KR20010003809A - Silicon-doped boron nitride coated fibers in silicon melt infiltrated composites - Google Patents

Abstract

PURPOSE: A silicon molten impregnated complex including fibers coated with a silicon-doped boron nitride is provided to have an enhanced anti-oxidation property in anhydride or hydride conditions. CONSTITUTION: First, a pre former including a mixture of matrix components containing particles selected from a group consisting of fibrous material coated with a silicon-doped boron nitride film, carbon, silicon carbide and blend thereof is selected. Then, high dense silicon-silicon carbide matrix complex is prepared by implementing the pre former with at least molten silicon. Therefore, the tensile strength of the silicon-silicon carbide matrix complex reinforced with fibrous material is increased. The fibrous material is selected from a fiber, a filament, a strand, a bundle, a whisker, a cloth, a pelt and a combination thereof.

Description

Silicon-doped boron nitride coated fibers in silicon melt infiltrated composites}

The U.S. Government may have certain rights in the invention under a government agreement with the Department of Energy (DOE), agreement number DEFC0292CE41000.

The present invention relates to high density ceramic matrix composites suitable for high temperature use in aqueous environments. The present invention also relates to silicon-doped boron nitride coated fibers in silicon melt impregnated ceramic matrix composites. More specifically, the present invention relates to a method for protecting ceramic fibers with a silicon-doped boron nitride coating in a silicon-silicon carbide ceramic matrix exposed to a wet, aqueous environment.

There is a need for a material having a structure for operating at high temperatures today. Most ceramic materials have long term stability against creep and chemical penetration experienced at temperatures above the operating range in conventional alloys. However, due to the low bursting energy of the ceramic, the ceramic is susceptible to destruction. As the cracks spread, very minor defects begin, which can develop and break through the ceramic components. Therefore, methods for improving the crack toughness, that is, the property of imparting toughness to ceramics without losing its excellent properties, continue to be pursued.

One way to impart toughness to the ceramic is to have a fiber-reinforced ceramic composite. Fiber-reinforced ceramics are commonly referred to as so-called ceramic matrix composites, or ceramic matrix composites (CMCs). Fiber-reinforced ceramic composites have higher temperature resistance and lighter weight than conventional superalloys used. As a result, its use can be considered in aircraft and generator systems. When used in this potent application, fiber-reinforced ceramic composites are introduced into harsh thermal and mechanical conditions. Although fiber-reinforced composites are designed to be used under matrix crack stresses, it is hard to avoid mechanically accidental overstress, either thermally or as a result of thermal impacts as a result of thermal shock.

Cracks occur in the fiber-reinforced composite matrix when the composite is introduced at a stress higher than the matrix crack stress. These cracks are still open even though the working stress continues to decrease to values below the matrix crack stress, exposing the coating and / or fibers to the environment. As a result, the presence of cracks in the fiber-reinforced composite matrix, in particular if the cracks pass through the thickness of the composite, affects the performance and durability of the composite.

Such cracks can act as a rapid route for transferring the environmental gas phase into the composite. Oxygen diffuses very quickly through extremely small cracks in the matrix. The fibers and any coatings that may be present on the fibers may be oxidized by oxygen diffusing through the cracks. Oxygen reacts with the fibrous coating and ultimately with the fibers, causing a local bond between the fibers and the matrix. At this bonded position, fiber breakdown is initiated as a result of stress concentration and fiber degradation. The same result occurs when the fiber ends are exposed. This process continues until the remaining fibers cannot carry the load and the composite breaks at a stress somewhat less than the final strength. The composite also loses its toughness aspect because of the strong bond between the fiber and the matrix. Thus, a serious problem of limiting the lifetime of ceramic matrix composites is that the fibers are oxidized on the basis of cracks after oxidation of the fibrous coating.

In general, carbon or boron nitride has been the material of choice for fiber coatings used in ceramic matrix composites for high temperature use. Such materials protect the fibers during composite processing and also provide weak fibers at the matrix boundaries, which increase the toughness of the composite by fiber pullout or fiber-matrix solution. However, carbon is oxidized in all oxygen-containing environments and boron nitride is easily oxidized and continuously volatilized at high temperatures, particularly in the high partial pressure atmosphere of water vapor, for example in fuel combustion products as a gas turbine engine. Oxidation and volatilization of the boron nitride film lead to bonding of the fibers and the matrix, thereby obtaining a brittle complex. Thus, it is desirable to have a fiber coating that exhibits a fiber-matrix solution, while being highly resistant to oxidation and high water environments.

