Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques最新文献

The article presents the results of modeling the three-dimensional distribution and accumulation of deformation defects in the volume of a single-crystal intermetallic compound with the L1₂ superstructure during deformation by uniaxial compression. The calculations are performed in a multilevel model of synthesis of dislocation kinetics and mechanics of a deformable solid for cases of deformation with and without taking into account the forces of end friction. The patterns of distribution of the intensity of plastic strain and the density of dislocations in the plane of the central longitudinal section of a deformed rectangular sample are presented. In a numerical experiment, brittle fracture of a deformed sample is obtained at a degree of strain close to the value of full-scale experiment. The influence of the end friction forces on the features of shape change and fracture of a single-crystal sample is analyzed. It is shown that due to the influence of end friction forces, a noticeable decrease in the degree of brittle fracture strain occurs. A statistical assessment of the degree of homogeneity of the distribution of deformation defects in the deformed volume is carried out. A comparison of the results of the numerical experiment obtained in the work with the results of mechanical tests and studies of the deformation relief of Ni₃Ge single-crystal intermetallic compound with the L1₂ superstructure shows good agreement.

Using the method of dynamic diffractometry with the use of synchrotron radiation beams, experimental studies of phase formation processes occurring during the high-temperature synthesis of mechanically activated powder mixture Ti + Al + C were conducted. High-temperature synthesis has been carried out in situ in thermal explosion mode using a microwave induction heater on an experimental complex adapted to the method of dynamic diffractometry. The experiments were conducted at the “Diffraction Cinema” station of VEPP-3, channel 5B, at the Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences. It has been experimentally shown that the synthesis of a composite material occurs in multiple stages. The onset of phase changes begins at a temperature of approximately 870°C. Initially, the formation of intermetallic compound TiAl₃ is observed. Then a Ti–Al melt is formed with the release of TiC grains, which provides the main heat release and initiates a thermal explosion reaction. Further, the Ti–Al melt due to the dissolution of TiC grains in it is saturated with carbon, and when the temperature reaches 1800°C, MAX phase Ti₂AlC crystallizes from it. The maximum amount of this phase is fixed at the exposure stage. With a decrease in temperature, along with Ti₂AlC, MAX phase Ti₃AlC₂ is formed. At this stage, by controlling the temperature, it is possible to control the content of MAX phases in the reaction product. The composition of the final product includes Ti₃AlC₂, Ti₂AlC, and TiC.

Data from the LASCO/C3 space telescope on board the SOHO space observatory are used to study the effect of solar cosmic rays on the telescope’s CCD detector. A special feature of the instrument is that it is located at the L1 Lagrange point of the Sun–Earth system at a distance of 1.5 million km from the planet and is not protected from charged particles by the Earth’s magnetic field. In the period from 2018 to 2024, a decrease in the instrument’s sensitivity is detected at a rate of 0.94 ± 0.03% per year and an increase in signal dispersion at a rate of 4.9 ± 0.1% per year. The main probable reason is the nonuniform decrease in the photometric sensitivity of the detector in different pixels. The effect of charged particles, the source of which are large solar flares, on the detector is also studied. According to the obtained data, the influence of individual flares on the detector is insignificant and cannot be detected within the measurement error. However, this effect can accumulate, which leads to significant changes in the sensitivity of the CCD over several years or more.

As part of the electric propulsion system integration with spacecraft, it is mandatory to verify its electromagnetic compatibility. Considering that electric propulsion systems of almost all types can operate under space conditions only, determination of their electromagnetic emission in ground conditions is not a simple task. This paper discusses the peculiarities of determining self electromagnetic emission from pulsed plasma thrusters under ground conditions. The international experience in studying emissions from such thrusters is analyzed, and approaches to designing test facilities are formulated. Experimental results obtained for the ablative pulsed plasma thruster APPT-50, which was developed at the Research Institute of Applied Mechanics and Electrodynamics of the Moscow Aviation Institute (RIAME MAI), are compared with similar results for foreign analogs. On the basis of comparison, the possibility of obtaining preliminary estimates for the spectrum of emission from pulsed plasma thruster was confirmed when using metallic vacuum chambers equipped with radio-transparent windows to transmit the emission to the apertures of the pick-up antennas.

In the paper, the results of an experimental study of the integral characteristics of a laboratory model of a radio-frequency ion thruster with a beam diameter of 80 mm and krypton as the propellant are presented. The obtained characteristics are compared with the results of tests of the laboratory model using xenon as the propellant. The impact on the service life of the accelerating grid of the ion-extraction system of the thruster and the efficiency of ion-beam focusing of the use of krypton instead of xenon, which is most often used, is estimated. Surface erosion of the accelerating grid under the effect of xenon and krypton ions incident on the grid during operation taking into account the operating modes of the laboratory model of the radio-frequency ion thruster considered during the experiments is modeled. Based on the performed studies, it is possible to estimate the change in the integral characteristics of the radio-frequency ion thruster in the case of using a cheaper propellant compared to xenon. The obtained results can be applied to optimize the existing models of radio-frequency ion thrusters in order to achieve the highest efficiency of their operation using krypton.

