Ceramic matrix composites

Abstract

A method for forming a non-oxide ceramic matrix composite, e.g. SiC / SiC, comprises forming a prepreg composition from fibres of non-oxide material (e.g., silicon carbide) and a non-oxide powder (e.g., silicon carbide). The prepreg composition is consolidated, followed by pressure infiltrating the prepreg with a fluid polymer and cross-linking under pressure to form a pre-ceramic. The pre-ceramic is heat treated to form the non-oxide ceramic matrix composite (CMC). The steps of pressure infiltrating, cross-linking, and heat treating, may be repeated (on the resultant non-oxide CMC) to increase the densification of the CMC. A nuclear fusion reactor may comprise the composite, preferably a breeder blanket comprising the composite.

Description

Field of the Invention

[01] The present disclosure relates to ceramic matrix composites, in particular a method of manufacturing such a composite and potential uses thereof. In particular, the present disclosure is concerning a technique for producing a silicon carbide fibre-reinforced silicon carbide composite (SiC / SiC) and the application of such a composite in components for fusion reactors. Background

[02] SiC / SiC is a type of ceramic matrix composite (CMC) garnering recent interest as an alternative to metal alloys in applications such as gas turbines and nuclear fission cladding. SiC / SiC, and CMCs more generally, are a system of materials that are made up of ceramic fibres or particles that lie in a ceramic matrix phase. Desirable properties of SiC / SiC composites include high thermal, mechanical, and chemical stability while also providing high strength-to-weight ratio.

[03] Existing approaches to manufacturing SiC / SiC are chemical vapour infiltration (CVI), slurry infiltration and hot pressing (HP), and polymer infiltration and pyrolysis (PIP).

[04] CVI produces high-purity SiC, but the resulting composite is very porous (10-20%), negatively impacting performance, and this gets worse as parts become thicker. It is currently not feasible to make parts >1 mm thick without significant internal porosity. The process is also very slow (weeks of continuous CVI required per part), expensive and unable to do complex forms, such as curves, as the raw fibre preform can only be shaped using weaving (flat panels) or braiding (tubes). Moreover, CVI SiC / SiC typically has a fibre-volume ratio of 30-40 vol%, negatively impacting strength.

[05] Slurry infiltration and HP provides a dense product but is limited in geometry because it applies uniaxial loading during hot-pressing. It also requires equipment that is very expensive, that does not scale particularly well and is not readily available at relevant sizes. The application of pressure can also damage the fibres in the composites and can create cracks within the matrix and along interphases. Moreover, the temperatures used during HP are often over the temperature limit of the fibres, causing detrimental grain growth, deformation, and loss of tensile strength.

[06] PIP involves the infiltration of a precursor polymer followed by a heat-treatment to convert the polymer into SiC. During this process, the polymer will undergo considerable volume shrinkage (~65-70%), meaning that multiple PIP cycles are required to densify the composite (typically 8-10) and, thus, is very time-consuming and expensive. The process also has issues around forming complex geometric as the material starts from raw fibre and can only be shaped using weaving (flat panels) or braiding (tubes). The PIP matrix also remains semi-amorphous, even after high-temperature heat-treatments designed to crystallise it, which negatively impacts on the materials high-temperature properties and irradiation resistance.

[07] Hence, an alternative route to the manufacture of SiC / SiC (and similar) composites which are high-density, high-purity, and can be formed to the geometries and wall-thicknesses required by the fusion industry and other sectors is desirable. Summary

[08] The present invention is defined according to the independent claims. Additional features will be appreciated from the dependent claims and the description herein. Any embodiments which are described but which do not fall within the scope of the claims are to be interpreted merely as examples useful for a better understanding of the invention.

[09] The example embodiments have been provided with a view to addressing at least some of the difficulties that are encountered with current approaches to producing ceramic matrix composites such as SiC / SiC, whether those difficulties have been specifically mentioned above or will otherwise be appreciated from the discussion herein.

[10] In one aspect of the invention there is provided a method for forming a non-oxide ceramic matrix composite such as SiC / SiC. The method comprises forming a prepreg composition from fibres of non-oxide material (e.g., silicon carbide) and a non-oxide powder (e.g., silicon carbide), consolidating the prepreg composition, forming a pre-ceramic composition by pressure infiltrating the consolidated prepreg composition with a fluid polymer and cross-linking under pressure, and heat treating the pre-ceramic composition to form the non-oxide ceramic matrix composite (CMC). The steps of pressure infiltrating, cross-linking, and heat treating, may be repeated (on the resultant non-oxide CMC) to increase the densification of the CMC; for example, the steps may be repeated two to three times.

