JP2991738B2 - Fiber reinforced ceramic matrix composite member and method of manufacturing the same - Google Patents

Description

The present invention relates to a ceramic composite member and a method of manufacturing the same, and more particularly, in one aspect, to a ceramic matrix composite member reinforced with ceramic fibers.

BACKGROUND OF THE INVENTION The use of ceramics in the form of high temperature working components, such as parts for power generating devices such as automotive engines, gas turbines, etc., is of interest due to the light weight and high temperature strength of certain ceramics. . One example of a typical component is a gas turbine engine strut. However, a monotonous ceramic structure without reinforcement is brittle. Without the assistance of added and mixed reinforcing structures, such members cannot meet the reliability requirements required for harsh applications as described above.

In order to overcome such disadvantages, several ceramic matrix composites that are resistant to fracture have been reported. These are blended with fibers of various sizes and types, such as long fibers or filaments, short fibers or chopped fibers, whiskers, and the like. For simplicity, all such fibers will be referred to herein simply as "fibers". Some fibers are coated with certain materials to avoid vigorous reactions between the reinforcement and the matrix. However, in such coatings,
Some consist of various forms of carbon and other materials that oxidize when exposed to air at a predetermined high operating temperature. The inclusion of such fibers in the ceramic matrix was to counter the brittle fracture behavior.

One problem with using oxidizable fibers, such as carbon, as reinforcement in ceramic composites is that the system may be unstable to the environment of use. In other words, if cracks are present in the ceramic matrix, even if they are micro-cracks, there is a possibility that oxygen in the air at the high operating temperature found in the high temperature part of the engine for power generation will come into contact with oxidizing fibers. It will happen.
Such oxidation of the reinforcing fibers weakens or destroys the fibrous structure or its function, and its structural components are weakened to an unacceptable degree.

Another problem relates to the fact that the high temperatures in sintering the ceramic particles around the reinforcing fibers limit the types of fibers that can be used. For example, many fibers degrade above about 1000 ° C,
This temperature is much lower than the temperature required for sintering the ceramic particles.

SUMMARY OF THE INVENTION Briefly, the present invention, in one aspect,
An environmentally stable fiber reinforced ceramic matrix composite comprising oxidatively stable reinforcing fibers (eg, ceramic fibers) and a matrix dispersed around the fibers. As used herein, the term "oxidatively stable" with respect to a fiber is subject to substantial oxidation and / or environmental degradation at predetermined operating conditions of temperature and atmosphere (e.g., air). Shall mean fibers that do not.
The matrix is a mixture comprising ceramic particles bound together by a ceramic phase.

In an aspect of this method, the present invention provides a method for mixing a substantially uniform distribution of a matrix mixture of a discontinuous material containing ceramic particles in a liquid that is compatible with a ceramic matrix precursor that changes to a ceramic phase upon heating. The present invention provides a ceramic matrix precursor that has been used. The slurry is sprinkled as a matrix mixture around the oxidation-stable fibers to form a prepreg preform. The preform is heated to a processing temperature in an oxidizing atmosphere such as air. The temperature is at least equal to or higher than the temperature required for the precursor to change to a ceramic phase and lower than the temperature that would cause the ceramic in the preform to deteriorate. According to the present invention, such temperatures can range from about 600 to 1000 ° C. Upon such heating, the ceramic precursor changes to, for example, an amorphous or crystalline ceramic phase, for example, by decomposition. This ceramic phase binds ceramic particles from the slurry around the fibers into a ceramic matrix. The reinforced ceramic matrix composite member is preferably substantially entirely bonded to a ceramic oxide, but is stabilized in an oxidizing atmosphere, so is environmentally stable, has high strength, Moreover, it has high resistance to destruction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Thanks to the fracture-resistant fiber reinforced ceramic matrix composite, design engineers for high temperature components of power generating engines, such as automotive engines, turbine engines, etc., specify strong and lightweight components can do. However, some of such known composites are environmentally unstable when cracks occur that expose the oxidizable portion to air. In addition, some of the known processes may leave undesirable levels of porosity in the product. Also, due to the much higher sintering temperature required and the fiber degradation temperature below this required sintering temperature,
The types of fibers that can be included in a sintered ceramic reinforced composite are limited.

