Showing papers in "Journal of Surface Investigation-x-ray Synchrotron and Neutron Techniques in 2016"

Formation features of structure-phase states of Cr–Nb–C–V containing coatings on martensitic steel

Abstract: By methods of modern physical materials science the investigations analysis of phase composition, defect substructure, mechanical and tribological properties of Cr–Nb–C–V containing coatings formed in surfacing on martensitic wear resistant steel Hardox 450 were carried out. It was shown that surfacing resulted in the formation of high strength surface layer 6 mm in thinness. This layer had wear resistance 138 times greater than that of the base and friction coefficient 2.5 times less. On the basis of the investigations by methods of X-ray structural analysis and transmission diffraction electron microscopy it was shown that increase strength and tribological properties of surfacing metal were caused by its phase composition and state of defect substructure, namely, availability of interstitial phases (more than 36%) and martensitic type of α-phase structure.

Neutron diffractometer for real-time studies of transient processes at the IBR-2 pulsed reactor

Abstract: A specialized diffractometer intended for use in studying real-time transient processes in condensed media, which also allows the recording of Bragg diffraction and small-angle neutron scattering spectra, has been created at the Frank Laboratory of Neutron Physics, Joint Institute for Nuclear Research. Frequently, only the given formulation of the experiment with the continuous recording of information on the process enables us to obtain data required for the correct interpretation of events. One of the crucial parameters of such experiments is the minimal time interval in which sufficient statistics can be acquired. The diffractometer parameters make it possible to measure diffraction and small-angle spectra within minute and even second (for certain types of transition processes) ranges. The possibilities of neutron scattering are discussed as applied to the study of transient processes, the diffractometer design is described, and its main characteristics and the test experiment results are presented.

In-vitro dissolution and structural and electrokinetic characteristics of titanium-oxynitride coatings formed via reactive magnetron sputtering

Abstract: The results of investigation into the structure and in-vitro dissolution of titanium-oxynitride coatings deposited via reactive magnetron sputtering are presented Data on the electrostatic and ζ surface potentials enable estimation of their contribution to adsorption processes and coating dissolution in vitro Sample cultivation in a solution simulating the composition of the inorganic part of human blood plasma leads to surface mineralization, reduces the value and sign of the surface potential, and alters the surface wettability The coating prevents the transition of iron ions into a solution and does not induce the calcification of an artificial surface

Plasma electrolytic saturation of titanium and its alloys with light elements

Abstract: This review is devoted to analyzing the results of the thermochemical treatment of titanium-alloy surfaces under plasma action in electrolytes. Plasma electrolytic saturation (PES) with light elements is found to have advantages over alternative methods. Electrolyte compositions by means of which titanium is rapidly saturated with nitrogen, carbon, boron, and oxygen are presented. The treatment modes and characteristics of the modified layers, such as the phase and elemental composition, surface roughness and microhardness, friction coefficient, wear rate, and corrosion resistance, are discussed. Attention is paid to the thermophysical and electrochemical aspects of PES, in particular, to the specifics of titanium heating and its anodic dissolution and oxidation.

Morphology of anodic alumina films obtained by hard anodization: Influence of the rate of anodization voltage increase

Abstract: The influence of the anodization voltage ramp on the morphology and thickness homogeneity of porous anodic alumina films was studied. The samples were prepared in the oxalic acid at 120 V during the hard anodization process. As a nondestructive characterization method, the smallangle Xray scattering technique was used. The analysis of diffraction patterns allows determining the mean value and dispersion of interpore distance and the channel tortuosity with high accuracy. The increase of voltage ramp at the initial stage of hard anodization process was shown to lead to reduction of mechanical deformation (tortuosity) of anodic alumina film during crystallization.

