RU2173911C2 - Production of electric-arc plasma in curvilinear plasma guide and application of coating on supporting structure - Google Patents

Abstract

FIELD: method and device for production of plasma of electric-arc discharge and its use for application of coating on the supporting structure. SUBSTANCE: separated plasma of an electric-arc discharge is produced with the use of an electric-arc discharge on a cold cathode by passing it through a curvilinear plasma guide. The mentioned plasma is produced inside the curvilinear plasma guide, and electric current is passed through it in the longitudinal direction producing a magnetic field that is homogeneous in length, thus providing for application of a high-quality coating by spraying. EFFECT: enhanced efficiency of cleaning and activation of the supporting structure surface and enhanced quality of coating. 12 cl, 2 dwg, 1 tbl

Description

 The present invention relates to a method and apparatus for producing an electric arc plasma and to its use for coating a substrate.

 In recent decades, vacuum electric arc plasma sources have been widely used in industry for deposition of coatings based on metals, their alloys and compounds onto products. They are used for applying on machine parts, tools, consumer goods, etc. wear-resistant, corrosion-resistant, decorative coatings, coatings with the required electrical and magnetic characteristics and other coatings with special properties. Vacuum arc plasma sources are also used to obtain ion beams used for ion implantation in ion accelerators, as well as in rocket power plants.

 The prior art.

The process of obtaining a plasma stream in a vacuum electric arc source is as follows. On a cooled cathode made of the material on the basis of which it is required to obtain a coating, a high-current arc discharge is ignited in a vacuum. The ignition of an arc discharge, as a rule, is carried out either by mechanical rupture of the electrical contact between the cathode and a special electrode, or using a high-voltage or laser spark. An arc discharge on a cold cathode is contracted into cathode spots ranging in size from several microns to hundreds of microns and current densities of up to 10 ⁶ -10 ⁸ A / cm ^{2 in them} . Each spot emits a stream of metal plasma in a direction approximately perpendicular to the surface of the cathode. In the absence of magnetic and electric fields, the cathode spots randomly move along the cathode surface. Electric and magnetic fields can be used to control the movement of spots, holding them on the working surface and forcing them to move along the desired trajectories.

 Each spot makes a corresponding contribution to the plasma flow, which has a distribution close to cosine with an axis perpendicular to the cathode surface. Due to the peculiarities of burning a vacuum arc on a cold cathode, in particular, creating a positive space charge near the cathode, plasma ions are accelerated to energies from units to hundreds of electron volts in the direction perpendicular to the cathode surface.

 The plasma flow obtained in the electric arc source is highly ionized. The degree of ionization for a number of materials approaches 100%. Plasma contains a significant amount of two- and three-fold ionized particles. This is a significant advantage over sources based on the phenomena of sputtering (including magnetron) and evaporation (electron beam, laser radiation, etc.) of the material, where the material flows have a low degree of ionization. A high degree of ionization allows you to control the flow using electromagnetic fields, to control and control the energy of atoms entering the substrate, and increases the reactivity of the vaporized material during the formation of compounds with both the reaction gas and directly with the material of the coated substrate.

To deposit coatings, the plasma flow is directed onto a substrate, to which, as a rule, an accelerating voltage is applied to obtain the required energy of ions arriving at the surface. The coating process usually consists of two stages. At the first stage, at a sufficiently deep vacuum (at a pressure of 10 ^-4 mmHg and below), an accelerating voltage of up to 1000-1500 V is applied to the substrate. Ions of the cathode material are accelerated near the substrate in the Debye layer and bombard its surface. When bombarded by ions, the surface is cleaned of contaminants, the so-called "ion cleaning" process. After conducting "ion cleaning", the voltage applied to the substrate is reduced to values from several tens to several hundreds of volts and the particles arriving on the substrate condense on its surface, forming a coating corresponding to the cathode material. To obtain coatings of complex composition, reaction gas is introduced into the working chamber, as a rule, up to pressures of 10 ^-2 -10 ^-4 mm Hg. In this case, it is possible to obtain coatings based on compounds of the cathode material with the reaction gas.

 The problem with electric arc plasma sources is that the arc discharge, along with the vapor component, generates droplets of molten substrate material - macroparticles. Such particles have characteristic sizes from tenths of a micron to tens of microns. Particles can fall on the coated substrate, forming irregularities in the structure of the coating, defects in the form of depressions and protrusions. This phenomenon significantly narrows the scope of electric arc plasma sources. The presence of particles in the plasma stream does not allow coating on parts with a high class of surface cleanliness, on a tool with sharp sharpening, significantly reduces the performance of coatings, such as wear resistance, electrical and magnetic properties.

In addition, electric arc sources practically do not allow coating on the basis of relatively fusible materials, such as, for example, aluminum and others, in the stream of which there are a large number of large particulates. In particular, upon receipt of ceramic coatings based on Al ₂ O _{3, the} presence of Al particulates violates the insulating properties of the coatings. This also applies to the application of diamond-like coatings using a carbon cathode, where the particles are particles of soot.

 Various methods are used to reduce the amount of particulate in the plasma stream. The first group of methods consists in using various magnetic and electric fields near the surface of the cathode, which can increase the speed of movement of arc spots on the surface of the cathode. This leads to a decrease in the number of generated particles and their sizes. The second group of methods consists in the use of various plasma-separator filters. Such devices are placed between the cathode and the sprayed substrate so that they allow the vapor component of the plasma stream to pass through and block the passage of particulates.

