying with crystal structure analysis that the optimum doping level is in the range of 0 ≤ x ≤ 0.08 because the amount of semiconducting β-FeSi2 drastically drops at x ≥ 0.09. Our study reveals that by judging the variation of the crystal structures, we could achieve the optimum doping level for improving TE transport properties.

The effect of direct energy deposition arc mode on the porosity of AA5087 aluminum alloy

The paper evaluates the effect of the welding mode of the CMT-based direct energy deposition arc (DED-Arc) process on the porosity of AA5087 aluminum alloy walls. Three welding modes were used to produce the walls: cold metal transfer (CMT), CMT-Pulse (CMT-P), and CMT Cycle-Step (CMT-CS) with heat inputs of 128.5 J/mm, 150.4 J/mm, and 152 J/mm, respectively. Porosity was assessed with a light microscopy (LM) and computer tomography (CT). The wall produced with the lowest heat input had the lowest average porosity of 0.641 % compared to CMT-P (0.799 %) and CMT-CS (0.766 %). CT results followed the same trend with porosity of 0.21 %, 0.32 %, and 0.27 % for CMT, CMT-P, and CMT-CS, respectively. The porosity level strongly correlates with the hydrogen content. The lowest porosity (CMT) at the lowest hydrogen content (5.29 ppm) is associated with lower hydrogen solubility in a molten pool at lower heat inputs. Most of the detected pores in all modes ranged from 51 to 100 μm in size.

Arc and molten pool behavior on quality of hybrid cold metal transfer and tandem pulsed narrow gap gas metal arc welds: a study

ABSTRACT This research proposes a novel hybrid cold metal transfer (CMT) and tandem Pulsed gas metal arc welding (P-GMAW) process for narrow gap welding (NGW) of high strength low alloy (HSLA) steel plates. Investigating three sets of lead and trail wire feed speed (WFS) ratios [WFSL/T - 1.4, 1, 0.7], the study delves into the complex arc and metal transfer behavior within the narrow gap. Utilizing synchronized arc images and current-voltage waveforms, the research assesses their influence on fusion and mechanical properties. The root pass employs the single wire CMT process, while filling and closing passes leverage tandem P-GMAW, effectively minimizing incomplete fusion and reducing heat input. Results indicate that a lower WFSL/T (0.7) reduces the molten pool hump and overflow within the narrow gap while enabling direct weld arc engagement with the previously deposited layer, enhancing weld penetration. WFSL/T of 1.4 and 0.7 revealed higher and lower Charpy impact toughness.

Investigating the Influence of Al Contents on Microstructure and Mechanical Properties of Ni3Al Superalloy Fabricated by Twin Wire‐Based Direct Arc Energy Deposition

In situ synthesis of Ni3Al by simultaneously feeding both Ni and Al wires into the molten pool is a common wire‐based additive manufacturing technology for Ni3Al superalloys. However, Ni3Al superalloys within a composition gap still have not yet been synthesized. The optimal composition range has also not been investigated yet. Herein, Ni3Al superalloys with Al equivalents between 17 and 25 at.% are fabricated by twin wire‐based direct arc energy deposition by adjusting the relative feeding speed. Microstructural analysis shows that the solidification products generate no γ′ precipitation when Al content is 17 at.%. Al promotes the formation of γ′ phase, as the Al content increases, the deposited Ni3Al superalloys with 20–25 at.% Al consist of dendritic γ + γ′ dual phase and interdendritic γ′ single phase. The proportion of γ + γ′ dual phase gradually increases with decreasing Al contents, whereas the tensile strength and elongation gradually increase. The Ni3Al superalloys (20 at.% Al) with the most γ + γ′ dual phase exhibit the highest tensile strength and elongation (939 MPa and 25.7%, respectively). Fracture analysis shows that the dislocation decomposition and stacking fault shearing mechanisms allow dislocations to continuously cut through γ′ precipitations to maintain deformation, which is responsible for high tensile strength and ductility.

