JP2002069603A - Method and apparatus for thermally spraying using electro-magnetically accelerated plasma - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an apparatus for plasma spraying which uses a high density pulse plasma at ultra-high speed, can be applied to all materials of metals, ceramics, plastics, or the like, and gives a sprayed layer with lowered impurities. SOLUTION: The thermal spraying method using electro-magnetically accelerated plasma comprises four processes characteristically. In the first process, a finely powdered thermally spraying material is intermittently supplied into a cylinder having an opening at a forward end and being sealed up with an electrical insulator at a backward end. In the second process, a pulsed voltage is applied between the inside surface of the cylinder and an anode placed in the center of the cylinder in the long direction immediately after feeding the finely powdered thermal spraying material to generate a high temperature pulse plasma in inside of the cylinder. In the third process, the high temperature pulse plasma is electro-magnetically accelerated toward the opening of the cylinder to melt the powdered thermally sprayed material fed in the cylinder by the high temperature pulse plasma into liquefied fine particles. The fourth process make the liquefied fine particles jet out from the opening of the cylinder together with the electro-magnetically accelerated high temperature pulse plasma.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for thermal spraying using electromagnetically accelerated plasma.

[0002]

2. Description of the Related Art In a thermal spraying method using plasma, fine powder materials such as ceramics, metals, and plastics are heated by plasma and melted to form liquid fine particles. This is a method in which high-speed collision is performed to form a film of the material on a base material. In such plasma spraying, there is a limit to the speed at which the material fine powder collides with the substrate, and there is also a limit to the density of the plasma jet. As a result, there is a large number of voids in the coating of the material formed on the base material, so that it is very difficult to form a dense coating. On the other hand, a method of electromagnetically accelerating the plasma to increase the speed of the plasma jet is known as a Reagan spraying method. This rail gun spraying method is performed as follows. That is, a sprayed material having conductivity is disposed between two rail-shaped conductors connected to a pulsed large current power supply, then the switch is closed, and a pulsed large current is supplied from the pulsed power supply to the rail and the conductive sprayed material. . As a result, a magnetic field is generated in a space surrounded by the rail and the sprayed material, and the rail and the sprayed material receive Lorentz force in a direction in which the space is expanded. At this time, the rail is firmly fixed, and only the sprayed material is kept movable. Thus, the sprayed material receives the Lorentz force and moves between the rails while accelerating.
When a large pulse current is applied, the rail gun also has the effect of heating the sprayed material, whereby the sprayed material is turned into plasma. The heated and accelerated thermal spray material collides with the surface of a solid substrate placed near the gun outlet, and a film of the material is formed on the solid surface. At this time, since the plasma for heating and accelerating the thermal spray material has a much higher speed and higher density than in the case of the above-mentioned plasma thermal spraying, the adhesion to the base material is higher,
A dense film can be obtained. However, in the case of this method, since a method of applying a large pulse current to the sprayed material is employed, there is a problem that the material is limited to a conductive material such as a metal. In addition, the shape of the starting sprayed material is generally plate-shaped, so that the particle size of the sprayed coating is smaller than that of a general plasma sprayed coating using a fine powder as a starting spraying material. Not very uniform. Therefore, there is a problem that the film thickness tends to be non-uniform. Furthermore, since the insulating member holding the railgun electrode is exposed to a high-temperature plasma flow during the formation of the thermal spray coating, there is a problem that the insulating member is mixed as an impurity into the thermal spray coating.

