JPH07110978B2 - Method for producing preform for fiber-reinforced metal matrix composite material - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The method of the present invention relates to a method for producing a preform required for producing a fiber-reinforced metal matrix composite material using aluminum borate whiskers, which makes it easy to obtain a preform of stable quality. Therefore, it can be applied to the strengthening of various metals.

[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. Fibrous substances include alumina fibers, alumina silica fibers, silicon carbide fibers, silicon carbide whiskers,
Silicon nitride whiskers, potassium titanate whiskers,
Many ceramic-based fibers such as aluminum borate whiskers 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 use a slightly complicated method for compounding them.

As a method for producing a fiber-reinforced metal matrix composite material which has been reported so far, a method in which a preform of a fiber is prepared in advance and a melt of a metal is infiltrated into the void portion under pressure is used. After uniformly mixing the metal powder, heating and pressurizing and sintering, forming a metal film on the fiber, then pressurizing at high temperature to integrate.
There is a method in which a molten metal is forcibly stirred and fibers are added to make it uniform, and then the mixture is cooled to form a composite.
At present, some of these methods are the most productive, so there are several examples on an industrial scale, which are expected to develop in the future.

As a method for producing a fiber-reinforced metal matrix composite material using aluminum borate whiskers as the reinforcing fibers, the present inventors have prepared a whisker preform and then preheated it to obtain a molten state. We proposed a method of pressure infiltration of metallic aluminum alloys. (Japanese Patent Application 1-24
No. 2949)

[0005]

The performance of the composite material obtained by the above method depends on the performance of the preform. As the performance of the preformed body required at that time,
Mechanical strength that can withstand pressure infiltration of molten metal, uniform distribution of whiskers, and dimensional accuracy.

[0006] The preform is usually obtained by subjecting a slurry in which whiskers are dispersed in a solvent such as water to papermaking or squeezing. When the preform is produced using aluminum borate whiskers, There was a problem shown in. The first problem is that when the pH of the slurry is outside the neutral range, the shape retention of the molded product in the wet state deteriorates, and it is difficult to obtain sufficient mechanical strength. It has been confirmed that since aluminum borate is a solid acid, the slurry easily becomes acidic, and when the pH is less than 5, the molded body in a wet state becomes weak such that it is deformed by its own weight.

The second problem is that the volume fraction of aluminum borate whiskers (hereinafter referred to as Vf) when preparing a preform.
Was difficult to control, and in particular, it was impossible to produce a preform having Vf of less than 20%. Normally, when making a fully reinforced composite material, Vf is set to about 30% in order to maximize the mechanical strength, but when making a partially reinforced composite material, the interface between the reinforced portion and the non-reinforced portion is used. Vf because it is necessary to select a tool when stress is generated or machining is performed due to the difference in the coefficient of thermal expansion
Is often around 10 to 15%. Vf can be lowered by using whiskers having a large aspect ratio, for example, those having an aspect ratio of about 500 or more, but at present, such aluminum borate whiskers are difficult to synthesize. As described above, when producing a fiber-reinforced metal-based composite material using aluminum borate whiskers as reinforcing fibers, a method that is not affected by the pH of the slurry and that reduces Vf has been required.

[0008]

Means for Solving the Problems The present inventors have conducted many test studies in view of such circumstances, and as a result, heat-treated aluminum borate whiskers are dispersed in a solvent to form a slurry or paste. We found that the intended problems could be solved by wet-molding things,
The method of the present invention could be accomplished.

Aluminum borate whiskers used in the method of the present invention are disclosed in JP-A-63-319297 and JP-A-63-31.
9298, JP-A-2-107600, 2-164797 and 2
-164798 and Japanese Patent Application No. 1-270858 and Japanese Patent Application No. 2-
It can be easily produced by the method of using alkali metal hydrochlorides, sulfates, carbonates, etc. shown in No. 128566 as a melting agent for whisker growth. ₂ O ₃ / 2B ₂ O
Are those represented by ₃ or 2Al ₂ O ₃ · B ₂ O _3, the fiber diameter is 0.1 to 10μm or less and a fiber length to from 2 500μm or less, the aspect ratio is preferred that of from 10 100.

