JPH0226877A - Fiber-reinforced ceramic composite material reinforced with dispersed particles and its production - Google Patents

Abstract

PURPOSE:To obtain the title fiber-reinforced ceramic composite material having excellent fracture toughness by composing the composite material out of a ceramic matrix, the fiber dispersed in the matrix, and the ceramic fine particles of the same or different kind. CONSTITUTION:An organometallic polymer such as polysiloxane is dissolved in a solvent such as toluene, and the ceramic particles of Al2O3, etc., to be used as the matrix are dispersed in the soln. to produce a liq. impregnant. The fiber is then continuously passed through the impregnant to uniformly deposit the impregnant on the fiber surface. The content of the fiber in the mixture is preferably controlled to about 30-40vol.%. The obtained material is heated to 700-800 deg.C in gaseous N2 or gaseous Ar to make the organometallic polymer infusible. The obtained formed product is then sintered in gaseous Ar or gaseous N2 under pressure or at atmospheric pressure. By this method, the desired fiber-reinforced ceramic composite material reinforced further with dispersed particles is obtained. The composite material is excellent in fracture toughness and flexural strength.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention further strengthens the fiber-reinforced ceramic composite material by particle dispersion, and in particular, the fracture toughness value has been surprisingly improved. The present invention relates to a ceramic composite material that is expected to be applied to rings or turbine rotor blades of gas turbine engines, and a method for manufacturing the same.

[Conventional technology] Ceramics have better heat resistance and oxidation resistance than metal materials, and also have excellent heat insulation properties, so they have attracted attention as heat-resistant structural materials that can replace metals. however,
Ceramics are composed of covalent and ionic bonds, and cannot be deformed or stretched due to dislocations like metal materials. Stress concentrates on minute defects inside the material and scratches on the surface, making it easily broken. Therefore, it has the disadvantage of being extremely brittle and having poor fracture toughness.

The resistance of a material to brittle fracture is generally determined by the fracture toughness value K
For example, the KIO of silicon nitride material is 5 to 7 MN/m'', which is extremely low compared to 34 MN/m'' of aluminum alloy, which is said to be relatively brittle among metal materials. In order to apply engineering ceramics to reciprocating engines or gas turbine engines, it is necessary to have a fracture toughness value of at least 10 MN/m'' or more.

Therefore, various methods have been studied to improve the brittleness of structural ceramics.

Among these, the particle dispersion strengthening method in which various particles are mixed and dispersed in a ceramic matrix and the fiber reinforcement method in which various fibers are dispersed in the ceramic matrix are attracting attention.

Fibers for fiber-reinforced ceramics (hereinafter referred to as FRC) can be broadly divided into short fiber type and long fiber type.

Long fibers include glass-braided metal fibers, carbon-side L ceramic fibers, etc. Carbon w1#@ has high strength and high elastic modulus, making it suitable for composite materials, but it has the drawback of being susceptible to oxidation. Ceramic fibers such as silicon carbide and alumina are spun and heat-treated from organic raw materials, have a high melting point, and are most commonly used. Short fibers refer to whiskers, which are needle-shaped single crystals, or chopped long fibers. Whiskers exhibit ideal strength as FRC fibers, but
Disadvantages include that it is difficult to uniformly disperse in the matrix and that it is expensive.

Regarding the ceramics that serve as the matrix, A.I.
20: l, mullite, ZrO2, Si, N,, SiC
Attempts have been made to combine many ceramics, from oxides such as glass to non-oxides, with fibers.

For patents on mm-reinforced ceramic materials,
A sintered body of spinel (M go-A I203) mixed with silicon carbide short fibers (Japanese Patent Application Laid-Open No. 62-119175), a sintered body of alumina mixed with silicon carbide short fibers (Japanese Patent Laid-Open No. 62-1191)
9174), Carbon continuous fiber reinforced SiC composite
1. -247663), ceramic composites made by adding carbon fiber to metal oxides or metal carbides and sintering them at the same time as pressure (JP-A-50136306), silicon carbide fiber-reinforced ceramic composites (JP-B No. 6L-35996), etc. be.

