JPH08143376A - Ceramic-based fiber composite material - Google Patents

Abstract

PURPOSE: To obtain a fiber composite material having macro-breaking resistance comparable to that of a continuous fiber composite material and having low macro-anisotropy and high reliability. CONSTITUTION: Bundles 3 of fibers each formed by bundling plural ceramic fibers 2 are dispersed in a ceramic matrix 4 to obtain the objective fiber composite material. A Ti-contg. coating layer is preferably formed on the periphery and edge faces of each of the bundles 3. An interfacial layer of at least one of carbon and boron nitride may be formed on the periphery while forming Ti-contg. coating layers on the edge faces.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic-based fiber composite material, and in particular, it has macro fracture resistance characteristics equivalent to those of continuous fiber composite materials, and has a small macro anisotropy in material characteristics and high reliability Ceramic-based fiber composite material

[0002]

2. Description of the Related Art Generally, a ceramic sintered body has little strength decrease up to a high temperature, and has various characteristics such as hardness, electric insulation, wear resistance, heat resistance, corrosion resistance, and lightness as compared with conventional metal materials. Since it is excellent, it is used in a wide range of fields as electronic materials and structural materials such as heavy electric equipment parts, aircraft parts, automobile parts, electronic devices, precision machine parts, and semiconductor device materials.

However, the ceramics sintered body is weaker in tensile stress than compressive stress, and has a defect of so-called brittleness in which fracture progresses at a stretch under this tensile stress. For this reason, in order to enable the application of the ceramic component to the site where high reliability is required, it is strongly required to increase the toughness and increase the fracture energy of the ceramic sintered body.

That is, gas turbine parts, aircraft parts,
Ceramic structural parts used for automobile parts, etc.
High reliability is required in addition to heat resistance and high temperature strength. In order to meet this demand, composite materials such as fibers, whiskers, plates and particles made of inorganic substances and metals are dispersed and compounded in a matrix sintered body to improve fracture toughness value, fracture energy value and thermal shock resistance. Researches for practical use of ceramic composite materials are being carried out by research institutes inside and outside Japan.

However, in a ceramic-based fiber composite material in which the above composite material is dispersed and composited in a matrix sintered body, since the composite material and the ceramic matrix are firmly bonded at the interface, cracking occurs once. In some cases, when the occurrence of cracks occurred, the composite material was insufficiently able to prevent the progress of cracks, and the composite material was instantly destroyed.

Therefore, particularly in the fiber composite material, a composite material in which a sliding layer made of carbon (C), boron nitride (BN), silicon carbide compound (Si-C-O) or the like is formed on the surface of the fiber. Is also being developed. This sliding layer is formed by coating the fiber surface with carbon (C), boron nitride (BN), a silicon carbide compound (Si-C-O), or the like.

By forming this sliding layer, the strong bonding strength between the composite fiber and the ceramic matrix is relaxed. That is, even when excessive stress acts on the composite material and displacement occurs between the fiber and the matrix, delamination and slip in the slip layer absorb the strain difference between the two, so that the crack development is deflected. In some cases, the fracture resistance can be increased, and the fiber pull-out resistance contributes to obtain a composite material having a high toughness value.

[0008]

However, in a conventional composite material system in which composite materials such as particles and whiskers are dispersed and composited, the above composite material is effective in order to improve the fracture resistance at a relatively micro level. However, there was a drawback that the effect of improving the resistance against macro-level destruction was small. It has been confirmed by experiments by the present inventors that whiskers are more effective than particles as a reinforcing material in order to improve fracture resistance at a macro level, and it is more effective to compound continuous fibers. Has been done.

However, it is difficult to uniformly disperse the reinforcing materials such as whiskers and continuous fibers in the matrix, and it is difficult to mix these composite materials in the matrix at a high content. However, there is a problem that the manufacturing cost is significantly increased. Particularly in the case of continuous fibers, it is practically impossible to arrange them in the material quite uniformly, so that macroscopic anisotropy occurs in the composite material characteristics, and the usage of the material is restricted, Depending on the use position and direction, there was a problem such as reduced durability.