Surface layer structure degradation of rails in prolonged operation

Abstract: By methods of optical, scanning and transmission electron microscopy and microhardness measurement the transformation regularities of structure-phase states, defect substructure, fracture surface and mechanical properties of rail surface layer up to 10 mm deep in process of long-term operation (passed tonnage of gross weight 1000 mln tons) were revealed According to the character of fracture and level of structure imperfection the three layers were detected: surface, transition and boundary ones It has been shown that the surface layer ~20 μm in thickness has a multiphase, submicro- and nanocrystalline structure and it contains micropores and microcracks The increased density of bend extinction contours at 2 mm depth from the tread contact surface was noted, and it was shown that the maximum amplitude of stress fields was formed on the interphase boundary the globular cementite particle–matrix The evaluation of stress fields was done

The role of interface surfaces in the formation of the properties of polymer nanocomposites

Abstract: The key role of polymer matrix–nanofiller interface surfaces in determination of the structure and properties of particulate-filled polymer nanocomposites is shown. Aggregation of the initial particles of the nanofiller results in a dramatic decrease in the surface area and can cause a transition of the originally postulated nanocomposite to the class of microcomposites. The suppression of aggregation provides a significant improvement in the characteristics of the polymer nanocomposites.

Effect of the microstructure of SHS powders of titanium carbide–nichrome on the properties of detonation coatings

Abstract: Experiments are carried out for the self-propagating high-temperature synthesis of TiC–NiCr cermets, implemented in a mechanically activated powder mixture of Ti–C–NiCr in the free combustion mode and under pressure. It is found that an increase in the volume fraction of the binder decreases the size of TiC inclusions in particles obtained by the mechanical grinding of synthesized cermet compacts. A CCDS2000 computerized facility developed at the Lavrentyev Institute of Hydrodynamics, Siberian Branch, Russian Academy of Sciences, is used to sputter the coatings. The results of comparison of the characteristics of detonation coatings made from the powders produced in this work and commercial Cr3C2–NiCr powder are given. The prospects of employing the self-propagating high-temperature synthesis of TiC–NiCr powders for the thermal spraying of wear resistant coatings are discussed.

Use of gadolinium as a reference layer for neutron reflectometry

Abstract: The possibility of using gadolinium as a reference layer to obtain information on the phase of the complex reflection coefficient in neutron reflectometry is considered in this paper. The results of model numerical experiments for a simple one-layer Si/Ti (90 A) system are presented.

Emission and optical properties of SiO2/Si thin films

Abstract: The energy-band parameters and the emission and optical properties of SiO2/Si films of different thicknesses prepared by thermal oxidation and ion bombardment are studied. It is shown that the band gap E g of the SiO2/Si film with a thickness of 30–40 A is 8.8–8.9 eV. In the transition layer, the E g value and secondary-electron emission coefficient σm steadily decrease with increasing depth.

Effective sputtering yields of titanium, titanium nitride, and molybdenum induced by nitrogen ions and ions of nitrogen-oxygen mixtures

Abstract: This work is dedicated to studying the effects of nitrogen ions and ions of nitrogen and oxygen mixtures on the surface of titanium, titanium nitride, and molybdenum. The usage of magnetron sputtering systems as a model device to study the effect of reactive gases on elements of electric jet engines is proposed and justified. The processes of sputtering of a surface exposed to non-monoenergetic ion beams are studied. The effective sputtering yields of titanium, titanium nitride, and molybdenum induced by argon and nitrogen ions and ions of nitrogen-oxygen mixtures at various intermediate-energy ion beams are determined. It is shown that the sputtering yields of reactive-gas ions are significantly lower than the sputtering yields of inert gases.

Low energy selective etching of metal films in oxygen-containing high-density argon plasma

Abstract: The results of investigating the influence of the ion energy (E i < 200 eV) on the etching of nanoscale Cu, Pt, Ta, and Ti films in an oxygen-containing high-density argon plasma of low-pressure (P < 0.4 Pa) inductive high-frequency (HF) discharges are presented. It is demonstrated that, in Ar plasma, the selective etching of metal films is achieved at ion energies close to the sputtering threshold. The selectivity of Cu, Pt, and Ta etching with respect to Ti etching increases sharply in Ar/O2 plasma with a small (less than 5%) oxygen addition. Depending on the energy of incident Ar+ ions, the yields of Ta, Pt, and Cu sputtering in Ar plasma are in good agreement with semiempirical calculations.

