JPH11256253A - Carbon fiber for composite material and composite material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aluminum base composite material free from the generation of deterioration in the boundary between carbon fiber and a matrix even in the case thermal stress is applied and maintaining thermal expansibility and thermal conductivity and to provide carbon fiber. SOLUTION: This carbon fiber for a composite material is the one provided with a coating layer in which silicon carbide contains in the boundary with the carbon fiber, silicon oxide contains on the surface side, and silicon carbide and silicon oxide are mixed in the middle, and the aluminum base composite material is the one in which the carbon fiber for a composite material provided with such coating layer is dispersed into a matrix of aluminum or an aluminum alloy. Thus, even in the case thermal stress is applied, its thermal expansibility and thermal conductivity are maintained without generating deterioration in the boundary, and its reliability is high.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to carbon fibers for composites,
The present invention relates to a method for producing a carbon fiber for a composite material, and an aluminum-based composite material.

[0002]

2. Description of the Related Art In recent years, there has been a demand for a highly reliable material having low thermal expansion which does not generate thermal distortion and excellent heat conduction in order to enhance heat radiation, as electronic equipment and other industrial members. Conventionally, as a material applied to such a requirement, a Ni-alloy such as a Fe-Co alloy (Kovar), a 42 alloy, a Cu-W alloy, or the like is generally used as a material having good thermal expansion characteristics. Further, as a material having a high thermal conductivity, Cu,
There is a highly conductive metal such as Al. In recent years, there has been proposed a composite material in which carbon fibers having a small coefficient of thermal expansion are used as a dispersing material, and a matrix is formed of aluminum or the like having a high heat conduction property (see, for example, JP-A-1-319).
639, JP-A-4-147654).

[0003]

However, the carbon fiber, which is the dispersant of the above-mentioned prior art, has poor wettability with the matrix aluminum and aluminum alloy.
There was a problem that sufficient interfacial properties could not be obtained at the time of compounding. The thermal expansion coefficient of the carbon fiber is -1 × 1
For 0 ⁻⁶ / ° C., the coefficient of thermal expansion of aluminum is 24
Since it is × 10 ⁻⁶ / ° C., the difference is large. When thermal stress is repeatedly applied, a large stress is generated at the interface between the carbon fiber and the aluminum or aluminum alloy matrix, and the interface peels off. As a result, there is a problem that thermal expansion characteristics and thermal conduction characteristics are deteriorated. In view of the above problems, the object of the present invention is to provide a highly reliable thermal expansion property and a heat conduction property that are not deteriorated at an interface between a carbon fiber and a matrix even when a thermal stress is applied. An aluminum-based composite material and a carbon fiber used for the same are provided.

[0004]

According to the present invention, in a carbon fiber provided with a coating layer, the coating layer is silicon carbide at the interface with the carbon fiber, silicon oxide on the surface side, and silicon oxide at the middle. A composite material carbon fiber provided with a coating layer characterized by being mixed with silicon. It is preferable that the composition of the coating layer changes in a gradient manner so that the proportion of silicon oxide increases toward the surface side away from the interface with the carbon fiber.
Further, the present invention provides a coating layer in which a ceramic precursor polymer is adhered to carbon fibers and baked to form silicon carbide at the interface with the carbon fibers, silicon oxide on the surface side, and a mixture of silicon carbide and silicon oxide in the middle. This is a method for producing a carbon fiber for a composite material, characterized by forming, for example, polycarbosilane as a ceramic precursor polymer.

The present invention is also an aluminum-based composite material, characterized in that the carbon fibers for a composite material provided with the coating layer are dispersed in a matrix of aluminum or an aluminum alloy, and the composite material provided with a coating layer is provided. The aspect ratio of the carbon fibers for use is preferably 8 to 40. The aluminum alloy of the matrix is S
An aluminum alloy containing 12 to 25% by weight of i is preferable. Furthermore, it is preferable that the carbon fiber for composite material provided with the coating layer is oriented in a direction in which thermal expansion of the composite material is to be suppressed.

