JPH01145104A - Manufacture of high-density sintered body - Google Patents

Abstract

PURPOSE:To simplify a process by a method wherein processes which have been separated independently from each other so far as various processes of evaporation or ultra-critical extraction from a cast molded body and drying of a film on the surface of a molded body are completed in a process by applying an ultra-critical extraction method to the process. CONSTITUTION:Metallic or ceramic powder is made slurry by dispersing the same into a dispersant obtained by adding a dispersing medium to extractable substance by an ultra-critical fluid and a molded body containing the dispersing medium or the dispersant is obtained by performing cast molding of the slurry. A film is formed by applying the slurry to the whole of the surface of the molded body. An extractable ingredient within the dispersing medium to be contained into the molded body and film is removed through extraction by the ultra-critical fluid and a porous molded body with the film is formed. Then the film is made a film imprevious to gas by heating the porous molded body with the film. Hot isotropic pressurizing treatment of the molded body with the film which has been made a film imprevious to gas is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a method for obtaining a high-density sintered body from metal powder or ceramic powder.

[Prior art] Ceramic powder is made into a slurry using water as a dispersion medium, and after adjusting the properties of the slurry by adding a deflocculant, etc., this slurry is cast into a plaster mold, and a portion of the water is absorbed into the plaster mold. The most common method is to solidify the slurry to form a molded body, and then dry the molded body by air drying, humidity-controlled heating, etc. to remove the dispersion medium and create a molded body that can be subjected to the sintering process. It is well known as a cast molding method.

Various types of dispersion media are used, but heating evaporation is generally adopted as a means for removing them, and if the dispersion medium is paraffin, heating pyrolysis is used, but both methods are long-term. The problem is that it takes time.

On the other hand, hot isostatic compression treatment is known as an effective method for converting a porous molded body obtained by various molding methods such as cast molding, plastic molding, or pressure molding into a high-density sintered body.

This method is generally conducted at a temperature of about 500 to 2200°C and a temperature of about 100°C.
Sintering is progressed while compressing the molded body isotropically using gas under the condition of ~3000 kg/cn (-G).

In carrying out this sintering, it is necessary to perform a sealing treatment on the molded body in advance so that the gas pressure is applied to the pores of the molded body without allowing gas to enter the pores of the molded body.

An effective method thereof is the method described in Japanese Patent Publication No. 59-35870 or West German Patent No. 3403917.

Among these, the technology described in the former is a method that uses a porous molded body of silicon nitride at a temperature below the sintering temperature of silicon nitride (
an inner porous layer of a first material comprising a high melting point glass, a high melting point glass-forming substance or a high melting point metal substance that can be added to the membrane impermeable to high pressure gas at a temperature of 1300 to 1600 °C), and the temperature in the inner porous layer The temperature is also low (60
After applying an outer porous layer of a second material consisting of a low-melting glass or a low-melting glass-forming substance that can be converted into a membrane impermeable to high-pressure gases at temperatures between 0 and 1100°C, the porous compact is first subjected to a degassing treatment. The outer porous layer is then subjected to a heat treatment at a temperature necessary to form a high-pressure gas impermeable membrane, but at a temperature that maintains the inner porous layer's porous nature. After heating to the temperature required to form a membrane impermeable to high-pressure gas while maintaining the gas pressure outside these layers greater than the gas pressure inside the layers, the porous compact is heated to a temperature of 1700 to 1800°C. , pressure 2000
It discloses a technique of performing hot isostatic pressurization at ~3000 atm.

To form a porous layer on the surface of a porous compact, first, powder is dispersed in water to create a slurry, the porous compact is immersed in this slurry, and then this is dried. It is necessary to repeat the time-consuming drying operation twice to form the two outer porous layers.

On the other hand, West German Patent No. 3403917 discloses a method for densifying porous ceramics having a complicated shape, which includes the following seven steps. That is, a. A first capsule layer is formed by immersing the preformed porous ceramic molded body in a suspension in which a substance containing no sintering aid is dispersed in a solvent.

b9 Evaporate the solvent.