Ceramic matrix composites of interest for engine applications focus on carbon-carbon composites and silicon carbide composites having a carbon matrix comprising carbon fibers, wherein the fibers are typically coated. An important limitation in the use of carbonized structural materials is that they are easily oxidized in high temperature, oxidizing atmospheres. Oxygen penetrates the surface of the carbonized material and seeps into the pores of the invariably existing gaps, oxidizing the surface of the pores and continuing to weaken the material. Oxidizing atmospheres reaching the fibers, carbon and graphite fibers severely degrade the composite structure. The approach to overcoming the oxidation of carbon-carbon composites has been to use glass-forming agents as oxidation inhibitors. The glass-forming agent is used as a coating surrounding the outer carbon-carbon composite. Although much progress has been made in carbon-carbon composites, there is still a need for improved ceramic composites with high temperature and mechanical capabilities.

Silicon carbide-silicon carbide composites are silicon carbide matrices comprising silicon carbide fibers. The method for producing the silicon carbide composite is to use chemical vapor infiltration. Here, the fabric layer made of fibrous material is coated with boron nitride by chemical vapor infiltration. It takes about one day to deposit about 0.5 μm of the coating material. The fabric layer is then coated with silicon carbide by chemical vapor infiltration for about 10-20 days. The approach to overcome oxidation of silicon carbide composites has been to use oxygen-erasing sealant-forming regions in intimate contact with ceramic fibers and solution bonding layers as disclosed in US Pat. No. 5,094,901.

There is a need for an improved ceramic matrix composite that successfully protects reinforcing fibers from oxidation and hydrous environments. There is still a need to produce ceramic matrix composites that take less time than chemical vapor infiltration methods for silicon carbide-silicon carbide composites and carbon-carbon composites. There is still a need to produce silicon-silicon carbide matrix composites and articles made from molten silicon infiltrates that can protect in anhydrous and hydrous environments at high temperatures greater than about 600 ° C.

This need has been met by the development of fiber-reinforced silicon-silicon carbide matrix composites having improved oxidation resistance in anhydrous or hydrous environments and at elevated temperatures. The present invention provides a method for protecting the fiber-matrix boundaries in a silicon-silicon carbide matrix by coating the fibers with silicon-doped boron nitride. The fibers are further protected by the addition of silicon in the boron nitride film forming the glassy material. The decisive factor is the ratio of silicon to boron in the coating, such as atomic ratio or weight ratio, which is necessary to maintain the toughness of the composite while improving the oxidation resistance of the composite, especially in an aqueous environment.

An advantage of the present invention is to protect the composite properties when the silicon-silicon carbide matrix composite is introduced at a stress higher than the matrix crack stress. Since the silicon-doped boron nitride coating protects the underlying fiber, the toughness of the overall silicon-silicon carbide composite is maintained in oxidative and hydrous environments.

In short, one aspect of the present invention

Selecting a preform containing a fibrous material having at least one silicon-doped boron nitride film and a mixture comprising fibers coated with a matrix constituent material comprising particles selected from the group consisting of carbon, silicon carbide and mixtures thereof step;

A method for increasing the toughness of a fiber-reinforced silicon-silicon carbide matrix composite, comprising infiltrating at least molten silicon into the preform to produce a high density silicon-silicon carbide matrix composite with reinforcing fibers.

In another aspect of the invention, there is provided a fiber-reinforced silicon-silicon carbide matrix composite with improved oxidation and volatilization resistance, comprising silicon-doped boron nitride coated fibers in a silicon-silicon carbide matrix.

Another aspect of the invention includes a product for use in an engine, wherein the product consists of a ceramic matrix composite having an elemental silicon phase, a silicon carbide phase, and a coated fibrous material, wherein the fibrous material is at least one Silicon-doped boron nitride film.

The reinforced-fiber silicon-silicon carbide matrix composites of the present invention comprise a high density matrix comprising an elemental silicon phase and a silicon carbide phase, and a reinforced silicon carbide-containing fiber having at least one silicon-doped boron nitride film, It has thermal and chemical and mechanical stability in aqueous environments at processing temperatures of 1420 ° C. and above.

FIG. 1 schematically shows the solution properties and environmental stability aspects with silicon content in silicon-doped boron nitride type fiber coatings.

