JPH0825813B2 - Method for producing fiber-reinforced ceramics - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a gas turbine component, a diesel component, etc.
The present invention relates to ceramics used in a high temperature or corrosive / abrasive environment, and particularly to a method for producing fiber-reinforced ceramics in which ceramic short fibers are added to ceramics in order to impart strength and toughness.

[Prior Art] Strength and toughness are required in high temperature or corrosive / abrasive environment such as gas turbine parts, diesel engine parts, supercharger parts, heat exchanger parts in the fields of energy, materials, transportation, etc. The use of ceramics for machine structural parts is expected.

Generally, ceramic materials have a drawback of low toughness, and fiber reinforcement, particularly reinforcement by short fibers, has been studied as the most promising method for strengthening the toughness of the ceramics.

Conventionally, in this strengthening method, ceramic powder and short fibers are mixed as they are and then pressure-sintered to obtain fiber-reinforced ceramics, but the directions of the short fibers in this ceramic are random.

[Problems to be Solved by the Invention] However, when reinforcement is required for a load in a specific direction, for example, when strength is required in a direction in which a centrifugal force is applied such as a rotating machine part, the direction of dispersed fibers is random. If so, the strength can be improved to some extent in all directions, but there is a problem that the strength in a specific direction cannot be improved as desired.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for producing a fiber-reinforced ceramic having strength in a specific direction.

[Means for Solving the Problems] In order to achieve the above object, the present invention disperses ceramic short fiber and ceramic raw material powder forming a matrix in a dispersion liquid, After filling the inside of a mold made of a porous body, the dispersion is made into a porous body by pressurizing the mud with a pressure of tens of atmospheric pressure or centrifugal force toward the porous body of the form. While being discharged through, the ceramic short fibers are oriented parallel to the surface of the porous body to form a compact consisting of the ceramic short fibers and the ceramic raw material powder. It was designed to be transformed.

[Operation] According to the above configuration, the ceramic short fibers and the ceramic raw material powder are dispersed in the dispersion liquid to make mud (mudification step), and the mud is filled in the mold, and then the mold The dispersion is discharged through the surface of the porous body by pressurizing the mud to tens of atmospheric pressure by hydrostatic pressure or centrifugal force toward the porous body formed on the surface, and at the same time, the short ceramic fibers are porous by the discharge. It is oriented parallel to the surface of the body (pressure molding step). Therefore, by densifying the compacted ceramic short-fibers and the ceramic raw material powder that have been transferred (densification step), fiber-reinforced ceramics having excellent strength in a specific direction can be obtained.

Hereinafter, the mudification process, the pressure molding process and the densification process in the present invention will be described for each process.

(1) Sludge process The ceramic powder mainly constitutes the matrix of the fiber-reinforced ceramics of the present invention, and satisfies the final object of the present invention such as strength and toughness as a mechanical structural material. Is silicon carbide, silicon nitride, alumina, mullite, zirconia, or one of them.
It must contain 70% or more. For these ceramic powders, for example, boron, aluminum, carbon, etc. may be added to silicon carbide, and alumina, yttria, ceria, aluminum nitride, etc. may be added to silicon nitride to promote sintering. It is known and it is permissible to add these sintering promoters to the ceramic powder. Silicon carbide is a solid solution having a composition of (SiC) 1-x (AlN) x, (x = 0 to 1) with aluminum nitride, and silicon nitride is a solid solution with alumina and aluminum nitride. Between (Si ₃ N ₄ ) 1-x (Al ₂ O ₃ · Al
N) x, (x = 0 to 0.67), and zirconia forms a solid solution with yttria, magnesia, ceria, etc., and changes mechanical properties, thermal properties, corrosion resistance, etc. It is known to be made. The ceramic powder used in the method of the present invention may be a solid solution ceramic powder containing silicon carbide, silicon nitride, zirconia or the like as a main component. It is also known that mechanical properties may be improved when other ceramic powders such as titanium carbide, silicon nitride or alumina, zirconia, silicon carbide, etc. are dispersed in silicon carbide. Like, silicon carbide,
Ceramic powder containing silicon nitride, alumina, or the like as a main component and other ceramic powder for dispersion strengthening added thereto may be used.

As the short ceramic fibers, it is preferable to use whiskers made of a single crystal of a ceramic similar to the matrix from the viewpoint of strength and thermal and chemical stability.
Further, it is desirable that the ceramic short fibers have a high elastic modulus equal to or higher than that of the matrix, and reduce the load on the matrix as much as possible when stress is applied. Further, the ceramic short fibers need to be sufficiently stable against heating in a densification step such as sintering in the latter stage of the production method of the present invention. As the ceramic short fibers satisfying such a condition, only a silicon carbide whisker is used for a matrix containing silicon carbide as a main component, and silicon carbide is used for a matrix containing silicon nitride as a main component. Or for a matrix based on silicon nitride whiskers, alumina, mullite, or zirconia,
Whiskers of silicon carbide, silicon nitride or alumina can be used.

