JPH0613432B2 - Fiber reinforced Si ▼ Lower 3 ▲ N ▼ Lower 4 ▲ Sintered body and its manufacturing method - Google Patents

Description

The present invention relates to a Si ₃ N ₄ ceramic containing a ceramic fiber and having excellent strength and toughness, and a method for producing the same.

[Prior Art] Ceramics are used as electrical functional materials and mechanical structural materials because of their excellent properties. However,
In the case of utilizing mechanical properties, there is a problem of sudden breakage or large strength variation due to the brittleness of ceramics, and it has not been widely put into practical use.

Therefore, various attempts have been made to improve the reliability or strength of ceramics. Especially Al ₂ O ₃ , ZrO ₂ , S
For iC and Si ₃ N ₄ , the manufacturing conditions including components have been studied in detail.

Furthermore, it has been attempted to achieve strength improvement by incorporating fibers, and metal fibers and ceramic fibers have been studied. Furthermore, ceramics containing ceramic whiskers are also being investigated as a fiber seed.

For example, JP-A-58-104069 proposes a silicon nitride sintered body in which fibrous silicon carbide is dispersed.

[Problems to be Solved by the Invention] However, even in these attempts, sufficient results have not yet been obtained by examining the components and manufacturing conditions, and also in the case of fiber compounding, the cost is high or the dispersion is uniform. It has been pointed out that it is difficult.

An object of the present invention is to provide a novel fiber-reinforced Si ₃ N ₄ sintered body and a method for producing the same, which solves the problems of the conventional method.

[Means for Solving Problems] In view of the above situation, the present inventors have conducted various studies to obtain a sintered body excellent in high temperature strength, toughness, and reliability, and as a result, Al _{2 of} the present invention has been obtained. One or more selected from the group consisting of O ₃ , AlN, ZrO ₂ , Y ₂ O ₃ , MgO, CeO ₂ and La ₂ O ₃ and containing 0.5 to 40 weight percent of SiC whiskers , The SiC whiskers are parallel to the inner surface of the mold by the action of centrifugal force, and the fiber-reinforced Si ₃ N ₄ sintered body and Al ₂ O ₃ , which are distributed and evenly distributed from the inner peripheral portion to the outer peripheral portion of the mold. AlN, ZrO ₂ , Y ₂ O ₃ , M
A slurry obtained by dispersing Si powder containing 0.5 to 40% by weight of one or more selected from the group consisting of gO, CeO ₂ and La ₂ O ₃ and a SiC whisker in a solvent. , Mold the SiC whiskers parallel to the inner surface of the mold and distribute and distribute at a uniform density from the inner peripheral portion to the outer peripheral portion of the mold by placing the solvent in a mold that permeates only the solvent and applying a centrifugal force. Then, a method for producing a fiber-reinforced Si ₃ N ₄ sintered body is reached, which is characterized in that the molded body is heated and nitrided in a nitrogen atmosphere, and then sintered and densified in a nitrogen atmosphere at a higher temperature.

The ceramic sintered body of the present invention is substantially composed of a Si ₃ N ₄ matrix and SiC whiskers uniformly distributed in the matrix with a certain directionality.

Si ₃ N ₄ is dense due to one or more sintering aids selected from the group consisting of Al ₂ O ₃ , AlN, ZrO ₂ , Y ₂ O ₃ , MgO, CeO ₂ and La ₂ O _3. It is a sintered body.

The amount of sintering aid is preferably 0.5 to 40 weight percent of silicon nitride. If it is less than 0.5%, it is difficult to densify the sintered body, and the addition amount is insufficient. When it exceeds 40% by weight, high temperature characteristics such as high temperature strength and oxidation resistance are significantly deteriorated, which is not preferable. More preferable results can be obtained by adding two or more kinds of these sintering aids, not just a single one.

For whiskers, in addition to SiC, Si ₃ N ₄ , Al ₂ O ₃ , ZrO ₂ , C, potassium titanate, etc. can also be used, but especially SiC has excellent performance, and SiC whiskers when oriented further The fiber length is preferably at most about 60 μm. This is because the long fibers do not adversely affect the densification.

