JPH0891947A - Production of sintered body by hot isotropic pressurization - Google Patents

Abstract

PURPOSE: To obtain a sintered body having high density and excellent properties in high yield by putting a shaped body to be treated in a glass container, putting a lid having an air hole on a sheath, enabling the lid not to move by its weight or by fixing the lid to the sheath and treating by hot isotropic press(HIP). CONSTITUTION: This method for producing a hot isotropic pressurized sintered body is to deaerate and seal a shaped body to be treated in a glass container having no clearance between the shaped body and the container to make a glass capsule, put the glass capsule in a heat resistant sheath, cover the total system with the sheath and a lid to leave no space, make an air hole on the lid attached to the sheath, put glass pieces in the hole and treat the capsule by HIP. The figure shows an example. The shaped body 1 having a cylindrical shape is put into the cylindrical glass container capable of receiving the shaped body without leaving a clearance and having a reaction protecting layer 7 comprising boron nitride, then, deaerated and sealed. The capsule is put into the sheath 3 made of graphite and a reaction-protecting layer 4 made of boron nitride is formed. The lid 5 is put on the sheath 3 and glass beads 6 are filled in the air hole. This is treated by HIP.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a sintered body by hot isostatic pressing (HIP) using a glass capsule.

[0002]

2. Description of the Related Art The glass capsule HIP method uses
Heat the capsule that has been degassed and sealed by placing it in a glass gas impermeable container that can be softened without damage under high temperature and high pressure, and apply Pascal pressure of several tens to several hundreds MPa (megapascal) by pressure medium gas to burn. It is a way to conclude. Regarding the encapsulation of the object to be processed, a method of degassing and encapsulating the object to be processed in a preformed glass container, a method of coating the object to be processed with molten glass under vacuum, and a glass while heating the periphery of the object to be processed There is a method in which the gas-impermeable layer of the molten glass is formed around the object to be processed by surrounding the object to be treated with vacuum and completely enclosing it in advance with the glass-forming substance. The main purpose of this glass capsule is to prevent the pressure medium gas from entering the object to be burned,
In the case of a breathable object, the isotropic pressure effect on the object disappears when direct contact between the pressurized gas and the object occurs,
The progress of densification is hindered.

[0003] The exposure of the object to be treated into the pressurized gas is often due to the viscosity of the capsule glass decreasing as the temperature rises, and the glass covering the periphery of the object to be run off. As a result, the object to be treated may be exposed by floating on the molten glass. For example, when the object to be processed is covered with a relatively large amount of glass and is installed in a vessel such as a sheath, the object to be processed is immersed in the glass melt whose viscosity has been reduced by heating. Is in a closed state. At that time, if the specific gravity of the object to be processed is smaller than the specific gravity of the glass melt, the object to be processed floats above the glass melt, and the possibility that the object to be processed is exposed to the pressurized gas is significantly increased.
In order to avoid this phenomenon, a method of installing a weight on the object to be processed is adopted.

[0004]

Generally, in the glass capsule HIP method, even when the densified sintered body exceeds the specific gravity of glass, the object to be treated is in the form of a compact or a powder agglomerate. , As its bulk density is initially lower than the specific gravity of glass, it is possible to accurately understand the possibility of exposure to pressurized gas in advance for the object to be processed that passes through the stage of lower than the specific gravity of glass. Is difficult to do. This is because it affects the floating prevention of the object to be fired, but the viscosity of the glass and the surface tension change with the temperature rise, the volume change of the object to be processed and the glass in the pressurizing process, and in parallel with this, the object to be fired This is because the density that changes with the progress of sintering, and further, processing conditions and subtle differences in operation are involved in a complicated manner, and whether or not the object to be processed is exposed on the glass is determined. Due to such a complicated relationship, the effect of shielding the gas from the capsule, and the firing efficiency as a result thereof are likely to make a considerable difference.