Atomic insights on nanoindentation-induced plastic-deformation behavior of tetrahedral amorphous carbon film

The nanoindentation-induced deformation behavior of the Cr-doped diamond-like carbon (DLC) films was clarified with Cr concentration varying from 0 to 16.5 at.% by experiment and molecular dynamics simulation. The Cr-DLC films were fabricated by a direct cathode vacuum arc technique and Cr dopants existed in the form of stripes owing to the deposition features. Results showed the addition of Cr facilitated the transformation of sp3-C bonds to sp2-C bonds, resulting in a decrease of the hardness and elastic modulus. Especially, the sp2 nano-crystallites with the lamellar structure were found in the Cr (16.5 at.%)-DLC film. During nanoindentation, the ring-like cracking on the surface and lateral crack at the interface are exhibited in the Cr-free DLC film, while the introduction of Cr makes the DLC film alleviate the cracking trend. According to the atomic-scale analysis, Cr can significantly improve the plasticity of the DLC film because the Cr-rich cluster with a high free volume can facilitate the shear transformation zones percolation and the shear bands (SBs) nucleation by collective coordinated vortex-like movements of atoms. The Cr-free DLC film can hardly accommodate high plastic strain with very few fine SBs and blockage of the SBs.

Predictive analysis of the scoliotic curve using a subject's 3D model.

A predictive analysis of the conservative scoliosis treatment is necessary, in which a 3D model of an optimal treatment algorithm is a basic part in the design of a prosthetic corset. Since CAD technology has proven to be very useful in the field of prosthetics and orthotics, we used an open-source software to plan the correction of the scoliotic curve on a virtual model of the subject's torso. The shape of the scoliosis was simplified by means of a directional polygon, which was drawn in a reverse manner depending on the directional arcs of the scoliotic curve. The resulting scoliosis correction, simulated in a predictive analysis, was defined by changing the Cobb angle, eccentricity, and torso height. With the proposed low-cost method of predictive analysis, it is possible to help CPOs to a more accurate and effective design of orthoses and corrective aids and to comprehensively determine the entire treatment procedure.

Experimental study on the underwater DC arc behaviors regulated by an external transverse magnetic field

An arc discharge in water can generate extremely high voltage, which has great potential to be used in DC fault protection. The voltage characteristic is closely related to the arc behaviors. However, due to the complexity of the gas–liquid mixed environment, the arc shape is difficult to observe directly. In this letter, an observation device is specially designed and underwater arc motion with millisecond-scale duration is clearly photographed. The corresponding relationship between the arc behaviors and the varied voltage is revealed. Additionally, the random behaviors of underwater arc are controlled stably by applying an external transverse magnetic field. The enhanced cooling mechanism and the directional arc motion characteristics are discussed. We demonstrate that fast elongation of the arc column and continuous heat exchange between phase surfaces are the keys to realizing a rapid increase of underwater arc voltage.

Microstructure evolution and mechanical performance of tetrahedral amorphous carbon coatings with dense droplets during annealing

Tetrahedral amorphous carbon (ta-C) coatings with approximately 50% sp3C were deposited onto cemented carbide alloy YG6 and Si wafers via direct vacuum cathode arc (DVCA) evaporation at different substrates temperatures. Coated specimens were annealed in a 5 Pa argon atmosphere. The micromorphology and chemical bonding structure of these coatings with different treatments were characterized using field emission scanning electron microscopy (FE-SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The mechanical performance was tested using a nanoindenter and film stress instrument. The obtained ta-C coatings contained dense droplets of various sizes (“abnormal particles” (An-Ps)). The densities of the An-Ps were controlled by the graphite cathode target arc rather than the substrate temperature, and their ID/IG ratios were close to their counterpart coating matrix. Increasing the substrate temperature was beneficial for increasing the sp2C fraction and the number of aromatic ring sp2C sites. Growth, coalescence, and leveling-diffusion of aggregates in the coating matrix and An-Ps occurred during annealing, which was related to the existing state of the sp2C sites, including the olefinic chain and aromatic ring. The residual stress variation with annealing temperature also depended on the sp2C state. The residual stress in the coating increased during annealing when the number of aromatic ring sp2C sites exceeded a certain critical value.

