Vanadium Aluminum Alloys Research Articles

Phase Transformation of AlV55 Alloy at High Temperature

Vanadium–aluminum alloy is an important intermediate alloy for preparing aviation grade titanium alloys, and its product quality directly affects the finished product quality of titanium alloys. In this study, focusing on the problems of high powder content (19.8%) and low product yield in AlV55 alloy products, we conduct research on alloy quality control technology and implement a vanadium–aluminum alloy cooling crystallization control process. The research results indicate that there are three phases in AlV55 alloy, namely Al8V5, AlV, and Al2V3 phases. As the temperature decreases, the AlV phase gradually decomposes into Al8V5 phase and Al2V3 phase, and the proportion of Al8V5 phase is positively correlated with the fineness. Rapid cooling can reduce the formation of Al8V5 phase. The experimental results show that high-temperature water quenching can increase the proportion of vanadium–aluminum solid solution phase in the alloy from 19.03% to 31.76%, and reduce the fine powder rate to 13.2%, providing important product quality control means and technical support for the production of vanadium–aluminum alloys.

Phonon scattering at the interfaces of epitaxially grown Fe2VAl/W and Fe2VAl/Mo superlattices

We investigated the cross-plane thermal conductivity and boundary thermal resistance of epitaxially grown superlattice samples. These included iron vanadium aluminum alloy (Fe2VAl) and tungsten (W) or molybdenum (Mo) prepared by radio frequency magnetron sputtering. We used out-of-plane X-ray diffraction measurements to confirm the epitaxial growth of the superlattices. The superlattice with the shortest period of 1.9 nm showed satellite reflections indicating a highly ordered structure. Misfit dislocations in the 2-nm-thick Mo layer were also identified by high-resolution transmission electron microscopy. We attribute these features to the large lattice mismatch between the Fe2VAl and Mo lattices. The cross-plane thermal conductivity of the superlattice decreased as the number of interfaces increased because of thermal resistance at interlayer boundaries. A simulation of the thermal conductivity by the constant boundary resistance model reproduced the experimental data but with some deviations for samples with a smaller period (less than 20 nm). This deviation from the simulation results indicates that the phonon modes contributing to the thermal transport changed and/or the phonon scattering probability at the interfaces decreased. The superlattice of Fe2VAl/W with a period thickness greater than 20 nm had a boundary thermal resistance approximately twice as large as that of the Fe2VAl/Mo superlattice. This result provides clear evidence for the effects of the mass difference of layers on phonon scattering at an interface.

Semiconductor-Like Behavior of Electric Transport in Fe–V–Al-Based Metallic Alloys and Their Uncommon Magnetic Properties

A brief survey of experimental and theoretical works on the study of electronic transport and magnetic properties of iron–vanadium–aluminum alloys of composition close to Fe2VAl is presented. These alloys consist of “good” metals, but manifest uncommon “semiconductor-like” kinetic and thermal properties in the region of low temperatures, and an anomalous behavior of magnetic characteristics at higher temperatures. These anomalies are explained by the existence of a narrow pseudo-gap in the density of electronic states at the Fermi level EF and also by a strong effect of the processes of scattering of charge carriers by local magnetic moments.

Artificial Ageing of Aluminum Alloys. Statistical Studies of Results

The materials used in aircraft industry beside the light specific weight, must respond to some specific requirements for creation of new materials and also the improvement of the material properties used in the present.In modern aircraft construction there are many casting pieces, such as props, fittings, flanges, handles, crossing tight bodies, etc. Casting alloys used are based on aluminum alloys, magnesium-lithium alloys, vanadium-aluminum alloys, titanium alloys, etc.Aluminum alloy, the ones which are light and have good physical and mechanical properties, are part of common materials used in producing some components found in aircraft technology. In terms of experimentally point of view, the application of different artificial ageing heat treatments leads to an improvement of the mechanical properties compared with the results registered by natural aging.Experimental researches made on samples of ATSi6Cu4Mn aluminum alloy artificially aged by unconventional heat treatments highlights the obtaining of improved mechanical properties, the results representing a very useful database under the terms of the data being properly recorded.The verification by a statistical test of the experimental data registration in a normal distribution represents in this case the necessary condition for the validation of the results.

Variation of activation energy of hydrogen absorption of vanadium as a function of aluminum

Hydrogen absorption kinetics of vanadium–aluminum alloys in the temperature range of 624–924 K have been studied. These alloys were prepared by the aluminothermy process and refined by electron beam melting. The data of instantaneous reacted fractions at four different temperatures were obtained using the pressure drop method and these data were linearly fitted to a suitable reaction mechanism function. Three-dimensional diffusion appears to be the intrinsic rate limiting step of the hydrogen absorption. The rate constants were obtained from the slope of the linearly fitted curves. Apparent activation energies were calculated using the Arrhenius equation. The activation energies were increased linearly with aluminum content resulting in a decrease in the hydrogen absorption rate. The variation in standard entropies and enthalpies of vanadium–hydrogen solid solution has been studied as a function of aluminum content.

Hydrogen absorption kinetics of V–Al alloy

The vanadium–aluminum alloy has been prepared by aluminothermy process. The alloy ingot obtained was refined by electron beam melting and homogenized by vacuum arc melting technique. The refined alloy was crushed into small pieces. These pieces were kept isothermally in a thermobalance attached to the Sieverts apparatus for the hydrogen charging. Reacted fraction α was calculated using isothermal thermo-gravimetry method. The reacted fraction α–t data thus obtained have been linearly fitted over a suitable reaction mechanism function. Rate constants at different temperatures are determined using slope of these linearly fitted curves. Activation energy of hydrogen charging has been calculated using Arrhenius equation.

