JPH0264068A - Production of fiber reinforced silicon carbide ceramics - Google Patents

Abstract

PURPOSE:To obtain the subject ceramics having excellent strength, toughness, etc., and suitable for structural material, etc., by forming a void-containing preformed article from fine powder of silicon carbide, a heat-resistance inorganic short fiber and silicon carbide ceramic precursor and filling silicon into the voids. CONSTITUTION:Fine powder of silicon carbide is mixed with a heat-resistant inorganic short fiber (e.g., SiC whisker) and the mixture is formed. The obtained formed article is impregnated with a solution of a silicon carbide ceramic precursor (e.g., a hexane solution of a polycarbosilane), dried and calcined. The above process is performed once or more to obtain a preformed article having a void ratio of <=20%. The objective high-density ceramic can be produced by filling silicon into the voids of the obtained preformed article. The breakage of the heat-resistant inorganic short fibers can be prevented and the short fibers are uniformly and three-dimensionally dispersed in the silicon carbide ceramics.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention proposes a method for manufacturing fiber-reinforced ceramics, particularly a method for manufacturing silicon carbide ceramics reinforced with fibers that have excellent strength and toughness. It is.

[Conventional technology]

Recently, new uses for ceramics have been considered, such as heat-resistant structural materials and biological hard tissue substitute materials. However, the basic problem with this ceramic is that it lacks the strength and toughness to be used in such applications.

To overcome these problems, fiber-reinforced ceramics in which heat-resistant inorganic fibers are added to ceramics have been proposed. For example, as one of typical known fiber reinforced ceramics, A1.0. -5iC Wis force-There is a composite material. Regarding the mechanical properties of this composite,
Research by Matsubara, Okuno, Watanabe, Matsuo et al. (Ceramic Industry Association, Vol. 7)
This is discussed in detail in the Abstracts of the High Temperature Materials Basics Conference, pp. 14-19).

Also, JP-A-52-81309 and JP-A-58-1
45668 and JP-A-62-12671 both propose manufacturing techniques for ceramic composite materials in which silicon carbide ceramics are reinforced with fibers.
Furthermore, “Toyota Central Research Institute R&D Review” (vol.
20 m3/41986) discloses various types of "ceramic fiber reinforced ceramics", all of which propose hot press sintering methods.

[Problem to be solved by the invention]

In the case of each of the above-mentioned conventional techniques, although ceramics with slightly improved toughness can be obtained by reinforcing fibers, the necessary conditions as a structural material and a substitute material for biological hard tissues such as artificial bones and artificial tooth roots; The reality is that we have yet to develop fiber-reinforced ceramics that have extremely high strength and strength.

In other words, fiber-reinforced ceramics manufactured using these conventional techniques are made denser by forming the green body using a dry forming method, or by pressurizing and sintering a relatively low-density green body. , Additive 5 For example, heat-resistant inorganic fibers such as whiskers were significantly deformed, and in extreme cases even broke. As a result, even though the heat-resistant inorganic fibers were combined, neither the toughness nor the strength was improved that much. Furthermore, in the case of each of the above-mentioned conventional technologies, there was a general tendency for heat-resistant inorganic fibers to be easily oriented in two-dimensional directions, resulting in anisotropy in strength and toughness, which must be taken into consideration during use. There was also the problem that it was not possible.

In addition, in the case of the above-mentioned conventional technology, especially when short fibrous heat-resistant inorganic fibers and ceramic fine powder are wet-mixed and dried and then dry-formed, grain boundaries where the fiber entanglement does not become continuous occur. This remained, and this was the cause of the destruction. In the end, even though heat-resistant inorganic short fibers were composited with ceramic and 7x, no improvement in toughness or strength could be obtained.

An object of the present invention is to overcome the problems faced by known fiber-reinforced ceramics among the various problems faced by the above-mentioned ceramic-nox reinforcement technology.