 The electromagnetic methods of the first group are much simpler to implement than the methods of separation of the plasma flow. However, they are ineffective and do not exclude the generation of particles by an arc discharge. A significant amount of molten metal droplets are retained in the plasma stream.

 Separation methods are based on the deviation of the vaporized ionized plasma component from a rectilinear trajectory. For this purpose, a longitudinal magnetic field is superimposed on the plasma stream. In the interval between two Coulomb collisions, each charged plasma particle moves along the field along a helical path. If the field is homogeneous, then the axial line of the trajectory practically coincides with one of the field lines of force. The movement of electrons and ions across field lines is only possible due to Coulomb collisions. In each collision, the particle moves a distance of the order of the Larmor radius. If collisions rarely occur, then the particle appears to be attached to the field lines of force. Such a plasma is called "magnetized." If the plasma parameter: ρ / λ >> 1 (ρ is the mean free path, λ is the average Larmor radius), then the particle can shift a noticeable distance across the field only after passing a very long path along the field line.

 The “magnetization” is different for the ionic and electronic components of the plasma. In order to ensure the “magnetization” of the ion component of the plasma of heavy metals, magnetic fields of up to several tens of kiloersted are required. The creation of such magnetic fields requires very large and complex systems. Therefore, in practice, systems are used that provide the “magnetization” of only the electronic component. Due to this, the electrons can only move freely along the field lines of the field, and the magnetic field itself does not significantly affect the movement of ions. In this case, the electrons will be attached to the lines of force of the magnetic field, and the ions will be held in the same region of space by the electric field created by the electronic component. In addition, the magnetization of electrons and a sharp decrease in the transverse mobility of the electron component of the plasma make it possible to create an electric field perpendicular to the magnetic field, which leads to ion drift in the desired direction. Thus, by creating a corresponding magnetic field uniform in length and a corresponding electric field, it is possible to deflect the plasma flow in the desired direction along the lines of the magnetic field and transport it to a substrate located outside the direct line of sight of the arc discharge cathode. The particles do not change their trajectories under the influence of electromagnetic fields, they move along direct trajectories and do not fall on the substrate.

 Plasma separation methods are much more effective for cleaning particles from plasma flow than the first group of methods. However, existing separators have very low throughput and, accordingly, such systems have low productivity.

 The mechanism of material evaporation by an arc discharge is described in many works and patents. An example of this early work is US Pat. No. 4,854,582 (Edison), which describes the use of vacuum arc evaporation to form a coating on a substrate. U.S. Patent 2,972,695 (Wroe); 3,783,231 (Sablev et.al); 3,793,179 (Sablev et.al.) give examples of installations using a magnetic field and a special configuration of electrodes to stabilize the vacuum arc on the working surface of the electrodes, increase the evaporation rate and direct the plasma flow to the substrate.

 Examples of the first group of methods for reducing the generation of particles from the surface of the cathode are given in US patents 4,673,477 (Ramalingam et.al.); 4,724,058 (Morrison, Ir.); 4,849,058 (Veltrop et.al.), which use a magnetic field to control the movement of cathode spots along special paths and increase the speed of their movement. In US patent 5,269,898 (Welty) it is also shown that the introduction of the axial component of the magnetic field on a long cylindrical cathode accelerates the movement of the arc and reduces the generation of particulate matter.

 The use of methods for separating plasma from particles is described in US patents 4,452,686 (Aksenov et. Al.); 5,282,944 (Sanders et.al.); 5,279,723 (Falabella et.al.): 5,480,572 (Welty); Aksenov et. al. "Transport of Plasma. Streams in a Curvilinear Plasma-optics System." Soviet Journal of Plasma Physics 4 (4), 1978.

 US 4,452,686 discloses a magnetic island type plasma separator. It is a cylindrical tube, at one end of which there is an arc plasma source. On the outside there is a solenoid that creates a longitudinal magnetic field inside the pipe. A solenoid is coaxially located in the center of the tube, which blocks line of sight from the cathode to the substrate. The external and internal solenoids create such a magnetic field configuration that the lines of force pass through the pipe and bend around the internal solenoid, passing between the solenoid and the pipe walls. The plasma emitted by the source is deflected by magnetic and electric fields and sent between the walls of the pipe and the central solenoid. The particles are not deflected by magnetic and electric fields and are deposited on the central solenoid. According to the authors, the transmittance of such a separator is about 10%.

US Pat. No. 5,282,944 describes a device operating on a principle similar to the previous one. The cathode is a cylinder coaxial with the outer tube, the working surface of which is the outer surface. In this case, the plasma is emitted in the radial direction to the walls of the pipe and with the help of an external electromagnetic field is rotated 90 ^° and sent to the exit of the pipe where the substrate is located.

 In the aforementioned work, Aksenov et. al. "Transport of Plasma ..." describes a curved plasma separator. The plasma generated by a standard electric arc source is directed into a plasma duct, which is a quarter of a torus. A longitudinal magnetic field is created inside the plasma duct using solenoids covering the plasma duct. A voltage is applied to the plasma duct body, creating a radial electric field. The plasma emitted by the source is transported along the magnetic field lines through the plasma duct. The particles move rectilinearly and are deposited on the walls of the plasma duct.

