Evaporation Of Alloys Research Articles

Growth of Spontaneous Nucleation AlN Crystals by Al-Base Alloy Evaporation in Nitrogen Atmosphere

Aluminum nitride (AlN) crystals with areas ranging from 1 mm2 to 2 mm2 were successfully grown through spontaneous nucleation at 1700 °C using a modified vapor transport method. In this approach, Cu–Al alloy served as the source of aluminum (Al), and nitrogen (N2) was employed as the nitrogen source. The morphology and crystalline quality of the AlN crystals were characterized by a stereo microscope, Raman spectrometer, photoluminescence (PL) and secondary-ion mass spectrometry (SIMS). Deposited on the graphite lid, the as-grown AlN crystals exhibited both rectangular and hexagonal shapes, identified as m-plane and c-plane AlN, respectively, based on Raman spectroscopy. The full width half maximum (FWHM) values of E2 (high) for the rectangular and hexagonal grains were measured to be 6.00 cm−1 and 6.06 cm−1, respectively, indicating high crystalline quality. However, PL and SIMS analysis indicated the presence of impurities associated with oxygen in the crystals. This paper elucidates the growth mechanism of the modified vapor transport method and highlights the role of the Cu–Al alloy in sustaining reactions at lower temperatures. The addition of copper (Cu) not only facilitates sustainable reactions, but also provides a novel perspective for the growth of AlN single crystals.

Advancing Manganese Content Prediction in Submerged Arc Welded Metal: Development of a Multi-Zone Model via the Calphad Technique

Manganese is a vital element in determining the mechanical properties of submerged arc welded metal. To ensure a reliable weld, the equilibrium model has been used for decades to predict and control the manganese content, particularly when MnO-bearing fluxes are applied. However, the equilibrium model only considers chemical interactions within the weld pool zone, leading to significant inaccuracies. To address this limitation, we propose a multi-zone model that accounts for all of the essential reaction zones in the submerged arc process via the Calphad technique. The model’s accuracy is verified by predicting the manganese content, the flux oxygen potential, and the neutral point location for the typical MnO-bearing fluxes covering acidic, neutral, and basic fluxes. The results indicate that the multi-zone model offers superior accuracy compared to the equilibrium model, which neglects significant oxygen improvement and alloy evaporation in the droplet zone. Further analysis of thermodynamic data reveals that the multi-zone model provides a more representative depiction of the variation trends in oxygen and manganese contents during the submerged arc welding process compared to the equilibrium model. Furthermore, this model can be utilized in the optimization of the submerged arc welding process, leading to improved quality and efficiency in heavy engineering industries. This study may provide an improved method for predicting the manganese content in welded C-Mn steel and deepen the understanding of manganese transfer mechanisms during the submerged arc welding process.

Thermodynamics of formation and evaporation of lead-tin alloys

Only a few works have been devoted to thermodynamic studies of the lead-tin system by methods including the volatile components evaporation process. When the binary system is separated into metals by distillation, the volatile component is removed from the alloy and the low-volatile component accumulates in the bottom products, that is, there are alloy composition changes over the entire concentration range. It is necessary to know the boundaries position of the melt and vapor coexistence fields on the state diagram, especially for solutions beneficiated with non-volatile metal to assess the quality of the vapor phase by the content of the low-volatile component. In this regard, the study has been completed with the purpose to clarify the values of the thermodynamic functions of the formation and evaporation of lead-tin melts required to calculate the boundaries of the liquid and vapor coexistence fields on the state diagram that enables us to judge the amount of a low-volatile component in the vapor phase under equilibrium conditions. The thermodynamic activity of lead was calculated, as well as the numerical integration of the Gibbs-Duhem equation using the substitution proposed by Darken is the thermodynamic activity and pressure of saturated tin vapor Based on the values of the saturated lead vapor pressure, determined by the boiling point method (isothermal version) for alloys predominantly of the lead edge of the phase diagram. The thermodynamic constants thus obtained will add to the base of physicochemical data and will be used to calculate the boundaries of the vapor-liquid equilibrium fields on the phase diagram, allowing to determine the possibility and completeness of the distillation separation of metals.