[Means to solve the problem]

Therefore, in order to achieve the above-mentioned purpose, the present inventors conducted research on the manufacturing technology of high-density silicon carbide ceramics reinforced with heat-resistant inorganic fibers, and as a result, they came up with a new method that involves the steps described below. did. That is, the present invention comprises: (1) a step of mixing silicon carbide fine powder and heat-resistant inorganic short fibers and then molding this mixture to obtain a green body; (2) adding silicon carbide to the green body; A process of impregnating with a raw ceramic precursor solution, drying, and subsequently firing the process one or more times to obtain a preform with a porosity of 20% or less; (3) a preform obtained by the process in the above process; A process of obtaining silicon carbide ceramics reinforced with heat-resistant inorganic fibers by filling the voids of the body with silicon, and silicon carbide ceramics reinforced with fibers.

It is characterized by manufacturing soybean paste.

According to such a method, the heat-resistant inorganic short fibers are hardly damaged during compositing, and moreover, the inorganic short fibers are extremely uniformly dispersed three-dimensionally in the fiber-reinforced ceramics and are mutually bonded. By intertwining, a continuous, high-density molded body can be manufactured. As a result, silicon carbide ceramics reinforced with heat-resistant inorganic fibers having excellent strength and toughness can be easily and reliably produced.

[Function] Next, the details of the manufacturing method of the present invention will be explained separately for each step.

The first step of the method of the present invention is a step of wet-mixing silicon carbide fine powder and heat-resistant inorganic short fibers, and then molding the mixture to form a green body.

The silicon carbide fine powder used as the base material in this step preferably has an average particle size of 2 μm or less, and is produced, for example, by a silica reduction method, a CVD method, an alkoxide method, or a direct reaction method. Note that a sintering aid may be added to this silicon carbide fine powder.

Further, the heat-resistant inorganic short fibers have an average length: 1
It is preferably 0 mm or less and has an average aspect ratio of 10 to 10,000. For example, at least one selected from SiC whiskers and chopped fibers can be used.

The dispersion medium used in wet mixing the silicon carbide fine powder and the heat-resistant inorganic short fibers is, for example, water or various organic solvents. The wet mixing method is preferably a method that does not damage the fibers as much as possible. For example, high speed mixer, ball mill,
A method of mixing and adjusting in the presence of a solvent using an ultrasonic disperser or the like is applied.

The content of silicon carbide fine powder contained in the prepared slurry is 5 to 35% by weight, and the content of heat-resistant inorganic short fibers is 1 to 35% by weight.
The content is preferably 15% by weight.

In addition, during the above wet mixing, a binder or a dispersant as described later may be added as necessary.

First, as a binder, for example, an organic binder such as polyacrylic acid ester, polymethyl methacrylate, polyvinyl alcohol, polyvinyl butyral, polyethylene oxide, polymethacrylic acid ester, methylcellulose, urethane, or various ceramic precursor solutions, A material consisting of at least one selected from those having the action of a so-called binder is used. As a dispersant, for example, any one selected from triolein, methyl oleate, natural fish oil, synthetic surfactants, benzenesulfonic acid, allylsulfonic acid, phosphate, polycarboxylic acid, etc. Use.

Next, in this step, the slurry prepared as described above is wet-molded to produce a green body. First, the reason why the green body is produced in this way is that it is necessary to avoid damaging the heat-resistant inorganic short fibers and to ensure that the short fibers are uniformly dispersed three-dimensionally in the matrix. This is because it is necessary in particular to produce a molded article in which no grain boundaries remain between secondary particles so that fibers do not become continuously entangled.

Methods for such wet molding include paper molding and casting molding, among which paper molding is particularly preferred.

In this step, before or after drying the wet-formed molded body, in order to increase the density, pressing such as a rubber press may be applied within a range that does not damage the heat-resistant inorganic short fibers.

Further, the wet-molded product may be further dried or fired in air, water vapor, nitrogen gas, or an inert gas atmosphere. In this case, the drying or firing is limited to merely maintaining the shape of the molded body.