The present invention has been made in order to solve the above-mentioned problems, and in particular, it has macro fracture resistance characteristics equivalent to those of continuous fiber composite materials, and has small macro characteristic anisotropy and reliability. An object is to provide a ceramic-based fiber composite material having high cost.

[0011]

In order to achieve the above object, the inventors of the present invention prepared a fiber composite material using various fibers and ceramics sintered bodies, and examined the morphology of the fibers and the ceramic matrix and the fibers. The effects of the bonding state on the dispersibility of the fiber, the initial fracture strength of the matrix, the fracture resistance of the material, the amount of strain, the toughness and the anisotropy of the material properties were comparatively investigated. As a result, especially when a short fiber bundle formed by bundling a plurality of ceramic fibers is dispersed and arranged in the ceramic matrix, the fibers can be uniformly dispersed at a high content rate, and the fiber composite has large fracture resistance and little anisotropy. We have obtained the knowledge that materials can be obtained for the first time. The present invention has been completed based on the above findings.

That is, the ceramic-based fiber composite material according to the present invention is characterized in that a fiber bundle formed by bundling a plurality of ceramic fibers is dispersed and arranged in a ceramic matrix. In addition, T is placed on the outer peripheral portion and the end face portion of the fiber bundle.
It is preferable to form a coating layer containing i. Further, a coating layer made of Ti may be formed on the end face portion of the fiber bundle, and an interface layer made of at least one of carbon (C) and boron nitride (BN) may be formed on the outer peripheral portion of the fiber bundle. . The length of the fiber bundle is 1 of the diameter.
It is recommended to set it up to 30 times.

Various ceramics can be used as the ceramics forming the matrix of the ceramic-based fiber composite material. For example, silicon carbide (S
iC), aluminum nitride (AlN), silicon nitride (Si
₃ N ₄ ), boron nitride (BN), sialon (Si-A)
-ON) and other non-oxide ceramics, alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), titania (TiO ₂ ), mullite (3Al ₂ O ₃ .2Si)
O ₂ ), beryllia (BeO), cordierite, zircon, spinel (MgAl ₂ O ₄ ) and other oxide ceramics, and molybdenum silicide and other silicide ceramics are used alone or in combination of two or more. To be done. Also,
If necessary, a sintering aid or additive such as yttrium oxide, aluminum oxide, cerium oxide, magnesium carbonate, calcium carbonate, or silicic acid is added to the ceramic raw material powder for forming the matrix. It is also possible to form the matrix during the reactive sintering process.

The fiber bundles arranged in the matrix are compounded in a predetermined amount in order to enhance the toughness of the composite material. The fiber bundle has a diameter of 0.1 to 1.
After forming a long fiber bundle of about 5 mm, the long fiber bundle is cut into a length 1 to 30 times the diameter. The cross-sectional shape of the fiber bundle is not particularly limited, and may be circular, rectangular,
Any shape such as an ellipse may be used, but a circular cross section that minimizes the surface area per volume of the fiber bundle is most preferable.

The material of the ceramic fibers constituting the fiber bundle is not particularly limited, and ceramic fibers having the same composition as the constituent material of the matrix can be used. Specific examples of such ceramic fibers include silicon carbide fibers (SiC, Si-C-O, S).
i-Ti-C-O, etc.), SiC coated fiber (core wire is, for example, C), alumina fiber, zirconia fiber, carbon fiber, boron fiber, silicon nitride fiber, Si ₃ N ₄ coated fiber (core wire is, for example, C) And mullite (3Al ₂ O ₃ · 2SiO
_{2 ~2Al 2 O 3 · SiO 2} ) has fibers, it may use at least one selected from these.

The fiber bundles are dispersed and arranged in the matrix so that the fiber volume ratio (Vf) is 2% or more with respect to the whole composite material. However, the fiber volume ratio is 4
If the amount exceeds 0%, it becomes difficult to uniformly arrange the matrix matrix around each fiber bundle, and the strength characteristics of the composite material are rapidly deteriorated due to the occurrence of defects such as voids. Therefore, the preferred amount of addition that produces a combined effect is 1
It is in the range of 0 to 30% by volume.