C0 The thus obtained molded body is immersed in a second suspension in which a sinterable material or a substance containing a plurality of sintering aids is dispersed in a solvent to form a second capsule layer. .

d. Evaporate the solvent.

e. The molded body thus obtained is heated to a high temperature, f'j1. Sinter sufficiently in a protective gas atmosphere.

f, Mt A molded body having a densely sintered surface is subjected to hot isostatic heat treatment by a known method.

g1 Both capsule layers are mechanically removed.

That is what it is.

In this case as well, two porous layers are formed on the surface of the porous molded body.
In order to form a layer, the operation of evaporating the solvent was repeated twice. Naturally, when forming porous layers, it is necessary to repeat the evaporation operation as many times as the number of layers to be formed.

In this way, the above-mentioned general casting method and the
Publication number 9-35870 or West German patent 3403917
A high-density sintered body of metal powder or ceramic powder can also be manufactured by applying the high-density sintered body manufacturing method disclosed in . FIG. 2 is a process diagram showing this manufacturing method.

That is, this method involves the steps of obtaining a molded body by casting a slurry of metal powder or ceramic powder, removing the dispersion medium from this molded body by evaporation, etc., immersing the molded body in the slurry, and then drying it. Film formation in which the operation is repeated until a predetermined thickness is reached to form a first layer film, and the molded body is further immersed in a slurry ~ and then the operation of drying is repeated until a predetermined thickness is reached to form a second layer film. It consists of a drying process, an impermeable film forming process of heating the membrane, and a hot isostatic compression process.

[Problems to be Solved by the Invention] However, the above-mentioned method for producing a high-density sintered body has the disadvantage that it is necessary to repeat similar operations four times in order to form a film. Similar operations are repeated too many times, which not only makes the operations themselves complicated, but also requires separate processing over a long period of time.

This invention was made to solve the problems of the prior art, and aims to provide a method for manufacturing a high-density sintered body that can simplify the process.

[Means and effects for solving the problems] This invention has the following features:
By applying the supercritical extraction method, it is possible to complete the processes that were previously separated, namely evaporation of the dispersion medium from the cast molded body or supercritical extraction, and drying the film on the surface of the molded body, in one step. This is what I did.

Specifically, (A) metal powder or ceramic powder is dispersed in a dispersion medium in which a dispersant is added to a substance extractable by a supercritical fluid to form a slurry, and this slurry is cast to form a dispersion medium and a dispersion medium. A step of obtaining a molded body containing a dispersant, (B) dispersing metal powder or ceramic powder in a dispersion medium in which a dispersant is added to a substance extractable by a supercritical fluid to form a slurry, and using this slurry as a slurry of the molded body. (C) extractable components in the dispersion medium contained in the molded body and the membrane are extracted and removed by the supercritical fluid to form a porous molded body with a membrane; (D) heating the porous membrane-attached molded body to make the membrane a gas-impermeable membrane; and (E) hot isostatic heating of the membrane-attached molded body with the membrane made to be a gas-impermeable membrane. This is a method for producing a high-density sintered body of metal powder or ceramic powder, which consists of 5 steps of applying pressure treatment.

In the present invention, metal powder or ceramic powder refers to 2% N
1-98% Fe powder, 5UA316 powder.

Metal powders such as stellite powder, ceramic powders such as alumina, silicon carbide, silicon nitride, and zirconia.

It refers to powders including metal and ceramic composite powders such as tungsten carbide-cobalt and titanium nitride-nickel.

There are no particular restrictions on the supercritical fluid used here, but substances such as carbon dioxide, ethane, ethylene, and monochlorotrifluoromethane are preferred because they are easy to handle and have a critical temperature close to room temperature.

Substances that can be extracted by supercritical fluid, which is the main part of the dispersion medium, include methyl alcohol, ethyl alcohol, n-10-vinyl alcohol, i-propyl alcohol, n-butyl alcohol, i-butyl alcohol, and S-butyl alcohol. Examples include lower alcohols such as butyl alcohol and t-butyl alcohol, acetone, stearic acid, stearyl alcohol, and paraffin.

