JPH01246331A - Production of whisker preform - Google Patents

Abstract

PURPOSE:To produce whisker preform having uniform strength and density by producing slurry of the whisker using alumina sol as binder, adding basic compound to increase the viscosity and dewatering at the time of producing the whisker preform for fiber reinforced metallic material using the whisker as reinforced material. CONSTITUTION:The alumina sol as the binder is added to K2TiO2 whisker or SiC whisker so as to come to 1-50wt.% of solid content in the whisker and water is added to make the slurry-state having 10-50wt.% concn. of the solid content in the whisker. The basic compound of ammonia water, ethylamine water solution, etc., is added to this slurry and pH in the slurry is adjusted to 7.5-11, to increase the viscosity of the alumina sol. A cylindrical shaped filter device 3 composing of wire gauze having about 200mesh at the bottom part 2 is laid on thick filter paper 4 and the slurry is charged in it and on the slurry, the same wire gauze 2' and thick filter paper 4' are laid and the slurry is pressurized with a plunger 5 and after dewatering, heating and drying are executed, to produce the whisker perform having uniform strength and density for producing the fiber reinforced metal material.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing whisker preforms for composite materials containing whiskers or the like as reinforcing materials in a matrix metal.

(Prior art) Fiber-reinforced metal materials (FRM) are made of fiber-reinforced metal materials (FRM), which use whiskers such as potassium titanate and silicon carbide, which have high strength and high elasticity, as reinforcing materials, and metals and alloys such as aluminum as matrix.
), the so-called melt pressure casting method is known, which consists of first placing a whisker aggregate preform in a mold, then compressing the molten matrix metal into the preform and solidifying it. There is.

To describe this kind of FRM preform manufacturing method more specifically, (A) JP-A-61-127836 as an example using potassium titanate whiskers; (B) Special example as an example using silicon carbide whiskers. 1977
-121196, JP-A-59-227761, JP-A-60-55000, JP-A-60-65200, and the like.

By the way, in the above-mentioned examples using silicon carbide whiskers, a method of dispersing the whiskers in water or an organic solvent, press-molding and drying the dispersed whiskers has been commonly used as a means for forming the whisker preform. However, in such a method, if the pressure is small and the volume content of whiskers is low, the strength after drying is very weak, and the preform itself becomes plastic due to subsequent press-fitting of molten metal. The problem is that the whiskers are not uniformly dispersed within the IJx metal, and as a result, it does not function effectively as a reinforcing agent.

On the other hand, methods of adding an organic binder to increase the strength of the preform after drying are disclosed in JP-A-59-121197, JP-A-60-210600, and JP-A-61-1974.
It is disclosed in No. 4. However, in these methods, it is essential to incinerate and remove the organic components in advance before press-fitting the molten metal.

Furthermore, a method has been reported in which an inorganic binder is added to the whisker dispersion liquid in order to prevent plastic deformation and give strength to the preform. For example, JP-A-61-127836 describes binders such as sodium silicate and lithium silicate.

Further, JP-A-60-204660 describes the addition of boric acid and the like.

However, as mentioned above, in the method of adding an inorganic binder to the whisker dispersion and then drying it to obtain a preform, it is difficult to efficiently filter and dehydrate the slurry (as seen in JP-A-60-204660). In order to carry out this process, it is necessary to use a low-viscosity binder, and therefore, during filtration and dehydration, a large amount of the binder component flows out together with the filtrate, resulting in a very poor binder yield. In addition,
When the obtained whisker cake is heated and dried, the migration of the binder tends to be severe, and as a result, the binder tends to move to the surface layer of the preform. had the disadvantage that it was very weak and had a non-uniform structure that could not withstand the press-fitting of molten metal.

(Means for Solving the Problems) The object of the present invention is to provide a preform in which the various problems mentioned above are improved or solved.Therefore, an alumina sol is used as a binder, and is uniformly dispersed in water together with whiskers. The alumina sol is thickened by making the pH of the slurry basic using a basic compound,
The present invention provides a novel method comprising forming a whisker cake as it is or by applying pressure and dehydration, and further heating and drying this cake.

As mentioned above, when the whisker slurry using alumina sol as a binder is made basic, the viscosity of the alumina sol increases, so that the viscosity of the entire slurry also increases. Therefore, during the filtration (dehydration) process, the alumina sol that acts as a binder is rarely squeezed out, and in addition, binder migration does not occur when the dehydrated whisker cake is heated and dried. Of course, such features result in the completed preform having a strong structure that is uniform from the surface layer to the interior (the binder distribution is also uniform).

The content of the alumina sol used as a binder in the present invention varies depending on the whisker used, but is preferably 1 to 50 wt%, more preferably 2 to 2 Qwt% of the whisker solid content. If the amount of binder is small within the above range, the strength of the obtained preform will be insufficient, while if it is too large, the voids in the preform will be filled, resulting in a negative effect on the proper processing of the metal. There is.