The present invention avoids the known problems noted above, and is an improved method for making a reinforced ceramic matrix composite that is environmentally stable, has high strength and high fracture resistance at lower processing temperatures. To provide a method.
An important basis of the present invention is the use of ingredients that can be stabilized at lower temperatures, and one product after heating for stabilization is preferably one in which almost all of the ceramic oxide is bound together. It is a member that is. The use of such components eliminates the possibility of degradation due to oxidation during use of the component.

Typical examples of ceramic particles used as ceramic materials are oxides of elements such as Al, Si, Ca, Hf, B, Ti, Y and Zr, and mixtures and combinations thereof. Commercially available materials such as Al ₂ O ₃ and Si
O ₂ , CaO, ZrO ₂ , HfO ₂ , BN, TiO ₂ , 3Al ₂ O ₃・ 2SiO ₂ , Y ₂ O ₃
There are CaO.Al ₂ O ₃ and various clays and glass fibers. In evaluating the present invention, ceramic particle sizes ranging from about 75 microns to 0.2 microns in diameter were tested as matrix components. One aspect of the invention relates to the fact that each such ceramic, when used as a structure, shrinks when fired to a high consolidation temperature. For example, one form of alumina is 1400
It shows a linear shrinkage in the range of about 3-4% at ° C.

Various ceramic precursors that can be used as matrix precursors and infiltrants, as described below, were evaluated in connection with the present invention. When such precursors are used in combination with ceramic particles as binders, it is possible to produce stable composites at considerably lower processing temperatures. Such precursors that change to a ceramic phase upon decomposition, for example, upon heating, can be in the form of a solid or liquid or a mixture thereof for practicing part of the present invention. These are usually classified as organometallic compounds, sol-gels or metal salts. The materials used in this evaluation include polycarbosilane, silicone, and metal salts (vinylpolysilane, dimethylsiloxane,
Ceramic precursors such as hafnium oxychloride), silica and alumina sols, aluminum isopropoxide, monoaluminum phosphate and other phosphates. Table I below shows specific forms of these precursors.

According to the method of the present invention, a discontinuous material consisting of ceramic particles, a ceramic precursor, and optionally a binder is dispersed in a liquid to form a matrix mixture slurry. The term "discontinuous material" as used herein shall mean powder, particles, small pieces, flakes of material, whiskers, and the like. A characteristic of the liquid of this slurry is that it is compatible with the ceramic precursor and, if a binder is used, the binder, and preferably is a solvent for it. This results in a matrix mixture in which the precursor is substantially uniformly distributed in the slurry with the ceramic particles and any binders present. This liquid can be, for example, aqueous or organic, depending on the precursor or its mixture and the binder if present. As already mentioned, the precursor is preferably dissolved in the liquid, in which case the liquid acts as a solvent. Typical organic liquids used as solvents include
Ethyl alcohol, trichloroethane, which can keep the binder, polymer and / or infiltrant in solution;
There are methyl alcohol, toluene and methyl ethyl ketone. The required amount of solvent depends on the solubility and saturation limit of the binder / polymer and the desired viscosity of the slurry.
Preferably, the solvent is in the range of 20-30% by weight. Increasing the amount of solvent beyond this only increases the drying time required to evaporate excess solvent.

With respect to the ceramic particles in the slurry, it has been found that such particles should be included in the range of more than 40% and up to about 90% by weight, based on the sum of the ceramic particles and the precursor. Below 40% by weight, the ceramics are insufficient to form a matrix around the reinforcing fibers in the composite member and the pores become too large. About 90% by weight
Is exceeded, there is insufficient bonding of the ceramic particles around the reinforcing fibers by the changed ceramic phase of the precursor. The preferred range of ceramic particles relative to the total of particles and precursor is 50-80% by weight, especially about 70-80% by weight.

In order to obtain adequate fluidity and bonding, the ceramic precursor should be included in the matrix mixture slurry in a range of about 10-40% by weight of the total of this precursor and ceramic particles, and 10-30% by weight. Has been found to be preferred. Less than about 10% by weight results in insufficient flow of the ceramic phase and poor bonding with the ceramic particles after heating resulting in decomposition of the precursor. Above about 40% by weight, too many pores are formed in the matrix phase due to decomposition of the precursor.

