JPH08208317A - Alumina sintered body and method for producing the same - Google Patents

Abstract

(57) [Summary] [Object] To provide an alumina-based sintered body having excellent oxidation resistance at high temperature and further having excellent strength and fracture toughness from room temperature to high temperature, and a method for producing the same. An alumina sintered body containing an alumina mother phase and anisotropic second-phase crystal grains, wherein the alumina mother phase has an average crystal grain size of 10 μm or less, The second phase crystal particles having a length of 20 μm or more are present in an amount of 1 to 20% by volume in the total amount of the sintered body, and the second phase crystal particles are La ₂ O ₃ .11Al ₂ O ₃ , CaO.6Al ₂ O ₃ ，
Those containing at least one of SrO · 6Al ₂ O _3, and BaO · 6Al ₂ O ₃ is desirable. Such an alumina-based sintered body is manufactured by adding the second phase crystal powder as a seed crystal in advance or by setting the average crystal grain size of the raw material powder of La, Ca, Sr, and Ba to 1 to 10 μm. .

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an alumina-based sintered body excellent in high-temperature strength characteristics, high-temperature stability and oxidation resistance and a method for producing the same, and particularly to the aerospace industry, smelting industry, chemical industry. The present invention relates to an alumina-based sintered body of a high temperature resistant structural material used in gas turbines, engine parts and the like, and a method for producing the same.

[0002]

2. Description of the Related Art Alumina-based sintered bodies have hitherto attracted attention as a high temperature resistant structural member because of their excellent environmental resistance and high temperature strength. In addition, various composites have been tried in order to further improve the high temperature strength and fracture toughness. For example, Al ₂ O ₃ -SiC composite, Al
₂ O ₃ -ZrO ₂ composite material, β-Al ₂ O having shape anisotropy
_Three crystal dispersed alumina materials are known (Japanese Patent Laid-Open No. 61-
122164, JP-A-63-139044, JP-A-63-134551 and the like), and such a composite material can improve strength and toughness as compared with a pure alumina sintered body. it can.

[0003]

However, in the above Al ₂ O ₃ —SiC composite, since non-oxide SiC is dispersed in alumina, it is used at a high temperature in an oxidizing atmosphere. In some cases, there was a problem of lack of oxidation resistance.

Al ₂ O ₃ -ZrO ₂ composite material is 9
Since the strength sharply decreases at a temperature near 00 ° C., there is a problem that it is not suitable for use in a state where stress acts at high temperature.

Further, the β-Al ₂ O ₃ -dispersed alumina material disclosed in Japanese Patent Laid-Open No. 63-134551 is a β-Al ₂ O ₃ -dispersed alumina material.
Since the growth rate of Al ₂ O ₃ crystal is low, it is difficult to develop in the alumina base material (about 5 to 10 μm), and there is a problem that the contribution to the improvement of strength and toughness is small. For example, the fracture toughness at room temperature, 3.2~3.4MPa · m ^1/2
It was small.

It is an object of the present invention to provide an alumina-based sintered body which is excellent in oxidation resistance at high temperature and further excellent in fracture toughness and high temperature strength, and a method for producing the same.

[0007]

The inventors of the present invention have found that not only the dispersion of the second phase crystal having an anisotropic shape but also the dispersion of the second phase crystal having an anisotropic shape can be realized in the compounding for simultaneously increasing the room temperature strength, the high temperature strength and the fracture toughness of alumina. As a result of repeated research from the viewpoint that it is important that a certain amount of anisotropic crystals have a certain size or more, it was found that an alumina matrix having an average crystal grain size of 10 μm or less and a length in the major axis direction of 20 μm. The present invention has been found out that the above-mentioned second phase crystal particles can effectively suppress the development of cracks and the deformation due to the sliding of grain boundaries at high temperatures when the amount of the second phase crystal particles is 1 to 20% by volume in the total amount of the sintered body. .

Further, the present inventors have found that the growth of anisotropic second-phase crystal grains is promoted by adding the second-phase crystal as a seed crystal as a raw material powder, and the length in the major axis direction is 20 μm. The inventors have found that they can grow as described above and have completed the present invention.

Further, the present inventor has found that Al ₂ O ₃ powder and L
When a powder containing a specific element of a, Ca, Sr, or Ba is mixed, shaped, and sintered, the average crystal grain size of the powder containing La, Ca, Sr, or Ba is 1 to 10 μm. Found that the nucleation rate of the second phase crystal becomes slower, the diffusion distance of the element atoms forming the second phase crystal becomes shorter, and the growth rate of the second phase crystal in the alumina matrix becomes faster. The present invention has been reached.

