Electrolyte-plasma treatment (EPT) has become widespread in industry as an alternative to traditional chemical, electrochemical and mechanical methods of improving the surface quality of products made of metallic materials. The advantages of EPT are a high intensity of smoothing of microroughnesses, the use of low-concentration salt solutions as electrolytes, and the ability to process items of complex shape. The main disadvantage of the method is its high energy consumption; therefore, the method сan be classified as energy-intensive production. To reduce the energy intensity and increase the efficiency of the EPT process of metallic materials while maintaining high intensity, processing quality and environmental safety, we proposed a fundamentally new pulse method (pulsed EPT), which combines the advantages of both electrochemical processing and EPT. The method is realized by combining two alternating stages within one millisecond pulse: electrochemical and electrolyte-plasma. The high efficiency of the developed method is achieved due to the main intensive metal removal during the implementation of the electrochemical stage with a high current density and optimization of the duration of the electrolyte-plasma stage, which provides a high surface quality. A decrease in the repetition period of pulses with a decrease in their duration makes it possible to increase the electrochemical component of the process and to provide a more intensive metal removal, to remove significant surface irregularities. An increase in the pulse repetition period with a simultaneous increase in their duration permits to increase the electrolyte-plasma component of the process and achieve a low roughness with a general decrease in the energy intensity of the process. As a result of the work, the influence of the pulse characteristics of the developed process, the concentration and temperature of the electrolyte on the current density and the duration of the electrochemical and electrolyte-plasma stages has been investigated, a comparative analysis of the efficiency of using the pulsed EPT process instead of the traditional process at constant voltage has been carried out. It has been found that the metal removal rate in the developed pulse process is more than five times higher than the removal rate in the process based on the use of constant voltage, and is 40 μm/min, while the energy costs for the implementation of the pulse process is 19 % less.
However, the ECP in its classical form has a number of significant drawbacks. One of them is a dependence of treatment modes and electrolyte compositions on the processed material. In addition, aggressive expensive electrolytes that require special technologies for disposal are used for ECP. Electrolytes in ECP often require heating to a temperature of 60–90 °C. Processing at such temperatures causes significant harm to the environment and production personnel. To eliminate the existing disadvantages of the ECP and expand its technological capabilities, a processing method with application of pulsed unipolar and bipolar modes has been proposed. As a result, fundamentally new processes of pulse ECP with a pulse duration of 0.05–20.00 ms have been developed. They provide a reduction of energy costs for the process and high efficiency of polishing in comparison with traditional DC polishing. The rate of smoothing micro-roughness of the treated surface related to the total metal removal is significantly increased. The use of pulse modes in comparison with traditional ECP allows processing in universal electrolytes of simple compositions based on sulfuric and orthophosphoric acids without addition of chromium anhydride. Application of the developed pulse modes, which will provide at low metal removal a significant change in surface roughness, is the most appropriate for the ECP of precise parts, products or parts of small cross-section and rigidity, such as medical devices for minimally invasive surgery, precision engineering parts, etc. The paper presents results of a study for influence of pulsed unipolar and bipolar ECP modes on the surface quality of stainless steel specimens, as well as a comparative analysis of the efficiency of using pulsed ECP modes instead of DC polishing. The technological parameters of ECP using pulsed modes, providing the highest quality surface polishing with high efficiency of micro-roughness smoothing and low energy consumption have been established in the paper.
