Metal Vapor Research Articles

Suppression of denudation zone using laser profile control in vacuum selective laser melting

A vacuum selective laser melting method with a beam profile control was developed to fabricate the high quality 3D object. To investigate the quality of 3D fabrication, the denudation zone (DZ) as a quality indicator was evaluated to make a single bead. The main challenge is to clarify the correlation between the DZ and beam profiles. The beam profiles, such as a Gaussian mode, a doughnut mode, and a flat-top mode, were formed in several modes, by a dioptric system with a beam shaper. A stainless steel 316L (SS316L) powder was irradiated in arbitrary pressure to form a single bead, and then the DZ was measured. As a result, it was found that the flat-top mode recorded the minimum value of the DZ under atmospheric pressure. Thus, the dynamics of the metal vapor while the laser irradiation were observed by the Schlieren imaging technique under atmospheric pressure. The average velocity of metal vapor with flat-top mode was the slowest, i.e., 0.199 m/s. It was found that the DZ becomes small depending on the dynamics of metal vapor. The ambient pressure was reduced to 300 Pa in order to reduce the gas movement, and the DZ with flat-top mode was improved to record a minimum value of 0.048 mm, 1/3 of the DZ at atmospheric pressure.

Experimental study of the electron beam application for evaporation of cobalt, tin and copper

Studies on the kinetic theory of the evaporation of metals in vacuum have already existed, and there have been various applications, such as evaporation filming and powder making in vacuum. However, the vast amount of needed physical parameters has become an obstacle in achieving an accurate measurement, which limits their applications in turn. In addition, there is a lack of experimental research data and simple measurements about the intensive evaporation with the electron beam technology at high temperatures. In this study, a new thermogravimetric analysis (TGA) measuring device was designed for evaporation with the electron beam technology, to track the temperature and mass of the molten pool in real time and obtain abundant and instantaneous experimental data with complete details during the evaporation process. The starting evaporation temperature and the evaporation rate of cobalt, tin, and copper have been measured. In this study, the starting evaporation temperatures of cobalt, tin, and copper are 2173±5 K, 1970±5 K, and 1523±5 K respectively. At 2200–2271 K, the evaporation coefficient of Co is stabilized at around 0.5 with a decreasing tendency; at 1873–2050K, the evaporation coefficient of Cu decreases rapidly from 0.88 to 0.39; at 1979–2038 K, the evaporation coefficient of Sn increases from 0.27 to 0.64.

Adsorption of cadmium vapor by calcium-based adsorbents in simulated flue gas: Experimental and density functional theory studies

Calcium-based adsorbents are considered as effective high-temperature adsorbents for the removal of heavy metal in the furnace. In this work, the adsorption characteristics and reaction mechanism of calcium-based adsorbents for cadmium vapor were investigated by adsorption experiments and density functional theory (DFT) methods. The adsorption experiments showed that the adsorption performance of CaO for cadmium vapor was significantly better than Ca(OH)2, Calcite and CaSO4. The adsorption capacity of CaO adsorbent for cadmium increased firstly and then decreased with the increase of temperature. The enhanced trapping capacity of CaO for cadmium vapor with increasing temperature was associated with enhanced chemisorption, while the decrease in trapping capacity at high temperature could be attributed to adsorbent sintering. In addition, the results of DFT calculations showed that CaO had good adsorption capacity for various Cd species, and the order of the adsorption capacity was: CdO > CdCl2 > CdCl > Cd. The chemisorption mechanism dominated the adsorption of Cd species on the CaO (001) surface, and the central O site was the reactive site and electron transfer channel for the adsorption of Cd. This work provided a reference for the application of heavy metal vapor capture technology based on calcium-based minerals.

Fume emissions by electric arc during gas metal arc welding

The influence of welding arc regime on the welding fumes formation is studied by numerical modeling via description of separate processes inside the space charge regions near electrodes in the welding arc with consumable electrode. The modeling comprises the calculation of temperature profiles for electrons and heavy component, calculation of space distribution of gas components’ number densities, of gas particles’ mean free pathes, of electric potential and field, calculation of the heat transfer from electrode wire (anode) to molten pool (cathode). The formation of high temperature metal vapor from molten pool to environment as a function of arc current is demonstrated. The nucleation in the plasma of welding fumes is considered with taken into account ionization of vapor atoms via their interaction with nucleus surface. The growth of nucleus droplets via vapor condensation and coalescence is calculated. The coagulation of solid primary particles for various values of welding current is calculated and inhalable particle size distribution is demonstrated.