Effect of aluminum on solubility and β phase stability of vanadium–hydrogen system

Effect of aluminum on hydrogen solubility and β phase stability of vanadium–hydrogen system have been investigated employing thermo gravimetric (TG), differential thermal analysis (DTA) and X-ray diffraction technique. Vanadium aluminum alloys have been prepared by aluminothermy process followed by electron beam refining and vacuum arc melting. High purity vanadium is used for the comparative study. The hydrogen solubility decreases with aluminum content and with temperature. Substantial variation of hydrogen desorption mechanism from α as well as from β phase was observed due to the aluminum content. Desorption kinetics and modification of phase stability are the two possible reasons for the observed phenomenon.

High-performance boron-doped vanadium–aluminum alloy membranes for hydrogen separation

In this letter, our aim is to explore the properties of a new class of high-performance membranes for hydrogen separation applications prepared from boron-doped vanadium–aluminum alloys. In particular, we present the first hydrogen permeation characteristics of Pd-coated V99.8−xAlxB0.2 (x=0, 10) alloy membranes. Membranes have been investigated in the pressure range 1.5–3.0bar under pure hydrogen and hydrogen–carbon dioxide gas mixture at 400°C. Hydrogen flux is found on the order of 48mL/min/cm2 for a Pd-coated V99.8B0.2 alloy membrane (thickness: 0.5mm) using pure hydrogen as the feed gas.

Terminal solid solubility of hydrogen in V–Al solid solution

Hydrogen solubility was studied in vanadium and series of vanadium aluminum alloys at varying temperatures and pressures. The alloys were prepared through aluminothermy followed by electron beam refining and consolidation through vacuum arc melting. The consolidated buttons were hot rolled into 1.2mm strips. The strips were cut into small pieces. The specimens so obtained were annealed to release the stresses developed during hot-rolling. Hydrogen gas was charged in the specimens at present temperatures and pressures. It was observed that hydrogen solubility decreases linearly with aluminum contents. The decrease in the hydrogen solubility with the aluminum content has been explained on the basis of increase in the Fermi energy level arising from the contribution of electrons by the solute aluminum atom to the valence band of the host matrix vanadium.

ICP-AES Determination of 15 Kind of impurity elements in the Vanadium-aluminum alloy

In order to solve the current lack of detection method of impurity elements in the vanadium-aluminum alloy, this paper established by inductively coupled plasma atomic emission spectrometry (ICP-AES) direct simultaneous determination of 15 kind of micro or trace impurity elements, including boron, tungsten, silicon, iron, lead, tin, arsenic, nickel, chromium, cobalt, copper, phosphorus, manganese, magnesium, molybdenum. Vanadium-aluminum alloy sample was digested as the solution with hydrochloric acid and nitric acid, and then by nebulizer spray aerosol was introduced in the plasma torch, the elements in the 8000-10000K high temperature was excited and emission of characteristic lines, by detecting the signal intensity of the characteristic lines for quantitative analysis. Method detailed study between the sample substrate the vanadium and aluminum as well as the co-existing elements disturbing effect, and through the optimal analysis spectral line and the background adjusted the position to avoid the spectrum disturbance. Selects the method which the substrate match and the synchronized background adjust unify to eliminate highly concentrated the vanadium aluminum base body to the test solution atomization, transmission, ICP balanced and the stimulation and the element determination each kind of disturbing effect factor, and optimize the operation control parameters of the spectrometer. In this law determination aerospace rank's vanadium-aluminium alloy impurity element's result indicated: detection limit 5.0 ∼ 100μg / L, the background equivalent concentration of 5-95μg / L; recovery rate of 95.3% to 110.0%; in content ≥0.010% RSD≤4.88%; between 0.001% and 0.010% content scope RSD≤8.89%. The actual sample results were the same as the Germany GfE company which is the world-class manufacturer of the vanadium-aluminium alloy, and detection elements and scope over the Gfe. Method measured the European standard samples of the vanadium-iron alloy consistent with the standard value, whose matrix composition similar to the vanadium-aluminium alloy.

The high-temperature oxidation behavior of vanadium-aluminum alloys

The oxidation behavior in air of pure vanadium, V-30Al, V-30Al-10Cr, and V-30Al-10Ti (weight percent) was investigated over the temperature range of 700–1000° C. The oxidation of pure vanadium was characterized by linear kinetics due to the formation of liquid V2O5 which dripped from the sample. The oxidation behavior of the alloys was characterized by linear and parabolic kinetics which combined to give an overall time dependence of 0.6–0.8. An empirical relationship of the form: ΔW/A=Bt + Ct1/2 + D was found to fit the data well, with the linear contribution suspected to be from V2O5 formation for V-30Al and V-30Al-10Cr, and a semi-liquid mixture of V2O5 and Al2O3 for V-30Al-10Ti. The parabolic term is presumed related to the formation of a solid mixture of V2O5 and Al2O3 for V-30Al and V-30Al-10Cr, and TiO2 for V-30Al-10Ti

V-Al合金の低酸素圧高温酸化

V-Al合金の低酸素圧高温酸化