JP6982401B2 - Manufacturing method of carbon short fiber reinforced composite material - Google Patents

Description

The present invention relates to a composite material that is lightweight and has excellent wear resistance even at high temperatures, and is suitable for structural members such as brake members.

Disc brakes are a type of braking device and are mainly used in railway vehicles, automobiles, bicycles, and the like. By sandwiching the brake disc that rotates with the wheels from both sides with the brake pads, frictional force is generated, and the kinetic energy is converted into heat energy for braking. Steel materials such as stainless steel and chrome steel are usually used for brake discs of railway vehicles and automobiles.

However, in recent years, in order to improve running performance and fuel efficiency, it has been required to reduce the weight of the vehicle body and the unsprung weight, and the change of the brake disc to a material lighter than the steel material is being considered. As one of such materials, carbon fiber reinforced silicon carbide ceramics, which are lightweight and have high strength, are attracting attention. Carbon fiber reinforced silicon carbide ceramics are made by melt-impregnating a C / C (carbon fiber reinforced carbon) composite material with metallic silicon and reacting the carbon of the matrix in the C / C composite material with silicon to form silicon carbide. .. Silicon carbide has strong wear resistance and heat resistance, and is also extremely excellent in chemical stability, and is therefore suitable for imparting strength to a material.

Recently, the use of carbon fiber reinforced silicon carbide ceramics for brake discs has been studied. In order to improve the damage tolerance of carbon fiber reinforced silicon carbide ceramics, a brake disc having a core body and a friction layer is known.

For example, Patent Document 1 describes a brake or clutch comprising a carbon fiber reinforced porous carbon object having a friction surface and a core body, and the carbon object and the core body are interconnected with each other. A friction element is disclosed in which at least a part of the pores in an object is filled with silicon and silicon carbide, and the friction element is connected to the core body via a silicon carbide high temperature resistant bonding layer containing silicon carbide on a side away from the friction surface. Has been done. The friction element of Patent Document 1 is obtained by placing the carbon object on a core body and infiltrating it with liquid silicon to make it ceramic.

Patent Document 2 discloses a friction body having a friction layer and a core body, which is made of porous carbon in which silicon is infiltrated and reinforced with carbon fibers. The friction body of Patent Document 2 is obtained by molding a friction layer, putting it in a molding mold of a core body, molding the friction body together with the core body, and pyrolyzing and infiltrating silicon.

Special Table No. 10-507733 Gazette Japanese Unexamined Patent Publication No. 2002-255665

However, in the methods of Patent Documents 1 and 2, a boundary layer formed by silicon infiltration is formed at the boundary between the carbon object or the friction layer and the core body, and the boundary layer causes problems such as strength reduction and peeling. May occur.
Therefore, an object of the present invention is to provide a carbon short fiber reinforced composite material having a base material portion and a sliding portion having different physical characteristics without forming a boundary layer.

The carbon short fiber reinforced composite material of the present invention has a base material portion and at least one sliding portion in contact with the base material portion, and the base material portion and the sliding portion each have at least a plurality of SiC. The average diameter of the plurality of carbon short fiber bundles containing the carbonized short carbon fiber bundle and the SiC matrix existing between the plurality of carbon short fiber bundles and contained in the base material portion is the sliding portion. It is characterized in that it is larger than the average diameter of a plurality of carbon short fiber bundles contained.
Further, it is preferable that 80% or more of the plurality of carbon short fiber bundles contained in the base material portion has a larger fiber diameter than the plurality of carbon short fiber bundles contained in the sliding portion.

One short carbon fiber bundle contained in the base portion is made of 15 00 or more 40 00 present less carbon fiber, and 25 00 present one of the short carbon fiber bundle 500 or more contained in the sliding portion It is preferably composed of the following.

