Search Results (283)

During high-current vacuum arcing, asymmetric arcing with off-center plasma columns may occur due to stochastic discharge initiation and mechanical motion, receiving less research attention than symmetric arcing. The objective of this paper is to numerically analyze the influence law of asymmetric arc ignition on arc parameters. For 60 mm diameter contacts, three arc conditions of symmetric arcing, 33% arc offset, and 67% arc offset were modeled. The results show that the arc offset causes asymmetry in the arc’s distribution. For 33% offset, the pressure and number density on the side away from the root of the arc is about 50% of root values, while these parameters fall below 20% for the 67% offset. Simultaneously, arc offset elevates peak parameter values: under 33% offset, maxima for ion pressure, ion density, ion temperature, electron temperature, and current density rise 12%, 11%, 6%, 6%, and 14% versus symmetric arcing; during 67% offset, these escalate significantly to 67%, 61%, 12%, 18%, and 47%. This study contributes to providing reference for the analysis of vacuum interruption processes under asymmetric arcing conditions. Full article

Vacuum degassing (VD) is a critical refining step in electric arc furnace (EAF) steelmaking for producing clean steel with reduced nitrogen and hydrogen content. This study develops an Effective Equilibrium Reaction Zone (EERZ) model focused on denitrogenation (de-N) by simulating interfacial reactions at the bubble–steel interface (Z1). The model incorporates key process parameters such as argon flow rate, vacuum pressure, and initial nitrogen and sulfur concentrations. A robust empirical correlation was established between de-N efficiency and the mass of Z1, reducing prediction time from a day to under a minute. Additionally, the model was further improved by incorporating a dynamic surface exposure zone (Z_eye) to account for transient ladle eye effects on nitrogen removal under deep vacuum (<10 torr), validated using synchronized plant trials and Python-based video analysis. The integrated approach—combining thermodynamic-kinetic modeling, plant validation, and image-based diagnostics—provides a robust framework for optimizing VD control and enhancing nitrogen removal control in EAF-based steelmaking. Full article

This work provides a comprehensive investigation into the synergistic effects of zirconium and oxygen on the microstructural evolution, high-temperature oxidation resistance, and mechanical properties of γ-phase Ti52AlxZr alloys (x = 0, 0.5, 1, and 2 at.%) under systematically controlled oxygen concentrations. Unlike prior studies that have examined these alloying elements in isolation, this study uniquely decouples the contributions of interstitial (oxygen) and substitutional (zirconium) solutes by employing low (LOx) and high (HOx) oxygen levels. Alloys were synthesized via vacuum arc melting and subsequently subjected to homogenization annealing at 1250 °C for 100 h to ensure phase and microstructural stability. Characterization techniques including scanning electron microscopy (SEM), X-ray diffraction (XRD), and electron backscatter diffraction (EBSD) were employed to elucidate phase constitution and grain morphology. Zirconium addition was found to stabilize the γ-TiAl matrix, suppress α₂-phase formation, and promote grain coarsening in LOx specimens. Conversely, elevated oxygen concentrations led to α₂-phase precipitation along grain boundaries. Mechanical testing, comprising Vickers hardness and uniaxial compression at ambient and elevated temperatures (800 °C), revealed that both zirconium and oxygen significantly enhanced strength and hardness, with Ti52Al2Zr delivering optimal mechanical performance. Moreover, zirconium substantially improved oxidation resistance by promoting the formation of a thinner, adherent Al₂O₃ scale while simultaneously inhibiting TiO₂ growth. Collectively, the findings demonstrate the critical role of zirconium in engineering advanced γ-TiAl-based intermetallics with superior high-temperature structural integrity and oxidation resistance. Full article

