Al Single Crystals Research Articles

Сцинтиляційні матеріали на основі твердих розчинів ZnSxSe1–x

Composite materials based on ZnSxSe1–x solid solutions are promising materials for gamma and X-ray detectors. However, influence of compositions and particle size on scintillation properties is unclear, which prevents their application. This paper reports on the complex study of microcrystalline ZnSxSe1–x powdered scintillations, prepared by solid phase synthesis from ZnS and ZnSe initial compounds. ZnSxSe1-x solid solutions were obtained in the range of x from 0.07 to 0.86 and in the following sizes: 200—250, 140—200, 140—80 µm, and less than 80 µm. X-ray diffractions of powder ZnSxSe1–x shows formation of a cubic lattice of sphalerite structure. ZnSxSe1–x powders demonstrate a presence of a luminescence band in the 590—615 nm regions, while an increase in sulfur concentration leads to a shift of the maximum intensity of X-ray induced luminescence to the short-wave region, which is associated with an increase of the band gap width. The best parameters of X-ray induced luminescence are obtained for the solid solution with 39 at.% of sulfur. The ZnS0,39Se0,61 solid solutions obtained under these conditions have an X-ray induced luminescence intensity that is 4 times higher than that of ZnSe(Al) single crystal and a relatively low level of afterglow. In ZnSxSe1–x solid solutions, increasing of particle size leads to shifts of the X-ray induced luminescence to the longwave region. The highest intensity of the X-ray induced luminescence corresponds to the ZnS0,39Se0,61 composition with the particle size of less than 80 µm. Also, ZnS0,39Se0,61 solid solutions, with particle size less than 80 microns, are more homogeneous in composition, which is why the process of solid phase reaction in them passes more efficiently. It is shown that the ZnSxSe1-x composite scintillators can be used as gamma and X-ray detectors. It has been established that the effectiveness of these materials depends on their composition. ZnS0,5Se0,5 and ZnS0,39Se0,61 composites demonstrate the best scintillation characteristics, with twice as high an efficiency as that of the «commercial» ZnSe(Al) composite.

Growth of Porous Anodic Alumina on Low-Index Surfaces of Al Single Crystals

The pseudoepitaxial growth of amorphous anodic alumina with ordered porous structure within single crystal grains of aluminum substrates is an amazing feature of the self-organization process, which occurs during anodization. Here, we used single crystal Al(100), Al(110), and Al(111) substrates to inspect the effect of aluminum crystallography on anodization rates and the morphology of the resulting alumina films grown under different anodization conditions. The difference in the kinetics of porous film growth on various substrates is described in terms of the activation barrier of aluminum atom release from the metal surface to the oxide layer. Scanning electron microscopy and small-angle X-ray scattering are applied for quantitative characterization of different kinds of ordering in anodic alumina films. The highest number of straight channels was found in porous anodic alumina grown on Al(100) substrates, whereas Al(111) was proved to induce the best orientational order in anodic alumina with the forma...

Pressure-induced itinerant electron metamagnetism in UCo0.995Os0.005Al ferromagnet

The effect of external hydrostatic pressure on magnetic properties is studied for the UCo0.995Os0.005Al single crystal. At ambient pressure, the ground state is ferromagnetic. Even lowest applied pressure 0.11GPa is sufficient to suppress ferromagnetism. A sharp metamagnetic transition is observed only in magnetic fields along the c axis of the crystal, similar to previously studied itinerant electron metamagnet UCoAl. Temperature dependence of the susceptibility for various pressures shows a broad maximum at Tmax ~ 20K. The experimental data are analyzed with the theory of itinerant electron metamagnetism, which considers anisotropic thermal fluctuations of the uranium magnetic moment. The observed pressure dependence of the susceptibility at Tmax and the temperature for the disappearance of the first-order metamagnetic transition are explained with the theory.

