RU2707688C1 - Device for forming coating from cubic tungsten carbide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to chemical deposition of a coating by deposition of a compound using electric discharges and plasma jets, and can be used in engine building, aircraft engineering and machine building. Device for forming a coating from cubic tungsten carbide on a metal substrate has a source of tungsten- and carbon-containing plasma, a chamber whose volume is limited by two metal covers which are fixed to it by bolt joints. As source of tungsten- and carbon-containing plasma there used is coaxial magnetoplasma accelerator, in which cylindrical electroconductive barrel is made of two electroconductive cylinders of inner cylinder from graphite and external cylinder from strong non-magnetic material, central electrode consisting of graphite tip and steel shank. Barrel and central electrode are electrically connected by fuse link made of pressed mixture of powders of tungsten and soot in atomic ratio C:W from 0.30:0.70 to 0.65:0.35. Housing of said accelerator is made of magnetic material, is conjugated with external metal cylinder and covers zone of fuse connection. Key and capacitor bank connected to the first bus line are connected in series to the second bus duct connected to the shank of the central electrode. Free end of the barrel of the accelerator is inserted into the reactor chamber through an axial hole in its first metal side cover.

EFFECT: obtaining coating from cubic tungsten carbide with thickness of 30–50 mcm and hardness of 30,8±0,5 to 32,5±0,7 GPa on a metal substrate.

1 cl, 3 dwg, 1 tbl

Description

The invention relates to the field of metallurgy, in particular to chemical coating by deposition of compounds using electrical discharges and plasma jets, and can be used in engine building, aircraft building and mechanical engineering.

A magnetron sputtering device is known for producing cubic tungsten carbide coatings [K. Fuchs et al. Reactive and non-reactive high rate sputter deposition of tungsten carbide // Thin Solid Films. - 1987. - T. 151. - No. 3. - S. 383-395], containing a vacuum chamber filled with acetylene, in which an anode with a molybdenum or cemented carbide substrate and a cathode that is a source of coating material (tungsten or hexagonal carbide) are mounted at a distance of 60 mm from each other. tungsten). The substrate is combined with a water cooling system to control the temperature from 100 to 200 ° C and is under the electric potential from 0 to 1000 V.

The presence of combustible gas, the need to use water cooling and the application of an electric potential to the substrate technically complicates the device.

A device for producing a coating of cubic tungsten carbide [Voevodin A. A. et al. Nanocrystalline WC and WC / a-C composite coatings produced from intersected plasma fluxes at low deposition temperatures // Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films. - 1999. - T. 17. - No. 3. - S. 986-992], taken as a prototype, containing a chamber to which a turbomolecular vacuum pump is connected, a cylinder with argon, equipped with a pressure gauge. The chamber contains a magnetron, which is a source of tungsten-containing plasma, a graphite target, and a 440C stainless steel disk substrate located at a distance of 5 cm from the graphite target. A laser is installed outside the camera, on the optical axis of which there is a system of mirrors and lenses, a window in the camera opposite the graphite target. The generated tungsten and carbon-containing plasma flows are directed to the substrate

Such a device allows to obtain films with a thickness of up to 0.5 μm with nanocrystalline cubic tungsten carbide with a particle size of 5-10 nm in an amorphous carbon matrix, however, it is technically complex, containing two high-energy devices.

The technical result of the proposed invention is the development of a device for forming a coating of cubic tungsten carbide.

The proposed device for forming a coating of cubic tungsten carbide, as in the prototype, contains a chamber to which a pump is connected, an argon cylinder equipped with a pressure gauge, a source of tungsten-containing plasma, and means for fixing the metal substrate.

According to the invention, a coaxial magnetoplasma accelerator is used as a source of tungsten and carbon-containing plasma, in which a cylindrical electrically conductive barrel is made of two electrically conductive cylinders: an inner cylinder of graphite and an outer cylinder of durable non-magnetic material, a central electrode consisting of a graphite tip and a steel shank. The barrel and the central electrode are connected by an electrically fused jumper made of a compressed mixture of tungsten and soot powders in an atomic ratio C: W from 0.30: 0.70 to 0.65: 0.35, placed on top of a conductive carbon layer deposited on the surface of the insulator separating the electrically conductive barrel from the Central electrode. The housing is made of magnetic material, is interfaced with an external metal cylinder and overlaps the area of the fusible link. The length of the part overlapping the zone of placement of the fusible bridge is 40-50 mm, and its outer surface is conical. The solenoid is made in one piece with the flange and the cylindrical part, in which the housing is placed and strengthened by a threaded plug, strengthened by a durable fiberglass housing and pulled together by powerful conductive pins between the flange and the fiberglass thrust ring. The conductive studs are electrically connected by a conductive ring. An external power supply busbar is connected to the conductive studs. The second busbar of the power supply circuit is connected to the shank. A key and a capacitor bank connected to the busbar are connected in series to the second busbar. The free end of the accelerator barrel is inserted into the chamber through an axial hole in its first metal side cover and is hermetically fixed by means of o-rings located between the flange and the side cover and studs connecting the ring resting on the flange and the first side cover. Inside the chamber, tie rods are provided for fixing the metal substrate parallel to the first side cover. The chamber through the first valve is connected to the foreline pump and through the second valve is connected to a cylinder filled with argon. The chamber volume is limited by two side covers that are bolted to it.