[0006]

The carbon fiber for a composite material of the present invention has a coating layer in which silicon carbide is provided at the interface with the carbon fiber, silicon oxide is provided on the surface side, and silicon carbide and silicon oxide are provided in the middle. Silicon carbide at the interface with
By providing a coating layer that is inclined to silicon oxide as it moves away from the interface with the carbon fiber and becomes closer to the surface, the surface of the carbon fiber coating layer becomes wettable with aluminum, aluminum alloy, which is the matrix of the composite material And the adhesion can be increased at the interface of the matrix. The aluminum-based composite material in which the carbon fibers for a composite material provided with the coating layer of the present invention are dispersed in a matrix of aluminum or an aluminum alloy can suppress deterioration of thermal expansion characteristics and the like.

That is, in the conventional composite material, a good interface could not be obtained due to poor wettability between the carbon fiber and aluminum or aluminum alloy, but silicon carbide was used at the interface with the carbon fiber and silicon oxide was used at the surface side. In the middle, by providing a coating layer in which silicon carbide and silicon oxide are mixed, in particular, by providing a ceramic coating layer whose composition changes in a gradient at the interface, thermal expansion deterioration due to the interface between carbon fiber and matrix, etc. Can be suppressed. That is, by providing a coating layer of silicon carbide at the interface with the carbon fiber and silicon oxide on the matrix side, it is possible to increase the adhesion at the interface, and the composition of the coating layer is inclined to change at the interface. Can reduce the stress due to the difference in thermal expansion between them.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION A carbon fiber provided with a coating layer of the present invention has a ceramic precursor polymer adhered to its surface and is baked to form a coating layer of silicon carbide on the carbon fiber side. The composition changes in a gradient manner toward the surface side (matrix side) away from the surface, and silicon oxide is formed on the surface. The attachment of the ceramic precursor polymer to the surface of the carbon fiber is performed by immersing the carbon fiber in a coating solution in which the polymer is dissolved. For example, the coating solution is a 3% polycarbosilane solution using hexane as a solvent. In addition, firing is performed in an atmosphere of nitrogen + oxygen at 1150.
It is preferably carried out at a temperature of from 1250C to 1200C.
The coating layer is formed by attaching a ceramic precursor polymer to a carbon fiber molded body and firing it, or attaching a ceramic precursor polymer to the carbon fiber and firing it to form a coating layer, and then forming the carbon fiber molded body. Is what you do. The thickness of the coating layer is 1 μm to 5 μm
m is preferable.

[0009] The coating layer of carbon fiber is used to obtain adhesion to carbon fibers dispersed in the composite material and adhesion to aluminum and aluminum alloy of the matrix of the composite material. By forming a coating layer in which silicon carbide, silicon oxide on the surface side, and silicon carbide and silicon oxide in the middle are mixed, thermal expansion is caused by a gradient change in composition, particularly from silicon carbide to silicon oxide. The stress caused by the difference can be reduced. Carbon fibers have good adhesion to silicon carbide and a small difference in thermal expansion. The silicon oxide on the matrix side has good wettability with the matrix aluminum and aluminum alloy, and has a small difference in thermal expansion with silicon carbide. Therefore, it is important that the carbon fiber side of the coating layer is turned into silicon carbide and the matrix side is turned into silicon oxide by firing.

The aluminum-based composite material of the present invention is obtained by dispersing a composite carbon fiber provided with a coating layer as described above in aluminum or an aluminum alloy.
It is composed of aluminum or an aluminum alloy as a high thermal conductive metal matrix in which carbon fibers having low thermal expansion are dispersed. The aluminum-based composite material in which carbon fibers provided with a coating layer are dispersed according to the present invention is used, for example, as a substrate on which a semiconductor device is mounted. The aspect ratio of the carbon fibers dispersed in the matrix is preferably 8 to 40. In this range, an anchor effect occurs between the matrix of the aluminum or aluminum alloy and the carbon fiber provided with the coating layer, and interfacial delamination due to thermal stress does not occur, so that a more reliable composite material can be obtained. Aspect ratio 8
If it is smaller, the carbon fibers are too fine to obtain a predetermined volume filling rate. If it is larger than 40, the fiber breakage is remarkable at the time of producing the carbon fiber molded body, and a predetermined volume filling rate cannot be obtained. A more suitable aspect ratio is 10 to 30.