[11] Preparing the prepreg with non-oxide powder (e.g., via an aqueous slurry infiltration) results in fewer densification cycles being required, while cross-linking under pressure results in improved strength while likewise reducing the number of densification cycles required. The pressure applied during the pressure infiltration and cross-linking phase may be about 6 bar, and the temperature from about 200 to 250 degrees C, which yields an energy efficient manufacturing process while achieving low cycles for densification.

[12] In an example, forming the prepreg comprises forming the prepreg with peel and stick properties by adding binder and tackifier additives at the infiltration stage; the additives may be polymers belonging to the alcohol family of organic compounds; for example, at least one of the polymers may be ethylene based. Beneficially the prepreg may be made easier to shape into complex moulds and to stack multiple layers of prepreg in a suitable mould. For example, layers of prepreg material may be stacked between 1 to 6 mm thick, e.g., thicker than 3 mm, without issue following the present techniques. In some examples, a debind step comprising heat treatment may be performed between consolidation and pressure infiltration to remove binders / tackifiers (if present) and, for some ceramics, pre-sinter the composition, while also providing the benefit of opening porous and flow channels ready for the pressure infiltration.

[13] Overall, the example method improves on the existing methods of manufacture of CMCs (such as SiC / SiC) in its ability to produce high-purity CMC which are dense throughout the material, at scale, in complex geometries, and all within a reduced timeframe at reduced cost.

[14] In an example, the method may include coating the non-oxide ceramic matrix with a nonoxide composition such as silicon carbide, which renders the CMC particularly suitable for use in fusion reactor components due to being hermetic to hydrogen. Alternatively, the coating of an environmental barrier coating would make the composite more suited to other applications, such as aerospace.

[15] Suitably, in another aspect of the invention there is provided a nuclear fusion reactor comprising non-oxide ceramic matrix composite formed according to the aforementioned method. In particular, the fusion reactor may comprise a vacuum vessel and a breeder blanket for the vacuum vessel, with the breeder blanket comprising SiC / SiC composite (or another non-oxide ceramic matrix composite) provided with a suitable SiC (or similar) coating.

[16] As used herein, unless otherwise expressly specified, all numbers such as those expressing values, ranges, amounts or percentages may be read as if prefaced by the word “about”, even if the term does not expressly appear. The term “about”, or substantially, when used herein means +1- 5% of the stated value. Also, any numerical range recited herein is intended to include all sub-ranges subsumed therein, and the terms “from” and “to” a pair of values are intended to indicate such values are included in the range. Singular encompasses plural and vice versa. Additionally, although the present invention has been described in terms of “comprising”, the processes, materials, and coating compositions detailed herein may also be described as “consisting essentially of’ or “consisting of’. Brief Description of the Drawings

[17] For a better understanding of the present disclosure reference will now be made by way of example only to the accompanying drawings, in which:

[18] Fig. 1 shows an example method for manufacture of a ceramic matrix composite such as SiC / SiC; and

[19] Fig. 2 shows an example method of storage of a prepreg formed in the method of claim 1;

[20] Fig. 3 shows example microstructure of an SiC / SiC composite;

[21] Fig. 4 shows a zoomed in view of an example matrix of an SiC / SiC composite;

[22] Fig. 5 shows improvements arising from repeat treatments of an example SiC / SiC composite;

[23] Fig. 6 shows an example nuclear fusion reactor Detailed Description

[24] At least some of the following example embodiments provide an improved technique for the production of ceramic matrix composites (CMC) such as silicon carbide silicon carbine (SiC / SiC). The example technique produces composites that are dense through the entire thickness of the material, may be formed in a variety of geometries, and are much more efficient at achieving the desired densification.

[25] Figure 1 shows an example method 100 for forming a non-oxide ceramic matrix composite. That is, a fibre reinforced material formed from any suitable ceramic material which may be categorised as a non-oxide: for example, carbides, borides, nitrides, and silicides. The following will be primarily described with reference to the preferred embodiment of forming an SiC / SiC ceramic matrix composite.

