JP2746441B2 - A1 Lower 2 O Lower 3 Manufacturing method of base ceramics - Google Patents

Description

The present invention relates to a method for producing Al ₂ O ₃ based ceramics,
In detail, jigs and tools such as cutting tools and die drawing plugs that require toughness and wear resistance, electronic components such as ceramic heaters that require electrical conductivity and thermal shock resistance, and corrosion resistance and oxidation resistance TECHNICAL FIELD The present invention relates to a method for producing an Al ₂ O ₃ -based ceramic suitable for use in mechanical parts such as a mechanical seal and a pump that require high performance, wear resistance and fracture toughness.

(Prior art) Al ₂ O ₃ -based ceramics have excellent corrosion resistance, oxidation resistance, and wear resistance, and are more economical than ceramics such as Si ₃ N ₄ that have been frequently used as engineering ceramics. In addition, its usefulness has been reviewed in recent years because sintering can be performed at a low temperature. However, there is a disadvantage that the strength, high-temperature strength, fracture toughness and thermal shock resistance are inferior to Si ₃ N ₄ . Thus, many studies have been made to improve the strength and toughness by uniformly dispersing high-strength needle-like crystals in Al ₂ O ₃ -based ceramics. As a result, the SiC whiskers Al ₂ O ₃ Al ₂ O ₃ based ceramic material (hereinafter, referred to as SiC whiskers dispersed Al ₂ O ₃ based ceramic material) dispersed in the matrix and a method of manufacturing the same have been developed.

For example, US Pat. No. 4,543,345 discloses that 0.3 μm Al
After dry mixing ₂ O ₃ powder and SiC whisker, the mixture is
1850 ° C., 41 MPa, SiC whiskers dispersed Al ₂ O ₃ group method of manufacturing a ceramic of uniaxial pressure sintering at a 45 minute conditions are presented, according to the fracture toughness value 8~9Kg / mm ^3/2 It has been improved and the breaking strength has been obtained up to 800MPa (81.6Kg / mm ² ).

However, in the above method, the mixing of SiC whiskers is performed by a dry mixing method, and the dry mixing method is extremely difficult to uniformly disperse the SiC whiskers. There is often a problem that a very small portion is present, and as a result, high strength and high toughness as described above are difficult to obtain stably, and strength and toughness may be lower than conventional Al ₂ O ₃ based ceramics. There is a point.
The reason is that if such a cohesive portion is present, pores are present inside the cohesive portion, so that the sintered ceramics have reduced strength due to the pores. In addition, since the above mixture contains SiC whiskers, sintering is performed at a high temperature of 1800 ° C. or higher, and except for the very small part of the SiC whiskers, almost no crystal grain growth occurs due to the crystal grain growth suppressing action of the SiC whiskers.
The reason is that abnormal crystal grain growth occurs during sintering in the extremely small portion of C whiskers, so that coarse crystal grains are generated and strength and toughness are reduced.

As a countermeasure, SiC whiskers are added to a solvent to form a slurry, and the slurry is mixed with Al ₂ O ₃ powder for a sufficiently long time to form a slurry.
It is conceivable to make the dispersion of iC whiskers uniform. However, if the mixing is performed for a long time, the acicular SiC whiskers are lost during the mixing, and the aspect ratio is significantly reduced. Therefore, the above method has a drawback that the SiC whisker does not contribute to the improvement of the strength and the toughness, and the strength and the toughness of the sintered body are rather lowered, and the above problem cannot be solved.

Therefore, further studies have been made to solve such problems, and as a result, an improved SiC whisker dispersion Al ₂ O ₃
Manufacturing methods for base ceramics have been developed. That is, JP-A-63-30378 discloses that a SiC whisker is added to ethanol, ultrasonic energy is applied to obtain a SiC whisker dispersion, and then the SiC whisker dispersion and slurry Al ₂ O ₃
A method for producing an Al ₂ O ₃ -based ceramic in which SiC whiskers are dispersed and stirred by a wet mill such as a ball mill or the like, and the mixture is dried, granulated, molded, and uniaxially pressed and sintered. According to this, a material having a breaking strength of 83 kg / mm ² was obtained.