The aluminum-based composite material of the present invention uses aluminum or an aluminum alloy having high thermal conductivity as a matrix.
An aluminum alloy containing 2 to 25% by weight is suitable in terms of difference in thermal expansion coefficient from carbon fiber, workability, and impregnation. If the amount of Si is less than 12% by weight, the difference between the coefficient of thermal expansion of the matrix and the coefficient of thermal expansion of the carbon fiber becomes large, the stress at the interface becomes large, and a sufficient anchor effect cannot be obtained. If the content is 25% by weight or more, the primary crystal Si increases and the workability deteriorates, and also at the time of compounding, the melting point of the matrix is increased, impregnating property is deteriorated, and composite defects such as cracking and crushing of the composite may occur.

The carbon fibers provided with the coating layer dispersed in the matrix are preferably oriented in a direction in which the thermal expansion of the composite material is to be suppressed. By setting the aspect ratio to 8 to 40 and orienting the carbon fibers in a direction in which thermal expansion of the composite material is to be suppressed, the anchor effect can be more effectively exhibited.

[0013]

Embodiment 1 A first embodiment of the present invention will be described with reference to Table 1. The carbon fibers dispersed in the composite material had a fiber diameter of 10 μm, and a carbon fiber molded body was manufactured such that the aspect ratio of the carbon fibers became 10 after molding. In this production, the carbon fiber was stirred in an aqueous solution containing an inorganic binder as a main component, and then this slurry was put into a mold and vacuum dewatered from the bottom of the mold, and the dimensions were 100 mm × 100 mm × 20 mm.
Was obtained. The longitudinal direction of the carbon fiber is oriented in the plane direction. That is, since the carbon fiber was subjected to suction dehydration, a carbon fiber whose longitudinal direction was oriented in the plane direction was obtained from the resistance of dehydration. Also, carbon fiber molded bodies having various volume filling rates were produced.

Next, the carbon fiber molded body according to the embodiment of the present invention is subjected to a treatment for forming a coating layer, and the comparative example is not treated. In the treatment for forming the coating layer according to the embodiment of the present invention, the carbon fiber molded body is dried and dipped in a coating solution to adhere. The coating solution is a 3% polycarbosilane solution (solvent is hexane). In order to attach the coating solution to the carbon fiber molded body, the coating solution is immersed in a 3% polycarbosilane solution, which is 30% at a reduced pressure of 30 cmHg.
Degas in a vacuum. This was repeated three times. After immersion in vacuum,
The carbon fiber molded body was dried in the air for 24 hours, and further dried for 6 hours.
Dry at 0 ° C. under reduced pressure. After drying, firing was performed at 1200 ° C. for 2 hours in a nitrogen + oxygen (2%) gas. On the carbon fiber surface after firing, silicon carbide was confirmed on the fiber side and silicon oxide on the surface layer by Auger analysis.

Both the carbon fiber molded article treated with the coating layer of the present invention and the carbon fiber molded article without the treatment of the comparative example were heated to 700 ° C. in a preheating furnace, and the atmosphere in the furnace was argon. Preheating was performed in an atmosphere. Next, the fiber molding taken out of the preheating furnace was placed in a casting mold having a cavity of the same shape as the carbon fiber molding and preheated to 250 ° C. Then, after clamping with a pressure casting apparatus by a molten metal forging method, a 20% Al—Si alloy at 750 ° C. is cast at an injection speed of 10 cm / sec, and 1000 atm after the casting.
After pressurizing and holding for 1 minute at the pressure described above, solidification was performed. Thus, an aluminum-based composite material in which carbon fibers were oriented and dispersed in the metal matrix in the plane direction was produced. A thermal shock test for applying a thermal stress to these composite materials was performed.
As the test conditions, a heating atmosphere of 200 ° C. and a cooling atmosphere of −30 ° C. were prepared and thrown alternately, and the thermal characteristics were evaluated 1000 times.

As is clear from Table 1, the carbon fiber provided with the coating layer according to the embodiment of the present invention in which the carbon fibers are dispersed has a coefficient of thermal expansion (/ ° C.) of 15% to 40% for all the volume filling ratios. And the thermal conductivity (W / mK) is higher than that of the comparative example before the test, and stable thermal characteristics are obtained even after adding a thermal history (after the thermal shock test).