Further, the method for producing a carbon short fiber reinforced composite material of the present invention is a carbon short fiber for a base material obtained by coating 1500 or more and 4000 or less carbon short fiber bundles per fiber bundle at a pitch and then crushing the carbon short fibers. A step of mixing a phenol resin in a bundle to obtain a mixture for a substrate portion in the form of particles, and a carbon short of 500 or more and 2500 or less per fiber bundle, which is composed of the same carbon fibers as the carbon short fiber bundle. A step of mixing a phenol resin with a carbon short fiber bundle for a sliding portion obtained by coating a fiber bundle at a pitch and then crushing the carbon bundle to obtain a particulate mixture for the sliding portion, and the sliding portion in a molding die. A step of adding the mixture for carbon dioxide and the mixture for the base material and press-molding under heating to obtain a cured product, and a step of firing the cured product at 2000 ° C. or higher to obtain a fired body. Including the step of impregnating the fired body with silicon by the silicon melt impregnation method in vacuum, the number of carbon short fiber bundles for the base material portion is 1.6 from the number of carbon short fiber bundles for the sliding portion. It is characterized by more than double the number.
Further, in the present invention, it is preferable that the carbon short fiber in the sliding portion has a higher SiC conversion rate than the base material portion.
In the present invention, by having the above structure, it is possible to obtain a carbon short fiber reinforced composite material having high strength and high toughness without forming a boundary layer between the base material portion and the sliding portion. ..

According to the present invention, a carbon short fiber reinforced composite material having a sliding layer having high wear resistance, high strength, and high toughness without forming a boundary layer between the base material portion and the sliding portion can be obtained. Can be provided. When such a carbon short fiber reinforced composite material is used, for example, as a disc brake, the wear resistance can be remarkably improved as compared with the conventional case.

The carbon short fiber reinforced composite material of the present invention is produced by a silicon melt impregnation (MI) method, and the carbon short fiber reinforced composite material has a base material portion and at least one sliding in contact with the base material portion. The base material portion and the sliding portion each include a plurality of carbon short fiber bundles in which at least a part thereof is made of SiC, and a SiC matrix existing between the plurality of carbon short fiber bundles. The average diameter of the plurality of carbon short fiber bundles contained in the base material portion is larger than the average diameter of the plurality of carbon short fiber bundles contained in the sliding portion. Hereinafter, each of the above requirements will be described.

The carbon short fiber reinforced composite material has a base material portion and at least one sliding portion integrated with the base material portion. Specifically, it may have a structure having one base material portion and one sliding portion, or may have a structure in which the base material portion is sandwiched between the two sliding portions.

The ratio (weight ratio) between the base material portion and the sliding portion in the carbon short fiber reinforced composite material is approximately 3: 1 to 5: 1.
The base material portion and the sliding portion constituting the carbon short fiber reinforced composite material each include a plurality of carbon short fiber bundles in which at least a part thereof is made of SiC. The at least partially turned into SiC short carbon fiber bundles, refers to a short carbon fiber bundle partially or wholly silicon carbide of the carbon fibers contained in the fiber bundle. These carbon short fiber bundles may be oriented in parallel in the base material portion and the sliding portion, or may be randomly oriented two-dimensionally or three-dimensionally. In addition, "parallel" means that the carbon short fiber bundles are arranged in parallel in the length direction thereof, but it means that all the carbon short fiber bundles are arranged accurately in one direction. It is not necessary, and a part may be oriented out of parallel.

Commercially available carbon fibers can be used as the raw material for the carbon short fiber bundle. There are various types of carbon fibers having high strength and high elastic modulus, and it is preferable to use high-strength pitch-based carbon fibers for the brake disc, which is a preferred embodiment of the present invention.

The average diameter of the plurality of carbon short fiber bundles contained in the base material portion is larger than the average diameter of the plurality of carbon short fiber bundles contained in the sliding portion. That is, the plurality of carbon short fiber bundles contained in the base material portion are thicker on average than the plurality of carbon short fiber bundles contained in the sliding portion.
Preferably, 80% or more of the plurality of carbon short fiber bundles contained in the base material portion is thicker than the plurality of carbon short fiber bundles contained in the sliding portion. The difference in thickness is preferably about 45 to 65%.