[0003]

SUMMARY OF THE INVENTION The present invention relates to a thermal spraying method using an ultra-high-speed and high-density pulsed plasma, which can be applied to all materials such as metals, ceramics and plastics, and has a low impurity content. It is an object of the present invention to provide a plasma spraying method and apparatus for providing a reduced material coating.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, a step in which the fine powdered spray material is supplied in a pulsed manner into a cylinder whose front end is opened and the rear end is sealed with an electric insulator, and immediately after the supply of the fine powdered sprayed material At the same time, a pulse voltage is applied between an anode disposed in the center of the cylinder along the longitudinal direction of the cylinder and a wall surface of the cylinder, and a high-temperature pulsed plasma is generated in the cylinder. Causing the high-temperature pulsed plasma to be electromagnetically accelerated toward the cylindrical body opening, and melting the fine-powder spray material supplied into the cylindrical body by the high-temperature pulsed plasma to form liquid fine particles. A method for spraying by electromagnetically accelerated plasma is provided, comprising a step of injecting liquid fine particles of the sprayed material out of the cylinder together with the electromagnetically accelerated high-temperature pulsed plasma from a cylindrical body opening. Further, according to the present invention, there is provided an apparatus for carrying out the above-mentioned method, comprising: a cathode comprising a cylindrical body having an open front end and a rear end sealed with an electric insulator; An anode disposed along the length of the cylindrical body, a thermal spray material supply device for supplying a fine powdery thermal spray material into the cylindrical body in a pulsed manner, and applying a voltage between the anode and the negative electrode. And a pulse power supply that is applied in a pulsed manner and immediately after the supply of the fine powdered spray material into the cylinder.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The spraying method using electromagnetically accelerated plasma of the present invention is different from the conventional railgun spraying method in which the sprayed material is limited to a conductor. It has an advantageous feature that it can be applied to any material regardless of the conductor and the insulator.

The principle of the thermal spraying method of the present invention will be described with reference to the drawings. FIG. 1 is an explanatory sectional view of a plasma injection device (plasma gun) used in the present invention. FIG. 1 (a)
FIG. 1B is a vertical cross-sectional view of the cylindrical body. In FIG. 1, 1 is a cylinder (cylindrical body),
2 denotes an anode, 3 denotes a tip opening, and 4 denotes an electric insulator. P indicates pulse plasma, and R indicates magnetic flux. FIG. 1 shows that a capacitor bank (pulse power supply) applies a voltage between a cylinder 1 forming a cathode and an anode 2 so that a pulsed plasma P generates a magnetic flux (magnetic field) formed by a current flowing in the direction of arrow Q. 3) shows a state in which the electromagnetic force is accelerated by R.
The plasma P in the cylindrical body 1 receives Lorentz force due to the magnetic field R formed in the cylindrical body, is acceleratedly moved in the direction of the distal end opening 3, and is emitted as high-speed plasma from the opening 3. In this case, the speed of the plasma ejected from the opening 3 is usually 2 km / sec or more, preferably 3 km / sec or more. The upper limit is not particularly limited, but usually,
It is about 20 km / sec. The electromagnetic force for accelerating the plasma formed in the cylinder is 1 MPa (megapulse) or more, preferably 2 MPa or more. The upper limit is not particularly limited, but is usually about 50 MPa.

The cylinder 1 is formed of a conductive material such as copper or carbon. The shape is usually a cylinder, but it may be a polygonal cylinder such as a hexagon or octagon in cross section. The inner diameter D of the cylinder 1 is 1 to 10 cm, preferably 2 to 5 cm. The length (the length from the left end surface of the insulator 4 to the front end surface of the opening 3) L is 30 to 200 c
m, preferably 40-80 cm. Also, the L /
The D ratio is 200-3, preferably 40-10.

The anode 2 is made of a conductor such as copper or carbon, and has a circular or polygonal (quadrilateral, 6
(Rectangular, octagonal, etc.). Its diameter is usually 1 to 5 cm, preferably 1 to 2 cm.

The voltage applied between the anode 2 and the cathode 1 is a pulse voltage. The peak voltage of this pulse voltage is usually 3 kV or more, preferably 5 kV or more. The upper limit is not particularly limited, but is usually about 30 kV. The pulse current generated by application of the pulse voltage is a peak current, which is usually 80 kA (ampere) or more, preferably 100 kA or more. The upper limit is not particularly limited, but is usually about 300 kA. The voltage application time for generating the pulse voltage is generally 0.01 to 10 msec, preferably 0.1 to 10 msec.
0.5 ms.

