JPH0479990B2 - - Google Patents

Description

[Detailed description of the invention] (a) Technical field The present invention forms a hard ceramic coating with excellent corrosion resistance, oxidation resistance, and chemical resistance on the surface of a base material without losing the properties of the base material. The present invention relates to a method for manufacturing heat-resistant parts.

(b) Technical background Ceramics are hard and have properties such as excellent heat resistance, chemical stability, and high-temperature oxidation resistance, so they are useful as coating materials.

For example, carbon materials such as carbon sintered bodies or carbon fiber-reinforced composite materials (hereinafter collectively referred to as carbon materials) have excellent high-temperature strength, but their drawbacks are poor high-temperature oxidation resistance and wear resistance. ing.

Therefore, it is easy to imagine that in order to eliminate this drawback, the surface of the carbon material should be coated with hard ceramics.

However, it is not easy to coat ceramics uniformly and to a desired thickness.

Conventional methods for coating ceramic powder include (i) a method in which the ceramic powder is made into a slurry, the parts to be coated are dipped in the slurry, and the parts to be coated are pulled up;

(ii) A method in which a ceramic phase is deposited on the part to be coated using a gas phase reaction.

is being carried out. However, although method (i) is simple, it is difficult to achieve uniform coverage, and (ii)
Although the method allows for coating with good adhesion,
None of these methods are preferable as the precipitation rate is slow and the cost is high.

Therefore, there is a need for the development of a method that can quickly deposit a ceramic layer of a uniform and desired thickness.

(C) Disclosure of the Invention The present invention aims to compensate for the above-mentioned drawbacks of the prior art and to provide a new method for quickly forming a ceramic coating with excellent adhesion to a desired thickness.

That is, the present invention was developed as a result of studies aimed at forming a uniform, stable, and desired thickness ceramic coating layer on a substrate to which ceramic coating is desired.
The authors have discovered a method of irreversibly forming a ceramic powder layer on a base material by applying the principle of electrophoretic deposition, rather than simply attaching a slurry physically.

This invention will be explained in detail below.

First, since the method of this invention deposits ceramic powder particles onto a substrate by electrophoresis, the substrate itself must be conductive or have its surface treated to be conductive. It is.

In order for a particle to be electrophoresed in a liquid, it must become electrically charged in the liquid.

Since ceramic powder itself does not ionize, a charged carrier is attached to the ceramic powder, and by electrophoresis of the carrier, the ceramic powder is simultaneously migrated and deposited on the base material.

The carrier used at this time may be any carrier that can adhere to the ceramic powder and be ionized in the liquid. However, it is undesirable to interfere with the sintering of the ceramic after it has been electrophoretically deposited on the substrate.

As such a carrier, polycarboxylic acid resin (anionic type) used in ordinary electrodeposition coating is used.
Polyamide resin (cationic) etc. can be used.

This carrier can also function as a so-called primary binder that maintains the shape of the ceramic powder layer, but a primary binder component may be separately added to the carrier.

Ceramic powder, which is the main raw material powder in this invention, needs to be sufficiently finely pulverized in order to be stably dispersed in a liquid and to facilitate electrophoresis.
Practically speaking, it is preferable to have a particle size of 40 μm or less. One type of ceramic powder may be used, or a mixed powder of two or more types may be used, and additives such as sintering aids and lubricants may be used as necessary.

The ceramic powder is prepared into an electrodeposition coating by sufficiently mixing it with a carrier, a sintering aid, a binder, etc., and dispersing it in a liquid such as water.

However, the fundamental difference from ordinary electrodeposition paint is that
In ordinary electrodeposition paints, most of the deposited solid content is resin, and the content of inorganic components such as pigments is suitably 5% by weight or less. This is natural for the purpose of obtaining a durable paint film without pinholes, but in this invention, most of the deposited solid content is ceramic powder, and the resin components such as the carrier form a stable powder layer. As long as it is sufficient to form pinholes, it is better to have as few as possible, and the presence of pinholes is not a problem.

In addition, in order to obtain a thin and uniform deposited layer of ceramic carrier on a substrate, it is desirable that the conductivity of the deposited layer is low, as in the case of ordinary electrodeposition paints.
If you want to obtain a slightly thicker deposited layer of 100 μm or more,
After making the deposited layer conductive by adding a conductive substance to the deposited layer on the base material obtained by electrophoresis, a deposited layer of ceramic carrier is further deposited on top of it by electrophoresis. That's fine.

A base material to be coated and a counter electrode are immersed in the ceramic carrier dispersion prepared as described above, and a DC voltage is applied to coat the ceramic carrier layer on the base material.

After drying the base material on which the coating layer has been formed in this way, it is heated to 300 to 1000°C to decompose or volatilize the carrier component in the coating layer. During this heating, the atmosphere may be selected from air, oxygen, compound gas, inert gas, etc. depending on the properties of the base material, carrier, and ceramics.

Since the carrier is decomposed or volatilized by heating, it is preferable to select and use a substance that does not leave a decomposition residue or a substance that does not adversely affect the final sintered body even if there is a residue. .