FIG. 2 is a graph showing the tensile stress-strain mode of silicon melt impregnated ceramic matrix composites reinforced with silicon carbide fibers coated with silicon-doped boron nitride containing 15 wt% silicon.

FIG. 3 is a graph showing coating material oxidation / volatility as a function of percent by weight of silicon in the coating for a 24-hour oxidation treatment in an atmosphere containing 10% oxygen and 90% water.

FIG. 4 is a graph showing the fiber coating aspect in the composite for different amounts of silicon doping, showing the final strength (ksi) and the percent strain at the final strength relative to the silicon weight percent.

The present invention relates to a process for producing silicon carbide-containing silicon carbide-containing fiber reinforced high density silicon-silicon carbide matrix composites and articles obtained by such methods, wherein the fibers are coated with one or more silicon-doped boron nitride films do. The matrix material obtained in the present invention is molten silicon impregnated silicon-silicon carbide with clean shape processing capability and ease of manufacture.

The present invention generally produces a high density ceramic matrix composite having a porosity of less than about 20 volume percent. The composite of the present invention comprises at least one silicon-doped boron nitride whose components comprise about 5% by volume of the composite and have a weight ratio of silicon to the total weight of the (B (Si) N) coating between about 5 and about 40% by weight. Film (B (Si) N); And

And a composite matrix having at least about 1% by volume substantially on elemental silicon comprising silicon. The elemental silicon phase substantially comprises silicon and may include other dissolved elements such as boron. By the present invention, it was further found that the coated fibers provide oxidative protection and toughness composites in high temperature anhydrous or hydrous environments.

Another embodiment of the invention

Depositing at least one silicon-doped boron nitride coating on the silicon carbide-containing fibrous material, wherein the coating substantially covers the outer surface of the fibrous material;

Mixing the particles selected from the group consisting of carbon, silicon carbide, and mixtures thereof with the fibrous material;

Molding the mixture into a preform;

Infiltrating the preform with a wetting agent comprising substantially molten silicon; And

Cooling the infiltrated preform to produce a silicon-silicon carbide matrix composite,

Wherein the weight ratio of silicon to the total weight of the B (Si) N coating is from about 5 to about 40 weight percent, provided by a method that can make the silicon-silicon carbide matrix composites with improved properties in oxidative and wet environments .

As used herein, "carbon" refers to graphite, particles, flakes, whiskers or amorphous fibers, monocrystalline, or polycrystalline carbon, carbonated plant fibers, lamp black, finely divided coal, charcoal And elemental carbon in all forms, including carbonized polymer fibers or felts such as rayon, polyacrylonitrile, and polyacetylene. "Fibrous material" includes fibers, filaments, strands, bundles, whiskers, fabrics, felts or combinations thereof. The fibers are continuous or discontinuous. Silicon carbide-containing fibers or fibrous materials include conventional commercially available materials, wherein silicon carbide surrounds the core or substrate, or silicon carbide is the core or support. Other core materials that silicon carbide can wrap include carbon and tungsten. The fibrous material may be amorphous, crystalline or mixtures thereof. The crystalline material may be monocrystalline or polycrystalline. Examples of silicon carbide-containing fibrous materials are silicon carbide, Si-C-O, Si-C-O-N, Si-C-B and Si-C-O-metals, with varying metal components, but titanium, zirconium or boron are common. There is a method in the art using organic precursors for producing silicon carbide-containing fibers, where such fibers can introduce various elements into the fibers. Examples of these fibers are Nicalon (registered trademark), Hi-Nicalon (registered trademark) and Hi-needle sold by Nippon Carbon Company, Ltd., Yokohama, Japan. Hilonical S (registered trademark); Tyranno® fiber, commercially available from Ube Industries, Ltd., Ube City, Yamaguchi, Japan; And Silamic® fiber, which is a registered trademark of Dow Corning Corporation, Midland, Mich., USA.

In carrying out the process of the invention, a coating system is deposited on the fibrous material, which keeps at least no part of the fibrous material exposed, and preferably covers the entire material. The coating system may contain one coating or a series of coatings. If only one coating is present, it is a silicon-doped boron nitride (B (Si) N) coating or a gradient coating of boron nitride to silicon-doped boron nitride. The coating should be continuous and have no significant porosity, preferably free of pores and of substantial uniformity. The silicon-containing compound in the coating is present in significant amounts such that the weight ratio of silicon to the total weight of the B (Si) N coating is from about 5 to about 40 weight percent. The preferred range is about 10 to 25% by weight and the most preferred amount is about 11 to 19% by weight.