In the present invention, a fine powdered sprayed material (hereinafter, also simply referred to as a material) is supplied into the cylindrical body 1 in a pulsed manner, and a pulse voltage is applied immediately after the supply, and generated by the application of the voltage. The material is ejected from the opening 3 to the outside of the cylinder at high speed together with the pulsed plasma. In this case, the speed of the material injected from the tip opening 3 varies depending on the type and size of the material, but is usually 50 m / sec or more, preferably 100 m / sec or more. The upper limit is usually 3
It is about 00 m / sec.

In the present invention, the supply of the material into the cylinder is performed in a pulsed manner, and the time from the start of the supply of the material to the end of the supply is generally 1 to 100 milliseconds, preferably 2 to 10 milliseconds. Milliseconds. The device for supplying the material into the cylinder may be any device that can supply the material into the cylinder in the short time, and various conventionally known devices can be used. Examples of such a device include a powder supply device provided with an electromagnetic valve, a powder ejection device provided with a powder ejection nozzle (see JP-A-2000-94332, and the like). The average particle size of the material is usually 1 to 200 μm.
m, preferably 10 to 100 μm, more preferably 30
８０80 μm. The amount of material supplied is D (cm)
Of the cross-sectional area of the cylindrical body (πD ^2/4) the ratio of the volume of material to ^{(cm 2) V (cm 3} ) [V / (πD 2/4)] is usually
The ratio is 0.1 to 1, preferably 0.2 to 0.6.

In the present invention, the pulse voltage is applied immediately after the supply of the material. The specific time is 2 to 30 m, which is the length of time from the end of the supply of the material to the start of the application of the pulse voltage. Seconds, preferably 3-6 ms.

The generation of pulsed plasma in the cylinder is as follows:
It can be carried out by various conventionally known methods. As such a method, any method may be used as long as a high-temperature heat required for plasma generation is applied to the cylinder. For example, a thin conductive wire (copper fine wire, nichrome wire, or the like) is stretched in the cylinder. In advance, there are methods of flowing a large current through this thin wire to explode (burn out) the fine wire, burning explosives in the cylinder, irradiating the cylinder with laser light, and injecting plasma into the cylinder. is there. In the present invention, a plasma gas is used for plasma generation, and the plasma gas may be any gas that shows a gaseous state at normal temperature. As such a gas, an inorganic gas such as an argon gas, a helium gas, a nitrogen gas, a xenon gas, or a hydrogen gas is used, and an organic gas such as methane can also be used. The method for supplying plasma gas into the cylinder is as follows:
There is no particular limitation, and there are a method of supplying the material continuously or discontinuously (pulsed) separately from the material, a method of supplying the material together with the material, and the like. The supply amount of plasma gas, the cross-sectional area of the cylindrical body of the inner diameter Dcm (πD ^2/4) the number of moles of the plasma gas for cm ² M ratio ^{[M / (πD 2/4} )] is 0.01 1
0, preferably in a ratio of 0.5 to 5.

Next, the method of the present invention will be described in more detail with reference to the drawings. 2 to 6 show process diagrams performed using the plasma spraying apparatus of the present invention. FIG. 2 shows a charging process diagram of the pulse power supply (capacitor bank). FIG. 3 is a view for explaining a material supply (spraying) process.
FIG. 4 is a diagram illustrating a pulse plasma generation process. FIG.
Shows a magnetic acceleration process diagram of a plasma containing a material. FIG.
Shows a process diagram in which a plasma containing a material is made to collide with a substrate surface. 2 to 6, 11 denotes a material injection device, 12 denotes a material, 13 denotes a pressurized gas pipe, and 14 denotes an opening / closing valve. W indicates a thin conductive wire, P indicates plasma, and S indicates a substrate. The same reference numerals as shown in FIG. 1 have the same meaning.