Influence of the thermal factor on the composition of electron­beam high­entropy ALTiVCrNbMo coatings

This paper reports results of studying the element and phase compositions of electron-beam coatings based on the high-entropy alloy AlTiVCrNbMo, depending on the deposition temperature (in the range of 300...700 °С). The high-entropy alloys were melted in an arc furnace in an atmosphere of high-purity argon. Vacuum condensates of the high-entropy alloy (AlTiVCrNbMo) with a thickness of 3–5 µm were obtained in the vacuum setup UVN-2M-1 at a working vacuum of 5·10 -5 mТоrr. The alloy evaporation was performed from the water-cooled ingot mold using an electron-beam gun with a power of 5 kW. Condensation of vapors of all the elements of the alloy was performed onto copper substrates at temperatures of 300, 500, 700 °C. Based on analysis of the element composition of materials of the target made of the high-entropy six-element alloy AlTiVCrNbMo and electron-beam coatings, based on it, we established the critical parameter (specific heat of vaporization of an element) that defined a selective change in the element composition. In accordance with a characteristic change in the composition of coatings of the multi-element high-entropy alloy, 3 groups of elements were distinguished: with a specific heat of evaporation of 280...350 kJ/mol (group 1), 420…460 kJ/mol (group 2), and 590…680 kJ/mol (group 3). It was shown that the formation of a single-phase coating of the high-entropy alloy (based on BCC of the crystalline lattice) occurs at the higher deposition temperature of 500...700 °C when the coating consists of not less than 5 elements. It was established that based on the conditions for an electron-beam process of materials formation, the results obtained can be divided into two types: those determined by the condition of evaporation of the target and those determined by the conditions of coating deposition. The density of flows of elements, evaporated from the target, is determined by their specific heat of evaporation. However, the ratio of atoms in the flow, derived in this way, may not be retained in the formed coating due to the secondary evaporation of elements from the growth surface. The obtained results allow us to substantiate principles for the selection of components for achieving the optimal element and phase compositions of high-entropy alloys.

Liquid Steel at Low Pressure: Experimental Investigation of a Downward Water Air Flow

In the continuous casting of steel controlling the steel flow rate to the mould is critical because a well-defined flow field at the mould level is essential for a good quality of the cast product. The stopper rod is a commonly used device to control this flow rate. Agglomeration of solid material near the stopper rod can lead to a reduced cross section and thus to a decreased casting speed or even total blockage (“clogging”). The mechanisms causing clogging are still not fully understood. Single phase considerations of the flow in the region of the stopper rod result in a low or even negative pressure at the smallest cross section. This can cause degassing of dissolved gases from the melt, evaporation of alloys and entrainment of air through the porous refractory material. It can be shown that the degassing process in liquid steel is taking place mainly at the stopper rod tip and its surrounding.The steel flow around the stopper rod tip is highly turbulent. In addition refractory material has a low wettability to liquid steel. So the first step to understand the flow situation and transport phenomena which occur near the stopper is to understand the behaviour of this two phase (steel, gas) flow. To simulate the flow situation near the stopper rod tip, water experiments are conducted using a convergent divergent nozzle with three different wall materials and three different contact angles respectively. These experiments show the high impact of the wettability of the wall material on the actual flow structure at a constant gas flow rate.

Effect Of Natural Convection On Directional Solidification Of Pure Metal

AbstractThe paper is focused on the modeling of the directional solidification process of pure metal. During the process the solidification front is sharp in the shape of the surface separating liquid from solid in three dimensional space or a curve in 2D. The position and shape of the solid-liquid interface change according to time. The local velocity of the interface depends on the values of heat fluxes on the solid and liquid sides. Sharp interface solidification belongs to the phase transition problems which occur due to temperature changes, pressure, etc. Transition from one state to another is discontinuous from the mathematical point of view. Such process can be identified during water freezing, evaporation, melting and solidification of metals and alloys, etc.The influence of natural convection on the temperature distribution and the solid-liquid interface motion during solidification of pure copper is studied. The mathematical model of the process is based on the differential equations of heat transfer with convection, Navier-Stokes equation and the motion of the interface. This system of equations is supplemented by the appropriate initial and boundary conditions. In addition the continuity conditions at the solidification interface must be properly formulated. The solution involves the determination of the temporary temperature and velocity fields and the position of the interface. Typically, it is impossible to obtain the exact solution of such problem. The numerical model of solidification of pure copper in a closed cavity is presented, the influence of the natural convection on the phase change is investigated. Mathematical formulation of the problem is based on the Stefan problem with moving internal boundaries. The equations are spatially discretized with the use of fixed grid by means of the Finite Element Method (FEM). Front advancing technique uses the Level Set Method (LSM). Chorin’s projection method is used to solve Navier-Stokes equation. Such approach makes possible to uncouple velocities and pressure. The Petrov-Galerkin formulation is employed to stabilize numerical solutions of the equations. The results of numerical simulations in the 2D region are discussed and compared to the results obtained from the simulation where movement of the liquid phase was neglected.

