CA2012240C

CA2012240C - Fiber reinforced ceramic matrix composite member and method for making

Info

Publication number: CA2012240C
Application number: CA002012240A
Authority: CA
Inventors: Michael L. Millard; Michael G. Harrison; Andrew Szweda
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1989-04-14
Filing date: 1990-03-15
Publication date: 2004-07-06
Anticipated expiration: 2010-03-15
Also published as: IT1241114B; DE4012229A1; IT9020023A0; IT9020023A1; GB2230259B; JPH0365570A; CA2012240A1; GB9001418D0; FR2645853A1; JP2991738B2; GB2230259A; FR2645853B1

Abstract

A method for making an environmentally stable, fiber reinforced ceramic matrix composite member includes use as a bonding agent of a ceramic precursor which transforms upon heating to a ceramic ceramic phase. The ceramic phase bonds together discontinuous material comprising ceramic particles, and reinforcing fibers at a relatively low processing temperature.

Description

20~22~40 FIBER REINFORCED CERAMIC MATRIX COMPOSITE
MEMBER AND METHOD FOR MAKING
This invention relates to ceramic composite members and method for making, and, more particularly in one form, to ceramic fiber reinforced ceramic matrix composite members.
CROSS REFERENCE TO RELATED APPLICATION
This application relates to co-pending Canadian application Serial No. 2,009,595 filed February 8, 1990 entitled °'Consolidated Member and Method and Preform for Making."
BACKGROUND OF THE INVENTION
Use of ceramics in the form of high temperature operating articles, such as components for power generating apparatus including automotive engines, gas turbines, etc., is attractive based on the light weight and strength at high temperatures of certain ceramics. One typical component is a gas turbine engine strut. However, monolithic ceramic structures, B

- 2 - ~~.~rr~~r without reinforcement, are brittle. Without assistance from additional incorporated, reinforcing structures, such members may not meet reliability requirements for such strenuous use.
In an attempt to overcome that deficiency, certain fracture resistant ceramic matrix composites have been reported. These have incorporated fibers of various size and types, for example long fibers or filaments, short or chopped fibers, whiskers, etc. All of these types are referred to for simplicity herein as "fibers". Some fibers have been coated with certain materials which have been applied to prevent strong reactions from occurring between the reinforcement and matrix. However, some coatings are of carbon, or forms of carbon, or other material which will oxidize if exposed to air at an intended elevated operating temperature. Inclusion of such fibers within the ceramic matrix was made to resist brittle fracture behavior.
One problem with the use of such oxidizing fibers, such as carbon, as reinforcement in ceramic composites is that the system can become environmentally unstable in use: cracks in the ceramic matrix, even microcracks, can make the oxidizable fiber available to contact with oxygen in air at elevated operating temperatures experienced in the hot sections of power producing engines. Such oxidation of reinforcing fibers weakens or destroys the fiber structure or its function, leading to unacceptable weakening of the structural member.