In carrying out the method of the present invention, the temperature at which the aluminum borate whiskers are heated is from 200 ° C to 1 ° C.
A temperature of 300 ° C. and a heating time of 30 minutes to 96 hours are preferable. The heat treatment temperature and the heat treatment time greatly affect the decrease in Vf, and Vf decreases as the treatment temperature increases and the treatment time increases. If the heat treatment temperature is less than 200 ° C, the preform obtained will not have sufficient strength to retain its shape, and conversely, the heat treatment temperature will be 1300 ° C.
If it exceeds, the boron oxide component in the aluminum borate whiskers gradually volatilizes and changes to α-type alumina, and the fiber diameter becomes large and the fiber length becomes short, so the aspect ratio becomes small and the reinforcing effect deteriorates. Therefore, it is not preferable.

In carrying out the method of the present invention, the heat-treated aluminum borate whiskers are dispersed in a solvent to prepare a slurry or paste. The dispersion solvent used at this time is preferably a highly polar solvent such as water or a lower alcohol, but other than this, ketones, paraffinic solvents, aromatic solvents and the like can also be used. The concentration of aluminum borate whiskers in the slurry or paste is preferably 2 to 50% by weight. If the concentration is less than 2% by weight, industrial efficiency is poor, and if the concentration exceeds 50% by weight, the viscosity of the slurry or paste becomes too high, and it becomes difficult to obtain a uniform preform.

In carrying out the method of the present invention, a surfactant or a dispersant may be appropriately added to improve the dispersibility of the aluminum borate whiskers. Although it is possible to obtain a preform having sufficient strength by the method of the present invention, in order to further improve the strength in a wet state, an organic binder such as polyvinyl alcohol resin, polyvinyl butyral resin and carboxymethyl cellulose is used. Further, in order to make the strength of the molten metal that can withstand high pressure during pressure infiltration, an inorganic binder such as silica or alumina may be added. In the practice of the method of the present invention, even when the pH of the slurry was significantly changed by adding the above-mentioned additive, the shape retention of the preform during wet was not deteriorated.

As a method for wet-forming the slurry or paste thus obtained, there is a papermaking method or a pressing method. The former is a method of performing natural filtration or suction filtration using a filter paper, a filter cloth, etc., which is suitable for forming into a sheet shape or a simple block shape, and it is preferable to lower the slurry concentration, but for paste-like ones Not applicable. In this papermaking method, since a large compressive force does not act on the whiskers, it is possible to make the Vf relatively low. On the other hand, the latter is a method of supplying the slurry or paste to a mold or resin mold with a drainage mechanism and performing pressure dehydration molding with an upper punch, which is suitable for molding a preform with a complicated shape. . In order to complete the dehydration quickly, it is preferable to increase the whisker concentration, and since the pressure is applied, Vf becomes higher than in the papermaking method.

If the aluminum borate whiskers are not heat-treated, the shape retention of the wet molded product is poor, and the minimum value of Vf that can be molded is about 20%. Is significantly improved, and Vf can be lowered to about 10% when the pressure during molding is low. This suggests that a preform having higher mechanical strength can be obtained when a preform having a high Vf is produced by applying external pressure.

The wet molded product thus obtained is removed from the filter paper or the mold, dried, and then heated to a temperature of 500 ° C. or higher in order to increase the strength of the molded product. A molded body is obtained. At this time, if an organic binder is added, sufficient degreasing must be performed, while if an inorganic binder is added,
It must be heated above ℃ to sinter.

[0016]

[Function] Aluminum borate is a composite oxide of aluminum oxide and boron oxide. Aluminum has six-coordinated oxygen, and boron has three- or four-coordinated oxygen, which is the most stable crystallographic structure. However, when two oxides are complexed, most of aluminum has a crystal structure in which only four oxygens are coordinated. On the surface of the powder, the aluminum in such a position acts to take in the ligand in the atmosphere. Further, when aluminum borate whiskers are dispersed in water, since hydroxide ions are coordinated, the hydrogen ion concentration in the water increases, and a so-called Lewis acid phenomenon in which the slurry becomes acidic appears.

When the aluminum borate whiskers used in the method of the present invention are produced, a step of treating with boiling water, boiling hydrochloric acid or the like is taken to remove the melting agent after the reaction. If the above-mentioned phenomenon occurs in this step and the hydroxyl group is coordinated at this time, it is difficult to easily desorb the hydroxyl group by drying at about 100 ° C. Can be desorbed.

