JP3311915B2 - Alumina sintered body - 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-based 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, smelting, and chemical industries. The present invention relates to an alumina-based sintered body of a high temperature resistant structural material used in a gas turbine engine part or the like.

[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 (Japanese Unexamined Patent Application Publication No.
No. 22164), Al ₂ O ₃ —ZrO ₂ composite material (see Japanese Patent Application Laid-Open No. 63-139944), Al
_{A 2} O ₃ —TiO ₂ composite material (see Japanese Patent Application Laid-Open No. Hei 7-257964) is known, and according to such a composite material, strength and toughness are improved more than a single sintered body of alumina. Can be.

[0003]

However, the above Al ₂ O
_{The 3-} SiC nanocomposite has a problem in that the non-oxide is dispersed in Al ₂ O ₃ , so that when used at a high temperature in an oxidizing atmosphere, the oxidation resistance is poor. Also,
The Al ₂ O ₃ -ZrO ₂ composite material has a problem that its strength is sharply reduced at a temperature around 900 ° C., so that it is not suitable for use in a state where a stress acts at a high temperature.

[0004] These materials are disclosed in Japanese Patent Application Laid-Open No. 7-257.
No. 964 discloses an Al ₂ O ₃ —TiO ₂ composite material,
Although the above problems can be solved to some extent, the effect of improving strength and toughness is small. In addition, when used at a high temperature of 1300 ° C. or higher, a reaction occurs in which Al ₂ O ₃ and TiO ₂ react with each other to form Al ₂ TiO ₅ , and the stability of material properties is lacking. was there.

An object of the present invention is to provide an alumina-based sintered body having high strength and toughness, and particularly excellent in oxidation resistance and stability of strength characteristics at high temperatures, and a method for producing the same.

[0006]

Means for Solving the Problems The present inventors diligently studied methods for improving high-temperature strength and fracture toughness in order to put alumina into practical use as a high-temperature structural material. As a result, titanium oxide (TiO 2) was contained in alumina crystal grains. ₂ ) and aluminum titanate (Al ₂ TiO ₅ ) are dispersed in a certain relative amount range, so that the plastic deformation resistance of the alumina crystal itself is improved and the internal stress generated by the precipitation of the dispersed phase causes cracking of the alumina crystal. It has been found that alumina can inhibit room temperature, absorb fracture energy, and significantly improve the strength and fracture toughness of alumina from room temperature to high temperature without impairing high-temperature stability. Further, they have found that, by dispersing and depositing a metal oxide different from the intragranular dispersed phase at the grain boundaries of alumina as a grain boundary crystal phase, the grain growth of alumina crystals is suppressed and the strength of the material is further improved. The present invention has been reached.

That is, the alumina-based sintered body of the present invention has an alumina crystal having an average particle diameter of 6 μm or less as a main phase, and contains titanium oxide (TiO ₂ ) and aluminum titanate (Al ₂ TiO) in the crystal grains of the alumina. ₅₎ is a alumina sintered body obtained by present as a dispersed phase, in the X-ray diffraction measurement, the Al ₂ TiO ₅ in (110) plane I (110 peak intensity of) Al ₂ TiO _5, TiO ₂ Assuming that the peak intensity of the (110) plane is I (110) TiO ₂ , I (110) Al ₂ TiO ₅ / [I (110) T
iO ₂ + I (110) Al ₂ TiO ₅ ], wherein the peak intensity ratio is 0.05 to 0.8,
Further, a grain boundary dispersed phase different from the dispersed phase is precipitated at a grain boundary of the alumina crystal at a rate of 3% by volume or more.

[0008]

According to the alumina-based sintered body of the present invention, the size of the alumina crystal grains constituting the main phase is reduced to 6 μm or less, and at the same time, aluminum titanate is included in the alumina crystal grains together with a large number of titanium oxides. At the same time, a large residual stress is generated around the aluminum titanate, and this stress greatly contributes to the toughness of the material.At the same time, the instability of the characteristics due to the reaction between titanium oxide and alumina at high temperatures is reduced or As a result, the strength from room temperature to high temperature and the fracture toughness can be further improved as compared with the conventional composite material without impairing the stability of alumina at high temperatures in crystallinity.

Further, according to the present invention, when Ti ions are present in the alumina crystal, the alumina grain growth is remarkably promoted in the sintering process, and the material strength is reduced by the crystal grain growth. The presence of a metal oxide other than the intragranular dispersed phase in the grain boundary as a grain boundary crystal phase suppresses alumina crystal grain growth, achieves finer alumina crystals, and further improves the strength of the sintered body Let it.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The alumina-based sintered body of the present invention has an alumina crystal having an average particle diameter of 6 μm or less as a main phase, and titanium oxide and aluminum titanate as an intragranular dispersed phase in the alumina crystal grains. It is important that you do. Here, the reason why the average particle size of the alumina crystal is set to 6 μm or less is important for increasing the strength of the sintered body, and if the average particle size of the alumina crystal is larger than 6 μm, improvement in strength cannot be expected. . In particular, it is desirable to be 4 μm or less.