Another problem relates to the fact that high sintering temperatures for ceramic particles about reinforcing fibers limit the kind of fibers which can be used. For example, many fibers deteriorate above about 1000°C, well below required ceramic particle sintering temperatures.
SUMMARY OF THE INVENTION
Briefly, in one form, the present invention provides a method for making an environmentally stable, fiber reinforced ceramic matrix composite member comprising oxidation stable reinforcing fibers, for example ceramic fibers, and a matrix interspersed about the fibers. As used herein, "oxidation stable"
in respect to fibers means fibers which substantially will not experience substantial oxidation and/or environmental degradation, at intended operating conditions of temperature and atmosphere. such as air.- The matrix is a mixture including ceramic particles bonded together with a ceramic phase.
In the method form, the present invention provides a ceramic matrix precursor, which transforms upon heating to a ceramic phase, mixed in a substantially uniform distribution in a matrix mixture slurry of discontinuous material comprising ceramic particles in a liquid compatible with the precursor. This slurry is interspersed about the oxidation stable fibers, as a matrix mixture, to provide a prepreg preform which is heated in an oxidizing atmosphere, such as air, at a processing temperature, at least at the temperature required to transform the precursor to a ceramic phase and less than that which will result in degradation of ceramic in the preform. Through the present invention, such temperature can be in the range of about 600-1000°C.
Such heating transforms the ceramic precursor, such as by decomposition, to a ceramic phase, for example of amorphous or crystalline form, which bonds together the ceramic particles from the slurry into a ceramic matrix about the fibers. Because components of this reinforced, ceramic matrix composite member are stabilized in an oxidizing atmosphere, preferably being substantially all ceramic oxides bonded together, the member is environmentally stable, and of high strength and high resistance to fracture.
DESCRIPTION OF THE DRAWINGS
Figure 1 is a graphical comparison of fracture resistance data for an unreinforced matrix, another reinforced matrix and a composite. reinforced member of the present invention.
Figure 2 is a fragmentary, sectional perspective view of a portion of a gas turbine engine strut.
Figure 3 is a fragmentary, diagrammatic sectional view of plies of ceramic matrix composite disposed about forming blocks.
Figure 9 is a fragmentary, sectional perspective view of the member of Figure 3 disposed in forming die portions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Fracture resistant, fiber reinforced ceramic matrix composites offer the designers of high temperature components for power generating engines, _5_ ~~...r~~~~
such as components for automotive engines, turbine engines, etc., an opportunity to specify strong, lightweight members. However, certain of such known composites are environmentally unstable upon the occurrence of cracks which expose oxidizable portions to air. In addition, certain known processing results in an undesirable level of porosity in the product.
Also, the kind of fibers which can be included in sintered ceramic reinforced composites has been limited based on the relatively high sintering temperatures required and a fiber deterioration temperature lower than the required sintering temperature.
The present invention provides an improved method for avoiding such known problems and for making an environmentally stable reinforced ceramic matriz composite member of high strength and high fracture resistance at lower processing temperatures. A
principal basis for the invention is providing ingredients which can be stabilized at a lower temperature; and, after a stabilizing heating, one product is a member preferably having substantially all ceramic oxides bonded together. Use of such ingredients eliminates the potential for member deterioration in use due to oxidation.
Typical of the ceramic particles used for ceramic matricies are the oxides of such elements as A1, Si, Ca, Hf, B, Ti, Y and Zr, and their mixtures and combinations. Such commercially available materials include A1203, Si02, CaO, Zr02, Hf02, BN, Ti02, 3A1203~2Si02, Y203 Ca0~A1203 and various clays and glass frits. Ceramic particle sizes in the range between about 75 microns to 0.2 micron in diameter 519 6L 1,~3D~V~-9~2~31~

have been tested as a matrix ingredient in the evaluation of the present invention. One form of the present invention addresses the fact that each of such ceramics, when used as a structure, will shrink when fired to an elevated consolidating temperature. For example, a form of alumina will experience a linear shrinkage in the range of about 3-4% at 1400°C.
Evaluated in connection with the present invention were a variety of ceramic precursors, which can be used as a matrix precursor as well as an infiltrant precursor, as described later herein. Use of such a precursor as a bonding agent in combination with the ceramic particles enables generation of a stable composite at a significantly lower processing temperature. Such precursors which transform, for example by decomposition upon heating, to a ceramic phase, can be in solid or liquid form, or their mixtures, for practice of portions of the present invention. Generally they are classified as organometallics, sol gels or metal salts. Included in the evaluation were the following ceramic precursors:
polycarbosilanes, silicones, metal salts (including vinylic polysilane, dimethyl siloxane, and hafnium oxychloride), silica and alumina sols, aluminum isopropoxide, mono aluminum phosphate and other phosphates. The following Table I identifies specific forms of such precursors.