Following laser-induced plasma stoichiometry with atomic absorption spectroscopy

Atomic absorption spectroscopy was used to measure the absolute vanadium and titanium masses present as neutral atoms in the plume formed by laser ablation of a titanium alloy sample. At delays between two and twenty microseconds, the absolute masses and temperatures were measured with time-resolved Boltzmann plots under pure helium and an 80:20 He/O2 mixture. The Boltzmann plots, which include the ground term (in contrast to emission-based measurements), produced high-quality estimates of the plasma composition. Under helium, the metal vapors persisted beyond the longest ∼20 μs delays measured. The V:Ti stoichiometry was approximately as expected from the nominal sample composition at all times under He. However, under He:O2, the atomic vapor disappeared entirely in under 10 μs and the stoichiometry became more enriched in vanadium at increasing delays. This enrichment is interpreted in terms of the difference in first oxide bond energies of the two metals. There was evidence of loss of metal even under helium within the investigated 20 μs window.

ANALYTICAL RELATIONS FOR CALCULATION THE CURRENT OF ARG DISCHARGE IN THE METALS’ VAPORS AT THE PHYSICAL CONDITIONS OF TECHNOLOGICAL PROCESS OF ELECTRON-BEAM DEPOSITION OF CERAMIC COATING

The article is devoted to the problem of calculation the value of current of non-self-sustained arc discharge, which is lighting and maintained in the metal vapours and active gases for porviding the chemical reaction between its in the technological process of evaporation of thin coatings. Obtaineed relations are generally based on Poisson equation for defining the distribition of electric field, Mendeleev – Clapeyron equation for defining the concentration of ions in saturated metals' vapours, as well as on equation of current continiouty in gas discharge. Formed set of equations for distribution of electric potential and discharge current in the spatial coordinates is transformed to cubic equation, which was solved analytically. Obtained simulation results are given and analyzed.

Модифікація поверхні базальтових волокон та вуглецевих матеріалів для покращення їх змочування легкоплавкими розплавами

The effect of metal coatings and coverings on wetting of substrates by In, Sn, Pb in vacuum 1—2•10-3 Pa in the temperature range 400—700 C was studied by the sessile drop method using the capillary purification method of melt. Substrates of hot-polished basalt material, MPG-6 graphite, composite materials based on high-modulus carbon fibers, tapes and fabrics used. Vanadium, niobium, copper and nickel metals were chosen for the coatings, which were sprayed on the materials by electron beam evaporation of metals in vacuum, and titanium, nickel powders for the coatings were used. The nature of the wetting angle dependence on the film thickness is a linear decrease in the angle with increasing film thickness. Studies have shown the possibility of using double films V—Cu, V—Ni for the manufacture of composite materials from basalt fibers.Wetting the vanadium and niobium coatings on surface of the basalt material at by lead, tin and indium improves with increasing film thickness and experimental temperature. The nature of the contact angle–coating thickness dependences for all studied systems is the same: the angle value decreases linearly with increasing film thickness from the angle wetting of the basalt surface to the wetting angle of the compact metal film (V, Nb). The coating thickness, when the contact angle wetting for all adhesive-active metals with high oxygen affinity does not change, is close, and for vanadium is 200•10-10 m, for niobium about 100•10-10 m. Studies have shown the possibility of using double V—Cu and Nb—Cu films for the manufacture of composite materials from basalt fibers and matrix metal. Keywords: contact angle wetting, metal coatings and covering, basalt and carbon materials, low-melting metals.

A novel method of hybrid plasma injection driven by the pulsed discharge of a metal-polytetrafluoroethylene-stacked capillary in high-pressure SF6.

A reliable and repeatable triggering technology for a megavolt gap switch with a low working coefficient η is an urgent need and a research focus. In this study, a novel method of hybrid plasma injection (HPI) driven by pulsed discharge inside a capillary was first proposed. The HPI actuator adopted a metal-polytetrafluoroethylene (PTFE)-stacked capillary, in which severe ablation could generate a hybrid plasma containing gas and metal vapor ionized component ejected outward from the nozzle. The HPI actuator could perform repeatedly with an extremely strong plasma injection and triggering ability and, thus, provided a solution for megavolt ultrafast bypass switches (UFBPSs). The evolution and the trigger properties of the HPI actuator were investigated, and the influence of the stacked material (Al, Zn, and Sn) and its proportion (3/15, 7/15, and 10/15) was studied, followed by the performance degradation in multi-shot. It was found that stacking chemically active and low-ionization-energy aluminum in a proportion of 7/15 strongly enhanced the HPI, with an initial velocity of 1200m/s and a maximum height of 7.5cm in 0.5 MPa SF6. In repeated operations, the HPI actuator performance degraded obviously due to capillary expansion and deformation, and the lifetime was tens of magnitude. Finally, the optimized HPI actuator was used to trigger a 7 cm-0.5 MPa SF6 gap, with a breakdown voltage of ∼1.5 MV. When a 100kV DC voltage was applied (η < 7%), the gap was successfully and continuously triggered for 27 shots with the trigger delay ranging from 301 to 670 µs, indicating that the HPI actuator could effectively and repeatedly trigger megavolt-magnitude SF6 gaps at a very low η and was a good solution for megavolt UFBPSs.