The diameter and length of the fiber bundle have a great influence on the dispersibility and orientation of the fiber bundle in the matrix, as well as the strength properties and macro fracture properties of the composite material. In the present invention, the diameter is 0. 1 mm to 1.5 mm,
A short fiber bundle having a length of 1 to 30 times the diameter is used. When the length of the fiber bundle is less than 1 times the diameter, the composite effect due to the fiber bundle is small, while when the length exceeds 30 times the diameter, the amount necessary to increase the macro fracture resistance. It becomes difficult to include the above fiber bundle in the matrix, and it becomes difficult to disperse the fiber bundle evenly, resulting in a composite material having large anisotropy. Further, when the diameter of the fiber bundle is less than 0.1 mm, the effect of preventing relatively macroscopic crack extension is small, and when the diameter of the fiber bundle is thicker than 1.5 mm, the boundary surface between the fiber bundle and the matrix matrix is small. In addition, stress due to the difference in thermal expansion easily occurs, and the matrix easily cracks, and in any case, it becomes difficult to significantly improve the composite effect of fiber reinforcement. Further, when the length of the fiber bundle is less than 0.1 mm, the effect of suppressing crack growth is small and the effect of improving toughness is also small.

That is, the diameter is 0.1 mm to 1.5 mm,
Moreover, by using a short fiber bundle having a length of 1 to 30 times the diameter, it becomes possible to sufficiently secure the effect of improving the toughness by the fiber composite while maintaining good shape imparting performance.
However, when the volume ratio of such a fiber bundle is less than 2%,
The volume ratio of the fiber bundle is preferably 2% or more because the effect of improving the toughness decreases.

The outer peripheral portion and the end surface portion of the fiber bundle may be directly bonded to the ceramic matrix, but only the end surface portion of the fiber bundle or the outer peripheral portion and the end surface portion are preliminarily T-shaped.
By forming a coating layer containing an active metal such as i, a compound such as TiN is formed by the reaction between Ti and the ceramic matrix, and through this compound, the end face portion or the outer peripheral portion of the fiber bundle is formed. The matrix and the matrix can be selectively and strongly bonded. Furthermore, the coating layer is effective for maintaining the shape of the fiber bundle because it covers the outer peripheral portion and the end face portion of the fiber bundle and integrally joins the plurality of fibers. The coating layer containing Ti is formed by depositing an active metal such as Ti on the outer surface of the fiber bundle by, for example, a sputtering method, and the thickness thereof is about 0.1 μm.

The Ti-containing coating layer may be formed only on the end face portion of the fiber bundle, while the interface layer having a thickness of 5 μm or less may be formed on the outer peripheral portion of the fiber bundle. This interface layer is formed on the outer periphery of the fiber bundle by carbon (C) or boron nitride (B).
N) is formed by coating.

A ceramic fiber bundle is formed by the interface layer,
The bond strength at the interface with the matrix is controlled by the direction, stress transmission to the fibers and delamination at the interface effectively occur at the time of stress loading, and the fibers pull out to improve the toughness of the material. That is, the shear strength of the fiber bundle does not reduce the initial fracture strength at the interface, and the slip resistance at the time of pulling out the fiber after the initial fracture increases, increasing the fracture energy of the material. You can

Further, by forming a ceramic single layer having a thickness of 10 μm or more, which is composed of only the matrix, on the entire surface of the composite material, and is constructed so that the interface portion between the fiber bundle and the matrix is not exposed on the surface of the composite material, It is possible to prevent thermal deterioration, oxidative deterioration, and strength reduction due to exposure of the. Further, it is possible to prevent deterioration of the sliding function due to the oxidation of C and BN components forming the interface layer formed on the surface of the fiber bundle, and it is possible to effectively prevent deterioration of the high temperature strength of the composite material. By forming the ceramic single layer with a thickness of 10 μm or more, the strength reduction preventing function can be sufficiently exhibited.

