JPH0586424A - Production of ceramic fiber performed body used for fiber-reinforced metal matrix composite - Google Patents

Abstract

PURPOSE:To produce a performed body for ceramic fiber-reinforced metal matrix composite free from reaction with molten metal and increased in mechanical strength. CONSTITUTION:Small amount of aluminum borate grains is added to a fiber reinforcement, and the resulting mixture is compacted. The resulting green compact is heated at high temp., by which aluminum borate is sintered. By this method, the fiber performed body for metal matrix composite increased in mechanical strength at high temp. can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a preform required in the process for producing a fiber-reinforced metal matrix composite material using ceramic fibers. The body is easily obtained.

[0002]

2. Description of the Related Art A material obtained by adding a fibrous substance to metal to improve its mechanical strength is called a fiber-reinforced metal matrix composite material. Examples of the fibrous substance used in the fiber-reinforced metal matrix composite material include alumina fibers, alumina silica fibers, silicon carbide fibers, silicon carbide whiskers, silicon nitride whiskers, potassium titanate whiskers and aluminum borate whiskers. Many ceramic-based fibers have been investigated. Since these fibers have poor wettability with molten metal and a chemical reaction occurs between the reinforcing fiber and the molten metal, it is necessary to take a slightly complicated method for compounding them.

The techniques reported up to now include a method of forming a fiber preform and infiltrating a metal melt into the void portion under pressure (pressure infiltration method), and a fiber and metal powder. After uniform mixing, heating with pressure and sintering (powder metallurgy method), method of forming metal coating on fiber in advance and pressurizing it under high temperature to integrate (prepreg molding method), molten state While forcibly stirring the metal of (1), fibers are added to make it uniform, and then the mixture is cooled to form a composite (molten metal mixing method). At present, these methods are the most productive, and there are several examples on an industrial scale, which are expected to develop in the future.

[0004]

The performance of the composite material produced by the pressure infiltration method depends on the performance of the preform made of the ceramic fiber, which can withstand the pressure infiltration of the molten metal. Performances such as mechanical strength, uniform fiber distribution, and dimensional accuracy are required. Such a ceramic fiber preform is obtained by forming a slurry in which fibers are dispersed in a solvent such as water, and molding this by papermaking or pressing.
At this time, in order to enhance the moldability, polyvinyl alcohol, carboxymethyl cellulose, starch and the like are usually added as organic binders at a maximum of about 5%. In order to obtain a preform for pressure infiltration, it is necessary to further dry the form and degrease it at 600 to 800 ° C.

The preform thus obtained does not have the strength to withstand the pressure infiltration because the organic binder is burned out. Therefore, a maximum of about 5% of an inorganic binder such as silica sol or alumina sol is added to the slurry to be prepared first, and after degreasing, 800-12
It is necessary to sinter at 00 ° C to develop strength.

Although such an inorganic binder develops strength, it has some problems. In the case of a silica-based binder, since silicon oxide has a small generation energy,
When it comes into contact with a molten metal that becomes complex at high temperature, a redox reaction is likely to occur and it is difficult to obtain a composite material having sufficient strength. Such a redox reaction is particularly likely to occur in an amorphous state, but in order to sufficiently crystallize the silica-based binder, 12
A temperature of 00 ° C or higher is required. However, the reaction with molten metal has been an unavoidable problem as long as a silica binder is used.

Further, in the case of an alumina-based binder, it is difficult to react with molten metal, but a sintering temperature of 1000 ° C. or higher is required, and a sintering temperature of 1300 ° C. or higher is required for crystallization. As described above, in order to produce a preformed body that has mechanical strength and does not react, it is necessary to sinter the inorganic binder at a high temperature. Such a high temperature treatment causes deterioration of the reinforcing fiber itself, and there is a drawback that the cost is industrially increased.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted many test studies to solve such problems, and as a result, have a high sintering action as an inorganic binder and have little reaction with molten metal. The inventors have found that the intended purpose can be achieved by using aluminum borate particles, and have completed the method of the present invention.