The mechanism by which fracture toughness of ceramics is improved by particle dispersion is as follows.
This is thought to be because the reinforcing particles somehow disperse or absorb the energy that causes the tip of the crack to advance further, causing a stress relaxation phenomenon. As an example of improving fracture toughness, there is an example in which TiC particles are dispersed in 5iaN-.

[The section that the invention attempts to solve J! ! ]'however,
When making the above-mentioned composite materials, there are two important considerations: chemical compatibility, that is, whether the fibers will maintain the desired strength without reacting with the matrix at the sintering temperature, and physical compatibility, that is, whether the difference in coefficient of expansion will damage the fibers. The fact is that the expected fracture toughness cannot be obtained only by fiber reinforcement or particle dispersion reinforcement, since the properties of composite materials such as fracture toughness are influenced by the properties of composite materials, such as fracture toughness.

The present invention was made in view of the above-mentioned problems with fiber-reinforced ceramic composite materials, and an object of the present invention is to provide a fiber-reinforced ceramic composite material with excellent fracture toughness and a method for manufacturing the same.

[Means for Solving the Problems] As a result of extensive research in order to solve the above problems, the inventors came up with a reinforcing material that combines fiber reinforcement and particle dispersion reinforcement.

Crack deflection is cited as a mechanism for improving fracture toughness due to particle dispersion. In other words, due to differences in various properties such as toughness and coefficient of thermal expansion between the matrix and the dispersed phase, as well as the state of the interface between the two, cracks propagate in a zigzag manner around the dispersed phase, and this causes the energy required for crack propagation to increase. Since it is consumed, fracture toughness improves.

Furthermore, the mechanism of improvement in fracture toughness due to fiber reinforcement is said to be due to the occurrence of pullout and deflection. That is, when whiskers are mixed as a dispersed phase, when the cracks pass through a place where the whiskers are present, the whiskers are pulled out from the matrix by the amount of gap created by the cracks. The amount of work done to pull out the whiskers consumes energy and improves toughness.

We have come up with the idea that if the crack deflection and pull-out mentioned above occur effectively at the same time, the fracture energy will increase tremendously and the fracture toughness value will increase significantly, and we have completed the present invention. It's arrived.

That is, the fiber-reinforced ceramic composite material of the present invention is one in which fiber reinforcement and particle dispersion reinforcement are performed at the same time. or different types of ceramic fine particles.

Further, the manufacturing method of the present invention includes a step of preparing an impregnating liquid by dispersing ceramic particles serving as a matrix in a solution in which an organic metal polymer is dissolved, and a step of continuously passing the fiber through the impregnating liquid for 1 m. a step of uniformly impregnating the fibers with the impregnating liquid; a step of laminating the fibers to form a laminate; a step of making the organometallic polymer in the laminate infusible; The gist is that the method consists of a step of sintering in gas under gas pressure or normal pressure.

The matrix ceramics include A1□01, mullite, Z r O2, Si 3 N 4, SiC,
Many ceramics can be used, from oxides such as glass to non-oxides. The reinforcing fibers dispersed in the ceramic matrix are S! [Fibers or long fibers may be used,
For the long fibers, glass-structured metal-side carbon-side L ceramic fibers can be used. In order to improve the oxidation resistance of these fibers or to control the interfacial bonding with the matrix, it is preferable to coat the fiber surfaces with ceramics or the like by CVD.

The reinforcing fibers are dispersed in the ceramic matrix using a known method.For example, in the case of long fibers, the fibers are immersed in a slurry of ceramic powder and then wound around a drum (filament winding method).
Alternatively, an unfired laminate is made by forming a sheet of fibers and alternately layering matrix powder (laminated method), and this laminate is molded into a mold and hot pressed.

Figure 1 is a diagram schematically showing the filament winding method. The long fibers 12 unwound from the spool 10 are immersed in a slurry-like impregnating liquid 16 mixed with matrix powder contained in an impregnating liquid layer 14 and passed through.
An impregnating liquid 16 is applied to the surface of the long fibers 12, and the fibers are wound onto a winding drum 18. The laminate 20 wound around the drum is removed from the drum 18 by cutting at an appropriate location, cut into a desired size, and laminated to an appropriate thickness. The stacked laminate 20 is degreased if necessary, then molded into a mold and hot pressed.

