JPH11236635A - Surface-modified ceramic fiber and aluminum matrix composite material using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce ceramic fibers providing an aluminum matrix composite material free from the peeling of a film even in a state of being repeatedly applied with heat and high in reliability and to provide an aluminum matrix composite material using the same, excellent in mechanical strength, the modulus of elasticity, wear resistance or the like. SOLUTION: The surfaces of ceramic fibers such as alumina fibers, alumina- silica fibers, carbon fibers, silicon carbide whiskers, potassium titanate whiskers, aluminum borate whiskers or the like are coated with lithium aluminate, and by using the fibers, a perform is formed, which is compounded with an aluminum alloy.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface-modified ceramic fiber whose surface is coated with lithium aluminate, and to an aluminum-based composite material using the same.

[0002]

2. Description of the Related Art Aluminum-based composite materials reinforced by ceramic fibers are excellent in mechanical strength, elastic modulus, abrasion resistance, and the like. Have been done. However, at the interface between the ceramic fiber and the aluminum alloy, there are problems of reaction and adhesiveness, and it has been difficult to secure long-term reliability in applications that are repeatedly heated, such as an internal combustion engine. In order to solve such problems, attempts have been made to coat the surface of ceramic fibers with certain compounds.

For example, (a) JP-A-7-82096 discloses a method of covering the surface of a fibrous substance with aluminum borate, and (b) JP-A-3-279468 discloses a method of covering a surface of an inorganic fiber with a metal oxide. (C) JP-A-5-85
No. 721 discloses that on the surface of aluminum borate, a chemical formula MAl ₂ O ₄ (where M is Mg, Ni, Cu, Zn, Mn
Etc.) or a method of forming a water-insoluble metal aluminate layer represented by CaAl ₄ O ₇ , (d) JP-A-7-2429
No. 04 proposes a method for uniformly attaching fine particles to the surface of a whisker.

However, in the method (a), the intended effect cannot be obtained because aluminum borate and the aluminum alloy react with each other. According to the methods (b) and (c), heat is repeatedly applied. In most cases, the oxide film and metal aluminate peel off the film and cannot suppress the reaction, and the method (d) also causes the film peeling due to the problem of the difference in the adhesiveness and the expansion coefficient of the film. Therefore, none of them has been practically used yet.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a ceramic fiber capable of providing a highly reliable aluminum-based composite material without peeling off a film even in a state where heat is repeatedly applied, a mechanical strength using the same, An object of the present invention is to provide an aluminum-based composite material having excellent elasticity and abrasion resistance.

[0006]

In view of such circumstances, the present inventors have conducted various tests and found that the surface of the ceramic fiber was coated with lithium aluminate, which was used to form a composite with an aluminum alloy. As a result, it has been found that the intended purpose can be achieved, and the present invention has been completed. That is, according to the present invention, a component capable of supplying aluminum oxide by heating and a component capable of supplying lithium oxide by heating are uniformly attached to the surface of the ceramic fiber and heated at a temperature of 700 ° C. or more. Thus, a film of lithium aluminate is formed on the surface of the ceramic fiber, and an aluminum-based composite material is prepared by compounding the molded product with an aluminum alloy.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The ceramic fiber used in the present invention is not particularly limited as long as it has a heat resistance of 700 ° C. or higher, but is generally alumina fiber, alumina silica fiber, carbon fiber, silicon carbide whisker. , Potassium titanate whisker, aluminum borate whisker and the like are suitable for use. Of these, aluminum borate whiskers have excellent properties as reinforcing fibers,
Since the properties are similar to those of lithium aluminate and the affinity and linear expansion coefficient of the film are similar, an aluminum-based composite material having particularly good physical properties is provided.

In the present invention, any component capable of supplying aluminum oxide when heated can be used as long as it becomes aluminum oxide when heated. Typical examples thereof include aluminum oxide and aluminum hydroxide. Inorganic salts containing aluminum such as aluminum sulfate, aluminum ammonium sulfate, aluminum nitrate, aluminum chloride, boehmite, organic substances containing aluminum such as aluminum propoxide,
And alumina sol. These may be used alone or in combination of two or more.

As the component capable of supplying lithium oxide upon heating used in the present invention, any component which can be converted into lithium oxide by heating can be used, and typical examples thereof include lithium chloride, lithium carbonate, and lithium carbonate.
Examples thereof include lithium sulfate and lithium nitrate. The mixing ratio between the aluminum compound and the lithium compound may be such that the molar ratio of the metal (Al: Li) is in the range of 10: 1 to 1:50. Lithium aluminate to be formed on the surface of the ceramic fibers, but need not be limited to the specific composition, LiAl ₅ O exhibit particularly good stability at high temperatures
₈ is preferred.