In contrast to the prototype, a coaxial magnetoplasma accelerator with an electrically fused jumper between electrodes made of a compressed mixture of tungsten and soot powders in an atomic ratio C: W from 0.30: 0.70 to 0.65: 0.35 is a single device for generating supersonic jets of tungsten and carbon-containing plasma during the formation of an arc discharge. Due to the action of a supersonic jet of tungsten and carbon-containing electrodischarge plasma, an insignificant volume of the metal substrate material is melted and materials are mixed in the boundary layer with subsequent crystallization, which ensures high adhesion of the coating to the substrate. The advantage of this structure is the formation of a coating with characteristics significantly exceeding the characteristics of the substrate in terms of strength properties.

The proposed device allows to obtain coatings of cubic tungsten carbide with a thickness of 30-50 μm and a hardness of 30.8 ± 0.5 to 32.5 ± 0.7 GPa on a metal substrate.

In FIG. 1 shows a device for forming a coating and cubic tungsten carbide.

In FIG. 2 shows an X-ray diffraction pattern of a coating formed as a result of deposition.

In FIG. Figure 3 shows a scanning micrograph of the cross section of the coating.

Table 1 presents the conditions for the formation of a coating of cubic tungsten carbide and the parameters of the deposited coating.

A device for forming a coating of cubic tungsten carbide (Fig. 1) contains a coaxial magnetoplasma accelerator, in which a cylindrical electrically conductive barrel is made of two electrically conductive cylinders: an inner cylinder 1 of graphite and an outer cylinder 2 of durable non-magnetic material (stainless steel), a central electrode consisting of a graphite tip 3 and a shank 4 of steel. The barrel and the central electrode are connected electrically by a fused jumper 5 made of a compressed mixture of tungsten and soot powders in an atomic ratio C: W from 0.30: 0.70 to 0.65: 0.35 with an average particle size of not more than 1 μm, placed on top of the conductive carbon layer deposited on the surface of the insulator 6, separating the conductive barrel from the Central electrode. The housing 7 is made of magnetic material and is coupled to an external metal cylinder 2, and overlaps the zone of placement of the fusible link 5. The length of the part overlapping the zone of placement of the fusible link 5 is 40-50 mm, and its outer surface is conical. The solenoid 8 is made in one piece with the flange 9 and the cylindrical part 10, which houses the housing 7 and is strengthened by a threaded plug 11. The solenoid 8 is strengthened by a strong fiberglass housing 12 and pulled by powerful conductive studs 13 between the flange 9 and the fiberglass stop ring 14. Conductive studs 13 electrically connected by a conductive ring 15, and busbar 16 of an external power supply circuit is connected to the conductive studs 13. The second busbar 17 of the power supply circuit is connected to the shank 4. To the second busbar 17, a key 18 and a capacitor bank 19 connected to the busbar 16 are sequentially connected.

The free end of the accelerator barrel is inserted into the chamber 20 through an axial hole in its first metal side cover 21 and hermetically fixed by means of o-rings 22 located between the flange 9 and the side cover 21, and studs 23 connecting the ring 24 abutting against the flange 9, and the first side cover 21. Inside the chamber 20, parallel to the first side cover 21, at a distance of 65 mm from the end of the free end of the accelerator barrel, using two tie rods 25, a substrate 26 is fixed in the form of a metal plate. The chamber through the first valve 27 is connected to the foreline pump. The chamber through the second valve 28 is connected to a cylinder filled with argon, and a pressure gauge. The volume of the chamber 20 is limited by two side covers 21 and 29, which are bolted to it.

The operation of the device is as follows. Between the inner cylinder 1 of the accelerator barrel and the tip of the central electrode 3, an electrically fused jumper 5 is placed, made of a pressed mixture of powdered tungsten and carbon black in an atomic ratio C: W from 0.30: 0.70 to 0.65: 0.35 with particle sizes not more than 1 μm, laid on top of the conductive carbon layer, previously deposited on the surface of the insulator 6 by spraying a Graphit 33 carbon spray. The accelerator is tightly joined to the outer side of the first cover 21 using a ring 24 and sealing rings 22. On the inner side of the first cover 21 at a distance of 65 mm from the end of the free end of the barrel, a metal substrate 26 is arranged parallel to the flange 9 and fixedly fixed with two tie rods 25. The first cover 21 is tightly joined with bolted joints with the accelerator and the substrate fixed on it. with the chamber 20. The opposite side of the chamber 20 is closed with a second cover 29. After that, the chamber 20 is evacuated through the first valve 27, then through the second valve 28 it is filled with argon at a pressure of 10 ⁵ Pa and at room temperature e.