The liquid in which the ceramic short fibers and the ceramic raw material powder are dispersed may be a liquid mainly containing a non-aqueous solvent such as hydrocarbon, alcohol or ketone in addition to water, or may be a solid at room temperature even if heated. It may be a wax, which becomes a liquid if done. Further, in order to improve the dispersion of the ceramic short fibers and the ceramic raw material powder, an acid or an alkali may be dissolved in the liquid to adjust the pH, or a dispersant such as an inorganic or organic electrolyte may be added. It is permissible to add an organic binder such as polyvinyl alcohol, polyvinyl butyral, an uncured phenol resin, a wax or an emulsion in order to increase the bonding strength after molding.

The above-mentioned ceramic short fibers, ceramic raw material powder and the dispersion liquid are thoroughly mixed and dispersed, and then introduced into a porous mold. It is necessary to select the material of this mold from the viewpoint of physical and chemical compatibility with the dispersion liquid and pressure resistance at the time of pressurization. And must be able to be filtered. As the mold material, the pressure is 10
In order to increase the pressure to 0 atmosphere or higher, a porous resin containing a ceramic powder filler, a porous ceramic (so-called unglazed), a sintered porous metal, or the like is used.

(2) Pressure molding process After introducing the above-mentioned mud into the mold, the ceramic short fibers in the mud are two-dimensionally parallel to the mold surface by applying pressure to the mud by air pressure, hydraulic pressure, etc. It is possible to perform molding by filtering the dispersion liquid while orienting the dispersion liquid. At this time, the ceramic raw material powder that will later form the matrix is mixed between the ceramic short fibers to form a compact.

The pressurization to the mud may be performed by rotating the entire mold and utilizing centrifugal force. In this case, the mold may be rotated by rotating the mold around a central axis within the product shape (for example, the central axis of a cylindrical product) or by rotating the central axis outside the product shape. It may have a shape in which it revolves around a large turning radius.

Regarding the pressing force, it is necessary to select the conditions that can obtain the highest orientation and packing density while considering the durability limit of the mold material as described above.

Further, in the case of a dispersion liquid such as wax that needs to be heated to be liquefied, it is necessary to control the surface temperature of the mold by heating it to a necessary temperature.

(3) Densification step After the molded body is taken out from the mold, the liquid is removed by drying and the organic binder and the dispersant are further removed by preliminary firing, and the like.

After this, the matrix portion composed of the ceramic raw material powder is densified. This densification may be performed by sintering under atmospheric pressure or atmospheric pressure, hot pre-sintering (uniaxial pressure sintering) in a mold filled with powder, and hot isotropy. Pressure sintering by a pressure press may be used. Further, for the ceramic short fibers and the voids of the ceramic raw material powder in the compact, polycarbosilane, a ceramic precursor such as polysilazane, a polymer, or a colloidal dispersion of a ceramic precursor such as colloidal silica or alumina sol, or a silicon halide, Even if aluminum halide is impregnated with a ceramic precursor gas in which hydrocarbon gas, ammonia, hydrogen, etc. are appropriately added to form a ceramic, and then densification is performed by the sintering method as described above. Good.

[Embodiment] A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

1 to 3 show each step of the method for producing a fiber-reinforced ceramic according to the present invention.

First, as shown in FIG. 2, a mold 1 is filled with a slurry 5 in which a ceramic short fiber 2 and a ceramic raw material powder 3 are dispersed in a dispersion liquid 4.

The mold 1 is formed according to the shape of the part to be molded, and has a porous body 6 on the entire surface of the mold cavity. The porous body 6 has a large number of pores, and the pore diameter is formed so that the ceramic raw material powder 3 and the ceramic short fibers 2 do not permeate at least on the mold surface. The ceramic short fibers 2 in the mud 5 are randomly dispersed in the form 1 at the time of filling, as shown in FIG.

In this state, when hydrostatic pressure or centrifugal force is applied from the side opposite to the porous body 6 in the pressurizing direction 7 shown by the arrow in the figure as shown in FIG. It is discharged to the outside of the mold 1 through the holes of the porous body 6 formed on one surface.
With this discharge, the ceramic short fibers 2 which have been randomly dispersed until now behave in the state of the least resistance,
As a result, it is oriented parallel to the surface of the porous body 6.

