GB2230259A

GB2230259A - Fibre reinforced composite member

Info

Publication number: GB2230259A
Application number: GB9001418A
Authority: GB
Inventors: Michael George Harrison; Michael Lee Millard; Andrew Szweda
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1989-04-14
Filing date: 1990-01-22
Publication date: 1990-10-17
Anticipated expiration: 2010-01-22
Also published as: IT9020023A1; FR2645853B1; IT1241114B; CA2012240A1; GB2230259B; JP2991738B2; CA2012240C; GB9001418D0; JPH0365570A; IT9020023A0; DE4012229A1; FR2645853A1

Description

1 1.1 5196L 13DV-9231 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.

This application relates to co-pending and concurrently filed application 6ased an U.S. 341001 entitled "Consolidated Member and Method and Preform for Making."

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, /M! # f 5196L I- 13DV-9231 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.

/M/ 11 5196L 13DV-9231 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 10OCC, well below required ceramic particle sintering temperatures.

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 -W,..1 5196L \I13DV-9231 temperature can be in the range of about 600-10000C. 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.

The present invention will be further described by way of example only with reference to the accompanying drawings in which:

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 4 is a fragmentary, sectional perspective view of the member of Figure 3 disposed in forming die portions.

Fracture resistant, fiber reinforced ceramic matrix composites offer the designers of high temperature components for power. generating engines, A, fl 5196L 13DV-9231 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 matrix 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 Al, Si, Ca, Hf, B, Ti, Y and Zr, and their mixtures and combinations. Such commercially available materials include A1203, Si02, CaO, ZrO2, HfO2, BN, Ti02, 3A1203.2SiO2, Y203 CaO-A1203 and various clays and glass frits. Ceramic particle sizes in the range between about 75 microns to 0.2 micron in diameter 5196L 13DV-9231 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 14000C.

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.

7Y 1 f.

TABLE I CERAMR--71MRSORS CERAMIC PHASE ONE AFTER NAME SOURCE FORM TRANSFORMATION CONDITION vin;-lic polysilane Dow Chemical liquid S102 amorphous dimethyl siloxane Owens Illinois solid S102 amorphous hafnium oxychloride CERAC solid 11f02 crystalline hexahydrate mono aluminum phosphate Calgary liquid Al(P04b crystalline aluminum isopropoxide Fisher solid A1203 amorphous tetra ethyl ortho silicate Fisher liquid Si02 amorphous 5196L 13DV-9231 -B- 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 )'y',L 1.

4- iu 5196L 13DV-9231 -g- 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%.

1 m A r, W, - 5196L 13DV-9231 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 10 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 polysilozane (GE), RTV (GE) and polycarbosilane (Union Carbide). Included as required were dispersants such as glycerol trioleate, marine oi.1, adipate polyester, sodium polyacrylate and phosphate ester. When epoxy resin was used as a binding system with the above preferred precursor and I... 1 5196L ceramic ranges, the epoxy was about 1-10 wt%, in respect to the mixture of precursor and ceramic particles.

13DV-9231 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 11

REINFORCEMENT FIBERS TYPE A. MONOFILAMENTS Sapphire Avco SCS-6 Sigma B. ROVINGS/YARN Nextel 440 Nextel 480 Sumitomo DuPont FP DuPont PRD-166 UBE Nicolon Carbon C. CHOPPED FIBERS/WHISKERS Nextel 440 Saffil CTE X 10-6 per OC 7-9 4.8 4.8 4.4 4.4 8.8 7.0 9.0 3.1 3.1 0 4.4 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 41,1\ 1 i., A. 1.

1 5196L 13DV-9231 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 epoxy was 1-10% of the sum of A1203, 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 was the combination solvent t'richloroethane 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 t C1 /-I'V'0 1 5196L 13DV-9231 the member, and preferably 30-40 voW 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 matrix.

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 - 10000C rather than at the generally much higher sintering temperature used in known methods, for example in the range of about.1300 - 16500C. 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 - 8000C. Such heating results in a ceramic matrix of ceramic particles bonded together through a -1114 1 5196L 13DV-9231 ceramic phase or phases. Generally the matrix has an open porosity 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 0.511 x 61' 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 1, as described, without dispersing the slurry about reinforcing fibers. The material in curve 1 is a monolithic matr ix of ceramic particles, ceramic precursor and epoxy binder which is low in strength and fails catastrophically in abrittle manner.