The method of the present invention is to decompose or volatilize the carrier by heating as described above, and then perform sintering under normal pressure or under sintering conditions depending on the properties of the ceramic powder.
Sintering is performed under reduced or increased pressure.

Although the sintering temperature varies depending on the type of ceramic, a range of 1000 to 2000°C is usually appropriate.

It is desirable that the coefficients of thermal expansion of the base material and the ceramic coating layer be as similar as possible.

Examples to which the method of the present invention described above can be employed include: (1) As mentioned earlier, high temperature oxidation resistance is improved by coating the surface of a carbon material with silicon carbide.

(2) By coating metal with ceramics,
Increases chemical stability and surface hardness.

(3) Coating ceramics with different types of ceramics to improve surface affinity and surface activity.

However, it can also be applied to bonding ceramics together or bonding ceramics and other materials.

Note that this electrophoretic deposition occurs only on conductive parts of the base material, so if a part of the base material is intentionally covered with an insulating film, no coating layer will be obtained on that part. Utilizing this fact, after applying an insulating film in an arbitrary pattern to the base material and partially covering it with a patterned ceramic coating or a type of ceramic, the insulating film is removed, and then another type of ceramic is applied. By coating, coatings with different coating components can be applied in stages.

As described above, the present invention relates to ceramic coatings, but it can also be applied to all powder substances such as metals, carbon, and inorganic powders.

The present invention will be explained in detail below with reference to Examples.

Example 1 Silicon carbide powder was finely pulverized to an average particle size of 2 μm, and alumina powder, which had been pulverized in the same way, was added thereto at a weight ratio of 5% by weight and mixed uniformly.

After thoroughly kneading this mixed powder with an acrylamide resin as a carrier, it is dispersed in the lustful fluid.
It was in the state of a so-called cationic paint.

Next, the surface-cleaned carbon plate to be coated and a stainless steel plate as a counter electrode are immersed in the liquid, and a DC voltage of about 200 V is applied for about 10 minutes while stirring and mixing the bath liquid, using the carbon plate as a cathode. Then, on the carbon plate, approx.
A 100 μm ceramic carrier layer was formed.
After this, wash thoroughly with water, dry, and then leave it in the air for 170 minutes.
℃ for 20 minutes to stabilize the deposited layer.

After that, it was further fired at 600°C for 1 hour to remove the resin content of the carrier, and then sintered at 2000°C in argon to obtain a carbon plate coated with silicon carbide ceramics.

The thus obtained coated carbon plate was heated at 800°C in air.
When heated for 1 hour, almost no weight loss was observed.

On the other hand, when a carbon plate without coating was subjected to the same heat treatment, almost the entire amount was burnt out.

Example 2 A dispersion liquid was prepared in the same manner as in Example 1 by adding 1% by weight of magnesia powder to finely ground alumina powder.

On the other hand, as a base material to be coated, a silicon nitride-magnesia sintered body made conductive by adding titanium nitride was used, and a ceramic carrier layer of about 100 μm was coated on the base material in the same manner as in Example 1. It was formed to a thickness.

After washing with water and drying, heat at 170℃ in an air atmosphere.
A stable deposited layer was obtained by heating for 20 minutes.

Thereafter, it was further heated to 600°C in air to decompose and volatilize the carrier resin. Then 1600℃ in air
The alumina coating layer was sintered.

Claims (1)

[Scope of Claims] 1. A carrier that can be ionized in a liquid is kneaded and adhered to a raw material powder containing one or more types of ceramic powder as a main component and mixed with a sintering aid, a binder, etc. Later, this is dispersed in a liquid,
A direct current voltage is applied between the conductive base material immersed in the liquid and a counter electrode to cause the raw material powder attached to the carrier to be deposited on the conductive base material by electrophoresis, and then heated to deposit the raw material powder in the deposit. 1. A method for producing ceramic-coated heat-resistant parts, which comprises decomposing or volatilizing the carrier, followed by firing. 2. The method for manufacturing a ceramic-coated heat-resistant component according to claim 1, wherein the base material is a carbon sintered body or a carbon fiber-reinforced carbon composite material. 3. The method for manufacturing a ceramic-coated heat-resistant component according to claim 1 or 2, wherein the base material has a conductivity of a specific resistance of 10 ⁴ Ωcm or less. 4. A method for manufacturing a ceramic-coated heat-resistant component according to claim 1, wherein the base material is a ceramic sintered body subjected to surface conductive treatment so as to have a conductivity of a specific resistance of 10 ⁴ Ωcm or less. . 5. The method for manufacturing a ceramic-coated heat-resistant component according to claim 1, wherein the carrier is a water-soluble or water-dispersible synthetic resin that can be ionized in a liquid. 6. The ceramic according to claim 1, characterized in that the deposit is formed partially using a conductive base material partially coated with an insulating material to form a deposit layer with a desired pattern. Method for manufacturing coated heat-resistant parts. 7. The method for manufacturing a ceramic-coated heat-resistant component according to claim 1, wherein the deposit layer has a conductivity of a specific resistance of 10 ⁴ Ωcm or less.