US Pat. No. 5,279,723 describes apparatus similar to the previous one using a plasma duct with an angle of 45 ^° . To reduce the reflection of particles from the walls of the plasma duct, a special lattice is used on the inner walls of the plasma duct.

 US Pat. No. 5,480,572 discloses a curved plasma separator with a rectangular long cathode, operating on a similar principle for a planar plasma source with a rectangular long cathode. Devices that create a magnetic field of a special shape, which ensures the movement of the arc along a long rectangular cathode and transportation of a flat wide beam along a curved plasma duct, are described.

 All of the above plasma sources with flow separation have not found any significant application in industry, since they have a relatively low coefficient of utilization of the plasma-forming material and low productivity. This is due to several factors.

 In the above studies, magnetic fields were used, the structure of which is different in the cathode region (the region of magnetic fields responsible for controlling the movement of cathode spots on the cathode surface) and in the plasma duct (where magnetic fields are responsible for transporting the plasma flow). This leads to the fact that the emitted plasma stream, before entering the region of a uniform magnetic field in the plasma duct, passes through the region of an inhomogeneous magnetic field. So, in the mentioned work of Aksenov et. al. The “Transport of Plasma...” Plasma flow was created in a standard electric arc source and before entering the region of uniform longitudinal magnetic field in the toroidal plasma duct, a region of weakened diverging magnetic field having a transverse radial component passed at the entrance to the plasma duct. In US Pat. No. 5,480,572, a magnetic field was created near a rectangular cathode having a component parallel to the surface of the cathode that allowed cathode spots to move along the cathode surface.

 Thus, in the considered plasma sources, the flow passes through the transverse magnetic field. Since the mobility of particles in a magnetized plasma across a magnetic field is limited, a so-called “magnetic plug” arises. In addition, when voltage is applied to the plasma duct body to ensure the drift of ions from the walls, a longitudinal component of the electric field that inhibits the ions appears in the transverse magnetic field (see the description of the effect in the aforementioned work by Aksenov et. Al. "Transport of Plasma ..." "Magnetic plug ") and the electrostatic barrier at the entrance to the plasma duct lead to large losses in plasma flux density.

 Another reason for the low efficiency of the considered sources is the low electron density inside the plasma duct. When burning an arc discharge between the cathode and anode located at the entrance to the plasma duct, the region of high electron density is also concentrated near the entrance to the plasma duct. As noted earlier, in the plasma only electrons are “attached” to the magnetic field lines, and ions are held in this region by the electric field created by the electronic component. At a low electron density, this field is small and does not prevent the drift of ions across the lines of force of the magnetic field and their deposition on the walls of the plasma duct. In addition, the high electron density concentrated at the entrance to the plasma duct creates an electric field that inhibits ions. These factors lead to low conductivity of the plasma duct.

 The low efficiency of plasma sources with flow separation is also determined by the effect of scattering of the flow on gas particles (residual or reaction) inside the plasma duct. If in electric arc sources without separation of the flow the distance from the cathode to the sprayed substrate is usually from 10 to 30 cm, then with the use of separators this distance increases to meters. A stream of plasma ions passing such a distance is neutralized, scattered, and loses its energy and direction of motion as a result of scattering by gas particles.

 The above reasons determine the low throughput of plasma ducts and, accordingly, the low efficiency of existing sources of separated electric arc plasma.

 The problems that arise when using the method of coating using electric arc plasma sources, both with flow separation and without separation, include the following. As noted earlier, a distinctive feature of the electric arc plasma production method is the high degree of ionization of the material emitted from the cathode. However, the degree of ionization of the reaction gas introduced into the vacuum chamber is not large. This leads to the fact that in the process of ion cleaning, the target surface is bombarded with practically metal ions. At accelerating voltages used in ion cleaning, the sputtering coefficient of the substrate by ions of the cathode material is usually less than unity. Therefore, during ion bombardment, along with the spraying of the substrate, the process of coating deposition also occurs. The deposition process on the one hand reduces the efficiency of cleaning the target surface from contamination, on the other hand, a coating is formed corresponding to the cathode material. In this way, a sublayer of material corresponding to the cathode material is formed between the target surface and the working coating. This leads both to a decrease in the adhesion of the working coating to the substrate, and to a deterioration in its operational properties.

 In addition, the low degree of ionization of the reaction gas limits the applicability of the electric arc deposition method, the creation of coatings with targeted predetermined properties, reduces the ability to control and control the energy of the atoms of the reaction gas, reduces their reactivity in the formation of compounds with both cathode material particles and the substrate material .

 These shortcomings could be eliminated by obtaining a stream of gas-metal plasma with a high degree of ionization of both the metal and gas components.

 Thus, despite the existing designs of the sources of the electric arc separated plasma, there is a need to create a highly efficient method for producing a stream of the electric arc separated plasma and to develop a source with high productivity, which forms a stream of controlled gas-metal plasma with a high degree of ionization of both metal ions and gas. Such a source will give further development to the method of electric arc coating production and will expand the field of its technological application both in industry and in scientific developments.

