JP3152853B2 - Alumina sintered body and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alumina sintered body having excellent high-temperature strength characteristics, high-temperature stability, and oxidation resistance and a method for producing the same, and particularly to the aerospace and space industries, the kneading industry, and the chemical industry. The present invention relates to an alumina-based sintered body of a high temperature resistant structural material used for a gas turbine engine part or the like and a method for producing the same.

[0002]

2. Description of the Related Art Alumina has been attracting attention as a high-temperature resistant structural member because of its excellent environmental resistance and high-temperature strength. Further, in order to further improve the high temperature strength and the fracture toughness, various composites have been attempted. For example, Al ₂ O ₃ —SiC nanocomposite, Al ₂ O
₃ -ZrO ₂ and the composite material is known (JP-61-1
22164, JP-A-63-139044, etc.), and the strength and toughness of such a composite material can be improved as compared with a pure alumina sintered body.

[0003]

[INVENTION point problem, however, in the above Al ₂ O ₃ -SiC nano components Jie Tsu DOO, Al ₂ O
_{Since the} non-oxide SiC is dispersed in ₃ , when used in a high temperature state in an oxidizing atmosphere, there is a problem that it lacks oxidation resistance.

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

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

[0006]

Means for Solving the Problems The present inventors have conducted intensive studies on methods for improving high-temperature strength and fracture toughness in order to put alumina into practical use as a high-temperature structural material.
The metal oxide raw material whose solid solubility limit changes in alumina due to the difference in atmosphere is added to alumina, and the fired sintered body is heat-treated by controlling the atmosphere, and fine particles are formed in the alumina crystal grains.
By dispersing and depositing a composite oxide of alumina and metal oxide , plastic deformation resistance can be improved and high-temperature strength can be improved.At the same time, the structure has a structure that prevents the propagation of cracks and absorbs fracture energy. It has been found that the fracture toughness can be improved by the method, and the present invention has been achieved.

Namely, the alumina sintered body of the present invention is a alumina sintered body comprising a metal oxide solid solution limit of the alumina by the difference in the atmosphere is changed, and alumina in the alumina crystal grains 1 μm of the composite oxide with the metal oxide
The particles are dispersed and precipitated with an average particle size of m or less. Ma
In addition, the metal oxide is 1 μm or less in the alumina crystal grains.
It is desirable that the particles are dispersed and precipitated with an average particle size. In particular, the metal oxide is titanium oxide , and the composite oxide is Al ₂ TiO ₅
It is desirable that

In the present invention, the second phase composed of a metal oxide or a composite oxide of alumina and the above-described metal oxide whose solid solubility limit in alumina changes due to a difference in atmosphere has a particle size of 1 μm in the alumina grains. It is important to disperse with the following average particle size. When the second phase is dispersed at the grain boundaries, room temperature strength and fracture toughness may be improved, but the high temperature strength of the material is reduced. In addition, the second phase is contained in the alumina grains.
The reason why the particles are dispersed with an average particle diameter of not more than μm is that when the average particle diameter of the second phase is larger than 1 μm, the high temperature strength and the fracture toughness are remarkably reduced. The particle size of the second phase is between 0.
It is desirable that the thickness be 5 μm or less. In particular, the metal oxidation
Things titanium oxide, the composite oxide is Al ₂ TiO ₅
At the same time, the compact is heated in a reducing atmosphere at a temperature of 1500 ° C. or more.
After sintering at a temperature, the sintered body is heated in an oxidizing atmosphere at 160
Heat treatment at a temperature of 0 ° C. or more, and within the alumina crystal grains and / or
Alternatively, it is desirable to deposit Al ₂ TiO ₅ at the grain boundaries.
No.

Metal oxides whose solid solubility limit in alumina varies depending on the atmosphere include TiO ₂ and Fe ₂ O.
₃ , MgTiO _{3 and the} like, among which TiO ₂ is most desirable.

Further, the alumina-based sintered body of the present invention is prepared by, for example, adding a metal oxide raw material whose solid solubility limit to alumina changes due to a difference in atmosphere into alumina, mixing and molding the alumina, and then forming the same. After sintering the sintered body in an atmosphere in which the solid solubility limit of the metal oxide in alumina increases, a sintered body in which the metal oxide forms a solid solution in the alumina crystal grains is produced. Heat treatment in an atmosphere in which the solid solubility limit of the product in alumina is reduced, and an average particle size of 1
It is produced by depositing a composite oxide of alumina having a size of not more than μm and the metal oxide .