The B (Si) N coating can be considered chemically as an atomic mixture of boron nitride (BN) and silicon nitride (Si ₃ N ₄ ), which can be amorphous or crystalline in nature. Different amounts of doping correspond to different ratios of BN to Si ₃ N ₄ , and the full range of B (Si) N compositions is considered from pure BN to pure Si ₃ N ₄ . At one extreme in this range, pure BN imparts good fiber-matrix peptizing properties for ceramic matrix composites, but inferior oxidation / volatile volatility. At another extreme, pure Si ₃ N ₄ has very good oxidation / volatility resistance but does not provide a weak fiber-matrix boundary for fiber peptising during composite breakdown. In the intermediate composition, there is a range of silicon content in which B (Si) N provides good fiber-matrix peptizing properties and has good environmental stability. This is represented schematically in FIG. 1.

The weight percent silicon in the B (Si) N coating is in the range of about 5 to about 40 weight percent, preferably about 10 to about 25 weight percent, most preferably about 11 to about 19 weight percent silicon.

Further, in addition to one or more B (Si) N films, other components containing B (Si) N (eg, multilayers of B (Si) N and initial and / or intermediate carbon layers), or B (Si) Subsequent to the initial layer of N, a film of silicon carbide or Si ₃ N ₄ , a silicon-wettable film additional layer on B (Si) N, such as carbon, or a combination thereof may be used.

Further examples of coating systems used in any combination with B (Si) N coatings on fibrous or fibrous materials include boron nitride, silicon carbide; Boron nitride, silicon nitride; Boron nitride, carbon, silicon nitride and the like. Examples of additional coatings on fibrous materials that satisfy the present invention include nitrides, borides, carbides, oxides, silicates, or other similar ceramic refractory materials. Representative examples of ceramic carbide films are carbides of boron, chromium, hafnium, niobium, silicon, tantalum, titanium, vanadium, zirconium and mixtures thereof. Representative examples of ceramic nitrides useful in the process of the present invention are nitrides of hafnium, niobium, silicon, tantalum, titanium, vanadium, zirconium or mixtures thereof. Examples of ceramic borides are borides of hafnium, niobium, tantalum, titanium, vanadium, zirconium and mixtures thereof. Examples of oxide films are oxides of aluminum, yttrium, titanium, zirconium, beryllium, silicon and noble metals. The thickness of the coating may be about 0.3 to 5 μm.

As discussed, the fibrous material may have one or more coatings. Additional protective films are wettable with silicon and are from about 500 mm 3 to about 3 μm. Representative examples of useful silicon-wettable materials are elemental carbon, metal carbide, metal coatings, which later react with molten silicon to form metal nitrides such as silicon oxides, silicon nitrides, and metal silicates. Elemental carbon is usually deposited on the underlying coating in the form of a pyrolytic carbon. Generally, the metal carbide is a carbide of silicon, tantalum, titanium, or tungsten. Generally, the metal silicate is a silicate of chromium, molybdenum, tantalum, titanium, tungsten and zirconium. The metal which subsequently reacts with the molten silicon to form the silicon oxide has a melting point higher than that of silicon and is preferably higher than about 1450 ° C. Typically, the metal and its silicate are solid in conventional methods. Representative examples of such metals are chromium, molybdenum, tantalum, titanium and tungsten.

Known techniques can be used to deposit the coating, which is generally deposited using low pressure techniques by chemical vapor deposition.

In this method, the fibers are bundled with tow and coated with a coating or with a combination thereof. The tow is formed into a structure, which is then infiltrated with molten silicon. In this way, boron nitride coatings on the fibers are often used to protect the fibers from penetration by molten silicon or against peptising. A silicon-doped boron nitride film is then added or in place of the undoped boron nitride film. In the present invention, the coating can be gradient from undoped boron nitride to silicon-doped boron nitride coating. Non-gradient coatings are also suitable for use in the present invention.

Another method used to prepare silicon carbide-silicon composites uses fibers in the form of fabrics or three-dimensional structures, which are laminated to the desired shape. The boron nitride film is deposited on the fabric layer by chemical vapor infiltration as mentioned above, and the silicon-doped boron nitride film is then used in addition to or instead of the undoped boron nitride film. Additional coatings of silicon carbide or silicon nitride may be present on the boron nitride coating. In the present invention, the coating can be gradient from undoped boron nitride to silicon-doped boron nitride coating. Non-graded coatings also satisfy the use of the present invention. The structure is then processed into a slurry and melt infiltrated with molten silicon. Molten silicon may contain trace amounts of other materials such as boron and molybdenum.