Low-carbon primary steelmaking using direct reduction and electric arc furnaces: Prospective environmental impact assessment

Low-carbon primary steelmaking using direct reduction and electric arc furnaces: Prospective environmental impact assessment

Comparative study of the microstructure evolution of dual-phase Al-Co-Cr-Fe-Ni high-entropy alloy prepared by direct laser deposition and vacuum arc melting

• Dual-phase Al 0.7 CoCrFeNi HEAs were fabricated by DLD and VAM. • BCC phase in VAM Al 0.7 showed basket-weave-like structure by spinodal decomposition. • DLD sample contained a higher content of FCC phase than the VAM sample. • The texture in BCC phase in DLD sample deviated from 〈0 0 1〉 orientation. Dual-phase (FCC + BCC) Al 0.7 CoCrFeNi high-entropy alloys were successfully fabricated by direct laser deposition (DLD) and vacuum arc melting (VAM). It has been found that there is a significant difference between the microstructures produced by the two methods. A hypoeutectic structure (primary FCC phase + lamellar FCC-BCC eutectic microstructure) was observed in the DLD sample, while BCC phase in the VAM sample displayed basket-weave-like structures by spinodal decomposition, which can be attributed to the different thermal gradients and cooling rates for the two processes. A higher percentage of FCC phase was found in the DLD sample (63 %), compared to the VAM sample (55 %). In both samples, FCC phase was rich in Fe, Co and Cr, whereas Al and Ni were segregated in BCC phase. Furthermore, chaotic grain orientations were observed in FCC phase in both samples. A strong 〈0 0 1〉 texture along the direction of solidification was formed in BCC phase in the VAM sample, while in the DLD sample the texture showed a deviation from 〈0 0 1〉 orientation because of the complex nature of the temperature field.

Erosional Damages on Concave Banks of Directional Arcs in Natural Torrent Bed

Erosional Damages on Concave Banks of Directional Arcs in Natural Torrent Bed

Elemental Analysis, Phytochemical Screening and Evaluation of Antioxidant, Antibacterial and Anticancer Activity of Pleurotus ostreatus through In Vitro and In Silico Approaches.

Oyster mushrooms form an integral part of many diets owing to their characteristic aroma, delicious taste and nutraceutical value. In this study, we examined oyster mushrooms by direct arc optical emission spectroscopy for the presence of various biologically important elements. Furthermore, we screened phytochemicals present in Pleurotus ostreatus by applying GC-MS. Additionally, the antioxidant, antibacterial and anticancer activities of the ethanolic extract of Pleurotus ostreatus were studied. Moreover, we docked the phytochemicals and examined their binding affinities with EGFR, PR and NF-κB proteins, which are overexpressed in breast cancer. The elemental analysis showed the presence of Fe, K, Na, Ca, Mg, Cr and Sr in the spectrum. Moreover, GC-MS data revealed the presence of 32 biologically active compounds in oyster mushrooms. The ethanolic extract displayed remarkable free radical scavenging activity (~50%) against DPPH. The mushroom has shown promising antibacterial activity against both Gram-positive (S. aureus) and Gram-negative bacteria (Pseudomonas aeruginosa, Proteus vulgaris and Proteus mirabilis). The present study also revealed that oyster mushrooms possess significant anticancer activity. The ethanolic extract inhibited the growth and proliferation of MCF-7 cells. It also induced cell shrinkage, membrane blebbing and nuclear fragmentation, resulting in apoptosis of malignant cells. The molecular docking analysis showed that ligand 15 (Linoleic acid ethyl ester), ligand 27 (Ergosta-5,7,9(11),22-tetraen-3-ol, (3. beta.,22E), ligand 28 (Stigmasta-5,22-dien-3-ol, acetate, (3. beta.,22Z), ligand 30 (Ergosta-5,7,22-Trien-3-Ol, (3. Beta.,22E) and ligand 32 (gamma. Sitosterol) exhibited better binding affinities with EGFR, PR and NF-κB proteins. This result provides a strong ground for confirmation of the in vitro anticancer effect of Pleurotus ostreatus. From the present in vitro and in silico studies, it can be concluded that Pleurotus ostreatus is a useful source of essential elements and reservoir of bioactive compounds which confer its significant antioxidant, antibacterial and anticancer properties.