[26] At step 102, the method comprises forming a prepreg composition. The prepreg composition comprises a plurality of fibres of non-oxide material, preferably silicon carbide (e.g. Hi-Nicalon Type S orTyranno SA3 or SA4). Preferably, the fibres may be heat treated to remove any protective sizing and subsequently recoated with an interphase coating (e.g. pyrolytic carbon or boron nitride).

[27] Suitably, forming the prepreg composition may comprise infiltrating the fibres with a slurry. The slurry is preferably aqueous (i.e., a water-based suspension) in order to reduce impact on human health and the environment and to increase the time available for subsequent lay-up of the prepreg. The slurry comprises a non-oxide powder composition, such as SiC, in which the power particles are preferably sub-micron-sized. Suitably these sub-micron powders are less toxic and cheaper to produce than the typical nano-scale powders used in alternative CMC techniques such as slurry infiltration and HP. Other example non-oxide compositions for the powder include zirconium diboride / carbide and hafnium diboride / carbide, optionally with minor additions of tungsten and / or SiC.

[28] The slurry may also comprise at least one kind of binder additive and at least one type of tackifier additive. In a preferred example, each of the binder and tackifier additives are a type of polymer, in particular polymers belonging to the alcohol family of organic compounds (for example, an ethylene based polymer). When infiltrated by a slurry comprising binders and tackifiers, the result is a prepreg with a “stickiness” or “tack” to it. This makes the prepreg prepared in this fashion particularly convenient for later stages of production because the prepreg is flexible and easily applied e.g. to a mould. The stickiness of the prepreg also enables the formation of thicker laminate stacks by inhibiting the individual prepreg layers from sliding during consolidation, often leading to defects, e.g. wrinkles.

[29] Notably the slurry does not comprise any (other) additives which are typically used in CMC manufacturing techniques to enhance later stages of production; e.g., additives required for sintering. This results in a very high purity CMC, as well as removing the need for manufacturing phases based around those additives (e.g., secondary phases during densification).

[30] Figure 2 shows an optional example process where the prepreg is prepared for storage (and later retrieval). That is, Fig. 2 shows an example process which may be taken between steps 102 and 104 (discussed below) in Fig. 1.

[31] Suitably, at step 202, the prepreg composition may be dried and arranged between two pieces of plastic release film. Put another way, each major surface of the prepreg composition may be wrapped in an easy release sealant layer. At step 204, the wrapped prepreg composition may be rolled and frozen (e.g., by storing in a freezer). At step 206, the rolled prepreg may be defrosted and unrolled, and then cut into suitably sized shapes. After cutting, the release film can be “peeled” to expose the “sticky” surfaces of the “peel and stick” prepreg.

[32] Returning to Figure 1, at step 104 the prepreg composition may be suitably shaped, which may be achieved via arrangement of the prepreg onto a suitable mould. Owing to the flexibility of the prepreg composition, the mould may be a flat sheet, comprise a curved geometry, or be a complex array of geometrical features such as flat surfaces, curves, recurves, tubes, cones, etc. Preferably, several layers of prepreg composition are stacked onto the mould based on a desired thickness of the resultant CMC. In particular, for uses in nuclear fusion components, it is desirable to produce CMCs with a thickness between 1 mm and 6 mm, for example about 3 mm. By way of example, for a SiC / SiC composite, assuming a 50% fibre volume fraction of the prepreg, then about 12 layers may be applied to the mould to achieve an approximately 3 mm thick composite.

[33] It will however be appreciated that this is but one example of shaping the prepreg. In another example, the prepreg may be shaped directly during the prepreg formation phase (at least in simply geometries such as flat sheets).

[34] At step 106, the shaped prepreg is consolidated (i.e., compacted), for example in an autoclave, as will be familiar to those in the art. In the present technique, consolidation may be performed by applying a pressure up to about 10 bar. Furthermore, in the present techniques consolidation may be performed at temperatures up to about 200 degrees C (centigrade). As will be familiar to those in the art, consolidation process is designed to remove macro-pores from the prepreg composition, leaving behind only micro-pore channels that can be filled later in the process.

[35] After consolidation, the consolidated prepreg may be optionally heat treated to remove polymers (i.e., binders and tackifiers) that are still left over from the slurry phase, as well as any impurities such as oxides, and to pre-sinter the non-oxide powders in the prepreg composition. The heat treatment also opens up porous and flow channels in the consolidated prepreg.