0 1.1 A r 14--,< v.,, 5196L 13DV-9231 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 1450-15000C, 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 _ r 5196L 13DV-9231 invention, generally about 600- 10000C. 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 compatable 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 providing 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 form.Ing blocks 24, such as of aluminum, as an initial IA A n 11 LX" 5196L 13DV-9231 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 articie 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 example in the range of 150-4000F, 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 10000C in a 'controlled manner to remove binders and plasticizers, and then to a processing temperature at which no degradation of fibers occurs, such as 10000C or above to sinter the preform into a substantially dense ceramic matrix composite article of Figure 2.

Atlf- i,I - 5196L 13DV-9X-.31 -is- The cross referenced, concurrently filed, related application No. C- e. cAO 0 14A -7 - (:;) the disclosure of which hereby is incorporated herein by reference, 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 MINERALOGICAL NAME COMPOSITION LATHY-TYPE CRYSTAL SHAPE Pyrophyllite A1203.4SiO2.H20 laminar Wollastonite CaO-SiO2 bladed/elongated with circular crystals Mica K20.3A1203.6SiO2.2H20 plate-like Talc 3M90.4SiO2.H20 flat flake Montmorillonite (Al,Fe,Mg)02.4SiO2-H20 elongated Kyanite 3A1203.3SiO2 bladedlelongated X i'V7 5196L 13DV-9231 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 example up to about 50 wt % of the sum of ceramic, precursor, optional binder and filler. The proportion is selected so that expansion of the filler counteracts porosity. Such porosity could result from shrinkage of the ceramic particles but primarily occurs at the lower processing temperature from 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 optional binder. Preferred as inorganic filler materials are those shown in the above Table TIT, 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 the incorporated, related application, reinforcing fibers which will expand relative to the matrix mixture enhance the capability of processing the preform at ambient pressure.

C__^/ A11p 5196L 13DV-9231 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.

1 -Y /.

1 Vil- A l?' A' 4-,f v

Claims

1. A method of making a fiber reinforced ceramic matrix composite member, comprising the steps of:

providing a ceramic matrix precursor which transforms upon heating to a ceramic phase, a liquid compatible with the precursor, and ceramic discontinuous material comprising particles; mixing together the ceramic matrix precursor, the liquid and the discontinuous material into a matrix mixture slurry in which the ceramic particles and precursor are substantially uniformly distributed; providing a plurality of oxidation stable reinforcing fibers; interspersing the matrix mixture slurry about the fibers to provide a prepreg preform; heating the preform in an oxidizing atmosphere at a processing temperature at least at a temperature required to transform the precursor to a ceramic phase and less than a temperature which will result in degradation of ceramic in the preform to transform the ceramic matrix precursor to ceramic phase-which bonds ceramic particles from the slurry into a ceramic matrix about the fibers and to provide an environmentally stable, high strength, high resistance to fracture ceramic matrix, fiber reinforced composite member.

2. A method as claimed in claim 1 in which:

the matrix mixture slurry comprises, by weight:

a) ceramic particles in the range of 5196L 13DV-9231 greater than 40,90' up to about 9090' of the sum of ceramic particles and ceramic precursor; and b) ceramic precursor in the range of about 10-4090' of said sum; and the reinforcing fibers are about 10-50 volume of the composite member.

3. A method as claimed in claim 1 or claim 2 in which the reinforcing fibers are ceramic fibers.

4. A method as claimed in any one of the preceding claims in which the prepreg preform is heated in air at a processing temperature in the range of 600-10000C.

5. A method as claimed in any one of the preceding claims in which a binder is provided and is included in the slurry in the range of up to about 20 weight 96) of the sum of ceramic particles, ceramic precursor and binder.

6. A method as claimed in claim 5 in which the matrix mixture slurry comprises, by weight:

70-80,10' of the sum of ceramic particles, ceramic precursor and binder, the ceramic particles being 50-805M, the ceramic precursor being 10-301%, and the binder being 1-20/10' of the sum; and 01 20-30/0 Of the liquid as an organic liquid.

