The article focuses on developing a model of a stationary temperature field inside a semi-infinite cylindrical sample partly immersed in electrolyte. Temperature calculation is carried out by solving a heat transfer equation separately for the immersed and protruding parts of the sample. The heat flux is set on the outer area boundaries; meanwhile heat flux density for the immersed part is linearly dependent on the vertical coordinate. Within the framework of the model, vertical and radial temperature gradients are worked out both in protruding and immersed parts of the anode. It has been established that the vertical coordinate of the sign reversal point of the heat flux density in the immersed part depends on heat exchange conditions in the protruding part.

The possibility of realizing surface plasma electrolyte modification of the steel surface by successive diffusion saturation and polishing by changing the value of the applied voltage is shown. The composition, structure and properties of the formed coating have been studied.

This article focuses on the study of the effect of anodic composition of electrolyte on electric conductivity of a vapour gaseous envelope, formed in the mode of anode stationary heating. The investigation methods were based on measuring current-voltage characteristics in aqueous solutions of ammonium chloride, chlorohydric acid and hydrobromic acid at equal anion concentrations. It has been established that conductivity in vapour gas medium is primarily determined by electric field intensity which varies depending on its composition and thickness, ion mobility considered as factor of secondary importance. It has been assumed that emissive capacity of aqueous solutions can be limited by a critical concentration of their components.

The study considers heat exchange in a three-phase system: electrolyte solution—vapour-gas envelope (VGE)—a titanium workpiece. The temperature of a workpiece, current intensity, heat fluxes from the envelope to the electrolyte and the workpiece were measured in an aqueous solution of ammonium chloride with addition of ammonia and glycerol. Addition of ammonia and glycerol proved to decrease current intensity, heating temperature, total energy liberation and heat fluxes to the solution and the sample. Furthermore, it was found that heat shares passing to the electrolyte and the workpiece are not affected by ammonia and glycerol concentrations. The addition of ammonia and glycerol affect heat exchange, increasing the VGE thickness due to intense evaporation of these elements.

The energy balance in a three-phase system "anode–vapor/gas envelope–electrolyte" and the results of experimental determination of the heat fluxes acting in the vapor–gas envelope are considered. To determine the fluxes quantitatively, the calorimetric method and the theory of inverse problems of the thermal conductivity of solid bodies are used. It is shown that heat fluxes into the anode and electrolyte increase with the voltage delivered to the electrochemical cell, whereas the heat flux associated with the vapor release to the atmosphere remains practically unchanged. An increase in the concentration of the current-conducting component in the electrolyte leads to a certain growth of the heat flux into the anode and to a decrease of the flux into the electrolyte. The stages of a nonstationary period of the process of plasma-electrolytic heating have been revealed, and it has been established that the time of heating the vapor–gas envelope is several times shorter than the time of heating a sample.

The study considers heat exchange relations in terms of anode plasma-electrolytic treatment of titanium. The density of heat fluxes from vapour-gas envelope (VGE) to the anode-sample, electrolyte and atmosphere are experimentally determined. A model of heating temperature calculation considering heat transfer to the atmosphere along the cross-section of the workpiece is developed. Interrelations between envelope thickness and voltage as well as temperature-voltage characteristic (TVC) of the process are found. It is established that, other conditions being equal, anode heating of titanium is characterized by higher temperature at lower values of current and density of the heat flux from the vapor-gas envelope, compared with treatment of steel workpieces. The resulting dependences are confirmed by numerical evaluation with the use of the developed model and are explained by lower specific heat conductivity of titanium, contributing to a decrease of heat transfer from the heated part of the sample to the part protruding over electrolyte surface. The heat flux from the envelope to the electrolyte is found to be determined by power input in the system and independent of the anode material. (C) 2016 Elsevier Ltd. All rights reserved.

