Near-surface Layers Of Materials Research Articles

Modeling surface structure of tribotechnical materials

Modern tribology makes it possible to correctly calculate, diagnose, predict and select appropriate materials for friction pairs, to determine the optimal mode of operation of the tribo-joint. The main parameter for solving friction problems and other problems of tribology is the topography of the surface. The main purpose of the models in these tasks is to display the tribological properties of engineering surfaces. In the framework of the classical approach, the topography of the surface is studied on the basis of its images from the point of view of functional and statistical characteristics: the evaluation of the functional characteristics is based on the maximum roughness along the height and the average roughness along the center line, and the statistical characteristics are estimated using the power spectrum or the autocorrelation function. However, these characteristics are not only surface properties. They depend on the resolution of the device for measuring the surface geometry and the length of the scan. However, the degree of complexity of a surface shape can be represented by a parameter called the fractal dimension: a higher degree of complexity has a larger value of this parameter. Fractal dimensionality is a characteristic of surface relief and makes it possible to explain tribological phenomena without the influence of resolution. This article provides an overview of mathematical approaches to the description of the relief of engineering surfaces, in particular statistical, stochastic and topological modeling, their limitations, advantages and disadvantages. The implementation of the principles of the theory of fractal structures is discussed, which makes it possible to introduce the degree of imbalance of the tribological system into the analysis of structure formation in the surface and near-surface layers of materials and to describe the development of friction and wear processes. This is the basis for controlling the structure of the surface layers of materials with given properties. The concept of fractals, used for the quantitative description of the dissipative structure of the tribojunction zone, makes it possible to establish a connection between its fractal dimension and mechanical properties, as well as critical states of deformation of metals and alloys. The course of research and stages of fractal modeling, the classification of methods of fractal analysis of the structure of engineering contact surfaces are considered. A critical analysis of modern models based on the energy-spectral density function, which are quite similar to fractal models, is presented. Readers are expected to gain an overview of research developments in existing modeling methods and directions for future research in the field of tribology

Features of thermal processes and the influence of pulsed heating of surface layers of titanium on the diffusion transfer of dopants during high-intensity ion implantation

Methods for modification of surface and near-surface layers of materials and coatings by ion beamshave prospects for application in many fields of science and technology. The method of high-intensityimplantation by high-power density ion beams with submillisecond duration involves significantpulsed heating of the irradiated target’s surface layer, followed by its rapid cooling due to heatremoval into the material due to thermal conductivity and the implementation of repetitively-pulsedradiation-enhanced diffusion of atoms to depths significantly exceeding the projective ion range. Thispaper considers features of thermal processes and the effect of pulsed heating of near-surface titaniumlayers on diffusion transfer under conditions of synergy of high-intensity titanium ion implantationand energy impact of a high-power density repetitively-pulsed beam on the surface to increase iondoping depth due to radiation-enhanced diffusion under conditions of limited heating of the entiresample. The paper presents the data of numerical simulation of dynamic changes in temperature fieldsin titanium and titanium self-diffusion under the action of ion beams with a submillisecond durationand a pulse power of tens of kW/cm2 and fluence of ions in a pulse 1.25×1015 ion/cm2.

Концепция микромоделирования процесса соединения разнородных материалов пластической деформацией

Introduction. Bond strength between dissimilar materials is the most important characteristic of laminated composites, which determines the success of its development for industrial use. In order to develop the theory of joining materials by plastic deformation, it is proposed to perform computer simulation of joint deformation of representative volumes of dissimilar materials on a microscale and compare the parameters of the stress-strain state with the previously presented theoretical mechanism. The aim of this work is to analyze the stress-strain state of dissimilar materials under plastic deformation on a microscale and to establish the location of the onset of fracture of surface oxide films. To achieve this aim, the following tasks of the work are formulated: 1) to study the surface profiles of dissimilar materials to be bonded by plastic deformation; 2) to simulate by the finite element method (FE) the plastic deformation of contact surfaces of dissimilar materials on a microscale; 3) to study the stages of joint deformation of dissimilar materials on a microscale and verify of the theoretical mechanism. Research methodology. The study of three-dimensional topography and roughness was carried out on a Veeco Wyko NT1100 Optical Profiling System. Deform-3D FE simulation package was chosen as the main research tool. Aluminum alloys AMg3 and D16 were chosen as the materials under study. Results and discussion. In this work, computer FE simulating of the joint deformation of the surface layers of AMg3 and D16 alloys on a microscale was performed, an analysis of the surface profiles of materials after various types of processing was carried out, the parameters of the stress-strain state were studied and compared with the parameters of the theoretical mechanism. Based on the results of the comparison, the adequacy of the proposed theoretical mechanism was assessed, and the practical difficulties of theoretical simulation of the joint deformation of dissimilar materials on the microscale were noted. Microscale FE simulation made it possible to study the flow of plastic deformation in the near-surface layers of materials, as well as to identify areas of the most probable fracture of surface oxide films and, consequently, areas of primary bonding of dissimilar materials.