Processes of Thermal and Cold Ionization of Metal Vapors in the Vicinity of the Critical Point of the Vapor–Liquid Phase Transition

Processes of Thermal and Cold Ionization of Metal Vapors in the Vicinity of the Critical Point of the Vapor–Liquid Phase Transition

Single-Step Electron Beam Evaporation for Schottky/Ohmic Drain in GaN-on-Si HEMTs Fabrication

This letter reports a novel method for fabricating Schottky/ohmic drain for GaN high electron mobility transistors (HEMTs). Without secondary photolithography or secondary metal evaporation, the Schottky/ohmic drain can be obtained by adjusting the direction of the electron beam evaporation. Besides, different metal/semiconductor interfaces can be simultaneously formed at this state, which are beneficial to enhance the shielding effect of the rough ohmic-drain metal morphology and modulate the electric field distribution on the drain side. By using Schottky/ohmic drain technology, the average breakdown voltage calculated from 50 devices each is improved from 895 V (ohmic drain device) to 1205 V for <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{L}_{\text {GD}} = 18\,\,\mu \text{m}$ </tex-math></inline-formula> , indicating enhanced off-state reliability characteristics for GaN HEMTs.

Characterization of the Anisotropy in the Microstructure and Mechanical Properties of Laser Powder Bed Fusion Ti6Al4V Alloys

Herein, near‐full‐density Ti6Al4V components are prepared by laser powder bed fusion (LPBF). The microstructural evolution and mechanical properties in different deposition planes are investigated to explore their anisotropic behavior. The internal defects of the LPBF‐fabricated Ti6Al4V components mainly included round‐like pores, primarily caused by metal vapor and entrapped gas during solidification. The microstructure of the horizontal plane consists of a large amount of α′/α martensite within a near‐equiaxed β matrix. In addition to similar acicular martensites, the columnar β grains within the vertical plane are induced by the steep thermal gradient along the deposition direction. Compared to that in the vertical plane, the microhardness in the horizontal plane is improved mainly due to the grain boundary strengthening mechanism. The transverse tensile strength and elongation are superior to the longitudinal ones, and the failure mode is transformed from ductile to brittle. Such anisotropic behavior in the tensile properties is primarily attributed to the varied microstructural evolution in the different deposition planes. This work demonstrates that LPBF‐fabricated Ti6Al4V alloys contain acicular α′/α martensites, which consequently enhance the strength/hardness properties, despite the anisotropic performances caused by the columnar β grains.

On the Practical Applicability of the Li Metal‐Based Thermal Evaporation Prelithiation Technique on Si Anodes for Lithium Ion Batteries

AbstractLithium ion batteries (LIBs) using silicon as anode material are endowed with much higher energy density than state‐of‐the‐art graphite‐based LIBs. However, challenges of volume expansion and related dynamic surfaces lead to continuous (re‐)formation of the solid electrolyte interphase, active lithium losses, and rapid capacity fading. Cell failure can be further accelerated when Si is paired with high‐capacity, but also rather reactive Ni‐rich cathodes, such as LiNi0.8Co0.1Mn0.1O2(NCM‐811). Here, the practical applicability of thermal evaporation of Li metal is evaluated as a prelithiation technique on micrometer‐sized Si (µ‐Si) electrodes in addressing such challenges. NCM‐811 || “prelithiated µ‐Si” full‐cells (25% degree of prelithiation) can attain a higher initial discharge capacity of ≈192 mAh gNCM‐811−1than the cells without prelithiation with only ≈160 mAh gNCM‐811−1. This study deeply discusses significant consequences of electrode capacity balancing (N:P ratio) with regard to prelithiation on the performance of full‐cells. The trade‐off between cell lifetime and energy density is also highlighted. It is essential to point out that the phenomena discussed here can further guide the direction of research in using the thermal evaporation of Li metal as a prelithiation technique toward its practical application on Si‐based LIBs.