Theory of an X-ray interferometer in the form of an array of planar compound refractive lenses

Abstract: The results of theoretical analysis of the interference pattern created by an X-ray multilens interferometer in the case of an arbitrary number of planar compound refractive lenses are presented. The full widths at half maximum of the resonance peaks in the transverse and longitudinal directions relative to the direction of synchrotron radiation are calculated at distances corresponding to the fractional Talbot effect. A relation between the widths is shown to exist that is very close to the width relation in the case of focusing by a single lens. A difference between the fractional and full Talbot effects is discussed, and the necessary conditions for the transverse and longitudinal coherence of radiation are analyzed, the satisfaction of which guarantees that undistorted interference peaks will be observed experimentally.

Application of a cryogenic moderator in the REMUR neutron reflectometer

Abstract: Examples of the application of a cryogenic moderator in the REMUR time-of-flight neutron reflectometer of the IBR-2 pulsed reactor (Dubna) are given. The results of two experiments are presented: spatial beam splitting upon reflection from a magnetically noncollinear film and the recording of a microbeam formed by a layered waveguide. A conclusion concerning the efficiency of the cryogenic moderator for experiments of this type is made.

Small-angle approximation and Oswald–Kasper–Gaukler theory of electron reflection from solids

Abstract: It is shown that the description of the process of electron ref lection from the surface of a solid in the small-angle approximation using the invariant embedding method is completely equivalent to Oswald–Kasper–Gaukler theory. The small-angle approximation is generalized to problems of the determination of the contributions of k-fold inelastic scattering to the energy spectrum of ref lected electrons. The theory is tested by comparing it with the results of other authors and with the data of exact calculations.

Multibeam X-ray lithography to form deep regular microstructures

Abstract: A method for the fabrication of regular microstructures with a high aspect ratio (for example, X-ray gratings) by direct multibeam vector recording in layers of an SU-8 resist is presented. An X-ray beam with a wavelength from 0.4 to 1.7 A is used for recording. The features of the method are described. The fabricated samples of regular microstructures of the SU-8 resist and gold-plated X-ray masks are presented as finished products.

Technique for the visualization and determination of the surface-erosion profile caused by ion bombardment

Abstract: A technique for the experimental high-precision measurement of the surface-material erosion profile caused by ion bombardment is proposed. It is based on the preliminary deposition of a coating consisting of submicron layers of different materials with different colors. The erosion profile is determined using multilayer copper and aluminum coatings. An important advantage of the proposed procedure is that the erosion profile of the surface treated with an ion beam can be estimated preliminarily without using complex measuring instruments.

Calculation of the electrical conductivity of a thin metal layer in the case of different specular reflectances of its surfaces

Abstract: The local electrical conductivity of a thin metal layer is calculated and modeled with the different specular reflectances of its internal surfaces taken into account. The dependence of the real and imaginary parts of the conductivity on the dimensionless frequency of electron collisions in the volume of the thin layer and on the dimensionless frequency of the external field is analyzed. The kinetic Boltzmann equation is used in the approximation of the electron relaxation time.

On the use of a composite moderator at the IBR-2 reactor: Advantages for the neutron-diffraction texture analysis of rocks

Abstract: A unique cold moderator based on a mixture of mesitylene and m-xylene is developed for the IBR-2 pulsed reactor. If combined with a standard warm-water moderator, it provides a high neutron flux in a wide wavelength range. The advantages of the use of this composite moderator in neutron-diffraction texture analysis are discussed using the example of a sample of slate (formed from five minerals) studied using the SKAT diffractometer. The diffraction data obtained in experiments with warm-water and composite moderators are compared.

