JP2747630B2 - Fiber reinforced ceramic molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an silicon nitride ceramic body reinforced fibers, and more particularly, Al ₂ O ₃ fibers together has improved the blended and green strength, sintered body excellent obtained therefrom The present invention relates to a ceramic molded body having high strength.

[0002]

2. Description of the Related Art In general, a ceramic sintered body is formed by molding a ceramic powder into a predetermined shape to form a green body.
Obtained by sintering. Ceramics are difficult to process once sintered, so they are formed into a desired shape before sintering. Examples of the method for producing such a ceramic molded body include a method of pressing using a mold, an injection molding method, a slip casting method by casting ceramic slurry into a gypsum mold, a cold isostatic pressing method by a rubber press, and the like. However, in order to obtain a molded product with a thin wall or a complicated shape,
A slip casting method, an injection molding method, a molding method using a doctor blade, or the like, in which a ceramic slurry (or a kneaded product of a resin or the like) is injected into a mold having a predetermined shape to form the molding, is preferable.

In the slip casting method, a ceramic raw material is powdered and dispersed in a medium such as water, and the obtained slurry is put into a gypsum mold to absorb and transmit moisture. A green compact with the ceramic powder solidified by this
Is obtained.

Since silicon nitride ceramics have excellent heat resistance, high strength, high hardness, and are relatively lightweight, they have been spotlighted as alternatives to metal materials. Since this silicon nitride ceramic is generally difficult to be sintered, Y ₂ O ₃ or Al ₂ O ₃
Powders of sintering aids and other additives are added, and a molded body is first manufactured by the above-described slip casting method and the like, and this is sintered.

[0005]

However, when a ceramic molded body is made by the above-described slip casting method or the like, the bonding force between the ceramic powder particles is not necessarily large even if a binder or the like is mixed with the ceramic powder. In addition, the mechanical strength of the molded article is not large, and the molded article is likely to be broken. Further, the ceramic molded body shrinks due to dehydration and drying in a gypsum mold, and cracks are likely to occur. For this reason, it has been difficult to produce a thin-walled molded article or a molded article having a complicated shape without fear of breakage or cracking.

Therefore, in the production of silicon nitride ceramics, for example, proposals have been made (for example, to increase the strength of a green body) by adding sintering aids such as Al ₂ O ₃ to fibers and adding them to raw materials. No. 2-9777).

By the way, although the Al ₂ O ₃ fibers includes unavoidably SiO ₂ reasons manufacturing, generally, Al ₂
It is known that the greater the amount of SiO ₂ contained in the O ₃ fiber, the greater the strength (tensile strength) of the Al ₂ O ₃ fiber itself. And SiO ₂ amount contained in al ₂ O ₃ fibers, an example of the experimental result of examining the relationship between the tensile strength of the fiber is shown in Figure 2, as can be seen from the graph shown in FIG. 2, SiO ₂ amount Al accordance There SiO ₂ amount increases up to about 3 wt%
The tensile strength of the ₂ O ₃ fiber increases rapidly. In addition, SiO
_When the amount of ₂ is about 3% by weight or more, the degree of increase in the tensile strength with respect to the increase in the amount of SiO ₂ gradually decreases, but the tensile strength of the Al ₂ O ₃ fiber increases with the increase in the amount of SiO _2. . Therefore, Al ₂ O having a high content of SiO _{2
When three} fibers are used, it can be said that the strength of the molded body is improved.

However, according to the study of the present inventors, a sintered body obtained by sintering a molded body using Al ₂ O ₃ fiber having a large content of SiO ₂ has a great decrease in mechanical strength,
It turned out that it cannot be used as a good ceramic member.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-mentioned problems of the prior art, to provide a silicon nitride-based ceramic molded body with sufficient mechanical strength to prevent its breakage and cracking, and to further bake it. It is an object of the present invention to provide a silicon nitride-based ceramic molded body in which the strength of the ceramic sintered body obtained by the above method does not decrease.

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above-mentioned object, and as a result, in Al ₂ O ₃ as a sintering aid component to be compounded in a fibrous form for reinforcing a molded product, If the amount of the SiO ₂ component contained therein is limited to a specific amount or less, the strength of the obtained sintered body at room temperature and high temperature is not substantially reduced, so that it has good mechanical strength. And completed the present invention.

That is, the fiber-reinforced ceramic molded body of the present invention in which Al ₂ O ₃ fibers are blended with ceramic powder mainly composed of silicon nitride is contained in the Al ₂ O ₃ fibers.
The amount of SiO ₂ is not more than 5% by weight of the whole Al ₂ O ₃ fiber.