The Impact of Direct Lightning Strike Damages on PV Modules in a Large Malaysian PV Farm

Many lightning risk analyses avoided considering the role of the PV Module’s aluminium frame as a natural lightning air termination system or if such a role is considered, assumed that the ‘thin’ aluminium frame, would not be damaged from metal melting and evaporation at the point of lightning stroke attachment. Although the IEC 62305 is not lacking in guidance on the use of thin metal sheets as air terminations, this aspect is not considered in PV farm design. To ensure correct inputs into the risk assessment calculation, the evaluation of interception and sizing efficiencies and the damage probabilities of the natural components have to be addressed. A comparative analysis is done between two types of air terminations; the PV-frame LPS and the finial-added LPS. The result indicates that for solar PV farms exceeding a certain size and operating in high ground flash density regions like Malaysia, the finial air termination may out-perform the PV-frame LPS.

Tunable, High-Power, Narrow-Linewidth Diode Laser for Potassium Alkali Metal Vapor Laser Pumping

This work proposes a method of compressing spectral linewidth and tuning the central wavelength of multiple high-power diode laser arrays in an external cavity feedback structure based on one volume Bragg grating (VBG). Through the combination of beam collimation and spatial beam technologies, a diode laser source producing 102.1 W at an operating current of 40 A is achieved. This laser source has a central wavelength of 766 nm and a narrow spectral linewidth of 0.164 nm. Moreover, a tuning central wavelength ranging from 776–766.231 nm is realized by precisely controlling the temperature of the VBG, and the locked central wavelength as a function of temperature shifts at the rate of approximately 0.0076 nm/°C. The results further prove that the smile under 1 μm can restrain the self-excitation effect of the emitting laser, which can influence the efficiency of the potassium alkali metal vapor laser pumping.

Metal spattering in laser scanning welding of T2 copper and welding quality

Considering that copper laser welding tends to produce spattering with poor weld formation, and porosity defects, the single-mode fiber laser was employed to conduct conventional laser linear welding and scanning welding experiments on T2 copper in this study. Using high-speed photography and image processing technology, the metal spattering during welding was studied. Then, the effect of different welding paths on the stability of the laser welding copper process was investigated. Besides, the welding quality of the samples under different welding paths was compared and explored from the perspectives of surface morphology, internal porosity, microstructure, mechanical properties and electrical conductivity of the joints. The results show that: compared with the conventional laser linear welding, laser scanning welding of “O” shape, “8” shape and “∞” shape trajectories can extend the cycle variation of keyhole, reduce the metal vapor and intensity of plasma eruption, improve the welding process stability, and inhibit the production of metal spattering, thus enhancing the welding formation and lowering the welding defects. Among them, the “O” shape scanning trajectory has the best inhibiting effect on metal spattering during welding, which reduces the spattering of the molten metal by 48.8% in the laser linear welding sample. The scanning welding samples under the “O” shape trajectory have flat, continuous, fine and uniform welding seam, with optimal shape, and narrow heat affected zone. The joint has the highest tensile strength of 234 MPa, which can reach 97.5% of the base metal strength. The porosity is the lowest of 1.33%, which is only 38% of the conventional laser linear welding sample. In addition, the highest conductivity is 71.79 mS/m, reaching 91.5% of base metal conductivity.

Nanoantennas Patterned by Colloidal Lithography for Enhanced Nanophosphor Light Emission.

Transparent coatings made of rare-earth doped nanocrystals, also known as nanophosphors, feature efficient photoluminescence and excellent thermal and optical stability. Herein, we demonstrate that the optical antennas prepared by colloidal lithography render thin nanophosphor films with a brighter emission. In particular, we fabricate gold nanostructures in the proximity of GdVO4:Eu3+ nanophosphors by metal evaporation using a mask made of a monolayer of polymer beads arranged in a triangular lattice. Optical modes supported by the antennas can be controlled by tuning the diameter of the polymer spheres in the colloidal mask, which determines the shape of the gold nanostructure, as confirmed by numerical simulations. Confocal microscopy reveals that metallic antennas induce brighter photoluminescence at specific spatial regions of the nanophosphor film at targeted frequencies as a result of the coupling between gold nanostructures and nanophosphors. Patterning of nanophosphor thin layers with arrays of metallic antennas offers an inexpensive nanophotonic solution to develop bright emitting coatings of interest for color conversion, labeling, or anti-counterfeiting.