Alloying and pressure effects on itinerant-electron metamagnetism of the UCoAl-based compounds

With the UCo1-xOsxAl single crystals, we studied interplay between alloying and pressure effects on magnetism of the itinerant electron metamagnet UCoAl. The Os alloying for x ≥ 0.005 switches the UCoAl to ferromagnetism. For the UCo0.995Os0.005Al single crystal, even lowest applied pressure 0.11 GPa is sufficient to suppress ferromagnetism. A sharp metamagnetic transition for various pressures is observed in magnetic fields along the c axis of the crystal. Concentration magnetic phase diagram of the UCo1-xOsxAl, which includes the quantum phase transition from ferromagnetic to metamagnetic state, and P–T–H phase diagram of the UCo0.995Os0.005Al are determined using the data of magnetization measurements at various pressures and temperatures.

Dependence of Strain Rate Sensitivity on the Slip System: A Molecular Dynamics Simulation

The strain rate of deformation might affect mechanical properties of metallic materials, especially at elevated temperatures. Due to the nature of dislocation slip, it is anticipated that strain rate sensitivity (SRS) depends on the slip system. While the dependency of SRS on the temperature and strain rate of the deformation is well recognized, its dependence on the slip system is not well understood. Accordingly, the molecular dynamics simulation was used to investigate the dependence of strain rate sensitivity of pure Al single crystals on the slip system. In this study, the embedded atom method (EAM) potential for Al was employed. SRS and shear strength of the material were studied in four different slip systems and at two temperatures of 300 and 500 K. It was found that SRS of the material depends on the slip system in addition to the temperature, and SRS was higher in less compact systems with more difficult slip. The dislocation theories were used to rationalize the simulation results.

Growth and characterization of an Al-doped GaSe crystal

A GaSe: Al (0.13wt%) single crystal was grown using the Bridgman method combined with a crucible rotation technique. A 35×19×5.5mm3 sample was cut from the as-grown crystal ingot. The GaSe: Al (0.13wt%) crystal has an indentation hardness of 2.27GPa, which is 2.6 times harder than the pure GaSe crystal. In particular, a sample with a thickness of 5.5mm has an infrared transmission of approximately 60%. The absorption coefficient of this sample is as low as 0.1cm−1 over the range of 0.83 to −14μm, which demonstrates its high optical quality. A crystal growth method with the described procedures may be suitable to grow other doped GaSe crystals.

Characterization of voids in shock-loaded Al single crystal by combining X-ray tomography and electron microscopy

A combination of X-ray tomography and electron backscatter diffraction (EBSD) was applied to investigate both the shape of voids and the plastic deformation around voids in an Al single crystal shock-loaded in the <1 2 3> direction. The combination of these two techniques allows the addition of crystallographic information to X-ray tomography and allows the addition of three-dimensional information to EBSD data. It is found that the voids are octahedral with {1 1 1} faces and that regular patterns of lattice reorientation exist around individual voids. The results provide new insights to the process of void growth during shock loading, which is important for both civil and military applications.

Non-spherical voids and lattice reorientation patterning in a shock-loaded Al single crystal

An Al single crystal shock loaded in the <1 2 3> direction and captured at incipient spallation was examined by combining X-ray tomography, electron backscatter diffraction on a scanning electron microscope, and transmission electron microscopy (TEM). Octahedral voids with {1 1 1} faces were a characteristic feature in the spall region. Regular patterns of lattice reorientation were found around individual voids, with lattice rotation being up to 25–30°. Each reorientation pattern consists of a number of reoriented zones. The direction of lattice rotation varies systematically from one zone to another. Four groups of reorientation patterns were identified morphologically in the same metallographic section, which result from different sectioning positions relative to the voids and thus provide equivalently a “serial sectioning” investigation of the deformed volume around the voids. An analysis of the observed reorientation patterns based on active slip systems rationalizes the key features observed and suggests that the systematic reorientation patterns result from the dominance of a single slip system in each individual zone. Microstructures revealed by TEM in the spall region show formation of dislocation cells and extended dislocation boundaries, illustrating the importance of plastic deformation during void growth.