Laser shock processing on selective laser melted 15-5PH stainless steel: Improving mechanical properties and wear resistance

Laser shock processing (LSP) is an effective mechanical surface hardening technology to refine the microstructure on the near-surface layer of material, thereby improving the mechanical properties, service lives, wear resistance, corrosion resistance and so on. In this work, the 15-5PH stainless steel experimental samples were fabricated by selective laser melting (SLM). Subsequently, a SIA-LSP-23 series LSP system with laser energy of 6 J, pulse width of 15 ns and spot diameter of 3 mm was applied to treat the surface of SLMed 15-5PH stainless steel experimental samples. Meanwhile, the mechanical properties, surface topography, microstructural evolution and wear behaviour of SLM 15-5PH stainless steel experimental samples prior and after LSP treatment were investigated. After the LSP treatment, the XRD diffraction peaks were shifted without any new phase formation. Since the severe plastic deformation, the surface roughness was increased. The tensile residual stress in near-surface layer was transformed to beneficial compressive residual stress. At the same time, the microhardness and the wear resistance of SLMed 15-5PH stainless steel were improved due to the refine effect of the microstructures induced by LSP.

AMn2O4 spinels (A - Li, Mg, Mn, Cd) as ORR catalysts: The role of Mn coordination and oxidation state in the catalytic activity and their propensity to degradation

Using the rotating disk electrode (RDE) and cyclic voltammetry (CV) techniques, we studied electrochemical behavior, including activity in the oxygen reduction reaction (ORR) in an alkaline solution, of different AMn2O4 (A=Mn(II), Mg(II), Li(I) and Cd(II)) oxides with the spinel structure. With the help of postmortem XPS characterization we demonstrate that the surface of the studied spinels (except for MgMn2O4) undergoes essential modification not only under potential cycling but also after contacting alkaline solution under open circuit conditions, and even during the electrode preparation. The widely studied Mn3O4 spinel demonstrates the strongest surface modifications due to the presence of easily oxidizable and unstable Mn(II). The results of this work are of importance for the field of electrocatalysis and emphasize significant influence of degradation processes occurring at the surface and in the near-surface layers of materials on their electrochemical characteristics.

Development of design solutions for improving the characteristics of capacitive sensitive elements of sensors of physical quantities

Capacitive measuring transducers are the most stable of the sensors of physical quantities, so they are used in such areas and on products in which the parameters of time and parametric stability are the main parameters. Such products and systems include rocket and space technology, aviation, military equipment and weapons. In addition, capacitive measuring transducers are energy-saving, since the sensor element does not consume electrical energy during operation. To achieve high time and parametric stability, the design of measuring transducers must be designed using certain design and technological solutions aimed at eliminating the occurrence of unintentional internal mechanical stresses, and compensating for thermal stresses. In addition, capacitive measuring transducers must be guaranteed to be sealed, and also during their manufacture, all parts undergo a degassing operation, in which moisture dissolved in the near-surface layers of materials is removed by heat treatment in vacuum, as well as using methods of heterization of vacuum cavities.

Численное моделирование динамики температурных полей в монокристаллическом кремнии при импульсно-периодической высокоинтенсивной ионной имплантации и энергетическом воздействии пучка на поверхность

Methods to modify surface and near-surface layers of materials and coatings by ion beams are used in many fields of science and technology. The method of high-intensity implantation by high-power density ion beams with submillisecond duration involves significant pulsed heating of the irradiated target’s near-surface layer, followed by its rapid cooling due to heat transfer into the material due to thermal conductivity and the implementation of repetitively-pulsed radiation-enhanced diffusion of atoms to depths exceeding the projective ion range. Using the numerical simulation, this work studies the dynamics of changes in temperature fields into silicon wafer under single-pulse and repetitively-pulsed exposure to submillisecond titanium ion beam with a pulsed power density in the range up to 109 W/m2. The conditions are determined under which the temperature in the ion-doped layer will correspond to the conditions of radiation-stimulated diffusion of the implanted element, and the temperature in the matrix material will not deteriorate its microstructure and properties.