(Problems to be Solved by the Invention) In the method described in JP-A-63-30378, the needle-like SiC whiskers are more uniformly dispersed, and the pores and coarse crystal grains are reduced. Low SiC whisker dispersion A
Since l ₂ O ₃ -based ceramics can be obtained, high strength and high toughness can be obtained more stably. However, the uniformity of the dispersion of the above-mentioned SiC whiskers is not sufficient, and
High toughness may not be obtained stably.

The present invention has been made in view of such circumstances, and its purpose is to solve the above-mentioned problems of the conventional one, and to reliably and uniformly disperse the needle-like SiC whiskers, and therefore always SiC whisker dispersion Al ₂ O ₃ with high strength and high toughness
An object of the present invention is to provide a method for producing an Al ₂ O ₃ -based ceramic from which a base ceramic can be reliably obtained.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a method for producing an Al ₂ O ₃ -based ceramic having the following configuration.

That is, the production method according to claim 1 is characterized in that O: 0.3 to 1.5 wt%
After dispersing the SiC whisker in a mixed solution of alcohol and water, then mixing the SiC whisker dispersion with a slurry-like Al ₂ O ₃ -based ceramic raw material, drying and granulating the mixture, This is a method for producing an Al ₂ O ₃ -based ceramic, which is formed and sintered.

The method according to claim 2, the amount of SiC whiskers of the SiC whiskers dispersion is, in the method of manufacturing Al ₂ O ₃ based ceramic material according to claim 1 is 20% or less with respect to the dispersion is there.

The method of claim 3 is a method for producing Al ₂ O ₃ based ceramic material according to claim 1 for drying the mixture by a spray drying method.

(Action) The present invention relates to the effect of S on the dispersibility of SiC whiskers in a solvent.
The effects of the amount of O in iC whiskers and the type of solvent were carefully investigated, and based on the findings obtained. That is,
O: 0.3 wt% or more of SiC whiskers are relatively easily dispersed in a solvent, and when the solvent is a mixed solvent of alcohol and water, the uniform dispersibility of the SiC whiskers is always extremely excellent. I got the knowledge.

Therefore, the manufacturing method of the Al ₂ O ₃ based ceramic material according to the present invention, as described above, first, O: The 0.3 to 1.5% of SiC whiskers are so dispersed in the mixed solution of alcohol and water. By doing so, based on the above knowledge, the SiC
It is possible to obtain a SiC whisker dispersion in which whiskers are always very uniformly dispersed. Further, the dispersion can be performed by applying vibration energy such as ultrasonic energy to the mixed solution obtained by adding SiC whiskers, and applying such energy hardly causes needle-like SiC whisker defects. Therefore, the SiC whisker dispersion liquid can be made to have needle-like SiC whiskers, which are almost free from defects, always dispersed very uniformly.

Then, the SiC whisker dispersion and the slurry-like Al ₂ O ₃ -based ceramic raw material are mixed. The mixing can be carried out by stirring with a conventional wet mill such as a ball mill. In this way, a mixture in which the slurry-like ceramic raw material and the dispersion are uniformly mixed is easily obtained, and since the SiC whiskers are extremely uniformly dispersed in the dispersion, the mixture is mixed with the SiC whiskers. Are always very uniformly dispersed. In addition, the above mixing may be performed to such an extent that the slurry-like ceramic raw material and the dispersion liquid are uniformly mixed, so that the mixing may be performed in a short time, and thus, the SiC whiskers are hardly deficient due to the mixing. Therefore, the mixture always has a very uniform dispersion of acicular SiC whiskers with almost no defects.