As the mold used for casting in step (A), if solidification of the slurry is achieved by absorbing the dispersion medium into the mold, a liquid-absorbing mold such as gypsum or porous resin is used.

Separately, when solidifying the slurry by freezing the dispersion medium, a mold made of a non-liquid absorbing material is used.

In order to achieve this purpose, materials such as wood, hard rubber, aluminum, stainless steel, and steel may be selected as appropriate in addition to tool steel.

The slurry concentration in this step A is 40 to 7 in terms of powder concentration.
It is preferable to set the concentration to 5% by volume. Outside this range, for example, if it is less than 40% by volume, the molded product after removing the dispersion medium tends to have a low density and cannot withstand handling. If it exceeds the volume percentage, the fluidity will be poor and there will be a tendency that it will not be possible to fill the mold properly.

In the present invention, it is necessary to add a dispersant to the dispersion medium in a range of more than 0.5% and less than 20%.

This effectively improves the fluidity of the slurry. As a dispersant, glycerin trioleate, natural fish oil 1 synthetic surfactant, benzenesulfonic acid,
Oleic acid, methyloctadiene, beeswax, stearic acid, etc. can be used.

The amount of dispersant added varies depending on the type of dispersant, but
It is desirable to keep the proportion in the total dispersion medium within the range of 20%. Even if the dispersant proportion exceeds 20%, there is no difference in the dispersion effect; rather, supercritical carbon dioxide This is undesirable as it increases the amount of substances that cannot be extracted and removed.

Moreover, if it is less than 0.5%, the viscosity of the slurry increases, making it difficult to cast the slurry.

The slurry in step (B) has a powder concentration of 10 to 75% by volume. In this case, too, if the slurry concentration is less than 10% by volume, the dispersion medium will need to be coated many times, which is time-consuming, while if it exceeds 75% by volume, the fluidity of the slurry will be poor and it will be difficult to form a uniform film. .

Also in this case, as in the case of step (A), it is necessary to add a dispersant to the dispersion medium. This effectively improves the fluidity of the slurry.

The film may be a single layer if it can be easily removed from the sintered body after the step (E), but if this removal operation is not easy,
Alternatively, if deterioration of the surface of the sintered body due to reaction with the inside becomes a problem, two layers are used.

When forming two layers, the first layer is made of an inert material that is difficult to sinter, and the second layer is made of an easily sintered material that can become a gas-impermeable film, but in order to make it easier to create a gas-impermeable film. The film may be composed of two layers having different sinterability.

Furthermore, a layer made of an inert substance may be formed between the molded body and these two layers to form a three-layer structure.

Step (C) is carried out in one step to extract the extractable components in the dispersion medium contained in both the molded body and the membrane.

Furthermore, step (D) is carried out at normal pressure or vacuum,
The atmosphere is determined depending on the material of the compact, and for example, in cases where thermal decomposition is a problem, such as silicon nitride, the atmosphere may be pressurized with nitrogen gas.

In the case of metal, an inert gas such as argon or nitrogen may be used, and hydrogen may be added to this if necessary.

In the case of non-oxide ceramics, it is desirable to carry out in an inert gas atmosphere, but in the case of oxide ceramics, air may be used.

Prior to performing step (D), a step may be added as necessary to heat and remove residual dispersion medium that could not be removed in step (C), or during step (D), residual dispersion medium may be removed by heating. The dispersion medium may also be removed.

The gas-impermeable membrane formed in this way is selected from materials that plastically deform while maintaining the gas-impermeable membrane following the shrinkage of the compact during hot isostatic pressing in step E. use.

[Embodiments of the invention] Hereinafter, this invention will be specifically explained based on Examples.

