Surface Engineering and Applied Electrochemistry最新文献

This article analyzes the deformation properties of concrete with non-metallic fibers (coconut and cane) and steel fibers. Using two variables of normal stress (σ_v/MPa) and different concentration of fiber content (r/%), a computational experiment was carried out. During the experiment, the properties of fiber-reinforced concrete samples with coconut, reed and steel fibers and reference concrete samples for tension, bending and compression were compared. The experiments led to the conclusion that all types of fibers can improve the mechanical properties of structural concrete. An analysis of the test results showed that the best way to improve the mechanical properties of concrete is to add 2% reed or coconut fiber and 1.5% steel to the concrete mixture. During the experiments, it was found that due to the impact strength of metal fibers, the compressive results of samples with steel fiber are much higher than for samples with plant fibers, while the bending strength and tensile strength are higher for samples with non-metal fibers. According to the results of the experiments, the relationship between the mechanical stress of fiber-reinforced concrete is as follows: concrete with steel fibers > concrete with reed fibers > concrete with coconut fibers.

Magnesium alloys have found extensive applications in industry due to their low density, exceptional strength-to-weight ratio and high damping capacity. Those bio-compatible alloys have been used as a versatile material for permanent implants in the body. High affinity for corrosion and subsequent degradation in the presence of corrosive anions require surface modification methods over these alloys. Anti-corrosion and wear-resistant plasma electrolytic oxidation (PEO) coatings on magnesium alloys are more cost-effective and environmentally friendly among various surface treatment methods. The surface characteristics, wear, and corrosion resistance of the sample can be improved with the addition of various micro/nano-particles or additives to the electrolyte. The effect of various PEO process parameters on the coating characteristics is further discussed in this review paper. The mechanisms underlying corrosion inhibition and the degradation of those coatings in the presence of corrosive environments are elaborated in this work.

The article considers arguments supporting and disproving the possibility of a solid-state approach to the analysis of the properties of RNA and other nucleic acids. Substantiations are given for the rationality of parallel indication of the electrophysical and phase properties of nucleic acids and their components taking into account the effects and mechanisms of action of the components of the medium. The dependence of such effects on the ionic composition of the medium and the degree of hydration of the sample is indicated. Methods are proposed for studying the dependence of the electrophysical properties of dehydrated solid-state RNA samples on the ionic composition of the medium, in particular, on the nature of the counterion. The set of methods used includes the direct visualization of charging of the surface of samples using the electron beam of a scanning electron microscope and oscillography of charge wave propagation, measurements of proton magnetic relaxation to estimate the spin–spin relaxation times and the fraction of protons with different degrees of mobility, analysis of the phase state of crystalline RNA and its salts by thermogravimetry, and analysis of the dispersion of the permittivity of crystalline RNA and its salts up to the ultrahigh-frequency range. Thus, for the tasks of creating bioelectronics/biomolecular electronics based on solid-state RNA, the following is experimentally proven: (a) the possibility of conducting an electrophysical signal on the surface of RNA granules, (b) the presence of a micro/nanostructure capable of conducting an electrophysical RNA signal, and (c) the dependence of signal conduction on the ionic composition of the medium and the degree of hydration of the sample. For solid-state RNA and its salt, the charging under the electron beam, the mobility of protons, and the frequency dependence (dispersion) of the permittivity in the radio frequency range (up to microwave frequencies) differ significantly.

A system of recurrent constitutive relations is written for the brittle fracture probability at micro-, meso-, and macroscale levels, and fatigue curves on defect levels are plotted at the one frequency symmetric loading, consisting of a finite number of blocks with different amplitudes and number of cycles. The results of calculations at different regimes of two block loading for 0.25% carbon steel are in satisfactory agreement with the known experimental data.

A model and results of quantum-chemical calculations of a hypothetical structure of Si₂MnS, similar to the cubic structure of F43m-β-MnS are proposed. The results of a comparative analysis of the gap width E_g of the Si₂MnS structure obtained in quantum-chemical numerical calculations of the electron position and the experimental results of measuring the photoconductivity spectrum of a Si sample doped with Mn and S impurity atoms are presented. The quantum-chemical calculations of the Si₂MnS structure were performed without a preliminary geometry optimization due to the fact that optimization and subsequent calculations by the density functional theory yields a fusion of the valence and conduction bands (VBM and CBM). Thorough theoretical studies, detailed quantum-chemical calculations, and experiments in the field of creating of a new class of hybrid compounds with a cubic lattice of the diamond type with the participation of elements of groups IV/III–V and IV/II–VI will allow predicting new structures in the future.

