Structure Of Near-surface Layer Research Articles

Формирование градиентных структур в титановом сплаве при обратимом легировании водородом

The possibility of transforming a large-plate structure and creating a gradient structure in samples of titanium alloy VT23 during thermal hydrogen treatment has been studied. It is shown that by varying the concentration-time parameters of hydrogenation annealing, it is possible to regulate the depth of hydrogen penetration and purposefully form the structure of near-surface layers. Subsequent low-temperature vacuum annealing makes it possible to transform the coarse-plate structure into a finely dispersed one with a hardness of up to 40 HRC. It was established that the thickness of a layer with a finely dispersed structure during unidirectional hydrogenation with a barrier coating is twice as large as during volumetric nonequilibrium hydrogenation in the absence of a coating.

Mathematical Modeling of Diffusion-Controlled Processes of the Near-Surface Layer Structure Evolution of W−Cu Composite Under Hightemperature Gas Flow

Mathematical Modeling of Diffusion-Controlled Processes of the Near-Surface Layer Structure Evolution of W−Cu Composite Under Hightemperature Gas Flow

Study of Radiation Damage Processes Caused by Hydrogen Embrittlement in Lithium Ceramics under High-Temperature Irradiation

The aim of this work is to study the hydrogenation processes in lithium-containing ceramics under high-temperature irradiation. Irradiation was carried out with protons with an energy of 1 MeV and fluences of 1015–1017 ion/cm2 at irradiation temperatures of 300–1000 K. The choice of irradiation conditions is due to the possibility of simulation of the radiation damage accumulation processes in the near-surface layer of Li2TiO3 ceramics, as well as establishing the dependences of changes in structural parameters during temperature heating of samples during irradiation. It has been established that at irradiation fluences of 1015–1016 ion/cm2, the formation of dislocation defects is observed, the density of which has a pronounced dependence on the irradiation temperature. At irradiation fluence above 5 × 1016 ion/cm2, an increase in the crystal structure deformation is observed, due to swelling processes as a result of implanted hydrogen accumulation in the near-surface layer structure. At the same time, an increase in the irradiation temperature leads to a decrease in the swelling value, which is due to the accelerated migration of implanted hydrogen in the near-surface layer and its release through the existing pores. Results of mechanical tests showed that the swelling of the crystal structure and its deformation leads to embrittlement and a partial decrease in the strength of the near-surface layer. The obtained research results will further allow us to evaluate the resistance of lithium ceramics to the processes of hydrogenation and destruction as a result of the formation of gas-filled cavities in the structure of the near-surface layer.

Study of Radiation Resistance to Helium Swelling of Li2ZrO3/LiO and Li2ZrO3 Ceramics

The key aim of this paper is to study the presence effect of LiO impurity phases in Li2ZrO3 ceramics on the resistance to helium swelling and structural degradation during implanted helium accumulation in the near-surface layer structure. The hypothesis put forward is based on a number of scientific papers, in which it was reported that the presence of two or more phases in lithium-containing ceramics led to a decrease in the rate of radiation damage and gas swelling due to the presence of additional interfacial boundaries that prevent the point defect accumulation. As a result of the evaluation of the crystal structure deformation, it was found that the presence of the LiO impurity phase in the structure of Li2ZrO3 ceramics led to a threefold decrease in the deformation of the crystal lattice due to helium swelling at doses of 5 × 1017–5 × 1018 ion/cm2. At the same time, the nature of the crystal lattice deformation for different ceramic types is different: in the case of Li2ZrO3 ceramics, an anisotropic distortion of the crystal structure is observed, in the case of Li2ZrO3/LiO ceramics, the crystal lattice deformation has an isotropic nature.

Thinning of the Backside of the InSb(100) Matrix Module and Its Effect on the Crystal Structure of Near Surface Layers

Thinning of the Backside of the InSb(100) Matrix Module and Its Effect on the Crystal Structure of Near Surface Layers

Адаптация структуры приповерхностных слоев антифрикционных медных сплавов при трении с различными смазочными материалами

Адаптация структуры приповерхностных слоев антифрикционных медных сплавов при трении с различными смазочными материалами

Flexible layer-based 2D refraction tomography method for statics corrections

Standard refraction traveltime tomography solutions for statics corrections do not allow irregular parameterization of the model, simultaneous inversion of velocity and depth parameters, or selection of the types of first arrival times to be inverted. An algorithm widely used to study and build crustal structure and velocity models from wide-angle seismic data was applied for the modeling and inversion of the velocity and structure of near-surface layers. This flexible tomographic solution allows the definition of complex heterogeneous models through trapezoids of irregular size to parameterize the model, and it allows the simultaneous inversion of head-waves and turning-rays, which can be defined independently for each layer interface. This work presents a study of the application of this flexible tomographic inversion algorithm to obtain the velocity model and geological structure of the near-surface weathering zone. The proposed workflow was evaluated on two synthetic models built with real topography, and geophysical and geological information was obtained from real cases. The first is a model with three layers with constant velocities, and the second is a model with two heterogeneous layers with lateral and vertical velocity variations in the weathering zone. For the second model, turning-rays crossing the weathering layer are considered in the tomography process. Synthetic seismic data were generated, and an initial model was built using traditional seismic refraction interpretation methods. Thereafter, inversion was performed using a 2D ray-based tomography algorithm to minimize first-arrival traveltime misfits by inverting the seismic velocities and the vertical position of the refractors. It was verified that the proposed workflow obtained the smallest relative errors in most parameters of the velocity model and consequently, for the statics corrections.