[36] This step may only be desirable however for certain non-oxide materials. For example, the step is not desirable ceramics which do not sinter; examples of such ceramics are hafnium carbide, or boride ceramics. In the example of producing a SiC / SiC composite, the consolidated prepreg may be heat treated to about 1650 degrees C to about 1850 degrees C. At this stage of production a SiC / SiC composite may be at approximately 65% to 70% of the ultimate desired density. For ceramics which do not pre-sinter, a heat treatment from about 300 degrees C to 500 degrees C may be appropriate.

[37] At step 108, the consolidated (and optionally heat treated) prepreg may be pressure infiltrated by a fluid polymer (for example, polycarbosilane and its derivations, such as allylhydridopolycarbosilane, or a phenolic resin) and cross linked (i.e., solidified) under pressure in order to form a pre-ceramic composition (i.e., above atmospheric pressure). Agents may be mixed into the fluid polymer prior to pressure infiltration in order to accelerate and / or increase cross-linking. As will be appreciated by those in the art, this process densifies the composition by forcing liquid polymer into the voids around the consolidated powder particles, thereby forming a network of non-oxide material (e.g., SiC) which bonds the particles together, thereby providing strength to the resultant CMC. Applying pressure during the cross-linking allows higher densities to be achieved in the resultant CMC.

[38] In an example, the fluid polymer may be pre-heated to reduce its viscosity priorto pressure infiltration. In the present examples, the polymer may be heated to about 60 degrees C, and then injected by applying pressure. The pressure is preferably about 6 bar.

[39] It will be appreciated that different pressures may be used based on the degree of preheating etc, however the present example has been found to provide an efficient route to production. It will be appreciated by those in the art that pressure infiltration may also comprise arranging the consolidated prepreg in a mould, or bath, into which is received the fluid polymer ready for infiltration.

[40] In an example, crosslinking may involve placing the polymer infiltrated specimen into a suitable oven and heating from about 200 degrees C to about 250 degrees C while maintaining the pressure from the pressure infiltration step (e.g., about 6 bar). The benefit of step 108 is that it allows the part to be densified more effectively and efficiently, because the non-oxide composite comprises powders and has been pre-consolidated and the use of pressure ensures even infiltration of the polymer, yielding densities >90%.

[41] At step 110, the pre-ceramic which results from the pressure infiltration and cross-linking is heat treated - i.e., pyrolysed - in order to form the non-oxide CMC - e.g., SiC / SiC. Here the heat treating may comprise heating the pre-ceramic / solid polymer material at from about 800 degrees C to about 1100 degrees C. In a preferred example, the preceramic is heated to about 1000 degrees C. At this phase the polymer part of the composition reduces weight by about 25-35% and reduces volume by about 50 to 70%.

[42] In an example, steps 108 and 110 may be repeated in order to further densify the CMC. That is, once a CMC has been produced after step 110, the resultant CMC may be used as the input to step 108, so that the CMC undergoes pressure infiltration by the (same) fluid polymer and cross-linking of that polymer. The pressure infiltrated and cross-linked CMC is then used as the input to step 110 so that is once again heat treated. At this stage steps 108 and 110 have, in essence, been performed twice. In an example, steps 108 and 110 may be performed either 3 or 4 times overall; i.e., the steps 108 and 100 are performed on the CMC two or three times.

[43] At this stage, optionally the CMC may be coated using a non-oxide composition. In an example the coating may be achieved by chemical vapour deposition. Preferably the CMC may be coated with SiC. This is particularly beneficially for intended uses in nuclear fusion reactors, for example in breeder blankets, where the CMC may be exposed to liquid metal / molten salts and needs to be hermetic to avoid hydrogen (namely tritium) escape. It will be appreciated that other industries may not require the CMC to be coated, or may desire the addition of a simple environmentally protective coating.

[44] Figures 3 to 5 show scanning electron microscope images of an example SiC / SiC produced using the above technique. Figure 3 shows the microstructure of an example SiC / SiC demonstrating good infiltration of the powders (particularly in between the bundles of fibres-the small circles). Figure 4, is a zoomed in view of the matrix showing small SiC particles surrounded by a network of polymer-derived SiC. Figure 5 shows the improvement in density of the SiC / SiC composite due to repeating steps 108 and 110, and in comparison to a CVI approach to SiC / SiC. Unlike CVI, the present technique is able to produce composites that are dense through the entire thickness.