Long-term operation of rail steel: Degradation of structure and properties of surface layer

Abstract: By methods of optical, scanning and transmission electron diffraction microscopy and microhardness and tribology parameters measurement the changes regularities of structure-phase states, defect substructure of rails surface after the long term operation (passed tonnage of gross weight 500 and 1000 mln. tons) were established. It is shown that the wear rate increases in 3 and 3.4 times after passed tonnage of gross weight 500 and 1000 mln. tons, accordingly, and the friction coefficient decreases in 1.4 and 1.1 times. The cementite plates are destroying absolutely and cementite particles of around form with the sizes 10–50 nm are forming after passed tonnage 500 mln tons. The appearance of dynamical recrystallization initial stages is marked after the passed tonnage 1000 mln tons. The possible mechanisms of established regularities are discussed. It is noted that two competitive processes can take place during rails long term operation: 1. Process of cutting of cementite particles followed by their carrying out into the volume of ferrite grains or plates (in the structure of pearlite). 2. Process of cutting, the subsequent dissolution of cementite particles, transition of carbon atoms to dislocations (into Cottrell atmospheres), transition of carbon atoms by dislocations into volume of ferrite grains or plates followed by repeat formation of nanosize cementite particles.

On the influence of a high-power ion beam on thin polymer layers deposited onto dielectric substrates

Abstract: The effect of a nanosecond high-power ion beam on thin polymer layers of chlorinated polyvinyl chloride and polymethyl methacrylate containing ferrocene as an additive is investigated Arrays of carbon nanofibers with a characteristic diameter of 30–160 nm and lengths of up to 15 m are formed on the surface of the chlorinated polyvinyl chloride The same effect on polymethyl-methacrylate layers leads to intense cavitation of the surface layer The possible mechanisms of the formation of carbon nanofibers in chlorinated polyvinyl chloride with ferrocene additive under the action of a high power ion beam are discussed

Cation distribution in Cu(Cr 2–x Al x )O 4 and Cu(Fe 2–x Al x )O 4 according to neutron-diffraction studies and their catalytic properties in the water-gas shift reaction

Abstract: The neutron structural analysis of Cu(Cr2 − x Al x )O4 and Cu(Fe2 − x Al x )O4 (0 ≤ x ≤ 2) nanopowders is performed. The samples are prepared by the thermal decomposition of mixed hydroxy compounds at 900°C. Different spinel phases are shown to form in Cu(Cr2 − x Al x )O4: a tetragonally distorted phase when x ≤ 1.0, a cubic phase when x > 1.25, and a mixture of both phases when 1 < x < 1.25. As Al3+ ions substitute Cr3+ ions, a number of Cu2+ ions move from tetrahedral spinel sites to octahedral ones: the degree of inversion δ changes from 0 for CuCr2O4 to ≈0.4 for CuAl2O4. In the Cu(Fe2 − x Al x )O4 system, the cubic spinel forms at all x, except x = 0. The degree of inversion δ varies from 1 for CuFe2O4 to ≈0.4 for CuAl2O4 as Al3+ ions substitute Fe3+ ions. The change in the activation energy of the water-gas shift reaction correlates with the inversion of Cu-containing spinels.

Procedure for determining defects in sputtered clusters of ionic crystals

Abstract: The results obtained using methods of total current spectroscopy (TCS) and secondary-ion mass spectroscopy (SIMS) under ion bombardment of LiF crystals are analyzed. It is shown that the majority of the products of crystal sputtering contain point defects. A procedure for determining defects in sputtered clusters of ionic crystals is developed.

Backscattered electron imaging of micro- and nanostructures: 5. SEM signal formation model

Abstract: A semiempirical model describing how images are formed in a scanning electron microscope operating in the backscattered electron collection mode is discussed. The model involves four imaging mechanisms. The model and the experiment are compared for grooves in silicon with rectangular and trapezoidal relief profiles.