Structure of Near-Surface Layer of High-Strength Steel Subjected to Abrasive Waterjet Cutting

This paper presents the results of a study into changes in the structure and microhardness in a near-surface layer of high-strength steel subjected to abrasive waterjet cutting using optical, scanning, and transmission electron microscopy, and X-ray diffraction.

Pulsed ion beam induced changes in a submicrocrystalline structure of the near surface layers of austenite steel

The topography and structure of near surface layers of submicrocrystalline austenite steel 12Kh18N10T after pulsed irradiation with C+ and H+ ions were investigated. Ion beam irradiation resulting in modification of the near surface layer and formation of a structure close to an equiaxed ultrafine grain structure with a high fraction of high-angle boundaries were shown.

Features of relief formation of the polycrystalline samples under the influence of a wide-aperture ion beam

The results of investigation of the cylindrical surface state after influence of wide- aperture ion beam are presented in this paper. Experiments were carried out on the parts of cladding tubes from E110 alloy (Zr-1%Nb) up to 500 mm length. The outer surface of the tubes was treated by Ar+ ions with energy 0.1-1.0 keV up to doses (1-10)× 1018 cm-2 on the installation KVK-10. Due to design features of the installation, the angle of incidence of particles on the surface varied from 0 to 90°. It is found that as a result of treatment made, smoothed relief of the surface forms and uniformity of near-surface layer structure improves. The statistical method suggested allowed to reveal features of the polycrystalline samples surface state with random and regular components, based on the results of profilograms analysis.

Evolution of the structure of near-surface ultrahigh molecular weight polyethylene nanolayers during orientational drawing

A comparative investigation of the surface structure of ultrahigh molecular weight polyethylene film filaments obtained with different draw ratios from xerogels prepared from 1.5 wt % polymer solutions in decaline and mineral oil has been performed using a SUPRA-55V scanning electron microscope and a nanoluminograph for recording thermoluminescence of ultrathin near-surface layers of solids. It has been found that, with an increase in the draw ratio, the luminescence intensity decreases, and the peaks responsible for the segmental mobility are shifted toward higher temperatures. It has been assumed that this is associated with the improvement of the structure of near-surface layers of the polymer (with a decrease in the number of microcavities and segments of molecules with a high degree of coiling). It has also been revealed that the peaks observed in glow curves of the oriented gel samples from polymer solutions in decaline are shifted more significantly than those of the gel samples from polymer solutions in mineral oil, and the extremely oriented films are characterized by a large discretization of kinetic units of motion.

Photoacoustic microscopy of the effect of mechanical processing on the martensite structure of near-surface layers in Cu-Al-Ni alloy single crystals

The near-surface layers in single crystals of copper-based alloys possessing shape memory and superelasticity have been studied using the photoacoustic microscopy (PAM) techniques. It is established that the PAM is advantageous to optical microscopy in studying the martensite structure, in particular, because this structure can be revealed without preliminary polishing of the sample surface. This circumstance allowed the effect of mechanical processing and related stresses on the twin structure in Cu-Al-Ni alloy single crystals to be studied. The sensitivity of PAM is sufficient to observe the structural transformations in samples at the early stages of martensite phase formation.

Inhomogeneous structure of near-surface layers in the ion-implanted NiTi alloy

This paper reports the application of nitrogen ion implantation for modification of a shape memory alloy. It is known that the problem of creating a protective surface coating for the shape memory alloy is the most acute for potential applications of this material. Thus, the problem of increasing surface protective properties and, at the same time, simultaneous preservation of functional properties of shape memory materials is a subject of research and development [Pelletier H, Muller D, Mille P, Grob J. Surf Coat Technol 2002;158:309.]. The surface characterization of nitrogen implanted (fluence 10 18 cm −2 and energy 50 keV) equiatomic commercial NiTi alloy samples was performed with the assistance of high resolution transmission electron microscopy (HTEM) techniques and modifications of phase composition before and after irradiation are studied at room and martensitic transformation temperatures by X-ray diffraction methods. Differential scanning calorimetry (DSC, TA Instruments) was used to characterize the transformation sequence and transformation temperatures for the initial and surface-modified materials. Experimental results of an inhomogeneous structure of near-surface layers in the ion-implanted NiTi alloy are discussed in this paper.