Additionally, CVD (chemical vapor deposition) is used to generate a ceramic matrix phase in the gaps between fiber preforms.
Alternatively, a sol-gel method in which fibers are impregnated with a gel polymer of metal alkoxide and then thermally decomposed to obtain metal oxides can be used. In the case of short fibers, a slip casting method is effective, in which the fibers are dispersed in a ceramic powder slurry, poured into a plaster mold, and a female mold that matches the mold is taken out and fired. *The appropriate amount of composite fibers is 30 to 40% by volume.

The fine particles dispersed in the ceramic matrix may be particles of a different type or the same type as the ceramic matrix.The reinforcement of the matrix is achieved by dispersing zero particles.
As expected from the N4-T i C findings, 2
The maximum effect is obtained between 0 and 25% by volume.

From the viewpoint of crack deflection, it is effective for the particle size of the particles to be dispersed to be uniformly present at the grain boundaries of the matrix in a fine state.

The most appropriate particle dispersion method is a method that utilizes thermal decomposition of organometallic polymers, since it is difficult to achieve uniform dispersion and create fine particles using the powder mixing method. That is, when an organometallic polymer containing metal elements such as silicon that forms ceramics is thermally decomposed in an inert atmosphere, organic components are separated and carbides or nitrides are obtained. Examples of organometallic polymers include polysiloxane, polysilazane, polycarbosilane, and polysilastyrene. Polycarbosilane produces silicon carbide as shown in formula (1), and polysilazane produces silicon carbide as shown in formula (2). Silicon nitride is obtained in this way.

(SiH(CHs)・CHz)n −+ SiC(1
) (S!RR'NHz)n −+ 5izN4
<2) Organometallic polymers are coated on the surface of ceramic particles that serve as a matrix, and then the ceramic particles are formed by a thermochemical reaction and the fine particles are dispersed. Therefore, the organic metal polymer is dissolved in a solvent (toluene, xylene, etc.), and the ceramic particles serving as a matrix are mixed therein, and the surfaces of the matrix particles are coated with the organic metal polymer.

In order to uniformly disperse the fibers in the matrix, the impregnating liquid is a mixture of matrix particles in a solution of the organometallic polymer, and the fibers are continuously passed through the impregnating liquid to coat the fiber surface with the impregnating liquid. Filament for uniform adhesion
By winding method. The amount of fibers dispersed in the ceramic matrix can be adjusted by the viscosity of the impregnating liquid and the rate of fiber passage, but the amount of fibers dispersed in volume %
The most preferable range is about 30 to 40%.

The material wound using the filament winding method is heated with nitrogen gas or argon gas before being sintered.
Or in a mixed gas stream of nitrogen gas and ammonia gas 7
At 00 to 800°C, the organometallic polymer is made infusible to form a vitrified ceramic layer, which is a precursor to fine particles, on the surface of the ceramic particles that serve as the matrix. After demagnetizing the organometallic polymer, the molded article is sintered in argon gas or nitrogen gas under pressure (~9 kg/em''G) or under non-pressurized air flow.

[Function] In the particle-dispersion-strengthened fiber-reinforced ceramic composite of the present invention, fine particles of the same type or different type as the matrix ceramic are dispersed in the grain boundaries, so crack deflection occurs and fracture toughness is improved. In other words, cracks propagate in a zigzag manner around the dispersed phase due to differences in properties such as toughness and coefficient of thermal expansion between the matrix and the dispersed phase of the fine particles, as well as the state of the interface between the two. Energy is consumed, fracture energy increases, and fracture toughness improves.

Further, since the ceramic composite of the present invention is reinforced by dispersing fibers, the fracture toughness is improved by fiber reinforcement. That is, when fibers are mixed as a dispersed phase, when the cracks pass through a location where the fibers are present, the fibers are pulled out from the matrix by the amount of gap created by the cracks. Energy is consumed by the amount of work done to pull out the fibers, increasing fracture energy and improving fracture toughness.