Hereinafter, the present invention will be described in detail. When producing ceramics mainly composed of silicon nitride, both α-type and β-type can be used as silicon nitride powder to be used. Examples of the production method include a direct nitridation method of Si, a reduction / nitridation method of silica, a thermal decomposition method of silicon diimide, and a gas phase reaction method of SiH ₄ + NH ₃ + N ₂ . The silicon nitride powder preferably has an average particle size of 0.01 to 3 μm, more preferably 0.1 to 1.5 μm.

In silicon nitride powder, as an inevitable component
Although SiO ₂ is contained, in the present invention, the amount of SiO ₂ derived from the silicon nitride powder is 3.0 to 7.
It is better to be about 5% by weight.

As described above, silicon nitride is not easily sintered by itself, and is usually sintered by adding a sintering aid. In the present invention, as the sintering aid, Al ₂ O ₃
Although fibers are used, a simple substance or a compound of Group IIIa element of the periodic table may be further added as a sintering aid component.

Al ₂ O ₃ used as a sintering aid in the present invention is fibrous. By using fibrous Al ₂ O ₃ , the molded body (green) is reinforced and its strength is improved.

The average diameter of the Al ₂ O ₃ fiber is 10 μm or less, especially 0.5 to 5 μm, and the fiber length is 10 to 500 μm, especially 100 to 300 μm.
μm is desirable. If the average diameter and the fiber length are too large, the dispersibility of the Al ₂ O ₃ fiber is reduced, and there is a large possibility that a molded article after sintering will have a defect, and the sintered density will be reduced. On the other hand, if the average diameter and the fiber length are too small, the effect of adding the Al ₂ O ₃ fiber to the molded article cannot be sufficiently obtained.

As described above, Al ₂ O ₃ fibers inevitably contain SiO ₂ for reasons of production. In the present invention, the amount of SiO ₂ contained in the Al ₂ O ₃ fibers (relative to Al ₂ O ₃ total fiber containing SiO ₂₎ to limit the 5 wt% or less. When the amount of SiO ₂ contained in the Al ₂ O ₃ fiber exceeds 5% by weight, the strength of the obtained sintered body is greatly reduced. Preferably, the amount of SiO ₂ contained in the Al ₂ O ₃ fiber is 3 to 5% by weight.

[0018] Incidentally, in the green body, but will also include SiO ₂ component derived from the silicon nitride powder, the amount of SiO ₂ component from the silicon nitride powder, the sintered body if the range mentioned above The high temperature strength does not substantially decrease. According to the study of the present inventors, the amount of SiO ₂ contained in the Al ₂ O ₃ fiber largely affects the strength of the sintered body. That is, when the Al ₂ O ₃ fiber contains a large amount of SiO ₂ , the Al ₂ O ₃ fiber is heated at a temperature lower than the sintering start temperature of the silicon nitride component during heating in the sintering step.
The softening of the ₂ O ₃ fiber occurs, and the components of the Al ₂ O ₃ fiber (Al ₂ O ₃
O ₃ SiO ₂ is added ingredients) ends up spread around in, therefore had originally exist Al ₂ O ₃ fibers position tends to become voids (defects). Therefore, if the amount of SiO ₂ contained in the Al ₂ O ₃ fiber is limited as described above,
The softening of the Al ₂ O ₃ fiber and the diffusion of its components at a low temperature can be prevented, and the generation of defects can be prevented.

The compounding ratio of the Al ₂ O ₃ fiber in the compact is
_When Y ₂ O ₃ is used in combination with ₂ O ₃ fiber, Al ₂ O ₃
Fibers from 0.5 to 5.5 wt%, a Y ₂ O ₃ 1.5 ~3.5 wt%
(Both with respect to the molded body). Al ₂ O ₃
If the fiber content is less than the lower limit described above, the reinforcing effect of the Al ₂ O ₃ fiber on the molded body is not sufficient, and the ceramic molded body is likely to be damaged or cracked. On the other hand, when the Al ₂ O ₃ fiber content is larger than the above upper limit, the strength of the obtained sintered body decreases. As a sintering aid, Y (with Al ₂ O ₃ fiber)
Other oxides can be added in addition to ₂ O ₃ .

The ceramic molded body of the present invention may optionally contain a small amount of an organic binder such as wax or resin, an organic substance, metal fibers, and the like, in addition to the above components.