Next, the reason why Vf is lowered when the hydroxyl group is eliminated and a preform having a good shape-retaining property can be obtained will be described. When the hydroxyl group is coordinated to the surface, the surface is hydrophilic and has a strong affinity for water and alcohol.
The force to attract the solvent to the surface layer acts more strongly than the aluminum borate whiskers aggregate with each other. Therefore, even when the whiskers come into contact with each other when the slurry or paste is wet-molded, the whiskers are likely to slip, the solvent removal property is deteriorated, Vf is increased, and the shape retention property is deteriorated.

On the other hand, when the heat treatment of the method of the present invention is carried out,
Since many hydroxyl groups are removed and the surface changes to the hydrophobic side, the cohesive force between the whiskers strengthens, and the force to remove the solvent acts. For this reason, if the whiskers come into contact with each other during wet molding, cohesion occurs immediately with a strong force without slipping, and the solvent can be easily removed.
Vf is lowered and shape retention is improved.

In order to re-coordinate the hydroxyl group to the part where the hydroxyl group is once eliminated, the coordination is impossible under the condition that it is dispersed in water, and it has to be treated with boiling water for about 1 hour, Under the condition that a slurry or paste is prepared for wet molding, the hydroxyl group before the heat treatment does not return to the coordinated state. The method of the present invention will be specifically described below with reference to Examples and Comparative Examples.

[0021]

Example 1 Average fiber diameter 0.5 to 1 μm, average fiber length
10 to 30 [mu] m, the formula _{9Al 2 O 3 · 2B 2 O} 3 at 120 ° C. temperature for 12 hours dried aluminum borate whiskers represented (trade name: Alborex G, manufactured by Shikoku Chemicals Corporation), respectively 100g Place each in seven quartz glass trays, and place these trays in 200, 400, 600, 800, 1
Ion-exchanged water with a conductivity of 1 μS / cm or less in a beaker is obtained by heating the whiskers after heat treatment for 6 hours in an electric furnace set to 000, 1200 and 1300 ° C.
Dispersed in 150 cc and irradiated with ultrasonic waves for about 5 minutes to prepare a slurry for papermaking molding. The obtained slurry was poured into a glass filter (3G-4) having an inner diameter of 30 mm and a height of 50 mm and suction filtration was performed to remove water, and then the paper product was taken out on a petri dish and its shape retention was examined. 100 of this paper
After drying at a temperature of ℃ for 4 hours and further heating at a temperature of 600 ℃ for 1 hour, the volume and weight were measured, and Vf was calculated from 3.0 g / cc of the density of aluminum borate. The results are as shown in Table 1, and it was confirmed that when the heat treatment was performed at a temperature of 200 ° C. or higher, the shape retention of the molded body in the wet state was improved and Vf was drastically reduced. . The preform prepared using the heat-treated aluminum borate whiskers had high mechanical strength and was able to sufficiently withstand the molten metal pressure infiltration.

[0022]

Comparative Example 1 A preform was prepared in the same procedure as in Example 1 except that the aluminum borate whiskers were not heat-treated. The obtained preformed body,
Vf was higher than that obtained in Example 1, poor shape retention, and weak mechanical strength. The results are shown in Table 1.

[0023]

[Table 1] The value indicated by * is a numerical value obtained by estimating the volume because the preform is deformed.

[0024]

Example 2 Average fiber diameter 0.5 μm, average fiber length 10 to
30 μm, 120 represented by the chemical formula 2Al ₂ O ₃ · B ₂ O ₃
Aluminum borate whiskers (trade name: Arbolex G, manufactured by Shikoku Kasei Kogyo Co., Ltd.) dried at a temperature of ℃ for 12 hours were placed in 5 quartz glass trays, 100 g each, and the trays were set to 200, 400, 600. After heating for 12 hours in an electric furnace set to a temperature of 800 and 1000 ° C, the whiskers obtained by cooling are heated in a beaker to a purity of 99.
% Industrial methanol (150 cc) was dispersed and the same treatment as in Example 1 was performed to confirm shape retention and V
When f was measured, the results were as shown in Table 2, and the same effect as in Example 1 could be confirmed. In this example, the Vf was lower than that in Example 1 because the aspect ratio was high and the polarity of the solvent was low.