SUMMARY OF THE INVENTION
One of the objects of the present invention is a method of creating an electric arc plasma, which consists in obtaining plasma using a vacuum electric arc discharge on a cold cathode by passing it through a curved plasma duct, while the electric arc plasma is created inside a curved plasma duct and an electric current is passed through it in the longitudinal direction with the formation of a longitudinal continuous and uniform along the entire length of the plasma duct between the cathode and the anode of the magnetic field and the electric field directed to nkam or from the walls of the plasma duct.

oт центра плазмовода, при этом анод размещают на выходе из плазмовода, а рабочую поверхность катода устанавливают параллельно поперечному сечению плазмовода в месте установки катода. Кроме того, электрический ток представляет собой электронный ток дугового разряда, используемого для генерации плазмы.In one preferred embodiment of the method, a curved plasma duct is made in the form of a part of a toroid with an angle of rotation α = Arccos (2r ² -R ² ) / R ² where r and R are the small and large radii of the toroid, respectively, and the cathode is placed inside the plasma duct with an offset from the longitudinal axis of the plasma duct to its wall with a smaller radius so that the center of the working surface of the cathode is located at a radius

from the center of the plasma duct, while the anode is placed at the exit of the plasma duct, and the working surface of the cathode is set parallel to the cross section of the plasma duct at the cathode installation site. In addition, the electric current is the electronic current of the arc discharge used to generate plasma.

 A magnetic field uniform in length is created inside the plasma duct, so that the magnetic lines of force are perpendicular to the working surface of the cathode and pass through the plasma duct parallel to its axis. An arc discharge is ignited between the anode and cathode, ensuring the passage of the electron arc current through the plasma formed inside the plasma duct. A positive or negative potential is applied to the plasma duct body. Since the electronic component of the plasma is magnetized, the lines of force crossing the cathode and passing near the axis of the plasma duct take a potential close to the potential of the cathode, and the lines of force near the walls of the plasma duct take the potential of the walls. Thus, an electric field is created in a magnetized plasma perpendicular to the walls of the plasma duct. The electric field provides an additional drift of ions from the walls or to the walls of the plasma duct (depending on the polarity and magnitude of the applied voltage).

 Due to the presence of magnetic and electric fields (see the mechanism described above), the ionized plasma component is transported along the magnetic field lines through the plasma duct to the exit. While the particles and the neutral component of the plasma are deposited on the walls of the plasma duct.

 The essence of the proposed method is as follows. Firstly, in creating a magnetic field, the lines of force of which are perpendicular to the working surface of the cathode and continuously pass through the plasma duct parallel to its axis. In this case, the plasma is emitted by the cathode directly in the region of a uniform magnetic field and transported along the plasma duct along a magnetic field uniform throughout its length. The paths of particles along the path pass along the lines of force of the magnetic field and do not cross them anywhere. This configuration of the magnetic field eliminates the appearance of both “magnetic plugs” and the electrostatic barrier when a potential is applied to the plasma duct body, which is observed in the structures described earlier.

 Secondly, in transmitting the electron discharge current through the plasma emitted into the plasma duct. Such a current in this case is the electron current of the arc discharge, which burns between the cathode and the anode located at different ends of the plasma duct. In this case, a high-density electron stream is created inside the plasma duct. As noted earlier, the presence of a magnetic field leads to the fact that the electrons can only move along the lines of force of the magnetic field and practically do not go to the walls of the plasma duct. The charge of such electrons concentrated along the axis of the plasma duct creates an electric field that holds ions in the same region of space and prevents them from escaping to the walls of the plasma duct.

 In addition, the directed motion of electrons leads, on the one hand, to ionization of the gas (residual or reaction) in the plasma duct, and on the other hand, to the acceleration of ions in this direction. Ionization of the gas inside the plasma duct leads to a decrease in the energy loss of the ions emitted by the arc discharge, due to scattering by gas particles, and the acceleration of ions to compensate for these losses.

 It should be noted that the formed gas ions are also accelerated towards the exit from the plasma duct, on the one hand, due to the directional movement of electrons, and on the other hand, due to the magnetoplasma-dynamic effect arising at the exit of the plasma duct, where the plasma flow interacts with a diverging magnetic field having radial component.

 Thus, a stream of gas-metal plasma is formed at the source exit, in which both the metal component generated by the arc discharge and the gas component formed by ionization of the gas in the plasma duct are strongly ionized. By changing the potential on the body of the plasma duct and thus increasing or decreasing the drift of ions to the walls of the plasma duct, it is possible to adjust the ratio of metal and gas ions in the plasma stream. Establishing such a potential that almost all the metal ions entering the plasma duct from the cathode drift to the walls; at the source output, a stream of almost gas plasma can be obtained. This flow is formed by those gas particles that were ionized close to the exit from the plasma duct and, having accelerated, reached the exit earlier than they condensed on the walls due to transverse drift. By establishing such a potential that metal ions drift from the walls of the plasma duct to the center, a stream of gas-metal plasma containing both metal ions and gas ions (residual or reaction) can be obtained at the source output.

 Thus, these two factors — the creation of a magnetic field whose lines of force are perpendicular to the working surface of the cathode and continuously pass through the plasma duct parallel to its axis, and the transmission of the electron current through the plasma, determine, on the one hand, the high transmittance of the ionized plasma component of the vacuum arc through the plasma duct, on the other hand, the ionization and acceleration of gas particles and, thus, the formation at the outlet of a stream of gas-metal plasma, in which both metal and Azov component.

