JPH0848571A - Embedding powder for firing of alumina ceramics, its production and production of alumina ceramics using the same - Google Patents

Abstract

PURPOSE:To obtain embedding powder for firing giving high strength, high toughness and high density SiC fiber reinforced Al2O3 ceramics by wet-mixing Al2O3 with a prescribed amt. of SiC and preburning the resultant mixture in an atmosphere of inert gas. CONSTITUTION:An Al2O3-based powdery mixture contg. 5-50vol.% SiC and <2vol.% SiO2 is prepd. by wet mixing and preburned once or more for >=1min each in an atmosphere of inert gas or nitrogen or in vacuum at 1,000-2,000 deg.C to obtain the objective embedding powder for firing of SiC fiber reinforced Al2O3 ceramics. It is preferable that the same components as sintering aids contained in ceramics to be fired are incorporated by <20vol.% in total into the embedding powder and the water content of the powder is regulated to <=0.1vol.%. The objective SiC fiber reinforced Al2O3 ceramics is produced by sintering using the embedding powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to firing of Al ₂ O ₃ -based ceramics, and more specifically, SiC having high strength and high toughness.
Filling powder for firing fiber-reinforced Al ₂ O ₃ -based ceramics, method of manufacturing the filling powder, and use of this filling powder for firing S
The present invention relates to a method for producing iC fiber reinforced Al ₂ O ₃ based ceramics.

[0002]

_2. Description of the Related Art Ceramics obtained by adding SiC whiskers to Al ₂ O ₃ are disclosed in US Pat. No. 4,543,345 as a material having high strength and high toughness. But the above S
Ceramics to which iC whiskers are added are manufactured by hot pressing, and it is difficult to manufacture complicated shapes with this method, and it is also difficult to manufacture large ones. Therefore,
Atmospheric pressure sintering has been attempted to solve this problem. For example, Terry N. Tiegs et al. J. Am. Ceram. Soc73
[5] (1990) 1440-1442, we tried atmospheric pressure sintering while changing the aspect ratio of the whiskers and the amount of sintering aid. Also,
Young-Wook Kim et al., J. Mat. Sci 26 (1991) 1316-1320, tried atmospheric pressure sintering by using a special method of precipitating aluminum hydroxide on a green body before sintering.

[0003]

Generally, in the case of fiber reinforced ceramics in which SiC whiskers are added to Al ₂ O ₃ , the SiC whiskers are entangled three-dimensionally in the atmospheric pressure sintering method, and the SiC whiskers are oxidized and evaporated. It is very difficult to obtain a sintered body that is dense enough to prevent sintering. Therefore, in the case of the pressureless sintering method, the amount of SiC whiskers added may not be sufficient, or J.Am.Ceram.Soc73 [5] (1990) 1
Like 440-1442, it is the current situation that sufficient strength and toughness cannot be obtained because the aspect ratio of the SiC whiskers is extremely small or the amount of sintering additive added is too large.

The present invention is directed to the densification of ceramics during atmospheric pressure sintering in the process of producing fiber-reinforced Al ₂ O ₃ -based ceramics of high strength and high toughness by atmospheric pressure sintering and hot isostatic pressing. It is an object of the present invention to provide a filling powder and a method for producing the same for more effectively performing the above.

[0005]

[Means for Solving the Problems] As a result of intensive studies conducted by the present inventors on the SiC fiber-reinforced Al ₂ O ₃ -based ceramics atmospheric pressure sintering method, as a result, It has been found that by burying and sintering, densification can be effectively promoted and high strength and high toughness ceramics can be manufactured.

The gist of the present invention is (1) SiC: 5 to 50 mass%, Si
This is a SiC fiber-reinforced Al ₂ O ₃ -based ceramic filling powder made of a mixed powder containing Al ₂ O ₃ as a main component, which does not contain O ₂ or is less than ₂ mass% at most.

(2) The SiC fiber-reinforced Al ₂ O ₃ -based ceramic filling powder according to (1) above, which contains less than 20 mass% of the same components as the sintering aid contained in the ceramic to be fired. is there.

(3) The filling powder for firing SiC fiber reinforced Al ₂ O ₃ based ceramics according to (1) or (2) above, which contains water in an amount of 0.1 mass% or less.