The ceramic fibers used in the method of the present invention are fibers usually used in fiber-reinforced metal matrix composite materials such as amorphous type, polycrystal type, single crystal type (whiskers) and the like. Alumina fiber, alumina silica fiber, mullite fiber, silicon carbide fiber, carbon fiber, zirconia fiber, silicon carbide whiskers, silicon nitride whiskers, potassium titanate whiskers, alumina whiskers, gypsum whiskers, magnesia whiskers, zinc oxide whiskers, mullite whiskers and ho Aluminum acid whiskers and the like. Among these, those in which the aluminum borate-based binder acts particularly effectively include those containing alumina components such as alumina fibers, alumina silica fibers, mullite fibers, alumina whiskers, mullite whiskers, and aluminum borate whiskers.

Aluminum borate particles which act as an inorganic binder include aluminum oxide components such as aluminum oxide, aluminum hydroxide, aluminum sulfate, aluminum nitrate and aluminum chloride and boric acid and boric anhydride components such as boric oxide in a stoichiometric amount. After mixing the theoretical amount,
It is obtained by reacting at a temperature of 800 to 1200 ° C. and has a chemical formula of 9Al ₂ O ₃ .2B ₂ O ₃ or 2Al ₂
It is represented by O ₃ · B ₂ O ₃ .

The aluminum borate particles obtained by the reaction usually have a particle size of about 1 to 30 μm, but 1 μm is necessary to maximize the sintering ability as an inorganic binder.
It is preferable to grind to less than. This pulverization method may be either dry type or wet type, but when pulverizing to less than 1 μm, wet ball mill pulverization should be performed. In carrying out the method of the present invention, a suitable amount of the aluminum borate binder added is 0.1 to 5% by weight based on the amount of fiber. In carrying out the method of the present invention, the sintering temperature of the aluminum borate binder is a temperature of 800 to 1300 ° C., and the higher the temperature, the higher the mechanical strength of the molded body, but
If the temperature exceeds 300 ° C., it changes to α-alumina, and the crystal grains grow large, so that the sintering effect is weakened, which is not suitable.

The steps of preparing a fiber preform using these main raw materials are as follows. First, the ceramic fibers are dispersed in a solvent to prepare a slurry or paste for wet molding. At this time, the concentration of the ceramic fiber is usually 2 to 50% by weight. When it is less than 2% by weight, industrial efficiency is poor, and when it is more than 50% by weight, the viscosity of the slurry becomes too high and the slurry becomes uniform. Not suitable because it is difficult to obtain a preform. As the dispersion solvent used at this time, those having high polarity such as water and lower alcohol are preferable, but ketones, organic solvents such as paraffinic or aromatic solvents can also be used.

Then, an organic binder such as polyvinyl alcohol resin, polyvinyl butyral resin, carboxymethyl cellulose or starch, and crushed aluminum borate particles are added as an inorganic binder to the prepared slurry, and they are sufficiently stirred. At this time, the addition amount of each of the organic and inorganic binders is preferably 0.1 to 5% by weight with respect to the fiber amount.

As a method of wet-forming the slurry or paste thus prepared, there are a papermaking method and a pressing method. The papermaking method is to perform natural filtration or suction filtration using a filter paper, a filter cloth, etc., and is suitable for forming into a sheet shape or a simple block shape. It is preferable to reduce the slurry concentration, and a paste shape Not applicable to things.
Since a large compressive force does not act on the whiskers, this method can achieve a relatively low whisker volume fraction (hereinafter abbreviated as Vf). On the other hand, the squeezing method
The slurry or paste is supplied to a mold or resin mold equipped with a drainage mechanism, and pressure dehydration molding is performed with the upper punch, which is suitable for molding complex shapes, and to complete dehydration quickly. It is preferable to increase the whisker concentration. Since the pressure is applied, Vf becomes higher than that in the papermaking method.

The wet molded product thus obtained is removed from the filter paper or mold, dried at a temperature of 100 to 200 ° C., and further degreased at 600 to 800 ° C.,
By sintering the aluminum borate particles at 800 to 1200 ° C., it is possible to obtain a ceramic fiber preform used for the target fiber-reinforced metal matrix composite material.