Features of Low-Energy He and Ar Ion Irradiation of Nanoporous Si/SiO2-Based Materials

Low-energy (50–200 eV) He and Ar ion irradiation of on Si/SiO2-based nanoporous materials is modeled with the use of the molecular dynamics method. The obtained results corroborate the experimentally observed effect of densification of near-surface layers of materials with small-size pores and low porosity due to the ion-induced pore collapse process. The differences in the He and Ar ion irradiation of nanoporous materials and the influence of ion energy on the intensity of structural changes are studied.

A Detailed Study of the 12C(d,p0)13C Reaction at Detector Angles between 135 ° and 170 °, for the Energy Range Ed,lab = 900-2000 keV

The differential cross sections of the 12C(d,po)13C reaction applied to the determination of the depth distribution of carbon in near-surface layers of materials were determined in the projectile energy region F,dtiab — 900-2000 keV (in steps of 25 keV) and for detector angles between 135 ° and 170 ° (in steps of 5 ° ) using as targets 99.9% purity self-supported natural carbon (98.9% 12C - 1.1% 13C) foils of nominal thickness ca. lxlO18 at/cm2. The overall error in the absolute differential cross section measurements varied between ~6-22%. The results were compared with already published data and the explanation of the occurring differences was attempted.

Ultrasonic Nondestructive Method for Stress Analysis of Structural Members and Near-Surface Layers of Materials: Focus on Ukrainian Research (Review)

The results obtained by Ukrainian researchers on the justification, development, and application of ultrasonic nondestructive methods (UNDMs) for evaluating stresses in structural members and near-surface layers of materials are briefly discussed. A distinguishing feature of Ukrainian methods is that they are capable of determining triaxial (including biaxial and uniaxial as partial cases) stresses, unlike non-Ukrainian methods applicable only to uniaxial stresses. The UNDMs are based on the laws of wave propagation in solids with initial (residual) stresses, including the laws of Rayleigh wave propagation. The results discussed were obtained in the National Academy of Sciences of Ukraine (S. P. Timoshenko Institute of Mechanics and E. O. Paton Institute of Electric Welding)

Ultrasonic nondestructive methods of stress analysis in materials and structural members (review)

Results of the justification, development, and application of nondestructive ultrasonic methods of stress analysis are briefly outlined (summarized). These are the results of cooperative research by the S. P. Timoshenko Institute of Mechanics and the E. O. Paton Institute of Electric Welding. The nondestructive ultrasonic methods are intended to determine triaxial (including biaxial and uniaxial) stresses in structural members and biaxial (including uniaxial) stresses in near-surface layers of materials

Optical properties of ion-modified metal surface in the infrared range

The results of study of ion-cleaned and -implanted surfaces of polycrystalline Be, Al, Ti, Fe, Cu, Mo, Zr, and W using optical and infrared (IR) spectroscopy are presented. It is shown that major changes in the optical reflectance spectra are observed in the range of 190–250 nm and are associated with both the formation of scattering centers and features of the chemical state of near-surface layers of materials. It is established using IR spectroscopy that treatment by Ar+ ion beam with a broad energy spectrum increases the reflection coefficient of the modified surface and additional resonance lines related to the formation of oxides themselves and hydroxyl groups are revealed in the reflectance spectrum in the case of formation of oxide film on the surface.

Quantitative analysis of hydrogen in thin films using Time-of-Flight Elastic Recoil Detection Analysis

Determination of atomic concentrations in thin films is one of the key problems in materials science. Time-of-Flight Elastic Recoil Detection Analysis is a powerful method for depth profiling of light and medium mass elements in near surface layers of material. However, due to poor detection efficiency those spectrometers are not commonly used for hydrogen analysis. We have performed some improvements in order to increase detection efficiency and to make spectrometer more suitable for hydrogen analysis. The spectrometer performance was tested on amorphous Si samples implanted with H − and D − and hydrogenised Si standard reference sample. Sensitivity for hydrogen in silicon matrix was found to be several tens of ppm with a surface depth resolution of ~ 15 nm.