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_g_ According to the method of the present invention, discontinuous material, comprising the ceramic particles, ceramic precursor, and optionally a binder, are dispersed in a liquid to provide a matrix mixture slurry. As used herein, the term "discontinuous material" is intended to mean powder, particles, small fragments, flakes of material, whiskers, etc. A
characteristic of the liquid of the slurry is that it be compatible with, and preferably a solvent for, the ceramic precursor, and for the binder if one is used.
This allows a substantially uniform distribution of the precursor in the slurry, along with the ceramic particles and optional binders to provide the matrix mixture. For example, the liquid can be aqueous or it can be organic, depending upon the precursor or mixture of precursors, and optional binder. As was stated, preferably the precursor will dissolve in the liquid, which in that case acts as a solvent. Typical organic liquids used as solvents include ethyl alcohol, trichlorethane, methyl alcohol, toluene and methyl ethyl ketone which allow the binders, polymers and/or infiltrants to dissolve into a solution. The quantity of solvent required depends upon the solubility and saturation limit of the binders/polymers and the desired viscosity of the slurry. The preferred limits range from 20-30 wt solvent. Additional solvent quantities will only induce prolonged drying times to evaporate the excess solvents.
In respect to the ceramic particles in the slurry, it has been recognized that such particles should be included in the range of greater than 40 wt% up to about 90 wt% of-the sum of ceramic particles and precursor. At 40 wt% or less, there is insufficient ceramic to provide a matrix about reinforcing fibers in the composite member and results in too much porosity; at greater than about 90 wt$. there is insufficient bonding, by the transformed precursor's ceramic phase, of the ceramic particles about the reinforcing fibers. The preferred range for the ceramic particles in that sum of particles and precursor is 50-80 wt%, and more specifically about 70-80 wt%.

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In the matrix mixture slurry, it has been recognized that the ceramic precursor should be included in the range of about 10-40 wt% of the sum of precursor and ceramic particles, preferably 10-30 wt%, to provide adequate flow and bonding. Less than about wt% provides insufficient ceramic phase for flow and bonding together the ceramic particles after precursor decomposition heating; at greater than about 40 wt%, decomposition of the precursor results in excessive porosity in the matrix phase.
The balance of the slurry generally is the liquid. However, such other materials as binders and plasticizers, herein generally called "binders", used temporarily to hold an uncured matrix together, can be included in the slurry. Binders to hold the preform together prior to heating at the processing temperature can be included up to about 20 wt% of the sum of ceramic particles, precursor and binder.
Greater than that will result in too much porosity.
Examples of such binders and of plasticizers evaluated (and one commercial source) are Prestoline Master Mix (P.B.S. Chemical), cellulose ether (Dow Chemical), polyvinyl butyral (Monsanto) butyl benzyl phthalate (Monsanto), polyalkylene glycol (Union Carbide) and polyethylene glycol (Union Carbide). Binding systems also used were epoxy resins, for example general purpose epoxy resin manufactured by Ciba-Geigy, silicones, for example polysiloxane (GE), RTV (GE) and polycarbosilane (Union Carbide). Included as required were dispersants such as glycerol trioleate, marine oil, adipate polyester, sodium polyacrylate and phosphate ester. When epoxy resin was used as a binding system with the above preferred precursor and 5196L 0 ~ G G. ~ ~ 13DV-9231 - 11 r, ceramic ranges, the epoxy was about 1-10 wt~, in respect to the mixture of precursor and ceramic particles.
Evaluated in connection with the present invention were a variety of ceramic reinforcement fibers including those shown in the following Table II, along with each of their coefficients of thermal expansion ( CTE ) TABLE II
REINFORCEMENT FIBERS
TYPE CTE x 10-6 per °C
A. MONOFILAMENTS
Sapphire 7-9 Avco SCS-6TM 4.8 Sigma 4.8 B. ROVINGS/YARN
Nextel~ 440 4.4 Nextel 480 4.4 Sumitomo~ 8.8 DuPont FP 7.0 DuPont PRD-166 9.0 UBE 3.1 Nicolon 3.1 Carbon 0 C. CHOPPED FIBERS/WHISKERS
Nextel 440 4.4 SaffilTM 8.0 In an Example 1 evaluated in connection with the present invention, the matrix mixture slurry included A1203 particles in the size range of about 0.2 - 50 B