Next, after drying and granulating the mixture, molding,
Sintered. In the above mixture, needle-like SiC whiskers having almost no defects are always extremely uniformly dispersed, and therefore, the compact before sintering has no agglomerated portion and minimal portion of SiC whiskers. Therefore, abnormal crystal grain growth is extremely unlikely to occur during the sintering, so that the sintered ceramic has no coarse crystals. In addition, the ceramic has no pores. Such ceramics have high strength and high toughness. Therefore, it is possible to surely obtain a SiC whisker-dispersed Al ₂ O ₃ -based ceramic having high strength and high toughness.

The reason why the amount of O in the SiC whisker is set to 0.3 to 1.5 wt% is that if the O content is less than 0.3 wt%, the uniform dispersibility of the SiC whisker in the solvent becomes unstable, and if the O content exceeds 1.5 wt%, the high-temperature strength decreases. Because it becomes.

It is desirable that the amount of the SiC whiskers in the SiC whisker dispersion be 20% or less of the dispersion. This is because the degree of uniform dispersion of the SiC whiskers is particularly improved.

Desirably, the mixture is dried by a spray drying method. By doing so, the mixture can be dried instantaneously, so that the time required from the generation of the mixture to sintering is reduced, and the sintering can be performed while maintaining a high degree of uniform dispersion of the SiC whiskers. Because it becomes.

The slurry-like Al ₂ O ₃ -based ceramic raw material is a mixture of powder of the Al ₂ O ₃ -based ceramic raw material and a slurrying solvent. The ceramic raw material includes only Al ₂ O _3, a case including Al ₂ O ₃ and one or more of TiC, TiN, and TiCN, and further includes a sintering aid such as Y ₂ O _3. There are cases. Si ₃ N
_When high strength and high toughness equivalent to those of ceramics such as ₄ are required, it is better to add not only Al ₂ O ₃ but also TiC or the like, or a sintering aid.

(Example) Example 1 After adding SiC whiskers adjusted to O: 0.3 wt%, 0.5 wt% or 1.5 wt% into a mixed solution of ethanol and water,
Ultrasonic energy was applied for 30 minutes to obtain a SiC whisker dispersion.

Next, a mixture of Al ₂ O ₃ powder and slurry and an organic binder for molding are added to the SiC whisker dispersion, and the mixture is stirred by a wet mill (ball mill) for 20 hours, and then dried by a spray drying method. Thus, a mixed powder was obtained. The composition of the powder is shown in Table 1 and the amount of SiC whiskers in the powder is 10, 20 or 30%. The spray drying method is a method in which a mixture is sprayed into a high-temperature drying atmosphere by a spray dryer while mixing the mixture with a stirrer or ultrasonic energy to evaporate the solution.

Next, the mixed powder was packed in a graphite mold, and subjected to uniaxial pressure sintering by a hot press for 45 minutes under a condition of a temperature of 1850 ° C. and a pressure of 200 kg / cm ^{2 in} an Ar atmosphere to obtain a sintered body. Obtained.

The sintered body was measured for relative density by the Archimedes method and for bending strength at room temperature and high temperature by the three-point bending method (span 30 mm, room temperature). The results are shown in Table 1 (Experiments Nos. 1 to 5). Flexural strength of the sintered body even at room temperature of Izure is 71.5Kg / mm ² or more, the bending strength at high temperature 39.0Kg
/ mm ² or more, which is higher than conventional Al ₂ O ₃ based ceramics. The relative density is 99.7% or more, which is a value very close to the theoretical density.

The microstructure of the sintered body was observed. The observation was performed at 10 locations per sintered body and 100 visual fields per location. As a result, no coarse crystal grains or aggregated portions of SiC whiskers were found. Further, as a result of examining the fracture portion of the test piece after the fracture, no agglomerated portion of the SiC whisker was recognized.