In this way, by making the average diameter of the carbon short fiber bundle in the base material portion larger than the average diameter of the carbon short fiber bundle in the sliding portion, the carbon short of the sliding portion is formed when silicon is melt-impregnated. While most of the fiber bundles are made of SiC, in the base material portion, since the carbon short fiber bundles are thick, silicon does not penetrate deep into the carbon short fiber bundles, and the fibers in the central part of the carbon short fiber bundles are formed. It remains as carbon short fibers without being made into SiC. Therefore, since the carbon short fiber bundle in the base material portion has few SiC fibers, it has higher brittleness than the sliding portion, and the sliding portion has wear resistance and heat resistance as compared with the base material portion. Although it is high, since most of the carbon short fiber bundles are made of SiC, the toughness is poor and the brittleness is increased. In this way, by having both a highly flexible base material portion and a high-strength sliding portion, in the present invention, the carbon short fiber that suppresses the occurrence of brittle fracture while ensuring wear resistance and strength. Reinforced composite materials can be provided.

It is preferable that each carbon short fiber bundle contained in the base material portion is composed of 1500 to 4000 carbon fibers. On the other hand, it is more preferable that each short carbon fiber bundle contained in the sliding portion is composed of 500 to 2500 carbon fibers. When the number of carbon fibers per carbon short fiber bundle contained in the base material portion exceeds 4000, voids are formed between the fiber bundles, which may become a fracture starting point and reduce the strength. In addition, the difference in heat conduction between the base material portion and the sliding portion becomes large, and cracks may occur in the sliding portion during heating. On the other hand, if the number is less than 1500, the SiC formation penetrates deep into the carbon short fiber bundle, so that the toughness is lowered.

Further, when the number of carbon fibers per carbon short fiber bundle contained in the sliding portion exceeds 2500, the carbon fibers remain in the sliding portion without being sufficiently made into SiC to the deep part of the carbon short fiber bundle. , The friction coefficient decreases and the wear increases. On the other hand, if the number is less than 500, the difference in thermal expansion between the base material portion and the sliding portion becomes large, and cracks may occur.

When the number of carbon fibers per carbon short fiber bundle in each of the base material portion and the sliding portion is within the above range, the carbon short fiber bundle contained in the base material portion and the carbon short fiber bundle contained in the sliding portion The difference in SiC formation due to the difference in thickness is appropriate, and the carbon short fiber reinforced composite material can be made into a material having high strength, high toughness, and excellent wear resistance.

The content of SiC can be determined by measuring the elemental concentration in the cross section of the carbon short fiber reinforced composite material by energy dispersive X-ray spectroscopy (EDX).

The base material portion and the sliding portion each have the carbon short fiber bundle and the silicon carbide matrix existing between the carbon short fiber bundles.
The silicon carbide matrix is a component that solidifies each carbon short fiber bundle and densifies the carbon short fiber reinforced composite material to impart strength as a material.

The silicon carbide matrix is obtained by calcining silicon (Si), for example, by calcining a phenol resin, pitch, or the like, or a mixture of a phenol resin, pitch, or the like with carbon powder and / or silicon carbide powder, usually at 2000 ° C. or higher. ) Is melt-impregnated to react and become SiC.
The silicon carbide matrix is preferably present in an amount of about 50% by weight or more and 70% by weight or less with respect to the carbon short fiber bundle.

Both the base material portion and the sliding portion may contain about 1 to 5 wt% of additives such as carbon black and Si in addition to the carbon short fiber bundle and the silicon carbide matrix as long as the effects of the present invention are not impaired. ..

The method for producing a carbon short fiber reinforced composite material of the present invention includes a step of mixing a phenol resin with a pitch-coated carbon short fiber bundle for a base material to obtain a mixture for the base material, and carbon for the base material. A step of mixing a phenol resin with a carbon short fiber bundle for a sliding portion coated at a pitch having an average diameter smaller than that of the short fiber bundle to obtain a mixture for the sliding portion, and a molding mixture for the sliding portion. And the above-mentioned mixture for the base material portion, and a step of obtaining a cured product by pressure molding under heating, a step of obtaining a fired body by firing the cured product at 2000 ° C. or higher, and the above-mentioned firing. It is characterized by having a step of impregnating a body with silicon by a silicon melt impregnation method in a vacuum.
It should be noted that the silicon impregnation by the silicon melt impregnation method may be performed at a temperature of about 1500 ° C. at which the silicon impregnation can be carried out.
Further, the method for producing a carbon short fiber reinforced composite material of the present invention is characterized in that the carbon short fiber in the sliding portion has a higher SiC conversion rate than the base material portion.