On the other hand, even if the specific gravity of the densified sintered body is lower than the specific gravity of the glass, it is not exposed if the sintering is completed only in the state where the viscosity of the glass is relatively high. Sometimes. However, as seen when sintering ceramics such as alumina and silicon nitride, in general, the temperature is often raised to a temperature at which the viscosity of the glass becomes considerably low, and the specific gravity of the object to be treated is lower than that of glass. In the case of passing through the steps, there is a strong possibility that the object to be treated will float above the melt from the state of being immersed in the glass melt. The easiest way to prevent exposure to the melt is to install a weight on the object to be treated and to suppress the overall floating, but depending on the weight and the shape of the object, the center of gravity, the installation position, etc. The effect is greatly affected and lacks stability. Although it does not float above the glass due to the weight, the effect loss of isotropic pressurization at the part that comes into contact with the weight and the glass covering the periphery of the object to be processed may melt depending on the total amount of glass and the installation container. Therefore, there are still some points to be improved in terms of exposure to the pressure medium gas centering on the upper part of the object to be processed.

[0006]

DISCLOSURE OF THE INVENTION The present invention relates to a glass capsule HIP method in which a glass melt is applied to an object to be treated, which has a lower bulk density than the specific gravity of the glass melt in a low viscosity state. Use of a sheath with a lid that features a shape and structure when installing a capsule in the HIP processing chamber to prevent exposure of the workpiece to the surface by floating and to prevent the glass melt from flowing down from the periphery of the workpiece. It corresponds to that. That is, the preformed object is put in a glass container having an inner shape such that there is no space with it, degassed and sealed, and a heat-resistant sheath having an inner shape similar to the outer shape of the glass capsule is used. After inserting the capsule, a lid having a weight that can be fixed to the sheath or is not easily movable is attached, and the entire glass capsule is covered with the sheath and the lid as closely as possible. At this time, when the object to be treated and the capsule glass material react with each other at a desired high temperature and high pressure, it is desirable to interpose a reaction preventive layer in advance between the object to be treated and the capsule glass. An example of such a reaction-preventing layer can be dealt with by coating the surface of the object to be treated with boron nitride, which is utilized in a normal firing operation as a high temperature release agent.

On the other hand, when the above-mentioned shaped glass container is not used, it is necessary to completely cover the periphery of the object to be treated with a powdery or particulate glass forming substance which forms a glass phase at a predetermined temperature. Then, the sheath is sufficiently filled, and the lid is attached to the sheath as described above. Alternatively, a gas-impermeable capsule is prepared by previously cooling the object-to-be-processed molded article that has been completely coated with molten glass by heating in a vacuum, and using a sheath that can be fitted to the capsule as described above. The same operation can be performed. The material of the sheath body should be stable under the desired high temperature and high pressure, at least not to be impregnated with glass under pressure, and the lid should be made of the same material. .

Here, the lid attached to the sheath is provided with one or several ventilation holes of a size that does not allow the object to be treated to float therein, and at least one of them has a glass piece or a high temperature in advance. The glass-forming substance such as powder and particles for forming a glass layer is sufficiently placed. This lid has a structure in which the lid itself cannot be pushed up due to the floating of the object to be processed when it is pressurized or levitated, for example, by providing threads on the lid side and the inner upper part of the sheath in the relation of male and female threads. You may use a method such as turning and fixing, or you may install a lid with a sufficient weight so that it will not lift when the object to be treated floats, so that the lid does not move. Keep it in good condition. Also, the lower surface of the lid may be a flat surface depending on the shape of the upper portion of the object to be processed, but it is better to use one having a plurality of protrusions. It is preferable that the protrusion used here has a flat tip.

When the glass and the sheath material react under the desired conditions, it is desirable to interpose a reaction preventive layer which does not react with either the glass or the sheath on the lower surface of the lid, the inside of the vent and the inner surface of the sheath. This reaction-preventing layer uses a film-like, sheet-like, or powder-like substance which is chemically stable per se under high temperature and high pressure. As the simplest example, it is also possible to mix the boron nitride powder with a volatile solution and apply the mixture to the inner surface of the sheath and the lower surface of the lid including the ventilation hole.

