JPH0714603B2 - Method for producing sintered ceramics containing fiber ceramics - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to a method for producing a ceramics sintered composite material using a fibrous material as a reinforcing material. More specifically, the fibrous material is uniformly dispersed in a matrix. The present invention relates to a method for easily producing a fiber-containing ceramics sintered composite material which has excellent mechanical strength and small variation.

[Technical background of the invention and its problems] A fiber-reinforced ceramics sintered composite material, in which various ceramics are used as a matrix and various fibrous materials are reinforced, has been widely studied as a useful new material.

Physical and chemical compatibility between the combined ceramic matrix and the fibrous material (for example, mutual wettability) acts as an important factor for improving the properties of these composites, especially the mechanical strength properties. .

However, more than that, the issue is whether the fibrous material is homogeneously dispersed in the molded body when the composite material is molded.

At present, for example, a winding method, a laminating method, a casting method, a slip casting method, a ball mill method, a kneader method or the like is applied as a method for manufacturing a composite molded body by dispersing a fibrous material in a ceramic matrix. For example, in the case of the slip casting method, a matrix component and a fibrous material are mixed, a dispersion liquid such as water is added to the mixture to form a slurry for casting, and the slurry is poured into a mold of a predetermined shape to be molded. It is a method of doing.

However, all of these methods require a step of mixing the ceramic matrix and the fibrous material by using some mechanical mixing means and attempting to homodisperse the latter.

In this case, when the mixing amount of the fibrous material is large, or when the difference in specific gravity between the ceramic matrix and the fibrous material is large, it is extremely difficult to uniformly disperse both. Moreover, the fibrous material may be damaged by the load from the mixing means (for example, a kneader blade).

The dispersion of the fibrous material in the matrix is not uniform,
Alternatively, if the fibrous material is damaged, the resulting composite may not exhibit the properties expected at the initial design stage. Furthermore, the mechanical strength characteristic originally possessed by the matrix itself is deteriorated.

[Object of the Invention] The present invention solves the above-mentioned problems and provides a method for producing a fiber-containing ceramics sintered composite material which enables uniform dispersion of a fibrous material in a ceramic matrix and does not damage the fibrous material. With the goal.

[Summary of the Invention] In the process of earnestly researching to achieve the above object, the present inventors mixed the ceramic matrix and the fibrous material by using a separate mixing means as in the prior art and used the latter as the former. Instead of dispersing the fibrous material in advance, the fibrous material is shaped into a dispersed form within the ceramic matrix, and if the matrix components are infiltrated, the fibrous material is homogeneous in the shaped composite material. The present invention has been developed based on the idea that it can be made into a dispersed form.

That is, in the method for producing a fiber-containing ceramics sintered composite material of the present invention, a porous fibrous body formed by previously shaping one or more fibrous materials into a dispersed form in the matrix is a porous type. A step of disposing inside (first step); a step of injecting a slurry containing a ceramics matrix component into the porous mold and allowing the porous fibrous body to infiltrate the matrix component (second step); And a step of sintering (third step).

The first step is, so to speak, a molding preparation step in which a porous fiber body described later is set in a mold for slurry casting.

The term "porous fibrous body" as used in the present invention means a molded body in which a fibrous material to be dispersed as a reinforcing material in a composite material is shaped into a predetermined shape.

The fibrous material to be used may have any fiber form such as long fiber, short fiber and whisker. The crystal structure thereof may be polycrystal, single crystal, or amorphous. In the case of long fibers, it may be woven or non-woven. In addition, these may be used alone or as a mixed fiber in which they are appropriately combined. Further, as the fibrous material, any material can be used as long as it can be shaped into a predetermined shape by means described below, for example,
Examples thereof include those made of ceramics such as silicon nitride, silicon carbide, alumina, zirconia, carbon, boron carbide and boron nitride; and those made of metals such as boron, tungsten and molybdenum or various alloys.