In the state shown in FIG. 2, the pulse power supply (capacitor bank) 15 is charged. After charging,
The on-off valve 14 attached to the pressurized gas pipe 13 connected to the material injection device 11 is opened and closed instantaneously (pulse-wise) to introduce the pressurized gas into the device 11, and the material in the device 11 is mixed with the cylinder. Pulses are injected into the cylinder from the through holes 10 formed in the wall 5 (FIG. 3). In this case, the pressurized gas for injecting the material into the cylinder also acts as a plasma gas.

Then, immediately after the injection of the material into the cylinder is completed, the pulse power supply 15 is turned on to burn out the conductive wires W stretched in the cylinder and to generate gas by the amount of heat generated at that time. Is turned into plasma, and a high-temperature pulsed plasma P is generated (FIG. 4). The position of the through hole 10 for ejecting the material may be near the conductive thin wire for generating plasma, and may be located in front of or behind the conductive thin wire, preferably slightly behind. The distance between the position of the through hole 10 and the conductor thin wire W is usually within 100 mm, preferably within 50 mm. The high-temperature plasma P thus generated is accelerated by the electromagnetic force generated in the cylinder toward the tip end opening 3 of the cylinder, and captures the material 12 present in the cylinder. Gather. The collected material is melted by the high-temperature plasma and converted into liquid fine particles (FIG. 5). The pulsed plasma P containing the liquid fine particles of the material is ejected at a high speed from the distal end opening 3 of the cylindrical body 1, collides with the substrate S, and a film of the material 12 is formed on the substrate surface (FIG. 6). .

The material film formed on the substrate S in this manner does not include voids because the speed of the pulse including the material injected from the tip opening 3 is very high.
It is very good in denseness and adhesion. In addition, since the high-temperature plasma P does not come into contact with the electric insulating material 4 in the coating, no contamination due to the electric insulating material 4 occurs. According to the present invention, a material coating having a thickness of 5 to 30 μm can be formed by one thermal spraying operation.

According to the present invention, a coating of a conductive or non-conductive material can be formed on a substrate. In the case of the present invention, in particular, a dense and good-adhesion film of a high melting point material such as boron carbide (B ₄ C), boron nitride (BN), tungsten carbide (WC), molybdenum, and tungsten is advantageously formed on a substrate. Can be formed. As the substrate, a plastic substrate or the like is used in addition to a ceramic substrate (silicon, glass, alumina, a metal substrate (SUS, tungsten, molybdenum, or the like)).

In the present invention, it is preferable that the supply (injection) of the material into the cylinder is performed in the shortest possible time and at a low cost. An example of the material supply (injection) device for this purpose is shown in FIG.
And FIG. FIG. 7 is an exploded explanatory view of the material supply device. In FIG. 7, reference numeral 101 denotes a first cylindrical body having a through hole 104, 102 denotes a second cylindrical body having a through hole 105, and 103 denotes a lid having a through hole 106 at the center thereof. The first cylindrical body 101 has lead wires 107 and 108 at the top.
Are embedded, and a conductive thin wire 109 is connected between each one end of the lead wires 107 and 108. The other end of each of the lead wires 107 and 108 is provided with a covered electric wire 11.
0 and 111 are connected. First cylindrical body 101 and second cylindrical body
Each of the cylinders 102 is an electric insulator (such as plastic)
It is formed with. In addition, a screw hole is formed in the cylinder wall so that the first cylinder and the second cylinder can be integrally connected. The conductor thin wire can be a copper wire, a nichrome wire, a tungsten wire, or the like, and the thickness of the thin wire is 50 to 200 μm, preferably 80 to 120 μm in diameter. Further, the number of one conductive thin wire stretched between the lead wires may be one or more (two to ten). The lid 103 includes a plate (disk) portion 112 and a tubular (cylinder) portion 113 erected at the center thereof. Plate part 11
2 has a large size and is used as a fixing means of the apparatus of the present invention. The size may be larger than the diameter of the plasma gun (cylinder) to which the device of the present invention is applied. At the outer peripheral edge of the plate portion 112, a through hole 114 for screwing is provided. Through-hole 10 of cylindrical body 113
6 is connected to the pressurized gas pipe 11 via a connection 118.
9 are connected. The material of the lid 103 is not particularly limited, but may be a metal such as iron or brass, a plastic, a ceramic, or the like.