In the present invention, the concentration of the dispersed slurry varies depending on the type and characteristics of whiskers used, but
Before the H adjustment, it is necessary that the slurry itself has good fluidity and that it can be easily dispersed. For example, the solid content of whiskers is 10 to 50w.
t% is preferred.

If the concentration is too low within the above range, even if the alumina sol is adjusted to basicity and thickened, the effect on the entire slurry will be small (the increase in slurry viscosity will be low), and therefore the binder during pressurization and filtration will be There is a disadvantage that the binder flows out and, in addition, binder migration occurs during heating and drying.

On the other hand, if the concentration is too high, it becomes relatively difficult to disperse the whiskers, and even if they can be dispersed, the viscosity increases significantly when adjusted to basicity, exhibits almost no fluidity, and is difficult to add. Even with subsequent pressurization and dehydration, large voids tend to form in the preform.

In the present invention, the degree of thickening of the whisker slurry when a basic compound is added varies somewhat depending on the type of whiskers and the concentration of the slurry. For example, at low concentrations (10-20%
), there is a tendency for the viscosity to begin to thicken around pH 7, 5 to 8, and to reach its maximum viscosity at pH 9 to 11.

On the other hand, at high concentrations (30-50%),
There is a tendency for viscosity increase to become noticeable around pH 7 to 8.

Therefore, the degree of viscosity increase can be changed as appropriate depending on the compression ratio during filtration and dehydration. However, a high viscosity is usually preferred as long as it can be compressed by pressure.

In the present invention, the basic compound is preferably one that evaporates by heating and drying and does not remain in the completed preform. For example, low-boiling organic amines such as ammonia water, ethylamine aqueous solution, diethylamine aqueous solution, etc. are used.

Organic hydroxyamines such as monoethanolamine can also be used because they are burnt out during preheating before metal injection. On the other hand, caustic soda and the like are not preferred because their sodium content remains as ash in the completed preform.

Next, in the present invention, the whisker cake is produced by pressurizing and filtering the slurry according to a conventional method. For example, the following methods can be cited as specific examples.

That is, it is relatively easy to first place water-absorbing sheets (for example, filter paper) on the top and bottom of a mold, pour the slurry between them, and then dewater by applying pressure.

In addition, if the viscosity increases significantly under basic conditions and exceeds 10,000 Cp, it may be molded as it is without applying pressure, and then dried.

The above-mentioned molding methods include: ① Pressurizing and dewatering using a mold that has been shaped into a completed preform;
■ A method in which the whisker cake is pressurized and dehydrated using a large mold and then formed into the shape of the completed preform by cutting, etc.; There are methods such as cutting the obtained preform and shaping it into a desired preform shape by cutting.

An appropriate one can be selected from these depending on the desired shape of the preform.

After pressurization and dehydration, the whisker cake is removed from the mold and dried in a blow dryer at approximately 105°C.

Even if it is molded as is without pressurization or dehydration, it is similarly dried in a blow dryer. The drying time can be changed as appropriate depending on the size of the whisker cake.

After drying, the obtained preform may be transferred to a mold for metal press-fitting, preheated as it is, and molten metal may be press-fitted therein. It is also possible to perform sintering if necessary to remove structural water from the alumina sol and then form a composite.

The present invention will be explained below with reference to Examples.

Examples 1 to 4 Potassium titanate whiskers (manufactured by Titan Kogyo, H
T-200) was added. This was sufficiently dispersed using a vortex stirrer to obtain a whisker slurry. The solid proportions at this time were as shown in Table 1 in weight percent.

Table 1 The obtained whisker slurry had a viscosity of 30 cp (type B viscosity) and a pH of 5. When 8% ammonia water was added dropwise to this whisker slurry to adjust the pH of the slurry to 8, the slurry became 1000 cp (B type accuracy). Spread this slurry on a wire mesh 2 (200 mm) at the bottom as shown in Figure 1.
Cylindrical filtration device (φ=8cm5h
= 10 cm) until it reached a height of 50 mm from the bottom. As shown in FIG. 2, the apparatus main body 3 was placed on top of thick filter papers 4. As shown in FIG. 2, a wire mesh 2' (φ=8 cm), which was the same as the wire mesh used at the bottom of the filter main body 3, was cut out and placed on top of the slurry. Furthermore, thick filter paper 4' (φ=8a) punched out on top of this wire mesh
10 sheets of m) were stacked. Pressure was applied from above the filter paper using a plunger 5 to perform dehydration and filtration. a when the thickness of the slurry before pressurization is a and the thickness after pressurization is b
/b was defined as the "compression ratio". Example 1 was obtained by setting this compression ratio to 1.7. Below, the compression ratio is 2.5.3.
4 were designated as Examples 2 and 3, respectively.

Example 4 was prepared by changing the composition of the whisker slurry as shown in Table 2 and setting the compression ratio to 1.9.

Table 2 The whisker cake taken out from the filtration device was dried in a blow dryer at 105°C to obtain a preform.

