JPH04139084A - Production of surface-coated carbon material - Google Patents

Abstract

PURPOSE:To improve the oxidation and wear resistances of a carbon material by coating the surface of the carbon material with a high m.p. metal by laser- plasma hybrid spraying or further coating the coated surface with a metal silicide. CONSTITUTION:The surface of a carbon material is coated with a high m.p. metal or the carbide thereof by laser-plasma hybrid spraying. The metal is Mo or W and the carbide is MoxCy or WC. The coated surface may further be coated with a metal silicide by laser-plasma hybrid spraying, plasma spraying or laser spraying. MoSi2 or WSi2 is used as the silicide.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention improves properties such as oxidation resistance and wear resistance by modifying the surface of carbon materials, and is applicable to the aerospace field, mechanical field, etc. The present invention relates to a method for producing a surface-coated carbon material to obtain an applicable carbon material.

[Prior Art] Carbon materials are the most heat-resistant materials in non-oxidizing atmospheres, and are therefore widely used as high-temperature members such as hot press molds, heat shielding materials, and inner walls of nuclear reactors.

However, in an oxidizing atmosphere, carbon materials are rapidly oxidized starting from a low temperature of about 500° C., and the excellent properties of carbon materials are not exhibited.

By the way, there are no materials other than carbon materials that maintain the same strength as at room temperature at temperatures exceeding 1,300 degrees Celsius, so improving the oxidation resistance of carbon materials is important for turbine blades and the main structure of spacecraft. It will dramatically expand the scope of its use in materials, rocket engine nozzles, etc., and will greatly contribute to the innovation of peripheral technologies.

Conventionally, various methods have been studied and put to practical use in order to improve the oxidation resistance of this carbon material. Among these, ceramic coating by chemical vapor deposition (hereinafter referred to as CVD) is the most commonly used method, and can coat various compounds. However, with this method, it is difficult to uniformly coat a large member, and for example, it is almost impossible to coat a material over 1 m due to equipment constraints. In addition, there were many drawbacks such as it took a long time to form a film and it was difficult to form a thick film.

Along with the above-mentioned CVD method, the most commonly used method is the plasma spraying method. The advantage of this method compared to the CVD method mentioned above is that it can spray even large base materials, but with normal thermal spraying, the temperature of the base material only reaches a few hundred degrees, and the sprayed coating cannot be coated. Since the reaction between the base material and the base material does not proceed, an oxidation-resistant film with good adhesion cannot be obtained.

In a reduced-pressure, non-oxidizing atmosphere, it is possible to heat the base material to a high depth, but in this case, the plasma speed is high and the spray powder reaches the base material without being fully dissolved. Thermal spraying is difficult because a dense film cannot be obtained and the electrical energy of the plasma is not imparted to the material, such as The, which is a non-conductive high melting point material.

[Problems to be Solved by the Invention] The technical problem of the present invention is to prevent the reaction at the interface between the base material and the thermal spray coating by appropriately heating the carbon material that is the base material when producing the surface-coated carbon material. The object of the present invention is to obtain a technology that effectively promotes the formation of a carbon material, thereby making it possible to form a thick film (and a dense film) with strong adhesion to carbon materials.

[Means and effects for solving the problems] The method of the present invention for solving the above problems is characterized by coating the surface of a carbon material with a high melting point metal or its carbide by laser-plasma hybrid spraying. It is something to do.

The coated carbon material obtained by the above method can be coated with metal sisoside by laser-plasma hybrid spraying, plasma spraying or laser spraying,
Further, the coated carbon material can be coated with an oxide film or an erosion/corrosion resistant film having heat insulating properties.

In the above method, as the high melting point metal or its carbide, at least one material selected from Mo, l'l, MOXCF or wc can be used,
In addition, as metal silicide, MOSi2 or 11
Sii can be used. Furthermore, an oxide film having heat insulating properties or an erosion-resistant film, ZrOx + HfO, + Al
* Single or multiple materials selected from Os + M g O and The2 can be used.

To explain the method of the present invention more specifically, first, carbon materials that can be used in the present invention include various carbon materials such as general carbon materials, special carbon materials such as isotropic carbon materials, and carbon fiber reinforced carbon composite materials. You can choose from them depending on the purpose.

Among them, carbon fiber reinforced carbon composite materials (hereinafter referred to as C/C
Abbreviated as composite. ) has particularly excellent high-temperature strength and is therefore extremely preferred as a structural material under high temperatures.