(4) After wet mixing, baking is performed once or more for 1 minute or more in an inert gas atmosphere at 1000 ° C. or more and 2000 ° C. or less, or in a nitrogen atmosphere or in a vacuum, and the above (1), (2 )
Alternatively, it is a method for producing a filling powder for firing SiC fiber-reinforced Al ₂ O ₃ based ceramics according to (3).

(5) The SiC described in (1), (2) or (3) above.
Use fiber-reinforced Al ₂ O ₃ based ceramic the firing filling powder is a manufacturing method of the SiC fiber-reinforced Al ₂ O ₃ based ceramics sintered.

[0011]

[Action] and SiC fiber-reinforced Al ₂ O ₃ based ceramic in the present invention are Al ₂ O ₃ based ceramics containing 5～30Mass% of SiC whiskers, 3 in order to densify Sintered
It contains a sintering aid of about 30 mass%. In addition, TiC, WC, VC, TiN, TiB ₂ and other carbides, nitrides,
It may be one to which particles such as boride are added.

The role of the filling powder is to control the atmosphere around the ceramic compact to be fired.
When firing ceramics, the influence of the atmospheric gas in the sintering furnace is very sensitively reflected and affects the sintering behavior of the ceramics. Therefore, the ceramic compact to be fired is embedded in the filling powder of the present invention and sintered to accelerate the sintering.

There are mainly three mechanisms by which the filling powder promotes sintering. The first point is to prevent the adverse effects of the released gas from the crucible and the released gas from the heater during sintering by filling powder. Therefore, by embedding the ceramic compact in some powder and sintering it, adverse effects can be removed and sintering can be promoted.

The second point is that SiC in the ceramic compact is
It is to suppress oxidative evaporation of fibers. At high temperatures such as the sintering temperature, the oxidation behavior of SiC fiber varies depending on the oxygen potential, which affects the densification behavior. Therefore, it is important to control the oxygen partial pressure. To create the proper atmosphere, SiC is 5 to 50 mass% and SiO ₂ is ₂ mass.
Filling powder composed of a mixed powder containing Al ₂ O ₃ as a main component, which is contained in an amount of less than 0.1%, is most effective.

The reason for limiting the content of SiC to 5 to 50 mass% is that if it is less than 5 mass%, the generation of SiO gas due to the oxidation and evaporation of SiC in the filling powder is insufficient, and the oxidation and evaporation of SiC from the sintered body becomes insufficient. Cannot be suppressed, and if the content exceeds 50 mass%, SiO
This is because the excessive generation of gas makes it difficult to proceed with sintering. The reason for limiting the content of SiO ₂ to less than ₂ mass% is
Since SiO ₂ is a source of SiO, if it exceeds ₂ mass%
This is because the SiO content becomes excessive and inhibits sintering. Also,
Moisture in the filling powder also raises the oxygen potential more than necessary, so the water content in the filling powder is limited to 0.1 mass% or less.

The third point is to suppress the evaporation of the sintering aid. Generally, in order to densify SiC fiber reinforced Al ₂ O ₃ based ceramics by pressureless sintering, an oxide having a low melting point is added as a sintering aid. However, these oxides have a high vapor pressure at the sintering temperature and may evaporate during the sintering to fail to serve as a sintering aid. Therefore, as in the present invention, by burying and sintering a ceramics compact that is fired in a filling powder containing less than 20 mass% of the same component as the sintering supplement, the sintering aid component around the compact is sintered. The vapor pressure is increased to suppress evaporation of the sintering aid from the compact. The reason for limiting the content to less than 20 mass% is that if the content is more than 20 mass%, the amount of evaporation from the filling powder will be too much and sintering will be hindered.

The method for producing filling powder according to the present invention is a method in which filling powder produced by wet mixing is left in an atmosphere of an inert gas such as argon at 1000 ° C. or more and 2000 ° C. or less such as argon or in a nitrogen atmosphere or in a vacuum for 1 minute or more. By performing baking once or more, filling powder having an excellent effect is produced. As a result, the water content in the filling powder can be reduced to 0.1 mass% or less, and the generation of unnecessary gas generated when heating to a high temperature can be prevented. For that purpose, it is necessary to air-bake at a temperature of 1000 ° C or higher, but if it exceeds 2000 ° C, the filling powder itself will be sintered, which is not good.