Comparative Example 1 A preform was obtained by filtration and drying without performing the pH:A adjustment using aqueous ammonia as in Example 1.

Comparative Example 2 A preform was obtained in the same manner as in Comparative Example 1 except that the alumina sol was removed.

The strength and density of the preforms obtained in Examples 1 to 4 and Comparative Examples 1 and 2 were determined.

The results are summarized in Table 3.

Note: The top surface of the circular center part of the obtained cylindrical preform, and 4 mm from the top surface, 3gg, 12 order, 16m+
At step a, cut into rounds, and check the hardness of the newly created upper surface.
The density of that part was measured. The strength of the preform was determined by the Brinell hardness test method of JISZ-2243. That is, the diameter of the indentation was measured using a steel ball with a diameter of 1Q mm and a test load of 4 kgf, and the value was calculated using the following formula.

Note 2: The density was determined by measuring the weight of a rectangular parallelepiped of 40 mm in length and width and 4 u in thickness at the center of the circle.

〔evaluation〕

In Examples 1 to 4, at each section of the preform,
The strength was found to be sufficient and constant.

Therefore, it was able to withstand the press-fitting of molten metal.

Furthermore, it was found that by changing the compression ratio as shown in Example 1.2.3, preforms with different strengths and densities could be easily produced.

Incidentally, increasing the compression ratio tended to increase both the strength and density of the preform.

Furthermore, by increasing the concentration of the dispersion slurry and increasing the ratio of binder, a preform with considerable strength and high density was obtained even at a low compression ratio (Example 4).

It is generally recognized that when the density of a preform is increased, the proportion of whiskers in a composite material naturally increases, and the strength of the composite material is improved.

As described above, according to the present invention, it is possible to obtain a required preform by appropriately changing the binder amount, dispersion concentration, and compression ratio.

On the other hand, in Comparative Example 1, the binder migrates to the surface layer during heat drying, so that only the strength of the surface layer portion is sufficient, and the amount of binder is insufficient in the one direction portion, resulting in a decrease in strength. In addition, there is no uniformity in density. This means that the preform is deformed by press-fitting the molten metal, making it uneven and
This means that only a composite material with no strength can be obtained. In addition, the viscosity of the whisker slurry is low and its fluidity is too high, so the compression ratio cannot be maintained high and the molding range of the preform tends to be narrow.

Next, regarding Comparative Example 2, the density of the obtained preform was somewhat uniform, but since it did not contain a binder, it was very brittle and could not be used as a preform.

Examples 5 and 6 Substantially the method of Example 1 was followed, but the potassium titanate whiskers of Example 1 were replaced with silicon carbide whiskers (
Dispersion was performed using Toka Whisker (manufactured by Tokai Carbon Co., Ltd.) to obtain a whisker slurry.

The slurry before adding ammonia water has a p15 and a viscosity of 20.
It was 0Cp. When the pH was adjusted to 8 by adding aqueous ammonia, the viscosity became 5000 cp. This slurry was put into the filtration device used in Example 1, and the compression ratio was set to 1.
．． Examples 5 and 6 were obtained by heating and drying as 1.3.
And so.

In addition, the whisker slurry of Example 6 was molded at a compression ratio of 1.3 with pH 5 without adjustment with aqueous ammonia.
Comparative Example 3 was prepared by heating and drying.

As in Example 1, the strength (Brinell hardness) and density of the preform were determined and are summarized in Table 4.

Table 4 [Evaluation] Examples 5 and 6 even when silicon carbide was used as the whisker.
As shown in Figure 2, a preform was obtained in which the strength of each part was sufficient and constant, and the density was also constant.

On the other hand, in Comparative Example 3, the binder migrated to the surface layer during heating and drying, and only the strength of the surface layer satisfied the conditions, while the inside became weak due to lack of binder. Of course, no uniformity in density was observed, and therefore it was not suitable for use as a preform for composite materials.

(Effect of the invention) In the present invention, in order to adjust the whisker slurry to basicity,
The alumina sol of the binder increases in viscosity and does not migrate even when heated and dried, making it possible to obtain a preform with uniform strength and density as a whole.

It also has the advantage that the strength and density of the preform can be easily adjusted by changing the amount of binder, compression ratio, etc.

[Brief explanation of the drawing]

FIGS. 1 and 2 show a specific example of an apparatus for producing whisker cake by pressurizing and filtering slurry. Figure 1 Figure 2

Claims (4)

[Claims] (1) A method for producing a whisker preform, which comprises adjusting a dispersed slurry containing whiskers and alumina sol to basicity, dehydrating it as it is or compressing it, and heating and drying it to obtain a preform. (2) The concentration of whiskers in the dispersed slurry is 10
~50 wt% (in terms of whisker solid content)
1) The method for producing the whisker preform described above. (3) Alumina content is 1 to 50w of whisker solid content
The method for producing a whisker preform according to claim 1, wherein the whisker preform is t%. (4) The method for producing a whisker preform according to claim (1), wherein the basicity is adjusted to a pH of 7.5 to 11.