Polycrystalline GeSn thin films on Si formed by alloy evaporation

Polycrystalline GeSn thin films on Si substrates with a Sn composition up to 4.5% have been fabricated and characterized. The crystalline structure, surface morphology, and infrared (IR) absorption coefficient of the annealed GeSn thin films were carefully investigated. It was found that the GeSn thin films with a Sn composition of 4.5% annealed at 450 °C possessed a desirable polycrystalline structure according to X-ray diffraction (XRD) analyses and Raman spectroscopy analyses. In addition, the absorption coefficient of the polycrystalline GeSn thin films in the IR region was significantly better than that of the single crystalline bulk Ge.

Vacuum arc on the polycrystalline silica cathode

Thin films of silica and its compounds are used in modern technology to produce Li-ion batteries, wear-resistant and protective coatings, thin-films insulators, etc. This coating is produced with CVD methods, with magnetron sputtering systems or with electron-beam evaporation. The vacuum arc evaporation method, presently, is not used. The paper demonstrates a possibility for a long-term operation of vacuum arc evaporator with polycrystalline silica-aluminum alloy (90% of silica) cathode and with magnetic system to create a variable form of arch-like magnetic field on the cathode surface. It was shown that archlike configuration of magnetic field provides a stable discharge and uniform cathode spots moving with the velocities up to 5 m/s with magnetic fields induction about 10 mT. Thus, there is no local melting of the cathode, and this provides its long-term work without chips, cracks and destruction. Cathodes spots move over the cathode surface leaving t big craters with melted edges on its surface. The craters size was 150-450μm. The cathode spot movement character and the craters on the cathode surface were like the spots movement, when working on the copper or aluminum cathodes. With the magnetic field induction less than 1 mT, the cathode spots movement was the same as that of on the silica mono-crystal without magnetic field. Thus, the discharge volt-ampere characteristics for different values of magnetic fields were obtained. Voltampere characteristics were increasing and were shifted to the higher voltage with increasing magnetic field. The voltage was 18.7-26.5 V for the arc current 30-140 A. So, it was confirmed that vacuum arc evaporation method could be used for effective evaporation of silica and silica-based alloys and for thin films deposition of this materials.

Low Pressure Effects in SEN‐Stopper Region in Continuous Casting

In the continuous casting of steel, the control of the flow to the mould is a critical issue as a constant mould level is essential for a good quality of the cast product. A stopper rod is a commonly used device to control the flow rate. Agglomeration of solid material near the stopper rod can lead to a reduced cross section and thus to a decreased casting speed or even total blockage (clogging). The mechanisms involved in clogging are still not fully understood. Single phase considerations of the flow in the region of the stopper rod result in a low or even negative pressure at the smallest cross‐section. This can cause degassing of dissolved gases from the melt, evaporation of alloys and entrainment of air through the refractory material. In this paper the criteria for degassing of liquid steel at low pressures are analyzed and compared with water. A mathematical model for a two phase flow situation (liquid steel/gas) in the SEN that links the pressure distribution and the throughput with the geometrical parameters, the amount of gas in the SEN and the pressure loss coefficient at the stopper rod is presented. An explanation theory for the diminishing influence of the gas injection on clogging is outlined.

High-temperature field evaporation and its connection with surface ionization

High-temperature field evaporation of metals and alloys and its connection with surface ionization are considered. The main parameters of the evaporation process (dependence of the evaporation rate on the emitter temperature and on the electric field at the emitter surface, the charge of the ions being evaporated and its temperature dependence, kinetic parameters of the evaporation process, as well as the state of the emitter surface under simultaneous action of high fields and temperatures) are analyzed. The similarity and the difference between field evaporation at high temperatures and surface ionization in a strong electric field are determined.