In the present invention, the mixture for the base material portion and the mixture for the sliding portion are each put into a molding die in the state of particles, and a carbon short fiber reinforced composite material having the base material portion and the sliding portion is integrally molded. Therefore, a boundary layer is not formed between the base material portion and the sliding portion, and there is no decrease in strength or peeling due to this boundary layer. Therefore, the carbon short fiber reinforced composite material of the present invention has high strength and high toughness, and when used as a disc brake, for example, the wear resistance can be significantly improved as compared with the conventional case.

The bending strength of the carbon short fiber reinforced composite material according to JIS R 1601 is usually 100 to 150 MPa, preferably 120 to 150 MPa. When the bending strength is within the above range, it can have sufficient strength when used as a disc brake, for example.

The fracture energy of the carbon short fiber reinforced composite material is usually 800 to ^{2000 J / m 2} , preferably 1200 to 2000 J / m ² . When the breaking energy is within the above range, it can have sufficient toughness to be used as a disc brake. In the present specification, the fracture energy is the energy that can be applied to an object before it is destroyed. Ceramic Society of Japan standard JCRS-201 "Ceramic system by quasi-static three-point bending fracture of Chevron notch test piece. Measured by the fracture energy test method for composite materials.

Hereinafter, the present invention will be described in more detail based on Examples, but the present invention is not limited to the following Examples.

[Example 1]
Short carbon fiber bundle for base section (diameter 7μm or 15μm or less; 4 mm or 14mm or less in length; 4,000 bundles) and the solution diluted to 35 wt% pitch in ethanol, the carbon short fiber bundles immersed in enough After soaking, the solution was taken out and dried at 100 ° C. or lower for 100 minutes or more to obtain a resin-coated fiber bundle aggregate. The fiber bundle aggregate was crushed to obtain a carbon short fiber bundle for a base material.
Carbon short fiber bundle for sliding part (diameter 7 μm or more and 15 μm or less; length 4 mm or more and 14 mm or less; 2500 bundles, that is, the number of carbon fibers in one fiber bundle with carbon fibers of the same diameter and length as for the base material part a modification of the 2500) Similarly, the solution diluted to 35 wt% pitch in ethanol, after which the carbon short fiber bundles were immersed in submerged sufficiently, dried over 100 minutes at 100 ° C. or less, the resin A coated fiber bundle aggregate was obtained. The fiber bundle aggregate was crushed to obtain a carbon short fiber bundle for a sliding portion.
Next, 40 to 50 wt% of the carbon short fiber bundle for the base material portion, 50 to 60 wt% of the phenol resin, (the total of the carbon short fiber bundle for the base material portion and the phenol resin is 100 wt%), and ethanol are mixed and used as a base. A mixture for the material part was obtained.
Similarly, 55 to 65 wt% of the carbon short fiber bundle for the sliding portion, 35 to 45 wt% of the phenol resin (the total of the carbon short fiber bundle for the sliding portion and the phenol resin is 100 wt%), and ethanol are mixed. A mixture for sliding parts was obtained.
The mixture for the sliding part, the mixture for the base material, and the mixture for the sliding part are put into the molding die in this order, heated at 100 ° C. or higher and at a pressure of 100 kgf / cm2 or higher, and molded to have a diameter of 150 mm × t15 mm. The cured product of was obtained.
The cured product was fired at 2000 ° C. or higher for 40 minutes or longer in a reducing atmosphere to obtain a fired product.
Further, the obtained fired body was impregnated with molten silicon in vacuum at about 1500 ° C. to obtain a carbon short fiber reinforced composite material.