This work focuses on the factors causing appearance of a steady and continuous vapour-gas envelope which functions as medium for plasma electrolytic saturation of metal and alloys with interstitialelements (nitrogen, carbon, and boron). It is established that second critical voltage associated with transition from the current oscillation mode to the stable heating is determined by anion emission from boiling electrolyte in the envelope and heat transfer conditions in the system. Stability of the interface electrolyte–envelope is provided by the energy liberation in the envelope due to the passage ofcurrent. Second critical voltage promoting the anion emission is calculated on the base of Gouy–Chapman model and Tonks–Frenkel aperiodic instability. Theoretical dependence of critical voltage on the electrolyte concentration is confirmed experimentally. The influence of the electrolyte concentration on the second critical voltage is explained by the ability of the electrolyte to emit anions. Effect of solution flow rate on this voltage accounts for heat transfer conditions. It should be noted that the anion emission explains the influence of electrolyte composition on the weight change of the anode sample, limit heating temperature (~1000°C) due to the limited emissivity of electrolyte, discrete current in the case of a small surface anode, and high-frequency pulse of the current.

In this work, we investigated the features of the anode plasma electrolytic saturation of titanium alloys with nitrogen and oxygen. In this case, the titanium samples may be heated to 1050 degrees C using aqueous solutions of ammonium chloride as working electrolyte. The weight of titanium samples is found to change due to their oxidation and anode dissolution. An X-ray diffractometer, a scanning electron microscope, nuclear proton backscattering and an optical microscope were used to characterize the phase and elemental composition of the modified layer. The electrolyte composition (10 wt% ammonium chloride, 5 wt% ammonia) and processing mode (850 degrees C, 5 min) of commercially pure titanium (CP-Ti) allowing to obtain the hardened surface layer up to 0.1 mm with microhardness of 220 HV were proposed. Surface roughness R-a of samples after their nitriding for 5 min at 800 degrees C decreases from 1.67 to 0.082 mu m. The anode plasma electrolytic nitriding could decrease friction coefficient and increase wear resistance of the CP-Ti. It is found that the anodic nitriding of low alloy titanium alloys reduces their corrosion rate in an aqueous solution of sulphuric (4.5%) and salt (0.2%) acids by 2 orders of magnitude. Results of cyclic testing show that anodic nitriding of commercial titanium leads to a decrease in corrosion rate by 8 times in solution of hydrochloric acid (6%) with addition of protein and vitamin. Copyright (C) 2016, The editorial office of Journal of Materials Science & Technology. Published by Elsevier Limited.

The results of an experimental study of the anodic plasma-electrolytic treatment of steel samples with a graphite coating are presented. The effect of the coating thickness, duration and temperature of the treatment on the thickness, elemental composition, and microhardness of the cemented layer is studied.

Приводятся результаты экспериментального исследования анодной электролитно-плазменной обработки стальных образцов с графитовым покрытием. Исследовано влияние толщины покрытия, продолжительности и температуры обработки на толщину, элементный состав и микротвердость цементованного слоя.

This study is devoted to the effect of the oxide layer formed upon anodic plasma-electrolytic carburization on the rate of carbon diffusion in low carbon steels upon application of an aqueous solution of ammonium chloride with glycerol as a working electrolyte. Approximate determinations of carbon distribution in the surface layer of low carbon steels after their anodic plasma-electrolytic carburizing confirmed the hypothesis that there is deceleration of carbon diffusion by the oxide layer. Different structures of the oxide layer were revealed that depend on the method of sample cooling after their saturation with carbon in an anodic vapor-gas envelope. A possibility of controlling the thickness of the oxide layer was shown, as well as clarification of the surface by the choice of an electrolyte and treatment mode, was shown. A reduction in the roughness of the carburized surface from 0.62 ± 0.02 to 0.22 ± 0.02 μm was revealed.

