Vol 54, No 5 (2018)

Electrospark treatment of OT4-1 titanium alloy was performed sequentially with a STIM-20N hard-alloy electrode (TiC–20% Ni) and carbon-containing material (graphite and carbon-based composite materials). Kinetics of the mass transfer of the hard-alloy electrode was studied. The cathode mass loss during the first minute of the treatment was established. The kinetics results were processed using the methods of mathematical statistics. The erosion resistance of the applied carbon-containing materials was determined. Phase composition and relief of the coatings formed were analyzed. It was found that the application of the carbon-containing material increases the content of refractory phases in the coatings. Increase in the time of the treatment using the carbon-containing materials decreases the roughness of the coatings.

The process of electrodeposition of copper coatings on a mild steel substrate was analyzed. The reasons for poor adhesion of the coatings from acid and alkaline cyanideless electrolytes were determined. It was shown that the problem of the direct copper coatings’ electrochemical plating on a steel substrate from cyanideless electrolytes results from the presence of the adjoint process of contact exchange in a copper ions–iron system. Good adhesion coatings can be developed only on termination of the contact exchange at the initial stage until the steel substrate under the sediment pores is not subjected to significant etching. In acid electrolytes, the adhesion is poor because of a large value of the contact exchange current. In alkaline cyanideless electrolytes iron is passivated, and adhesion of the coating is insufficient because of the presence of a separating passive film at the substrate–coating interface. In neutral electrolytes, it is possible to obtain a coating with a good adhesion to the substrate, but the results are not stable due to a low buffer capacity of the solution. During the deposition of a copper coating from acid electrolytes using a prenickel-plating, a thin nickel sublayer has pores through which the process of the contact exchange occurs. It is shown that, in order to develop coatings with a good adhesion, the minimum thickness of the nickel sublayer must be 3–5 μm.

Analytical research into the stability of axially asymmetric capillary waves on the surface of a volumetrically charged cylindrical jet of an ideal incompressible dielectric liquid that moves in an ideal incompressible dielectric medium made it possible to specify the conditions for realization of instability of waves with azimuthal numbers 1 and 2, which corresponds to excitement of bending and deformation waves. It was found that realization of the Kelvin-Helmholtz instability occurs on the media interface because of a tangential jump of the field of velocities on the jet surface for the axially asymmetric waves. The linear dimensions of wave numbers' ranges of unstable waves and the sizes of increments of instability are defined by values of the charging Weber’s parameters. The variation of dielectric permeability of a jet and medium affects the characteristics of wave motions, including those in the range of instability realization.

The first part of the theoretical study devoted to the description of the kinetics and mechanism of the lipid peroxidation process involving the complexes of cytochrome c and cardiolipin with account for the effect of an antioxidant is presented. The main components of the ROS (reactive oxygen species) and AOD (antioxidant defense) systems and their properties are considered. The key features of the activity of these systems and various channels of the influence of their components on each other, both intrasystemic and intersystemic, important for the optimal interaction of these systems in the organism, are discussed. Special attention is paid in the review to the experimental works where the properties and structure of the cytochrome c and cardiolipin complexes of various types, along with their peroxidase activity, are studied. In addition to two known ways to control the peroxidase activity of these complexes discussed in the literature, it is proposed to consider another way, which is connected with a possibility to include the lipophilic antioxidant molecules into the composition of the complexes under study. The proposed way to regulate the peroxidase activity, increasing the effectiveness of the peroxidase process control, opens up new opportunities to regulate the process of the apoptosis of cells. Based on the analysis of experimental works on this problem, a theoretical kinetic model of the peroxidase process is formulated, which includes two reaction pathways: an enzymatic pathway involving the complexes of cytochrome c and cardiolipin and a non-enzymatic pathway involving free radicals. A system of differential equations that describes the kinetics of the lipid peroxidation process is constructed with account for the inhibiting effect of the antioxidant. The obtained model system of the kinetic equations will be used to study and compare the antioxidant activity of vitamin E (α-tocopherol) and some of its homologues with a shortened side chain, relying on the available theoretical and experimental data.

In this research, AISI 316L austenitic stainless steel has been subjected to plasma nitriding and oxidation- nitridation heat treatment at several temperatures for different times. Plasma nitriding of the samples was performed in N₂/H₂ = 1/3 atmosphere at temperatures of 425, 450, and 475°C for 5 h. To study the effects of the combined nitridation-oxidation process on mechanical and physical properties, the samples have been exposed in O₂/H₂ = 1/5 oxidating atmosphere at 425, 450, and 500°C for 15, 30, and 60 min, respectively. The mechanical and physical properties of the samples were studied after nitridation-oxidation heat treatment. The microstructural properties were examined by optical microscopy and scanning electron microscopy; the phases were analyzed by X-ray diffraction. The wear behavior of the oxidized-nitrided samples was studied using pin-on-disk tribotesting. The hardness and depth of the nitrided layer were measured by a Vickers hardness tester. The corrosion resistance of both untreated and treated samples was tested by the Tafel polarization and potentiodynamic polarization in 3.5% NaCl solution at ambient temperature. The results indicate that the combined nitridation-oxidation heat treatment improves both the pitting corrosion and wear resistances of AISI 316L steel and further increases its hardness.

In this paper we present the results of the comparative study of the performance of two sulfuric and oxalic anodizing process already retained, based on the superposition of the surface responses. For this purpose two Doehlert experimental designs with three variables (temperature, current density, sulphuric acid concentration) and other three variables (temperature, current density, oxalic acid concentration) were realized. Three responses were studied, namely: growth rate, Vickers microhardness, wear rate after friction test of the anodic oxide layer. A comparative study based on the surface responses was carried out. Compared with the sulphuric acid bath, it was found that the oxalic acid bath affords low growth rates, high wear resistance and high microhardness but less ductile layers. The observed mechanical properties of the oxide layers can be related to their morphology revealed by the scanning electron microscopy and optical observations and their chemical composition determined by the glow-discharge optical emission spectroscopy.