The capsule fitted with the lid and housed in the sheath is placed in the processing chamber in the HIP apparatus, deaerated under vacuum, and then subjected to HIP processing under desired conditions. The pressurized medium gas species in the HIP process may be any as long as it is within the range generally recognized in the device specifications. By performing such capsule HIP, it is possible to manufacture a sintered body that has a specific gravity lower than that of glass with an excellent firing yield, with a sufficient gas shielding effect against the pressure medium.

[0011]

When the material to be treated is floated by the glass melt, the specific gravity of the material to be fired is lower than the specific gravity of the glass, and the HI until densification
This is because it is impossible to prevent the floating up to the exposure to the pressure medium gas during the P treatment period due to the decrease in glass viscosity. In the present invention, regardless of the viscosity of the glass, the density of the sintered body is not limited to that lower than that of glass, and even if it is high, the density of the sintered body is lower than that of glass halfway, and the glass is then densified with progress of densification. Even higher ones can be accommodated.

[0012] In the present invention, whether a preformed glass container is used as the encapsulant or a glass-forming substance which produces a glass melt at a high temperature later is used, the sheath in which the capsule is to be installed is used and the sheath is used. As the shape of the capsule, it is necessary to use a sheath with little or no gap between the capsule and the capsule at the stage of installing the capsule.
This is to make it possible to deal with P processing. The difference from the conventional technology is not mainly to completely suppress the floating itself of the object to be processed in the glass melt, but to prevent the exposure to the counter pressure medium gas during floating. It gives an effect. As can be seen from the fact that the glass material or the glass-forming substance is put in advance in at least one vent hole provided in the lid, at least the portion formed by the lid and the sheath installed on the sheath is At high temperature, it is filled only with the object to be treated and the glass melt. Here, the melt surface reaches at least the lower end of the vent hole, usually up to a certain position in the vent hole. However, even if the object to be processed floats, its upper part corresponds to the lower part of the fixed lid and cannot be further floated. Even in this case, the upper surface of the object to be processed always remains below the melt surface. Here, the size of the vent hole attached to the lid is made smaller than the size of the object to be treated in order to avoid further floating through the vent hole. The ventilation holes are provided to allow the pressure medium gas to directly act on the glass surface, and as can be seen in the example of the CIP (cold isotropic pressure) effect using a liquid as a pressure medium, liquefaction is achieved. Pascal pressure is applied to the periphery of the object to be processed by the glass melt, and the isotropic pressing effect is sufficiently exhibited.

The glass material or the powdery or particulate glass-forming substance is allowed to exist in advance in at least one vent hole provided in the lid because a small amount of voids or molten glass is present from the beginning. As a replenishing glass supply source, which is generated at the stage of forming, and further, the interior void portion composed of the sheath and the lid, which is caused by the densification shrinkage of the object to be processed, is continuously filled with the glass melt. Shows the action. Further, the protrusion is provided on the lower surface of the lid so that when the object to be processed is floated, especially when the upper surface of the object to be processed is a flat surface, if the lower surface of the lid is also a flat surface, there is almost no glass phase between the contact portions. This is because there is a possible situation, and the reason is to avoid this. The bottom surface of the lid, which has a projection with a sharp tip, can hold the floating upper surface of the object to be processed in a point contact state, so that the upper surface of the object is sufficiently covered with the glass phase and isotropic. The pressure can be applied sufficiently. It is preferable that a plurality of protrusions having the same shape are present in order to keep the floating object to be processed stable in the melt so that it is balanced.

