JPS6222954B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a workpiece storage structure for hot isostatic pressing, and more specifically, it melts glass with a low softening point and uses the glass as a sealing material for molding ceramics to be processed. The present invention relates to a structure for housing and combining formed objects to be processed, which has improved sealing performance in hot isostatic pressing of ceramics using a pressure medium gas.

The hot isostatic pressing (hereinafter abbreviated as HIP) process that uses glass as a sealing material allows for irregular shapes and can be used even at high temperatures that cannot be used with copper, steel, etc., which are normally used as encapsulants.
It has been attempted to be applied to the densification treatment of ceramics, which has advantages such as being able to be HIPed and is being developed as a high-temperature strength structural material in recent years. 2731) and a method of embedding a molded body in glass powder (see Japanese Patent Application Laid-Open No. 89405/1983).

In each of these methods, a carbon crucible such as a graphite crucible is usually used, and the glass is melted in the crucible to surround the molded object to be processed. However, the sintering temperature of ceramic powder is relatively low. When processing ceramics such as silicon nitride and silicon carbide using glass with a low softening point, the glass encapsulation method requires a high HIP temperature compared to the conventional metal powder molding process. Even in the granule embedding method, the ceramic molded body to be treated ends up being immersed in the glass bath in the same way. However, the specific gravity of ceramic molded bodies is 1.8 to 2.1 g/m ³ until they reach high density, while the specific gravity of glass is 2.2 to 2.3.
Since it is smaller than g/m ³ , when the glass melts as described above, the molded body floats up from the installation location, becomes easily moved, and is likely to come into contact with the carbon crucible.

In this case, the crucible has air permeability to allow the pressure medium gas to pass through, so when the object to be processed comes into contact with the carbon crucible, the gas used as the pressure medium during the HIP process enters through the contact area. The liver-kidney seal becomes incomplete and the purpose of HIP cannot be fully achieved. This also induces a reaction between trace amounts of oxygen contained in the pressure medium gas and the ceramics.
Furthermore, BN is added as a mold release agent inside the carbon crucible.
One idea is to attach powder to the glass, but even with this method, it is difficult to remove the solidified glass from the carbon crucible after treatment.

However, despite the drawbacks mentioned above, glass with a low softening point is easy to handle;
Since it has many advantages such as low cost and its use is industrially advantageous, it is equally desirable to improve the above-mentioned disadvantages.

The present invention, in response to the demands of the times, provides a processing object storage structure having an improved sealing structure that can more effectively achieve sealing with low softening point glass by overcoming the above-mentioned drawbacks. The purpose is to provide

However, the features of the present invention that achieve this purpose are
In the crucible for storing the processed material to be loaded into the HIP device, the processed material and the glass sealing material surrounding the processed material are stored, and the processed material and the glass sealing material are further kept in a flexible, non-ventilated crucible. The object is wrapped in a graphite foil or sheet, and a weight is placed on the upper surface of the structure so as to be freely movable.

Hereinafter, specific embodiments of the present invention will be further described in detail based on specific examples shown in the accompanying drawings.

The figure shows an example of the object storage structure of the present invention.
A workpiece 2 is placed in a crucible 1 with glass plates 3 above and below it,
3' and an intermediate glass powder 4. Between the crucible 1 and the objects 2 and glass 3, 3'4, the object 2 and the glass are A non-porous and flexible graphite foil or sheet 5, which constitutes the essential part of the present invention, surrounds the entire surface of 3, 3'4, and furthermore, on the upper surface thereof,
Object 2 to be treated during melting of the glass during HIP
A weight 6 that prevents floating is mounted freely.

Of these, the crucible 1 has air permeability to allow pressure medium gases such as Ar and N ₂ to pass through during HIP, and a carbon crucible is usually used.

On the other hand, the object to be processed 2 includes all materials to be subjected to HIP treatment, such as metals or ceramic powders, but ceramic materials are used because the HIP method, which uses glass as a sealing material, has excellent high-temperature processing and is suitable for HIP treatment of ceramics. is particularly effective, and ceramics containing silicon nitride, silicon carbide, or boron carbide as a main component, particularly ceramics containing silicon nitride as a main component, are the most preferable and are the mainstream of the treated material in the present invention. . The object to be processed 2 is usually not a powder, but is formed into a preformed body containing or not containing a known sintering aid, or a presintered body obtained by presintering this preformed body.

The glass used for the seal can be any glass that is normally used for HIP processing, such as silica glass, Vycor glass, or Pyrex glass, but it is possible to use any glass that is normally used for HIP processing, such as silica glass, Vycor glass, Pyrex glass, etc. Therefore, Pyrex glass is generally chosen as the most practical. In the figure, this sealing glass is composed of upper and lower glass plates 3, 3' and an intermediate glass powder 4, but it is also possible to use only the glass powder 4 instead of using both together. often,
Alternatively, it may be encapsulated in a glass capsule. However, in terms of the assembly arrangement within the crucible, the arrangement shown in the drawings is the most suitable even though there are variations in form. In addition to the above-mentioned plate shape and powder shape, glass in various shapes can be used.

Next, the surrounding by the graphite foil or sheet 5, which constitutes the main part of the present invention, prevents the intrusion of the pressurized gas that has passed through the crucible 1, which has air permeability, and also absorbs the isotropic compression force during HIP. It transmits information accurately to the object 2, and is particularly useful in HIP processing using pressurized gas, and must be non-porous and have the ability to cope with compressive deformation. Moreover,
Naturally, it is required to be insoluble during the HIP process because it cannot perform the above function if it is dissolved during the HIP process.