Vacuum arc thrusters (VATs) have recently gained significant interest as a micro-propulsion system due to their scalability, low cost, storability, and small form factor. While VATs offer an attractive propulsion solution for CubeSats, conventional propellant feed systems used in VATs require intricate mechanical moving parts, increasing overall system complexity and mission risk. A promising alternative is the use of VAT arrays, where multiple thin-layer VATs are arranged in a regularly spaced grid, thus enhancing reliability, increasing total impulse without a mechanical propellant feed system, and enabling integrated attitude control via off-axis thruster placement. However, VAT arrays require a larger power processing unit (PPU) and additional control system, posing challenges within CubeSat volume constraints. To address this, this study proposes a novel PPU design that enables the simultaneous operation of multiple VATs while minimising system mass and volume. Experimental results demonstrate the successful operation of VAT pairs using the proposed PPU concept, validating its feasibility as an efficient propulsion solution for CubeSats. Full article

The primary challenge associated with stainless steel in fuel cell operation is its susceptibility to corrosion, which leads to increased contact resistance and subsequent degradation of electrochemical performance. In general, the protective layers have been loaded onto the metal surface by widely used traditional techniques such as physical vapor deposition (PVD), or cathode arc ion plating. However, the above sputtering and evaporation ways require a high-vacuum condition, complicated experimental setups, higher costs, and an elevated temperature. Therefore, herein the achievement for uniform coatings over a large surface area has been realized by using a cost-effective strategy through a complete wet chemical process. The synergistic regulation of two conductive components and a plastic additive has been employed together with the entrapment of a surfactant to optimize the microstructure of the coating surface. The assembly of layered graphite and a polystyrene sphere could maintain both the high corrosion resistance feature and excellent electrical conductivity. In particular, the intrinsic vacant space in the above physical barriers has been filled with fine powders of indium tin oxide (ITO) due to its small size, and the interconnected conductive network with vertical/horizontal directions would be formed. All the key technical targets based on the U.S. Department of Energy (DOE) have been achieved under the simulated operating environments of a proton exchange membrane fuel cell. The corrosion current density has been measured as low as 0.52 μA/cm² (for the sample of graphite/mixed layer) over the applied potentials from −0.6 V to 1.2 V and its protective efficiency is evaluated to be 99.8%. The interfacial contact resistance between the sample and the carbon paper is much less than 10 mΩ·cm² (3.4 mΩ·cm²) under a contact pressure of 165 N/cm². The wettability has been investigated and its contact angle has been evolved from 48° (uncoated sample) to even 110°, providing superior hydrophobicity to prevent water penetration. Such an innovative approach opens up new possibilities for improving the durability and reducing the costs of carbon-based coatings. Full article

(AlTiV)_100−xCr_x high-entropy alloys (HEAs) is expected to solve the problem of poor corrosion-wear resistance of lightweight alloys. To elucidate its corrosion-wear mechanism, three (AlTiV)_100−xCr_x alloys were prepared by vacuum arc melting method by repeating the melting five times at 240 A current.and their microstructures, mechanics, corrosion, wear, and corrosion-wear behaviors were investigated. The results indicate that (AlTiV)_100−xCr_x is a single-phase with BCC structure and the VEC of Cr5, Cr10 and Cr15 were 4.0, 4.1 and 4.2 respectively. Their hardness increase and toughness and corrosion resistance decrease with the increase of Cr content (Cr5:537.5 HV_0.2/6.7%/1.86 × 10⁻⁸ A/cm²; Cr10:572.3 HV_0.2/5.6%/2.09 × 10⁸ A/cm²; Cr15:617.6 HV_0.2/3.8%/2.51 × 10⁻⁸ A/cm²). The wear volume and the corrosion-wear volume of AlTiVCr alloys are mainly caused by the abrasive wear. However, the fatigue wear of AlTiVCr alloys could be exacerbated by a decrease in material’s toughness, corrosion resistance, and an increase in solution corrosivity. Therefore, Cr10 presents the optimal wear resistance in the deionized water, while the optimal corrosion-wear resistance in the 3.5 wt.% NaCl solution is presented by Cr5. Compared to TC4, the wear and corrosion-wear resistance were improved by 56.4% and 65.5%, respectively. Full article