In FIG. 7, reference numerals 115 and 117 denote O-rings, and reference numeral 116 denotes a material for sealing a hole that can be broken by application of mechanical energy or thermal energy.

FIG. 8 shows a state diagram when the material supply device is applied to a plasma spraying device. In FIG. 8, 1
Reference numeral 21 denotes a set screw connecting the cylinders 101 and 102, 122 denotes a fixing bracket, and 123 denotes a set screw for fixing the lid 103 to the fixing bracket 122.
L indicates a powder filled in the through hole 105. In FIG. 8, 1 indicates a cylinder, 2 indicates an anode, and 10 indicates a through hole formed in a wall 5 of the cylinder 1. A indicates a plasma forming space for ejecting powder formed in the cylinder. In order to screw the lid 103 to the fixing metal fitting 122, the tip of the set screw is inserted into the through hole 11 formed through the peripheral edge of the plate body 112.
4 and screwed into the screw hole 124 of the fixing bracket 122. As shown in FIG. 8, the lower wall of the cylindrical body 1
It is cut into a flat shape and is easily fixed to the fixing bracket 122. The upper wall of the cylindrical body 1 is the first cylindrical body 1.
01 is cut into a planar shape to facilitate fixing.

In order to inject the powder L into the space A of the cylinder 1 using the apparatus shown in FIGS. 7 and 8, a pressurized gas is introduced into the through-hole 106 through the pressurized gas pipe 118. Next, covered wire 1
A high voltage is applied between 10 and 111 by a pulse power supply in a pulsed manner, and a large amount of current flows through the conductive thin wire 109. Then, the thin conductive wire explodes (burns out) instantly due to this large amount of current, and the sealing material 116 disposed near and above the fine wire is instantaneously burnt down due to the high-temperature heat generated at that time. Then, the through hole 105 is opened. When the through hole 105 is opened, the powder L filled in the through hole 105 is pulsed into the space A of the cylindrical body 1 below the powder L by the pressure of the pressurized gas connected to the pressurized gas pipe 119. It is injected. According to the above-described material injection device, it is possible to efficiently and pulsatively inject powder as a thermal spray material into a space before plasma is generated or into a space where plasma is generated at a predetermined time. . In addition, the amount of one injection can be increased.

[0023]

Next, the present invention will be described in more detail with reference to examples.

Example 1 A film of a material was formed on a substrate using the apparatus shown in FIG. The main operating conditions in this case are shown below. In addition,
As the material 12, fine powdered boron carbide B ₄ C having an average particle size of about 60 μm was used. In addition, the material supply device 1
As 1, one having the structure shown in FIGS. 7 and 8 was used.

(1) Cylindrical body 1 (i) Material: copper (ii) Inner diameter D: 4 cm (iii) Length L: 40 cm (iv) L / D: 10 (2) Anode 2 (i) Material: copper ( ii) Diameter: 1.5cm (iii) Length: 50cm

(3) Material supply device 11 (FIGS. 7 and 8) (i) Sealing material 116: polyvinylidene chloride film having a thickness of 40 μm (ii) Pressure of pressurized gas: 8 atm, inside cylinder 1 (Iii) Gas for pressurization (gas for plasma): Argon gas (iv) Thickness of copper fine wire 109: 100 μm in diameter (v) Voltage of pulse power supply for burning and burning copper fine wire: 1.0 kV (vi) Voltage (Vii) Supply amount of material L: 1.0 g