5jiN4 powder 92 parts by weight, Y2O3 powder 6 parts by weight, A
12,032 parts by weight, 20 parts by weight of paraffin (melting point 68°C), and 3 parts by weight of oleic acid as a dispersant (13% based on the total dispersion medium) were placed in a closed tank and stirred at 100°C for 2 hours to form a slurry. . Then, the pressure inside the tank was reduced to degas the slurry.

On the other hand, a mold made of stainless steel with a flat cavity of 70mm x 100mm x 10mm and equipped with cooling water pipes was cooled with cooling water at 20°C, and the slurry was poured into this mold at 4kg/cnf (gauge pressure). A molded body was formed by casting.

Then 84 parts by weight of Si3N4.12 parts by weight of Y20
35 parts by weight of mixed powder consisting of 3.4 parts by weight of Al2O3 was mixed with 65 parts by weight of i-propyl alcohol, immersed in the resulting slurry, held in air for 10 minutes, and immersed again for a total of 5 times. This was repeated to form a two-layered film.

Next, this compact was extracted with supercritical carbon dioxide at a pressure of 200 kg/cnt (gauge pressure) and a temperature of °C for 1.5 hours, and it was found that the weight was equivalent to the weight of the Habo powder. confirmed.

This molded body was set in a hot isostatic press apparatus, and subjected to vacuum degassing, making the porous membrane impermeable, and hot isostatic press treatment. FIG. 1 is a diagram showing the transition of heating and pressurizing conditions in the series of processing steps. That is, first, the vacuum degassing operation is
The porous membrane was made impermeable by holding it at 1000°C until it reached 0.2 Torr.
/co ((gauge pressure) held in nitrogen atmosphere for 10 minutes,
In addition, hot isostatic pressure treatment is performed at 1750℃ and 2000kg.
The sample was maintained in a nitrogen atmosphere of /Cr1l (gauge pressure) for 2 hours.

After cooling, the film was removed by sandblasting, and the theoretical density of the sintered body thus obtained was as high as 99.7%.

[Effects of the invention] This invention forms a molded body by casting a slurry of metal powder or ceramic powder, and then forms a film on the surface of the molded body to extract and remove extractable components. By using supercritical extraction, the steps of heating the body to make the membrane gas-impermeable and then subjecting it to hot isostatic pressure treatment can be performed in one step, which simplifies the process. It has the effect of

Furthermore, in the past, the solvent used during film formation was removed by evaporation, which caused shrinkage of the film, making it difficult to suppress the occurrence of cracks. The application of extraction has the effect that cracks do not occur and it becomes easier to obtain a healthy film.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the transition of heating and pressurizing conditions for a molded body in an embodiment of the present invention, and FIG. 2 is a process chart showing a method for manufacturing a high-density sintered body by a combination of conventional techniques.

Claims (3)

[Claims] (1) (A) Metal powder or ceramic powder is dispersed in a dispersion medium in which a dispersant is added to a substance that can be extracted with a supercritical fluid to form a slurry, and this slurry is cast and molded to form a dispersion medium and a dispersant. (B) Dispersing metal powder or ceramic powder in a dispersion medium containing a substance extractable by a supercritical fluid and adding a dispersant to form a slurry, and applying this slurry to the entire surface of the molded body. (C) a step of extracting and removing extractable components in the dispersion medium contained in the molded body and the membrane with the supercritical fluid to form a porous molded body with a membrane; D) heating the porous membrane-attached molded body to make the membrane a gas-impermeable membrane; and (E) hot isostatic pressing of the membrane-attached molded body that made the membrane gas-impermeable. 1. A method for producing a high-density sintered body of metal powder or ceramic powder, comprising five steps of applying. (2) The metal powder according to claim 1, wherein the substance extractable by the supercritical fluid that is the main part of the dispersion medium in steps (A) and (B) is paraffin. Or a method for producing a high-density sintered body of ceramic powder. (3) Claim 1, characterized in that the amount of the dispersant used in steps (A) and (B) is in the range of more than 0.5% and less than 20% of the total dispersion medium. A method for producing a high-density sintered body of metal powder or ceramic powder as described in 2.