[Table 1]

[0017]

Embodiment 2 A second embodiment of the present invention is shown in Table 2 and will be described. In the second embodiment, a carbon fiber molded body was manufactured by changing the aspect ratio of the carbon fiber. Carbon fiber (fiber diameter: 10 μm) was used as a dispersant, and carbon fiber molded bodies were produced from carbon fibers having various aspect ratios. The preparation is stirred in an aqueous solution containing an inorganic binder as a main component, and then the slurry is put into a mold and subjected to vacuum dehydration from the bottom of the mold.
Assuming a volume filling rate of 35%, dimensions 100 mm x 100 mm
A carbon fiber molded body of × 20 mm was obtained. The length of the carbon fiber is oriented in the plane direction due to dehydration resistance due to suction dehydration. Next, a treatment for forming a coating layer on the carbon fiber molded body was performed under the same conditions as in Example 1 and an aluminum-based composite material was manufactured under the same conditions as in Example 1.

A thermal shock test for applying a thermal stress to these composite materials was performed. The test conditions were a heating atmosphere of 200 ° C and-
Prepare a cooling atmosphere of 30 ° C and throw it in alternately.
The evaluation of the thermal characteristics was performed at 00 times. As is evident from Table 2, the dispersion of the carbon fibers provided with the coating layer according to the embodiment of the present invention has a thermal expansion coefficient (/ ° C.) and a thermal conductivity (W / mK), the properties before the test were improved, and stable thermal properties were obtained even after adding a thermal history (after the thermal shock test).

[Table 2]

[0019]

Embodiment 3 A third embodiment of the present invention will be described with reference to Table 3. In the third embodiment, impregnation is performed by changing the amount of Si in the Al—Si alloy of the matrix. Using a carbon fiber (fiber diameter: 10 μm) as the dispersing material and using a carbon fiber having an aspect ratio of 35, a carbon fiber molded body was produced under the same conditions as in Example 1 above, and then as in Example 1 above. Under the conditions described above, a process of forming a coating layer was performed on the carbon fiber molded body. Next, the fiber molded body taken out of the preheating furnace was placed in a casting mold preheated to 250 ° C. having a cavity having the same shape as the fiber molded body, and clamped by a pressure casting apparatus by a molten metal forging method. Al-Si alloy melt is cast at an injection speed of 10 cm / sec, and after casting, 10
After pressurizing and holding at a pressure of 00 atm for 1 minute, solidification was performed.
The volume filling factor is 25%.

A thermal shock test for applying a thermal stress to the aluminum-based composite material was performed. As the test conditions, a heating atmosphere of 200 ° C. and a cooling atmosphere of −30 ° C. were prepared and thrown alternately, and the thermal characteristics were evaluated 1000 times. As is evident from Table 3, the aluminum-based composite material in which the carbon fibers provided with the coating layers according to the examples of the present invention are dispersed has both a thermal expansion coefficient (/ ° C.) and a thermal conductivity (W / mK) which are tested. The previous characteristics are improved, and stable thermal characteristics are obtained even after adding a thermal history (after the thermal shock test).

[Table 3]

[0021]

According to the carbon fiber for a composite material of the present invention, it has good wettability with the matrix aluminum and aluminum alloy, and has an effect that good adhesion can be obtained at the interface of the matrix. According to the aluminum-based composite material, it is possible to provide a highly reliable composite material that maintains thermal expansion characteristics and heat conduction characteristics without causing deterioration at the interface between the carbon fiber and the matrix even when subjected to thermal stress. It is effective.

Claims (3)

[Claims] In a carbon fiber provided with a coating layer, the coating layer is made of silicon carbide at an interface with the carbon fiber, silicon oxide on the surface side, and a mixture of silicon carbide and silicon oxide in the middle. Carbon fiber for composite materials provided with a characteristic coating layer. 2. A coating layer in which a ceramic precursor polymer is adhered to carbon fibers and baked, so that silicon carbide is present at the interface with the carbon fibers, silicon oxide is present on the surface side, and silicon carbide and silicon oxide are mixed in the middle. The method for producing a carbon fiber for a composite material provided with a coating layer according to claim 1, wherein: 3. An aluminum-based composite material, wherein the composite carbon fiber provided with the coating layer according to claim 1 is dispersed in a matrix of aluminum or an aluminum alloy.