microns as the ceramic particles, a silicone commercially available as RTV as the ceramic precursor, and an epoxy resin marketed as bisphenol as the binder. In this typical mixture, by weight, A1203 was 70-80%. silicone was 10-30% and epo$y was 1-10% of the sum of A12~3, silicone and binder. With this mixture was the combination solvent trichloroethane and ethanol as the liquid in the amount of about 20-30 wt%, the balance, 70-80 wt%. being the above mixture of ceramic, precursor, and binder to provide the matrix mixture slurry.
In an Example 2, a combination of ceramic precursors were included. Such mixture included, by weight, 70-80% A1203 as the ceramic particles, 5-15%
silicone and 5-15% aluminum isopropoxide as the ceramic precursors. and, as the binder, epoxy in the amount of 1-10% of the sum of ceramic particles, precursor and binder. With this mixture w.as the combination solvent trichloroethane and ethanol as the liquid in the amount of about 20-30 wt%, the balance, 70-80 wt%. being the mixture of ceramic, precursors, and binder to provide the matrix mixture slurry.
In one form of the method of the present invention, each of the matrix mixture slurries of Examples 1 and 2 above was interspersed about reinforcing ceramic fibers in the form of a fabric.
In these examples, the reinforcing fibers were made of the Sumitomo yarn or rovings identified above, included in the range of 20 - 40 volume % of the member. In other forms and examples, the reinforcing ceramic fibers were filament wound. In the present invention, it has been recognized that the reinforcing fibers be included in the range of about 10-50 vol% of the member, and preferably 30-90 vol$. Less than 10 vol% provides insufficient reinforcement strength, and at greater than about 50 vol% the fibers are spaced too closely for the disposition about them of adequate matriz.
After allowing this prepeg to dry, to enable the majority of the solvent to be evaporated, the prepreg plies thus created were shaped and molded into a member, such as through use of compression molds, or an autoclave, to apply temperature and pressure, as is well known and practiced in the art. Thereafter, the member was cooled into a solid preform shape.
The preform was then heated at a processing temperature in the range of 600° - 1000°C rather than at the generally much higher sintering temperature used in known methods, for ezample in the range of about 1300 - 1650°C. This heating is conducted to remove organics such as the temporary binder and to transform through decomposition, the ceramic precursor into a ceramic bonding phase or phases. Through practice of the present invention of including a bonding precursor with the ceramic particles, the processing temperature can be maintained in a range much lower than that required to sinter together ceramic particles about reinforcement fibers. Also, it enables use of fibers which otherwise would be degraded or thermochemically damaged at the known, higher sintering temperatures.
In the above Examples 1 and 2, heating at the processing temperature was conducted in the range of about 600 - 800°C. Such heating results in a ceramic matrix of ceramic particles bonded together through a 519 6L ~1 ceramic phase or phases. Generally the matrix has an open gorosity in the range of about 5-30 vol%.
The present invention, in another form, includes additional steps for reducing or eliminating such porosity. In such form, additional ceramic precursor in liquid form, or dispersed in a liquid generally in high concentration, is applied to the above described ceramic matrix and infiltrated into the porosity. For example, the matrix can be immersed in the liquid ceramic precursor infiltrant and a vacuum applied to facilitate precursor penetration into the pores.
After drying, the infiltrated matrix is heated, as described above, to transform the infiltrant ceramic precursor into a ceramic phase or phases thereby eliminating certain porosity. Such pore infiltration and transformation heating can be repeated, as desired, to reduce or eliminate porosity from the matrix to a desired level.
The graphical comparison of Figure 1 is a stress vs. strain curve which shows the fracture resistance and toughness of the member made according to the present invention. The data in this Figure 1 were obtained by testing at room temperature. The specimens used were 0.5" x 6" x 0.1" rectangular test bars.
The data represented by curve 1 was from testing of a specimen made from the mixture of the above Example l, as described, without dispersing the slurry about reinforcing fibers. The material in curve 1 is a monolithic matrix of ceramic particles, ceramic precursor and epoxy binder which is low in strength and fails catastrophically in a brittle manner.