[0016]

FUNCTION It is considered that the crystal surface of aluminum borate has an atomic arrangement as shown in Chemical formula 1. That is, aluminum and boron alternately form a chain through oxygen, a hydroxyl group is bound to the surface direction from boron, the hydroxyl group originally bound to aluminum is desorbed, oxygen is an anion, and aluminum is positive. It's becoming an ion. This difference between boron and aluminum can be inferred from the fact that when boron oxide is left in water, it easily becomes boric acid, whereas aluminum oxide does not become aluminate (hydrated alumina). ..

[0017]

[Chemical 1]

By heating orthoboric acid (H ₃ BO ₃ ) at a temperature of about 200 ° C., the terminal OH groups are dehydrated and condensed,
It is a well known phenomenon that it becomes metaboric acid, and the OH group bonded to boron is highly reactive, and the binder used in the method of the present invention utilizes this phenomenon. .. Of course, the surface of the aluminum borate whiskers mentioned as an example of the reinforcing fiber of the method of the present invention also has similar characteristics, and if aluminum borate is crushed to increase the specific surface area, this characteristic becomes more remarkable. In particular, when the particle size is less than 1 μm, the reactivity becomes extremely large. Hereinafter, the method of the present invention will be specifically described with reference to Examples and Comparative Examples.

[0019]

Reference Example 1 Aluminum hydroxide having an average particle diameter of 2 μm and orthoboric acid crushed to less than 44 μm were mixed so that the molar ratio of aluminum and boron was 9: 2, and this mixture was heated to a temperature of 1200 ° C. 9Al ₂ O ₃ · 2B ₂ O Te
₃ particles were obtained. The particle size was about 4 μm. Next, the aluminum borate particles were dispersed in water to obtain a 30% slurry, and this slurry was pulverized by a wet ball mill to obtain a slurry having an average particle diameter of about 0.7 μm, which was stored in a slurry state without solid-liquid separation.

[0020]

Reference Example 2 Aluminum hydroxide having an average particle size of 1 μm and orthoboric acid pulverized to less than 44 μm were mixed so that the molar ratio of aluminum and boron was 2: 1, and the mixture was heated to a temperature of 1000 ° C. It was obtained _{2Al 2 O 3 · B 2 O} 3 particles Te. The particle size was about 1 μm. Next, the aluminum borate particles were dispersed in water to obtain a 30% slurry, and the slurry was pulverized by a wet ball mill to obtain a slurry having an average particle size of about 0.7 μm, which was stored in a slurry state without solid-liquid separation.

[0021]

Example 1 400 g of alumina short fibers having an average fiber diameter of 3 μm (trade name: Safill RF, manufactured by Imperial Chemical Industry, UK) were slurried with 4000 cc of water, and the boric acid obtained in Reference Example 1 was added to the slurry. After adding 20 g of aluminum particles, 800 cc of a 1% polyvinyl alcohol aqueous solution was added as an organic binder, and 0.4 g of a polyacrylamide polymer flocculant was further added to complete the raw material preparation.

Next, the slurry was wet-molded to a thickness of 80 mm while sucking water using a mold having an inner diameter of 100 mm with a vacuum drainage mechanism on the top and bottom. This molded product is demolded and
After drying at a temperature of 50 ° C., the organic binder was further degreased at 800 ° C., and then aluminum borate particles as an inorganic binder were sintered at 1000 ° C. to complete a preform. The volume ratio of the fiber at this time is 1
It was 8.5%.

This preform was preheated to 900 ° C. and
Set in a mold kept at 0 ℃, then 800 ℃
Aluminum casting material AC8A melted at the temperature of 80
When pressure infiltration was performed at a pressure of 0 atm, almost no change in the dimensions of the original preform was observed, segregation of the alloy composition was not observed even when observing the longitudinal section, and the inorganic binder of the present invention was used. I was able to confirm the effect of.