[0025]

Comparative Example 2 A preform was prepared in the same procedure as in Example 2 except that the heat treatment was not performed. The resulting preform has a V compared to that obtained in Example 2.
f was high, the shape retention was poor, and the mechanical strength was weak. The results are shown in Table 2.

[0026]

[Table 2]

[0027]

Example 3 In Example 1, an aluminum borate whisker heat-treated at a temperature of 1000 ° C. for 1 hour was used.
A slurry was prepared by dispersing in the same ion-exchanged water as used in 1. above, and then hydrochloric acid or aqueous ammonia was added to this slurry to adjust the pH to between 3 and 10. Using the obtained slurry, a preform was prepared under the same processing conditions as in Example 1, the shape retention was confirmed, and the Vf was measured. The results are shown in Table 3 and are in the vicinity of neutral. However, Vf tended to be slightly decreased, but the shape retention was not affected at all. This indicates that the mechanical properties of the preform do not deteriorate even if the pH of the slurry changes due to the addition of various additives.

[0028]

[Comparative Example 3] A test was conducted in the same manner as in Example 3 except that the heat treatment was not performed. The results are shown in Table 3, which shows that no shape was formed on the acidic side or the alkaline side. It becomes a preformed body that does not
It was found that the influence of H was great.

[0029]

[Table 3]

[0030]

[Example 4] A filter cloth was laid on a surface plate having a large number of holes for draining water having an inner diameter of 2 mm, and a cylindrical metal mold having an inner diameter of 80 mm and a length of 200 mm was erected on the surface of the surface of the surface, and then a first embodiment was prepared. 100g of aluminum borate whiskers heat-treated at 600 ° C for 3 hours in 500cc of deionized water containing 2% of polyvinyl alcohol resin as an organic binder and 1% of silica sol as an inorganic binder. Was prepared, and the total amount of the obtained paste was poured into a cylindrical mold. Then, the upper punch with a large number of holes for draining water, to which a filter cloth is attached, is gradually pushed into a cylindrical mold for dehydration, and when the molding thickness reaches 44 mm, the pushing is stopped and this state is maintained at about 5 mm. After holding for a minute, it was demolded to obtain a very good wet compact. The obtained molded product
Dry at 100 ° C for 4 hours and then at 600 ° C for 2 hours.
The polyvinyl alcohol resin was degreased by heating for 2 hours, and then the inorganic binder was sintered by heating at a temperature of 800 ° C. for 2 hours to obtain a preform having a Vf of 15%.

This preform is preheated to a temperature of 800 ° C. and set in a mold having an inner diameter of 100 mm heated to 300 ° C.,
Aluminum casting alloy AC8A melted at 800 ° C. was poured into a mold and infiltrated with a pressure of 70 tons by an upper punch to obtain a composite material. When the obtained composite material was cut into a semi-cylindrical shape and the composite surface was observed, no uneven portion or deformation of the preform was observed. In addition, when a test piece was cut out and subjected to a tensile test, it was confirmed that the strength development was 1.4 times that of the unreinforced aluminum cast alloy.

[0032]

[Comparative Example 4] Except that no heat treatment was carried out, the same treatment as in Example 4 was carried out. However, since sufficient dehydration could not be obtained, the molded article collapsed when demolded, and the molding thickness 44 mm, That is, a preform having a Vf of 15% could not be produced.

[0033]

According to the method of the present invention, V which is lower than that of the conventional method is obtained.
Even in the range of f, it is possible to produce an aluminum borate whisker preform having excellent shape retention and high mechanical strength, and a high-performance borosilane is produced by the pressure infiltration method using this preform. An aluminum acid whisker reinforced metal matrix composite material can be obtained.

Claims (2)

[Claims] 1. A preliminary process for a fiber-reinforced metal matrix composite material, characterized in that aluminum borate whiskers heat-treated in a temperature range of 200 ° C. to 1300 ° C. are dispersed in a solvent and wet-molded in the form of slurry or paste. Method for manufacturing molded body. 2. A chemical formula 9Al ₂ O ₃ · 2B ₂ O ₃ or 2Al ₂ O ₃ · B ₂ fiber-reinforced metal base according to claim 1 which comprises using aluminum borate whiskers represented by O ₃ Manufacturing method of preform for composite material.