[0010] In order to surface-treat these with ceramic fibers, a method in which the ceramic fibers are mixed with an aluminum compound and a lithium compound in a dry manner and heated at a temperature of 700 ° C or higher, or the same components as described above are slurried with a solvent The method of spray-drying and heating to 700 degreeC or more is common.
Similarly, a method in which a slurry is prepared, followed by solid-liquid separation followed by heating may be employed, but in this case, the amounts of aluminum and lithium remaining in the solid phase should be adjusted appropriately. That is, the aluminum compound can adjust the pH or the like to leave the entire amount in the slurry in the solid phase, but since the lithium compound does not precipitate in an aqueous system, the amount of water remaining in the solid phase during solid-liquid separation is calculated, The amount of lithium compound to be charged must be determined.

The amount of the lithium aluminate film formed on the surface of the ceramic fiber is 0.1 to 10% by weight, preferably 0.5 to 4% by weight based on the ceramic fiber. If the compounding ratio is less than 0.1%, the surface of the ceramic fiber cannot be sufficiently coated, and 10%
If the temperature exceeds the limit, the film on the surface of the ceramic fiber becomes thick, and when heating is repeated, a crack is generated in the film due to a difference in expansion coefficient between the fiber and the film, and the original purpose, reliability, is impaired.

The aluminum metal to be composited with the ceramic fiber having a lithium aluminate film formed on the surface is aluminum or an aluminum alloy, and the type thereof is not particularly limited.

[0013] Although lithium is a common element,
It is not used in actual applications of coating ceramic fibers with metal oxides or aluminates. Conventionally, in forming such a film, as a general method, a method of depositing a supply component of the film in an aqueous solution by adjusting the pH or the like, performing solid-liquid separation, and then heating, has been adopted. At that time, it is considered that the lithium salt was easily dissolved in water and hardly precipitated as a solid.

According to the inventor's knowledge, it takes 10 minutes for an alkali metal other than lithium to form a double salt with aluminum oxide.
A high temperature of over 00 ° C is required, but in the case of lithium 70
A double salt was formed at a temperature of about 0 ° C., and the obtained film was characterized by being highly stable, not reacting with the aluminum alloy, and not peeling off from the ceramic fibers even when repeatedly heated. In this regard, lithium aluminate has properties similar to glass among crystalline materials, similar to aluminum borate, etc., so that properties such as linear expansion coefficient are very similar. This is considered to be due to the fact that it is difficult to reduce.

[0015]

The present invention will now be described by way of Examples and Comparative Examples.
This will be specifically described. Example 1 1.67 g of lithium carbonate and 1.94 g of aluminum hydroxide were added to 100 g of alumina fibers having a thickness of 3 μm and a length of 200 μm, and mixed with a V-type blender, followed by heating at 800 ° C. for 2 hours. The surface of the fiber was coated. When the components of the coating were identified by XRD, LiAlO ₂ was detected. Next, using this surface-treated alumina fiber, a fiber volume ratio of 15% was used.
Was prepared and composited with aluminum alloy 6061. The thermal shock test of the aluminum-based composite material thus obtained was performed, and the cut surface of the sample after the test was observed, as shown in Table 1.

COMPARATIVE EXAMPLE 1 A preform having a fiber volume fraction of 15% was prepared without subjecting the alumina fiber to the surface treatment in the above-described embodiment, and a composite with aluminum alloy 6061 was subjected to a thermal shock test. Table 1 shows the test results.
As shown in FIG.

[Embodiment 2] Thickness 3 μm, length 500 μm
100 g of alumina silica fiber of
5 g and 9.0 g of alumina sol (active ingredient 20%) in 10
After being added together with 00 ml of water and treated by spray drying, the mixture was heated at a temperature of 1000 ° C. for 2 hours to coat the alumina silica fiber. When the components of the coating were identified by XRD, LiAl ₅ O ₈ was detected. Next, a preform having a fiber volume ratio of 10% was prepared using the surface-treated alumina silica fiber, and was composited with the aluminum alloy ADC12. The thermal shock test of the aluminum-based composite material thus obtained was performed, and the cut surface of the sample after the test was observed, as shown in Table 1.

[Comparative Example 2] In the above-mentioned embodiment, the alumina silica fiber was subjected to a fiber volume ratio of 1 without surface treatment.
0% preform is prepared and aluminum alloy ADC
12 and subjected to a thermal shock test. The test results were as shown in Table 1.

[Embodiment 3] Thickness 0.5 μm, length 20 μm
4 g of lithium nitrate and 15 g of aluminum propoxide in 100 g of aluminum borate whiskers of 1000 m.
ml of water, spray-dried, and the surface of aluminum borate whiskers was coated with lithium aluminate. Using this fiber, the fiber volume ratio was 30%.
Was prepared, heated at a temperature of 1000 ° C. for 2 hours, and then composited with an aluminum alloy AC8A. The thermal shock test of the aluminum-based composite material thus obtained was performed, and the cut surface of the sample after the test was observed, as shown in Table 1.

[Comparative Example 3] A preform having a fiber volume ratio of 30% was prepared in the same manner as in the above example without surface treatment of aluminum borate whiskers.
8A and a thermal shock test. The test results were as shown in Table 1.

