JPS5891061A - Silicon carbide ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to high strength silicon carbide ceramics.

Ceramics are used in mechanical parts that are used at high temperatures, such as gas turbine parts, bearings, rollers for high-temperature conveyance, etc.The biggest obstacle is that ceramic materials are brittle materials. This is due to a lack of reliability.

In order to improve this reliability, in addition to increasing the average strength level of the material, in the case of ceramics, which are particularly brittle materials, there is a method to improve this reliability.
At the same time, it is necessary to completely eliminate all relatively large defects or to remove portions having large defects.

Another effective method is to prevent stress concentration in some way and make it similar to a tough material, which is being studied in the case of zirconia ceramics.

Furthermore, another possibility for realizing highly reliable ceramic paulownia wood is to compositely strengthen it with ceramic fibers, but it is difficult to manufacture (2) due to dust, and at present it is difficult to manufacture using methods such as hot pressing. 17 were not made due to unproductive methods.

Furthermore, extremely high-strength ceramic paulownia wood is without exception dense, and the manufacturing of this dense sintered body is without exception accompanied by firing shrinkage. If mixed fibers are used, they will not shrink during firing and will not form dense ceramics, making it impossible to obtain high strength ones.

Note that densification can be achieved by applying pressure from one direction and sintering with a method such as hot pressing, but this is not suitable for mass production.

The present invention was discovered as a result of various investigations into these problems, and the gist of the invention is to attach ceramic fibers to reactive sintered (self-bonding) ceramics, which have the characteristic of not causing shrinkage during firing. By combining these two materials, we succeeded in creating a ceramic with excellent high strength, improved dimensional stability, and reliability.

That is, the gist of the present invention is a reactive sintered silicon carbide ceramic reinforced with silicon carbide fibers and/or silicon nitride fibers and having a bending strength of 50 K9/rIJj or h' at room temperature and 1200°C. That is.

Silicon carbide ceramics have significantly higher strength, especially high-temperature strength, than conventional ceramics, and one major reason behind this is that in recent years, improvements in manufacturing technology have made it possible to obtain even higher strength products. As a result, heat-resistant metals have come to be used in structural components that are used at high temperatures where they lose their mechanical strength, as well as components that require corrosion resistance, wear resistance, high Young's modulus, and light weight. There is.

Silicon carbide ceramic sintered bodies intended for high strength generally include hot pressed products, normal pressure pressed products, and reaction sintered products, each of which has all the characteristics.

In particular, silicon carbide ceramics produced by reaction sintering have minimal dimensional changes during sintering, and have excellent dimensional accuracy after firing, as well as excellent long-term strength and thermal shock resistance at high temperatures up to about 1350°C. However, in terms of strength, it is often slightly inferior to other straight bond products.

The sintered body according to the present invention has greater strength, which is one of the characteristics of reaction sintered products! It is something that we are prepared for.

The ceramic of the present invention can be manufactured by applying a general reaction sintering manufacturing method to its case.

That is, a predetermined amount of fiber is blended into a mixture consisting of silicon carbide (Sin) powder, carbon (C1 powder, and a binder), which is thoroughly mixed and then molded, which is then completely heat-treated to remove the volatile components of the binder. Then, this molded body is impregnated with metallic silicon (Si)'iz, and then heated and fired in a non-oxidizing atmosphere or under reduced pressure at a temperature above the melting point of silicon to react with carbon to form a silicon carbide substance consisting of a strong connective tissue. Ceramics can be made into ceramics.The obtained ceramics are usually mostly SiC, with the remainder being about 10 pieces of metal S.
It often consists of i.

(5) In the silicon carbide raw material 17 used in the present invention, either α type or β type crystal form can be used.
Types are often used. Purity of 98% or higher is preferable.
, but those of 90 to 98 inches can also be used effectively. The particle size is about 1 to 50μ in average particle size, preferably 5 to 20μ
It is best to use something of a certain degree.

Suitable carbon powders include graphite powder, carbon black, pitch, coke powder, and pyrolyzed carbon of carbohydrates and hydrocarbons.
It is best to use it as a fine powder of 50 mesh or less.