Further, it is useful for improving the properties of the composite material that the surface of these fibrous materials is subjected to a surface treatment before and after the shaping treatment so as to improve the compatibility with the ceramic matrix. For example, when the fibrous material used is a ceramic fiber, immersing the fiber in hydrofluoric acid removes the surface glass phase and improves compatibility with the matrix. Further, in the case of metal fibers or the like, when a vapor deposition film of ceramics such as silicon carbide is formed on the surface thereof, it can function as an antioxidant film.

The porous fibrous body is shaped into a predetermined shape by subjecting the above-mentioned various fibrous materials to, for example, press molding. The molding treatment may be performed in air at room temperature. For example, a fibrous material having a predetermined size, length, and material is filled in a molding die having a predetermined shape, and this is cold-pressed to form a fibrous body having a desired shape. Depending on the molding pressure at this time, the obtained fibrous body becomes dense or coarse. That is, the porosity of the fibrous body varies depending on the molding pressure. If the molding pressure is increased too much, the fibrous body becomes too dense and the slurry used in the second step does not impregnate the central part of the fibrous body, resulting in poor uniform dispersion of the matrix component and the fibrous material. On the other hand, if the molding pressure is too small, the fibrous material retains its elasticity, and it becomes difficult to shape it into a predetermined shape. Therefore, although it depends on factors such as the thickness and length of the fibrous material, the type of material used, the type of matrix used, and the quantity ratio relationship between the two, normally, the porosity of the obtained fibrous body is 20 to 80%. It is preferable that the molding pressure be controlled so that the pores formed between the fibers have a porosity of 10 to 1000 μm and complete shaping is possible.

The porous fibrous body thus shaped is set in a porous mold. The mold to be used must be a porous body in which only the dispersion liquid in the slurry exudes out of the mold when the slurry is injected as described later, and the matrix component remains in the mold.

Specifically, it is a mold having pores with a pore size smaller than the particle size of the matrix component. If the porosity is too small, it takes a long time to exude the dispersion liquid out of the mold and the productivity is lowered. Therefore, the porosity is usually preferably 15% or more.

For such a mold, an appropriate material may be selected in consideration of factors such as the type of matrix component, the type and properties of the dispersion liquid, and for example, a plaster mold, a combination of meshes, and a fiberboard mold. Are useful because they are easily available and can be easily processed into a predetermined shape.

The second step is a step of injecting a predetermined slurry into the system of the porous fibrous body and the mold set in the first step so that the matrix component is infiltrated into the fibrous body.

The slurry used consists of a matrix component and a dispersion. Specifically, it is formed by suspending a ceramic powder to be used as a matrix in a dispersion liquid such as water. When the difference in specific gravity between the two is large, an appropriate amount of a surface active agent such as a polycarboxylic acid salt or a borilioxyethylene derivative is further added to prevent separation of the matrix component and the dispersion liquid and achieve uniform suspension. Further, in the case where the molded composite material is subsequently sintered to obtain a sintered composite body, an appropriate amount of a predetermined sintering aid may be added to this slurry as one kind of matrix component.

Any matrix component may be used as long as it can form a matrix in relation to the fibrous material used. For example, various ceramic powders and their 2
A mixed powder of at least one species can be used.

The quantity ratio relationship between the matrix component and the dispersion liquid cannot be uniquely determined because it changes depending on the viscosity and the amount of inking that are suitable for impregnating the obtained slurry into the porous fibrous body.

When the slurry is poured into the mold, the slurry permeates the pores of the fibrous body and the fibrous body is immersed in the slurry. The dispersion then seeps out through the pores of the mold,
Only the matrix component is deposited on the fibrous body and remains to form a composite material composed of the matrix-fibrous molded body. Thus, the fibrous material in the molded ceramics composite material is present as it is as a fibrous body shaped into the originally designed dispersion form, and thus the dispersion is extremely uniform.

In the second step, when the treatment is performed under reduced pressure or high pressure, the surrounding atmosphere is changed, or the working temperature is changed, the degree of inking of the obtained composite composite material,
Therefore, since the degree of densification, the productivity, and the like change subtly, the casting process can be performed by appropriately combining the above-mentioned conditions in relation to the desired densification.

The third step is a step of sintering the molded body obtained by infiltrating the fibrous body with the matrix component in this manner.