 The proposed method is provided by a highly efficient source of arc gas-metal separated plasma with a productivity acceptable for industrial use and with advanced technological capabilities.

 None of the considered papers used the magnetic field of the claimed configuration and the transmission of the electron current of the arc discharge through the plasma inside the plasma duct.

от центра тороида, причем анод установлен на выходе из плазмовода.Another feature of the invention is that in a device for producing a stream containing a cold cathode made of vaporized material, an anode, a curved plasma duct made as part of a torus, an electromagnetic coil enclosing the plasma duct, as well as power sources for the plasma duct body, arc discharge and electromagnetic coils, a toroidal plasma duct is made with a rotation angle α = ArcCos (2r ² -R ² ) / R ² , where r and R are respectively the small and large radii of the toroid, the cathode is installed inside the plasma duct, and its working surface is parallel on the cross section of the plasma duct at the installation site of the cathode, offset from the longitudinal axis of the plasma duct to its wall with a smaller radius so that the center of its working surface is located at a radius

from the center of the toroid, and the anode is installed at the exit of the plasma duct.

In embodiments of the device, the end working surface of the cathode is made beveled with respect to the cross section of the inlet part of the plasma duct with a bevel angle
λ = ArcSinl / Ro,
where l is the distance from the beginning of the toroidal part of the plasma duct to the cathode surface, and the input flange of the plasma duct on which the cathode is mounted is isolated from the plasma duct body, and the anode is the walls of the vacuum chamber located behind the plasma duct or a hot ring electrode located between the plasma duct and the vacuum chamber, wherein the electromagnetic coil is wound along the plasma duct uniformly in the number of turns per unit length, and the power source of the plasma duct body has a positive or negative polarity.

 Another object of the invention is a method for producing a coating on a substrate, carried out by means of a curvilinear plasma duct using plasma of an electric arc discharge, which consists in ionically cleaning the surface of the substrate, saturating this surface with a reaction gas and applying a coating based on the cathode material, while the electric arc plasma is created inside a curvilinear plasma duct and an electric current is passed through it in the longitudinal direction with the formation of a longitudinal, continuous and uniform along the entire length of the plasma duct and between the cathode and anode of the magnetic field and the electric field directed to the walls or from the walls of the plasma duct, the substrate is placed on the exit side of the plasma duct and the potential is supplied to it, while ion cleaning is carried out in an inert gas medium at zero or negative potential on the plasma duct body, saturation of the surface of the substrate is carried out in a reaction gas medium or a mixture of reaction and inert gases at zero or negative potential on the plasma duct body, and when coating the plasma duct body, ozhitelny potential.

 In embodiments of this method, ion cleaning begins at zero voltage on the substrate and constantly raise it to the desired value; when the substrate is saturated with a reaction gas, the concentration of atoms of the reaction gas on the surface of the substrate is maintained no higher than the solubility limit of this gas in the substrate material; and after saturation of the surface of the substrate with reaction gas, a short-term ionic purification is carried out in an inert gas medium.

 The source, which forms the flow of separated gas-metal plasma, in which both metal and gas components are strongly ionized, has wider possibilities than current electric arc sources and allows the implementation of new technological processes.

 Firstly, such a device provides etching of the surface of the substrate by cathodic sputtering and thereby allows a more effective cleaning of the surface before coating. Using an inert gas as the working one and installing such a potential on the plasma duct body that “locks” it for the passage of metal ions (see above), an inert gas plasma flow is formed at the source output. Such a plasma flow provides etching of the substrate even at small accelerating voltages. This is due to the fact that, although at low accelerating voltages the sputtering coefficient is less than unity, those inert gas ions that condense on the surface desorb from it and do not form a film, as is the case with metal ion bombardment.

 Thus, the device provides effective cleaning and activation of the surface of the substrate, which in turn leads to improved adhesion of the coating to be applied further. In addition, the possibility of ion cleaning at low accelerating voltages significantly reduces the likelihood of microarcs on the surface of the substrate and thereby reduces its damage.

 Using such a source, it is possible to create the required surface micro-profile by etching by cathodic sputtering, for example, using the technology of “masks”.

 Secondly, the device provides a surface layer saturated with an active gas, such as a nitrided or cemented layer, on a substrate. By installing such a potential on the plasma duct body that "locks" it for the passage of metal ions, and using the reaction gas as a working gas, a stream of reaction gas ions can be obtained at the source output. The ions of such a gas, coming to the surface, react with the atoms of the substrate and form a surface layer saturated with atoms of the active gas. Thus, the source provides coatings with a sublayer saturated with active gas on the surface of the substrate. The operational characteristics of such coatings can be significantly higher than the characteristics of coatings deposited on the initial surface.

 Thirdly, the high degree of ionization of both the metal and gas components, and the absence of a neutral metal component and particulate in the flow, make it possible to control and control the energy of particles arriving at the substrate and increase the reactivity in the formation of compounds of both the vaporized material with the reaction gas and directly with the backing material. Good controllability of plasma flow parameters makes it possible to provide a different set of coating properties depending on their intended purpose. In particular, coatings with high dispersion. High dispersion determines the high strength properties of coatings, including greater ductility at high microhardness and high compressive stresses.