Study of the d + 11B system differential cross-sections for NRA purposes

The differential cross-sections of the 11B(d,α0,α2,p0) reactions for the determination of the depth distribution of boron in near-surface layers of materials have been determined in the projectile energy region Ed,lab=900−1200keV. The experiment was carried out in energy steps of 25keV and for four detector angles between 140° and 170° (in steps of 10°). The obtained experimental data are suitable for Nuclear Reaction Analysis (NRA) studies. A qualitative discussion of the observed cross-section variations through the influence of broad resonances in the d+11B system is also presented. The results are also compared to data from literature, when present, and are validated through a benchmarking experiment using a high purity thick B4C target.

Study of selected differential cross-sections of the 28Si(d, p0, p1, p2, p3) reactions for NRA purposes

The differential cross-sections of the 28Si(d,p0,p1,p2,p3) reactions for the determination of the depth distribution of silicon in near-surface layers of materials have been determined in the projectile energy region Ed,lab=1500–2000keV. The experiment was carried out in large energy steps of ∼50keV and for six detector angles between 145° and 170° (in steps of 5°). The obtained experimental data, although in principle suitable for Nuclear Reaction Analysis (NRA) studies, they present strong fluctuations, as expected from nuclear physics theory. A qualitative discussion of these fluctuations is also presented. The results are also compared to recent data from literature, taken at 150°.

A detailed study of the d + 10B system for nuclear reaction analysis – Part A: The 10B(d,p) 11B reaction in the energy region Ed,lab = 900–2000 keV

The differential cross-sections of the 10B(d,p 0,1,2,3,4–5,6) reactions for the determination of the depth distribution of boron in near-surface layers of materials have been determined in the projectile energy region E d,lab = 900–2000 keV. The experiment was carried out in energy steps of 25 keV and for eight detector angles between 135° and 170° (in steps of 5°). The obtained experimental data are suitable for nuclear reaction analysis (NRA) studies. A qualitative discussion of the observed cross-section variations through the strong influence of overlapping resonances in the d + 10B system is also presented.

A detailed study of the d + 10B system, for nuclear reaction analysis – Part B: The 10B(d,α 0) 8Be reaction in the energy region Ed,lab = 900–2000 keV

The differential cross-sections of the 10B(d,α 0) reaction, for the determination of the depth distribution of boron in near-surface layers of materials, have been determined in the projectile energy region E d,lab = 900–2000 keV. The experiment was carried out in energy steps of 25 keV and for eight detector angles between 135° and 170° (in steps of 5°). The obtained experimental data are suitable for nuclear reaction analysis (NRA) studies. The various aspects of the 10B(d,α) reaction, namely the absence of the α 1 transition from the experimental spectra, the induced background from three-body kinematics and the 8Be breakup are discussed and analyzed. The results are compared to the ones already existing in the literature and an attempt is made to explain the occurring similarities and differences. A qualitative description of the observed cross-section variations through the influence of overlapping resonances in the d+ 10B system is also attempted.

Structure and hot-rolled reinforcement rods properties evolution in the process of long service life

The physical nature of mechanical properties of hot-rolled reinforcement rods degradation during long-life operation is established by methods of transmission diffraction electron microscopy. It is shown that strength and plasticity properties decrease is due to cementite plates cutting and dissolution, microcracks formation process as a result of interstitial phase inclusions creation in the near-surface layer of material.

A detailed study of the 12C(d, p0)13C reaction at detector angles between 135° and 170°, for the energy range Ed, lab = 900–2000 keV

The differential cross-sections of the 12C(d,p0)13C reaction (applied to the determination of the depth distribution of carbon in near-surface layers of materials) were determined in the projectile energy region Ed,lab=900–2000keV (in steps of 25keV) and for detector angles between 135° and 170° (in steps of 5°) using as targets 99.9% purity self-supported natural carbon (98.9% 12C–1.1% 13C) foils of nominal thickness ca. 1×1018at/cm2. The overall error in the absolute differential cross-section measurements varied between ∼6% and 22%. The results were compared with already published data and the occurring differences were explained.

On Foundations of the Ultrasonic Nondestructive Method for Determination of Stresses in Near-Surface Layers of Solid Bodies

The ultrasonic nondestructive method for determining stresses in near-surface layers of solid bodies is based on the laws governing the propagation of elastic surface waves in bodies with initial (residual) stresses. These laws are established within the framework of the linearized three-dimensional theory of waves in bodies with initial (residual) stresses. The dispersion equations in associated problems are solved by computational methods. The nondestructive method and measuring instruments and devices are described. Some examples of nondestructive determination of welding-induced residual stresses and operating stresses in near-surface layers of materials are presented