As described above, according to this method, since the object to be treated can be always kept immersed in the glass melt during the HIP treatment process, it is exposed by the glass flowing down from the object to be treated at the time of melting, and the glass is not exposed. It is possible to sufficiently prevent the exposure due to levitation, and to exert an excellent gas shielding effect.
In addition, the sheath and lid used in this method can be used for most of the heat-resistant materials used in ordinary firing by providing a reaction-preventing layer on the inner surface of the sheath, as well as reaction and welding with glass. Since it can be prevented, the glass gob can be easily taken out after the HIP treatment, and the sheath and the lid can be reused.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments and the drawings based on the embodiments. Example 1 In FIG. 1A, a cylindrical shaped body 1 having a bulk density of 2.1 is prepared in advance by using a silicon nitride powder as a starting material by die molding or the like, and the processed body 1 is formed. , Pyrex (trade name) glass container with a bulk specific gravity of 2.3, which has a reaction-preventing layer 7 made of boron nitride on the inner surface so that it can be stored with almost no space, is degassed and hermetically sealed. The prepared capsule 2 is put into a graphite sheath 3 having a cylindrical bottom and having almost no gap when the capsule is installed.
The inner surface of the sheath is coated with boron nitride in advance to form the reaction preventive layer 4. Then, a lid 5 having a sufficient weight and having the same reaction preventing layer 4 on the lower surface and the vent is placed on the sheath 3. The lid 5 has five small protrusions on the lower surface, and has three vent holes, one of which is filled with Pyrex glass particles 6 up to the upper end of the lid. This is placed in the processing chamber in the HIP device and deaerated. Then, HIP processing is performed at a temperature of 1800 ° C. and a pressure of 200 MPa using Ar gas as the pressure medium gas. Here, the behavior of the object to be processed and the glass in the sheath inside the HIP processing chamber near the maximum temperature is shown in FIG. 1 (B). At this temperature, the Pyrex glass has a considerably reduced viscosity and is liquefied. This glass melt 1
Although the object 1 to be treated in the initial stage of sintering floated in 2, the series of HIP treatment steps passed without being exposed to the pressure medium gas by staying at the protruding end of the lower surface of the sheath lid 5. After the HIP treatment, a highly dense and uniform silicon nitride sintered body could be obtained from the glass gob.

Example 2 In FIG. 2, a columnar shaped body 1 is preliminarily produced by molding using a silicon nitride powder as a starting material, and the reaction-preventing layer 7 made of boron nitride is used as the object 1 to be treated. And the inner surface is coated with boron nitride to form a reaction-preventing layer 4
The object 1 to be treated was put into the cylindrical graphite sheath 3 having the above-mentioned shape so as to completely cover the object 1 with the glass substance forming particles 22 for forming Pyrex glass, and the graphite lid 5 having five small projections was attached. The glass substance forming particles 22 up to the bottom surface of the lid
Is filled. Inner upper surface of cylindrical sheath 3 and lid 5
On the side surface of the, the threads are respectively cut in the relationship of the male screw and the female screw, and by turning the lid 5 into the sheath 3, the lid is completely fixed to the upper part of the sheath. The lid 5 is provided with three ventilation holes of a size that cannot be penetrated by the object to be treated, and one of them has a glass substance forming particle 22 corresponding to the same Pyrex glass component filled in the sheath. To be filled. The sheath with a lid containing the object to be processed is placed in the processing chamber in the HIP device and sufficiently deaerated, and then the pressurized gas Ar is used.
1800 with almost no pressure applied until the glass melts
HIP treatment is performed at a temperature of 200 ° C. and a pressure of 200 MPa. Similar to the first embodiment, the object to be processed 1 is always present under the surface of the glass melt through a series of HIP processing steps, is never exposed to the pressure medium gas, and is high in the glass lump after the HIP processing. A dense and excellent silicon nitride sintered body could be obtained.