Example 2 The composition of the mixed powder according to Comparative Example 1 is shown in Table 2. As can be seen from Table ₂ , not only Al ₂ O ₃ but also TiC or TiN was added as a ceramic raw material. Such a mixed powder was obtained in the same manner as in Example 1.

A sintered body was obtained from the mixed powder in the same manner as in Example 1, and the same measurement was performed. The results are shown in Table 2 (Experiments Nos. 6 to 12). Flexural strength of the sintered body even at room temperature of Izure is a 97.5Kg / mm ² or more, higher than the conventional Al ₂ O ₃ based ceramic material, most of it is 100 Kg / mm ² or more, Si ₃
N is ₄ etc. of the ceramic is equal to or higher. Flexural strength at high temperatures is at 39.0Kg / mm ² or more, the conventional Al ₂ O ₃
It is higher than the base ceramics, most of which is 45 kg / mm ² or more, which is equal to or higher than ceramics such as Si ₃ N ₄ . The relative density is a value very close to the theoretical density.

Further, as a result of observing the microstructure of the sintered body in the same manner as in Example 1, no coarse crystal grains or aggregated portions of SiC whiskers were found.

Comparative Example 1 Table 3 shows the production conditions and composition of the mixed powder according to Comparative Example 1. Experiments Nos. 13 to 15 were performed in the same manner as in Experiment No. 6 of Example 2.
Using iC whiskers and ceramic raw materials, a sintered body having the same composition as that of Experiment No. 6 was produced by partially changing the production conditions.
That is, the solution for dispersing the SiC whiskers was a mixed solution of ethanol and water, ethanol or water, and the mixture was dried by spray drying or hot bath drying. The warm bath drying method is a method of immersing a container containing the mixture in warm water to warm the mixture, and evaporating the solution while stirring the mixture with a stirrer. Manufacturing conditions other than the above are the same as those in Experiment No. 6.

In Experiment No. 16, the amount of SiC whiskers in the dispersion was 35%, and in Experiment No. 17, the amount of O in SiC whiskers was 0.1% by weight. The other points are the same as in the case of Experiment No. 6.

The transverse strength of the obtained sintered body was measured at room temperature in the same manner as in Example 1. As a result, the experiment N
In many cases, the same bending strength as o.6 was obtained, but the reproducibility was a little poor, and some of them had extremely low strength. Table 3 shows flexural strength values of the low strength steels.
As can be seen from Table 3, these values are smaller than in the case of Experiment No. 6, and in particular, those of Experiments Nos. 13 to 14 and 17 are extremely small.

The microstructure of the sintered body was observed in the same manner as in Example 1, and as a result, coarse crystal grains and SiC were observed. Whisker agglomerated parts were observed at a few percent probability. Furthermore,
As a result of examining the broken portion of the low-strength material,
The presence of aggregated portions of C whiskers was observed. Therefore, it can be said that the bore of the agglomerated portion became the starting point of destruction and the strength was reduced.

(Effect of the Invention) According to the method for producing an Al ₂ O ₃ -based ceramic according to the present invention, it is possible to obtain a raw material in which sintering is performed in which needle-like SiC whiskers having no defect are always extremely uniformly dispersed.
It is possible to reliably and stably obtain a SiC whisker-dispersed Al ₂ O ₃ -based ceramic having high strength and high toughness.

Claims (3)

(57) [Claims] 1. O: 0.3 to 1.5 wt% of SiC whiskers are dispersed in a mixed solution of alcohol and water, and the SiC whisker dispersion is mixed with a slurry-like Al ₂ O ₃ -based ceramic raw material. A method for producing an Al ₂ O ₃ -based ceramic, comprising drying and granulating the mixture, molding and sintering the mixture. 2. The method for producing an Al ₂ O ₃ -based ceramic according to claim 1, wherein the amount of the SiC whiskers in the SiC whisker dispersion is 20% or less of the dispersion. 3. The method for producing an Al ₂ O ₃ -based ceramic according to claim 1, wherein the mixture is dried by a spray drying method.