The composition of the first atomic layer of Cu_3Au(001) crystal (about half-and-half copper and gold atoms) changes only slowly even at temperatures much higher than that of the order-disorder transition (T_C = 663 K). Theoretical and experimental works show a general trend of these changes but they differ in quantitative findings. In the present work we used directional elastic peak electron spectroscopy and directional Auger electron spectroscopy to investigate changes of atomic order and composition in the first atomic layers of the Cu_3Au(001) crystal during the sample temperature increase. The height of central maximum in DEPES polar profile of the sample investigated was measured as a function of sample temperature. It was found that the measured dependence is linear, but the slope of this dependence changes abruptly around T_C. This change seems to be connected with disappearance of the atomic order in the first and second atomic layers. In DAES the height of the Auger peaks for copper and gold low energy transitions (MVV and NVV, respectively) were measured in the dN(E)/dE mode as a function of the primary electron beam incidence angle. The composition of the first, second, and third atomic layers was determined by fitting the ratio of calculated DAES polar profiles for copper and gold to such a ratio for the measured profiles.
Physical foundations of directional auger electron spectroscopy (DAES) and calculation of DAES profiles in single scattering cluster approach are presented. Limitations of this method (application only to investigation of the crystalline structure of homogeneous samples) is shown and explained as the result of participation of inelastically scattered electrons in the Auger signal generation. To extend the DAES application for the interface structure, the use of as low as possible energy of primary electrons is proposed because in such a case the participation of inelastically scattered electrons becomes negligible and single scattering cluster calculation should describe correctly the DAES profiles for interfaces. Besides, the extension of single scattering cluster calculations to the second elastic scattering is recommended. To check the technical possibility of DAES use in the proposed version, the Auger spectrum of Cu LMM peaks was recorded for a Cu_3Au(001) sample with the use of a retarding field analyzer with the primary beam energy 1200 eV. Quality of this spectrum seems to be good enough for using in DAES.
In this work the influence of equal-channel angular pressing on strength and fatigue of an aluminum alloy has been studied. Transmission electron microscopy was applied to determine an average grain size, shape, and size of precipitates. The ultimate tensile strength and fatigue endurance limit of ultrafine-grained and coarse-grained samples were evaluated at 20°C and 175°C.
The process of a primary crystallization of the Fe_{72.5}Cu_{1}Nb_{2}Mo_{2}Si_{15.5}B_{7} alloys was investigated by differential thermal analysis (DTA), x-ray diffraction (XRD) and transmission electron microscopy (TEM). Amorphous ribbons were isothermally annealed for 0.5, 2, 6, 30 and 150 minutes at 520 °C. Both, the XRD and TEM study showed that the level of devitrification of the sample increases with the annealing time. The above mentioned techniques confirmed the presence of the nanocrystalline grains of the Fe_{3}Si phase and enable us to study the evolution of the identified phase.
Local atomic structure in Fe_{84}B_{16} metallic glass, prepared by melt-spinning technique in He atmosphere, was studied by electron diffraction (ED) reduced density function (RDF) analysis. RDF curves were also obtained from X-ray diffraction (XRD) patterns and compared with the data from ED. Atomic reduced density functions, G(r), calculated from ED and XRD patterns showed good agreement. Atomic structure model has been fitted to the experimental ED data using Reverse Monte Carlo (RMC) simulation.
The aim of this paper is to analyze the hot working behavior of two different steels based on 3% and 5% Cr steel chemistry, respectively. Hot deformation is studied by hot torsion tests in the range of temperatures 1000-1200°C and strain rates 0.01, 0.10, 1.00 s^{-1}. At given temperatures and strain rates flow curves exhibit a peak followed by a decline towards a steady state which is indicative of dynamic recrystallization. At constant strain, flow stress increases with increasing strain rate and decreasing temperature. The analysis of the constitutive equation relating peak flow stress, strain rate and temperature shows high activation energy values for both steels. Recrystallized volume fraction of steels after hot deformation is estimated based on the grain orientation spread as measured by electron backscattered diffraction technique, on the hot deformed and quenched materials.
We report on Kelvin probe force microscopy and electron backscatter diffraction measurements of 3C-SiC epitaxial layers grown on exactly oriented Si-face 4H-SiC (0001) substrates in a horizontal hot-wall chemical vapor deposition reactor, in the temperature range from 1150°C to 1620°C, under H_{2} or H_{2} +SiH_{4} atmosphere. The investigated layers were doped with nitrogen (for n-type) and aluminium (for p-type). The electron backscatter diffraction analysis revealed structure of polytype 3C blocks with a relative rotation of 60 and/or 120°. The Kelvin probe force microscopy measurements revealed cubic substructure as a equilateral triangle objects contrast which is characteristic of 3C silicon carbide polytype. The surface potential contrast was found to be dependent on the type and concentration of doping, which could be explained in terms of the impurities accumulation at block boundaries.