In order to explain the present invention in more detail, a comparative example outside the range described in the prior art or the present invention will be shown in comparison. (Comparative Example) A cylindrical silicon nitride molded body similar to that of the example is used as an object to be treated, and a capsule enclosed in a glass container is set in a sheath by the same method as that of the example 1. The case where the sheath was HIP-treated under the same conditions as in Example without using a lid was set as Comparative Example 1, and a material which does not react with glass at a high temperature on the capsule without using a lid, this time a prism made of a boron nitride sintered body. The case where the weight of the shape was directly placed on the glass capsule and the HIP treatment was performed under the same conditions as in the example was set as the comparative example 2. HIP in the case of Comparative Example 1 in which nothing such as a lid or weight is installed above the capsule
The object to be treated was exposed on the glass during the process. In the case of Comparative Example 2 in which a weight was placed on the glass, the object to be treated did not sink to the bottom of the sheath and was not exposed on the glass, but the surface of the object in contact with the bottom surface of the sheath and the lower surface of the weight was not exposed. At the center, the properties deteriorated and the uniformity became poor. Table 1
HIP for the object to be treated in Examples and Comparative Examples
The presence or absence of a gas shielding effect of the capsule at the time and the property characteristics of the processed object after HIP are shown. As the property characteristics, the bulk density, the relative density (%) of the processed object after HIP, the JIS extracted from the upper surface of the processed object, the central portion and the vicinity of the lower surface by the site
-The four-point bending strength value of the test piece according to R1601 was described.

[0018]

[Table 1]

[0019]

According to the present invention, the exposure of the object to be treated to the pressurized gas due to the floating in the molten glass, which is likely to occur at the time of glass capsule HIP of the object to be treated having a specific gravity lower than that of glass, is prevented. Therefore, Pascal pressure can be sufficiently applied to the surface of the object to be processed, and a highly dense and excellent sintered body can be obtained with a high firing yield.

[0020]

[Brief description of drawings]

FIG. 1 (A) is a cross-sectional view illustrating an example of an installation method at the start of HIP processing according to the present invention, and FIG. 1 (B) shows a glass melt in the vicinity of the maximum temperature during HIP processing. This is an explanation of the situation of the object to be processed in the above.

FIG. 2 is a cross-sectional view of an installed state explaining an example in which encapsulation different from that described in FIG. 1 is performed at the start of the glass capsule HIP process according to the present invention.

[Explanation of symbols]

 1 object to be treated 2 glass capsule 3 sheath 4 reaction preventive layer 5 lid 6 glass particles 7 reaction preventive layer 12 glass melt 22 glass substance forming particles

Claims (6)

[Claims] 1. A heat-resistant sheath having a bottom with an inner shape into which the capsule can be fitted, by placing a molded article to be processed in a glass container having an inner shape that conforms to the outer shape and degassing and sealing. Put a lid on the sheath with a ventilation hole smaller than that of the material to be fired, and fix the lid on the sheath by its own weight or by fixing it on the sheath so that the lid on the sheath does not move. A method for producing a sintered body, which comprises pressing. 2. A lid having a vent hole smaller than that of a material to be fired, which is covered with a powder, a glass-forming substance in the form of powder, particles or lumps which vitrifies at a desired high temperature, and which is filled in a heat-resistant sheath. A method for producing a sintered body, which is characterized in that the cap is placed on a packed bed and the cap on the sheath is immovable by being fixed by the weight of the cap or fixedly installed on the cap, and hot isostatic pressing is performed. 3. The method for producing a sintered body according to claim 1, wherein a capsule produced by completely coating a molded article to be processed with molten glass in a vacuum is used. 4. The same glass piece as the capsule glass or powder or particulate glass forming substance is previously put in at least one of the vent holes of the lid attached to the sheath. For manufacturing a sintered body of. 5. The method for producing a sintered body according to claim 1, wherein a lid having at least one protrusion having a non-planar tip on the lower surface is used. 6. A material which does not react with the material of the sheath and the lid and the glass at a desired high temperature and high pressure, and which itself is stable is interposed between the sheath and the lid and the surface of the capsule glass. The method for producing a sintered body according to claim 1.