The ceramic-based fiber composite material of the present invention, in which the fiber bundles are dispersed and arranged in the matrix, is manufactured as follows, for example. That is, a plurality of ceramic long fibers are bundled into a long fiber bundle, and the long fiber bundle is cut into a predetermined length to form a short fiber bundle, and an outer peripheral portion and an end face portion or an end face portion of the obtained short fiber bundle is formed. Only as needed, T
forming a coating layer or an interfacial layer containing i, and then uniformly mixing the short fiber bundle and the ceramic powder in a solvent, and filling the obtained mixture into a mold having a predetermined shape to obtain a molded body, The obtained molded body is dried and degreased, and then the obtained molded body is sintered in a non-oxidizing atmosphere by a hot pressing method, a reaction sintering method or an atmospheric pressure sintering method.

[0024]

According to the ceramic-based fiber composite material having the above-mentioned structure, the ceramic fibers as the reinforcing material are not in the form of a single fiber (monofilament) but are compounded as a fiber bundle obtained by bundling a plurality of ceramic fibers. It becomes possible to disperse and disperse uniformly in a matrix with a high fiber volume ratio, and a composite material with little anisotropy can be obtained.

In particular, one or both of the outer peripheral portion and the end face portion of the fiber bundle are firmly bonded to the matrix to improve the strength characteristics of the composite material, while inside the fiber bundle,
Since the bonding strength between the fibers and the interface between the fibers and the matrix is low, the fibers are likely to be pulled out due to the peeling at the interface. Therefore, even if a crack occurs in the matrix, after the crack tip reaches the inside of the fiber bundle, the development of the crack is effectively prevented, resulting in a high toughness with a large macro fracture propagation resistance. A composite material is obtained.

By forming a coating layer containing Ti on the outer surface of the fiber bundle, the bonding strength between the outer surface of the fiber bundle and the matrix can be further increased, and the strength characteristics of the composite material can be further improved. You can

Further, while the coating layer is formed only on the end face portion of the fiber bundle, and the interface layer made of carbon or boron nitride is integrally formed on the outer peripheral portion of the fiber bundle, the fiber bundle and the matrix are formed on the end face portion. While the strength of the composite material is improved by providing a strong bond with the composite material, it is possible to increase the fracture energy of the composite material because the slip resistance at the time of pulling out of the fiber can be increased in the outer peripheral portion,
It is possible to realize a macroscopic fracture propagation resistance equivalent to that of a continuous fiber composite material.

[0028]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

Examples 1 to 7 As shown in Table 1, 5 continuous SiC fibers having a diameter of 15 μm were used.
A long fiber bundle (yarn) having a diameter of 500 μm is formed by bundling 00 fibers, and the long fiber bundle is cut into a length of 4 mm, and the results are shown in Examples 1 to 1.
A cylindrical short fiber bundle for 2 was prepared. Examples 1-2
The short fiber bundles for Examples 3 to 5 were prepared by depositing Ti on the outer peripheral portion and the end surface portion of the short fiber bundles for use in the sputtering to form a coating layer having a thickness of 0.1 μm. Further, a coating layer made of Ti having a thickness of 0.1 μm is formed only on the end face portions of the short fiber bundles for Examples 1 and 2, while a thickness of 0.3 μm is formed only on the outer peripheral portion of the short fiber bundles.
A short fiber bundle for Examples 6 to 7 was prepared by forming an interface layer composed of m BN.

Next, each of the above short fiber bundles and Si _6-z Al _z O
A sialon powder having a composition of _z N _8-z (z = 2) was wet-mixed in an organic solvent to form a uniform raw material mixture. The mixing ratio of each short fiber bundle and sialon powder was set so that the fiber volume ratio Vf of each short fiber bundle contained in the composite material changed in the range of 20 to 40 vol% as shown in Table 1. .