Recently, there has been a tendency in the industry to use electrochemical processing methods based on the use of milli- and microsecond pulses of different polarity and amplitude instead of a direct current. The use of a pulsed current in many cases makes it possible to obtain the desired effect by cheaper means and to provide additional controllability of the electrochemical process by adjusting the time parameters of the current pulses. This also ensures reduction of the energy costs of the polishing and cleaning process of surfaces as compared to direct current processing and increasing the efficiency of processing when the rate of smoothing the surface microroughness referred to the total removal of the metal rises significantly. For example, the application of bipolar pulses in polishing of many metallic materials eliminates the use of expensive and hazardous chromium electrolytes. The use of pulse mode during electrolyte-plasma polishing makes it possible to achieve the reduction of energy consumption and to increase of process efficiency while maintaining high intensity, processing quality and environmental safety. In order to study the effect of pulses parameters and the duration of a pause between them on the characteristics of the surface of parts made of various metallic materials in electrochemical and electrolyte-plasma processing modes the special power supply was modeled, designed and manufactured. The power supply provides the possibility of regulation frequency, the duration of the positive and negative pulses and the duration of the pauses between them a wide range. It makes it possible to generate current pulses up to 50 A at a voltage of 0 to 400 V of positive and negative polarities and is able to regulate their duration in the range from 10.0 μs to 8.1 s with the possibility of changing the ratio of the pulse duration and pauses from 1:1 to 1:9.
Recently, there has been a tendency in the industry to use electrochemical processing methods based on the use of milli- and microsecond pulses of different polarity and amplitude instead of a direct current. The use of a pulsed current in many cases makes it possible to obtain the desired effect by cheaper means and to provide additional controllability of the electrochemical process by adjusting the time parameters of the current pulses. This also ensures reduction of the energy costs of the polishing and cleaning process of surfaces as compared to direct current processing and increasing the efficiency of processing when the rate of smoothing the surface microroughness referred to the total removal of the metal rises significantly. For example, the application of bipolar pulses in polishing of many metallic materials eliminates the use of expensive and hazardous chromium electrolytes. The use of pulse mode during electrolyte-plasma polishing makes it possible to achieve the reduction of energy consumption and to increase of process efficiency while maintaining high intensity, processing quality and environmental safety. In order to study the effect of pulses parameters and the duration of a pause between them on the characteristics of the surface of parts made of various metallic materials in electrochemical and electrolyte-plasma processing modes the special power supply was modeled, designed and manufactured. The power supply provides the possibility of regulation frequency, the duration of the positive and negative pulses and the duration of the pauses between them a wide range. It makes it possible to generate current pulses up to 50 A at a voltage of 0 to 400 V of positive and negative polarities and is able to regulate their duration in the range from 10.0 μs to 8.1 s with the possibility of changing the ratio of the pulse duration and pauses from 1:1 to 1:9.
Titanium and niobium alloys are widely used at present in aircraft, nuclear energy, microwave technology, space and ultrasonic technology, as well as in manufacture of medical products. In most cases production technology of such products involves an implementation of a quality polishing surface. Mechanical and electrochemical methods are conventionally used for polishing products made of titanium and niobium alloys. Disadvantages of mechanical methods are low productivity, susceptibility to introduction of foreign particles, difficulties in processing complex geometric shapes. These materials are hard-to-machine for electrochemical technologies and processes of their polishing require the use of toxic electrolytes. Traditionally, electrochemical polishing of titanium and niobium alloys is carried out in acid electrolytes consisting of toxic hydrofluoric (20–25 %), sulfuric nitric and perchloric acids. The disadvantage of such solutions is their high aggressiveness and harmful effects for production personnel and environment. This paper proposes to use fundamentally new developed modes of electrolytic-plasma treatment for electrolyte-plasma polishing and cleaning products of titanium and niobium alloys while using simple electrolyte composition based on an aqueous ammonium fluoride solution providing a significant increase in surface quality that ensures high reflectivity. Due to the use of aqueous electrolyte the technology has a high ecological safety in comparison with traditional electrochemical polishing. The paper presents results of the study pertaining to the effect of titanium and niobium electrolytic-plasma polishing characteristics using the developed mode for productivity, processing efficiency, surface quality, and structure and properties of the surface to be treated. Based on the obtained results, processes of electrolytic-plasma polishing of a number of products made of titanium alloys BT6 (Grade 5), used in medicine and aircraft construction, have been worked out in the paper.