Silicon-doped tetrahedral amorphous carbon (ta-C:Si) coatings are promising materials for achieving ultralow friction in water-lubricated environments, attributed to the formation of Si(OH)_x-based tribofilms. However, the deposition process via filtered cathodic vacuum arc (FCVA) often introduces large particles into the film, increasing surface roughness and causing accelerated wear during the initial sliding phase, despite the high hardness of the coating. In this study, ball-on-disk tribological tests were performed to investigate the wear behavior of ta-C:Si coatings under water lubrication. Friction coefficients, wear volume, and surface roughness were analyzed over various sliding durations. The Archard wear equation and the plasticity index were used to analyze wear and contact behavior. The friction coefficient decreased from 0.14 to 0.04 within the initial 100 m section, and the surface roughness of ta-C:Si decreased sharply from 0.35 μm to 0.01 μm based on the Rpk parameter during 10 h. Following this period, the plasticity index decreased from an initial value of 1.1 to below 0.6, transitioning to a fully elastic contact stage, marking the onset of steady-state wear after 10 h. These results indicate that the reduction in surface roughness plays a crucial role in stabilizing wear behavior and provide insights into optimizing the long-term performance of ta-C:Si coatings in aqueous environments. Full article

The significant phase transformation hysteresis in TiNi alloys limits their performance. To address this, copper (Cu) was added as an alloying element to reduce hysteresis. This study synthesized three compositions of Ti₅₀Ni_50−xCu_x (x = 0, 5, 7 at.%) shape memory alloys (SMAs) via vacuum arc melting to optimize the Cu content. The alloys were homogenized through hot rolling to maintain stable mechanical and shape memory properties. The hot-rolled Ti₅₀Ni₄₅Cu₅ alloy demonstrated excellent shape memory behavior, achieving 100% thermal recovery after one cycle at 4% and 6% strain and 99.2% recovery after six cycles at 4% strain. It also exhibited outstanding mechanical performance, with a tensile strength of 900 MPa and 40% elongation. Microscopic analysis using scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) revealed that Cu preferentially segregates at grain boundaries, suppressing the formation of the Ti₂(Ni,Cu) phase. This moderate segregation, combined with hot rolling, promotes the reprecipitation and uniform distribution of phases, reducing the likelihood of premature fracture caused by stress concentration during deformation. The moderate thickness and uniformly distributed martensite, as well as the Type II twins with strong deformation ability, significantly improved the shape memory properties of Ti₅₀Ni₄₅Cu₅. This study provides valuable insights into the microscopic mechanisms influenced by Cu in TiNi alloys and proposes a novel strategy for controlling precipitate phases through adjustments in alloy composition and optimized processing conditions. Full article

In the present work, chemical and ion beam surface treatments were performed in order to modify the electrochemical behavior of industrial austenitic–martensitic steel VNS-5 in 3.5 wt. % NaCl. Immersion for 140 h in a solution containing 0.05 M potassium dichromate and 10% phosphoric acid promotes formation of chromium hydroxides in the outer surface layer. By means of a new type of ion source, based on a high-current pulsed magnetron discharge with injection of electrons from vacuum arc plasma, ion implantation with Ar⁺ and Cr⁺ ions of the VNS-5 steel was performed. It has been found that the ion implantation leads to formation of an Fe- and Cr-bearing oxide layer with advanced passivation ability. Moreover, the ion beam-treated steel exhibits a lower corrosion rate (by ~7.8 times) and higher charge transfer resistance in comparison with an initial (mechanically polished) substrate. Comprehensive electrochemical and XPS analysis has shown that a Cr₂O₃-rich oxide film is able to provide an improved corrosion performance of the steel, while the chromium hydroxides may increase the specific conductivity of the surface layer. A scheme of a charge transfer between the microgalvanic elements was proposed. Full article