Oxide Scale Morphology and Chromium Evaporation Characteristics of Alloys for Balance of Plant Applications in Solid Oxide Fuel Cells

This article compares chromium evaporation characteristics of chromia- and alumina-forming alloys at high temperatures [1123 K and 1223 K (800 °C to 950 °C)] in humid air (3 and 12 pct H2O) and presents a mechanistic understanding of variation in chromium evaporation on the basis of their oxide scale morphologies. For this study, an alloy from each of the distinct chromia-forming, alumina-forming, and chromia-alumina transition characteristics was selected (i.e., an alumina-forming alloy (Aluchrom YHf), a chromia-forming alloy (AISI 310S-austentic stainless steel), and an alloy that undergoes transition from chromia to alumina formation (Nicrofer6025 HT)). For generating baseline chromium evaporation data, pure chromium oxide was also tested. The chromium evaporation rate decreased in the order pure chromium oxide > AISI 310S > Nicrofer6025 HT > Aluchrom YHf. Surface morphologies, cross sections, and chemical characteristics of oxide scales were examined by scanning electron microscopy and energy dispersive X-ray spectroscopy and focused ion beam. The variation in chromium evaporation of different alloys is explained on the basis of physical and chemical characteristics of the oxide scales.

Enhancement of the Service Lifetime of TiN Coated Punch Side pin by Adding a Small Amount of Yttrium

The Ti(Y)N coatings were successfully deposited onto 18-8 stainless steel substrates by the hollow cathode discharge (HCD) ion-plating method through the application of a Ti-Y(0.2 wt%) alloy evaporation source instead of pure titanium. The influence of Y on the adhesion of the TiN coating/substrate was studied. The results show that the adhesion of the coating to the substrate was evidently enhanced by adding a small amount of the rare-earth element yttrium. The Ti(Y)N coatings deposited on some punch side pins were presented and compared with the TiN coating. The service lifetime of Ti(Y)N coated the punch side pin is approximately 50% higher compared to that of TiN coated.

Study of the effect of low-power pulse laser on arc plasma and magnesium alloy target in hybrid welding by spectral diagnosis technique

In order to study the effect of laser pulses on arc plasma and target metal in the hybrid welding process, the spectra of the plasmas in the welding process of magnesium alloys are analysed in this paper. The acquisition system of plasma spectra is set up and the spectral lines of welding plasma are acquired. Compared with tungsten-inert gas (TIG) welding, the intensities of the spectral lines of magnesium increase sharply while those of Ar decrease for strong evaporation and ionization of magnesium alloys in low-power laser/arc hybrid welding. The electron temperature and density are estimated by the Boltzmann plot method and the Stark broadening effect. The result shows that the electron temperature of arc plasma in the hybrid welding process is much lower than that in TIG welding, especially in the laser beam-affected zone. In contrast, the electron density of the plasma is enhanced. The influences of laser parameters on electron temperature are also studied. The changes in electron temperature and density indicate that the effect of laser pulse on the target metal is the dominant factor influencing the electron temperature and density in low-power laser/arc hybrid welding.

The Composition Variation in Evaporation of Multi-Component Alloys by Electron Beam Physical Vapor Deposition

The Composition Variation in Evaporation of Multi-Component Alloys by Electron Beam Physical Vapor Deposition

Optical Properties of Amorphous Silicon-Yttrium Films

AbstractThis paper presents and discusses the results of measuring IR reflection and ellipsometric parameters, optical microscopy and AFM the mixed phase of amorphous Si:Y films with microcrystalline inclusions. These films were obtained by electron-beam evaporation of siliconyttrium alloys with different Y concentration (5-30 %) at two substrate temperatures (370 and 620 °C).

High resolution shadowing of Mycobacterium leprae

Metal shadow casting techniques for transmission electron microscopic examination was used to determine the morphological characteristics of Mycobacterium leprae in untreated and treated patients. This technique is used to visualize bacterial surface structures by thermal evaporation of platinum alloys under moderate vacuum. This method gives a high contrast image at relatively low resolution and is useful for correlating micro-morphology quantitatively to early therapeutic effects of anti-leprosy drugs. Using these techniques in untreated cases, the surface structures of M. leprae were uniformly filled with relatively homogenous protoplasm surrounded by a cell wall. Most of the bacilli had thick cell walls with prominent banded and fibrous structures on the surface of the cell body. The cell wall was not detached in any of the solid bacilli in untreated cases. The bacilli varied in size and some of them were swollen in their mid-portion. Some bacilli were very short and completely filled with cytoplasm; therefore, these short bacilli were counted as solid bacilli in electron microscopic morphological index (EM-MI) determination. During treatment, mainly the cytoplasms of the bacilli were affected, and degeneration was observed. Ultrastructurally, the cytoplasm was shrunken and detached from the cell wall indicating mild degeneration. After moderate degeneration, the cytoplasm appeared fragmented. In advanced degeneration, all structures except the cell walls collapsed completely and no fibrous or band structures were visible on the surfaces of the cell walls. Therefore, these bacilli were counted as non-solid bacilli for EM-MI determination. This study shows that transmission electron shadowing gives more accurate counts than standard light microscopy of intact M. leprae bacilli in patient specimens.