Abstract—Comparative studies of fractograms of Ti–6Al–4V titanium alloy under dynamic and quasi-static plastic deformation have been conducted. The specimens were fractures of cap-type parts obtained by the Eriksen cupping test under different deformation rates, namely quasi-stationary (low (dot {varepsilon }) = 1 s^–1) and at impact hydroforming (high (dot {varepsilon }) = 3828 s^–1). Significant differences in the nature of the fractures have been revealed. It is shown that slow deformation results in predominantly ductile transcrystalline fracture in the presence of individual domains of brittle intercrystalline fracture corresponding to the breakouts of groups consisting of several grains. During dynamic deformation, a predominantly ductile transcrystalline fracture is observed, which indicates an increase in plasticity. In this case, the edges of the dimples are smoother than in the case of quasi-static deformation, which indicates the occurrence of additional local plastic deformation at the last stage of fracture. The revealed features of titanium alloy fracture are one of the reasons that ensure a more uniform deformation under dynamic loading and an overall increase in technological plasticity.

It is established that the composition of aluminum alloys influence the properties of the formed oxide layer due to the introduction of atoms (Mg, Mn, Cu) into its structure. The use of a pulse mode in the process of electrochemical oxidation of aluminum alloys increases the microhardness of the oxide layer by two to five times in comparison with the use of a stationary mode. The ability to control the frequency of current pulses allows one to influence the rate of flow of the limiting stages of electrochemical processes by changing the concentration of components near the surface of the processed material and to select the optimal oxidation modes for processing various types of alloys.

The article presents the research results of the melt kinetics of multicomponent solders during induction heating. It is shown that a high-frequency electromagnetic field has an effect on contact interaction processes of low-melting and high-melting solder components as mainly resistive heating of the particles of the high-melting component and magnetic-dynamic effect on the solder components. In the process of the contact interaction of solder components, they are heated in a nonisothermal mode of the high-melting components dissolution in a low-melting one. The structure formation on the soldered surface that is not typical for cast alloys and the structure similar to cast dispersed and hardened composite materials in soldered seams are the results of such processes. The heating rate of the composite solder and the dissolution value of a high-melting component in a low-melting one have the greatest effect on the structure of a soldered seam.

The calculations of the load of an unstable two-port network were made. Traditional calculation methods involve laborious parameter redefinition and recalculation of the desired values. In contrast, a neural network includes possible changes in the two-port parameters in the training data. The feedforward neural network training data represents a set of load values and corresponding input current values. Such data are calculated using some change steps of the load and two-port parameters. The training data are split into training, validation, and test sets. It was established that in the training epochs, the neural network reveals that internal pattern in those three sets. Therefore, small errors are obtained. However, the errors appear for the extended control data in different step types. Combining training data with regular and irregular step change parameters eliminates this pattern, so the network shows the capability to generalize. A probability index of the quantification of training quality yields a trade-off between the size of the training data, the accuracy obtained, and the number of neurons. Because an unstable two-port has three parameters, unsatisfactory results were obtained using three base load values. In turn, four excessive base loads radically increase the precision and capability generalization of the network. The established features of the behavior of the neural network provide a base for solving practical “streaming” tasks of different physical nature based on known analogies.

Coatings in the Zr–Mo–Si–B and Hf–Mo–Si–B systems were obtained by spark plasma sintering (SPS) using ZrSi₂–MoSi₂–ZrB₂ and HfSi₂–MoSi₂–HfB₂ heterophase powders manufactured by the self-propagating, high-temperature synthesis method. The Zr–Mo–Si–B and Hf–Mo–Si–B coatings were characterized by a thickness of 1.3–1.4 mm, had a dense structure, and contained phases in wt %: 61 o-ZrSi₂, 15 h-ZrB₂, 15 t-MoSi₂, 8 m-ZrO₂, 1 c-ZrB and 53 o-HfSi₂, 14 h-HfB₂, 19 t-MoSi₂, 9 m-HfO₂, and 5 c-HfB, respectively. The coating hardness was 15–16 GPa, the elastic modulus was 265–268 GPa, and the elastic recovery was 38–39%. The Hf–Mo–Si–B coating was characterized by the minimal values of (a) specific wear rate of 4.2 × 10^–5 mm³ N^–1 m^–1 under sliding friction conditions, (b) crater volume of 5 × 10³ μm³ under impact-dynamic tests, and (c) oxidation rate of <2.3 × 10^–3 mg/(cm² s) at 1200°C. The SPS coatings are superior to niobium substrates in wear resistance by ~25 times and oxidation resistance by several orders of magnitude.