The capacitor bank 19 with a capacity of 6 mF is charged to a voltage of 3 kV. The key 18 is closed, after which a current starts flowing from the capacitor bank 19 through the busbar 16, the conductive ring 15, the studs 13, the flange 9, the turns of the solenoid 8, the housing 7, the outer metal cylinder 2, the inner cylinder 1, and the fusible link 5 in the power supply circuit of the accelerator , tip 3, shank 4, second busbar 17. In this case, the fusible jumper 5 heats up, melts, and its material goes into a plasma state with the formation of an arc discharge. The configuration of the plasma structure of the Z-pinch type with a circular plasma bridge is determined by the shape of the fusible bridge 5 and the presence of a cylindrical channel in the insulator 6. Further, the discharge plasma is compressed by the magnetic field of its own current and the axial field of the solenoid 8 and exists in the accelerator channel in the form of an extending Z-pinch with a circular a plasma jumper at the end, through which the current passes to the cylindrical surface of the accelerating channel of the inner cylinder, during the acceleration of the plasma jumper under the action of the Lorentz force. The plasma jet flows from the accelerating channel of the inner cylinder 1 into the chamber 20 filled with argon and acts on the surface of the substrate 26, forming a coating of cubic tungsten carbide. After coating deposition, the second cover 29 is opened and the metal substrate 26 with the deposited coating is removed from the tie rods 27.

At a charging voltage of 3 kV capacitor bank with a capacity of 6 mF and using an electrically fused jumper 5 made of a compressed mixture of tungsten and soot powders in the atomic ratio C: W 0.30: 0.70, a pulsed deposition mode of the coating on the substrate in the form of a copper 2 mm thick plates with linear dimensions of 100x100 mm, which ensured the following parameters of the arc discharge: amplitude of the arc discharge current 130 kA, arc discharge power 120 MW, pulse duration 300 μs.

The resulting coating was investigated using x-ray diffractometry and scanning electron microscopy.

The X-ray diffraction pattern of the coating formed as a result of deposition (Fig. 2) and the results of quantitative X-ray diffraction analysis (Table 1) showed the predominant content of the phase of cubic tungsten carbide in the structure of the obtained coating.

Scanning micrograph (Fig. 3) shows a transverse section of the coating with a thickness of ~ 50 μm.

The hardness of the obtained coating, determined by the Berkovich method, was 32.5 ± 0.7 GPa, Young's modulus 310 ± 5 GPa.

The results of the formation of a coating of cubic tungsten carbide on substrates of copper and titanium are shown in table 1.

Thus, the proposed device can be used to obtain coatings of cubic tungsten carbide of different thicknesses with characteristics significantly exceeding the characteristics of the substrate in terms of strength properties.

Table 1

Example No.
p / p Atomic ratio C: W Backing material Coating thickness, microns The amplitude of the arc current,
kA Arc discharge power, MW Pulse duration, μs Content WC _1-x ,
% WC content,
% Hardness, GPa Young's modulus one 0.30: 0.70 Copper fifty 130 120 300 99.5 0.5 32.5 ± 0.7 310 ± 5 2 0.65: 0.35 Copper thirty 120 110 310 95.0 5,0 31.7 ± 0.6 302 ± 4 3 0.50: 0.50 Titanium 40 125 115 305 92.0 8.0 30.8 ± 0.5 295 ± 4

Claims (1)

A device for forming a coating of cubic tungsten carbide on a metal substrate, comprising a chamber to which a pump is connected, an argon cylinder equipped with a manometer, a source of tungsten and carbon-containing plasma, and means for fixing the metal substrate, characterized in that the source of tungsten and carbon-containing plasma used a coaxial magnetoplasma accelerator in which a cylindrical electrically conductive barrel is made of two electrically conductive cylinders of the inner cylinder of gra a fit and an external cylinder made of durable non-magnetic material and a central electrode consisting of a graphite tip and a steel shank, while the barrel and the central electrode are connected by an electrically fused jumper made of a compressed mixture of tungsten and carbon black powders in an atomic ratio C: W of 0.30 : 0.70 to 0.65: 0.35, placed on top of the conductive carbon layer deposited on the surface of the insulator separating the electrically conductive barrel from the Central electrode, while the body of the said accelerator is made of m material, is interfaced with an external metal cylinder and overlaps the zone of placement of the fused jumper, while the length of the part of the body overlapping the zone of placement of the fused jumper is 40-50 mm, and its external surface is conical, while the solenoid of the said accelerator is made in one piece the flange and the cylindrical part in which the said housing is located is strengthened by a threaded plug and a durable fiberglass housing and pulled together by powerful conductive studs between the flange and the fiberglass a thrust ring, the conductive studs are electrically connected by a conductive ring, while the first busbar of the external power supply circuit is connected to the conductive studs, and the second busbar of the power supply circuit is connected to the shank, while a key and a capacitor bank connected to the second busbar are sequentially connected to the second bus duct, this free end of the accelerator barrel is inserted into the reactor chamber through an axial hole in the first metal side cover and hermetically fixed with by means of o-rings located between the flange and the first side cover and studs connecting the ring resting on the flange and the first side cover, tie rods are located inside the chamber for fixing the metal substrate parallel to the first side cover, while the chamber is connected through the first valve with a foreline pump and through a second valve connected to a cylinder filled with argon, and the chamber volume is limited by two side covers, which are attached to it by bolted connections.

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