The binder may be an organic material such as polyvinyl alcohol, methyl cellulose, styrene resin, furfural resin, thunol resin, or pitch, or a mixture thereof, which can easily decompose and remove volatile components with residual carbon during subsequent heat treatment. A vine is suitable.

In the present invention, the blending ratio of these is silicon carbide 100 (
(parts by weight) Based on K, the carbon content (C and silicon (6)) is generally suitable in the range of 20 to 50 parts by weight, and the binder is suitably in the range of 5 to 15 parts by weight based on these contents. be.

In the reactive sintering method of the present invention, a mixture consisting essentially of the following fibers is sufficient as a raw material, but of course a small amount of impurities that are included or mixed in during the grinding process are unavoidable. There is no problem even if other components or small amounts of other components that do not have any influence are included.

In the present invention, reinforcing fibers are added to these mixtures before forming a molded body.

The reinforcing fibers can be mixed sufficiently in advance as short fibers in the raw material mixture, or as long fibers in the form of a woven fabric or filament winding, and placed in a predetermined part of the molded body. can.

In the former case, the preferred embodiment is that the fiber diameter is 5 to 20
It has a diameter of about μ, a length of up to about 20 u, and a tensile strength of 200 kg/- or more.

In the latter case, various configurations are possible depending on the purpose, and the fiber length, diameter, number of bundles, etc., weaving method, weave compatibility, fiber count used, etc. can be selected depending on the purpose. . The use of such a woven fabric can be achieved by placing it in a predetermined position of a mold, for example, when you want to strengthen only the surface area, or when you want to increase the strength in a desired direction. 7, and one of the advantages of the reaction sintering method is that such use does not pose any problem.

When uniformly mixed with raw materials as short fibers, the appropriate blending amount of fibers is about 5 to 65% by weight in sintered ceramics, and usually 10 to 2%.
5chi seems to be optimal.

If it is too small, it will not be sufficient for the desired strength, and if it is too large, it will be difficult to fill the gaps between the fibers, making it impossible to obtain the effect of improving the strength, or using expensive fibers. This is because, in this case, the disadvantage is that the cost increases more than the performance improvement.

In addition, even when used in the form of a woven fabric, the appropriate proportion in the sintered body is about 5 to 65%, as in the case of short fibers, but the fiber density may be higher than this in some areas. There is also.

The optimal fiber used in the present invention is the same silicon carbide fiber as the cut piece. This is because, in the case of high Young's modulus ceramics such as those used in the present invention, the coefficients of thermal expansion of the fiber, the matrix ceramic, and the matrix must be the same or very similar, and the material must have a high-temperature strength higher than that of the matrix ceramic. This is because it must be done.

From this point of view, fibers that can be used in the present invention include popular silicon (SisN4) fibers, but alumina fibers and the like have a large coefficient of thermal expansion and are therefore unsuitable.

Similarly, the crystalline state of silicon carbide fiber (12) may be polycrystalline or single crystal (whisker), and may be -1 or α type (9). It may be β type.

As the molding method in the present invention, a method used in ordinary ceramic molding can be used. That is, press molding and extrusion molding are suitable, but slurry casting molding,
Injection molding or the like may also be used. The molded body is then heat treated (calcined) to decompose and remove the volatile components of the binder contained therein, and the appropriate temperature is about 250 to 1600°C, and the atmosphere is vacuum or argon. It is preferable to use an inert atmosphere such as in the middle of the air, but if the temperature is low, air may be used.

The unsintered compact thus obtained is generally 1
It is a porous body having a porosity of about 0 to 60 cm, and when it is impregnated with molten metal silicon and sintered at the same time, the ceramic of the present invention is obtained.

The porous body may be impregnated with molten silicon by degassing, or by immersing the molded body in the molten silicon while undergoing degassing treatment, or by partially immersing it and utilizing capillary action. Alternatively, the molded body may be placed in a vacuum or reduced pressure and heated above the melting point of silicon (10), and then the silicone vapor may be infiltrated.

It is also possible to form a silicon layer on the surface of the molded body in advance, and heat it to infiltrate the silicon layer.