Doping-induced temperature evolution of a helicoidal spin structure in the MnGe compound

Abstract: The helicoidal magnetic structure of a MnGe compound doped with 25% Fe is studied by means of small-angle neutron scattering in a wide temperature range of 10–300 K. Analysis of the scattering-function profile demonstrates that magnetic structures inherent to both pure MnGe and its doped compounds are unstable. The doping of manganese monogermanide is revealed to lead to higher destabilization of the magnetic system. In passing from MnGe to Mn0.75Fe0.25Ge, the magnetic-ordering temperature TN decreases from 130 to 95 K, respectively. It is demonstrated that, at temperatures close to 0 K, the intensity of the contribution to scattering from stable spin helices decreases and the intensity of scattering by spin helix fluctuations increases with increasing impurity-metal concentration. An increased intensity of anomalous scattering caused by spin excitations existing in the system is observed. Helicoidal fluctuations and spin excitations corresponding to low temperatures indicate the quantum nature of the instability in the doped compound. However, MnGe doping with Fe atoms has no influence on the compound’s magnetic properties at temperatures of higher than TN. The temperature range of short-range ferromagnetic correlations is independent of concentrations and is restricted by temperatures T ranging from 175 to 300 K.

Kinetics of the formation of pores and a change in the properties of materials in numerical models

Abstract: Vacancy-gas defects (VGDs) in thin layers of silicon carbide and a metal (SiC/Me) are formed upon 1–10-keV Xe++ ion implantation as the result of a first-order phase transition. The nonequilibrium stage of this transition is modeled by stochastic processes of point-defect clustering and the Brownian motion of cluster centers of mass under the action of potentials of their indirect elastic interaction in the crystal lattices of materials. A numerical experiment for studying pore formation during ion implantation is constructed on the basis of kinetic theory. Stochastic molecular dynamics makes it possible to analyze the formation of pores depending on functions of the nonequilibrium distribution of VGD nucleus clusters over sizes and coordinates of the layer volume. An example of calculation for conditions of phase-transition fluctuation instability is given.

Application of neutron stress diffractometry for studies of residual stresses and microstrains in reactor pressure vessel surveillance specimens reconstituted by beam welding methods

Abstract: The high-resolution neutron-diffraction technique is used to determine the residual stresses and microstrains in unirradiated reactor pressure vessel surveillance specimens reconstituted by means of different welding methods. Comparative analysis of the results demonstrates that the lowest level of residual stresses is observed in the specimens reconstituted via electron-beam welding. The level of microstrains thereof is maximum, indicating a high dislocation density in the material.

Technology of the deposition of composite coatings based on Ti–Al intermetallic compounds by vacuum-arc plasma discharge

Abstract: A technique for the deposition of composite coatings based on Ti–Al intermetallic compounds by vacuum-arc plasma discharge is developed. X-ray diffraction data on the obtained coatings are reported. The effect of deposition modes on the intermetallic-compound contents in the coatings is established.

Radiation effects in high-temperature composite superconductors

Abstract: We investigate how irradiation with high-energy ions (167-MeV 132Xe27+, 107-MeV 84Kr17+, and 48-MeV 40Ar8+) and 25-MeV protons affects the critical parameters of high-temperature superconductor tapes based on YBa2Cu3O7–x and GdBa2Cu3O7–x compounds The ion ranges in the multilayer structures under study and the thermal regimes of the irradiated samples are calculated using SRIM and thermal-peak models The calculated results make it possible to estimate the size of radiation-induced defects which serve as the pinning centers of Abrikosov vortices The performed investigations enable us to reveal that, in the irradiated structures, an increase in the critical current, improvement in the adhesion between the superconducting layer and the substrate, and a reduction in internal stresses are observed under exposure to low levels of Ar- and Kr-ion irradiation The critical current and the critical temperature decrease at higher fluences and, finally, the phenomenon of superconductivity disappears if the fluence continues to increase In the case of 25-MeV proton irradiation, the radiation resistance of the GdBa2Cu3O7–x samples is found to be higher than that of the YBa2Cu3O7–x tapes

Increase in fatigue life of steels by electron-beam processing

Abstract: Increase in fatigue life (by 3.5 times) of steels of different structural classes has been determined. By methods of transmission diffraction electron microscopy the variation of structure, phase composition and defective substructures parameters of material surface layer at different scale levels (from micro to nano) and the suppression of processes contributing to the formation of regions being the potential site of submicrocracks’ formation has been analyzed.