The above-mentioned metal oxide raw material includes metal oxide powder,
Any of a metal powder, an organic or inorganic substance containing the metal, and a solution thereof may be used. If the amount of addition is not less than the solid solution limit in an atmosphere where the amount of metal oxide solid solution in alumina is low,
Although the structure can be adjusted to a desired structure, in order to obtain a sufficient toughening effect, it is desirable to add the metal oxide raw material to the metal oxide in an amount of 0.5 mol% or more based on the total amount.

The mixed raw material obtained by adding the metal oxide raw material to the alumina powder is mixed by a desired molding means, for example, a known molding means such as a die press, a casting molding, an extrusion molding, an injection molding, a cold isostatic pressing and the like. Form into any shape.

Next, this molded body is sintered by a known sintering method, for example, a hot pressing method, a normal pressure sintering method, a gas pressure sintering method, and a hot isostatic pressure (HIP) treatment after sintering.
And HIP treatment after glass sealing, to a theoretical density ratio of 9
A dense sintered body of 5% or more is obtained. According to the present invention, it is important that the sintering atmosphere is an atmosphere in which the metal oxide can be more solid-dissolved in alumina.

According to the present invention, this sintered body is
It is important to perform a heat treatment at 1100 to 1800 ° C. for 10 minutes or more in an atmosphere having a small solid solubility limit of the metal oxide in alumina. By this treatment, the metal ions supersaturated in the alumina crystal can be finely dispersed and precipitated in the alumina crystal grains in the form of a metal oxide or a composite oxide of alumina and a metal oxide.

For example, titanium oxide is present in the form of TiO _{2 in} an oxidizing atmosphere, and hardly forms a solid solution with alumina by a normal firing method.
It changes from i ⁴⁺ → Ti ³⁺ , and a solid solution of several mol% in alumina can be obtained. Therefore, as described above, the metal oxide is TiO ₂
In the case of 1,500 ° C. in a reducing atmosphere such as H ₂
Baking at a temperature of 1800 ° C. for 0.5 hour, and in an oxidizing atmosphere such as the air at 1600 to 1800 ° C. for 10 minutes or more
By performing the heat treatment , Al ₂ TiO ₅ can be present in the alumina crystal grains and / or in the grain boundaries with an average particle size of 1 μm or less.

Here, if the amount of precipitation is small, the effect of improving the strength and toughness with respect to alumina cannot be sufficiently achieved, so that the amount of the precipitated phase is preferably 0.5% by volume or more based on the total amount.

[0017]

The valence of some metal ions changes due to differences in atmosphere at high temperatures. Especially 2 ⁺ → 3 ⁺ and 4 ⁺ → 3 ⁺ ,
Alternatively, the change in the opposite direction significantly changes the limit of solid solubility in alumina with the change in the metal ion radius. Therefore, by controlling the atmosphere of calcination and heat treatment for alumina containing such a metal oxide whose valence changes, the alumina phase of the present invention in which the second phase is finely dispersed and precipitated in the grains of alumina. A sintered body is obtained.

As described above, in the alumina-based sintered body of the present invention, a large number of oxide second-phase particles are finely dispersed and precipitated with an average particle diameter of 1 μm or less in the alumina particles. , And a high-temperature structural material having higher high-temperature strength and fracture toughness than before can be provided.

That is, although the conventional alumina-based sintered body has stable characteristics particularly from room temperature to a high temperature in an oxidizing atmosphere, dislocation motion tends to occur at a high temperature, so that the softening and plastic deformation occur. Further, at room temperature, cracks are apt to develop in the alumina crystal, so that the fracture toughness is low. The alumina-based sintered body of the present invention has solved the above-mentioned disadvantages of the conventional alumina-based sintered body.

[0020]

EXAMPLE Using alumina (Al ₂ O ₃ ) powder and titanium oxide (TiO ₂ ) powder as raw material powders, the composition ratio was adjusted as shown in Table 1, and the mixture was press-formed at a pressure of 1 t / cm ² and then 3 t Cold isostatic pressing (CIP) was performed at a pressure of / cm ² . Then, the obtained molded body was fired for 2 hours under the firing conditions shown in Table 1, and further heat-treated for 2 hours under the heat treatment conditions shown in Table 1.