CFD–DPM Simulation Study of the Effect of Powder Layer Thickness on the SLM Spatter Behavior

Selective Laser Melting (SLM) has significant advantages in manufacturing complex structural components and refining the alloy microstructure; however, spatter, as a phenomenon that accompanies the entire SLM forming process, is prone to problems such as inclusions, porosity, and low powder recovery quality. In this paper, a Computational Fluid Dynamics–Discrete Particle Method (CFD–DPM) simulation flow for predicting the SLM spatter behavior is established based on the open-source code OpenFOAM. Among them, the single-phase flow Navier–Stokes equation is used in the Eulerian framework to equivalently describe the effect of metal vapor and protective gas on the flow field of the forming cavity, and the DPM method is used in the Lagrangian framework to describe the metal particle motion, and the factors affecting the particle motion include particle–particle collision, particle–wall collision, fluid drag force, gravity, buoyancy force, and additional mass force. In addition, the equivalent volume force and fluid drag force are used to characterize the fluid–particle coupling interaction. For the spatter behavior and powder bed denudation phenomenon, the calculation results show that the spatter height and the drop location show a clear correlation, and the powder bed denudation phenomenon is caused by the high-speed gas flow, causing the surrounding gas to gather in the forming area, which in turn drives the motion of the powder bed particles. For the effect of powder layer thickness on spatter and powder bed denudation, the calculation results show that the effect of powder layer thickness on the number of spatters is large (when the thickness was increased from 50 μm to 100 μm, the number of spatters increased by 157%), but the effect on spatter height and drop location distribution is small. When the powder layer thickness is small, the width of the denudation zone is significantly larger, but when the powder layer reaches a certain thickness, the width of the denudation zone does not show significant changes. It should be noted that the presented model has not been directly validated by experiments so far due to the difficulty of tracking the large-scale motion of SLM spatter in real time by current experimental means.

Metal and Molecular Vapor Separation Analysis for Direct Determination of Mn and Cu by Atomic Absorption Detection, Free of Background Absorption

The metal and molecular vapor separation analysis (MMVSA) of solid samples with an atomic absorption detector (AA) was investigated for the direct determination of manganese and copper in biological materials. An open column made with a molybdenum tube (i.d. 1.22 mm) with three-ring supporters was developed. Pure argon as a carrier gas flowed at a flow rate of 4.0 mL min−1. An ultrasonic agitation method was used for suspending NIST standard reference material powders in water. Manganese and copper in the biological powders were completely separated from Al, Ca, Fe, K, Mg, Na, and Zn elements by MMVSA under optimal experimental conditions. Several NIST biological samples were directly analyzed with satisfactory results. It was found that manganese and copper in biological materials without interferences from matrix elements could be directly determined after only an ultrasonic agitation of the biological powders. The advantages of the slurry sampling of MMVSA are simplicity, low cost, a high speed of analysis, and rapid calibration.

Spatially resolved spectroscopy of alkali metal vapour diffusing inside hollow-core photonic crystal fibres

We present a new type of compact and all-glass based vapour cell integrating hollow-core photonic crystal fibres. The absence of metals, as in a traditional vacuum chamber and the much more compact geometry allows for fast and homogeneous heating. As a consequence we can fill the fibres on much faster timescales, ranging from minutes to hours. Additionally the all-glass design ensures optical access along the fibre. This allows live monitoring of the diffusion of rubidium atoms inside the hollow-core by measuring the frequency-dependent fluorescence from the atoms. The atomic density is numerically retrieved using a five-level system of Bloch-equations.

In situ monitoring of beam current in electron beam directed energy deposition based on adsorbed electrons

Electron beam directed energy deposition (EB-DED) is a promising and efficient additive manufacturing technology, but the vacuum environment challenges the in situ parameters monitoring. In this paper, an in situ beam current monitoring method is developed based on the absorbed electrons. A series of experiments show that there is a linear relationship between the absorbed electron current and the impinging beam current. However, this relationship only holds when the beam power density is relatively low. When the power density is high, the absorbed electron current will be lower than the theoretical value determined by the linear relationship. This is mainly due to the massive generation and ionization of metal vapor. The critical power density depends on the melting point of the material. Nonetheless, the deviation of the absorbed electron current at high power density can roughly determine the relative position between the focal spot and the workpiece surface. In addition, the slope of the linear relationship is material-dependent, so this method can also distinguish different materials.