Dynamical approach to displacement jumps in nanoindentation experiments

The load-controlled mode is routinely used in nanoindentation experiments. Yet there are no simulations or models that predict the generic features of force-displacement F-z curves, in particular, the existence of several displacement jumps of decreasing magnitude. Here, we show that the recently developed dislocation dynamical model predicts all the generic features when the model is appropriately coupled to an equation defining the load rate. Since jumps in the indentation depth result from the plastic deformation occurring inside the sample, we devise a method for calculating this contribution by setting up a system of coupled nonlinear time evolution equations for the mobile and forest dislocation densities. The equations are then coupled to the force rate equation. We include nucleation, multiplication, and propagation threshold mechanisms for the mobile dislocations apart from other well known dislocation transformation mechanisms between the mobile and forest dislocations. The commonly used Berkovitch indenter is considered. The ability of the approach is illustrated by adopting experimental parameters such as the indentation rate, the geometrical quantities defining the Berkovitch indenter including the nominal tip radius, and other parameters. We identify specific dislocation mechanisms contributing to different regions of the F-z curve as a first step for obtaining a good fit to a given experimental F-z curve. This is done by studying the influence of the parameters on the model F-z curves. In addition, the study demonstrates that the model predicts all the generic features of nanoindentation such as the existence of an initial elastic branch followed by several displacement jumps of decreasing magnitude, and residual plasticity after unloading for a range of model parameter values. Further, an optimized set of parameter values can be easily determined that gives a good fit to the experimental force-displacement curve for Al single crystals of (110) orientation. The stress corresponding to the maximum force on the elastic branch is close to the theoretical yield stress. We also elucidate the ambiguity in defining the hardness at nanometer scales where the displacement jumps dominate. For larger indentation depths where displacement jumps disappear, the indentation size effect is predicted. The approach also provides insights into several open questions.

Crystallography-Induced Correlations in Pore Ordering of Anodic Alumina Films

A crystallographic approach to tailoring the morphology and ordering degree of the porous structure of alumina films obtained by anodization of single-crystalline aluminum is discussed. The examination of porous structure of anodic alumina films formed on low-index and vicinal planes of Al single crystals under self-ordering conditions by high-resolution small-angle X-ray scattering revealed the existence of two pore growth directions on vicinal facets. The inclination of channels from the normal to the metal surface is explained by the competitive impact of electromigration driving force and the crystallographic anisotropy of the substrate. It was also shown that pores growing in different directions during anodization retain hexagonal domains with various in-plane orientations. These results for the first time demonstrate the strong correlations between the longitudinal alignment and in-plane packing options of pores in anodic alumina films.

Evaluation of copper, aluminum, and nickel interatomic potentials on predicting the elastic properties

Choice of appropriate force field is one of the main concerns of any atomistic simulation that needs to be seriously considered in order to yield reliable results. Since investigations on the mechanical behavior of materials at micro/nanoscale have been becoming much more widespread, it is necessary to determine an adequate potential which accurately models the interaction of the atoms for desired applications. In this framework, reliability of multiple embedded atom method based interatomic potentials for predicting the elastic properties was investigated. Assessments were carried out for different copper, aluminum, and nickel interatomic potentials at room temperature which is considered as the most applicable case. Examined force fields for the three species were taken from online repositories of National Institute of Standards and Technology, as well as the Sandia National Laboratories, the LAMMPS database. Using molecular dynamic simulations, the three independent elastic constants, C11, C12, and C44, were found for Cu, Al, and Ni cubic single crystals. Voigt-Reuss-Hill approximation was then implemented to convert elastic constants of the single crystals into isotropic polycrystalline elastic moduli including bulk modulus, shear modulus, and Young's modulus as well as Poisson's ratio. Simulation results from massive molecular dynamic were compared with available experimental data in the literature to justify the robustness of each potential for each species. Eventually, accurate interatomic potentials have been recommended for finding each of the elastic properties of the pure species. Exactitude of the elastic properties was found to be sensitive to the choice of the force fields. Those potentials that were fitted for a specific compound may not necessarily work accurately for all the existing pure species. Tabulated results in this paper might be used as a benchmark to increase assurance of using the interatomic potential that was designated for a problem.