Next, a method for producing the ceramic molded body of the present invention will be described. First, a dispersion medium composed of water or an organic solvent containing silicon nitride powder as a main component, Al ₂ O ₃ fibers, and, if necessary, other ceramic additives (including other sintering aids such as Y ₂ O ₃ ). And uniformly disperse into a slurry.

When water is used as the dispersion medium, it is preferable to add aqueous ammonia. Since NH ₄ OH has good dispersibility, a ceramic slurry having a high concentration and a low viscosity can be prepared, and after drying, a high-density compact can be obtained. In addition, impurities such as sodium and calcium do not remain in the molded product after sintering, and a high-purity sintered body can be obtained.
Further, since the glass phase at the grain boundaries can be reduced, the high-temperature strength of the sintered body can be kept high. When the glass phase at the grain boundaries increases, the strength of the sintered body at high temperatures decreases. When a highly polar organic solvent such as formamide is used as the dispersion medium, oxidation of silicon nitride can be prevented, which is suitable for keeping the high-temperature strength of the sintered body high.

In addition to the above components, a small amount of a binder or the like may be added as required.

Although not particularly limited in the present invention, the concentration of the slurry is preferably from 40 to 60% by volume from the viewpoint of moldability.

In order to mold the molded article, injection molding, slip casting, molding with a doctor blade, and the like are applied. In particular, good results are obtained in the case of slip casting.

In the case of the slip casting method, the slurry is cast into a mold made of a material having water absorption and permeability, such as gypsum. As the dispersion medium is dispersed through the mold, the slurry is dewatered. Thereafter, it is released from the mold and dried sufficiently. In the dehydration and drying process, there is a danger of breakage or cracking of the molded product, but it is uniformly dispersed and reinforced by ceramic fibers, or the ceramic powder works well as a binder, so that breakage and cracking are sufficiently prevented. can do.

Through the above steps, a silicon nitride-based ceramic molded body in which Al ₂ O ₃ fibers are uniformly dispersed can be obtained.
The compact is sintered by a known method to obtain a sintered body. In this sintering step, the Al ₂ O ₃ fibers in the compact are melted and flown at a temperature close to the sintering temperature of the silicon nitride particles. To lose the fiber shape and form a uniform ceramic. As a result, a sintered body having excellent mechanical properties and heat resistance can be obtained.

[0028]

According to the present invention, Al ₂ O ₃ , which is one of the sintering aid components of the compact, is introduced into a very fragile compact formed by solidifying the ceramic powder. Since the molded body was reinforced by this, the mechanical strength, elongation, distortion resistance, etc. of the ceramic molded body can be greatly improved,
As a result, breakage and cracking of the molded article are greatly reduced.

The SiO ₂ contained in the Al ₂ O ₃ fiber
Because defines the amounts of ingredients to 5 wt% or less, in the heating in the sintering step, Al ₂ O ₃ fibers are not able to soften so much at low temperatures, Al ₂ O at much lower temperatures than the sintering temperature The diffusion of the _three- fiber component to the surroundings can be prevented, so that defects such as voids do not occur in the portion where the Al ₂ O ₃ fiber was originally located. Therefore, a decrease in strength of the obtained sintered body is prevented.

[0030]

The present invention will be described in more detail with reference to the following examples.

Example 1 Silicon nitride powder (average particle size 0.3 μm, oxygen content 1.10%)
96.5 parts by weight and Y ₂ O ₃ powder (average particle size 1.4 μm) 2.5
Parts by weight were uniformly mixed with a ball mill. In addition, distilled water was used as a dispersion medium.

To a slip obtained by mixing for 13 hours by a ball mill, 1 part by weight of Al ₂ O ₃ fiber (average diameter 3 μm, average fiber length 100 μm) having an SiO ₂ content of 5% by weight was added, and further 3 hours. Mixed.

As described above, the slip obtained by mixing by a ball mill for a total of 16 hours was poured into a gypsum mold, and a rectangular parallelepiped shaped body having a size of 35 mm × 55 mm × 7 mm was formed by a slip casting method. After removing the molded body from the gypsum mold, the temperature was gradually increased from room temperature and dried at 180 ° C. for 1 hour.

The molded product did not break or crack during handling, and shrinkage after drying was small.

Next, the compact was heated at 1950 ° C. in nitrogen gas.
For 4 hours. The density of the obtained sintered body is 9
It was 7% or more, and the shape accuracy was good. When the cross section of the obtained sintered body was observed with a scanning electron microscope, the structure of the sintered body was dense, and no void serving as a defect was observed.