A novel modification to TW-GIA for controlling heat input of base metal

ABSTRACT Bypass coupling triple-wire gas indirect arc welding (TW-GIA) has been proposed to control the heat input of base metal and consequently improve the weld forming as per the requirement. The influence of the bypass current on arc behavior, welding stability, and weld forming have been investigated. Results showed that the wetting angle and reinforcement reduced gradually, and the weld bead penetration increased with the bypass current increase. The reason was that the workpiece heating mode was changed due to the bypass circuit coupling. It was observed that the heat source was composed of two indirect arcs and two direct arcs, and they were in a coupling state. When the bypass current was 280 A, the electrical parameters of arc fluctuations were at a maximum, and the coupled arc state was not conducive to obtain a stable welding process. Compared to the lack of sidewall fusion and incomplete joint penetration defects of the weld with TW-GIA, the good butt joint of 12 mm thickness steel plates was successfully obtained with bypass coupling TW-GIA under the same energy consumption.

Effect of arc voltage on process stability of bypass-coupling twin-wire indirect arc welding

With the development of bypass-coupling technique, the process window of twin-wire indirect arc welding has been effectively broadened, but the process stability is required to be further improved. In this paper, the influence of arc voltage on the stability of welding process was investigated through process experiments. It was found that the direct arc and indirect arc were alternately ignited. Under the condition of the output voltage at 32 V, the ratio of the indirect arc current to overall welding current was the largest. The weld was well formed with the output voltage above 32 V. Considering both the deposition efficiency and process stability, the desirable output voltage was 32 V.

Investigation of semiconductive Lu1-xScxNiSb solid solution

The electrokinetic and energetic characteristics of the semiconductor solid solution Lu 1- x Sc x NiSb were investigated in the ranges Т =80–400 K, х =0–0.10 . Samples were prepared using an electric arc furnace by direct arc melting of the constituent elements under a purified argon atmosphere (porous Ti was used as a getter). The alloys were annealed at 1 073 K for 720 hours and quenched in cold water. Phase analysis was performed using X-ray powder diffraction patterns of the synthesized samples. The elemental and phase compositions of the synthesized samples were examined by Scanning Electron Microscopy (SEM) using Tescan Vega 3 LMU scanning microscope. Microprobe analysis of the concentration of atoms on the surface of Lu 1- x Sc x NiSb samples, including x = 0–0.10, established their correspondence to the initial compositions of the alloys, and X-ray phase and structural analyzes showed no traces of extraneous phases on the diffractograms except for the main phase indexed in the MgAgAs structure type. The temperature dependencies of electrical resistivity ( r ( T )) were measured employing two-probe method on millimeter-scale, well-shaped pieces cut by spark erosion from the polycrystalline samples in the temperature range 80–400 K. Thermopower coefficient ( α ) was measured in relation to the pure copper in the temperature range 80–400 K. It has been experimentally established that in the Lu 1‑ x Sc x NiSb solid solution both structural defects of neutral and donor nature are simultaneously generated, the concentration of which increases with increasing content of Sc atoms. The observed high-temperature activation parts on the temperature dependences of the resistivity ln( ρ (1/ T )) for all Lu 1- x Sc x NiSb samples indicates the location of the Fermi level ε F in the band gap of the semiconductor, and positive values of the thermopower coefficient α ( T ) specify its position near the valence band. The main carriers of electric conductivity are free holes. From the high-temperature parts of the dependence α (1/ T ) the values of the activation energy ε 1 α are calculated, which are proportional to the amplitude of large-scale fluctuations of continuous energy bands. The calculated from the low-temperature parts values of activation energy ε 3 α are proportional to the modulation amplitude of small-scale fluctuations of strongly doped and compensated semiconductor. It was shown that the investigated semiconductor solid solution Lu 1- x Sc x NiSb is a promising thermoelectric material. Keywords : electric conductivity, thermopower coefficient, Fermi level, structural defect.