 Thus, an advantage of the present invention is the creation of a highly efficient stream of separated gas-metal plasma, in which both metal and gas components with a relatively high coefficient of utilization of the plasma-forming material and high productivity are highly ionized. This leads to the possibility of industrial application of the flow of separated electric arc plasma and the implementation of new technological processes.

 A brief description of the drawings.

The invention will now be described in exemplary embodiments with reference to illustrations, wherein
In FIG. 1 shows a device for producing plasma according to the present invention with its power sources.

 In FIG. 2 shows an enlarged view of the plasma duct with the designation of the radii of its rotation.

 A preferred embodiment of the invention.

 A device for producing a plasma generally consists of a curved plasma duct with a coil creating a magnetic field on it, a cathode assembly located at the input of the plasma duct, an anode located at the output of the plasma duct, and a power supply system.

A curved plasma duct is a part of a toroid made of a non-magnetic material with water-cooled walls. The angle of rotation of the plasma duct is determined from the condition that there is no direct visibility of the exit of the plasma duct from its entrance, i.e. points A, B and C should be located on one straight line (see Fig. 2), and is equal to
α = ArcCos (2r ² -R ² ) / R ² ,
where α is the turning angle, r is small, and R is the large radius of the walls of the plasma duct. The plasma duct can end with a cylindrical part, as shown in FIG. 1.

 On the outer surface of the plasma duct 1 is an electromagnetic coil 2 with a uniform number of turns per unit length.

At the inlet of the plasma duct, a cathode assembly is mounted on the flange 3. The flange is made of non-magnetic material and can be either electrically isolated from the plasma duct body or not. The cathode assembly consists of the following elements:
- water-cooled cathode holder 4, electrically isolated from the inlet flange;
- conical cathode 5, the taper angle of which is 8-10 ^o ;
- metal skirt 6, which is a continuation of the cathode;
- a protective screen 7, which is mounted on the cathode holder through an insulator and is electrically isolated from both the cathode and the plasma duct body;
- an igniting electrode 8 with an insulator located between the electrode and the skirt 6.

 At the other end, the plasma duct is mounted through an insulator on the vacuum chamber 9. An insulated electrode 10 can be located between the plasma duct and the chamber, which can be an anode of an arc discharge.

The power supply system consists of the following sources:
- power source 11 of the arc discharge, the negative pole of which is connected to the cathode, and the positive one - with the anode 10 or the camera body 9;
- power source 12 of the electromagnetic coil;
- bipolar power source 13 of the plasma duct body;
- source 14, forming a high voltage pulse ignition arc discharge.

 The substrate 15 is located in the installation chamber. Accelerating voltage from the substrate power source 16 can be applied to the substrate.

 On the wall of the plasma duct along a large radius is a removable grill 17.

,
где r и R малый и большой радиусы стенок плазмовода.The magnetic field in a toroid-shaped plasma duct is nonuniform in radius and varies in proportion to 1 / R _i , where R _i is the distance from the center of the toroid to the corresponding point inside the plasma duct. In order for the center of the working surface of the cathode and the emitted plasma stream to be in an equal position relative to the walls of the plasma duct, the cathode must be shifted to the wall with a smaller radius. The magnitude of the cathode displacement is determined from the condition of equality of magnetic fluxes through cross sections from the center of the indicated cathode surface to the wall with a smaller radius and from the center of this cathode surface to the wall with a large radius. From this condition it follows that the center of the cathode surface must be located relative to the center of the toroid at a radius

,
where r and R are the small and large radii of the walls of the plasma duct.

 In order to ensure the perpendicularity of the working surface of the cathode to the magnetic field lines, the working end surface of the cathode is beveled with respect to the cross section of the input part of the plasma duct. The bevel angle is γArcsinl / Ro, where l is the distance from the beginning of the toroidal part of the plasma duct to the cathode surface. Note that as the cathode is generated, the corresponding angle is maintained automatically, since the surface is produced perpendicular to the lines of force of the magnetic field.

 The plasma source works as follows. A voltage is applied to the electromagnetic coil 2. Inside the plasma duct 1, a continuous longitudinal magnetic field is created, parallel to the axis of the plasma duct, uniform in length. A high-voltage pulse is applied between the ignition electrode and the skirt 6 of the cathode 5, as a result of which an electrical breakdown occurs on the surface of the insulator and an electric spark occurs. An electric spark initiates ignition of an arc discharge between the cathode 5 and the anode 10. The wall of the vacuum chamber 9 and a special electrode 10, the anode, can serve as the anode.

 Since the magnetic field is parallel to the axis of the plasma duct 1 and perpendicular to the working surface of the cathode, the lines of force form an acute angle with the lateral surface of the cathode 5. It is known that the cathode spots of the arc move in the direction of the acute angle formed by the lines of force of the magnetic field with the surface of the cathode. Thus, the cathode spots move from the side surface to the working end surface of the cathode and are held there. The skirt 6, which is a continuation of the cathode 5, serves to make fuller use of the cathode material. In the above construction, the cathode can be produced up to a thickness of the order of a millimeter. The protective screen 7 serves to protect the cathode holder and from damage during arc runoff in case of emergency operation of the plasma source.

 The plasma stream is emitted directly in the region of a uniform magnetic field and transported along the magnetic lines to the exit of the plasma duct.