The SiC conversion rate, bending strength, and fracture energy of the obtained carbon short fiber reinforced composite material were measured by the following methods.
[SiC conversion rate]
The carbon short fiber reinforced composite was cut and polished to expose the cross section of the carbon short fiber bundle. The center of the carbon short fiber bundle was adjusted so that X-rays hit the center, and EDX analysis was performed. The SiC ratio of the carbon short fiber bundle was calculated from the obtained peak intensity ratios of Si and C. The cross sections of 10 different carbon short fiber bundles were analyzed by EDX, and the average value of the calculated SiC ratios was taken as the SiC conversion rate.
[Flexural strength]
A test piece of 3 mm × 4 mm × 40 mm was prepared, and the three-point bending strength (MPa) was measured at a crosshead speed of 0.5 mm / min by a method according to JIS R 1601.
[Destructive energy]
A 3 mm x 4 mm x 40 mm test piece was prepared, a straight notch with a depth of about 2 mm was formed in the center using a diamond blade with a thickness of 0.1 mm, and the fracture energy was measured in accordance with JCRS-201. did. The distance between the fulcrums was 30 mm, the crosshead speed was 0.01 mm / min, and the fracture energy (J / m ² ) per unit area up to 5% of the maximum load value was obtained.

[Example 2]
Short carbon fiber bundle for base section (diameter 7μm or 15μm or less; length 4mm or 14mm or less; 15 00 This bundle, i.e. carbon number of fibers of one fiber bundle carbon fiber of the same diameter and length as in Example 1 Is changed to 1500 fibers), and carbon short fiber bundles for sliding parts (diameter 7 μm or more and 15 μm or less; length 4 mm or more and 14 mm or less; 500 bundles , that is, carbon fibers having the same diameter and length as in Example 1) A short carbon fiber reinforced composite material was obtained in the same manner as in Example 1 except that the number of carbon fibers in one fiber bundle was changed to 500).
In the same manner as in Example 1, the SiC conversion rate, bending strength, and fracture energy of the carbon short fiber reinforced composite material were measured.

[Comparative Example 1]
The base portion and the sliding portion both below 15μm short carbon fiber bundle (diameter 7μm or more base material of Example 1; 4 mm or more 14mm or less in length; 40 00 This bundle, i.e. the same diameter and length as in Example 1 A carbon short fiber reinforced composite material was obtained in the same manner as in Example 1 except that the number of carbon fibers in one fiber bundle was changed to 4000).
In the same manner as in Example 1, the SiC conversion rate, bending strength, and fracture energy of the carbon short fiber reinforced composite material were measured.
The results of Example 1 and Comparative Example 1 are shown.
In Comparative Example 1, since the SiC conversion rate is smaller than that in Example 1, it can be seen that both the bending strength and the fracture energy are inferior.

Claims (2)

Phenol resin is mixed with carbon short fiber bundles obtained by coating 1500 or more and 4000 or less carbon short fiber bundles per fiber bundle at a pitch and then crushing them for a particulate base material. The process of obtaining the mixture and
The carbon made short fiber bundles and the same carbon fiber, phenol in one of the sliding portion for short carbon fiber bundle 500 2500 following the short carbon fiber bundle or lines per fiber bundle obtained by crushing after the coating at a pitch The process of mixing resins to obtain a particulate mixture for sliding parts,
A step of putting the mixture for the sliding portion and the mixture for the base material portion into a molding die and pressure molding under heating to obtain a cured product.
A step of obtaining a fired body by firing the cured product at 2000 ° C. or higher, and
The step of impregnating the fired body with silicon by the silicon melt impregnation method in vacuum,
Including
The number of carbon short fiber bundles for the base material portion is 1.6 times or more larger than the number of carbon short fiber bundles for the sliding portion.
A method for producing a carbon short fiber reinforced composite material.
The method for producing a carbon short fiber reinforced composite material according to claim 1, wherein the carbon short fibers in the sliding portion have a higher SiC conversion rate than the base material portion.