Before coating a carbon material with a film with excellent oxidation resistance,
It is desirable to preheat the carbon material in advance. This preheating process removes adsorbed water and other impurities on the surface of the carbon material and increases the surface temperature of the carbon material to improve its reactivity with high melting point metals or their carbides. is carried out by heating the carbon material to 1000°C or higher.

The present invention is characterized in that the first layer on the carbon material, ie, the coating of a high melting point metal or its carbide as a thermal stress relaxation layer, is performed by a laser-plasma hybrid thermal spraying method.

Here, the laser-plasma hybrid thermal spraying method refers to plasma spraying on the carbon material that is the base material, and at the same time,
In particular, the idea is to irradiate the base material with a carbon dioxide laser or the like, which has an extremely high absorption rate for carbon materials, and react with the carbon material at the same time as high-melting point metals or their carbides are sprayed, thereby improving the adhesion of the coating.

In this laser-plasma hybrid thermal spraying, a high-power laser, especially a carbon dioxide laser, which has an extremely high absorption rate for carbon materials, is used as the laser, and although it can be used under atmospheric pressure, it is better to perform hybrid thermal spraying under reduced pressure. desirable. In this case, the laser output is 2kW or more,
More preferably 3kw or more, and when spraying under reduced pressure, 500m+nHg or less, more preferably 35
It is best to keep it below 0 maHg.

According to this method, by using the high energy of the laser, it is possible to completely melt high melting point metals or their carbides that cannot be melted by plasma alone, and the carbon material itself is also heated by the laser to an extremely high temperature. In order to become
The reaction between the two also proceeds easily, and a highly adhesive coating film can be formed.

When a film of a high melting point metal or its carbide is formed on a carbon material by this method, a new reaction layer of carbide is generated between the carbon material and the film, so the adhesion of the film can be significantly improved. can. That is, according to the laser-plasma hybrid thermal spraying method, a reaction layer of 1 to 500 μm can be formed inside the carbon material, thereby improving the adhesion of the high melting point metal or its carbide.

In this laser-plasma hybrid thermal spraying method, new raw material powder is constantly supplied by plasma spraying, and the reaction between the thermal spray material and the carbon material occurs without interruption, so the thickness of the reaction layer can be freely controlled. . moreover,
According to this method, it is possible to make the reaction layer have a gradient composition by adjusting the laser output, the supply amount of raw material powder, etc., and therefore the effect of improving the adhesion of the film is large.

In addition, in this process, we use a material that reacts with carbon in the base material at high temperatures to form carbides and obtain great adhesion, and that is difficult to form carbides at the operating temperature (and has a high melting point that makes it difficult for carbon to pass through). It is necessary to use a metal or its carbide.In the present invention, a metal selected from among Mo, W, which is a metal with a large carbide formation free energy and a high melting point, or MOXCFI, which is a carbide thereof, is used. At least one kind of material is preferably used.In other words, in the case of a low melting point material, a material that does not melt when heated to the operating temperature and does not serve as a thermal stress relaxation layer, and that easily forms carbides at low temperatures. In this case, the film is likely to peel off due to volumetric expansion due to carbonization.In addition, materials with low free energy are not preferable because the carbonization reaction tends to proceed.

The thickness of the -th layer is preferably 10 to 300 LLm. In other words, if the film thickness is less than 0 μm, it cannot be expected to function as a thermal stress relaxation layer;
This is because if it exceeds 0 μI, the deposited film will be destroyed by the energy of laser plasma spraying.

The main purpose of the second layer is to improve the adhesion of the carbon material when applying the second layer, which will be explained below. it makes sense.

The second layer may be made of not only metal silicide, which will be explained in detail below, but also, for example, Al-Mg alloy or Cu.
, TiC, WC, Fe, etc. can also be used.

Here, when coated with Al-Mg alloy or Cu, the material is suitable for use as a reflecting mirror, etc., and TiC.

When coated with WC:, Fe, etc., it can be effectively used as machine tool parts having characteristics such as wear resistance.

Metal silicides suitable for coating as a second layer are:
It may be deposited by laser/plasma hybrid spraying, plasma spraying, or laser spraying. This layer is effective in preventing oxygen diffusion since the base material and the second layer are easily oxidizable materials. More specifically, when oxygen reaches this layer, Si in the metal silicide reacts with the oxygen to form SiO□, and this SiO□ layer prevents oxygen from dissipating.

As the metal silicide, it is preferable to use Mo5iz or WSii. That is, since the thermal stress relaxation layer of the -th layer is made of Mo, W, and their carbides, the above-mentioned MoSi or WSiz is preferable in terms of compatibility with them.