Electrolyte-plasma treatment has become widespread in the industry as an alternative to traditional chemical, electrochemical and mechanical methods of improving the surface quality of products made of metallic materials. Advantages ofelectrolyte-plasma treatment are a high intensity of microroughness smoothing, the use of low concentration salts solutions as electrolytes, the possibility of processing products of complex shape. The main disadvantage of this method is high power consumption, so the method can be considered in its classical form to the power-consuming. A possible way of reducing power consumption is treatment in unsteady modes that arise in the transition zone between a switching and stable electrolyte-plasma treatment process and is characterized by the periodic formation of a stable vapor-gas shell and a transition to an electrochemical process. The paper presents the results of a study of the influence of a high-gradient electric field under unsteady electrolyte-plasma treatment modes on the energy parameters of the process and the characteristics of the surface being treated. It is established that a high-gradient electric field has a significant effect on the decrease in specific power consumption, which is explained by a decrease in losses in the electrolyte and the influence of the field on the formation and maintenance of the vapor-gas shell. As a result of the study of the effect of a high-gradient electric field in unsteady EPT modes on characteristics of the surface layer was established that a significant impulse current density in the zone of predominantly electrochemical treatment leads to a selective etching of the surface and the formation of a characteristic micro relief of the surface with a developed porous microstructure with pore sizes from 0.3 to 2.5 microns. The most pronounced porous microstructure is provided at a voltage of 270–300 V and an additional inductance of 3.2 mH.
Thermo-physical peculiar features of anode electrolytic-plasma heating applied for heat and chemical heat-treatment have been investigated in the paper. The paper presents results of the investigations pertaining to influence of the operating voltage on current density, temperature and heating rate, heating power and changes in heat portion passing to the anode. Peculiar features of layer formation which are hardened by electrolytic-plasma carburizing have been presented in the paper.
The paper describes development of calculation and experiment model for metal removal in electrolyte-plasma treatment of rotational surfaces. The model for metal removal based on equality of pressures acting on the straight and curved sections of the vapor-gas blanket has been suggested and experimentally substantiated in the paper. The executed investigations have made it possible to determine dependences describing relationship between the intensity of dimensional electrolyte-plasma treatment of rotational parts and technological parameters of process. An expression for calculation of metal removal rate has been determined in the paper. Results of the work have been used for calculation of metal removal while developing technology of multi-stage cylindrical ultrasonic waveguides for blood clots destruction.
PARSHUTO AE, ALEXEEVYU.G., NISS VS, KOROLYOV A.Yu., SLEPNEV G.E. Development of an installation for microarc oxidation of alloys Aluminum and titanium
Electrolyte-plasma treatment has become widespread in the industry as an alternative to traditional chemical, electrochemical and mechanical methods of improving the surface quality of products made of metallic materials. Advantages of electrolyte-plasma treatment are a high intensity of microroughness smoothing, the use of low concentration salts solutions as electrolytes, the possibility of processing products of complex shape. The main disadvantage of this method is high power consumption, so the method can be considered in its classical form to the power-consuming. A possible way of reducing power consumption is treatment in unsteady modes that arise in the transition zone between a switching and stable electrolyte-plasma treatment process and is characterized by the periodic formation of a stable vapor-gas shell and a transition to an electrochemical process. The paper presents the results of a study of the influence of a high-gradient electric field under unsteady electrolyte-plasma treatment modes on the energy parameters of the process and the characteristics of the surface being treated. It is established that a high-gradient electric field has a significant effect on the decrease in specific power consumption, which is explained by a decrease in losses in the electrolyte and the influence of the field on the formation and maintenance of the vapor-gas shell. As a result of the study of the effect of a high-gradient electric field in unsteady EPT modes on characteristics of the surface layer was established that a significant impulse current density in the zone of predominantly electrochemical treatment leads to a selective etching of the surface and the formation of a characteristic micro relief of the surface with a developed porous microstructure with pore sizes from 0.3 to 2.5 microns. The most pronounced porous microstructure is provided at a voltage of 270–300 V and an additional inductance of 3.2 mH.