In addition, before the formed body is impregnated after wet molding,
Preliminary firing may be performed in air, water vapor, nitrogen gas, or an inert gas atmosphere.

The thus obtained green body preferably contains 1 to 45% by volume of heat-resistant inorganic short fibers, and particularly preferably 3 to 25% by volume. This range of the content of the heat-resistant inorganic short fibers is suitable for making the finally produced fiber-reinforced silicon carbide ceramics extremely excellent in strength and toughness.

Next, in the second step of the present invention, the formed body is impregnated with a silicon carbide ceramic precursor solution, dried, and then prefired to produce a preformed body having a porosity of 20% or less. It is a stage. When the formed body is impregnated with a silicon carbide ceramic precursor solution and dried, the voids in the formed body are filled with the silicon carbide ceramic precursor. As a result, the heat-resistant inorganic short fibers dispersed in the molded product will not be deformed or broken (
Become. That is, since the density of the formed body can be increased before firing, shrinkage is reduced during firing in the subsequent process, and as a result, deformation and breakage of the heat-resistant inorganic short fibers to be mixed are extremely effectively suppressed. Moreover, since the adhesion between the heat-resistant inorganic short fibers and the SiC matrix is excellent, it is possible to obtain fiber-reinforced silicon carbide ceramics with extremely high strength and toughness.

The silicon carbide ceramic precursor solution used in this step is one that produces silicon carbide ceramics by drying or firing, for example,
At least one selected from various organic solvent solutions of organic polymer compounds such as polycarbosilane is used.

By drying or firing this silicon carbide ceramic precursor solution, it is possible to obtain 10
~． Preferably, it yields 45% by weight of ceramic, and preferably has a viscosity of 10 to 700 cP.

According to the present invention, by impregnating the formed body obtained by wet-molding the slurry with a silicon carbide ceramic precursor solution and drying and firing it one or more times, the preformed body obtained in this step is It is necessary to set the porosity to 20% or less, and it is particularly preferable to set it to 15% or less from the viewpoint of maintaining strength.

The reason why the porosity of the preform is set to 20% or less is that if the porosity is greater than 20%, it becomes difficult to produce fiber-reinforced silicon carbide ceramics that have extremely high strength and toughness. .

In addition, in this second step, the operation of impregnating the formed body with a silicon carbide ceramic precursor solution, drying, and firing under normal pressure may be repeated, or only the operation of impregnating and drying may be repeated. .

Next, in the third step of the method of the present invention, the preformed body impregnated and dried or further prefired is
) is a step in which the remaining unoccluded voids are filled with silicon melt, and in this step, ceramics produced from silicon carbide ceramic fine powder and silicon carbide ceramic precursor solution and heat-resistant inorganic The short fibers are more strongly bonded to each other.

The silicon melt filling process is vacuum impregnation in which the melt is press-fitted into the voids remaining in the preform, or the preform is placed in the silicon melt under vacuum. By this treatment, the silicon carbide ceramic becomes denser, and a fiber-reinforced silicon carbide ceramic with high density and excellent strength and toughness can be obtained. Note that metal silicon is preferably used as the silicon used in this process.

As explained above, the first reason why fiber-reinforced silicon carbide ceramics with excellent strength and toughness can be produced by applying the method of the present invention is that the prepared slurry is wet-molded. It is in. That is,
By this wet molding, the silicon carbide ceramic fine powder and the heat-resistant inorganic short fibers are not oriented in a specific direction.
This is because the molded article has a structure that is dimensionally extremely uniformly dispersed. The second point is that the formed body is impregnated with a silicon carbide ceramic precursor solution, dried, and subsequently subjected to a firing treatment. That is, by this treatment, the voids of the formed body are filled with silicon carbide ceramics or its precursor, thereby increasing the density. The third point is that the silicon melt is filled into the few voids remaining in the preform. Such treatment prevents the ceramics from shrinking significantly, which prevents the heat-resistant inorganic fibers from being significantly deformed or broken, resulting in high strength and high toughness.

