JPH0678192B2 - Carbon-silicon carbide based composite material and method for producing the same - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention provides a matrix with a reinforcing material in a tightly dispersed state, and thereby toughness,
The present invention relates to a carbon-silicon carbide composite material having significantly improved physical properties such as mechanical shock resistance, thermal shock resistance, mechanical strength, sliding characteristics, abrasion resistance, and erosion resistance, and a method for producing the same.

[0002]

2. Description of the Related Art Generally, a carbon sintered body is used for various purposes because it has excellent heat resistance and good electrical conductivity. However, when it is used alone, it lacks mechanical strength. In many cases, it is used as a composite material reinforced with fibers or whiskers.

By the way, when a reinforcing material such as fibers or whiskers is compounded in a carbon matrix, if the reinforcing material and the matrix are different in type, a difference in expansion rate and contraction rate occurs during heating and cooling. However, there is a drawback that the tightness of the steel is lost and a sufficient reinforcing effect cannot be obtained.

In order to improve such drawbacks, a method of using carbon fiber as a reinforcing material and repeating pitch impregnation and firing a large number of times to combine carbon and carbon fiber has been carried out, but the operation is complicated and complicated. , You can't avoid limited applications because you can only get what is organizationally limited.

Further, although long fibers are usually used in carbon-carbon fiber composite materials, long fibers are inconvenient for making composite materials having no anisotropy in physical properties, and short fibers or whiskers are used. Is desirable. However, in this case, it is difficult to homogeneously mix the granular powder and the needle-shaped substance, and as a result, it is difficult to obtain a composite material having sufficient strength, and even if homogeneous mixing is possible, As described above, due to the difference in heat shrinkage between the matrix carbon and the short fibers or whiskers in the firing process, a dense one cannot be obtained, and the short fibers and whiskers tend to be aligned in the pressing direction during the molding of the raw material, There are drawbacks such as difficulty in obtaining a highly isotropic composite material.

[0006] As described above, the conventional method of manufacturing a composite material by incorporating the needle-shaped substance has various problems, and therefore the carbon composite material in which the needle-shaped substance is dispersed has preferable physical properties. In reality, it is difficult to spread as a general material. Furthermore, in the conventional acicular substance-dispersed carbon composite material, the scratches of the acicular substance, which are easily attached to the manufacturing process such as the mixing step, may affect the physical properties of the composite material.

By the way, the present inventor first (1) a method for producing a carbon / ceramic composite material in which ceramic particles such as boron carbide and silicon carbide are extremely uniformly dispersed (Japanese Patent Publication No. 58-38386), (2) ) While proposing an oxidation resistant carbon material (Japanese Patent Publication No. 62-12191), which is obtained by simultaneously impregnating boron carbide and silicon carbide particles and has extremely excellent oxidation resistance, (3) the composite material of (2) above It has been found that a carbon composite material having excellent oxidation resistance and large breaking energy can be obtained by further impregnating short carbon fibers.

Among these, the carbon composite material of (3) has the excellent characteristics as described above and has attracted attention, but as described above, due to the difference in heat shrinkage between the matrix phase and the fiber, It becomes inferior in tightness, it is inevitable that the bulk density after firing will decrease compared to the one not impregnated with fibers, and the fibers will be scratched during mixing of raw materials or molding, and the dispersion will be uneven. In addition, it has the drawback that silicon carbide powder must be impregnated at the same time to impart oxidation resistance. Further, as a method of imparting oxidation resistance, it is possible to use silicon carbide whiskers instead of carbon fibers, but in this case, whiskers having high hardness are more likely to be damaged during the mixing process. .

[0009]

SUMMARY OF THE INVENTION The present invention overcomes the disadvantages of such conventional carbon-based composite materials and provides a dense,
We also provide carbon-based composite materials that have no anisotropy in physical properties and have improved physical properties such as toughness, mechanical shock resistance, thermal shock resistance, mechanical safety, sliding properties, wear resistance, and erosion resistance. It was made for the purpose of doing.

[0010]

As a result of intensive research to develop a carbon composite material having the above-mentioned preferable properties, the present inventor has found that carbon, particulate silicon carbide and, in some cases, a specific amount of boron or boron. By firing a molded body containing a compound, the particulate silicon carbide can be crystal-grown in a carbon matrix to change from a particle-dispersed type to a fiber-dispersed type (needle-like substance dispersed type). The inventors have found that the object can be achieved, and have completed the present invention based on this finding.

That is, the present invention provides a composite material comprising a carbon-based matrix and acicular silicon carbide reinforcing material dispersed therein, wherein the acicular silicon carbide reinforcing material is formed by crystal growth in the matrix. And a carbon-silicon carbide based composite material.