Laminar-turbulent transition in a supersonic boundary layer during initiation of a pulsed surface discharge

The near-surface layer structure in a supersonic airflow (M = 1.5) behind the plane shock wave has been experimentally studied in a shock tube. The flow structure was visualized using nanosecond pulsed distributed surface discharge. Different structures of plasma glow have been observed for the laminar and turbulent flow regimes in the boundary layer. The position of a region of the laminar-turbulent transition for different flow densities (0.11 and 0.19 kg/m3) has been determined and the critical Reynolds number (Rek ∼ 2.4 × 105) for this transition has been evaluated.

Intermolecular interactions and the structure of near-surface layers in heterogeneous two-component systems based on nanocystallites of titanium dioxide

This contribution provides the theoretical background for the structure-determining role of hydrogen bonding in the formation of a near-surface layer of titania nanocrystallites, previously revealed by the authors in the investigation of IR experimental spectra of two-component solid mixtures of nanocrystalline titanium dioxide with benzophenone or 4-pentyl-4′-cyanobiphenyl. DFT calculations (B3LYP) in 6-31+G(d) basis set is used to simulate the structure and IR spectra of free molecules of water, 4-pentyl-4′-cyanobiphenyl, benzophenone and their H-complexes formed in the near-surface layers of titania nanocrystallites due to presence of water adsorbed on their surfaces. Using the results of simulation and analysis of IR spectrum bands corresponding to stretching vibrations of polar bonds O-H, C=O, C≡N, the formation mechanism of near-surface layers of titania nanocrystallites in the considered heterogeneous two-component systems is theoretically substantiated: they are formed by hydrogen-bonded complexes involving components of the mixture and water.

Cross-section transmission electron microscopy characterization of the near-surface structure of medical Nitinol superelastic tubing

The application of Nitinol in a wide variety of medical implants is progressively increasing because of its unique mechanical properties, durability and biocompatibility. However, as Nitinol consists of about 50 at.% of toxic Ni, certain applications are still hindered by the concern of free Ni release in the surrounding tissue. The latter is controlled by the structure of near-surface layers and can be strongly affected by various surface treatments. A proper application of advanced cross-section sample preparation techniques allows us to characterize the Nitinol near-surface structure down to the nanoscale by means of transmission electron microscopy (TEM). Elemental maps of the Ti, O and Ni distribution, concentration profiles, quantification of composition as well as atomic resolution images at the surface of a Nitinol tubing are presented and the results obtained with different sample preparation and analytical characterization techniques are compared. In addition to a strong decrease of Ni towards the surface of the oxide layer and a Ti depleted layer underneath the oxide, also a possible transformation from TiO to TiO(2) is documented.

Recrystallisation and dopant diffusion in amorphised germanium layers upon pulsed laser annealing

In the present paper the results of investigations of the recrystallisation process in amorphous Ge near-surface layers induced by laser annealing are reported. Amorphised layers were created by implantation of Ge single crystal with 150 keV Sn ions at a dose 1×10 16 cm −2. Structural changes and redistribution of dopants were caused in irradiated materials by a single nanosecond laser pulse. For a study of the near-surface layer structure before and after laser annealing, the reflection high-energy electron diffraction technique was applied. Dopant diffusion was investigated by means of secondary ion mass spectrometry. Changes for polycrystalline of the near-surface layer structure amorphised by Sn implantation, occurred independently of the phase transitions and of the dopant concentration (0–8%).

Implantation-assisted deposition of hard carbon coatings on steel substrates

Ion-implantation-assisted deposition of carbon during the implantation of carbon ions into a tool steel results in wear-resistant surface coatings of a new kind and of quite different quality: the wear rate is decreased by a factor of about 1000. The nuclear reaction 12C(d, p 0) 13C, in combination with Rutherford backscattering analysis, has been used to investigate this high wear resistance. By means of slanting deutron incidence and glancing proton detection the nuclear reaction 12C(d, p 0) 13C was used for carbon depth profiling within a near-surface layer structure 200 nm thick.

Structure of near surface layers of GaAs and Si crystals irradiated by powerful ion beams

We have studied the effect of hydrogen powerful ion beams (PIB) on the structures of GaAs and Si crystals. A “conversion” zone of a high defect concentration was formed in the near surface region. This “conversion” zone is the region where defects induced by stationary beams are escaping to the surface or annihilating at sinks. We used two direct methods of analysis: positron annihilation (PA) and Rutherford back scattering of channeled Ions (RBS/CI). Si and GaAs crystals were irradiated with 300 keV and 500 to 4800 keV beams from the modified “TONUS” and “VERA” accelerators.

Methods and apparatus for complete ellipsometry (review)

To monitor the structure of near-surface layers of ordered crystalline structures and their impurity composition, optical methods turn out to be useful. In this paper, the authors analyze complete ellipsometry, a method enabling the determination of the complete Stokes vector of the reflected light or all elements of the Muller matrix of the surface under study. It is significant that this measurement method is contact-free and non-destructive (unlike ionic and electronic methods) and can be employed in a wide range of temperatures in a vacuum and in corrosive media. In addition, the determining role of the surface layer of the object under study in the formation of the reflected wave and the concomitant high sensitivity of its polarization to structural changes in this layer make ellipsometry one of the basic methods for studying thin - from 0.1 to 20 nm - surface films and boundaries between media.