The balance of this slurry is almost liquid. But,
Other materials (commonly referred to herein as "binders"), such as binders and plasticizers, used temporarily to hold the uncured matrix together are included in the slurry. You can also. The binder to hold the preforms together before heating to the processing temperature,
Up to about 20% by weight of the total of the ceramic particles, precursor and binder can be included. If it is larger than this, the number of pores becomes too large. Examples of evaluated (commercially available) binders and plasticizers are the Prestoline Master Mix [Presto
line Master Mix, PBS Chemical (PB
S. Chemical)], cellulose ethers [Dow Chemical], polyvinyl butyral and butyl benzyl phthalate [Monsant
o)], and polyalkylene glycols and polyethylene glycols [Union Carbide (Union Carbide)
Carbide)]. Bonding systems also used were epoxy resins, such as general purpose epoxy resins from Ciba-Geigy, silicones, such as polysiloxane [GE], RTV [GE] and Polycarbosilane [Union Carbide (Union
Carbide)]. If desired, dispersing agents were included such as glycerol trioleate, fish oil, adipic acid polyester, sodium polyacrylate and phosphate esters. When an epoxy resin is used as the bonding system together with the preferred ranges of precursors and ceramics described above, the amount of epoxy is about 1 to 10% by weight based on the mixture of the precursor and the ceramic particles.

Various fibers were evaluated in connection with the present invention, including the ceramic reinforcing fibers shown in Table II below along with the coefficient of thermal expansion (CTE).

In Example 1, which was evaluated in connection with the present invention, the matrix mixture slurry had about 0.2 to 5 ceramic particles.
It contained Al ₂ O ₃ particles in the size range of 0 microns, silicone commercially available as RTV as the ceramic precursor, and epoxy resin marketed as bisphenol as the binder. In this exemplary mixture, Al ₂ O _3, based on the total of silicone and binder, Al ₂ O ₃ is 70 to 80% by weight, the silicone is 10 to 30 wt%, and epoxy 1-10 wt% Met. This mixture was combined with a mixed solvent of trichloroethane and ethanol in an amount of about 20-30% by weight as a liquid to form a matrix mixture slurry. 70-80 which is the rest of this slurry
% By weight was the above mixture of ceramic, precursor and binder.

In Example 2, a combination of ceramic precursors was included.
Such a mixture comprises, based on the sum of the ceramic particles, precursor and binder, 70-80% by weight of Al ₂ O ₃ as ceramic particles, 5-15% by weight of silicone and 5-15% by weight.
% By weight of aluminum isopropoxide as the ceramic precursor and 1 to 10% by weight of epoxy as binder. This mixture can be used as a liquid
The matrix mixture slurry was combined with a mixed solvent of trichloroethane and ethanol in an amount of 30% by weight. The remaining 70-80% by weight of the slurry was the above mixture of ceramic, precursor and binder.

In one embodiment of the method of the present invention, Examples 1 and 2
Each of the matrix mixture slurries was wrapped around reinforcing ceramic fibers in the form of a woven fabric. In these examples, the reinforcing fibers are Sumitomo as specified above.
Made from yarns or rovings and contained in the range of 20-40% by volume of the component. In other embodiments and examples, the reinforcing ceramic fibers were wound filaments. In the present invention, it has been recognized that the reinforcing fibers should be included in the range of about 10-50% by volume of the component, with 30-40% by volume being preferred. If it is less than 10% by volume, the reinforcing strength is insufficient, and if it is more than about 50% by volume, the fibers become too dense and the matrix cannot be properly distributed therebetween.

After drying the prepreg and evaporating most of the solvent, the resulting prepreg layer is subjected to temperature and pressure using a compression mold or an autoclave as is well known and practiced in the art. It was shaped and formed into a member. The member was then cooled to a solid preform shape.

The preform was then heated to a processing temperature in the range of 600-1000C. This temperature is much lower than the generally much higher sintering temperatures used in known methods (e.g., in the range of about 1300-1650C). This heating is performed for removing organic substances such as a temporary binder and changing the ceramic precursor by decomposition to form a ceramic binder phase. By practicing the present invention using a binder precursor containing ceramic particles, the processing temperature can be maintained in a range much lower than the processing temperature required to sinter the ceramic particles around the reinforcing fibers together. . In addition, other than the present invention, it is possible to use fibers which are deteriorated or thermochemically damaged at a known high sintering temperature.