According to the method of the present invention, such a carbon-silicon carbide based composite material is converted into carbon or carbon and 20% by weight or less of boron or 20% by weight of boron.
20 to 60 parts by weight of β-silicon carbide powder is added to 100 parts by weight of a powder mixture with a boron compound in an amount of 1% by weight or less, and the obtained raw material mixture is molded into a desired shape, and then 2100
It can be produced by firing at a temperature of ˜2500 ° C. for a time sufficient to form acicular silicon carbide.

The composite material of the present invention comprises 40 to 80% by weight of carbon constituting the matrix and 40 to 30% by weight of acicular silicon carbide as a reinforcing material. Carbon constituting the matrix may be replaced with boron carbide B ₄ C within a range not exceeding 20% based on the weight thereof.
Further, the matrix should contain other metals, for example, carbides such as zirconium, titanium, lanthanum, chromium, iron, aluminum, magnesium, etc., nitrides and borides in an amount within the range not impairing the basic physical properties. You can also

Next, the acicular silicon carbide has a diameter of 1 to 5 μm,
It has a length of 10 to 100 μm and its aspect ratio is 5 or more, preferably 10 to 30. Outside of this range, a sufficient reinforcing effect cannot be obtained.

In the method of the present invention, the carbon powder and the β-silicon carbide powder are added to the former 20 to 6 per 100 parts by weight of the former.
A mixture of 0 parts by weight is used as a raw material mixture. As the carbon raw material, petroleum coke, pitch coke, resin and the like are used in powder form. In addition, natural graphite or the like can be partially used for improving sliding properties and other physical properties.

The carbon raw material may contain boron or a boron compound in order to promote the growth of acicular silicon carbide during sintering. This content needs to be 20% by weight or less in terms of boron with respect to carbon, and if the amount is larger than this, β-silicon carbide is transformed into α-silicon carbide during sintering, resulting in coarse particles. A crushed granular material or a plate-like material is produced, and the material does not become acicular.

Next, as a raw material for forming acicular silicon carbide as a reinforcing material, it is necessary to use β-silicon carbide among the many known silicon carbides, that is, cubic 3C type. This β silicon carbide is usually 2
When firing at a temperature of 200 ° C. or higher, secondary recrystallization occurs and coarse plate-like crystals are formed. Therefore, in order to form acicular β-silicon carbide, firing at a temperature of 2000 ° C. or lower was required. When mixed with carbon powder and fired according to the method of the invention, surprisingly, even at a temperature of 2300 ° C. or higher, plate-like crystals do not occur and needle-like crystal growth occurs.

In a preferred embodiment of the method of the present invention,
Carbon, β-silicon carbide and optionally boron or boron compound are mixed in powder form, respectively, and press-molded, and then calcined at a temperature of 800 to 1500 ° C., or a pitch binder or a thermosetting resin is used. A molded body is produced by molding using the above.

At this time, since silicon reacts with carbon at a temperature of 1500 ° C. or lower to form β silicon carbide, the above β
It is also possible to replace at least part of the silicon carbide with silicon or a silicon-forming substance such as chaff ash.

In the production of this molded product, if necessary, a part of the particulate β-silicon carbide is replaced with acicular silicon carbide short fibers or whiskers within the range where the object of the present invention is not impaired. be able to. Further, for the purpose of promoting and controlling the growth of acicular silicon carbide, controlling the morphology, or controlling the interface state with the carbon matrix, substances that normally affect the grain growth and crystal structure transition of silicon carbide, such as lanthanum. Metal compounds such as chromium, iron, titanium, aluminum, and magnesium, and nitrogen compounds may be added, and substances for improving oxidation resistance, such as zirconium, titanium, and carbides or borides of aluminum, may be added. You may add.

Then, the molded body thus obtained is
100-2500 ° C, preferably 2200-2400 ° C
Bake at the temperature of. The firing time is sufficient to form acicular silicon carbide in the matrix. This time depends on the composition of the raw material mixture and the firing temperature,
It is usually about 2 to 10 hours, but it may take a longer time depending on the case. By this calcination, β-silicon carbide is crystal-grown into acicular silicon carbide to form a densely dispersed high-density composite having no voids with the matrix.

[0022]

The present invention will be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

Example As the carbon, raw coke powder having a grain size of 100 mesh or less was used, and this was used together with a weight average grain size of 0.27 μm and Si.
2. A β-silicon carbide powder having a C content of 98% by weight [manufactured by Ibiden Co., Ltd.] or an α-silicon carbide powder and a boron carbide powder [manufactured by Denki Kagaku Kogyo Co., Ltd. No. 1200], and having a weight average particle diameter of 3.
5 μm zirconium boride powder (Hermann
C. (Manufactured by the same company) are mixed at a ratio shown in Table 1 so as to be sufficiently homogeneous, pressure-molded, then calcined at 1000 ° C. to prepare a molded body, and then baked under the conditions shown in Table 1. Then, a carbon composite material was manufactured.

