JPS6146433B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a high-density ceramic sintered body, and more specifically, a preformed or presintered porous ceramic body is previously formed into a block by pressure forming, and then this is formed into a block by hot isostatic pressing (hereinafter referred to as
The present invention relates to a method for manufacturing high-density ceramic sintered bodies using the HIP method. In recent years, there has been active development of equipment that operates at high temperatures, including high-temperature gas turbines, diesel engines, and MHD power generation, with the aim of improving thermal efficiency, saving fuel, reducing pollution, and reducing weight. However,
The development of these devices is focused on the development of high-temperature structural materials, and the formation of these materials is attracting attention, but conventional heat-resistant metals do not necessarily have sufficient mechanical strength under such high temperatures. From the perspective of conserving heat-resistant metal materials, which are scarce in resources, progress is being made in the development of ceramics made from materials such as Si, A, C, and N, which are relatively abundant on earth, as high-temperature structural materials. Further, the importance of the development of such high-temperature structural materials for use as tools as high-hardness members and as corrosion-resistant materials is similarly recognized, and great interest is being focused. Recently, as a method for manufacturing such ceramic sintered bodies, the HIP method has been used to mold ceramic powder into a predetermined shape using a high-temperature, high-pressure pressurized gas such as Ar gas or _N2 gas, or a pre-sintered body of the ceramic powder is used. A method has been proposed to increase the density by acting on a sintered body. In this HIP method, a ceramic molded body or pre-sintered body is placed in a high-pressure container with a built-in heating device, and a pressure of about 1000 atmospheres and a pressure medium gas at a temperature of about 1500°C are applied to this body. It is sintered by the action of temperature and pressure. Since the sintered body thus obtained is subjected to isotropic pressure, it has an excellent property of having approximately the same strength in all directions. However, when this HIP method uses Ar gas as a pressure medium and a heating medium, Ar gas is expensive, so after HIP processing, the Ar gas in the high pressure container is always collected in a gas holder, and therefore the high pressure It is unavoidable that air gets mixed in when the container is opened and closed to load and take out the molded object, and that various impurity gases generated by the decomposition of oil and other substances adhering to the molded object are unavoidable. The purity of the Ar gas gradually decreases, leaving the problem of contamination of the compact by impurity gases such as oxygen and carbon dioxide contained in the Ar gas. The impurities in this Ar gas are about 200 ppm at most, but under a high pressure of 1000 atmospheres, even a simple calculation shows that the absolute amount of impurities is 20% at normal pressure.
This corresponds to that of Ar gas, and since the surface of the molded body or pre-sintered body is extremely activated at high temperatures of 1500°C or higher, even trace impurities tend to react with the surface of the molded body or pre-sintered body. situation. In particular, oxygen as an impurity is the most problematic, and even if there are several tens of ppm of oxygen, a contamination layer of several tens of micrometers, such as an oxide layer or a decomposition layer, will be formed on the surface of the sintered body, and the sintering Physical properties will be significantly reduced. Therefore, unless the problem of contamination of the sintered body due to impurities is solved, it will be difficult to put the sintering technology of the sintered body using the ArHIP method into practical use. On the other hand, one way to solve the problems of the HIP method is to bury ceramic powder in a pre-made mold inside a HIP capsule filled with secondary pressure medium particles, and then charge the capsule into a HIP furnace. There is a method of performing HIP treatment under a primary pressure medium gas atmosphere at high temperature and pressure. This method of consolidation using a secondary pressure medium is different from the normal HIP method that does not use a secondary pressure medium, because the mold itself filled with ceramic powder is embedded in a capsule filled with secondary pressure medium particles. , there is no opportunity