The most distinctive feature of the particle dispersion-strengthened fiber-reinforced ceramic composite of the present invention is that the above-mentioned improvement in fracture toughness due to particle dispersion and improvement in fracture toughness due to fiber reinforcement occur simultaneously and effectively, resulting in improved fracture toughness. This is a significant increase.

In the manufacturing method of the present invention, ceramic particles serving as a matrix are mixed with a solution containing an organometallic polymer to form an impregnating liquid, and the fibers are impregnated with this impregnating liquid, so that the organometallic polymer is demagnetized. After that, when the fiber laminate is sintered in an inert atmosphere, organic components are separated due to thermal decomposition of the organometallic polymer, fine carbides or nitrides are precipitated at matrix grain boundaries, and particle dispersion is strengthened. A fiber-reinforced ceramic composite can be obtained.

[Examples] Preferred embodiments of the present invention will be described below to clarify the present invention more specifically, but the present invention should not be construed to be limited to the extent possible by the description of the embodiments described below.

(Example 1) 42 g of polysilastyrene (trade name, PSS-400) manufactured by Nippon Soda Co., Ltd. was dissolved in 110 g of toluene as a solvent. This solution was placed in a separately prepared polyethylene pot with an internal volume of 500 cc, and silicon nitride powder (product name: CC-0A, manufactured by Ube Industries, Ltd.) 98 was added to it. Put 300g of cylinder-shaped cobblestones, close the bot base, and raise the pot to 50r.
pm and mixed for 16 hours to prepare an impregnation solution.

This impregnation liquid was poured into the impregnated layer, and the
Attach the HM-60.2 manufactured by Petka (product, pitch type) or the IM40.6 manufactured by Toho Rayon (product, bread type) to the spool stand, and roll the impregnated liquid into the impregnated layer at a winding speed of 3 am/sec. The carbon fibers were uniformly impregnated with the impregnating liquid, and the carbon mm holding the impregnating liquid was wound up on a winding drum.

In addition, before winding the carbon fiber onto the winding drum,
Hot air heated to 0 to 50° C. was supplied to volatilize toluene from the carbon m fibers, and the polysilastyrene was wound up in a state in which it had adhesive properties. In addition, since adhesive carbon fibers are wound onto the winding drum, the parts that come into contact with the laminate should be treated with fluorine, etc. so that the carbon 1M fiber laminate can be easily removed. Good.

The carbon fiber laminate removed from the winding drum is cut into an arbitrary shape and then subjected to a biaxial pressure press, or a cold or hot isostatic press (C, ■, P or H-I-
The molded product was molded and pressurized at P), placed in an oven maintained at the appropriate temperature of f&50°C, and left for 24 hours to completely volatilize the toluene.

Subsequently, the polysilastyrene contained in this molded body was subjected to a demagnetization treatment. For the demagnetization treatment, the molded body was subjected to a temperature gradient of 3° to 5°C/hour under N2 gas pressure (~5 kg/cm"G).
The sample was heated to 600°C to completely vitrify it.

In sintering this molded body, fine boron nitride powder was applied to the surface of the degreased molded body to perform masking. This molded body is heated under gas pressure (9 kg/in the case of nitrogen gas).
em"G, 2kg/c for argon gas) 20
Heating at a temperature gradient of 0°C/hour and heating at a temperature of 1650°C
Sintering was performed under conditions of time holding.

For comparison, as a conventional example, an impregnating liquid that does not use an organometallic polymer was prepared, and a laminate impregnated with pitch-based and bread-based carbon fibers was created in the same manner as above, and cut in the same manner as above. This was then pressure-molded to obtain a molded body, which was made infusible under the same conditions as above, and then sintered to obtain a sintered body.

The bending strength and fracture toughness KIO of the obtained sintered bodies of the present invention example and the conventional example were measured, and the results are shown in Table 1.

(Leaving space below) Table 1 As is clear from Table 1, the examples of the present invention show an improvement of about 40% or more in both bending strength and fracture toughness in the pitch system compared to the conventional example, and also in the bread system. Both bending strength and fracture toughness values were as high as about 40% or more, confirming the effectiveness of the present invention.

(Example 2) In order to prevent surface oxidation of the same carbon fibers (pitch type and bread type) used in Example 1, silicon carbide was deposited on the fiber surface by chemical vapor deposition (CvD). Using this carbon fiber, a sintered body was obtained using the same impregnating liquid composition, winding conditions, degreasing and sintering conditions as in Example 1.