(4) Pulse power supply 15 (i) Applied voltage (peak voltage): 5.9 kV (ii) Voltage application time: 300 microseconds (iii) Voltage application start time: After supply of material L into the cylinder is completed : 4 milliseconds (5) Conductor fine wire W (i) Material: copper wire (ii) Thickness: diameter 100 μm (6) State in cylinder 1 (i) Temperature (peak temperature of plasma): about 10,000 ° C (Ii) Pulse current (peak current) between the cylinder 1 and the anode 2: 100 kA (iii) Electromagnetic force: about 10 MPa

(7) Tip opening 3 of cylinder 1 (i) Outflow velocity of pulsed plasma from opening: 2.5 m
(Ii) Injection speed of material L from opening: 2.5 km / sec (8) Substrate S (i) Material: SUS304 (stainless steel) (ii) Thickness of material coating on substrate surface: 10 μm (iii) Uniformity and denseness of the coating: good

[0029]

According to the present invention, it is possible to easily and efficiently form a high-quality coating made of various kinds of fine powder materials on a substrate. Therefore, the present invention is advantageously applied as a method for forming films of various materials in the electric and electronic fields.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of a thermal spraying apparatus (plasma gun) used in the present invention.

FIG. 2 shows a charging step of a pulse power supply in the plasma spraying apparatus of the present invention.

FIG. 3 is an explanatory view showing a process of supplying a material for thermal spraying into a thermal spraying apparatus.

FIG. 4 is a diagram illustrating a process of generating pulsed plasma in the thermal spraying apparatus.

FIG. 5 is a diagram illustrating a process of electromagnetically accelerating pulsed plasma in a thermal spraying apparatus.

FIG. 6 is an explanatory view of a process in which pulsed plasma containing a material for thermal spraying collides with a substrate.

FIG. 7 is an exploded view of the powder injection device.

FIG. 8 shows a state diagram when the powder injection device is applied to a plasma spraying device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylindrical body (cathode) 2 Anode 3 Opening 4 Electrical insulator 5 Cylindrical wall 11 Material injection device 12 Material 13 Pressurized gas pipe 15 Pulse power supply 101 First cylindrical body 102 Second cylindrical body 103 Cover 109 Conductor thin wire 116 Sealed Stopping material 119 Pressurized gas pipe 122 Fixing metal L Material (powder)

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shuzo Fujiwara 1-1-1, Higashi, Tsukuba, Ibaraki Pref., National Institute of Advanced Industrial Science and Technology (72) Inventor Junya Kitamura 2-8-1, Tsuda Yamate, Hirakata-shi, Osaka 4D075 AA18 AA87 CA13 CA18 CA22 CA23 DA06 DB01 DB04 DB13 DB14 DB31 EA02 EA15 EA17 EB01 EB05 4F033 AA01 BA05 CA04 DA01 EA01 HA01 4K031 DA04 EA01 EA07

Claims (3)

[Claims] A step of supplying a fine powdery spray material in a pulsed manner into a cylindrical body having a front end opened and a rear end sealed with an electrical insulator; and immediately after supplying the fine powdery spray material, Applying a pulse voltage between an anode disposed in the center of the cylinder along the length direction of the cylinder and a wall surface of the cylinder, and generating high-temperature pulsed plasma in the cylinder; Electromagnetically accelerating the high-temperature pulsed plasma toward the cylindrical body opening, and melting the fine-powder spray material supplied into the cylindrical body by the high-temperature pulsed plasma to form liquid fine particles; And a step of injecting liquid fine particles of the thermal spray material together with the electromagnetically accelerated high-temperature pulsed plasma out of the cylinder. 2. The method according to claim 1, wherein the electromagnetic force for accelerating the pulsed plasma is 1 MPa or more. 3. An apparatus for carrying out the method according to claim 1, wherein the cathode comprises a cylindrical body having an open front end and a rear end sealed with an electrical insulator; An anode disposed along the longitudinal direction of the cylindrical body, a thermal spraying material supply device for supplying a fine powdered thermal spraying material into the cylindrical body in a pulsed manner, and a voltage pulse between the anode and the cathode. And a pulse power source for applying the fine powdered spray material immediately after the fine powdered spray material is supplied into the cylindrical body.