Example 4 0.3 μm in thickness and 10 μ in length
m of silicon carbide whiskers, and 8.6 of lithium carbonate
g and alumina sol (active ingredient 20%) 0.6 g as 100
The mixture was added with 0 ml of water, suction-filtered, and solid-liquid separated. The solid was formed, heated at a temperature of 700 ° C. for 2 hours, and a fiber volume ratio of a silicon carbide whisker whose surface was coated with lithium aluminate was obtained. A 15% preform was prepared, and this was combined with aluminum alloy AC8A. The thermal shock test of the aluminum-based composite material thus obtained was performed, and the cut surface of the sample after the test was observed, as shown in Table 1.

[Comparative Example 4] In the above-described embodiment, the fiber volume ratio was 15 without the surface treatment of the silicon carbide whiskers.
% Preform was prepared and this was
A thermal shock test was conducted by combining with C8A. The test results were as shown in Table 1.

Example 5 0.3 μm in thickness and 10 μ in length
1.3 g of lithium chloride and 2.3 g (1%) of aluminum hydroxide are added to 100 g of potassium titanate whiskers of m, uniformly mixed and molded to form a molded body having a fiber volume ratio of 15%. By heating at a temperature of 700 ° C. for 2 hours, a preform made of potassium titanate whiskers whose surface was covered with lithium aluminate was prepared, and this was combined with aluminum alloy AC8A. The thermal shock test of the aluminum-based composite material thus obtained was performed, and the result of observing the cut surface of the sample after the test is shown in Table 1.
As shown in FIG.

Comparative Example 5 A preform having a fiber volume fraction of 15% was prepared without performing the surface treatment of potassium titanate whiskers in the above-described example, and this was combined with an aluminum alloy AC8A to conduct a thermal shock test. went. The test results were as shown in Table 1.

Example 6 0.5 μm in thickness and 20 μ in length
m aluminum borate whiskers 100 g, lithium carbonate 0.7 g and aluminum hydroxide 1.2 g were added,
The mixture is uniformly mixed and molded to produce a molded body having a fiber volume ratio of 15%, which is heated at a temperature of 1000 ° C. for 2 hours to obtain a preform made of aluminum borate whiskers whose surface is coated with lithium aluminate. It was prepared and composited with aluminum alloy AC8A. The thermal shock test of the aluminum-based composite material thus obtained was performed, and the cut surface of the sample after the test was observed, as shown in Table 1.

Comparative Example 6 A preform having a fiber volume fraction of 15% was produced without performing the surface treatment of aluminum borate whiskers in the above-mentioned example, and this was combined with an aluminum alloy AC8A and subjected to a thermal shock test. Was. The test results were as shown in Table 1.

[Comparative Example 7] 0.5 μm in thickness and 20 μ in length
To 100 g of aluminum borate whiskers of m m, 10 g of alumina sol (20% of active ingredient) was added together with 1000 ml of water, and the pH was adjusted to precipitate alumina sol, followed by solid-liquid separation. A molded body was produced and heated at a temperature of 1000 ° C. for 2 hours to prepare a preform, which was composited with an aluminum alloy AC8A. The thermal shock test of the aluminum-based composite material thus obtained was performed, and the cut surface of the sample after the test was observed, as shown in Table 1.

Comparative Example 8 0.5 μm thick and 20 μm long
m of aluminum borate whiskers of 100 m, 7 g of alumina sol (20% of active ingredient) and 1.5 g of magnesium chloride.
g was added together with 1000 ml of water, and the pH was adjusted to precipitate alumina and magnesia, followed by solid-liquid separation. Using this, a molded product having a fiber volume fraction of 15% was produced.
A preform was prepared by heating at a temperature of 0 ° C. for 2 hours, and this was combined with an aluminum alloy AC8A. The thermal shock test of the aluminum-based composite material thus obtained was performed, and the cut surface of the sample after the test was observed, as shown in Table 1.

[Comparative Example 9] 0.5 μm in thickness and 20 μ in length
m aluminum borate whiskers (100 g), magnesium chloride (1.5 g) was added together with water (1000 ml),
Was adjusted to precipitate magnesia, followed by solid-liquid separation. Using this, a molded body having a fiber volume ratio of 15% was produced.
A preform was prepared by heating at a temperature of 000 ° C. for 2 hours, and this was combined with an aluminum alloy AC8A. The thermal shock test of the aluminum-based composite material thus obtained was performed, and the cut surface of the sample after the test was observed, as shown in Table 1.

[0030]

[Table 1]

Claims (4)

[Claims] 1. A surface-modified ceramic fiber whose surface is coated with lithium aluminate. 2. The surface-modified ceramic fiber according to claim 1, which is coated with a lithium aluminate represented by a chemical formula of LiAl ₅ O ₈ . 3. An alumina fiber as the ceramic fiber,
The surface-modified ceramic fiber according to claim 1, wherein any one of alumina silica fiber, carbon fiber, silicon carbide whisker, potassium titanate whisker, and aluminum borate whisker, or a mixture of two or more thereof is used. 4. An aluminum-based composite material using a ceramic fiber whose surface is coated with lithium aluminate.