Next, the sintered body was subjected to a three-point bending test in accordance with JIS K 1602, and the bending strength at room temperature and at 1300 ° C. was measured. The results are shown in FIG. FIG.
In the graph shown in (1), the horizontal axis represents the ratio (% by weight) of the total amount of oxygen in the molded body, and the bending strength value is plotted in terms of the mixing ratio of the ceramic component in the molded body. The same applies to the following comparative examples and reference examples.

Comparative Examples 1 and 2 Silicon nitride powder (average particle size 0.3 μm, oxygen content 1.10%)
96.5 parts by weight and Y ₂ O ₃ powder (average particle size 1.4 μm) 2.5
Parts by weight and the content of SiO ₂ is 15% by weight (Comparative Example 1) or 28
% (Comparative Example 2) Al ₂ O ₃ fiber (average diameter 3 μm,
Except for using 1.0 part by weight of an average fiber length of 100 μm, a molded body was produced in the same manner as in Example 1, and a sintered body was produced in the same manner as in Example 1. The strength at room temperature and 1300 ° C. of these sintered bodies was measured in the same manner as in Example 1. The results are shown in FIG. As in Example 1, the cross sections of these two sintered bodies were observed with a scanning electron microscope. However, in the sintered bodies of Comparative Examples 1 and 2, Al ₂ O ₃ fibers were melted and diffused. Some voids were considered.

Reference Examples 1 to 3 The following three types of sintered bodies were produced in order to examine the effect of the SiO ₂ component not derived from the Al ₂ O ₃ fiber on the strength of the sintered body.

First, as Reference Example 1, the oxygen content was 1.09.
% Silicon nitride powder (average particle size 0.3 μm) 96.5 parts by weight,
2.5 parts by weight of Y ₂ O ₃ powder (average particle size 1.4 μm) and Al ₂ O ₃ powder with purity of 99.9% by weight or more (average particle size 1.2 μm)
1 part by weight, and a molded article was produced in the same manner as in Example 1. Further, a sintered body was manufactured in the same manner as in Example 1, and the obtained sintered body was treated at room temperature and in the same manner as in Example 1.
The strength at 1300 ° C. was measured.

In Reference Examples 2 and 3, the oxygen content was
A sintered body was produced in the same manner as in Reference Example 1, except that silicon nitride powders (average particle diameter: 0.3 μm) of 1.13% and 1.15% were used.
Then, as in Example 1, room temperature and 1300 ° C.
Was measured for strength. The strength test results of Reference Examples 1 to 3 are also shown in FIG.

As can be seen from the above, the sintered body in this example has good strength at room temperature and at 1300 ° C., respectively. On the other hand, the strength of the sintered body of each comparative example is small. In addition, the greater the amount of Al ₂ O ₃ fiber added, the greater the decrease in strength.

In comparison with the comparative example and the reference example, the absolute amount of SiO ₂ contained in the sintered body does not directly affect the strength of the sintered body, but is attached to the Al ₂ O ₃ fiber. The amount of SiO ₂ introduced into the system affects the strength of the sintered body,
_It can be seen that the greater the amount of SiO ₂ contained in the ₂ O ₃ fiber, the lower the strength of the sintered body.

[0043]

As described above, the silicon nitride-based ceramic compact of the present invention contains Al ₂ O ₃ fibers, and has an improved strength. Therefore, the silicon nitride-based ceramic molded body according to the present invention has no risk of breakage or cracking even if the molded body is thin or has a complicated shape. Further, the amount of SiO ₂ contained in the Al ₂ O ₃ fiber is limited to a small amount, and the strength of the obtained sintered body does not decrease for the above-mentioned reason.

The sintered body obtained from the ceramic molded body of the present invention has good mechanical strength and heat resistance, and is suitable for use in automobile parts such as turbocharger rotor blades.

[Brief description of the drawings]

FIG. 1 is a graph showing the strength at room temperature and 1300 ° C. of each sintered body in Examples, Comparative Examples, and Reference Examples.

FIG. 2 shows the amount of SiO ₂ contained in Al ₂ O ₃ fiber and the amount of Al ₂ O ₃
It is a graph which shows the relationship with the tensile strength of a fiber (single fiber).

Claims (1)

(57) [Claims] 1. A ceramic powder mainly composed of silicon nitride.
In the fiber-reinforced ceramic green body obtained by blending Al ₂ O ₃ fibers, wherein the amount of SiO ₂ contained in the Al ₂ O ₃ fibers is less than 5 wt% of the Al ₂ O ₃ entire fiber Fiber-reinforced ceramic molded body.