for impurities in the HIP furnace to come into contact with the surface of the compact or pre-sintered compact, and the problem of contamination of the sintered compact due to impurities is temporarily prevented. When enclosing a material and performing HIP processing, the secondary pressure medium will also be compacted due to the HIP conditions (temperature, pressure) for compaction, and after processing, it is difficult to take out the object inside. Not only is this extremely difficult, but when the pressure medium is to be reused, it must be re-pulverized, which is complicated. Therefore, it is desirable to use ceramic materials that are difficult to sinter as the secondary pressure medium, but these materials are usually made into ultrafine powder of several micrometers due to the manufacturing process, and it is difficult to use this material for HIP processing. If used, the filling rate is poor and extreme shrinkage occurs during HIP, often resulting in capsule breakage. In view of the above-mentioned facts, the present invention aims to improve the method for producing high-density sintered bodies by the HIP method, and is intended to improve the method of producing high-density sintered bodies by HIP, and to achieve a method that does not cause capsule breakage during HIP treatment, provides smooth processing effects, and can be carried out within the HIP furnace. The object of the present invention is to provide a method for manufacturing a high-density ceramic sintered body that is not affected by impurities. Therefore, the method of the present invention, which is suitable for such purpose, is a method for producing a high-density ceramic sintered body by subjecting a preformed or presintered ceramic porous body to HIP treatment, in which the ceramic porous body is It is characterized by embedding it in condensed powder and once press-molding it into a simple-shaped block, placing the block in a HIP treatment capsule and sealing it, and subjecting it to a predetermined HIP treatment. It is something. Hereinafter, specific embodiments of the method of the present invention will be explained in more detail. First, the basic structure of the method of the present invention is to first form a block with a simple shape by embedding a preformed or presintered ceramic porous body in a hard-to-sinter powder and press-forming it. The second step is to put the block into a normal HIP capsule, seal it, and perform HIP treatment. The preformed or presintered ceramic porous body used in the first step of the present invention is
Ceramic powders such as oxides and nitrides such as Si, A, and Mg, or powders containing sintering aids such as Y ₂ O ₃ and MgO are preformed by compression molding, injection molding, etc. It is obtained by pre-sintering the sintered material using _N2 gas atmosphere sintering method, hot press sintering method, etc. In addition, the hard-to-sinter powder used to embed the preformed or pre-sintered ceramic porous body includes BN, Si ₃ N ₄ , A ₂ O ₃ , TiO ₂ , ZrO ₂ , etc. The powder is appropriately selected from among the difficult-to-sinter powders according to the type of porous ceramic body and HIP conditions. In order to embed preformed or presintered ceramics in these hard-to-sinter powders and press-form them, a rubber mold is usually used to maintain the shape of the hard-to-sinter powders. A mold or the like made of a flexible sheet material is used, the mold is filled with hard-to-sinter powder, the ceramic porous body to be treated is buried in the mold, and cold isostatic pressure treatment or the like is performed. For this pressure forming, it is sufficient to press the hard-to-sinter powder and the porous ceramic body with a pressure suitable for forming a block, and there are not necessarily strict conditions such as temperature and pressure, but the work process For ease of use, compaction is performed at room temperature for 2 to 3 minutes at ^{approximately} 1000 to 4000 kg/cm2, and the hard-to-sinter powder is compacted at least 50 to 80 kg/cm2.
% relative density is desirable, and since the cold isostatic pressing process uses isostatic pressure, the internal preformed body or preliminary sintered body is less likely to be damaged during pressure forming, so it is most effective. This is a pressure treatment. The types and characteristics of the hard-to-sinter powder, which is the secondary pressure medium in which the ceramic porous body is embedded, will be exemplified below.

[Table] As is clear from the above table, the apparent density of BN is extremely low if it is simply filled with hard-to-sinter powder.For example, the apparent density of BN is 17.7% in terms of relative density.