In Examples 1 and 2 above, the heating at the processing temperature was about 600 to 8
Performed in the range of 00 ° C. Such heating results in a ceramic matrix in which the ceramic particles are bonded together via a ceramic phase. Generally, the matrix has an open porosity in the range of about 5-30% by volume.

The invention, in another aspect, includes the additional step of reducing or eliminating porosity as described above. In such an embodiment, another ceramic precursor, in liquid form or usually in a form dispersed in liquid at a high concentration, is used to infiltrate the pores of the ceramic matrix. For example, the matrix can be immersed in a liquid ceramic precursor infiltrant and the pressure reduced to facilitate penetration of the infiltrant into the pores. After drying, some pores are removed by heating the infiltrated matrix in the same manner as described above to convert the infiltrant ceramic precursor to a ceramic phase. Such infiltration of pores and heating for conversion can be repeated as desired to reduce or eliminate the porosity (rate) of the matrix to a desired degree.

The comparative graph of FIG. 1 is a stress-strain curve showing the fracture resistance and toughness of a member made according to the present invention. First
The data in the figure was obtained from a test at room temperature. The specimen used was a 0.5 "x 6" x 0.1 "rectangular test rod.

The data shown by curve 1 is the test results for a sample prepared as described above from the mixture of Example 1 above.
However, in this case, the slurry was not dispersed around the reinforcing fibers. The material of Curve 1 is a monotonous matrix of ceramic particles, ceramic precursor and epoxy binder, having low strength and rapidly brittle fracture. Monotonous ceramics of this type are not candidates for important shapes in structural applications because they are not resistant to defects and consequently have low toughness.

The data represented by curve 2 in FIG. 1 was obtained by testing specimens of the same size and shape made from the same mixture as the specimen used to obtain the data of curve 1. However, in this case the mixture is about 30% by volume
And dispersed on a reinforcing fiber fabric made of Sumitomo yarn. The material shown by curve 2 is a ceramic composite in which the same monotonous matrix material as in curve 1 is compounded between and around the fiber reinforcement. This material has high strength as the load is transferred to high strength fibers and exhibits favorable fracture features and toughness. Such composite behavior allows parts made therefrom to exhibit long life even after failure has occurred.

As can be seen from FIG. 1, the reinforced ceramic matrix composite of Curve 2 has significantly higher strength and toughness than the member of Curve 1.

FIG. 1 shows, for comparison, sapphire reinforcing fibers in an Al ₂ O ₃ matrix at approximately 1450-1500 ° C.
Curve 3 is also shown, which shows a sintered part (much above the usable temperature range of the fibers identified in Table II).
No precursor was included in such a composite with 55% by volume aluminosilicate and 45% by volume sapphire fibers. This required the mixture to use a sinter consolidation temperature that was significantly higher than the processing temperature used in the process of the present invention (typically around 600-1000 ° C). The material of curve 3 is stronger than the material of curve 2 with toughness behavior. Such improved properties are the result of using higher strength reinforcing fibers with a thermally compatible matrix to allow effective transfer of load from the matrix to the fibers.

As can be seen by comparing Curve 2 representing the present invention with Curve 3 representing a member made in a different manner, the present invention provides enhanced strength and toughness without the need for consolidation at extremely high temperatures. Provide a ceramic composite material. This is the result of the use of ceramic precursors in the present invention, such ceramic precursors decompose at lower temperatures into a ceramic phase that bonds the ceramic particles and reinforcing fibers together in the composite member. It is.

A typical example of a component that can be made in accordance with the present invention is an airfoil strut useful in the hot section of a gas turbine engine. An example of such a strut is shown in a partially sectional perspective view in FIG. The strut, generally indicated at 10, includes a strut body 12 having a leading edge 14 and a trailing edge 16. Struts 10 are sometimes referred to as hollow struts due to the presence of a plurality of cavities 18 separated by ribs 20.