In addition, SiC whiskers are easy to disperse and are highly practical. The amount of fiber components can occupy 0.1 to 45 volume percent of the sintered body. This is because if it is less than 0.1 volume percent, there is no effect of addition, and if it exceeds 45 volume percent, a dense sintered body cannot be obtained. Furthermore, the fibers must be oriented in one direction. If the orientation is insufficient, problems occur such that it is difficult to densify the molded body, the strength of the sintered body is low, and the variation reliability is reduced.

The Si ₃ N ₄ matrix, which is made of Si in the compact, is converted to Si ₃ N ₄ by reactive sintering in nitrogen at a temperature of 1300 ° C to 1450 ° C.

Since it is difficult to make a dense sintered body only by reactive sintering,
Sintering is recommended in nitrogen at 1700 ℃ to 1900 ℃. It is preferable but not essential to pressurize the nitrogen gas to suppress decomposition of Si ₃ N ₄ . In some cases, hot isostatic pressing with high pressure nitrogen gas gives desirable results.

Next, a method for manufacturing the ceramic sintered body of the present invention as described above will be described.

First, there is obtained a ceramic molded body composed of Si particles, ceramic particles, and SiC whiskers, in which the SiC whiskers are oriented in a direction along the outer shape of the ceramic molded body. Such a molded article of the present invention is obtained by a novel molding method which is an improvement of the slip cast method, which is a molding method usually used in the method for producing ceramics.
That is, centrifugal force is used to achieve the orientation of the fiber components. Even if the slurry is simply injected into the mold, not only the orientation of the fiber component is insufficient, but also the fiber component cannot be uniformly distributed. On the other hand, if centrifugal casting that applies a centrifugal force is adopted, it is possible to obtain a uniform orientation and a uniform distribution of fiber components and the like.

FIG. 1 is a schematic view of an example of a centrifugal casting molding apparatus. Inside a closed container 1, a mold 3 rotatable by a rotation drive device 2 is provided. Vacuum suction can be performed by a vacuum pump (not shown). The mold 3 is made of a material that can pass only the solvent of the slurry 6 containing the sintered material 5 described later, for example, gypsum, filter paper, etc. Especially, for these gypsum and filter paper, the mold production is easy. It is suitable because it is available and inexpensive. It is also possible to obtain a preferable result by using a reduced pressure atmosphere during casting. Note that FIG. 1 shows a state where the sintered body material 5 is being formed from the slurry 6 on the inner wall of the mold 3 by centrifugal force. Therefore, in the present invention, Si powder and Al
₂ O ₃ , ZrO ₂ , Y ₂ O ₃ , one or more selected from the group consisting of MgO, CeO ₂ and La ₂ O ₃ and SiC whiskers as a fiber component, for example, water, alcohol, acetone, hexane It is mixed with a solvent such as the above to obtain a slurry, which is subjected to centrifugal casting.

This makes it possible to obtain a molded product in which the fiber components are oriented along the outer shape of the molded product and are uniformly dispersed.

Then, as described above, the compact is reacted and sintered in nitrogen at 1300 ° C to 1500 ° C to convert Si of the matrix of the compact into Si ₃ N ₄
And Then, it is further sintered in nitrogen at 1700 ° C to 1900 ° C to obtain a fiber-reinforced Si ₃ N ₄ sintered body. It is preferable to pressurize the nitrogen gas in order to suppress decomposition of Si ₃ N ₄ , and it is also preferable to use a hot isostatic press using high-pressure nitrogen gas.

[Example] Si powder 75 wt% of Example 1 the average particle diameter of 0.7μ, Al _2O 5 wt%, Y ₂ O ₃
A slurry was obtained by mixing and dispersing 5% by weight and 15% by volume of SiC whiskers having a diameter of 0.3 μ and a length of 60 μ in ethanol. The slurry was subjected to centrifugal casting to orient the whiskers parallel to the inner surface of the mold to obtain a molded body. The obtained molded body has an outer diameter
The length was 30 mm, the inner diameter was 20 mm, and the length was 60 mm. When the cross section of this molded body was observed, the SiC whiskers were oriented parallel to the inner surface of the molding die, and the orientation intervals were uniform from the inner peripheral side of the molded body to the outer peripheral portion thereof. The molded body was 1380 in a nitrogen stream.
Nitriding was carried out at 0 ° C. to obtain a reaction sintered body, which was further sintered at 1750 ° C. and 5 atmospheric pressure nitrogen for 2 hours.