For comparison, the same carbon fiber was immersed in an impregnating liquid that did not dissolve the organometallic polymer, wound up, and degreased and sintered under the same conditions to obtain a conventional sintered body.

The bending strength and fracture toughness values of the obtained sintered bodies of the present invention example and the conventional example were measured and shown in Table 2.

Table 2 As is known from Table 2, the conventional example has a bending strength of 12.3 kgf/am'' and a fracture toughness value of 6.
5MN/m”, bending strength of bread type is 11.1kg
f/- wheel 2, the fracture toughness value was 5.7 MN/floor 1, whereas in the example of the present invention, the bending strength was 17 MN/story in the pitch system.
．． 5kgr/+am2, fracture toughness value 8゜2 MN
/ m'-pan system bending strength is 15.8kgr1
The fracture toughness value was 8.2 MN/wheel 7, and the bending strength and fracture toughness values were both significantly improved, confirming the effect of the present invention.

Example 3 64.6 g of polysilazane (trade name: NCP-200, product containing 65% toluene solution) manufactured by Chisso Corporation was dissolved in 87.4 g of toluene as a solvent.

Pour this solution into a separately prepared polyethylene pot with an internal volume of 500 cc, and add silicon nitride powder (manufactured by Ube Industries, Ltd.),
Product name: CC-0A) 98 was added to 6 and then 1
300g of 2.5mmφ high alumina cylinder type cobblestone
Then, the pot lid was closed and the pot was mixed at 5 Qrp- for 16 hours to prepare an impregnating solution.

This impregnating liquid was poured into the impregnated layer, and carbon m-fiber (Co., Ltd.)
Attach the HM-60.2 manufactured by Betka (product, pitch type) or the IM40.6 manufactured by Toho Rayon (product, bread type) to the spool stand, and roll the impregnated liquid into the impregnated layer at a winding speed of 3 cm/sec. The carbon fibers were uniformly impregnated with the impregnating liquid, and the carbon fibers holding the impregnating liquid were wound up on a winding drum.

Thereafter, lamination, degreasing, and sintering were carried out under the same conditions as in Example 1 to obtain a sintered body of an example of the present invention. For comparison, as a conventional example, an impregnating liquid that does not dissolve polysilazane was prepared, and a sintered body of the conventional example was obtained in the same manner.

The bending strength and fracture toughness values of the obtained sintered bodies of the present invention example and the conventional example were measured and shown in Table 3.

Table 3 As is known from Table 3, the conventional example has a bending strength of 9.5 kgf/am'' and a fracture toughness value of 5.6 in the pitch system.
MN/+*”, bending strength of bread type is 9゜0kgf
/am'', and the fracture toughness value was 5.1 MN/@'', whereas in the example of the present invention, the bending strength was 13.
5kg4/am”, fracture toughness (1 is 8.0MN/-Y,
In the bread system, the bending strength was 12.8 kg and the fracture toughness value was 7.3 MN/@'', and high values of around 40% were obtained for both the bending strength and fracture toughness values, confirming the effect of the present invention. Ta.

(Example 4) In order to prevent surface oxidation of the same carbon fibers (pitch type and bread type) used in Example 1, silicon carbide was deposited on the fiber surface by chemical vapor deposition (CV D ). Using this carbon fiber, a sintered body was obtained under the same impregnation liquid composition as in Example 3 and the same winding conditions, degreasing and sintering conditions as in Example 1.

For comparison, the same carbon fiber was used as a conventional example, immersed in an impregnating liquid that did not dissolve the organometallic polymer, wound up, and degreased and sintered under the same conditions to obtain a sintered body.

The bending strength and fracture toughness values of the obtained sintered bodies of the present invention example and the conventional example were measured and shown in Table 4.

(The following is a margin) As is clear from Table 4, the present invention example has superior values of bending strength and fracture toughness of about 40% for both pitch and bread systems compared to the conventional example, and the present invention The effect was confirmed.