_15_ ~~~.2r~~~
Monolithic ceramics of this type are not viable candidates for critical shapes in structural applications due to their intolerance to defects and subsequent low toughness.
The data represented by curve 2 of Figure 1 was from testing of a specimen of the same size and shape as that used for curve 1 data, made from that same mixture. However, the mixture was interspersed about a reinforcing fiber fabric of Sumitomo yarn included at about 30 vol% of the member. The material in curve 2 is a ceramic composite in which the same monolithic matrix material in curve 1 has been incorporated throughout and around the fiber reinforcements. The material has high strength because the load is now transferred to the high strength fibers and the material exhibits graceful fracture and toughness.
This type of composite behavior allows a part to have extended life after the initial onset of fracture.
As can be seen from Figure 1, the reinforced ceramic matrix composite member of curve 2 is significantly stronger and tougher than that of curve 1.
Included for comparison in Figure 1 is a curve 3 representing use of saphhire reinforcing fibers in a matrix of A1203 and sintered at about 1450-1500°C, well above the temperature capability of the fibers identified in Table II. No precursor was included in such a composite, which was 55 vol.% aluminosilicate and 45 vol % sapphire fibers. Accordingly, this mixture necessitated use of the sintering, consolidation temperature significantly higher than the processing temperature used in the method of the _16_ invention, generally about 600° - 1000°C. The material in curve 3 exhibits higher strength than curve 2 with tough behavior. These improved properties represent the benefits of using a higher strength reinforcing fiber with a thermally computable matrix to enable load transfer from the matrix to the fiber in an efficient manner.
As can be seen from the comparison of curve 2, representing the present invention, and curve 3, representing a member made by a different method, the present invention provides a high strength, tough, reinforced ceramic composite made without ultra high temperature consolidation processing. This occurs through use, in the present invention, of a ceramic precursor which decomposes at a lower temperature to a ceramic phase which bonds together the ceramic particles and reinforcing fibers into a composite member.
Typical of members which can be made according to the present invention is an airfoil shaped strut, useful in a gas turbine engine hot section, and shown in the fragmentary, sectional perspective view of Figure 2. The strut, shown generally at 10, includes a strut body 12 having leading edge 14 and trailing edge 16. Strut 10 is sometimes referred to as a hollow strut because of the presence of a plurability of cavities 18 therein separated by ribs 20.
Strut 10 can be made by groviding a plurality of plies such as laminations, sheets, tape, etc., made as described above. The fragmentary sectional view of Figure 3 is diagrammatic and representative of disposition of such plies, identified at 22, about forming blocks 24, such as of aluminum, as an initial formation of the preform configuration of a portion of the strut of Figure 2 in relation to the shape of that finished strut. In reality, each ply for this member will have a thickness dependent on fiber and form, as is well known in the art. For example, typical thicknesses are in the range of about 0.008-0.020 inches. However, as is well known in the art, the number of plies actually required to provide such a laminated structure would be many more than those presented for simplicity in Figure 3. Additional individual fibers 25 are disposed between plies within potential spaces between plies at the edge curvature regions of blocks 24 to reduce voids.
After formation of the member of Figure 3 assembled about forming blocks 24, the assembly is placed within appropriately shaped, mating forming dies 26A and 26B in Figure 4 for the purpose of laminating the member into an article preform.
Typically, a pressure, represented by arrows 28, in the range of about 150-1000 pounds per square inch, is applied to the member while it is heated, for ezample in the range of 150-400°F, for a time adequate to allow proper lamination to occur. Such a temperature is not adequate to enable consolidation of the materials of construction to occur.
After lamination, the preform thus provided is removed from the forming dies and the forming blocks are removed. The preform then is placed in a furnace, and heated to a temperature below 1000°C in a controlled manner to remove binders and plasticizers, and then to a processing temperature at which no degradation of fibers occurs, such as 1000°C or above to sinter the preform into a substantially dense ceramic matrix composite article of Figure 2.