Since this film has a strong adhesion to the second layer, it is possible to produce the film by low-pressure plasma spraying alone, but if denseness is required, a laser-plasma hybrid spraying method is preferred.

The thickness of the second layer is preferably 50 to 300 microns.

That is, if it is less than 50 μm, it will be quickly worn out due to repeated use, and if it exceeds 300 μm, cracks will easily occur due to the dense film.

In the present invention, the third layer is coated with an oxide film as a heat shielding film by laser-plasma hybrid spraying or plasma spraying. This layer is provided to prevent the thermal stress between the lower layers from increasing rapidly when the ambient temperature changes suddenly. Therefore, it is preferable to use a material with low thermal conductivity. In the present invention,
Zr0a, Hf0a, A120m, MgO and The,
is preferably used.

The third layer can be densified by laser-plasma hybrid spraying, but with the exception of ThOz, a film with low thermal conductivity can also be obtained by forming a film using plasma spraying alone and making it porous. . However, even in this case, it is preferable to partially perform laser-plasma hybrid thermal spraying in order to increase the adhesion with the lower layer.

The thickness of the third layer is preferably in the range of 300 to 1000 μm. If it is thinner than 300 μl, the properties as a heat insulating material will not be satisfied, and if it exceeds 1000 μl, the thermal stress of the film will become too large, promoting peeling.

The fourth layer, which is optionally deposited when ThO□ is not used for the third layer, is a ThO□ layer formed by laser-plasma hybrid spraying. In plasma spraying, the temperature is low and the spray powder is heated only for a short time, making it difficult to produce a high-strength coating.

Conversely, an infrared laser such as a carbon dioxide laser has a wavelength that is extremely well absorbed by oxides and has a high energy density, so it can be heated to a temperature that can melt ThOa in a short time, making hybrid thermal spraying effective.

Note that in an oxidizing atmosphere of 1500° C. or higher, the amount of oxygen permeating through the oxide layer is large, so the life of the second layer, the oxygen barrier layer (metal silicide layer), is shortened. When used for a long time in such an atmosphere, there should be no P between the second and third layers.
It can be coated by a laser-plasma hybrid thermal spraying method, an electrochemical plating method, etc., which does not create oxides such as t, Ir, Rh, etc., and which makes it difficult for oxygen to pass through.

By the above method, a carbon material with excellent oxidation resistance can be manufactured.

In particular, when laser-plasma hybrid thermal spraying is used to form the above-mentioned coating, it is difficult to form the first layer coating due to the high energy of the laser and the constant supply of completely melted spraying material due to the laser-plasma hybrid thermal spraying. At the same time, a reaction layer with the high melting point metal or its carbide is generated in the interior direction of the carbon material, and the properties of the reaction layer (density, thickness, presence or absence of graded composition) are measured by laser output.
It can be freely controlled by adjusting the amount of raw material powder supplied. Furthermore, unlike other thermal spraying methods, the thermal spraying method using a laser allows the coating to be performed after completely melting the thermal spray powder, making it possible to produce a dense coating.

[Example] (Example 1) Isotropic graphite was placed in a vacuum chamber for laser-plasma hybrid thermal spraying and heated to 0. The pressure was reduced to ITorr. After holding at 0.1 Torr for about 5 minutes, the surface of this isotropic graphite was preheated with a carbon dioxide laser until it became red hot, and pretreatment such as impurity removal was performed. The laser output at this time is 3kw
Met. Thereafter, while maintaining a non-oxidizing atmosphere, the above carbon material was coated with gastric material, Mo, and IC by laser-plasma hybrid spraying. Laser output is 3 km,
The plasma spraying output was 800A. - A heating test was conducted on the obtained material under an inert atmosphere to check for peeling of the film. The results are shown in Table 1.
The ○ mark in each table below indicates that there was no peeling.

Table 1 Temperature 1000℃ 1500℃ Holding time (Hr) 12 2W coated graphite O
○ MO-coated graphite ○ ○ Arm C-coated graphite ○ ○ (Comparative Example 1) Isotropic graphite similar to that used in Example 1 was placed in a vacuum chamber and heated to 0. After holding at ITorr for about 5 minutes, the surface of this isotropic graphite was preheated with a carbon dioxide laser until it became red hot, and pretreatment such as impurity removal was performed. The laser output at this time was 3 kW. After this, A
W and Mo were coated on the carbon material by plasma spraying at a pressure of 100 Torr. Further, the anus was similarly coated by plasma spraying at a pressure of 30 OTorr. The plasma spraying output was 800A.