A molded body 8 composed of the oriented ceramic short fibers 2 and the ceramic raw material powder 3 is taken out of the mold 1 and densified as shown in FIG.

 Specific examples 1 and 2 will be described in detail below.

Example 1 The composition has a composition of 80% by weight of silicon nitride-6% by weight of aluminum nitride-14% by weight of alumina, and a part of the aluminum nitride and the alumina has a Si-Al-O-N compound between them. The formed ceramic raw material powder (65 parts by weight) and the surface-treated silicon carbide whiskers (35 parts by weight) were sufficiently dispersed with 80 parts by weight of an ethanol solution as a dispersion liquid to obtain a slurry. The female die of the gas turbine vane was made of a porous material made of resin containing a ceramic powder filler. The mud was introduced into this mold by air pressure pressurization of 0.2 atm, and after filling, the hydrostatic pressure was applied to the mud by a hydraulic cylinder to raise the pressure to 30 atm. After the ethanol solution in the mud was sufficiently filtered through the pores of the mold, the molded body was taken out from the mold and dried sufficiently. Then, in a nitrogen atmosphere, the temperature and pressure were raised to 2,000 ° C. and 100 atm to sinter and densify. The obtained molded sintered body,
The silicon carbide whiskers are two-dimensionally oriented substantially parallel to the vane surface of the vane, especially at the leading and trailing edges of the blade.
Even a one-dimensional orientation was seen parallel to the edges. Due to this orientation, shrinkage due to sintering is large in the blade thickness direction, small in the blade height direction and width direction, and 98% of the theoretical density.
It was confirmed that the above densification was achieved.

Example 2 60 parts by weight of ceramic raw material powder made of silicon carbide containing 0.5% of boron, surface-treated silicon carbide whiskers
40 parts by weight and 100 parts by weight were dispersed in an aqueous solution to obtain mud. A cylindrical female mold was made using porous silica-alumina ceramics, and after introducing mud by air pressure into the mold, the mold was rotated at 1,000 RPM with the center axis of the cylinder as the rotation axis. After the rotation was stopped, the excess mud in the mold was discharged, and the cylindrical molded body was taken out and then dried sufficiently.

After placing this compact in a high-pressure furnace and once applying a vacuum, the molten polycarborasilane is impregnated by the pressure of an inert gas of 100 atm. Was converted to silicon carbide based ceramics. After repeating this treatment 5 times, it was densified at 1,900 ° C. and 2,000 atm in a hot isostatic press. The obtained cylindrical shaped sintered body has a dense composition in which silicon carbide whiskers are two-dimensionally oriented almost parallel to the cylindrical surface, and is sufficiently applied as a component for gas turbine combustors, high temperature heat exchangers, etc. It turned out to be possible.

[Effects of the Invention] As is apparent from the above description, the present invention exerts the following excellent effects.

(1) Ceramic short fibers and ceramic raw material powder are dispersed in a dispersion liquid to make it into a slurry, and the slurry is filled in a mold having a porous body and the dispersion liquid in the slurry is made porous by a pressing force. The ceramic short fibers can be two-dimensionally oriented in parallel with the surface of the porous body by allowing the ceramic short fibers to permeate, and the strength and toughness in that direction can be enhanced.

(2) Since the ceramic short fibers are oriented in a specific plane direction, sintering shrinkage of the matrix is facilitated in the direction perpendicular to the plane, and a matrix containing almost no residual pores or defects is obtained, and the strength and strength are improved. A fiber-reinforced ceramic having high toughness can be obtained.

[Brief description of drawings]

1 to 3 are diagrams showing each step of the manufacturing method of the present invention. In the figure, 1 is a mold, 2 is a ceramic short fiber, 3 is a ceramic raw material powder, 4 is a dispersion, 5 is mud, 6 is a porous body,
Reference numeral 7 is a pressurizing direction.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideo Ohashi 3-1-15-1 Toyosu, Koto-ku, Tokyo Ishikawajima Harima Heavy Industries Ltd. Technical Research Institute (56) Reference JP-A-60-105502 (JP, A)

Claims (1)

[Claims] 1. Short ceramic fibers and ceramic raw material powder for forming a matrix are dispersed in a dispersion to form a mud, which is filled in a mold made of a porous material and then Towards the porous body of the mold, press the mud with a pressure of several tens of atmosphere or centrifugal force and discharge the dispersion through the porous body while the ceramic short fibers are parallel to the surface of the porous body. A method for producing a fiber-reinforced ceramic, which comprises orienting to form a compact made of short ceramic fibers and ceramic raw material powder, and then sintering the matrix ceramic raw material powder to densify it.