That is, the alumina-based sintered body of the present invention contains the alumina matrix and at least La, Ca, Sr, Ba, S.
An average particle diameter of the alumina matrix, which is an alumina-based sintered body containing anisotropic second-phase crystal particles composed of a complex oxide with Al and containing one of m, Nd, and Ti. Is 10 μm or less, and the length in the major axis direction is 20 μm.
The second phase crystal particles of m or more are 1 to 20 in the total amount of the sintered body.
It is present by volume%. In addition, the second phase crystal grains are L
a ₂ O ₃ · 11Al ₂ O ₃ , CaO · 6Al ₂ O ₃ , S
It is desirable to include at least one of rO · 6Al ₂ O _3, and BaO · 6Al ₂ O _3.

Further, the method for producing an alumina-based sintered body of the present invention is the second phase crystal powder comprising a complex oxide containing at least one of La, Ca, Sr, Ba, Sm, Nd, and Ti. , Al ₂ O ₃ powder, La, Ca, S
This is a method in which powder containing at least one of r, Ba, Sm, Nd, and Ti is added, mixed, molded, and sintered.

Further, according to the method for producing an alumina-based sintered body of the present invention, Al ₂ O ₃ powder, La, Ca, Sr and B are added.
A method for producing an alumina-based sintered body, which comprises producing a sintered body composed of an alumina mother phase and second-phase crystal grains by mixing with a powder containing at least one of a, shaping and sintering. The average crystal grain size of the powder containing La, Ca, Sr, and Ba is 1 to 10 μm.

The present invention will be described in detail below. Conventionally, in the β-Al ₂ O ₃ -dispersed alumina disclosed in the above publications, the crystal growth of the anisotropic second phase formed in the alumina base material is controlled by the diffusion of atoms.

The second phase crystal obtained by the ordinary firing method has a length of about 10 μm in the major axis direction. Therefore, the effect of crack bridging and deflection was small, and the contribution to the improvement of strength and toughness was small.

In the alumina-based sintered body of the present invention, the average crystal grain size of the alumina mother phase is controlled to 10 μm or less, and the anisotropic second phase crystal grains having a major axis length of 20 μm or more. The presence of a certain amount of satisfactorily solves the above problems and realizes high strength and high toughness.

That is, the average crystal grain size of the alumina matrix is 10
If it is larger than μm, the strength of the sintered body is lowered, and the strengthening and toughening effects by the anisotropic second phase crystal grains are remarkably lowered. The average crystal grain size of the alumina mother phase is preferably 8 μm or less.

The second phase is La ₂ O ₃ .11Al ₂
O ₃ , CaO · 6Al ₂ O ₃ , SrO · 6Al ₂ O ₃ and BaO · 6Al ₂ O ₃ , Sm ₂ O ₃ · 11Al ₂ O
₃ , Nd ₂ O ₃ .11Al ₂ O ₃ , Al ₂ TiO _{5 and the} like are desirable.

Of these, La ₂ O ₃ .11Al ₂ O
₃ , CaO · 6Al ₂ O ₃ , SrO · 6Al ₂ O ₃ and BaO · 6Al ₂ O ₃ are easy to grow in an anisotropic shape, and the strength and Young's modulus of the crystal itself are high and stable even at high temperature. Therefore, it is a preferable second phase crystal.

Further, in the alumina-based sintered body of the present invention, the second phase crystal grains having a length in the major axis direction of 20 μm or more are
It is important that 1 to 20% by volume is present in the total amount. 1% of the total amount of second phase crystal grains with a length in the major axis direction of 20 μm or more
This is because if the content is less than the volume%, the effect of strengthening and toughening the material cannot be sufficiently exhibited, and if it exceeds 20 volume%, the strength of the sintered body is rather lowered. Second
If the length of the phase crystal grains in the major axis direction is 20 μm or more,
From the viewpoint that both strength and toughness of the sintered body are improved, the total amount is preferably 3 to 10% by volume. From the viewpoint of strength of the sintered body, it is most desirable that the amount of the anisotropically-shaped second phase crystal particles is 5 to 60% by volume in the total amount. As the second-phase crystal particles, there are plate-like particles and whisker-like particles, and the length in the major axis direction in the present application means the maximum length of particles having various shapes.

As shown in FIG. 1, the alumina-based sintered body of the present invention is composed of an alumina matrix 1 and anisotropic second-phase crystal grains 2.