In this paper, a new TaMoNbTiZr multielement alloy has been designed, using chemical elements that exhibit extremely low bio-toxicity for the human body. The alloy was obtained by melting in vacuum arc remelting (VAR) equipment MRF ABJ 900 from high-purity chemical elements (99.5%) as mini-ingots having about 40 g weight each. The biocompatible alloys underwent changes in hardness after performing the annealing at 900 °C for 2 h, followed by cooling in water. The new alloy had an average hardness in the cast state of 545 HV0.5, and after heat treatment, it hardened to a value of 984 HV0.5, over 40% higher than that in the casting state, which ensures a longer working period. To use them as materials for medical instruments, their biocompatibility was highlighted through specific laboratory tests. For this, mesenchymal stem cells isolated from bone tissue and a human fibroblast cell line were cultured in vitro on the TaMoNbTiZr alloy’s surface. The biocompatibility of the alloy with the biological environment was evaluated by analyzing cell viability, adhesion, and proliferation, and in parallel, the cytolysis effects manifested by the increase in lactate dehydrogenase activity in the culture media were analyzed. Full article

The effect of different Fe contents on the phases of Sm–Co–Fe ternary alloys during solidification is investigated herein by melting the alloys using a non-consumable vacuum arc furnace. In particular, the phases of the Sm_25.5Co_balFe_x (x = 19, 21, 23, and 25 wt.%) alloys are investigated after solidification and aging. The results obtained from Cai Li’s modified Miedema model show a strong interaction between the Sm–Co alloy atoms. Additionally, the results obtained from the Toop geometric model show a strong interaction between the Sm–Co–Fe ternary alloy atoms, enabling the formation of intermetallic compounds. The experimental results show that when the Sm content is 25.5 wt.%, the SmCo₅ phase gradually decreases as the Fe content increases and disappears when the Fe content is 25 wt.%. Thermodynamic calculations show that when the Fe content is 19 wt.%, there is a region where the SmCo₅ and Sm₂Co₁₇ phases co-exist. As the Fe content increases, this region gradually decreases. For a 25 wt.% Fe content, the Sm₂Co₁₇ and SmCo₅ two-phase region does not appear when the Sm content varies. The samples are aged at 1143 °C for 12 h, then melted and cut. The phase results obtained by scanning are consistent with the calculated results. In this study, the effect of each constituent element of Sm–Co–Fe ternary alloys on their solidification phases is investigated, providing a strong foundation for studying the 2:17-type Sm–Co magnetic materials obtained after melting and aging a five-element Sm–Co alloy. Full article

In this work, two alloys of Ni₃₅Al₃₀(FeCo)₂₅Cr_10-xMo_x (x = 0, 5) were prepared via the vacuum arc melting method, and the effects of Mo on the microstructure, mechanical properties, and friction and wear properties of the alloys were investigated. The addition of Mo improved the mechanical properties, wear resistance, and corrosion resistance of the alloy system. With the addition of trace amounts of Mo, the precipitate phase of the alloys transformed from spherical to acicular and plate-like. The precipitated phases in a co-lattice relationship with the matrix allow for a substantial increase in the strength of the alloy at both room and elevated temperatures without a significant loss of plasticity. Ni₃₅Al₃₀(FeCo)₂₅Cr₅Mo₅ has excellent mechanical properties, with a hardness of 558.2 HV; a yield strength of 1320 MPa at 600 °C; and a yield strength of 537 MPa at 850 °C. As the temperature increased, the wear mechanism changed from abrasive wear to adhesive wear. At 600 °C, Ni₃₅Al₃₀(FeCo)₂₅Cr₅Mo₅ had the lowest wear rate of 1.78 × 10⁻⁵ (mm³/Nm). The precipitated phases, which have high hardness and maintain a conformal interface with the matrix, play an important role in slowing delamination wear, keeping the wear rate of this alloy low at both room and high temperatures. Electrochemical experiments on the two alloys at room temperature revealed that Ni₃₅Al₃₀(FeCo)₂₅Cr₅Mo₅ exhibited excellent resistance to pitting, with a pitting potential of 0.016 V. Full article