Enforcing Full Arc Consistency in Asynchronous Forward Bounding Algorithm

The AFB BJ+ DAC* is the latest variant of asynchronous forward bounding algorithms used to solve Distributed Constraint Optimization Problems (DCOPs). It uses Directional Arc Consistency (DAC*) to remove, from domains of a given DCOP, values that do not belong to its optimal solution. However, in some cases, DAC∗ does not remove all suboptimal values, which causes more unnecessary research to reach the optimal solution. In this paper, to clear more and more suboptimal values from a DCOP, we use a higher level of DAC* called Full Directional Arc Consistency (FDAC*). This level is based on reapplying AC* several times, which gives the possibility of making more deletions and thus quickly reaching the optimal solution. Experiments on some benchmarks show that the new algorithm, AFB BJ+ FDAC*, is better in terms of communication load and computation effort.

A direct dc arc emission spectrometry determination of chlorine impurities in nuclear grade graphite

In the present study, the direct current arc atomic emission spectrometry (dc arc AES) method was proposed for direct determination of chlorine impurities in nuclear-grade graphites and graphite foils in the range of 1‐–100 ppm in order to meet nuclear power industry requirements. The procedure is based on near-infrared (NIR) AES approach for determination of non-metal impurities, contrary to the most common vacuum ultraviolet AES approach. Carbon dc arc in argon atmosphere was used as radiation source. This radiation source employs standard extra high purity 6 mm diameter standard shaped graphite electrodes and standard vertical spectroanalytic stand, but employs several improvements as well: special protective fused quartz tube, and specially built fiber optic refocuser. Registration of spectra was performed via a novel compact tunable spectrometer with linear complementary metal oxide semiconductor array (CMOS) detector. As the work in near-infrared spectral range is hampered by spectral interference factors, measures were taken to counter them. Due to specifics of the radiation source, the excitability of chlorine was studied both in air and argon in presence of carbon, as well as in its absence. Artificial standards for calibration of the spectrometer were prepared by mixing extra high purity NaCl and graphite powder and evaluated by two independent approaches: indirectly by dc arc AES determination of Na, and directly by water extraction and photometrical determination of Cl. The characteristics of evaporation and excitation in dc arc of chlorine from both standards and real nuclear graphite samples were studied due to the differences in the nature of chlorine source in them. The detection limit of was determined 0.8 μg/g. The whole cycle of measurement, including sample preparation is about 10 min.

Nanoindentation-induced deformation behaviors of tetrahedral amorphous carbon film deposited by cathodic vacuum arc with different substrate bias voltages

The diamond-like carbon (DLC) thin films were deposited using a direct cathode vacuum arc (DCVA) technology at a variety of substrate bias voltages from 0 to −50 V. The cross-sectional morphologies, compositions, chemical state, and surface roughness of the prepared DLC films were investigated and highly controlled by the bias voltage. The detailed microstructure of the DLC films and interfaces were observed by transmission electron microscope (TEM). The mechanical properties of the DLC films were obtained by nano-indentation test and significantly depended on the applied bias voltages. The deformation mechanisms and crack initiation/propagation of the DLC films at different substrate bias voltage (SBV) in the nano-indentation process were analyzed by TEM and clarified by evolution models. There were three forms to release the energy induced by indenter for the DLC films with an amorphous structure, as follows: (i) the plastic deformation stemmed from the flow of a large number of C atoms; (ii) the formation and slip of the shear bands; (iii) the cracking at the position of stress concentration.