Next, a method for producing the alumina-based sintered body of the present invention will be described. In order to produce the alumina-based sintered body of the present invention, it is first necessary to produce a synthetic powder of anisotropic second-phase crystals. That is, the α-Al ₂ O ₃ powder, the powder that produces the second-phase crystals, and the synthetic powder of the second-phase crystals are added, mixed, molded, and sintered to obtain the alumina-based sintered material of the present invention. A union is obtained.

As the synthetic powder of the second phase crystal, known compositions such as oxide powder, metal powder, organic and inorganic materials containing the metal and a solution thereof are used, and the composition of the second phase crystal having a predetermined anisotropic shape. And the mixed powder is calcined to produce a second phase crystal. When the calcination temperature is low, the reaction rate is slow, the size of the obtained second phase crystal is small, and more intermediate compounds may remain. Therefore, the above-mentioned crystal growth promoting effect is small. Therefore, the calcination temperature is preferably 1100 ° C or higher, and particularly preferably 1300 ° C or higher.

The addition amount of the synthetic powder composed of the second phase crystals is preferably 3 to 50% of the total amount of the second phase crystals in the sintered body. When the added amount of the synthetic powder is less than 3% of the total amount of the second phase crystals, the seed crystal addition effect is small, and the added amount of the synthetic powder is 50% of the total amount of the second phase crystals.
This is because if it is more than%, the amount of raw materials involved in the reaction during firing is small and the crystal growth rate tends to be lowered. The amount of the synthetic powder added is 5 to 30% of the total amount of the second phase.
Is particularly preferable from the viewpoint of forming the texture of the sintered body of the present invention.

The above-mentioned mixed powder is molded into a desired shape by a known molding technique such as a die press, a casting molding, an extrusion molding, an injection molding, a cold isostatic pressing and the like. A known sintering method such as a hot pressing method, a normal pressure firing method, a gas pressure firing method, a hot isostatic treatment (HIP) treatment after these firings, and a HI after glass sealing are performed on the molded body.
P treatment is performed to obtain a dense sintered body having a theoretical density ratio of 95% or more. If the sintering temperature is low, it is difficult to densify. On the contrary, if it is too high, abnormal grain growth of the alumina matrix crystal is likely to occur, so that the temperature range of 1500 to 1800 ° C., particularly 150 ° C.
A temperature of 0 to 1750 ° C. is suitable.

Further, according to the manufacturing method of the present invention, the Al ₂ O ₃ powder and the powder containing La, Ca, Sr and Ba are mixed, shaped and sintered to form an alumina mother phase and a second phase crystal. In the method for producing an alumina-based sintered body consisting of particles,
The average crystal grain size of the powder containing La, Ca, Sr, Ba is 1
By setting the thickness to 10 μm, the growth of the second phase crystal is promoted.

The average crystal grain size of the raw material powders of La, Ca, Sr, and Ba is set to 1 to 10 μm. When the average grain size is smaller than 1 μm, the length of the second phase crystal grains in the major axis direction is 10 μm. The second-phase crystal particles, which can generate only a small amount and have a length in the major axis direction of 20 μm or more, in 1% of the total amount of the sintered body.
This is because it becomes difficult to make it exist at 20% by volume.
Further, when the average crystal grain size of the raw material powder of La, Ca, Sr, and Ba is larger than 10 μm, the unreacted phase and the intermediate product are likely to remain in the sintered body due to insufficient reaction, and the crystal grows sufficiently. Because it will not do. This La, Ca, S
The average crystal grain size of the raw material powders of r and Ba is preferably 2 to 8 μm from the viewpoint of the development and reactivity of the second phase crystals.

The specific manufacturing method of the present invention is as follows.
At least one of the raw material powders containing a, Sr, and Ba is mixed with the alumina raw material powder. The alumina raw material powder preferably has an average crystal grain size of 1 μm or less in order to prevent abnormal growth of the alumina mother phase. In addition, as a mixing method, it is desirable that the crushing time is short if the raw material powders of La, Ca, Sr, and Ba can be mixed sufficiently uniformly so as not to be crushed so much. For example, it is mixed and pulverized in a rotary mill within 24 hours.

The alumina powder of the present invention can be obtained by molding and firing such a mixed powder by the same method as described above.

The high-strength and high-toughness alumina-based sintered body of the present invention may be manufactured by adding a certain amount of oxide such as magnesia, zirconia, or mullite. In this case,
It has a small effect on the properties of the sintered body and has the effect of improving the sinterability and toughness.