20 ~I 2 2~4 0 The cross referenced related Canadian application Serial No. 2,009,595 addresses the problem of shrinkage of consolidated ceramic particles and resultant porosity. According to the invention of such cross referenced application, such shrinkage is counteracted by mixing with the ceramic particles, prior to consolidation, particles of an inorganic filler which will exhibit net expansion relative to the ceramic particles during heating to the consolidation temperature. Tested in the evaluation of that invention are the inorganic filler materials, of lathy-type crystal shape, and identified in the following Table III.
TABLE III
FILLER MATERIALS
IDENTIFICATION LATHY-TYPE
MINERALOGICAL CRYSTAL
NAME COMPOSITION SHAPE
Pyrophyllite A1203 ~ 4Si02 ~ H20 laminar Wollastonite Ca0~Si02 bladed/elongated with circular crystals Mica KZO ~ 3A1203 ~ 6Si02 ~ 2H20 plate-like Talc 3Mg0~4Si02~H20 flat flake Montmorillonite (Al,Fe,Mg)OZ~4SiO2~H20 elongated Kyanite 3A1203 ~ 3Si02 bladed/elongated ,, , p12~~p Such filler materials can be used in one form of the present invention to counteract porosity created during heating at the processing temperature. The proportion of the filler in that above mixture is selected so that expansion of ' the filler counteracts such porosity however generated.
When the inorganic filler of the related application is included in the matrix mixture of the present invention of ceramic particles and precursor, and optional. binder, such filler can be included in an amount, for exartg~le up to about 50 wt ~
of the sum of ceramic, precursor, optional binder and filler.
The proportion a.s selected so that expansion of the filler counteracts porosity. Such porosity could result frown shrinkage of the ceramic particles but primarily occurs at the lower processing temperature frcan transformation or volume change of materials during heating of the preform of the present invention in an oxidizing atmosphere, as has been described herein.
Typically, the porosity control mixture of ceramic particles and filler will be, by weight, 50-93~ ceramic particles and 7-50~ inorganic filler, with the porosity control mixture representing, by weight, greater than 40~ up to about 90~ of the matrix mixture of particles, precursor and optiar~al. binder.
Preferred as inorganic filler materials are those shown in the above Table III, and having a lathy-type crystal shape. In particular, pyrophyllite and wollastonite have been found to be especially useful as fillers. Also, as described in the disclosure of Canadian application No. 2,009,595, reinforcing fibers which will expand relative to the matrix mixture enhance the capability of processing the preform at ambient pressure.
B

fizz t The present invention has been described in connection with typical, though not limiting, examples and embodiments, and their related data. However, those skilled in the art will readily recognize that the present invention is capable of a variety of modifications and variations within the scope of the appended claims.