Next, each raw material mixture obtained is filled in a molding die and molded, and the obtained molding is air-dried and then heated at a temperature of 800.
Degreasing was performed at ℃ for 1 hour, the obtained degreased molded body was filled in a carbon mold, and further, at a temperature of 155 under N ₂ gas atmosphere.
The ceramic-based fiber composite materials according to Examples 1 to 7 having a length of 50 mm, a width of 50 mm, and a thickness of 5 mm are manufactured by hot-press sintering while simultaneously heating at 0 ° C. for 2 hours and applying a pressure of 40 MPa. did.

As shown in FIG. 1, the ceramic-based fiber composite material 1 according to each example has a structure in which short fiber bundles 3 formed by bundling a large number of SiC fibers 2 are dispersed and arranged in a ceramic matrix 4 made of sialon. Have.

Comparative Example 1 Comparative Example 1 was carried out in the same manner as in Example 1 except that a single short fiber (monofilament) having a length of 0.5 mm was used without forming a fiber bundle. A ceramic-based fiber composite material was produced.

Comparative Example 2 A thickness of 0.3 μm was formed on the outer peripheral portion of the single short fiber prepared in Comparative Example 1.
Comparative Example 1 except that an interface layer composed of m BN was formed.
A ceramic-based fiber composite material according to Comparative Example 2 was manufactured by performing the same treatment as described above.

In order to evaluate the properties of the ceramic-based fiber composite materials according to the examples and comparative examples thus prepared,
Cut out multiple test pieces by changing the direction from each composite material,
For each test piece, a three-point bending strength test was performed after measuring the density, and the fracture energy was calculated from the initial fracture stress and the stress-strain curve, and the results shown in Table 1 below were obtained. Each measured value is an average value of a plurality of test pieces cut out from one composite material. Further, the breaking energy values were compared with each other by using the case of Example 4 as a reference value 1.

[0036]

[Table 1]

As is clear from the results shown in Table 1 above,
The composite material of each example in which short fiber bundles formed by bundling ceramic fibers are dispersed and arranged in a matrix, each has a dense and dense structure structure, a high initial fracture stress, and a large fracture energy, It did not cause catastrophic fracture and showed macroscopic fracture resistance characteristics equivalent to those of continuous fiber composite materials. That is, as shown in FIG. 1, after the tip of the crack 6 that has propagated in the matrix 4 reaches the inside of the short fiber bundle 3, the development of the crack 6 is prevented, and the entire composite material is destroyed. It is considered that the resistance increased.

Further, since the fiber material is not arranged as a single fiber (monofilament) but a plurality of fibers are arranged as a fiber bundle, the fiber bundle is formed into a matrix even when the fibers are contained at a high fiber volume ratio. A composite material that can be uniformly dispersed in the material and has little macro-anisotropic material properties was obtained. By the way, it was confirmed that the variation of the characteristic values of a plurality of test pieces cut in different directions from each example is within ± 10% despite the hot press sintering method, and the anisotropy is extremely small. It was

As shown in FIG. 2, the composite materials according to Examples 1 and 2 have a structure in which a large number of fiber bundles 3 made of SiC fibers 2 are embedded in a matrix 4. The interface of the fiber 2 was peeled off and many SiC fibers 2 were pulled out. It is considered that the toughness value of the composite material is increased by pulling out these fibers 2.

As shown in FIG. 3, the composite materials according to Examples 3 to 5 have a structure in which short fiber bundles 3 in which many SiC fibers 2 are bundled are dispersed and arranged in a matrix 4. A coating layer 5 containing Ti is integrally formed on the outer peripheral portion and the end surface portion of the bundle 3. When the fracture surface of this composite material was observed, it was confirmed that the interface between the fiber 2 in which Ti was present and the matrix 4 were firmly bonded, and the two were integrated and fractured. On the other hand, since the inside of the short fiber bundle 3 has a weak interfacial bonding force, the pull-out phenomenon of the SiC fiber 2 is noticeably observed as shown in FIG. 3, and this pull-out improves the toughness value of the composite material. It is thought that it was done.