Formation of β‐FeSi2 with electron beam evaporation

AbstractIn the formation of β‐FeSi2 by means of FeSi2 alloy evaporation, there are problems that the vapor pressure of Fe and Si is low and that there is a vapor pressure difference of close to one order of magnitude between Fe and Si. In this paper, by using electron beam (EB) evaporation equipment, these problems are resolved and the success of β‐FeSi2 formation is reported. First, the Fe and Si composition ratio of the EB evaporated film of FeSi2 alloy is analyzed by XPS. It is confirmed that the ratio is almost 1 to 2. Next, a sample with FeSi2 alloy EB evaporated on a Si substrate is annealed within a nitrogen environment by using an infrared heating furnace (at 700 to 900 °C) so that β‐FeSi2 is synthesized. Also, it is found that the β‐FeSi2 layer is made thicker and the optical absorption characteristic is improved by vapor‐depositing an Fe layer between the FeSi2 alloy layer and a Si substrate. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(1): 9–15, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10118

Structure and Mössbauer spectra for the Fe–Cr system: From bulk alloy to nanoparticles

The structure and hyperfine fields of Fe1−xCrx (x=0.0236–0.803) nanoparticles (average size of 27±2 nm) are studied at room temperature by combined x-ray diffraction and Mössbauer spectroscopy techniques. They are produced by fast evaporation of bulk alloys at 3 Torr Ar pressure. The bulk alloys of any composition are shown to exhibit a bcc structure, whereas the nanoparticles demonstrate a mixture of bcc and tetragonal σ phases in the Cr range from 24.4 to 83.03 at. %. At the Cr content of 2.36 at. % the lattice constant for nanoparticles is larger than that of the bulk alloy, though the values of hyperfine fields on Fe nuclei do not differ. The Mössbauer spectrum of nanoparticles contains an oxide doublet in addition to the sextet specific to that of the bulk alloy. In both cases the width of the sextet lines is rather narrow. However, even at ∼8 at. % Cr the lines of the sextet are broadened so much that it can be decomposed by two-three components. This is explained by freezing the high-temperature ferromagnetic fcc phase regions in the bcc lattice. As the Cr content increases, the Mössbauer spectra become more complex, transforming finally into a paramagnetic singlet. A complete ferromagnetic→paramagnetic transition is observed for the bulk alloy at 68 at. % Cr and for nanoparticles at 35 at. % Cr. The results are discussed under the assumption that at high temperatures the alloys are not homogeneous and exhibit fluctuations of the composition. With decrease of temperature these fluctuations result in decomposition of the alloy into two phases for nanoparticles whereas they are frozen at the cluster level in the bulk alloys holding a macroscopic homogeneity.

Special aspects concerning the electron beam deposition of multi-component alloys

PVD coatings deposited by electron beam evaporation have been used for many years. This technology is principally qualified to deposit alloys by evaporation from a single-crucible. In the last time the electron beam evaporation of multi-component alloys plays a more and more important role. Taylor-made substrate layer systems with special functions can be obtained. The composition of the liquid evaporation pool is strongly influenced by the saturation vapor pressures of the particular elements and their differences. The authors have investigated the parameters influencing the layer composition and have developed a mathematical model for the calculation of the evaporation and deposition parameters. The so-called activity coefficients of the elements represent the interaction between the components in the liquid evaporation pool. It was found, that there is a strong influence of the activity coefficients on the evaporation in addition to the effect of the different saturation vapor pressures of the elements. The results will be presented at the example of the electron beam evaporation of a special iron–chromium–nickel alloy. Experimental and calculated data will be compared. The developed model for the calculation of the evaporation and deposition parameters of multi-component alloys is universally valid and therefore useful for a lot of applications.

An Investigation of Evaporation of Liquid Alloys of Iron with Copper

The Knudsen method of mass-spectrometry and the integral option of the Knudsen effusion method realized under conditions of ultrahigh oilless vacuum are used in the overall temperature range from 1440 to 1916 K to investigate the evaporation of pure iron and copper and of a dilute liquid Fe–Cu solution with the copper content ranging from 0.17 to 10.1 at. %. The obtained data are used to calculate the values of standard sublimation enthalpy for Fe and Cu, as well as the partial and integral thermodynamic characteristics of liquid alloys of iron with copper. Significant positive deviations from Raoult's law are observed.