Claims

1. A method of making a fiber reinforced composite member having controlled porosity in its matrix comprising the steps of:
making a polymer composite member by a method comprising the steps of:
providing a polymer substance which transforms upon heating in an oxidizing atmosphere to yield a ceramic phase, ceramic particles, and a vehicle compatible with the polymer substance and the ceramic particles;
mixing together the polymer substance, the ceramic particles and the vehicle into a matrix mixture slurry in which the polymer substance and ceramic particles are substantially uniformly distributed;
providing a plurality of oxidation stable reinforcing fibers;
interspersing the matrix mixture slurry about the fibers to provide a prepreg element; and molding at least one prepreg element into a polymer composite member at a first elevated temperature; and heating the polymer composite member in an oxidizing atmosphere at a second processing temperature to transform the polymer substance to yield a substantially crystalline ceramic phase which bonds ceramic particles from the slurry into a ceramic matrix about the fibers.

2. The method of Claim 1 in which:
the matrix mixture slurry comprises, by weight:
a) vehicle, as an organic liquid, in the range from 20 percent to 30 percent of the slurry;
b) ceramic particles in the range of 40 percent to 90 percent of the slurry; and c) polymer substance in the range of 10 percent to 40 percent of the slurry; and the reinforcing fibers are from 10 to 50 percent by volume of the composite member.

3. The method of Claim 2 in which the polymer substance is comprised of a silicone resin.

4. The method of Claim 3 in which the silicone resin is comprised of a plurality of siloxane groups.

5. The method of Claim 2 in which the polymer substance is comprised of a silicone resin and silicon-free resin.

6. The method of Claim 2 in which the ceramic phase produced by transformation of the polymer substance is substantially silica.

7. The method of Claim 2 in which the ceramic particles are comprised of material selected from the group consisting of oxides of A1, Si, Y, Zr, compounds therebetween, and mixtures and combinations thereof.

8. The method of Claim 2 in which the reinforcing fibers are ceramic fibers.

9. The method of Claim 1, including the additional step of drying the prepreg element to remove substantially all of the vehicle before the prepreg element is molded.

10. The method of Claim 1, in which the amount of porosity in the matrix, by volume thereof, is from 5 to 30 percent.

11. The method of Claim 1 in which the oxidizing atmosphere is air.

12. The method of Claim 1 in which the second processing temperature is in the range of 600°C to 1000°C.

13. The method of Claim 1 in which the prepreg element is provided in the form of a prepreg ply made by a method comprising the steps of:
providing the plurality of fibers in the form of a ply; and interspersing the matrix mixture about the fibers in the ply.

14. The method of Claim 13 in which the prepreg element is provided in the form of a plurality of prepreg plies disposed in predetermined positions.

15. The method of Claim 1 for making the composite member in a higher density in which:

after heating the polymer composite member in an oxidizing atmosphere to transform the polymer substance to yield a ceramic phase, the composite member is exposed to a ceramic infiltrant precursor which infiltrates open structure in the member; and thereafter the infiltrated member is heated in an oxidizing atmosphere to transform the infiltrated ceramic infiltrant precursor to yield a ceramic phase.

16. The method of Claim 1 in which:
the matrix mixture slurry further includes a particulate inorganic filler which exhibits net expansion relative to the ceramic particles when heated at the second processing temperature; and the proportion of the inorganic filler in the matrix mixture is selected so that expansion of the filler counteracts, to a preselected extent, shrinkage created in the preform during heating at the second processing temperature.

17. The method of Claim 16 in which the particulate inorganic filler is selected from the group consisting of pyrophyllite, wollastonite, mica, talc, kyanite and montmorillonite.

18. The method of Claim 17 in which:
the matrix mixture slurry comprises, by weight:
a) vehicle, as an organic liquid, in the range of 20 percent to 30 percent of the slurry;
b) ceramic particles in the range of 40 percent to 90 percent of the slurry;
c) polymer substance in the range of 10 percent to 40 percent of the slurry; and d) inorganic filler in the range of 0 to 50 percent of the slurry; and the reinforcing fibers are from 10 to 50 percent by volume of the composite member.

19. The method of Claim 18 in which, by weight;
a) the ceramic particles are in the range of 50 percent to 93 percent of said sum; and b) the inorganic filler is in the range of 7 percent to 50 percent, based on the total weight of ceramic particles and inorganic filler.