In any case, the infiltration of silicon, the reaction with carbon in the molded body, and sintering are carried out simultaneously, and the appropriate conditions are as follows.

First, the atmosphere and 12 are non-acidic (arsenic or under vacuum,
The temperature is about 1550-1750°C.

The silicon carbide sintered ceramics obtained in this way can easily have a bending strength of 50 Kg/m-a or more at both room temperature and high temperature of 1200°C, and other In terms of physical properties, it is comparable to ordinary reaction sintered silicon carbide ceramics.

As described above, the present invention provides a high-strength reaction-sintered silicon carbide ceramic, which has great practical value.

Example 1 Specific surface area 2 rr? /g spurity 98% or more”2 α
For 100 parts by weight of silicon carbide powder, 50 parts of graphite powder of 200 mts or less, β silicon carbide polycrystalline fiber (Nippon Carbon Co., Ltd. Nikakuchi: y N L M-102;
Water was added to a mixture consisting of 15 parts (diameter: 15 μm, average length: 5 μm) and 12 parts of methylcellulose, thoroughly kneaded, and then extruded into a 7-molding machine to form a mixture with cross-sectional dimensions of 6.5 x 65 mm.
A rod-shaped molded body of ms was obtained. This rod-shaped body was cut into lengths of 100 mm, heat treated in air at 280°C, the binder was removed, carbon was 62% by weight, and silicon carbide fiber was 10% by weight.
, and a formed body having a bulk density of 162, the remainder being silicon carbide. This rod-shaped molded body was then placed upright in a graphite crucible, and at the bottom of the graphite crucible, 4% of 5iOs was added to silicon.
Put the ft-mixed powder compact into the crucible, heat it to 1650°C in a vacuum, and heat it to f? L0 The reaction sintered body thus obtained contains silicon carbide and approximately 1
It contained 1% metallic silicon.

This sintered body was processed into a rod-shaped body of 6 x 60 mm, and the bending strength and stress impact temperature were measured.
t shown in the table.

Example 2 Woven silicon carbide fiber (Nikalon S manufactured by Nippon Carbon Co., Ltd.; weaving method: Sateen weave, mesh t1--300-5
00g/rr? ) was coated with the same base material of graphite, α-silicon carbide, and binder as in Example 1), and a similar mixture of graphite, α-silicon carbide, and binder was sandwiched between them and press-formed. 7, Ro5
A molded body of X5QX101]vR was obtained.

This molded body was heated in air at 280° C. to remove the binder, and a molded body was obtained having a bulk density of 1.66 and consisting of 29 parts by weight of carbon, 15 parts by weight of Phi-no-Ki, and the remainder silicon carbide.

This molded body was then subjected to reaction sintering in the presence of silicon in the same manner as in Example 1 (2) to obtain a reaction sintered ceramic, a clay containing approximately 12% silicon. was measured in the same manner as in Example 1, and the results are shown in Table 1.

COMPARATIVE EXAMPLE Table 1 shows the results of measurements on sintered ceramics obtained using a mixture similar to Example 1 but without fibers.

Table 1 Note that the thermal shock resistance temperature difference is the temperature difference at which a decrease in strength occurs when a bending strength measurement sample that has been heated in advance in an electric furnace is rapidly cooled in water.

(14) Procedural amendment band (issued) April 1980 Haruki Shimada, Commissioner of the Patent Office 1, Indication of the case 1983 Patent Application No.] 88381 2, Name of the invention Silicon carbide ceramics 3, Make amendments Relationship with the Patent Case Patent Applicant Address 2-1-2 Marunouchi, Chiyoda-ku, Tokyo Name (
004) Asahi Glass Co., Ltd.

Claims (1)

[Claims] Reactive sintered silicon carbide ceramics reinforced with Il+ silicon carbide fibers and U/or silicon nitride fibers and having a bending strength of 50 to 9/- at room temperature and 1200°C ( 2) The silicon carbide ceramic according to claim 1, wherein the fiber content is from 5 to 65 g by weight (3) Claim 1 or 2, wherein the fiber is a silicon carbide fiber. The silicon carbide ceramic (4) according to claim 6, in which the fibers are present in the form of a woven fabric.