As described above, the coated fibrous material is admixed with a matrix constituent material comprising one or more carbon or silicon carbides or a mixture of carbon and silicon carbide materials. Other elements or compounds may be added to the mixture to provide different composite properties or structures. The specific composition of the mixture is experimentally determinable and depends largely on the particular composition desired, i.e. the specific properties expected in the composite. However, the mixture can always contain sufficient elemental carbon, or silicon carbide, or a mixture of carbon and silicon carbide to reliably produce the silicon-silicon carbide matrix composite of the present invention. Specifically, the preform should contain sufficient elemental carbon or silicon carbide or a mixture of carbon and silicon carbide, and in general, most or all of them may be provided by the mixture, some of which may be sacrificial on the fibrous material. Provided to react with the molten silicon wetting agent to produce a composite of the present invention containing silicon carbide and silicon. In general, the elemental carbon may be from about 0%, about 10 or 20% by volume to about 100% by volume of the mixture.

The mixture of carbon or silicon carbide or the preform of carbon and silicon carbide may be in powder form and have an average particle size of less than about 50 μm, more preferably less than about 10 μm. The molten silicon that infiltrates the preform consists essentially of silicon, but may also contain elemental boron, which has limited solubility in molten silicon. Silicon wetting agents may also contain boron containing compounds or other elements or compounds.

The mixture in the form of preforms containing carbon or silicon carbide or a mixture of silicon carbide and carbon is wetted with molten silicon wetting agent. In carrying out the process of the invention, the preform is contacted with the silicon wetting agent by means of infiltration. Infiltration means allow silicon infiltration to infiltrate into the preform. US Pat. No. 4,737,328, which is incorporated herein by reference, discloses infiltration techniques. In the process of the present invention, sufficient molten silicon wetting agent is infiltrated into the preform to produce the composite of the present invention. Specifically, the molten silicon wetting agent is fluid and highly reactive with any carbon present in the preform to form silicon carbide. Pockets on silicon are also formed in the matrix.

The period of time required for the infiltrant is experimental and depends largely on the size of the preform and the degree of infiltration required. In general, less than about 60 minutes and often less than about 10 minutes are complete. The resulting infiltrated body is cooled in the atmosphere and there is no damage at this rate.

The composite of the present invention consists of a coated fibrous material and a matrix phase. The matrix phase is dispersed through the coated fibrous material and is generally substantially space filled and commonly interconnected. In general, the coated fibrous material is wholly wrapped by the matrix phase. The matrix phase contains a phase mixture of silicon carbide and silicon. The fibrous material comprises at least about 5%, or at least about 10%, by volume of the composite. The matrix comprises the silicon carbide phase in an amount of about 5 to 95 volume percent of the composite, or in an amount of about 10 to 80 volume percent, or about 20 to 60 volume percent. The matrix may contain the elemental silicon phase at about 1-30% by volume of the composite volume.

The following examples further illustrate the invention and do not limit the invention.

Example

The high-nikalon silicon carbide fiber tow was coated with a 1 μm thick coating of B (Si) N containing about 15% silicon by weight. The coated tow is preimpregnated with a carbon-containing slurry and wound onto a drum to prepare a unidirectional dendritic tape. The slurry (from which the matrix of the composite preform is derived) was subjected to 300 g of zirconia grinding media, 35 g of silicon carbide powder, 15 g of carbon powder, 8 g of polyvinyl butyral resin, 14 g of furfuryl alcohol-derived resin, dispersant 2 g, 40.32 g of toluene and 26.77 g of 4-methyl-2-pentanone were added to a 250 mL volume polyethylene bottle. The mixture was shaken on a paint shaker for 10 minutes to mix the ingredients and then placed on a ball mill for 1 hour to fully homogenize the mixture. After drying for 2 hours, the tape is cut out of the drum, cut into pieces and placed by hand on a 6-ply composite with 4 plies reinforced in the 0 ° direction and 2 plies reinforced in the 90 ° direction, followed by 120 during a heating press. Lamination at 100 pounds per inch ² for 15 minutes at < RTI ID = 0.0 >