20. A fiber reinforced composite member having environmental resistance comprising:
a plurality of oxidation stable reinforcing fibers;
a ceramic matrix comprising ceramic particles interspersed about the reinforcing fibers;
a ceramic phase bonding together the ceramic particles and the reinforcing fibers; and controlled porosity distributed throughout the ceramic matrix, wherein the ceramic phase is formed by heating in an oxidizing atmosphere a polymer composite member comprising the reinforcing fibers, the ceramic particles and a polymer substance interspersed about the ceramic particles and the reinforcing fibers, so that the polymer substance is transformed to yield the ceramic phase.

21. The member of Claim 20 in which, by volume, the reinforcing fibers comprise from 10 percent to 50 percent of the member.

22. The member of Claim 20 in which, by volume, the porosity comprises from 5 percent to 30 percent of the matrix.

23. The member of Claim 20 in which the reinforcing fibers are ceramic, thereby defining a ceramic matrix, ceramic fiber reinforced, composite member.

24. The member of Claim 20 which includes in the ceramic matrix a filler of an inorganic material having a lathy-type crystal shape.

25. The member of Claim 20 in which by weight:
the ceramic particles are in the range of 7 percent to 50 percent of the sum of ceramic particles and ceramic bonding phase;
the ceramic bonding phase is in the range of 1 percent to 20 percent of said sum; and the reinforcing fibers are in the range of 10 percent to 50 percent by volume of the member.

26. The member of Claim 25 in which a filler of an inorganic material having a lathy-type crystal shape is included in the range of 7 percent to 50 percent of the sum of ceramic particles, ceramic bonding phase and filler.

27. A fiber reinforced composite member comprising a plurality of plies molded at a first elevated temperature and pressure into a predetermined shape, each ply further comprising:
a plurality of oxidation stable reinforcing fibers in the form of a fabric;
a ceramic matrix comprising ceramic particles interspersed about the reinforcing fibers; and a ceramic bonding phase bonding together the ceramic particles and the reinforcing fibers, wherein the ceramic bonding phase is formed by heating in an oxidizing atmosphere to a second elevated temperature a polymer composite member comprising the reinforcing fibers, the ceramic particles and a polymer substance as hereinbefore defined previously interspersed about the ceramic particles and reinforcing fibers, so that the polymer substance is transferred to yield the ceramic bonding phase.

28. The member of Claim 27 in which the fiber fabric is from 10 percent to 50 percent by volume of the member.

29. The member of Claim 27 in which reinforcing fibers in fabric form are ceramic, thereby defining a ceramic matrix, ceramic fiber reinforced composite member.

30. The member of Claim 27 which includes in the ceramic matrix a filler of an inorganic material having a lathy-type crystal shape.

31. The member of Claim 27 in which, by weight:
the ceramic particles are in the range of 7 percent to 50 percent of the sum of ceramic particles and ceramic bonding phase;
the ceramic bonding phase is in the range of 1 percent to 20 percent of said sum; and the reinforcing fibers in the form of a fabric axe in the range of 10 percent to 50 percent by volume of the member.

32. The member of Claim 31 further including a filler of an inorganic material having a lathy-type crystal shape in the range of 7 percent to 50 percent of the sum ceramic particles, ceramic bonding phase and filler.

33. A polymer matrix composite member comprising:
a matrix of a polymer substance which transforms upon heating in an oxidizing atmosphere to yield a ceramic phase;
a plurality of oxidation stable reinforcing fibers distributed in predetermined positions within the matrix;
ceramic particles uniformly distributed throughout the matrix; and the ceramic phase bonding together the ceramic particles and the reinforcing fibers.

34. The member of Claim 33 in which the polymer substance comprises a silicone resin.

35. A fiber reinforced composite member when produced by a method as claimed in any one of Claims 1 to 19 and 35.