Further, in the method of the present invention, it is also possible to produce a fiber-containing ceramics sintered composite material having a more complicated shape by using the conventional slip casting method together.

[Examples of the Invention] Examples 1 to 5 The following five types of fibrous materials were prepared. A: Silicon nitride whiskers with a diameter of 0.5 μm and a length of 10 to 100 μm, B:
Silicon carbide whiskers with a diameter of 0.5 μm and a length of 10 to 100 μm,
C: Alumina short fiber with a diameter of 3 μm and length of 1 mm, D: Boron long fiber with a diameter of 0.1 mm; E: A and B mixed at 50% by weight respectively.
Incidentally, among these materials, A, B, C are all those whose surface is treated with hydrofluoric acid to remove the glass phase on the surface,
D is a surface coated with silicon carbide by a vapor deposition method and subjected to an antioxidant treatment.

Each of these materials was put into a mold and press-molded. The molding pressure was controlled so that the ratio of the volume occupied by each fiber material in the finally obtained fiber body was 30% by volume.

Each fibrous body was placed in a gypsum mold with an average pore size of 0.05 μm and a porosity of 20%.

Next, 93% by weight of silicon nitride powder having an average particle size of 1 μm, 5% by weight of yttria powder having an average particle size of 0.9 μm, and 0.1% of an average particle size.
1 part by weight of a mixed powder composed of 2% by weight of alumina powder having a diameter of μm was dispersed in 1 part by weight of water to prepare a slurry containing the mixed ceramic powder.

This slurry was poured into the mold in the atmosphere. Slurry was continuously replenished as the amount of slurry in the mold decreased due to water leaching. During this process, the gypsum mold was kept at a temperature of about 50 ° C.

A composite material having a length of 30 mm, a width of 40 mm and a thickness of 15 mm was obtained.

Next, these fiber-containing ceramic composite materials were hot pressed in a nitrogen stream at a pressure of 400 kg / cm ^{2 at} the indicated temperature for 1 hour to obtain a ceramics sintered composite material.

The relative density ratio, the bending strength at room temperature, and the Weibull coefficient of these fiber-containing ceramics sintered composite materials were measured according to the following specifications, and the results are collectively shown in the table.

ρmeans .: Bulk density of the composite material determined according to JIS C2141.

ρth .: The theoretical density of the composite material calculated from the blending ratio of the matrix components and the fiber content based on the theoretical density of each matrix component and the fiber alone.

Bending strength: Compliant with JIS R1601 Weibull coefficient (m): P = 1-exp (-6S ^m ), P = measurement failure probability, b = constant, S = strength, m = Weibull coefficient The Weibull distribution (formula) is used for rearranging, and the Weibull coefficient at that time is obtained by the least square method. The larger the m value, the more uniform the dispersion of the fibers.

For comparison, the same fiber-containing ceramics sintered composite material and matrix as in Examples 1 to 5 except that the conventional ball mill method, kneader method, and sheet lamination method were used to disperse the fibrous material. Hot-pressed materials containing only the components were manufactured, and their properties are also shown in the table.

[Effects of the Invention] As is clear from the above description, in the method of the present invention, the fibrous material to be dispersed is shaped into the dispersion form in the composite material from the beginning, so that the dispersion in the composite material is as designed. As a matter of course, it is uniform, and since the fibrous material is not dispersed in the matrix component by using the conventional mechanical mixing means, the material is not damaged. Therefore, the matrix component is not damaged. Even if there is a large difference in specific gravity between the fibrous material and the fibrous material, or even if the fibrous material content is high, the fibrous material can be evenly dispersed and present in the ceramic matrix. Since the ceramics sintered composite material can be efficiently produced, its industrial value is great.

Claims (1)

[Claims] 1. A step of disposing in a porous mold a porous fibrous body obtained by previously forming one or more kinds of fibrous materials in a dispersed form in a matrix thereof; A step of injecting a slurry containing a ceramics matrix component into the inside of the porous fibrous body to infiltrate the matrix component; and a step of sintering. Production method.