 To equalize the flux density over the radial section, the plasma duct 1 can end with a cylindrical part with an electromagnetic coil that creates a magnetic field uniform in cross section.

 In order to increase or decrease the drift of ions from the walls of the plasma duct or to the walls of the plasma duct, a positive or negative voltage is applied to the body of the plasma duct 1. To reduce the distortion of the electric field created by the applied voltage, the input flange 3 of the plasma duct can be isolated from the walls.

 The neutral plasma component and the particles move along rectilinear trajectories and are deposited on the walls of the plasma duct. To reduce the reflection of particulates, a lattice 17 is placed on a wall with a large radius. For the convenience of maintenance and cleaning of the source, the lattice 17 is removable.

 After the plasma stream leaves the source, it is directed to the substrate 15, to which an accelerating voltage can be applied.

When applying insulation coatings, for example, based on Al ₂ O ₃ , not the chamber wall 9, but a special hot electrode 10 can be used as the anode of the arc discharge. The electrode is heated by the arc current and there is no formation of an insulation coating on it that prevents the burning of the arc discharge.

 The technological process of coating is as follows. An inert gas, such as argon, is fed into the vacuum chamber of the installation. The potential of the plasma duct 1 is set to zero or negative, so that the plasma duct is "locked" to the ions of the cathode material. In this case, a gas plasma flow is formed at the source output. An accelerating voltage is applied to the substrate 15. Plasma ions bombard the surface of the substrate, leading to its dispersion. Thus, the surface of the substrate 15 is cleaned of contaminants and activated. To reduce the likelihood of microarcs on the surface of the substrate, ion cleaning begins at small accelerating voltages and gradually raise it from the desired value.

 After ion cleaning, the inert gas is replaced by a reaction gas. At the source output, a plasma flow of the reaction gas is formed. Gas ions arriving at the surface diffuse into the surface layer of the substrate 15. In this case, the diffusion process is activated by ion bombardment. Upon receipt of the diffusion sublayer, technological parameters are set such that the concentration of gas ions on the surface does not exceed the solubility limit of this gas in the substrate material 15. In this case, a solid gas solution is formed in the substrate material and a layer of chemical compounds of gas ions with substrate atoms is not formed on the surface, which both prevents the diffusion of particles into the substrate 15 and impairs the adhesion of the further coating to the substrate.

 After the process of forming a diffusion layer, as a rule, a short-term ionic purification is carried out in order to remove traces of chemical compounds of the reaction gas from the substrate material from the surface.

 Then, a positive potential is established on the plasma duct body, “opening” the plasma duct 1 for metal ions. Reduce the potential on the substrate 15 to the desired value. The flow of gas-metal plasma, coming to the substrate, condenses and forms a coating.

 Thus, the surface is prepared before coating and the coating is formed with a diffusion sublayer.

The plasma flow cross section that was obtained in the source is 600 cm ² . When the source was operating in gas plasma mode at zero potential on the plasma duct body and using argon gas, etching of a 40X steel substrate was obtained (see Table 1).

 Using this method of etching using masks (masking part of the substrate surface), gas-dynamic grooves were obtained on the working surfaces of gas-dynamic bearings.

Nitrogen gas was used to saturate the surface of the substrate with reaction gas. At a nitrogen pressure of 5 • 10 ^-3 mm Hg and the voltage on the 350V substrate for 20 min, a nitrided layer was obtained on steel 40X with a size of 60 μm, and on steel P6M5 with a value of 40 μm. With increasing nitrogen pressure on the surface of the substrate, a layer of nitrides of alloying elements begins to form - the “white layer”, which both prevents the flow of nitrogen into the substrate and worsens the adhesion of the coating to the substrate. Therefore, after the process of saturation of the substrate with nitrogen — nitriding, a short-term ionic purification was performed in order to etch the “white layer”.

 Below are the characteristics of titanium nitride coatings obtained on the proposed device. For comparison, in table. 2 shows the characteristics of coatings obtained on traditional plasma sources.

 A feature of the structure of coatings applied using a patentable source is its high dispersion. Dispersion and the absence of particulate matter determine the high strength properties of the coatings, in particular the high ductility at high microhardness and high compressive stresses. Etching of the substrate before coating provides high adhesion between the coating and the substrate. In addition, the coating is almost non-porous.

At the proposed source, coatings based on aluminum of the AlN and A ₂ O ₂ types were obtained. Coatings are good dielectrics with a uniform structure without foreign inclusions.

In addition, using several sources, both multilayer systems of the type TiN (C) - Al ₂ O ₃ - TiN (C) and composite coatings of the type (Zr - Al) N, (Mo-Al) N, (Zr-Mo ) N. Note that neither one nor the other coatings from traditional sources can be obtained.

 Coating a high-precision and sharpening tool, a small-sized tool showed that the coating practically does not change the geometry of the tool and does not violate the sharpening of its edges. Note that the presence of particulates in the plasma flows of traditional sources makes it practically impossible to coat such an instrument.

 Coating parts of machines with a high class of surface cleanliness, in particular the plunger of fuel pumps, allowed them to increase their service life by 6 times without compromising performance.

 Testing a tool with combined layers — a diffusion layer (nitrided) + a coating (titanium nitride) showed that such layers have a wear resistance of 2–3 times higher than similar coatings without a diffusion sublayer.