[0030]

In the alumina sintered body of the present invention, the alumina matrix having an average crystal grain size of 10 μm or less has a length in the major axis direction of 20.
The presence of 1 to 20% by volume of the second phase crystals of μm or more in the total amount can effectively suppress the development of cracks in the sintered body and the deformation due to the sliding of grain boundaries at high temperature.

Further, by adding the second phase crystal powder as the raw material powder, the second phase crystal powder as the raw material powder becomes a seed crystal for crystal growth, which significantly promotes the growth of anisotropic crystals, and the crystal in the major axis direction is increased. It is possible to grow the length to 20 μm or more.

Furthermore, La, Ca, Sr,
By setting the average crystal grain size of the Ba oxide powder to 1 to 10 μm, the nuclei of the second phase crystals are reduced, the diffusion distance of the elements forming the second phase crystals is shortened, and the anisotropic shape of Two phase crystals can be grown.

That is, the second phase crystal is formed in the alumina matrix by the reaction of the element forming the second phase crystal and Al ₂ O ₃ . Since the atoms of the element forming the second phase crystal are difficult to diffuse in the alumina mother phase, the final length in the major axis direction of the second phase crystal depends on the element raw material powder.
The smaller the average crystal grain size of the raw material powder, the more uniform the distribution of the element in the matrix and the formation of a large number of second-phase crystal nuclei, but since the crystal growth due to diffusion is slow, the second-phase crystal grows large. Can not. In the manufacturing method of the present invention, the average crystal grain size of the specific element oxide powder forming the second phase is set to 1 to 10 μm.
Therefore, the length of the second phase crystal in the major axis direction is 10 μm.
Can be developed above.

[0034]

【Example】

Example 1 One of lanthanum oxide, calcium carbonate, strontium carbonate and barium carbonate, and aluminum oxide were used as starting materials, and were each La ₂ O ₃ .11.
Al ₂ O ₃ , CaO · 6Al ₂ O ₃ , SrO · 6Al ₂
O ₃ and BaO · 6Al ₂ O ₃ were mixed and the mixed powder was calcined at a temperature of 1600 ° C. for 5 hours to obtain a synthetic powder of anisotropic second-phase crystals.

The composition of the sintered body was obtained by using the synthetic powder of this second phase crystal, at least one of lanthanum oxide, calcium carbonate, strontium carbonate and barium carbonate, and aluminum oxide. formulated so as to become shown, after the mixed powder was press-molded at a pressure of 1t / cm ^2, was added isostatic pressing at a pressure of 3t / cm ^2. The above-mentioned molded product is 1700 ° C in the atmosphere.
Calcination was performed for 5 hours at normal pressure. Sample No. 6 and sample No. No. 7 was fired at 1750 ° C. for 5 hours to grow grains. The ratio of the second phase crystal powder in Table 1 indicates the ratio to the amount of the second phase in the sintered body.

[0036]

[Table 1]

When the obtained sintered body was identified by X-ray diffraction measurement, the sintered body was found to be α-Al ₂ O ₃ and La ₂ O ₃ .multidot.
11Al ₂ O ₃ , CaO ・ 6Al ₂ O ₃ , SrO ・ 6A
It was found to be composed of 1 ₂ O ₃ and BaO.6Al ₂ O ₃ (second phase). The sintered body was cut out and polished to a mirror surface, and the structure was observed with an optical microscope and a scanning electron microscope. Further, the average crystal grain size of the alumina mother phase and the volume fraction of the total amount of the second phase crystals of 20 μm or more were measured by the lattice point number counting method. The results are shown in Table 1.

Further, the sintered body was ground to a shape specified in JIS-R1601 to prepare a bending sample. This sample was subjected to a 4-point bending bending strength test at room temperature and 1400 ° C. based on JIS-R1601. Further, the fracture toughness (K _1c ) was measured by the Vickers indentation method. Table 1 shows the measurement results.

From the results shown in Table 1, the alumina-based sintered body obtained according to the present invention is superior in room temperature strength (580 MPa or more) to conventional alumina materials and alumina-based composite materials other than the present invention. It is understood that it exhibits high temperature strength (380 MPa or more) and fracture toughness (4 MPa · m ^1/2 or more).