7. A method as claimed in any one of the preceding claims ih which:

the ceramic precursor is material selected 5196L 13DV-9231 1 from organometallics, sol gels, metal salts, and their mixtures; and the ceramic particles include material selected from oxides of Al,Si, Ca, Hf, B, Ti, Hf, Y, Zr and their mixtures and combinations.

8. A method as claimed in any one of the preceding claims in which:

a plurality of fibers are provided in the form of a ply; and the matrix mixture is interspersed about the fibers in the ply to provide a prepreg ply.

9. A method as claimed in claim 8 in which a plurality of prepreg plies are laminated into a prepreg preform prior to heating.

10. A method as claimed in any one of the preceding claims fo making the composite member in a higher density, in which:

after heating the preform in an oxidizing atmosphere to transform the ceramic matrix precursor to 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 into a ceramic phase.

5196L 13DV-9231

11. A method as claimed in any one of the preceding claims in which:

A the matrix mixture slurry includes, in addition to the ceramic particles, a particulate inorganic filler which will exhibit net expansion relative to the ceramic particles when heated at the processing temperature; the proportion of the inorganic filler in the matrix mixture being selected so that expansion of the filler counteracts porosity created in the preform during heating at the processing temperature.

12. A method as claimed in claim 11 in which the matrix mixture slurry includes a binder and comprises, by weight:

a) ceramip particles in the range of greater than 4000' up to about 900/06 of the sum of ceramic particles, ceramic precursor, inorganic binder and filler; b) ceramic precursor in the range of about 10-401/10' of said sum; c) binder in the range of up to about 20,90' of said sum; and d) inorganic filler in the range of up to about 50.00' of said sum.

13. A method as claimed in claim 12 in which, by weight; a) the cermaic particles are in the range of about 50-8T00' of said sum; 1 5196L 13DV-9231 1 b) the ceramic precursor is in the range of about 10-30%' of said sum; c) the binder is in the range of about 1-20/10' of said sum; and d) the inorganic filler is in the range of about 7-50/10' of said sum.

14. A fiber reinforced composite member of improved environmental resistance and an improved combination of high strength and high resistance to fracture, comprising:

a plurality of reinforcing fibers; 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.

15. A member as claimed in claim 14 in which the reinforcing fibers are 10-50 voll' of the member.

/0

16. A member as claimed in claim 14 or claim 15 in which a plurality of plies comprising ceramic bonded ceramic particles and reinforcing fibers are bonded together.

17. A member as claimed in. anyone of claims 14 to 16 in which the reinforcing fibers are ceramic, thereby defining a ceramic matrix, ceramic fiber reinforced composite member.

5196L 13DV-9231

18. A member as claimed in any one of claims 14 to 17 which includes in the ceramic matrix a filler of an inorganic material having a lathy-type crystal shape.

7

19. A member as claimed in any one of claims 14 to 17 in which, the ceramic particles are in the range of 7-50 wt.%) of the sum of ceramic particles and ceramic bonding phase; the ceramic bonding phase is in the range of 1-20 wti'D' of said sum; and the reinforcing fibers are in the range of 10-50 volume 5% of the member.

20. A member as claimed in claim 19 in which a a filler of an inorganic material having a lathy-type crystal shape is included in the range of about 7-50 wt% of the sum of ceramic particles, ceramic bonding phase and filler.

21. A method of making a fiber reinforced ceramic matrix as claimed in claim 1 substantially as hereinbefore described in any one of the examples.

22. A fiber reinforced matrix when produced by a method as claimed in any one of claims 1 to 13 and 21.

23. A fibre reinforced matrix as claimed in claim 14 substantially as hereinbefore described in any one of the examples.

5196L 13DV-9231 P#6 EolboMUmdonWC1R4TP.Purtherooplu=yboobUmedftmThePatantOffice- 5Wes Branch, St Mary Cr&y. Orpin"n. Xent SRS M. brinted by Muluplex techWques lt& St Uny Cray. Kent. Con. 1187