(Example 5) In Examples 1 to 4, test results were shown for composite materials using carbon fiber, but in this example, tungsten fiber was used, which has superior strength, elastic modulus, melting point, or decomposition point to carbon fiber. used.

When tungsten fibers are heated above 1300°C, grains grow and become easier to cut, so doria (ThO□) is
．． Fibers doped with 5% and which do not cause grain growth upon heating were used.

The tungsten fibers used were manufactured by Nippon Tungsten Co., Ltd. and had a fiber diameter of 50 μm. Since it would take time to wind the fibers one by one using the filament winding method, 50 fibers were collected and soaked in the impregnating liquid. It passed through the impregnated layer and was wound up on a winding drum.

The impregnating liquid used was 211 of the polysilastyrene mixed with silicon nitride of Example 1 and the polysilazane mixed with silicon nitride of Example 3. The zero winding conditions, degreasing, and sintering conditions were as in Example 1. Alternatively, a sintered body was obtained in the same manner as in Example 3. In addition, for comparison, a sintered body of the conventional example was prepared by impregnating tungsten fiber with an impregnating liquid that did not dissolve the organometallic polymer, followed by degreasing and sintering under the same conditions. did.

The bending strength and fracture toughness values of the obtained sintered bodies of the present invention example and the conventional example were measured and shown in Table 5.

(The following is a blank space) Table 3 As is clear from Table 5, the examples of the present invention obtained superior values of bending strength and fracture toughness of over 60% in the polysilastyrene system compared to the conventional examples. In the polysilazane system, excellent bending strength and fracture toughness values of over 40% were obtained, confirming the effects of the present invention.

[Effects of the Invention] As explained above, the fiber-reinforced ceramic composite material reinforced by particle dispersion of the present invention comprises a ceramic matrix, fibers dispersed in the ceramic matrix, and ceramics of the same or different types dispersed in the ceramic matrix. It is characterized by consisting of fine particles,
Cracks and deflections occur due to fine particles dispersed in the matrix grain boundaries, improving fracture toughness, and fracture energy increases due to pull-out of IIaM dispersed in the matrix, which increases the fracture toughness value as well as the bending strength. I was able to improve it significantly.

Although conventional ceramics have various excellent properties, they are brittle materials that are susceptible to sudden changes in strength due to impact, and their applications are limited. +o is significantly improved for a certain fracture toughness value,
In both cases, 7 MN/m" or more can be obtained, so it is fully possible to apply it to cylinder liners, piston rings, etc. in reciprocating engines, and to turbine rotor blades in gas turbine engines.

In the manufacturing method of the present invention, ceramic particles serving as a matrix are mixed with a solution containing an organometallic polymer to form an impregnating liquid, and the fibers are impregnated with this impregnating liquid. After that, when the fiber laminate is sintered in an inert atmosphere, organic components are separated by thermal decomposition of the organometallic polymer, fine carbides or nitrides are precipitated at matrix grain boundaries, and particle dispersion is strengthened. A fiber-reinforced ceramic composite can be obtained. In addition, when carbon fiber is used, it is coated with an organic metal polymer, and a thin film coating process of silicon carbide and silicon nitride is performed through a thermochemical reaction, which has the secondary effect of improving the oxidation resistance of carbon IIM. can be expected.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the filament winding method. 10... Spool, 12... Long fiber, 14... Impregnated layer, 16... Impregnated liquid, 18... Winding drum,
20...Laminated body.

Claims (2)

[Claims] (1) A fiber-reinforced ceramic composite material reinforced by particle dispersion, characterized by comprising a ceramic matrix, fibers dispersed in the ceramic matrix, and fine ceramic particles of the same or different types dispersed in the ceramic matrix. (2) A step of preparing an impregnating liquid by dispersing ceramic particles serving as a matrix in a solution in which an organic metal polymer is dissolved, and a step of uniformly applying the impregnating liquid to the fibers by continuously passing the fibers through the impregnating liquid. a step of laminating the fibers to form a laminate; a step of making the organometallic polymer in the laminate infusible; and a step of pressurizing the laminate in argon gas or nitrogen gas or A method for producing a fiber-reinforced ceramic composite material reinforced by particle dispersion, characterized by comprising a step of sintering at normal pressure.