The struts 10 can be made from a plurality of layers such as laminations, sheets, tapes, etc. made as described above. The partial cross-sectional view of FIG. 3 is a representative example schematically showing the arrangement of such layers. This layer is shown as 22 around a forming block 24, such as aluminum. This figure shows the preform shape of a portion of the strut of FIG. 2 initially formed in relation to the shape of the strut of the final product. In practice, each layer of the member will have a thickness depending on the fiber and configuration, as is well known in the art. For example, a typical thickness is about 0.008-
It is in the range of 0.020 inches. However, as is well known in the art, the number of layers actually required to obtain such a laminated structure will be greater than that simplified in FIG. Block 24 to reduce voids
Additional individual fibers 25 are distributed between the layers within the space that can occur between the layers of the curved region of the edge.

After assembling around the forming block 24 to form the component of FIG. 3, the assembly is assembled into a suitably shaped mating forming die shown in FIG. 4 to laminate the components to form a preform of the article. Put in 26A and 26B. Usually, during the appropriate time for proper lamination to occur
The member is heated, for example, to a temperature in the range of 150-400 ° F. while applying a pressure in the range of approximately 150-1000 pounds per square inch as represented by arrow 28. Such temperatures do not cause compaction of these building materials.

The preform obtained after lamination is removed from the forming die, and the forming block is removed. Next, put this preform in a furnace, heat it to a temperature below 1000 ° C while adjusting to remove the binder and plasticizer, and then heat it to a processing temperature such as 1000 ° C or more where fiber deterioration does not occur. The preform is sintered into the substantially dense ceramic matrix composite article of FIG.

A co-pending US Patent Application No. 341,001 1989 filed concurrently with the present application, the disclosure of which is incorporated herein by reference,
It concerns shrinkage of the compacted ceramic particles and the resulting pores. According to the invention of the related application, such shrinkage is counteracted by mixing the ceramic particles with the inorganic filler particles prior to consolidation. Such fillers exhibit a net expansion for the ceramic particles while being heated to the consolidation temperature. At the time of evaluation of the invention, the lath-type crystalline inorganic filler specified in Table III below was tested.

Fillers as described above can be used, in one aspect of the invention, to counteract pores created during heating to the processing temperature. The proportion of the filler in the mixture is selected such that the expansion of the filler cancels the generated pores.

When including the inorganic filler of the related application in the matrix mixture of the present invention comprising ceramic particles and a precursor and optionally including a binder, such a filler comprises a ceramic, a precursor, and optionally a binder. , And fillers, for example, up to about 50% by weight. The proportion is chosen such that the pores are offset by the expansion of the filler. Such porosity can result from the shrinkage of the ceramic particles, but, as already mentioned, is primarily due to material conversion or volume change during heating of the preform of the present invention in an oxidizing atmosphere. Occurs at lower processing temperatures. Typically, the pore control mixture of ceramic particles and filler is 50-93% by weight of ceramic particles and 7-50% by weight of inorganic filler, the pore control mixture comprising particles, precursor and case. From about 40% to about 90% by weight of the matrix mixture consisting of the binder present. Preferred as inorganic fillers are those having the lath-type crystal form shown in Table III above. In particular, pyrophyllite and wollastonite have been found to be particularly useful as fillers. Also, as included in the disclosure of the related application above, reinforcing fibers that expand against the matrix mixture enhance the processability of the preform at ambient temperature.

The invention has been described with reference to non-limiting exemplary embodiments and examples and associated data. However, it will be readily apparent to one skilled in the art that the present invention is capable of various modifications and variations within the scope of the appended claims.

[Brief description of the drawings]

FIG. 1 is a graph showing a comparison of the fracture resistance data for an unreinforced matrix, another reinforced matrix, and a composite reinforced member of the present invention. FIG. 2 is a partial sectional perspective view of a part of the gas turbine engine strut. FIG. 3 is a partial schematic cross-sectional view of a ceramic matrix composite layer disposed around a forming block. FIG. 4 is a partial cross-sectional perspective view of the member of FIG. 3 disposed within a forming die. 10 ... airfoil struts, 22 ... individual layers, 24 ... forming blocks, 26 ... forming dies.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-197472 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C04B 35/80

Claims (13)