 Coatings obtained on a patentable source have high corrosion resistance. After testing titanium nitride coatings in climatic chambers in the atmosphere of sea air and saline solutions, no traces of corrosion were found. Note that coatings obtained from traditional sources have pores and corrode in a humid air environment.

 When using a cathode of high-strength graphite on a patented source, diamond-like coatings with a thickness of 1.2 μm were obtained. Tests have shown the high efficiency of such a film to protect the surface of parts from external influences, in particular to protect the surface of parts from beryllium.

 Thus? the proposed source forms a stream of separated electric-arc gas-metal plasma with a high degree of ionization of the metal and gas components, has greater productivity and wider technological capabilities compared to existing electric-arc plasma sources.

Claims (12)

 1. A method of obtaining an separated electric arc plasma, which consists in obtaining a plasma using a vacuum electric arc discharge on a cold cathode by passing it through a curved plasma duct, characterized in that the electric arc plasma is created inside a curved plasma duct and an electric current is passed through it in the longitudinal direction with the formation of a longitudinal continuous and uniform along the entire length of the plasma duct between the cathode and the anode of the magnetic field and the electric field directed to the walls or from the walls lasovoda. 2. The method according to claim 1, characterized in that the plasma duct is made in the form of a part of a toroid with an angle of rotation
α = Arccos (2r ² -R ² ) / R ² ,
where r and R are respectively small and large radii of the toroid,
and the cathode is placed inside the plasma duct with an offset from the longitudinal axis of the plasma duct to its wall with a smaller radius so that the center of the working surface of the cathode is located at a radius

from the center of the plasma duct, while the anode is placed at the exit of the plasma duct, and the working surface of the cathode is set parallel to the cross section of the plasma duct at the installation site of the cathode.  3. The method according to claim 1, characterized in that the electric current is an electronic arc current used to generate plasma. 4. A device for producing a stream of separated electric arc plasma containing a cold cathode made of vaporized material, an anode, a curved plasma duct made in the form of a part of a toroid, an electromagnetic coil enclosing the plasma duct, as well as power sources for the plasma duct body, arc discharge and electromagnetic coil, different the fact that the toroidal plasma duct is made with an angle of rotation
α = Arccos (2r ² -R ² ) / R ² ,
where r and R are, respectively, the small and large radii of the toroid,
the cathode is installed inside the plasma duct, and its working surface is parallel to the cross section of the plasma duct at the installation site of the cathode, offset from the longitudinal axis of the plasma duct to its wall with a smaller radius so that the center of its working surface is located at a radius

from the center of the toroid, and the anode is installed at the exit of the plasma duct. 5. The device according to claim 4, characterized in that the working surface of the cathode is made beveled with respect to the cross section of the inlet part of the plasma duct with a bevel angle
γ = Arcsin l / Ro,
where l is the distance from the beginning of the toroidal part of the plasma duct to the working surface of the cathode,
and the inlet flange of the plasma duct, on which the cathode is mounted, is isolated from the plasma duct body.  6. The device according to p. 4, characterized in that the anode is the wall located behind the plasma duct of the vacuum chamber or a hot ring electrode located between the plasma duct and the vacuum chamber.  7. The device according to claim 4, characterized in that the electromagnetic coil is wound along the plasma duct uniformly in the number of turns per unit length, and the power source of the plasma duct body has a positive or negative polarity.  8. The method of obtaining a coating on a substrate, carried out by means of a curved plasma duct using plasma of an electric arc discharge, which consists in ionically cleaning the surface of the substrate, saturating this surface with a reaction gas and applying a coating based on the cathode material, characterized in that the arc plasma is created inside a curved plasma duct and passed through it in the longitudinal direction, an electric current with the formation of a longitudinal, continuous and uniform along the entire length of the plasma duct between the cathode and anode m the magnetic field and the electric field directed to the wall or from the walls of the plasma duct, while ion cleaning is carried out in an inert gas at zero or negative potential on the plasma duct body and voltage on the substrate located on the outlet side of the plasma duct, the substrate surface is saturated at the indicated potentials in the environment of the reaction gas or a mixture of reaction and inert gases, and when coating is applied to the plasma duct body, a positive potential is supplied. 9. The method according to claim 8, characterized in that the plasma duct is made in the form of a part of a toroid with an angle of rotation
α = Arccos (2r ² -R ² ) / R ² ,
where r and R are the small and large radii of the toroid, respectively
and the cathode is placed inside the plasma duct with an offset from the longitudinal axis of the plasma duct to its wall with a smaller radius so that the center of the working surface of the cathode is located at a radius

from the center of the plasma duct, while the anode is placed at the exit of the plasma duct, and the working surface of the cathode is set parallel to the cross section of the plasma duct at the installation site of the cathode.  10. The method according to claim 8, characterized in that the ion cleaning begins at zero voltage on the substrate and constantly raise it to the desired value.  11. The method according to claim 8, characterized in that when the substrate is saturated with a reaction gas, the concentration of reaction gas atoms on the surface of the substrate is maintained no higher than the solubility limit of this gas in the substrate material.  12. The method according to claim 8, characterized in that after saturation of the surface of the substrate with reaction gas, a short-term ionic purification is carried out in an inert gas medium.

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