The bulk density of this carbon composite material was determined and the structure was observed. The results are shown in Table 1.

[Table 1]

As can be seen from Table 1, in the case of mixing only β-silicon carbide (No. 1), formation of acicular silicon carbide was not observed even at the treatment of 2300 ° C. However, in this case, β-silicon carbide was not transferred to α-silicon carbide and remained as β-silicon carbide. This suggests that if heat treatment is performed for a longer time, crystal growth into acicular silicon carbide occurs and a dense carbon composite material can be obtained.

In the case of adding 3.3 parts by weight of boron carbide and 2 parts by weight of zirconium boride together with β-silicon carbide (No. 2), granular and rod-shaped crystal growth was observed. When the content of boron carbide is increased to 7.3 parts by weight (No.
3), the used β-silicon carbide particles have an average particle size of 0.27μ
As shown in the micrograph of FIG. 1, despite the small m, the growth of acicular silicon carbide having a length of about 50 μm and a large aspect ratio of 10 to 20 was observed.
It can be seen that the boron carbide promotes the growth of acicular silicon carbide.

Here, zirconium boride was added for the purpose of improving the oxidation resistance, but even in the sample without zirconium boride (No. 4), the same needle as the sample with zirconium boride added was used. The growth of silicon carbide was observed. That is, it can be seen that the influence of zirconium boride on the growth of acicular silicon carbide is small.

When the amount of boron carbide reaches 13 parts by weight (the ratio of boron to carbon is about 20 mol%) (No.
5), rod-shaped or granular silicon carbide having an aspect ratio of 5 or less was found, and they tended to be united with each other. According to X-ray diffraction, this rod-shaped silicon carbide was transformed into α-silicon carbide, which indicates that needle-shaped silicon carbide with a large aspect ratio is unlikely to be formed in this sample even if the heat treatment time is further extended. It is guessed that. Further, in the case of heat treatment at 2100 ° C. for 1 hour (No. 6 and No. 7), formation of acicular silicon carbide was not observed.

Further, a sample (No. 2) having a small amount of boron carbide, in which only rod-shaped silicon carbide having a small aspect ratio was observed by heat treatment at 2300 ° C. for 1 hour,
By performing the treatment at the same temperature for 3 hours (No. 8), as shown in FIG.
As shown in the photomicrograph of, the aspect ratio is 10-2.
The formation of needle-shaped silicon carbide of 0 is observed, and it is understood that the influence of the heat treatment time is large. It is inferred that even in the sample (No. 7) at 2100 ° C. in which the formation of needle-shaped silicon carbide was not observed, the needle-shaped silicon carbide may be generated if the heat treatment is performed for a long time in the industrial furnace. Further, in the case of using α silicon carbide (No. 9), formation of acicular silicon carbide was not observed at all.

Looking at the bulk density, the sample in which silicon carbide grows only in a granular form (No. 1) has a bulk density of 2 even though it contains the largest amount of silicon carbide having a large specific gravity. , 104 g / cm ^{3, which} is the lowest.

On the other hand, in the case of the needle-like grown sample, (N
o. 3), has a high bulk density of 2,138 g / cm ³ . In addition, a sample (No.
In 2), the bulk density is higher than this because it contains a large amount of silicon carbide having a large specific gravity.
If this sample was treated at the same temperature for a longer period of time (N
o. 8), the acicular silicon carbide grows remarkably, and the bulk density further increases to 2,224 g / cm ³ . These indicate that the growth of acicular silicon carbide does not lead to a densification of the composite material, but rather a densification.

[0032]

According to the present invention, it is dense, has no anisotropy in physical properties, and has toughness, mechanical shock resistance, thermal shock resistance, mechanical safety, sliding characteristics, wear resistance, erosion resistance, etc. A carbon-silicon carbide composite material having improved materials is obtained.

[Brief description of drawings]

FIG. 1 is a micrograph showing an example of the structure of a ceramic material of the present invention.

FIG. 2 shows the different structure of the ceramic material of the present invention.
Micrograph showing an example

Claims (3)

[Claims] 1. A composite material comprising a carbon-based matrix and acicular silicon carbide reinforcement dispersed therein, wherein the acicular silicon carbide reinforcement is formed by crystal growth in the matrix. A carbon-silicon carbide based composite material characterized by being present. 2. 20 to 60 parts by weight of β-silicon carbide powder is added to 100 parts by weight of carbon or a powder mixture of carbon and 20% by weight or less of boron or 20% by weight or less of a boron compound in terms of boron. In addition, after the obtained raw material mixture is formed into a desired shape, it is fired at a temperature of 2100 to 2500 ° C. for a sufficient time to form acicular silicon carbide. Production method. 3. The production method according to claim 2, wherein a zirconium boride or carbide is added to the raw material mixture.