[45] Compared to other techniques (not shown), unlike HP the present method is not limited to any specific geometries because pressure is not applied at high-temperatures (>1000°C). This enables the use of an autoclave to form and consolidate more complex composite structures at low temperatures (<200°C). The pressure applied during pressure infiltration is also to the infiltrating polymer and not the part itself. Crosslinking is also done at comparatively low temperatures (e.g., 200-250°C), enabling the use of more complex and lower-cost moulds. Heattreatments at higher temperatures (>800°C) are conducted without pressure in a furnace. Unlike PIP, the present technique pre-fills the fibres with powders (i.e., the prepreg formation), which means that fewer polymer infiltration cycles are needed for densification (e.g., the 3 to 4 shown in Fig. 5) instead of the usual 8-10. Moreover, the negative effects associated with the semi-amorphous state of the final polymer-derived SiC matrix are minimised as most of the matrix composition is made from crystalline powder particles.

[46] Figure 6 shows an example nuclear fusion reactor 600 comprising a non-oxide ceramic matrix composite. The non-oxide ceramic matrix composite may be suitably formed using the method 100 above. In particular the reactor 600 may comprise SiC / SiC ceramic composite.

[47] Here the reactor 600 comprises, inter alia, a vacuum vessel 602, a plurality of first wall modules 604, and a plurality of breeder blanket modules 606. In a preferred example of the reactor 600, the breeder blanket modules may suitably comprise SiC / SiC.

[48] Other examples uses of CMCs may include accident-tolerant and GEN VI fuel cladding and other in-core materials, thruster chamber lining and nozzles in advanced (lightweight) rocket systems, and shrouds, blades and combustion chamber liners for next generation aircraft.

[49] In summary then, example techniques for the manufacture of ceramic matrix composites such as SiC / SiC have been described. The described exemplary embodiments provide for a more efficient and environmentally friendly approach to CMC manufacture, as well as resulting in an improved material.

[50] The CMC described herein may be manufactured industrially. An industrial application of the example embodiments will be clear from the discussion herein.

[51] Although preferred embodiment(s) of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made without departing from the scope of the invention as defined in the claims.

[52] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[53] All of the features disclosed in this specification, and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[54] Each feature disclosed in this specification may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[55] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification, or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A method for forming a non-oxide ceramic matrix composite, comprising:forming a prepreg composition from fibres of non-oxide material and a non-oxide powder;consolidating the prepreg composition;forming a pre-ceramic composition by pressure infiltrating the consolidated prepreg composition with a fluid polymer and cross-linking under pressure;heat treating the pre-ceramic composition to form the non-oxide ceramic matrix composite.

2. The method of claim 1, wherein the fibres of non-oxide material comprise silicon carbide.

3. The method of claim 1 or 2, wherein forming the prepreg comprises infiltrating the fibreswith an aqueous slurry comprising the non-oxide composition.

4. The method of any preceding claim, wherein the powder of non-oxide composition comprises silicon carbide.

5. The method of any of claims 3 or 4, wherein the slurry comprises at least one of a binder additive and a tackifier additive.

6. The method of claim 5, wherein the additives are polymers belonging to the alcohol family of organic compounds.

7. The method of any preceding claim, wherein the pressure infiltration comprises pre-heating the fluid polymer.

8. The method of any preceding claim, wherein the pressure infiltration comprises applying a pressure of up to 6 bar.

9. The method of any preceding claim, wherein the cross-linking comprises heating at about 200 degrees C to about 250 degrees C.

10. The method of any preceding claim, wherein the heat treating comprises heating at about 800 degrees C to about 1100 degrees C.

11. The method of any preceding claim, further comprising, in order, pressure infiltrating with the fluid polymer, cross-linking, and heat treating, the non-oxide ceramic matrix composite.

12. The method of claim 11, further comprising repeating the steps of pressure infiltrating with the fluid polymer, cross-linking, and heat treating two or three times.

13. The method of any preceding claim, further comprising heat treating the prepreg composition to about 1650 degrees C to about 1850 degrees C, between the steps of consolidation and pressure infiltration.

