Влияние внешнего электрического поля на оптический разряд в скоростном потоке

The influence of an electric field on the plasma of an optical discharge in subsonic and supersonic air flows has been studied experimentally. The presence of a weak electric field practically does not affect the size of the plasma formation, but, regardless of the configuration of the field lines and the polarity of the applied voltage, it leads to a decrease in the probability of optical breakdown. The experiment has shown that the plasma created by focused laser radiation is very sensitive to the presence of an electric field. When a voltage exceeding 22 kV was applied to the ring electrodes, powerful quasi-stationary streamers were formed in the flow. The presence of an optical discharge plasma made it possible to create an electric discharge in fields with an intensity below the breakdown threshold of the medium. The effect of quenching and the processes of development of an optical discharge were studied depending on the speed and characteristics of the electric field. Quenching of the optical discharge was observed when a voltage of 22 kV and higher was applied. Despite the preservation of the geometric dimensions of the optical discharge, the high-temperature region in the flow can be increased by using electric streamers. This leads to an increase in the energy supplied to the flow, and thus allows combustion to be initiated and flame stabilized at higher flow rates. Key words: experimental modeling, laser radiation, optical breakdown, electric field, electric discharge, sub- and supersonic air flow.

IMPROVING THE SURFACE STRUCTURE OF MASSIVE PARTS BY THE PLASMA METHOD

An increase in the reliability of the operation of large-sized and massive parts by plasma hardening of their surfaces is substantiated. It has been established that the formation of several structural zones of different microhardness is observed in detail along the depth of hardening, indicating the formation of a gradient-layered structure. It has been proved that at ultrafast heating rates, which occur during surface plasma hardening, phase and structural changes move to the high temperature region, changing the kinetics of the appearance and growth of new phase nuclei. In this case, fine-grained austenite is formed, which is transformed into a highly dispersed martensitic structure, which increases the strength and reliability of the surfaces of the parts.

The differential analysis for temperature distribution diagnostics of arc current-carrying region in sheet slanting tungsten electrode inert gas welding with the electrostatic probe

An electrostatic probe differential analysis method is used to diagnose the arc current-carrying region of the sheet slanting tungsten electrode. Based on the local thermal equilibrium condition and energy transition model with charged particles collision, the temperature distribution in the current-carrying region of different welding process parameters is solved by saturated ion current. The results show that the temperature distribution range in the width direction of sheet slanting tungsten electrode expands, the arc high-temperature region shifts integrally, and the temperature in the thickness direction of sheet slanting tungsten electrode would be symmetrical. The guide effect of the hypotenuse of sheet slanting tungsten electrode for arc current and the inertia drag effect of arc would mainly change the temperature distribution. The variation of the inclination angle of the hypotenuse of sheet slanting tungsten electrode will aggravate the shift of the arc high-temperature region. The larger inclination angle will enhance the guiding effect, and then the inertia drag effect would be in a dominant position with a smaller inclination angle. With the increase of welding current, both the arc stiffness and the guiding effect would be intensified, the latter should make the arc high-temperature zone shift to the position with a small discharge gap.

THE MECHANISM OF THE FORMATION OF CRACKS IN THE LASER-DEPOSITED NICKEL ALLOY SYSTEM NI–CR–B–SI ON THE SURFACE OF STRUCTURAL STEEL TYPE 30CGSA

The mechanism of crack formation in the deposited layers is investigated. In accordance with this mechanism, cracks are of the nature of “hot” cracks. The reasons that enhance crack formation during surfacing of powder materials of the Ni–Cr–B–Si system are examined and identified. Foci of “hot” small cracks are formed, as a rule, in the high-temperature region. At the second stage, the focus develops, developing into transcrystalline destruction. The second stage of development is associated with the process of accumulation of internal welding stresses in the area of the source. The main parameters that determine the technological strength of the metal during surfacing or welding are: the length of the temperature range of brittleness (TIC), the level of ductility of the metal in the TIC and the intensity of the shrinkage deformation of the metal in the TIC. It was established that it is possible to increase the service life of the restored product several times in comparison with the new part by eliminating cracks in the deposited layer.

Analysis of fluid inclusions in vein quartz of the Fenkina-Lampi deposit by gas chromatography

The composition and content of fluid inclusions in the main structural and technological types of vein quartz of the Fenkina-Lampi deposit were studied by gas chromatography. It is shown that H2O dominates (90–99%) in the gases composition released from quartz under heating to 1000°C, CO2, CO, N2 and hydrocarbon compounds contents are much less. Quartz is characterized by high gassing in the high-temperature region (600–1000°C) comparable to gassing in the low-temperature interval (100–600°C), which is a negative indicator of the quality of quartz as a raw material for high-quality glass melting. It is necessary to develop a special purification technology for this quartz, which will take into account the features of its saturation with gas-liquid inclusions.

Dielectric behaviors and relaxor characteristics in Bi0.5Na0.5TiO3-BaTiO3 ceramics

Microstructure and dielectric behaviors of heating/cooling and bias-field were investigated in lead-free ceramics ([Formula: see text])[Formula: see text][Formula: see text][Formula: see text]BaTiO3 (BNT[Formula: see text]BT, [Formula: see text], 0.02, 0.04, 0.06, 0.08 and 0.10). The relaxor characters and the Vogel–Fulcher law of frequency-dependent dielectric properties were analyzed. Three dielectric anomalies with pronounced frequency dispersion at [Formula: see text], a maximum dielectric with variable frequency-dispersion at [Formula: see text] and a third Maxwell–Wagner-type relaxation over a wide temperature range in high-temperature region were observed. The significant dielectric thermal hysteresis, low barrier energy, high freezing temperature in heating process and the maximum dielectric tunability appeared in [Formula: see text] ceramic.