Reflection high energy electron diffraction is a popular technique to characterize arrangements of atoms near a surface. However, Japanese researchers recently demonstrated experiments in the same geometry, however, conducted using positrons. In this context, detailed comparisons of basic results expected for diffractions of electrons and positrons seem to be interesting. Subsequently, in the current work the growth of single atomic layers of Ge on the Ge(001) substrate is assumed and intensities of reflected beams for electrons and positrons are computed by using dynamical diffraction theory for the case of the off-symmetry azimuth. Shapes of respective theoretical rocking curves are analyzed and then the features of intensity oscillations expected during the regular, continuous deposition of the material are discussed.
Three-dimensional electron diffraction tomography allows one to obtain structure information from nanocrystals. However, in order to get accurate results the dynamical theory must be used due to the strong dynamical interaction between electrons and matter. Full structure refinement using dynamical theory has been in use for some time, in spite of being hampered by the fact that the intensities are very sensitive to variations of thickness and of the orientation of the sample. A remedy to this problem is the technique called precession electron diffraction. The use of precession electron diffraction in combination with electron diffraction tomography results in more accurate structure parameters and lower figures of merit in the structure refinement. The principles of electron diffraction tomography, precession electron diffraction and dynamical refinement will be demonstrated on the structural analysis of a nanowire of Ni₃Si₂.
X-ray diffraction analysis, scanning and transmission electron microscopy, thermal analysis and measurement of chemical composition were implemented to determine structure, thermal stability and chemical composition of the decagonal quasicrystal in Al_{73}Cu_{11}Cr_{16} alloy produced by long-term mechanical alloying of elemental powders followed by annealing at 700°C. According to the TEM investigation such a technique permits to produce a single-phase nanostructural quasicrystal with grain size about 60 nm. Differential thermal analysis revealed that the decagonal phase does not exist above 923°C and undergoes incongruent two-stage melting coming to the end at 1100°C.
The root of single-crystalline turbine blade made of CMSX-4 superalloy were studied. The studied blade was produced by the Bridgman technique in industrial ALD furnace at withdrawal rate of 3 mm/min. The samples for investigations were cut from the blade root parallel to the withdrawal direction. Metallographic sections of longitudinal samples planes were prepared for further investigations. The samples were analysed using scanning electron microscopy and the Laue diffraction studies. The crystal orientations in macro-scale were determined by analysis of the Laue pattern and local crystal orientations were studied by electron backscattered diffraction technique. Morphology of dendrites were examined by analysis of scanning electron microscopy macro-images. Study of subgrain structure was performed by X-ray diffraction topography. The sharp parallel contrast bands, visible on the X-ray topograms, were related with dendrite cores, arranged with the same direction. Additionally, the low angle boundaries were formed in certain samples, visible on the topograms as contrast shifts. Step changes of local crystal orientation in certain areas were observed on the electron backscattered diffraction maps. The electron backscattered diffraction crystal orientation maps were related to the misorientation visualized in topograms.
In this paper the structural and Mössbauer spectral properties of multiferroic ceramic Bi_5Ti_3FeO_{15} powders prepared by high-energy ball milling of polycrystalline precursor material (mixture of Bi_2O_3, TiO_2 and Fe_2O_3 powders) are presented. Mechanical synthesis was performed by high-energy vibratory mill. The X-ray diffraction methods were applied for the structure characterization of the studied samples. The parameters of diffraction line profiles were determined by PRO-FIT Toraya procedure. The crystallite sizes and lattice distortions were analyzed using the Williamson-Hall method. Investigations of hyperfine interactions in the studied materials were carried out by the Mössbauer spectroscopy. The powder morphology was analyzed by scanning electron microscopy and transmission electron microscopy techniques. It was found that during high-energy milling phase transitions, a decrease in crystallite size and amorphization process are observed.
Iron nanoparticles were prepared by selective leaching method. Initially the rapidly solidified AlFe11 alloy was prepared and consequently the aluminium matrix was dissolved from this alloy in 20% NaOH solution. This process was carried out at 0 and 80°C. At lower temperature, the iron nanoparticles covered by thin layer of Fe(OH)₃ were successfully obtained. The size of formed nanoparticles was about 8 nm and the particles exhibited massive agglomeration. It is not limitation of the process, because the application of nanoparticles is as a precursor for production of bulk nanocrystalline materials (metals, alloys and metal matrix composites). At higher temperature, the selective leaching process failed and iron was oxidized to different hydroxides. Aluminium containing waste liquid from selective leaching was used for production of powder Al₂O₃. Initial alloys and products were characterized by X-ray diffraction, scanning electron microscopy, and high resolution transmission electron microscopy.