Further, in the composite materials according to Examples 6 to 7 in which the interface layer made of BN was formed on the outer peripheral portion of the fiber bundle,
Since the interface layer has a certain amount of sliding function, the initial fracture stress tends to be slightly reduced as compared with Examples 3 to 5, but the amount of fracture strain increases conversely and shows excellent fracture resistance characteristics. It was

On the other hand, as shown in FIG. 4, the composite materials 1a according to Comparative Examples 1 and 2 have a structure in which SiC fibers 2a as single fibers (monofilaments) are dispersed and arranged in a matrix 4a made of sialon. The composite materials of these comparative examples have a high initial fracture stress as compared with the examples, and are excellent in strength, but on the other hand, they have the property that cracks easily propagate at once and the fracture strain resistance is small and the fracture progress resistance is small. Turned out to be small. Further, in the comparative example, the fiber volume ratio Vf was high, and the dispersed state of the fibers in the matrix was non-uniform, so that it was confirmed that the material properties were anisotropic and non-uniform. By the way, the variation in the measured values of a plurality of test pieces collected by changing the cutting direction was as large as ± 30%.

[0043]

As described above, according to the ceramic-based fiber composite material of the present invention, the ceramic fibers as the reinforcing material are not in the form of a single fiber (monofilament) but as a fiber bundle obtained by bundling a plurality of ceramic fibers. Since it is made into a composite, it is possible to disperse and arrange it uniformly in the matrix with a high fiber volume ratio, and a composite material with little anisotropy can be obtained.

In particular, the outer peripheral portion and the end face portion of the fiber bundle are firmly bonded to the matrix to improve the strength characteristics of the composite material, while the bonding strength of the fibers and the interface between the fibers and the matrix is improved inside the fiber bundle. Therefore, the fiber tends to be pulled out due to the peeling of the interface. Therefore, even if a crack occurs in the matrix, after the crack tip reaches the inside of the fiber bundle, the development of the crack is effectively prevented, resulting in a high toughness with a large macro fracture propagation resistance. A composite material is obtained.

Further, by forming a coating layer containing Ti on the outer surface of the fiber bundle, the bonding strength between the outer surface of the fiber bundle and the matrix can be further increased, and the strength characteristics of the composite material can be further improved. You can

Further, while the coating layer is formed only on the end face portion of the fiber bundle, and the interface layer made of carbon or boron nitride is integrally formed on the outer peripheral portion of the fiber bundle, the fiber bundle and the matrix are formed on the end face portion. While the strength of the composite material is improved by providing a strong bond with the composite material, it is possible to increase the fracture energy of the composite material because the slip resistance at the time of pulling out of the fiber can be increased in the outer peripheral portion,
It is possible to realize a macroscopic fracture propagation resistance equivalent to that of a continuous fiber composite material.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing a structure of a ceramic-based fiber composite material according to an embodiment of the present invention.

FIG. 2 is a perspective view showing a broken portion of a fiber bundle of the composite material according to Examples 1 and 2.

FIG. 3 is a perspective view showing a fractured part of a fiber bundle of the composite material according to Examples 3 to 5.

FIG. 4 is a partial cross-sectional view showing a conventional composite material in which single fibers (monofilaments) are arranged in a matrix.

[Explanation of symbols]

 1,1a Ceramics-based fiber composite material 2,2a SiC fiber (ceramics fiber) 3 Fiber bundle (short fiber bundle) 4,4a Ceramics matrix (sialon) 5 Coating layer 6 Crack (crack)

Claims (4)

[Claims] 1. A ceramic-based fiber composite material characterized in that a fiber bundle formed by bundling a plurality of ceramic fibers is dispersed and arranged in a ceramic matrix. 2. The ceramic-based fiber composite material according to claim 1, wherein a coating layer containing Ti is formed on the outer peripheral portion and the end surface portion of the fiber bundle. 3. A coating layer containing Ti is formed on the end face of the fiber bundle, and an interface layer made of at least one of carbon (C) and boron nitride (BN) is formed on the outer periphery of the fiber bundle. The ceramic-based fiber composite material according to claim 1. 4. The ceramic-based fiber composite material according to claim 1, wherein the length of the fiber bundle is 1 to 30 times the diameter.