The resulting laminate composite preform was placed in an oven at 120 ° C. overnight to cure the resin in a matrix. Although the binder was incinerated and the silicon melt infiltration was carried out in one continuous operation, this process can be carried out separately. The composite preform was placed on a carbon fabric wick and supported on a boron-nitride coated graphite plate. Sufficient silicon (Si-5% B alloy) was placed on the wick to fully saturate the wick and fill the preform upon melting. The assembly was then placed in a vacuum furnace containing a carbon electrical resistance heating element and a carbon insulator, and the vacuum furnace was evacuated using a mechanical vacuum pump at 2 Torr to 20 mTorr. The initial heating rate of the vacuum furnace was up to 450 ° at 0.75 ° per minute. Slow heating rates are used to limit the burn rate of the polyvinyl butyral binder and the pyrolysis rate of furfuryl resin. The heating rate is then raised to 450-550 ° C. at 1 ° C. per minute. The vacuum furnace was heated to 1380 ° C. at a rate of 4 ° C. per minute and held at 1380 ° C. for 10 minutes to keep the vacuum furnace temperature at equilibrium. The vacuum furnace was then heated to 1380-1430 ° C. at a rate of 3 ° C. per minute, held at 1430 ° C. for 20 minutes, and then cooled to 1350 ° C. at a rate of 3 ° C. per minute. The vacuum furnace controller is then programmed to cool the vacuum furnace to room temperature at a rate of 5 ° C. per minute, provided that the heat capacity of the vacuum furnace prevents the vacuum furnace from cooling it quickly in practice.

After cooling, the infiltrated composite body was removed from the attached carbon fabric wick and the straightened tensile bar was mechanized from the composite panel using diamond abrasive cutting and grinding. This bar was subjected to a tensile test for failure in an Instron test machine and the strain was measured with a contact elongation strength meter. A typical resulting stress-strain curve is shown in FIG. 2. High strength and high strain after matrix cracking indicate a suitable fiber-matrix solution for fracture.

Figure 3 shows B (Si) N oxidation / volatility (mass loss) as a function of weight percent silicon during 24 hours of oxidation in an atmosphere of 10% oxygen and 90% water. For low amounts of silicon, the volatilization rate is high and then decreases with increasing silicon content below about 15% silicon by weight. The oxidation / volatility rate does not change much, which then indicates that at least 15% by weight of silicon is desirable for maximum resistance to oxidation in the wet atmosphere.

4 shows an embodiment of a fibrous coating in a composite during different amounts of silicon doping. In a pure boron nitride coating (0% silicon), boron nitride is chemically penetrated during the melt infiltration process. The data in FIG. 4 for 0% silicon is for a composite with a pure boron nitride film and an additional protective film of carbon and silicon nitride. All other data are for coatings without additional silicon nitride coatings. The addition of silicon increases the chemical resistance of the coating to molten silicon during composite processing, very good both strength and strain values at about 15% by weight silicon, and very good without additional silicon nitride coating. Above about 20% by weight, the coating no longer provides an easy solution of the fibers and the matrix, and the composite becomes more brittle, accompanied by a decrease in strength and breaking strain.

The present invention makes it possible to produce fiber-reinforced silicon-silicon carbide matrix composites having improved oxidation resistance in anhydrous or hydrous environments and at elevated temperatures.

Claims (28)

