JPS6234711B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot isostatic pressing process using a pressure medium gas, particularly a hot isostatic press process using a glass having a low softening point or a glass that dissolves the pressure medium gas as a sealing material. This invention relates to a method for improving sealing performance.

The hot isostatic pressing (hereinafter abbreviated as HIP) treatment method that uses glass as a sealing material allows for irregular shapes, and can be used at high temperatures that cannot be used with copper, steel, etc., which are normally used as encapsulants. The glass capsule method (see Japanese Patent Publication No. 46-2731) and the method of embedding the molded body in glass grains (Japanese Patent Publication No. 55-89405)
(see Japanese Patent Publication No. 2003-111000), etc., and are currently used in the molding process of ceramic powder, which is currently being widely developed as a high-temperature structural material.

However, the sintering temperature of heat-resistant ceramic powder is high, and therefore the HIP temperature _{is higher} than that in conventional metal powder compacting. ) when processing ceramics such as
Since the temperature is about 10.degree. C., the conditions are the same in both the glass encapsulation method and the glass bath method, and the ceramic molded body to be treated is immersed in the glass bath and its surroundings are covered with molten glass. In this case, the specific gravity of the ceramic molded body is 1.8 to 2.1 g/cm ³ until it reaches high density, and the specific gravity of glass is 2.2.
If it is smaller than ~2.3, part of the molded body may come out from the glass bath, resulting in incomplete sealing.
This is because when Ar or _N2 gas is used as a pressure medium during the HIP process, the pressure medium gas comes into direct contact with the molded body, inducing a reaction between the trace amount of oxygen contained in the gas and the ceramics. Since the pressurized gas enters the pores of the ceramic molded body, the pressure of the pressurized gas no longer acts as a driving force for densification, resulting in a situation where the intended pressure effect cannot be obtained.

On the other hand, low softening point glasses, such as Pyrex glass, dissolve pressure medium gas in a specific temperature and pressure range, and this gas accumulates in the pores of the molded body, creating an internal pressure, and completely melting. densification through HIP processing may not be achieved.

However, although it has these disadvantages, glass with a low softening point has many advantages such as ease of handling and low price, and its use is extremely industrial, so it is difficult to improve the above disadvantages. They are equally desired.

An object of the present invention is to provide an improved sealing method that can more effectively utilize a glass sealing material, which is an extremely useful sealing material, by overcoming the drawbacks of glass, in response to the trends of the times. It is something to do.

That is, the feature of the present invention that achieves this object is that the entire surface of the ceramic powder compact is immersed in a glass bath and the entire surface of the compact is sintered under pressure at high temperature using gas as a pressure medium. Covering with powder as an inner layer made of a material that sinteres at a temperature lower than the temperature at which the compact material is sintered, and during the HIP process, after first sintering the covering material to form an airtight layer, Furthermore, the temperature is raised to a temperature at which the molded body is sintered, and HIP treatment is performed.

Hereinafter, specific embodiments of the present invention will be further described.

First, in the HIP treatment method, which is the basic treatment method of the present invention, a ceramic powder compact is encapsulated in a glass capsule or embedded in a glass powder granule, immersed in a glass bath, and exposed to Ar under high temperature. This is a pressure sintering method using an inert gas such as N ₂ gas as a pressure medium.

Here, as the ceramic powder, silicon nitride,
It is a ceramic whose main component is either silicon carbide or boron carbide (B ₄ C), and it is usually formed as a preform or a pre-sintered body by pre-sintering it, and it is enclosed in a glass capsule or glass powder. It is embedded in granules and subjected to subsequent HIP treatment.

These preformed and presintered molded bodies may contain a sintering aid such as Y ₂ O ₃ powder, Al ₂ O ₃ powder, MgO powder, etc., in addition to the ceramic powder alone.

On the other hand, there are a glass capsule encapsulation method and a method of embedding it in glass powder as a means of covering the molded object to be treated, but in either case, the same state will be exhibited if heated above the softening point of the glass. This is as mentioned above; however, in the former case, degassing is easy because the only part to be degassed and sealed is inside the capsule to avoid the influence of residual air during encapsulation. The only difference is that in the latter case it is necessary to evacuate the entire furnace.

The glasses used in the present invention include silica glass, Vycor glass, and Pyrex glass, but silica glass may form a reaction layer with the molded product, and Vycor glass is difficult to remove after processing. Therefore, Pyrex glass is the most preferred and usually used. In addition, HIP treatment is carried out in a HIP furnace by raising the temperature and pressure in an atmosphere gas such as Ar or _N2 , which prevents local distortion of the glass capsule or prevents the glass powder particles from fusing together. In order to prevent high-pressure gas from entering the object and making HIP treatment impossible before a dense glass layer is formed on the outer surface of the object, the HIP treatment is first performed at an atmospheric pressure of 100 atmospheres or less. The temperature is raised above the softening point of the glass so that the glass can easily flow plastically, and when glass powder is used, a dense glass layer is formed on the outer peripheral surface of the object to be treated. specified
Let the HIP temperature and pressure increase. However, as will be described later, in the present invention, the coating material forms a sintered layer between the glass coating and the molded object to be treated, so the HIP method described above is not necessarily required.

That is, the present invention involves layering a specific coating material over the entire surface of the molded article to ensure seal integrity during the HIP process as described above.

Therefore, prior to encapsulation in the glass capsule and embedding in the glass powder, the entire outer surface of the molded object to be processed is covered, sintered at a temperature lower than the sintering temperature of the molded object, and the HIP treatment temperature is A material powder that does not melt is deposited in a layer.