Работа посвящена изучению влияния оксидного слоя, образующегося при анодной электролитно-плазменной цементации, на скорость диффузии углерода в малоуглеродистых сталях при использовании водного раствора хлорида аммония с глицерином в качестве рабочего электролита. Приблизительные оценки распределения углерода в поверхностном слое малоуглеродистых сталей после их электролитно-плазменной анодной цементации подтвердили гипотезу торможения диффузии углерода оксидным слоем. Обнаружена различная структура оксидного слоя, зависящая от способа охлаждения образцов после их насыщения углеродом в анодной парогазовой оболочке. Показана возможность управления толщиной оксидного слоя, а также осветления поверхности, выбором электролита и режимов обработки. Обнаружено уменьшение шероховатости цементованной поверхности от 0.62 ± 0.02 мкм до 0.22 ± 0.02 мкм.

It is shown that films of titanium dioxide obtained by anodic plasma electrolytic processing of commercial titanium in an aqueous solution of ammonium chloride are photosensitive. Incident photon to charge carrier efficiency (IPCE) in the near ultraviolet (366 nm) reached 8.5%. Magnitude of the photocurrent generated by the films obtained under optimum processing conditions decreases no more than 20% at the transition from the ultraviolet to the mixed light.

It is shown that films of titanium dioxide obtained by anodic electrochemical and thermal processing of technical titanium in an aqueous solution of ammonium chloride are photosensitive. The conversion efficiency of photon energy to current (IPCE) in the near ultraviolet (λ = 366 nm) reached 8.5%. The value of the photocurrent generated by the films obtained under optimum processing conditions, decreases in the transition from the ultraviolet to the mixed light and is not more than 20%.

The possibility of improving roughness of mild steel after its anodic cementation at reduced content of ammonium chloride and glycerine in working electrolyte is shown. The method of parts flow-around with distributed longitudinal streams is used, allowing to reduce thickness dispersion of case-hardened layer vertically. Examples of practical application of anodic cementation are given.

Изучено влияние концентраций хлорида аммония и углеродсодержащих добавок на толщину мартенситного слоя, образующегося после анодной цементации малоуглеродистых сталей. Определены углеродные потенциалы электролитов, содержащих хлорид аммония (10 масс. %) и 10 масс. % одного из углеродсодержащих компонентов (ацетон, глицерин, этанол, пропанол-2, этиленгликоль, сахарозу). Методом ядерного обратного рассеяния протонов определены распределения концентраций кислорода, углерода и азота в поверхностных слоях ряда конструкционных сталей, модифицированных нагревом в электролите, содержащем 10% хлорида аммония и 20% карбамида. Показана возможность поверхностного упрочнения стали 12Х18Н10Т путем ее цементации без опасности межкристаллитной коррозии.

The studies were devoted to the effect of concentrations of ammonium chloride and carbon-containing additives on the depth of martensite layer formed after anode carburization of low-carbon steels. The carbon potentials of electrolytes were determined to contain ammonium chloride (10 wt %) and 10 wt % of a carbon-containing component (acetone, glycerin, ethanol, propanol-2, ethylene glycol, saccharose). Nuclear proton backscatterring was applied to determine the concentration distribution of oxygen, carbon, and nitrogen in the surface layer of some structural steels modified by heating in electrolyte containing 10% ammonium chloride and 20% of carbamide. The capability of surface strengthening of 12Kh18N10T steel due to its carburization without the hazard of intercrystalline corrosion was demonstrated.

The possibility to increase the corrosion stability of steel 45 by its anodic electrothermochemical oxidation in aqueous solutions of ammonium acetate (10–15%) is shown. Tests of oxidized samples in a sulfuric acid solution (0.5 M) allowed finding a shift of their potential to the positive range (up to 0.3 V) with respect to the platinized electrode, which was accompanied by a decrease in the conductivity of the oxide layer. The minimum corrosion rate [0.7 g/(m2 day)] in the 5% NaCl solution was obtained for the specimen oxidized at a voltage of 200 V.