In addition to graphite, there are also foils and sheets made of high-melting point metals such as molybdenum that satisfy this function, but they all have difficulties in terms of cost, so graphite foils or sheets known under the trade name Graphoil are the most useful. In particular, this graphite foil or sheet 5 also has a role as a mold release material, and after processing, the glass solidified thereon can be easily taken out from the crucible.

Furthermore, in the above structure, a weight 6 is placed on the upper surface of the workpiece 2 and the seal glass 3, 3'4, which are surrounded by an air-impermeable graphite foil or sheet 5. As mentioned above, this is to suppress the floating of the object to be processed 2 that floats up when the glass is melted, and it may be made of a high-temperature material and heavy enough to suppress the object to be processed, which has a specific gravity smaller than that of glass, from floating. For example, silicon nitride, tungsten, molybdenum, etc. are used. The weight 6 needs to move freely in the direction along the inner wall surface of the crucible in order to accommodate deformation during processing, so that a load is applied to the object to be processed and the graphite sheet or foil on the top surface of the glass. There is.

In addition, in the figure, 7 is a mold release agent layer made of BN powder sprayed or applied inside the crucible, and although it is not particularly essential, it combines with the mold release effect of graphite foil or sheet to facilitate removal after processing. Of course, you need to get used to it.

The object storage structure of the present invention has the above-mentioned configuration, and is mainly used for HIP processing using gases such as Ar and _N2 as the pressure medium.
The material is charged into a HIP furnace and subjected to HIP treatment, but HIP treatment generally involves raising the temperature first and then applying pressure after completing the glass seal in order to avoid trapping gas remaining in the object. , it is common to reach a predetermined temperature, then increase the pressure and further increase the temperature. Therefore, if Pyrex glass is used as glass, it will soften and melt when the temperature exceeds 1200℃.
The objects to be treated, which have not yet been densified, float due to their light specific gravity, push up the upper non-porous graphite foil or sheet, and a portion of the objects to be treated float up from the glass bath.

However, at this time, since the weight 6 is present above, this floating can be suppressed and the intrusion of atmospheric pressure, which is a pressure medium, can be prevented, and a perfect sealing state can be maintained.
Note that the gas released from the object to be processed flows out through gaps in the glass because the glass seal is not yet completed in the early stages of HIP.

After the glass is melted, the Pyrex glass has the function of dissolving the gas, so it is dissolved into the glass, and the object to be processed can be densified at the required HIP temperature and pressure. After the treatment, the gas dissolved in the glass is vaporized again, making the glass foamy and making it easier to remove the glass.

Thus, the structure of the present invention not only prevents pressure medium gas from entering the workpiece by surrounding the workpiece with an air-impermeable graphite foil or sheet and placing a weight on top, but also prevents pressure medium gas from entering the workpiece. Even if the object to be treated has a tendency to float during treatment, which is a problem during treatment, it can be pressed down with a weight and, in combination with its air-impermeability, a perfect seal can be achieved.

Moreover, the graphite foil or sheet in the present invention has flexibility, does not inhibit the densification of the processed material in any way, and also has the effect as a mold release agent.
It is highly effective in easily removing solidified glass from a carbon crucible, and it is highly effective in making it possible to easily remove solidified glass from a carbon crucible. This method is extremely effective in producing sintered bodies.

Examples of the present invention will be further described below.

Example Purity 99%, α phase 70%, average particle size approximately 1 μm
The Si ₃ N ₄ powder was placed in a silicone rubber tube and the tube was plugged, followed by isostatic pressing at a pressure of 5000 Kg/cm ² to produce a preformed body (approximately 18 mmφ×30 mm) with a relative density of 58%.

This preformed body was embedded in a graphite crucible whose inner surface was coated with BN, with the upper and lower glass plates made of Pyrex glass and the intermediate powder made of Pyrex glass, and the entire surface was surrounded by graphite foil. Place it, place a weight on it, and HIP it.
loaded into the device. Raise the temperature inside the HIP device to 300℃,
After vacuuming to approximately 10 Torr, 15Kg/cm ² of N ₂
Inject the gas and perform the exhaust operation twice to obtain a volume of 30Kg/ ^cm2 .
_N2 gas was injected. After raising the temperature to 1200° C. to soften and melt the glass, N ₂ gas was supplied and the temperature was further raised to perform HIP treatment at 1750° C. and 2000 Kgf/cm ² for about 2 hours.

The molded body taken out from the HIP machine was entirely covered with dark glass, but after removing the graphite foil and glass,
The surface of Si ₃ N ₄ was clean with no trace of pressure gas intrusion, and its relative density was 98.5%.

[Brief explanation of the drawing]

The figure is a schematic cross-sectional view showing one example of a processing object storage structure according to the present invention. 1... Crucible, 2... Processing object, 3, 3'... Glass plate, 4... Glass powder, 5... Graphite foil or sheet, 6... Weight, 7... BN mold release agent layer.

Claims (1)

[Scope of Claims] 1 A structure in which a ceramic molded body to be treated is housed in a crucible having air permeability and subjected to hot isostatic press treatment, wherein the molded body to be treated is formed inside the crucible. The entire surface is surrounded by a flexible non-porous graphite foil or sheet together with the sealing material glass, and a weight is placed on the top surface of the non-porous graphite foil or sheet. A processing object storage structure characterized by: 2. The processed material storage structure according to claim 1, wherein the crucible having air permeability is a carbon crucible. 3. The object storage structure according to claim 1 or 2, wherein the ceramic molded object to be treated is a molded object containing silicon nitride as a main component. 4 Processing object The processing object according to claim 1, 2 or 3, in which the entire surface of the molded object is surrounded by upper and lower glass plates and glass powder filled between them. Item storage structure. 5. The object storage structure according to claim 1 or 4, wherein the glass is Pyrex glass.