It is important that titanium oxide and aluminum titanate are present simultaneously as an intragranular dispersed phase in the alumina crystal. Here, titanium oxide is TiO ₂
, Aluminum titanate is Al
_{2 This} is a compound represented by TiO ₅ . When only titanium oxide is dispersed in the alumina crystal, the effect of improving strength and toughness is small, and when used at high temperature, the reaction of Al ₂ O ₃ and TiO ₂ to form Al ₂ TiO ₅ This causes a problem that the characteristics of the material become unstable.
Conversely, when the disperse phase is only aluminum titanate, a coarse precipitate phase is likely to be formed, and the strength of the material may be reduced.

When titanium oxide and aluminum titanate are simultaneously present in the grains of the alumina crystal phase, a large residual stress is generated around the aluminum titanate, greatly contributing to the toughness of the material, and at the same time, the titanium oxide and the alumina at a high temperature. Can reduce or suppress the instability of the characteristics due to the reaction. In order to sufficiently exhibit the above-mentioned effects, in X-ray diffraction measurement, the peak intensity of the (110) plane of the Al ₂ TiO ₅ is reduced to the peak intensity of the (110) plane of the I (110) Al ₂ TiO ₅ and TiO _2. Is I (110) TiO ₂ , I (110) Al ₂ TiO ₅ /
_{[I (110) TiO 2 +} I (110) Al 2 TiO 5] peak intensity ratio represented by the 0.05 to 0.8, in particular, in particular 0.1 to 0.6
It is important to control within the range.

That is, when the peak intensity ratio is smaller than 0.05, it means that the precipitation of the TiO ₂ phase is large, and the effect of improving the strength and toughness is small.
This means that a large amount of Al ₂ TiO ₅ is precipitated, and as described above, a coarse precipitated phase is likely to be formed, and the strength of the material may be reduced.

On the other hand, if the amount of Ti contained in the alumina sintered body in the present invention is too small, TiO ₂ or Al ₂ T
The effect of improving strength and toughness cannot be expected because the amount of deposited TiO ₅ is reduced, and TiO ₂ having a solid solubility limit or more reacts with Al ₂ O ₃ to form a large amount of coarse Al ₂ TiO ₅ at grain boundaries. Therefore, it is desirable that the amount of TiO ₂ is 0.5 to 8 mol%, particularly 1 to 4 mol%, based on Al ₂ O ₃ . Note that, as described above, when Ti ions are present in the alumina crystal, the grain growth of alumina tends to be remarkably promoted in the sintering process. Therefore, depending on the content of Ti ions, the strength of the material is reduced by the crystal grain growth. There are cases.
Therefore, according to the present invention, by allowing a metal oxide different from the intragranular dispersed phase to be present at the grain boundaries of alumina as a grain boundary crystal phase, the grain growth of alumina crystals can be suppressed, and the refinement of alumina crystals can be achieved. Can be achieved, and the strength of the sintered body is further improved.

In this case, the amount of the grain boundary dispersed phase needs to be 3% by volume or more in the total amount. In order to effectively suppress the grain growth of alumina, the grain boundary dispersed phase is particularly dispersed in 5% by volume or more. Is preferred. As the above-mentioned grain boundary dispersed phase, an oxide stable at a high temperature or a composite oxide containing two or more kinds of metals is suitable, but the effect of suppressing the grain growth and affecting the sinterability, stability and high-temperature characteristics of the material are preferable. From the above, in particular, one metal oxide or a composite oxide of two or more metals of the Group 2A to 4A elements of the periodic table and Si, especially MgAl ₂ O ₄ , Y
_{3 Al 5 O 12, LaAl 11} O 18, Si 2 Al 6 O 13, Z
rO ₂ and HfO ₂ are most preferred. In addition, some Ti
Ions may react with the grain boundary dispersed phase, but have little effect on the strength and toughness of the material.

In order to produce the alumina sintered body of the present invention, first, a molded body made of a mixture of a substance containing Ti ions and alumina powder is produced. At this time, the substance containing Ti ions may be any of titanium oxide powder, titanium metal powder, organic and inorganic salts containing titanium, and a solution thereof.

As a molding method, it can be formed into an arbitrary shape by well-known molding means, for example, a die press, a casting molding, an extrusion molding, an injection molding, a cold isostatic pressing and the like.

Next, the molded body is subjected to 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 these 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, during this firing, firing is first performed in an atmosphere containing a reducing gas such as Ar, He, H ₂ , H ₂ / N ₂ , and Ti
Dissolve ions. The temperature during the solution treatment was 120
Set to 0-1750 ° C.