Microstructure Evolution and Texture Development in a Cu-8.5%AT. AL Material Subjected to Hydrostatic Extrusion

AbstractThe aim of the present paper was to investigate microstructure and texture evolution of two single crystals and polycrystal of Cu-8.5%at.Al material. All of mentioned samples were deformed by HE to achieve true strain ε = 1.17. For microstructure analyzes observations by transmission electron microscope (STEM) were done. Crystalline size for samples after SPD were determine using XRD method. The global texture measurements were done using Bruker D8 Discover diffractometer equipped in Cr radiation. Microstructure investigations revealed nanocrystalline structure in single crystals with initial orientations &lt;110&gt; and &lt;100&gt; and polycrystalline Cu-8.5%at.Al material after SPD. The global texture measurements have shown the stability of initial orientation of &lt;100&gt; Cu-8.5%at.Al single crystal after HE, whereas the same SPD process strongly brakes up the orientation &lt;110&gt; Cu-8.5%at. Al single crystal.

The effect of crystal orientation on the aluminum anodes of the aluminum–air batteries in alkaline electrolytes

Recently, aluminum–air (Al–air) batteries have received attention from researchers as an exciting option for safe and efficient batteries. The electrochemical performance of Aluminum anode remains an active area of investigation. In this paper, the electrochemical properties of polycrystalline Al, Al (001), (110) and (111) single crystals are investigated using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) in 4 M NaOH and KOH. Hydrogen corrosion rates of the Al anodes are determined by hydrogen collection. Battery performance using the anodes is tested by constant current discharge at 10 mA cm−2. This is the first report showing that the electrochemical properties of Al are closely related to the crystallographic orientation in alkaline electrolytes. The (001) crystallographic plane has good corrosion resistance but (110) is more sensitive. Al (001) single crystals display higher anode efficiency and capacity density. Controlling the crystallographic orientation of the Al anode is another way to improve the performance of Al–air batteries in alkaline electrolytes.

Control of γ lamella precipitation in Ti–39 at.% Al single crystals by nanogroove-induced dislocation bands

We attempted to control γ lamellae precipitation in Ti–39at.% Al single crystals by nanogrooving process (NGP) intending to introduce periodic dislocation bands as preferential nucleation sites of γ-TiAl lamellae precipitates. In NGP, grooves were formed along the trace of (0001) basal plane on the surfaces of single crystal of α2-phase supersaturated with Al-atoms by nano-scale plastic deformation using diamond knives with the edge angle of 60°. The widths of grooves ranged from 180nm to 1860nm for the load per knife-edge length in the range from 0.3N/mm to 8.3N/mm. Beneath the grooves, dislocation bands consisting of both basal dislocations and non-basal dislocations were formed. After aging at 1073K for 1×104s, pairs of γ lamellae were found to form only beneath the grooves to depths greater than 30μm, meaning that the location of γ lamellae could be controlled by NGP. Increasing the aging temperature to 1173K provided even greater control, with arrays of γ lamella bundles exhibiting a periodicity identical to that of the nanogrooves, and even near the surface no γ lamellae were formed in un-deformed regions. No concentration gradient was found within individual γ lamellae, which had a near-equilibrium Al concentration; thinner γ lamellae tended to have a slightly lower Al concentration. These results indicate that the precipitation of γ lamellae can be effectively controlled by introducing periodic dislocation bands using NGP, which opens new avenue for the manufacturing of near- or sub-wavelength grating structures with ultra-high aspect ratios through the selective dissolution of these γ lamellae.

Indentation depth-dependence of the hardness of NiTi shape memory alloy and Al single crystal: phase transition versus plasticity

The depth-dependence of the nanoindentation hardness in phase transition NiTi shape memory alloys and elastoplastic Al single crystals was examined through experimentation. The results indicated that there was a strong depth-dependence of hardness in both NiTi shape memory alloys and Al single crystals, and that the measured hardness correlated with different depth-dependences in each. The energy approach and dislocation plasticity method were used to explain the observed differences. The analysis indicated that the hardness of NiTi mainly comes from the resistance to the phase transition, and follows a reciprocal relationship with the indentation depth. The hardness of Al single crystal was found to originate from the plastic deformation through dislocation motion and the hardness scales with an inverse square-root of indentation depth, and surface effects become more prominent at extremely small indentation depths. The theoretical rationales were supported by the experimental results.