It can be seen that the amount of deformation of the capsule would be extremely large if this was subjected to HIP processing as it is. Next, as mentioned above, the hard-to-sinter powder material containing the blocked ceramic porous body is
It is loaded into a HIP processing capsule and moved to the second HIP processing. The capsule in this case is usually preferably made of a gas-impermeable material such as glass used in HIP processing, and is required to be large enough to accommodate the block. The capsule loaded with the blocks is then subjected to HIP treatment, but prior to the HIP treatment, the air remaining in the capsule is removed by degassing and the capsule is sealed. In addition, during deaeration, since the hard-to-sinter powder which is the secondary pressure medium has already been densified to some extent by the cold isostatic pressure treatment, there is no particular fear of scattering. HIP processing is performed under an inert gas atmosphere such as Ar gas or _N2 gas, but the HIP temperature is 1500
℃ or higher, preferably 1700℃ or higher, and the higher the temperature, the easier the densification becomes. Therefore, although there is no particular upper limit for the HIP temperature, it must naturally be below the decomposition temperature of ceramics, and this decomposition temperature also increases as the HIP pressure increases, but at least the decomposition temperature at the pressure during HIP treatment It is preferable to carry out the process at a temperature lower than 100°C. Next, it is best to carry out HIP at a pressure of 500 atm or more; if it is less than 500 atm, the HIP process will take a long time and the amount of decomposition reaction of the ceramic will increase in proportion to the time, resulting in a weight loss of the sintered body. Not only that, but it becomes difficult to achieve high density itself. Therefore, the HIP pressure should be at least 500 atm, preferably 700 atm.
It is desirable that the pressure be above atmospheric pressure. On the other hand, the higher the HIP pressure, the more likely it is to suppress the decomposition reaction of ceramics and achieve higher density. , as the HIP processing equipment becomes larger, it becomes impractical. Therefore, practically, it is desirable to perform HIP treatment at a pressure of up to 2500 atmospheres. Moreover, it is preferable that the HIP treatment time is in the range of 20 minutes to 5 hours. It goes without saying that the above-mentioned HIP treatment temperature, pressure, and time should be appropriately selected depending on the type, size, etc. of the ceramic porous body to be treated. Note that the hard-to-sinter powder, which is the secondary pressure medium, is peeled off by appropriate means after the HIP treatment. As described above, the ceramic porous body subjected to the HIP treatment becomes a high-density sintered body with a relative density of 98% or more. As described above, the method of the present invention involves embedding a preformed or presintered ceramic porous body in hard-to-sinter powder, forming it into a block by pressure forming, and subjecting it to HIP treatment. Since the degree of shrinkage of the capsule can be increased compared to when it is molded immediately from powder, the amount of shrinkage of the capsule is small, and therefore there is no breakage of the capsule, and there is no HIP failure, as well as processing efficiency. It is possible to obtain a high-density ceramic sintered body that is smooth and has uniform strength in all directions. In addition, in the method of the present invention, a preformed body or a presintered body is preformed into a block into a simple shape by pressure molding and subjected to HIP treatment, so that molding is easy and the capsule for HIP treatment can also be a simple shape block. Therefore, it is easy to manufacture, and degassing and sealing during HIP processing can be easily performed, so a sintered body with a complicated shape can be easily manufactured. Furthermore, according to the method of the present invention, the preformed body or presintered body is formed into blocks and subjected to HIP treatment, so that contamination of the surface of the sintered body by impurity gases such as oxygen contained in Ar gas is avoided. The method of the present invention is extremely effective as a method for producing high-density ceramic sintered bodies, as it has the advantage of not causing any sintering.

Claims (1)

[Scope of Claims] 1. A method for producing a high-density ceramic sintered body by subjecting a preformed or pre-sintered ceramic porous body to hot isostatic pressing, wherein the ceramic porous body is difficult to sinter. A simple-shaped block is formed by embedding it in a ceramic powder and press-molding it, and then inserting and sealing the block into a capsule for hot isostatic pressing. A method for producing a high-density ceramic sintered body, comprising hot isostatic pressing in a high-temperature, high-pressure gas atmosphere at the sintering temperature of the porous body. 2 The hard-to-sinter powder is BN, Si ₃ N ₄ , A ₂ O ₃ ,
The method for producing a high-density ceramic sintered body according to claim 1, wherein the powder is at least one kind of powder selected from the group consisting of TiO ₂ and ZrO ₂ . 3. The method for producing a high-density ceramic sintered body according to claim 1 or 2, wherein the hot isostatic pressing temperature is 1500°C or higher. 4. A method for producing a high-density ceramic sintered body according to any one of claims 1 to 3, wherein the hot isostatic pressing treatment pressure is 500 to 2,500 atmospheres. 5. A high-density ceramic sintered body according to any one of claims 1 to 4, wherein a porous ceramic body is embedded in hard-to-sinter powder and then cold-press-formed. Production method.