The resulting sintered body has a relative density of 95% and room temperature bending strength of 70 kg / mm.
² ) It had excellent properties of 1200 ° C bending strength of 70Kg / mm ² and K _{IC of} 9.5MN / mm ^3/2 .

Example 2 A ceramic sintered body was manufactured in the same manner as in Example 1 by mixing the sintering aid used shown in Table 1 and 15% by volume of the same SiC whiskers as in Example 1 together with Si powder.

The characteristics of the obtained sintering are also shown in Table 1. From these results, it was found that when the amount of the sintering aid was less than 0.5% by weight or more than 40% by weight, the characteristics of the sintered body were significantly deteriorated, which was 0.5-40% by weight of the present invention. It is clear that the range is the optimum range of the amount of sintering aid.

The Weibull coefficient of room-temperature bending strength of each sample is as shown in Table 1, and it is clear that each sample has a Weibull coefficient of 20 or more and high reliability.

Example 3 A slurry was prepared by adding Si powder containing 5 weight percent Al ₂ O ₃ and 5 weight percent Y ₂ O ₃ as a sintering aid and SiC whiskers having a diameter of 0.3 μ and a length of 50 μ as shown in Table 2. Then, a sintered body was obtained by the same manufacturing method as in Example 1.

Table 2 shows the results of confirming the characteristics of the obtained sintered body.

From these results, it was found that the appropriate addition amount of SiC whiskers when added together with the above-mentioned sintering aid is 0.1 to 45% by volume, and from this table, the Weibull coefficient of room temperature bending strength is 20 or more for all. It can be seen that high reliability is obtained.

[Effects of the Invention] The present invention is characterized in that the above-mentioned whisker fibers are oriented in a ceramic molded body having a ceramic matrix and SiC whiskers as fibers as described above, and has excellent strength and toughness. Fiber reinforcement that combines
It provides Si ₃ N ₄ ceramics. In particular, it is extremely effective as a high temperature structural material in that it has high strength at high temperature and high toughness. For example, it can be used for a gas turbine structural material. This is because conventional ceramics lack high temperature strength and toughness and have not been put into practical use, and a great effect is expected.

Furthermore, the method of the present invention has the advantage that, in addition to realizing the fiber-reinforced Si ₃ N ₄ sintered body, centrifugal casting can be adopted, so that the manufacturing cost can be reduced and the sintered body can be economically supplied.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically explaining an example of a centrifugal cast molding apparatus.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masaya Miyake 1-1-1 Kunyokita, Itami City, Hyogo Prefecture, Sumitomo Electric Industries, Ltd. Itami Works (56) Reference JP-A-58-91073 (JP, A) JP-A-56-169166 (JP, A) JP-A-56-22678 (JP, A)

Claims (2)

[Claims] 1. Al ₂ O ₃ , AlN, ZrO ₂ , Y
₁ powder selected from the group consisting of ₂ O ₃ , MgO, CeO ₂ and La ₂ O ₃ or a mixture of Si powder containing 0.5 to 40 weight percent of two or more and 0.1 to 45 volume percent in the sintered body. A slurry obtained by dispersing SiC whiskers having a fiber length of 60 μm or less in a solvent is placed in a mold that allows only the solvent to permeate, and a centrifugal force is applied to make the slurry parallel to the inner surface of the mold and the inner circumference of the mold. Forming a molded body of Si in which the whiskers are distributed and oriented at a uniform density from the portion to the outer peripheral portion, heat-nitriding the molded body in a nitrogen atmosphere, and then sintering and densifying in a nitrogen atmosphere at a higher temperature. A method for producing a fiber-reinforced Si ₃ N ₄ sintered body, comprising: 2. Al ₂ O ₃ , AlN, ZrO ₂ , Y
1 or 2 or more selected from the group consisting of ₂ O ₃ , MgO, CeO ₂ and La ₂ O ₃ and containing 0.5 to 40 weight percent and SiC whiskers having a fiber length of 60 μm or less corresponding to 0.1 to 45 volume percent. In the sintered body, the whiskers are distributed and oriented parallel to the molding rotation axis direction by the action of centrifugal force at the time of molding and at a uniform density from the inner peripheral portion to the outer peripheral portion of the sintered body at room temperature. A fiber reinforced Si ₃ N ₄ sintered body, which has a bending strength of 55 kg / mm ² or more from 1 to 1200 ° C. and a Weibull coefficient of 20 or more.