Al ₂ O ₃ , ZrO ₂ , BN, etc. are used as the coating material, and among them, BN powder is the most suitable, but
It is related to the ceramic molded body to be subjected to HIP treatment, and is not necessarily limited to BN powder. However, BN powder has good mold release properties,
It is necessary to form a BN powder layer on the outer surface directly covering the molded object to be processed. Therefore, a BN powder layer for facilitating mold release is used as an inner layer, and the coating material characterized by the present invention is adhered to the outer surface thereof.

Of course, this coating material does not exclude metal powders, but is limited to Mo, Pt, Cr, etc. In the case of Cr, the above-mentioned materials are preferred because it has difficulty in peeling off after treatment.

In order to maintain the shape of these coating materials, a mold made of a flexible sheet material such as a rubber mold is used as necessary, and the coating material powder is filled into the mold, and the required amount is filled into the mold. The molded body to be treated is buried and layered by hydrostatic pressure treatment or the like at room temperature.

The thickness of this coating material is 0.3mm for one or more layers.
It is preferably 0.5 mm or more. In any case, this coating material is preferably heated to 1200℃ during the HIP process.
The degree of sintering must be sufficient to form an airtight sintered layer on the outer surface of the molded body to be treated and achieve densification by HIP treatment.

The types of coating materials, the temperature and pressure conditions at which they are sintered to form an airtight layer, as well as the types of ceramic molded bodies to be subjected to HIP treatment, HIP temperature and pressure are as follows.

Coating material Al ₂ O ₃ 1200℃ 1000Kgf/cm ² or more ZrO ₂ 1350℃ 1000Kgf/cm ² or more BN 1650℃ 1800Kgf/cm ² or more Ceramic molded body Si ₃ N ₄ 1750℃ 2000Kg/cm ^{2 or more SiC 1850℃ 2000Kg/cm 2} or more ² or more B ₄ C 1850℃ 2000Kg/cm ² or more Therefore, when the above-mentioned coating material is selected and the treatment is carried out on the object to be treated selected from the above-mentioned ceramic molded objects, the pressure and temperature curves shown in the attached drawings are applied. First, the coating material is sintered at position A,
Next, at position B, the molded body covered with the coating material is sintered.

Therefore, according to the method of the present invention, when processing using a pressure medium gas in a glass bath, even if there is a difference in specific gravity and the seal may float out of the glass bath during the processing, the seal will remain intact. It is completely perfect, and high density can be expected through accurate isotropic compression through HIP processing.

As described above, the method of the present invention takes advantage of the advantages of using low softening point glass as a sealing material while overcoming its drawback in sealing performance, thereby greatly contributing to the industrial use of HIP processing.

In addition, when glass that dissolves pressure gas, such as Pyrex glass, is used as a sealing material, furthermore, after pressure sintering is completed, the pressure gas dissolved in the glass is vaporized again to make the glass into a foamed state, By cooling this, the attached glass can be easily removed with a small external mechanical force, killing two birds with one stone.

Hereinafter, the present invention will be further explained with reference to examples.

Example Si ₃ N ₄ powder containing 2.5% Y ₂ O ₃ with an average particle diameter of about 1 μm and about 70% α phase was isostatically compression molded at a pressure of 5000 Kgf/cm ² to obtain a molded body with a relative density of 62%. Ta.

Apply BN to a thickness of 0.3 mm on the surface of this molded body,
Furthermore, Al ₂ O ₃ was applied to the outer surface to a thickness of 0.3 mm, and the crucible was placed in a graphite crucible embedded in Pyrex glass, and inserted into a HIP device. As mentioned above, Al ₂ O ₃ is sintered at 1200℃ and 1000Kgf/cm ² or more, so a sintered state is obtained at this position (position A in the attached drawing) during HIP, and then by increasing temperature and pressure.
BN is also sintered at the predetermined temperature and pressure, and
HIP processing temperature and pressure of Si ₃ N ₄ molded body is 1750
The temperature and pressure were increased to 2000 Kgf/cm ² or higher (position B in the attached drawing).

After the HIP treatment, the temperature was lowered to 500° C. while maintaining the pressure at 2000 Kgf/cm ² , and then the pressure was reduced and allowed to cool. The glass-covered molded body was taken out from the crucible, heated again to 1100°C in an electric furnace, held for 30 minutes, and then cooled.

The glass covering the molded body had become foamed glass due to the vaporization of the pressure medium gas dissolved in the glass, and it was extremely easy to remove the sealing material. The obtained molded body was a high-density sintered body with a relative density of 98.5%, and was a homogeneous product with appropriate isotropic compression throughout.

[Brief explanation of the drawing]

The figure is a chart showing aspects of temperature and pressure during HIP processing.

Claims (1)

[Scope of Claims] 1. In a hot isostatic pressing method in which a ceramic powder compact is immersed in a glass bath and pressure sintered using a pressure medium gas at high temperature, the entire surface of the compact is is covered with a powder made of a material that is sintered at a temperature lower than the temperature at which the compact material is sintered with BN as an inner layer and does not melt during hot isostatic pressing, and the coating is removed during the hot isostatic pressing process. The powder material is first sintered into an airtight layer and then
A hot isostatic pressing method for ceramics, further comprising raising the temperature to a temperature at which the compact is sintered. 2. The hot isostatic pressing method for ceramics according to claim 1, wherein the ceramic powder compact is a compact containing silicon nitride, silicon carbide, or boron carbide as a main component. 3. The hot isostatic pressing method for ceramics according to claim 1 or 2, wherein the coating material is a material selected from Al ₂ O ₃ , ZrO ₂ and BN. 4. A hot isostatic pressing method for ceramics according to claim 1, 2 or 3, wherein the glass is Pyrex glass.