Example 2 Lanthanum oxide, calcium carbonate, strontium carbonate and barium carbonate were heat-treated at 1600 ° C. for 20 hours to obtain a coarse oxide raw material powder having an average particle size of 5 μm or more. These powders were pulverized with a rotary mill into various particle sizes shown in Table 2. Further, the above raw materials were weighed with alumina raw material powder (average crystal grain size 0.8 μm) in a composition shown in Table 2, mixed in a rotary mill for 10 hours, shaped and fired in the same manner as in Example 1 above.

[0041]

[Table 2]

When the obtained sintered body was identified by X-ray diffraction measurement, the sintered body of the present invention was found to have α-Al ₂ O ₃ and La _{2
O 3 · 11Al 2 O 3,} CaO · 6Al 2 O 3, SrO
· 6Al was found to be composed by _{2 O 3, BaO · 6Al 2} O 3 ( second phase). Further, the structure was observed in the same manner as in Example 1 above to measure the average particle size of the alumina matrix and the volume fraction of the total amount of the second phase crystals having a diameter of 20 μm or more, and further, 4 points at room temperature and 1400 ° C. The bending transverse strength was measured and the fracture toughness (K _1c ) was measured. The measurement results are shown in Table 2.

From the results shown in Table 2, the alumina-based sintered body obtained according to the present invention is superior in room temperature strength (580 MPa or more) to conventional alumina materials and alumina-based composite materials other than the present invention. It can be seen that it exhibits high temperature strength (410 MPa or more) and fracture toughness (4.7 MPa · m ^1/2 or more). For sample No. 15, it was confirmed that the unreacted phase remained in the sintered body.

[0044]

EFFECT OF THE INVENTION In the alumina-based sintered body of the present invention, an anisotropic second phase having a length in the major axis direction of 20 μm or more is added to an alumina matrix having an average crystal grain size of 10 μm or less in a total amount of 1 to 20. By making it exist by volume%, it is possible to effectively suppress the development of cracks in the sintered body and the deformation due to the sliding of grain boundaries at high temperature, and it is possible to have excellent strength and fracture toughness from room temperature to high temperature.

Further, according to the method for producing an alumina-based sintered body of the present invention, by adding the second phase crystal powder as the raw material powder, the second phase crystal powder as the raw material powder becomes a seed crystal for crystal growth. , Significantly promotes the growth of anisotropic crystals,
The length in the major axis direction can be 20 μm or more, and the alumina-based sintered body of the present invention can be easily obtained.

Further, the second phase La, Ca, Sr, Ba
By setting the average crystal grain size of the raw material powder of 1 to 10 μm, the nuclei of the second phase crystals are reduced, the diffusion distance of the elements forming the second phase crystals is shortened, and the anisotropic second phase is formed. By growing crystals, the alumina-based sintered body of the present invention can be easily obtained.

[Brief description of drawings]

FIG. 1 is a structural diagram of an alumina-based sintered body of the present invention.

[Explanation of symbols]

 1 ... Alumina mother phase 2 ... Second phase crystal particles

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[Procedure amendment]

[Submission date] March 2, 1995

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Name of item to be corrected] Figure 1

[Correction method] Change

[Correction content]

FIG.

Claims (4)

[Claims] 1. An alumina matrix and at least La, Ca,
What is claimed is: 1. An alumina-based sintered body, which contains one of Sr, Ba, Sm, Nd, and Ti and has anisotropic second-phase crystal grains made of a composite oxide with Al. Alumina-based sintering characterized in that the second phase crystal grains having an average crystal grain size of 10 μm or less and a length in the major axis direction of 20 μm or more are present in an amount of 1 to 20% by volume in the total amount of the sintered body. body. 2. The second phase crystal grains are La ₂ O ₃ .11Al ₂
The alumina sintered body according to claim 1, containing at least one of O ₃ , CaO · 6Al ₂ O ₃ , SrO · 6Al ₂ O ₃ and BaO · 6Al ₂ O ₃ . 3. La, Ca, Sr, Ba, Sm, Nd, T
a second phase crystal powder containing at least one of i and composed of a composite oxide with Al, Al ₂ O ₃ powder, La, C
A method for producing an alumina-based sintered body, which comprises adding and mixing powder containing at least one of a, Sr, Ba, Sm, Nd, and Ti, shaping and sintering. 4. An Al ₂ O ₃ powder and a powder containing at least one of La, Ca, Sr and Ba are mixed, shaped and sintered to form an alumina mother phase and second phase crystal grains. A method of manufacturing an alumina-based sintered body, the method comprising the steps of: producing an alumina-based sintered body, wherein the powder containing La, Ca, Sr, and Ba has an average crystal grain size of 1 to 10 μm. A method for producing a bound body.