[0024]

EXAMPLE 2 Fiber diameter 0.5 to 1 [mu] m, fiber length 10 to 30 [mu] m, the formula 9Al ₂ O ₃ · 2B aluminum borate whisker represented by ₂ O ₃ (trade name: Alborex G, manufactured by Shikoku Chemicals Corporation ) 400 g to 4000
Dispersed in cc of water to form a slurry, 40 g of the 30% slurry of aluminum borate particles shown in Reference Example 2 and 400 cc of a 2% solution of polyvinyl alcohol as an organic binder were added to the slurry, and a polyacrylamide-based polymer was added. The raw material preparation was completed by adding 0.4 g of a coagulant.

The obtained slurry was wet-molded by the same method as in Example 1, dried, degreased and sintered to complete a preform having a whisker volume ratio of 19.5%. This preform is preheated to 800 ° C and set in a mold kept at a temperature of 200 ° C, and then aluminum wrought material A-6061 melted at a temperature of 800 ° C is pressure infiltrated at a pressure of 1000 atm. As a result, almost no change in the dimensions of the original preform was observed, segregation of the alloy composition was not observed even when observing the longitudinal section, and the effect of the inorganic binder of the present invention could be confirmed. ..

[0026]

Example 3 400 g of alumina-silica short fibers having an average fiber diameter of 2.8 μm (alumina / silica = 47/52, trade name: Kaowool, manufactured by Isolite Industrial Co., Ltd.) were dispersed in 4000 cc of water to form a slurry, and this slurry was used as a reference example. The raw material adjustment was completed by adding 20 g of aluminum borate particles shown in 3 and 800 cc of a 1% solution of starch as an organic binder, and further adding 0.4 g of a polyacrylamide polymer flocculant. The obtained slurry was wet-molded in the same manner as in Example 1, dried, degreased and sintered, and then a preform having a whisker volume ratio of 24.5% was completed.

[0027]

Example 4 Silicon carbide whiskers having a fiber diameter of 0.3 to 0.5 μm and a fiber length of 5 to 15 μm (trade name: TWS-1)
00, manufactured by Tokai Carbon Co., Ltd.) 400 g to 4000 c
64 g of a 30% slurry of aluminum borate particles obtained in Reference Example 4,
400 cc of a 2% solution of polyvinyl alcohol was added as an organic binder, and then 0.4 g of a polyacrylamide-based polymer flocculant was added to complete the raw material adjustment. Further, wet molding was carried out in the same manner as in Example 1, and drying, degreasing and sintering were carried out to complete a preform having a whisker volume ratio of 20.0%.

[0028]

Comparative Example 1 A preform was prepared without adding aluminum borate in Example 2, and then aluminum wrought material A-6061 was similarly pressure infiltrated. About 30% of dents were generated in the depth direction, and a good metal-based composite material could not be obtained.

[0029]

[Comparative Example 2] 30% colloidal silica (trade name: Snowtex, manufactured by Nissan Chemical Industries, Ltd.) instead of the slurry of aluminum borate particles added in Example 2
Was used to prepare a preform by the same method. When the preformed body thus obtained was infiltrated with the aluminum wrought material A-6061 under pressure in the same manner as in Example 2, the preformed body did not significantly deform, but the magnesium component in the alloy was silica. As a result of the reaction, a magnesium deficient layer was generated in the central part of the composite material.

[0030]

According to the method of the present invention, the sintering strength is high,
And it is possible to obtain a preform for producing a fiber-reinforced metal matrix composite material having low reactivity with a matrix metal,
By using this preform, various high performance fiber-reinforced metal matrix composite materials can be obtained by the pressure infiltration method.

Claims (4)

[Claims] 1. A method for producing a ceramic fiber preform for use in a fiber-reinforced metal matrix composite material, which comprises using aluminum borate particles as a binder. 2. The method according to claim 1, wherein the size of the aluminum borate particles used as the binder is smaller than 1 μm. 3. A chemical formula 9Al ₂ O ₃ · as a binder
The method of claim 1, wherein the use of aluminum borate particles represented by 2B ₂ O ₃ or _{2Al 2 O 3 · B 2 O} 3. 4. The ceramic fiber of the preform has a chemical formula of 9Al ₂ O ₃ .2B ₂ O ₃ or 2Al ₂ O ₃ .B _2.
A method according to claim 1, characterized in that it is constituted by aluminum borate whiskers represented by O ₃ .