Thereafter, the above solid solution is subjected to a heat treatment in an oxidizing atmosphere such as air at a temperature in the range of 1350 to 1650 ° C. to precipitate Ti ions in the form of titanium oxide and aluminum titanate in alumina crystal grains. be able to. Here, according to the present invention, it is important to set the heat treatment temperature in an oxidizing atmosphere to a temperature range of 1350 to 1650 ° C. This is because if the heat treatment is performed at a temperature lower than 1350 ° C., a precipitation phase of aluminum titanate cannot be obtained, so that the effect of improving the strength and toughness is small, and at a low temperature, the ion diffusion rate required for the precipitation is low. A long period of days is required. On the other hand, when the heat treatment is performed at a temperature of 1650 ° C. or more, the precipitation phase becomes coarse, and the strength of the material decreases. In order to obtain high strength and toughness, it is preferable that the heat treatment for precipitation is performed particularly in the range of 1350 ° C to 1550 ° C.

In the production of the alumina sintered body of the present invention, it is particularly effective to carry out the precipitation treatment in an oxidizing atmosphere by microwave heating. This is Ti
In the process in which ions are precipitated from the alumina crystal, the rate at which oxygen ions diffuse from the outside to the inside of the sintered body is rate-limiting. There is no problem when the size of the sintered body is small,
When the size of the sintered body is 10 mm or more, it takes a long time to precipitate solid solution ions inside the sintered body. This may cause a problem of non-uniform structure formation in which a deposited phase near the surface of the sintered body grows large. Microwave heating promotes the vibration of the crystal lattice and the diffusion of ions along the crystal grain boundaries, and terminates the precipitation in a short time. Therefore, the above-mentioned problems are solved, and a uniform precipitate structure is obtained.

The microwave heating at this time is desirably at a frequency of 1 GHz or more.

[0022]

EXAMPLES As raw material powders, alumina (Al ₂ O ₃ ), titanium oxide (TiO ₂ ) and magnesium carbonate (Mg) were used.
Using CO ₃ ), yttrium oxide (Y ₂ O ₃ ), and hafnium oxide (HfO ₂ ), the composition was adjusted to the composition ratio shown in Table 1, and a mold was formed at a pressure of 1 t / cm ² and then 3 t / cm 2.
Hydrostatic pressure treatment was applied at a pressure of ² . As shown in Table 1, firing conditions were as follows: firing in an H ₂ atmosphere;
The heat treatment was performed at a temperature of from 1 to 1700 ° C. The heat treatment of some of the samples was performed by microwave heating.

The obtained sintered body was polished to the shape specified in JIS-R1601, to prepare a bending specimen. This sample was subjected to a four-point bending strength test at room temperature and 1400 ° C. based on JIS-R1601. Further, the fracture toughness (KIC) was measured by the Vickers indentation method. From the data of the X-ray diffraction measurement, the diffraction intensity ratio of the precipitated phase in the sintered body was measured. Also, from the scanning electron micrograph,
The average particle size of the alumina matrix phase and the volume fraction of the grain boundary dispersed phase were quantitatively measured. The results are shown in Table 2.

[0024]

[Table 1]

[0025]

[Table 2]

From the results shown in Tables 1 and 2, based on the present invention, an alumina-based sintered body in which titanium oxide and aluminum titanate obtained by the solid solution-precipitation process are finely dispersed in alumina crystal grains is shown. , All have room temperature strength of 500 MPa
3. 1400 ° C. strength 350 MPa or more, fracture toughness
It was as excellent as 5 MPa · m ^1/2 or more.

On the other hand, Comparative Sample Nos. 12 and 13
Has no precipitation phase in the grains, and Sample No. 14 has a low precipitation temperature, so that the precipitation phase is only titanium oxide and no aluminum titanate is present. Sample No. 15 has a high deposition temperature and therefore has a relatively large amount of aluminum titanate. Samples Nos. 16 and 17 are those in which the matrix phase is grown, and both are stronger than the sintered body of the present invention. It can be seen that the toughness is low.

[0028]

As described above in detail, according to the present invention, in an alumina-based sintered body, titanium oxide and aluminum titanate are simultaneously precipitated and dispersed at a specific ratio in alumina crystals, thereby increasing the temperature from room temperature to high temperature. A sintered body having high strength, high toughness, and excellent crystal stability at high temperatures can be produced. Thereby, the use of the alumina-based sintered body can be further expanded.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C04B 35/10 C04B 35/46

Claims (2)

(57) [Claims] An alumina crystal having an average particle diameter of 6 μm or less is used as a main phase, and titanium oxide (Ti) is contained in the alumina crystal grains.
O ₂ ) and aluminum titanate (Al ₂ TiO ₅ )
There a alumina sintered body obtained by present as intragranular dispersed phase, in the X-ray diffraction measurement, the Al ₂ TiO ₅ in (110) plane I (110) peak intensity of Al ₂ TiO _5, TiO ₂
When the peak intensity of the (110) plane is I (110) TiO ₂ ,
_{I (110) Al 2 TiO 5} / alumina sintered to _{[I (110) TiO 2 +} I (110) Al 2 TiO 5] peak intensity ratio represented by is characterized in that 0.05 to 0.8 body. 2. The alumina-based sintered body according to claim 1, wherein a grain boundary dispersed phase different from said intragranular dispersed phase is present at a grain boundary of said alumina crystal at a ratio of 3% by volume or more.