The manufacturing method of the above-mentioned SiC fiber-reinforced Al ₂ O ₃ based ceramic the firing filling powder of SiC fiber-reinforced Al ₂ O ₃ based ceramics to be used may be a conventional pressureless sintering method, for example, sintered The temperature is 1500 to 1900 ° C, and the operation is performed in a nitrogen atmosphere.

[0019]

EXAMPLES Examples of the present invention will be described below.
First, SiC whiskers, other additive particles, sintering aids,
After wet mixing Al ₂ O ₃ powder and molding binder,
Spray dried, press molded and then in nitrogen at 800 ° C
Was heated to remove the binder to obtain a molded body. next,
Put the filling powder shown in Table 1 into a graphite container, bury the molded body in it, and sinter under normal pressure in a nitrogen atmosphere at 1500 ° C to 1900 ° C. Pressed (HIP). After that, the density of each sintered body,
The bending strength was measured. The results are shown in Table 2. The density was measured by the Archimedes method, and the bending strength was measured by a 3-point bending test in accordance with JIS. Further, as a comparative example, the same measurement as that of the example was carried out for the one embedded in the filling powder of the comparative example shown in Table 1 and sintered. The results are also shown in Table 2.

[0020]

[Table 1]

[0021]

[Table 2]

Inventive example 1 has the upper limit of the amount of SiC in the filling powder, and inventive example 4 has a value close to the lower limit, both of which are successfully densified by pressureless sintering and further theoretical density by HIP treatment. The density is close to 100 (%) and the strength is about 780N.
Higher than / mm ² Further, although 2 and 3 of the present invention example are the same molded body, since the filling powder of 2 of the present invention example contains the same component as the sintering aid, the density is slightly higher than that of 3 of the present invention example. Is high. In addition, in Invention Example 5, although the filling powder is wet mixed and the heat treatment after drying is performed in a vacuum, a high sintered density is obtained.

On the other hand, in Comparative Example 1, since the amount of SiC in the filling powder is too small, the sintered density cannot be sufficiently increased.
The sintering density does not increase because the amount of O ₂ is too large. Further, in Comparative Example 3, since the amount of SiC in the filling powder is too large, the sintered density is not sufficiently increased. In Comparative Example 4, since the filling powder was not subjected to the heat treatment after wet mixing and drying, the moisture content in the filling powder was high and the sintering density did not increase, and in Comparative Example 5, the heating treatment temperature of the filling powder was too low. Low sintering density. Comparative Example 6
Since the heating temperature of the filling powder was too high, the filling powder was sintered during the heating treatment and could not be used as the filling powder. In Comparative Example 7, no filling powder was used during sintering, and the sintered density did not increase.

[0024]

As is apparent from the above description,
According to the present invention, since the filling powder contains an appropriate amount of SiC, SiO ₂ , and a sintering aid to reduce the amount of water, oxidative evaporation of SiC from the compact is prevented during normal pressure sintering, It is possible to obtain SiC fiber reinforced Al ₂ O ₃ based ceramics with high strength and high toughness and high density.

Claims (5)

[Claims] 1. A SiC fiber-reinforced Al ₂ O, characterized in that it is composed of a mixed powder containing Al ₂ O ₃ as a main component, which is SiC: 5 to 50 mass% and does not contain SiO ₂ or is less than ₂ mass% at most. Filling powder for firing ₃ series ceramics. 2. The filling powder for firing SiC fiber-reinforced Al ₂ O ₃ based ceramics according to claim 1, which contains less than 20 mass% of the same components as the sintering aid contained in the ceramic to be fired in total. 3. The filling powder for firing SiC fiber reinforced Al ₂ O ₃ based ceramics according to claim 1 or 2, which contains water in an amount of 0.1 mass% or less. 4. After wet mixing, baking is performed once or more for 1 minute or more in an inert gas atmosphere at 1000 ° C. or more and 2000 ° C. or less, or in a nitrogen atmosphere or in a vacuum, at least once. 2. The method for producing a filling powder for firing SiC fiber reinforced Al ₂ O ₃ based ceramics according to 2 or 3. 5. A method according to claim 1, wherein the SiC fiber-reinforced Al ₂ O ₃ based ceramic the firing buried SiC fiber-reinforced, characterized in that sintering using powder Al ₂ O ₃ based ceramics Manufacturing method.