Table 2 shows the condition of the obtained thermal spray coating.

Table 2 (Comparative Example 2) Comparative Example 1 except that the spraying pressure was 100 Torr.
wC was coated on isotropic graphite under the same conditions as in
Since the WC was not sufficiently melted, erosion of the carbon material occurred and no film formation was observed.

(Example 2) The II-, Mo- and WC-coated graphite on which the first layer film was formed according to Example 1 was placed in the vacuum chamber used for forming the first layer film, and the pressure was reduced to 0.1 Torr using a vacuum pump. . After that, Ar gas was introduced to maintain the inside of the vacuum chamber at 300 Torr, and Mo
Si2 was coated by plasma spraying. The output during plasma spraying was 800A.

The obtained sample was subjected to a heating test under an inert atmosphere to check for peeling of the film. The results are shown in Table 3.

Table 3 Temperature 1000℃ 130
0℃ 1500℃ holding time (Hr) l
1 1W/MoSix coated graphite ○
○ ○Mo/&4osiz coated graphite ○
O○WC/&4oSi 2 coated graphite O○
○ (Example 3) The same conditions as Example 2 were used, except that a laser-plasma hybrid spraying method was used when coating MOSi2.
A film was formed on the carbon material. In the MoSi2 coating by laser-plasma hybrid thermal spraying, the laser output was 2 kW and the plasma spraying output was 800 A.

The obtained sample was subjected to a heating test in the air to examine the state of peeling of the film. Further, a similar heating test was also conducted on the sample obtained in Example 2. The results are shown in Table 4.

Surface temperature 1000℃ 130
0℃ 1500℃ holding time (Hrl 1
1 1 [Sample of Example 2] W/Mo5ia coated graphite ○ ○ OMo/
MoSi2 coated graphite ○ 0OIC/Mo5zz
Coated graphite O○ ○ [Sample of this example] W/MoSix coated graphite ○ ○ ○Mo/
MoSi 2 coated graphite ○ ○ ○IC/M
oSi2 coated graphite O○○ (Example 4) II/Mo5iz coated graphite, Mo/MoSi2 coated graphite, and IC/Mo5ii coated graphite obtained in Example 3 were coated with ZrO□ and The, respectively. I did it. Regarding ZrO□ coating, T
The coating of hO□ was performed by laser-plasma hybrid spraying.

The coating conditions of 2rO□ by plasma spraying were such that the plasma current was 85OA.

W/Mo51g/Zr0z/ obtained by the above method
Th0t coated graphite, Mo/Mo5iz/Zr0z/Th
02 coated graphite and WC/Mo5ia/Zr0z/Th
A heating test was conducted on the 0z coated graphite under an inert gas atmosphere. The results are shown in Table 5.

Table 5 Temperature 100
0℃ 1500℃W/Mo5z2/zro2/r
ho2 coated graphite ○ ○Mo/Mo5iz/Z
r0z/Th0z coated graphite O○IC/Mo5z2/
Zr0 The reaction at the interface of the film is effectively promoted, thereby forming a dense film with strong adhesion to the carbon material.

Claims (6)

[Claims] 1. A method for producing a surface-coated carbon material, which comprises coating the surface of a carbon material with a high-melting point metal or its carbide by laser-plasma hybrid spraying. 2. A method for producing a surface-coated carbon material, which comprises coating the coated carbon material obtained by the method according to claim 1 with metal silicide by laser-plasma hybrid spraying, plasma spraying, or laser spraying. 3. A method for producing a surface-coated carbon material, which comprises coating the coated carbon material obtained by the method according to claim 2 with an oxide film having heat insulating properties or an erosion- and corrosion-resistant film. 4. In the method according to any one of claims 1 to 3, as the high melting point metal or its carbide, Mo,
A method for producing a surface-coated carbon material, characterized in that at least one material selected from W, Mo_xC_y, or WC is used. 5. 4. The method for producing a surface-coated carbon material according to claim 2 or 3, wherein MoSi_2 or WSi_2 is used as the metal silicide. 6. In the method according to claim 3, as the oxide film having heat insulating properties or the erosion- and corrosion-resistant film, ZrO_2, HfO_2, Al_2O_2, MgO
A method for producing a surface-coated carbon material, characterized in that a single material or a plurality of materials selected from ThO_2 and ThO_2 are used.