卷 54, 编号 6 (2018)

The paper describes deposition of Ti–Ni–Zr–Mo–Al–C composite coatings on the Ti6Al4V alloy by electrospark alloying in a medium consisting of granules of individual metals and a Ti₃Al + 10%C alloy. The mass transfer pattern during deposition is studied; it is found that the mass transfer coefficient is 18%. The thickness of the deposited coatings is about 50 μm. According to X-ray diffraction analysis, the coating composition is represented by AlNi₂Ti, MoNi₄, and NiTi intermetallic compounds. The average roughness of the coatings R_a is about 3 μm. The microhardness of the deposited layer is three times higher than that of the Ti6Al4V titanium alloy. The wear resistance of the Ti–Ni–Zr–Mo–Al–C coating to dry sliding friction against steel R6M5 is five times higher than that of the Ti6Al4V alloy. The presence of a Ti–Ni–Zr–Mo–Al–C coating on the Ti6Al4V alloy leads to a twofold increase in the surface resistance to high-temperature gas corrosion. The proposed approach makes it possible to obtain electrospark composite coatings based on multicomponent alloys, which are not inferior to coatings prepared by conventional electrospark alloying, in an automatic mode without sophisticated hardware and software.

Nanocrystalline iron coatings were electrodeposited at six different current densities, from 1 to 25 A dm^–2 from a bath containing iron(II) sulfate at 60 and 80°C. The impact of the current density on the bath deterioration was investigated. The bath color changed from emerald green (485 nm maximum absorption wavelength, λ_max) to turbid yellow (λ_max = 470 nm) with some orange precipitates after electrodeposition up to 10 A dm^–2. Further electrodeposition up to 25 A dm^–2 changed the bath colour to dark brown (λ_max = 435 nm). Ultraviolet-Visible spectra were recorded to verify the bath deterioration, which, in turn, prevented the coating growth. The color change and also the shift of the maximum absorption wavelength were discussed in terms of the crystal field theory and also of the anodic oxidation of the hexaaquairon(II) ion to the hexaaquairon(III) ion on the anode surface. The Pourbaix diagram for iron was used to interpret these results and the instability of the bath which was utilized here for electrodeposition of nanocrystalline iron coatings. Addition of saccharin also led to the bath instability. The influence of the bath instability on the average grain size, appearance, surface morphology and thickness of the coatings was discussed. The results proved that the iron(II) sulfate solution is an unstable bath for electrodeposition of nanocrystalline iron coatings.

This work is aimed at the study of the corona-discharge motor (CDM), whose torque is produced due to the electric dipole moment, which appears at the corona discharge. The physical mechanisms and features of the CDM operation that allow us to form a calculation base for the design and construction of the CDM, are identified and discussed. The motor power consumption, dipole moment generation, rotor torque as well as some specific effects inherent to this type of motor, arising from numerical calculations which take the pulse character of the supply voltage of the corona discharge into account, are considered. It is found that the motor rotation at a constant angular rate and a synchronous rotation with the torque are impossible. The obtained results can be used as a prerequisite for engineering calculations of the corona-discharge motors.

Three compounds based on heterocyclic amides were synthesized, purified, characterized, and evaluated as corrosion inhibitors for carbon steel in 1.0 M H₂SO₄ solution using various techniques such as the weight loss, hydrogen evolution, thermometric, and potentiodynamic polarization. Effects of raising the concentration (50, 100, 150, 200 ppm) of amide compounds and temperatures were analyzed. The percentage inhibition efficiency went up with increasing inhibitor concentrations but decreased with temperature. Thermodynamic activation parameters were computed and discussed. It was found that the heterocyclic amide compounds reduce the weight loss, the amount of hydrogen evolved, the corrosion current density; thus the inhibition efficiency increases indicating the inhibiting power of these compounds. The maximum corrosion inhibition efficiency obtained by using 200 ppm from compound 3 is 95%. The potentiodynamic polarization curves proved that amide compounds act as inhibitors of a mixed type. The inhibition action of the three compounds was due to blocking the surface of the electrode by adsorption the inhibitor molecules according to the Langmuir isotherm. The data obtained via different techniques are in good agreement with each other and illustrate that the prepared amides can be considered to be potential nontoxic corrosion inhibitors.

The commercial primary alkaline zinc–manganese cells after current loads and thermal treatment are studied using electrochemical impedance spectroscopy. The components of electric circuits and spectrum data responding to the changes in the investigated samples are identified on the basis of the analysis of impedance spectra and model equivalent circuits. It is found experimentally that the capacity dispersion is a parameter sensitive to any effects on alkaline zinc–manganese cells. The model of the electrode–electrolyte interface is used to evaluate the endurance of primary cells at thermal action.

This paper deals with the development of a voltage nanosecond pulse generator for electrical discharge micromachining. The generator is based on the usage of a half-bridge circuit in the output stage and the RC–circuit in the control chart for the formation of a working voltage pulse. A computer simulation of the generator and an experiment on the implementation of the electrical discharge micromachining were performed.