Wrought Mg-Zn-Ce alloy (ZE10) has been pre-compressed and subsequently subjected to tensile loading. Due to a fibre texture of the samples, the level of pre-compression stress significantly influences the subsequent tensile behaviour. The acoustic emission technique was used for monitoring active deformation mechanisms during mechanical testing. The obtained acoustic emission results are correlated to the stress-time curves and the differences in the acoustic emission count rate were used to reveal changes in underlying deformation mechanisms. Firstly, a compression-tension cycle was monitored by the acoustic emission technique. Then, the samples were deformed to specific points on the stress-time curve, where acoustic emission exhibits strong changes in the activity. The following microstructure analysis of the samples, deformed to different strain-levels, by using electron back scattered diffraction method brought a detailed insight into active deformation mechanisms. Twinning during the pre-compression was followed by detwinning during the tensile loading. Two consecutive acoustic emission peaks, which appeared at larger strains, are explained by interplay of detwinning and dislocation slip and a nucleation of compression twins, respectively.
The magnetic properties including magnetic structure of poly and nano samples of TbMnO_{3} are determined. All the samples investigated are antiferromagnets. In these samples the Mn ad Tb moments order antiferromagnetically at different temperatures and form modulated magnetic structure described by the propagation vector k=(k_{x},0,0) with different value of k_{x} for the Mn and Tb sublattices. Comparison of the data for poly and nano samples indicates the decrease of the moment and increase of the k_{x} component of propagation vector in the nano specimens. The wide Bragg peak related to the Tb sublattice suggests that the magnetic order has the claster-like character. The magnetic moments value in both sublattices is smaller, whereas the k_{x} values are larger for nano samples.
In the work a brief discussion of the structural and magnetic properties of the manganites from the point of view of the micro- and macrostructures is presented. The influence of stoichiometry with the different oxygen parameter δ and doped atoms is discussed. The correlation between the crystal structure parameters and magnetic properties for some manganites is presented.
The aim of this study is to present the special features and properties of the two alloys of similar average chemical composition Ni₅₅Fe₂₀Cu₅P₁₀B₁₀, processed through two different routes. The first alloy was melt-spun after the ejection of homogeneous liquid using a traditional single chamber crucible, and the second alloy was ejected from a double chamber crucible as two separate liquids: i.e., Ni₄₀Fe₄₀B₂₀ and Ni₇₀Cu₁₀P₂₀, mixing only at the orifice area. The studies of the microstructure of the composite alloy were performed through the use of transmission electron microscopy and scanning electron microscopy. The Ni₅₅Fe₂₀Cu₅P₁₀B₁₀ two-chamber melt-spun (TCMS) alloy, as well as the homogeneous Ni₅₅Fe₂₀Cu₅P₁₀B₁₀, Ni₄₀Fe₄₀B₂₀, and Ni₇₀Cu₁₀P₂₀ alloys, were heated to elevated temperatures and their characteristics studied by means of differential scanning calorimetry. The temperature resistivity change method was applied to the examination of the Ni₅₅Fe₂₀Cu₅P₁₀B₁₀ TCMS alloy. The phase composition after heat treatment was investigated using X-ray diffraction. The results of the microstructure examination show that the TCMS alloy is an amorphous/amorphous composite, and is notable for its Ni-Fe-B and Ni-Cu-P stripes resulting from its differentiated chemical composition. Another unique feature of the TCMS alloy is that it retains its wood-like morphology even after high-temperature heat treatment. The crystallisation of the TCMS alloy starts from the Ni-Cu-P constituent and ends with the Ni-Fe-B areas of the sample. The results are discussed on the basis of previous work completed on amorphous matrix composites.
In this work the topologically close-packed phases precipitated during annealing of CMSX-4 single-crystal superalloy at temperature 1100°C were investigated. Microstructural analyses were carried out by means of scanning- and transmission electron microscopy as well as scanning-transmission electron microscopy in high angle annular dark field mode. Chemical composition in nanoareas was determined using energy dispersive X-ray spectroscopy. Scanning electron microscopy investigation has shown that the topologically close-packed precipitates were formed already after 50 h of annealing at temperature 1000°C. With prolongation of the annealing time up to 2500 h the change of the morphology of topologically close-packed particles from blocky to needle-like occurred. Selected area electron diffraction analysis indicated that the topologically close-packed precipitates are the orthorhombic P phase. Quantitative energy dispersive X-ray spectroscopy analysis revealed that the topologically close-packed precipitates are enriched mostly in Re and W.
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