A technological scheme for producing a high-temperature layered-fibrous composite material by solid-phase diffusion welding in vacuum under load from a workpiece with initially layered components—niobium foils and unidirectionally oriented carbon fibers—is presented. The composite structure was formed in two stages. After the first stage, the structure was monitored for the connectivity of its components. Then the second-stage heat treatment was performed, completing the technological process. The longitudinal and transverse structure of the composite was studied using a scanning electron microscope equipped with an energy-dispersive microanalyzer. Data were obtained on the distribution of niobium and carbon in the cross section. The structure includes layers of solid solutions of carbon in niobium, Nb–C intermetallic compounds, and carbon fibers. Composite samples were tested under bending conditions, and the dependence of their strength on temperature in the range of 20 to 1400°C was obtained. The strength values correspond to the requirements for structural materials used in parts for the high-temperature circuit of gas turbine engines. The stress–strain curves showed the non-brittle failure of the composite material containing brittle components (intermetallic compounds and carbon fibers), which was also confirmed by the morphology of the fracture surfaces.

AISI 304 steel samples cut from a forged rod were rolled at room temperature using longitudinal and cross schemes, after which they were subjected to various heat treatments with cooling from temperatures of the two-phase α′ + γ- and single-phase γ-regions to fix different phase compositions. The phase composition was studied, the volume fractions of austenite and α′-martensite, crystallographic texture, structure and substructure of two-phase steel were determined, uniaxial tension tests of rolled sheets in different directions were carried out to evaluate the anisotropy of mechanical properties. It was found that the occurrence of γ → α′ phase transformations during deformation significantly depended on the rolling scheme and conditions, and the amount of remaining austenite varied within 15–29%. The reverse α′ → γ phase transformation initiated by annealing in the single-phase γ-region leads in the case of longitudinal rolling to the multiplication of the γ-phase texture components and the appearance of an additional orientation {113}〈332〉, while in the cross scheme the texture of deformed austenite is preserved. Quenching in the two-phase region at 700°C does not lead to a fundamental change in the austenite texture but ensures the appearance of additional martensite components {110}〈001〉 and {112}〈111〉. The texture features affect the anisotropy of elastic properties and yield strengths: the anisotropy of the Young’s modulus of samples consisting entirely of austenite is higher (E_TD/E_RD = 1.67) compared to 1.25 for samples of quenched two-phase steel.

Using elemental analysis, X-ray diffraction, and high-resolution transmission electron microscopy, it was shown that nanocrystals of M–Pt solid solutions with a face-centered cubic structure are preferably formed during the coreduction of metal precursors (M ²⁺ (M = Fe, Co, Ni) and [PtCl₆]^2–) by an alkaline hydrazine hydrate solution with the predominant (during synthesis) content of Fe and Co in the phase of solid solutions being ≈11.5 ± 0.5 and ≈16.9 ± 1 at %, respectively. A comparison of the results of high-resolution transmission electron microscopy, elemental analysis, X-ray phase analysis, and X-ray structural analysis demonstrated that in the Fe–Pt and Co–Pt systems, in addition to the M–Pt solid solutions with the face-centered cubic structure, which were revealed by X-ray diffraction methods, nanodispersed metal phases, practically inaccessible for registration, were formed in regions above and below the limits of Fe and Co contents. However, in the nanostructured Ni–Pt system, there was no upper limit of Ni content in the solid solutions of the face-centered cubic structure up to 40 at %. Therefore, the phase compositions were represented by two types of face-centered cubic structures: a pure Ni phase and solid solution phases with a Ni content of 10–12 and 40 at %. The ideas about the nature of these structural-phase features are presented.

The crystallographic texture of bainitic and martensitic steels determined at room temperature is related to the texture of the prior austenite owing to the orientation relationship between the parent and daughter phases. This allows, in particular, to judge about the deformation or recrystallization of austenite. It becomes possible to analyze the effect of hot rolling on the austenite structural state, which precedes quenching. The structures and textures of bainitic and martensitic steels have been analyzed using electron backscatter diffraction. In the case of single-pass rolling, the state of prior austenite can be estimated based on the morphology of austenite grains reconstructed on the basis of the electron diffraction data. In the case of multi-pass hot rolling, which proceeds with a gradual decrease in temperature, such an estimate is difficult due to peculiarities of structure development. At the same time, this can be performed based on of the analysis of crystallographic texture of steel. As a quantitative characteristic of the structural state of austenite, a scalar parameter is proposed that depends on the relative intensity of texture components formed during the phase transformation.

In situ transmission electron microscopy observations showed that one or more liquid Pb nanoinclusions attached to a fixed dislocation segment in an Al matrix exhibit quasi-one-dimensional thermal motion localized near the dislocation line as fixed segments are traps for the nanoinclusions. The use of longitudinal component of the trajectories of their thermal motion makes it possible to determine the diffusion coefficients of individual nanoinclusions in a wide range of temperatures and sizes. To determine the diffusion coefficients, the root-mean-square displacement of a one-dimensional Brownian oscillator under the action of a linear restoring force as a function of movement time, obtained by M. von Smoluchowski, was used. However, this expression does not quite correctly describe the thermal motion of inclusion attached to a dislocation segment fixed at its ends as this expression does not take into account the deceleration of inclusion near its fixed ends that leads to underestimation of the value of the diffusion coefficient of the inclusion. In the present paper, this equation is modified. The application of the modified equation demonstrated that it described the behavior of experimental dependences of a root mean squared displacement of liquid Pb nanoinclusions attached to fixed dislocation segments in an Al matrix on the movement time quite better than the equation used before. This made it possible to significantly increase the accuracy of determination of the diffusion coefficients of the nanoinclusions.