The obtained sintered body was processed into a mirror surface, and the particle size of 100 precipitated particles in the alumina crystal particles was measured on a scanning electron microscope photograph, and the average value was calculated. Further, the sintered body was polished to the shape specified in JIS-R1601 to prepare a bending sample.

The sample was subjected to a four-point bending strength test at room temperature and 1400 ° C. based on JIS-R1601. In addition, the fracture toughness (K
_IC ) was measured. Further, crystals other than α-Al ₂ O ₃ in the sintered body were identified by X-ray diffraction measurement. Table 1 shows the results.

[0023]

[Table 1]

From the results shown in Table 1, the second particles are contained in the alumina particles.
Alumina sintered body of the present invention in which phases are finely dispersed (sample N
o. 1 to 7) are conventional alumina sintered bodies (sample Nos. 1 to 7).
8) and a composite sintered body of alumina and oxide (sample No.
9, it can be seen that the flexural strength and the fracture toughness at room temperature and 1400 ° C. are significantly improved as compared with those of (9, 10). Special
Sample No. 2 in which the second phase was precipitated at the grain boundaries and in the grains. 3 and
No. 6 has a flexural strength at room temperature of 600 MPa or more and fracture toughness
Had a high strength and a high toughness of 4.6 MPa · m ^1/2 . FIG. The organization chart of No. 5 is shown. In FIG. 1, reference numeral 1 denotes an alumina crystal, and reference numeral 2 denotes an Al ₂ TiO ₅ crystal.

[0025]

According to the alumina sintered body of the present invention, a metal oxide raw material whose solubility limit in alumina changes due to a difference in atmosphere is added to alumina, mixed, and molded. after the metal oxide by firing at a predetermined atmosphere to produce a sintered body in which a solid solution in alumina, heat-treated sintered body in a predetermined atmosphere, before and alumina in the alumina crystal grains
Since the composite oxide with the metal oxide is dispersed and precipitated with an average particle size of 1 μm or less, it is excellent in oxidation resistance at high temperatures, and can be significantly improved in fracture toughness and high-temperature strength.

[Brief description of the drawings]

FIG. 1 is a structural diagram of Sample No. 5.

[Explanation of symbols]

1 ・ ・ ・ Alumina crystal 2 ・ ・ ・ Al ₂ TiO ₅ crystal

Claims (6)

(57) [Claims] An alumina-based sintered body containing a metal oxide whose solid solubility limit in alumina changes due to a difference in atmosphere, wherein alumina and the metal oxide are mixed in alumina crystal grains.
An alumina-based sintered body, wherein the composite oxide is dispersed and precipitated with an average particle size of 1 μm or less. 2. The method according to claim 2 , wherein the metal oxide is contained in the alumina crystal grains.
Characterized by being dispersed and precipitated with an average particle size of 1 μm or less.
The alumina-based sintered body according to claim 1, wherein 3. A method according to claim 1 , wherein said metal oxide is contained in said alumina crystal grains.
And / or composite oxidation of alumina and the metal oxide
That the particles are dispersed and precipitated with an average particle size of 1 μm or less.
The alumina-based sintered body according to claim 1 or 2, wherein: 4. The method according to claim 1, wherein the metal oxide is titanium oxide ,
Alumina sintered body according to any one of claims 1 to 3 product is characterized in that it is a Al ₂ TiO _5. 5. A method for adding a metal oxide raw material whose amount of solubility in alumina changes depending on the atmosphere to the alumina, mixing and molding the same, and then forming the formed body into a solid solution limit of the metal oxide in alumina. After sintering in an atmosphere in which the amount increases to produce a sintered body in which the metal oxide forms a solid solution in the alumina crystal grains, this sintered body has a reduced solid solubility limit of the metal oxide in alumina. heat treatment in an atmosphere, a flat in an alumina grain
Composite of alumina having an average particle diameter of 1 μm or less and the metal oxide
A method for producing an alumina-based sintered body, characterized by depositing an oxide . 6. A method according to claim 1, wherein said metal oxide is titanium oxide,
The compact is Al ₂ TiO ₅ and the compact is reduced atmosphere.
After firing at a temperature of 1500 ° C. or more in an atmosphere, this sintering
Heat-treating the body in an oxidizing atmosphere at a temperature of 1600 ° C. or higher,
The alumina crystal grains and / or Al ₂ TiO ₅ in the grain boundary
6. The alumina according to claim 5, wherein the alumina is deposited.
Manufacturing method of sintered body.