Software system for management of organ transplant centers

The adsorption of NO and N2O on clean and oxygen saturated Al(100) single crystal was studied at low temperatures (down to 80 K) by means of XP spectroscopy. It has been shown that the adsorption of NO and N2O is dissociative as well as associative. In addition, upon adsorption of NO, formation of N2O(a) is observed; this being due to the catalytic activity of the metal substrate. The initial sticking probability coefficients of NO and N2O at 80 K are 1 and 0.0016, respectively. The negative charge transfer from the Al atom to the adsorbate molecules is 0.51 e− for N2O(a) and 0.54 e− for NO(a).

Strain rate effect of high purity aluminum single crystals: Experiments and simulations

In order to study the strain rate effect on single crystal of aluminum (99.999% purity), aluminum single crystals are fabricated and subjected to uniaxial compression loading at quasi-static and dynamic strain rates, i.e., from 10−4s−1 to 1000s−1. The orientation dependence is also investigated with single slip or multi slip. The stress–strain curves of pure Al single crystals along two orientations and at different strain rates are obtained after measuring initial orientation using the Laue Back-Reflection technique.Crystal Plasticity Finite Element Method (CPFEM) with three different single crystal plasticity constitutive models is used to simulate the deformations along two orientations under various strain-rates. The classical and two newly developed single crystal plasticity models are used in the investigation. The simulation results of these models are compared to experimental results in order to study their abilities to predict finite plastic deformation of single crystalline metal over a wide strain rate range.

A massively parallel cellular automaton for the simulation of recrystallization

A new implementation of a cellular automaton for the simulation of primary recrystallization in 3D space is presented. In this new approach, a parallel computer architecture is utilized to partition the simulation domain into multiple computational subdomains that can be treated as coupled, gradually coupled or decoupled entities. This enabled us to identify the characteristic growth length associated with the space repartitioning during nucleus growth. In doing so, several communication strategies between the simulation domains were implemented and tested for accuracy and parallel performance. Specifically, the model was applied to investigate the effect of a gradual spatial decoupling on microstructure evolution during oriented growth of random texture components into a deformed Al single crystal. For a domain discretized into one billion cells, it was found that a particular decoupling strategy resulted in faster executions of about two orders of magnitude and highly accurate simulations. Further partition of the domain into isolated entities systematically and negatively impacts microstructure evolution. We investigated this effect quantitatively by geometrical considerations.

Evolution of Recrystallization Textures in Plane-Strain Compressed (001)[110] Aluminum Single Crystals

The (001)[110] orientation of Al single crystal is known to be metastable with respect to plane strain compression to form the (112)[1 1-1] and (112)[-1-1 1] orientations, known as the copper orientations. The copper orientations did not transform into the cube texture {001}&lt;100&gt; after recrystallization (Rex), at variance with expectation. When Al single crystals were plane-strain compressed and recrystallized (Rexed), their Rex orientation varied with reduction in thickness. These results are discussed based on the strain-energy-release-maximization theory, in which the Rex texture is determined such that the absolute maximum stress direction (AMSD) due to dislocations in deformed materials is parallel to the minimum Young’s modulus direction in Rexed grains and other conditions, whereby strain energy release can be maximized. AMSD is obtained from slip systems activated during deformation and their activities, which were calculated from the VPSC code.

Modeling of the temperature-dependent ideal tensile strength of solids

To reveal the fracture failure mechanisms of single crystals at elevated temperatures, a new temperature-dependent ideal tensile strength model for solids has been developed, based on the critical strain principle. At the same time, the uniaxial tensile strength model, based on the critical failure energy density principle for isotropic materials that was presented in the previous study, is generalized to multi-axial loading and to cubic single crystals. The relationship between the two models is discussed, and how to obtain the material properties needed in the calculations is summarized. The two well-established models are used to predict the temperature-dependent ideal tensile strength of W, Fe and Al single crystals. The predictions from the critical strain principle agree well with the predictions from the critical failure energy density principle. The theoretical values from the critical strain principle at 0 K is in reasonable agreement with the ab initio results. The study shows that the temperature dependence of the ideal tensile strength is similar to that of Young’s modulus; that is, the ideal tensile strength firstly remains approximately constant and then decreases linearly with the temperature. The fracture failure for single crystals at elevated temperatures has been identified, for the first time, as a strain-controlled criterion.