(57) [Claims] 1. A ceramic matrix precursor which changes into a ceramic phase by heating, a liquid compatible with the precursor, and a discontinuous material comprising ceramic particles are prepared. The continuous material is mixed together to form a matrix mixture slurry in which the ceramic particles and precursors are substantially uniformly distributed, providing a plurality of oxidatively stable reinforcing fibers, and combining the matrix mixture slurry with the fibers. A prepreg preform is scattered around the preform, and in an oxidizing atmosphere, the temperature of the preform is higher than a temperature required to change the precursor into a ceramic phase, but is lower than a temperature that causes deterioration of ceramics in the preform. The ceramic matrix precursor is changed by heating to a lower processing temperature, A fiber comprising changing ceramic particles from a slurry into a ceramic phase that binds the fibers in a surrounding ceramic matrix, and obtaining a fiber-reinforced ceramic matrix composite member that is environmentally stable, has high strength, and has high fracture resistance. A method for producing a reinforced ceramic matrix composite member. 2. A matrix mixture slurry comprising: (a) ceramic particles ranging from more than 40% to about 90% by weight of the total of ceramic particles and ceramic precursor; and (b) about 10 to 40 of said total. The method of claim 1, comprising a range of weight percent of the ceramic precursor, wherein the reinforcing fibers are about 10-50% by volume of the composite member. 3. The method according to claim 2, wherein the reinforcing fibers are ceramic fibers. 4. The method of claim 2 wherein the prepreg preform is heated in air at a processing temperature in the range of about 600-1000 ° C. 5. The method of claim 2, wherein a binder is provided and included in the slurry up to about 20% by weight of the total of the ceramic particles, ceramic precursor and binder. 6. The slurry of the matrix mixture comprising the ceramic particles, the ceramic precursor and the binder in a total of 70-80.
% By weight (including 50 to 80% by weight of the ceramic particles, 10 to 30% by weight of the ceramic precursor, and 1 to 20% by weight of the binder), and 20% by weight of the liquid as an organic liquid.
The method of claim 5 comprising about 30% by weight. 7. The ceramic precursor is a material selected from the group consisting of organometallic compounds, sol-gels, metal salts and mixtures thereof, wherein the ceramic particles are Al, Si, Ca,
3. The method according to claim 2, comprising a material selected from the group consisting of oxides of Hf, B, Ti, Hf, Y and Zr and mixtures and combinations thereof. 8. The method of claim 1 wherein the plurality of fibers are in the form of a layer and the matrix mixture is scattered around the fibers in the layer to obtain a prepreg layer. 9. The method of claim 8, wherein a plurality of prepreg layers are laminated into a prepreg preform prior to heating. 10. A method of manufacturing a composite member having a higher density, comprising: heating a preform in an oxidizing atmosphere to convert a ceramic matrix precursor into a ceramic phase;
The composite member is brought into contact with a ceramic infiltrant precursor that infiltrates the open structure in the member, and then the infiltrated member is heated in an oxidizing atmosphere to infiltrate the ceramic infiltrant precursor into a ceramic phase. 2. The method according to claim 1, wherein 11. The matrix mixture slurry also includes, in addition to the ceramic particles, a particulate inorganic filler that exhibits a net expansion to the ceramic particles when heated to the processing temperature, wherein the inorganic filler in the matrix mixture is Of the
2. The method of claim 1, wherein the expansion of the filler is selected to counteract the porosity created in the preform while being heated to the processing temperature. 12. The matrix mixture slurry comprising a binder, wherein (a) the ceramic ranges from greater than 40% to about 90% by weight of the total of the ceramic particles, ceramic precursor, inorganic binder and filler. Particles, (b) a ceramic precursor in the range of about 10-40% by weight of the total;
12. The method of claim 11, comprising: (c) a binder in the range of up to about 20% by weight of the total; and (d) an inorganic filler in the range of up to about 50% by weight of the total. 13. The method according to claim 13, wherein (a) the ceramic particles have a total of about 50
(B) the ceramic precursor is in the range of about 10-30% by weight of the total, (c) the binder is in the range of about 1-20% by weight of the total, 13. The method of claim 12, wherein (d) the inorganic filler ranges from about 7 to 50% by weight of the total.