Example (1) Silicon carbide fine powder 100 with an average particle size of 0.3 μm
Parts by weight, 0.5 parts by weight of carbonized boron powder bundle with a specific surface area of 27.8 m"/g, 4 parts by weight of novolac type phenolic resin (fixed carbon content 51.6% by weight), average length 46 μm
A slurry was prepared by mixing 18 parts by weight of SiC whiskers having an average aspect ratio of 153, 5 parts by weight of polyethylene oxide, 7 parts by weight of polycarbosilane, and 340 parts by weight of hexane in a ball mill for 24 hours.

Next, this slurry was poured into a mold equipped with a screen with a 0.04 fin opening, filtered by suction, and then dried. After that, it was rubber pressed at a surface pressure of 3 t/cm2, and then heated with argon gas. It was baked in an atmosphere at a temperature of 1150°C for 2 hours.

The obtained green body had a bulk density of 1.62 g/cm2,
The amount of SiC whiskers contained in the molded body is 15
．． It was 4% by volume.

(2) On the other hand, 120 parts by weight of hexane was added to 100 parts by weight of polycarbosilane to completely dissolve the polycarbosilane, resulting in 36.5% by weight of SiC (in terms of St C).
A containing silicon carbide ceramic precursor solution was prepared. The viscosity of this silicon carbide ceramic precursor solution was about 230 cP when measured using a B-type viscometer.

(3) After impregnating the formed body of (11) with the silicon carbide ceramic precursor solution prepared in (2) above,
It was dried at 0°C for 2 hours, then at 40°C for 2 hours, and then fired at 1150°C for 2 hours in an argon gas atmosphere.

(4) Impregnation of the above-mentioned formed body, subsequent drying and pre-calcination are repeated 9 times, and then 2 times under an argon gas atmosphere.
Porosity: 14.2% after firing at a temperature of 000℃ for 12 hours
A preformed body was obtained.

(5) The preform obtained in this way was
It is placed in a mold heated to 0°C, and 1500
A silicon melt melted at a temperature of 0.degree.

The fiber-reinforced silicon carbide ceramic thus obtained had a porosity of 0.3%, a bending strength measured according to JIS-R1601 of 960 MPa, and a bending strength measured by the indentation method using Shinryo's equation. The required fracture toughness value was 8.9 MPa-m"", and it was confirmed that the fiber-reinforced silicon carbide ceramic had the high strength and toughness required as a heat-resistant structural material.

〔Effect of the invention〕

As explained above, according to the manufacturing method of the present invention, in addition to wet forming the slurry, silicon melt is press-fitted into the voids after using a silicon carbide ceramic precursor solution. The heat-resistant inorganic short fibers used in the mixture cause almost no damage.
Moreover, it is possible to produce a high-density molded product in which the heat-resistant inorganic short fibers are uniformly dispersed three-dimensionally in the fiber-reinforced silicon carbide ceramic and intertwined with each other, and it has both high strength and fracture toughness. Silicon carbide ceramics reinforced with fibers can be easily obtained.

Therefore, it is possible to provide a material suitable as a heat-resistant structural material or a substitute material for biological hard tissue.

Claims (3)

[Claims] 1. In producing fiber-reinforced ceramics made by mixing and reinforcing fibers into a matrix of carbide ceramics, carbonization reinforced with fibers is characterized by passing through the following steps (1) to (3). Method for manufacturing siliceous ceramics. (1) A step of mixing silicon carbide fine powder and heat-resistant inorganic short fibers and then molding this mixture to obtain a formed body. (2) Obtaining a preformed body having a porosity of 20% or less by impregnating the formed body with a silicon carbide ceramic precursor solution, drying it, and subsequently firing it one or more times. (3) A step of obtaining silicon carbide ceramics reinforced with heat-resistant inorganic fibers by filling silicon into the voids of the preform obtained by the treatment in the above steps.