14. The method of any of claims 1 to 12, further comprising heat treating the prepreg composition to about 300 degrees C to about 500 degrees C, between the steps of consolidation and pressure infiltration.

15. The method of any preceding claim, further comprising arranging the prepreg composition onto a mould prior to consolidating.

16. The method of claim 15, wherein arranging the prepreg composition onto a mould comprises stacking a plurality of layers of prepreg composition onto the mould.

17. The method of claim 16, wherein stacking a plurality of layers of prepreg composition onto the mould comprises stacking layers thicker than 3 millimetres.

18. The method of any preceding claim, wherein consolidating the prepreg composition comprises applying a pressure up to about 10 bar to the prepreg composition.

19. The method of any preceding claim, wherein consolidating the prepreg comprises heating the prepreg up to about 200 degrees C.

20. The method of any preceding claim, further comprising coating the non-oxide ceramic matrix.

21. The method of claim 20, wherein the coating comprises a non-oxide composition.

22. The method of claim 21, wherein the coating comprising non-oxide composition comprisessilicon carbide.

23. A nuclear fusion reactor comprising non-oxide ceramic matrix composite formed according to the method of any preceding claim.

24. The nuclear fusion reactor of claim 23, comprising a vacuum vessel and a breeder blanket for the vacuum vessel, the breeder blanket comprising non-oxide ceramic matrix composite formed according to claim 22.03 07 24Amendments to the Claims have been filed as follows:CLAIMS1. A method for forming a non-oxide ceramic matrix composite, comprising:forming a prepreg composition from fibres of non-oxide material and a non-oxide powder;consolidating the prepreg composition;forming a pre-ceramic composition by pressure infiltrating the consolidated prepreg composition with a fluid polymer and cross-linking, wherein the pressure infiltrating and cross linking is performed under positive pressure;heat treating the pre-ceramic composition to form the non-oxide ceramic matrix composite.

2. The method of claim 1, wherein the fibres of non-oxide material comprise silicon carbide.

3. The method of claim 1 or 2, wherein forming the prepreg comprises infiltrating the fibreswith an aqueous slurry comprising the non-oxide powder.

4. The method of any preceding claim, wherein the powder of non-oxide composition comprises silicon carbide.

5. The method of any of claims 3 or 4, wherein the slurry comprises at least one of a binder additive and a tackifier additive.

6. The method of claim 5, wherein the additives are polymers belonging to the alcohol family of organic compounds.

7. The method of any preceding claim, wherein the pressure infiltration comprises pre-heating the fluid polymer.

8. The method of any preceding claim, wherein the pressure infiltration comprises applying a pressure of up to 6 bar.03 07 249. The method of any preceding claim, wherein the cross-linking comprises heating between 200 degrees C and 250 degrees C.

10. The method of any preceding claim, wherein the heat treating comprises heating between 800 degrees C and 1100 degrees C.

11. The method of any preceding claim, further comprising, in order, pressure infiltrating with the fluid polymer, cross-linking, and heat treating, the non-oxide ceramic matrix composite.

12. The method of claim 11, further comprising repeating the steps of pressure infiltrating with the fluid polymer, cross-linking, and heat treating two or three times.

13. The method of any preceding claim, further comprising heat treating the prepreg composition between 1650 degrees C and 1850 degrees C, between the steps of consolidation and pressure infiltration.

14. The method of any of claims 1 to 12, further comprising heat treating the prepreg composition between 300 degrees C and 500 degrees C, between the steps of consolidation and pressure infiltration.

15. The method of any preceding claim, further comprising arranging the prepreg composition onto a mould priorto consolidating.

16. The method of claim 15, wherein arranging the prepreg composition onto a mould comprises stacking a plurality of layers of prepreg composition onto the mould.

17. The method of claim 16, wherein stacking a plurality of layers of prepreg composition onto the mould comprises stacking layers thicker than 3 millimetres.

18. The method of any preceding claim, wherein consolidating the prepreg composition comprises applying a pressure up to 10 bar to the prepreg composition.CM19. The method of any preceding claim, wherein consolidating the prepreg comprises heating the prepreg up to 200 degrees C.

20. The method of any preceding claim, further comprising coating the formed non-oxide ceramic matrix.

21. The method of claim 20, wherein the coating comprises a non-oxide composition.

22. The method of claim 21, wherein the coating comprising non-oxide composition comprisessilicon carbide.

Images