We demonstrate tunable ferrimagnetic properties in both bulk and thin film ferrimagnetic DyCo₃ compatible with the hosting of topological magnetic chiral textures, namely skyrmions suitable for integration into spintronic applications with classic, neuromorphic and quantum functionalities. The bulk samples were prepared by arc-melting of stoichiometric mixtures under purified argon atmosphere and the thin films by Ultra-High-Vacuum magnetron sputtering from a stoichiometric target. Magnetometry allows us to extract the main magnetic properties of bulk and thin films: the saturation magnetization, the magnetic anisotropy and their variation with temperature. These results are successfully complemented by band structure ab initio DFT calculations. Based on the critical magnetic parameters extracted from experiments, we performed micromagnetic simulations that reveal the skyrmionic potential of our samples in both continuous thin film and nano-patterned architectures. Full article

Due to the huge component space of refractory high-entropy alloy, the traditional, experimental “trial and error method” can not meet the design requirements. In order to improve the “trial and error method”, guidance is provided for the prediction and design of refractory high-entropy alloys. Based on the literature data, a comprehensive dataset was constructed, including the composition, phase composition, and strength data of various high-entropy alloys. On this basis, nine regression models were established for strength prediction. By comparison, the XGBoost (XGB) model achieves better prediction performance in the test set; the root mean square error (RMSE) is 195.53 MPa, and the coefficient of determination (R²) is 0.87. By using Shapley additive interpretation (SHAP) to analyze the explainability of the model, it was found that the key characteristics affecting the mechanical properties of the high-entropy alloy were mixed entropy and electronegativity. In order to further evaluate the precision of the model, through the vacuum arc melting preparation, Ti27.5Zr26.5Nb25.5Ta8.5Al12 high-entropy alloys were experimentally verified. The alloy experiments’ yield strength was 1356 MPa, predicting strength was 1304.71 MPa, external validation error was 3.81%, and the average accuracy of the model was 87.38%. Full article

Boron nitride (BN) ceramic is an important support material in aerospace, arc discharge devices, and vacuum electronics. The electron emission properties of BN surfaces are of significance among various space applications. In this work, by preparing BN thin films and microstructured BN bulks, we have investigated the influence of the surface physical properties on the electron emission coefficient (EEC). The results showed that the surfaces of BN films, which were prepared by magnetron sputtering, produced serious gas adsorption and organic contamination when they were left for 10 days, and these surface modifications made the EEC of BN film surface decrease to a certain extent. The argon ion cleaning experiments indicated that the process of ion cleaning was able to partly eliminate the surface adsorption and contamination for the BN film. The EEC of the cleaned BN film surface was significantly improved compared to that of the original polluted BN film surface, with an EEC peak value of about 3.2 instead of 3.0 for the original polluted surfaces. By contrast, the EEC curves of the BN bulk show some difference, with the peak values of the EEC curves being 2.62 for the untreated BN bulk. The results of laser etching on the BN bulk surface to form microarray structures show that the EEC of BN bulk decreases significantly with the increase of the average aspect ratio of the microstructures. The EEC peak values of the BN bulks decrease from 2.62 to 1.16 when the porosity of the BN bulk reaches 49.11% and the aspect ratio reaches 1.36, indicating that constructing a surface microstructure is an effective method to achieve EEC reduction. By employing the electron trajectory tracking algorithm and the phenomenological model of electron emission, the effect of microstructure on EEC for BN bulk was quantitatively explained. The results of the study are of engineering application significance for vacuum devices involving the electron emission process of BN ceramic. Full article