Selecting a preform containing a mixture of a fibrous material coated with a silicon-doped boron nitride film and a matrix constituent material comprising particles selected from the group consisting of carbon, silicon carbide and mixtures thereof; And Infiltrating at least molten silicon with the preform to produce a high density silicon-silicon carbide matrix composite reinforced with fibrous material. The method of claim 1, And wherein the fibrous material is selected from the group consisting of fibers, filaments, strands, bundles, whiskers, fabrics, felts, and combinations thereof. The method of claim 2, The fibrous material is a continuous or discontinuous phase. The method of claim 2, Wherein the fibrous material contains silicon carbide, wherein the silicon carbide surrounds the core or substrate, or the silicon carbide is the core or support. The method of claim 1, Silicon-doped boron nitride films with fibrous material, and Boron nitride; carbon; Carbides of boron, chromium, hafnium, niobium, silicon, tantalum, titanium, vanadium, zirconium and mixtures thereof; Nitrides of hafnium, niobium, silicon, tantalum, titanium, vanadium, zirconium and mixtures thereof; Borides of hafnium, niobium, tantalum, titanium, vanadium, zirconium and mixtures thereof; And a further coating selected from the group consisting of oxides of aluminum, yttrium, titanium, zirconium, beryllium, silicon, precious metals and mixtures thereof. The method of claim 5, And wherein the further coating is selected from the group consisting of boron nitride, carbon, silicon carbide, silicon-doped boron nitride, silicon nitride, and mixtures thereof. The method of claim 1, And wherein the silicon-doped boron nitride film contains about 5 to 40 weight percent silicon. The method of claim 7, wherein And wherein the silicon-doped boron nitride film contains about 10 to 25 weight percent silicon. The method of claim 8, Wherein the silicon-doped boron nitride film contains about 11-19 weight percent silicon. The method of claim 1, The carbon in the mixture is elemental carbon, graphite, particles, flakes, whiskers, amorphous fibers, monocrystalline or polycrystalline carbon, carbonated plant fibers, lamp black, finely divided coal, charcoal, carbonized polymer fibers , Felt, rayon, polyacrylonitrile, polyacetylene and mixtures thereof. The method of claim 1, Wherein the silicon-silicon carbide composite has a high density matrix comprising an elemental silicon phase and a silicon carbide phase, and a porosity of less than about 20% by volume. A fiber-reinforced silicon-silicon carbide matrix composite with improved oxidation and volatilization resistance comprising a silicon-doped boron nitride coated fibrous material in a silicon-silicon carbide matrix. The method of claim 12, A composite in which the fibrous material comprises fibers, filaments, strands, bundles, whiskers, fabrics, felts or a combination thereof. The method of claim 13, A composite in which the fibrous material contains silicon carbide, wherein silicon carbide surrounds the core or support, or silicon carbide is the core or support. The method of claim 12, Wherein the silicon-silicon carbide composite has a high density matrix comprising an elemental silicon phase and a silicon carbide phase, and a composite having less than about 20 volume percent porosity. The method of claim 12, The composite wherein the silicon-doped boron nitride film contains about 5 to 40 weight percent silicon. The method of claim 16, The composite wherein the silicon-doped boron nitride film contains about 10 to 25 weight percent silicon. The method of claim 17, The composite wherein the silicon-doped boron nitride film contains about 11 to 19 weight percent silicon. The method of claim 12, Silicon-doped boron nitride films with fibrous material, and Boron nitride; carbon; Carbides of boron, chromium, hafnium, niobium, silicon, tantalum, titanium, vanadium, zirconium and mixtures thereof; Nitrides of hafnium, niobium, silicon, tantalum, titanium, vanadium, zirconium and mixtures thereof; Borides of hafnium, niobium, tantalum, titanium, vanadium, zirconium and mixtures thereof; A composite having an additional coating selected from the group consisting of oxides of aluminum, yttrium, titanium, zirconium, beryllium, silicon, precious metals and mixtures thereof. An article consisting of a ceramic matrix composite comprising an elemental silicon phase, a silicon carbide phase and a coated fibrous material, wherein the fibrous material has at least one silicon-doped boron nitride coating. The method of claim 20, An article for use in an engine, wherein the fibrous material comprises fibers, filaments, strands, bundles, whiskers, fabrics, felts, or a combination thereof. The method of claim 20, An article for use in an engine wherein the fibrous material contains silicon carbide, wherein silicon carbide surrounds the core or support, or wherein silicon carbide is the core or support. The method of claim 20, An article for use in an engine, wherein the composite has a high density matrix and less than about 20 volume percent porosity. The method of claim 20, A product for use in an engine, wherein the silicon-doped boron nitride film contains about 5 to 40 weight percent silicon. The method of claim 24, A product for use in an engine, wherein the silicon-doped boron nitride film contains about 10 to 25 weight percent silicon. The method of claim 25, An article for use in an engine, wherein the silicon-doped nitride film contains about 11-19 weight percent silicon. The method of claim 20, Silicon-doped boron nitride films with fibrous material, and Boron nitride; carbon; Carbides of boron, chromium, hafnium, niobium, silicon, tantalum, titanium, vanadium, zirconium and mixtures thereof; Nitrides of hafnium, niobium, silicon, tantalum, titanium, vanadium, zirconium and mixtures thereof; Borides of hafnium, niobium, tantalum, titanium, vanadium, zirconium and mixtures thereof; A product for use in an engine having an additional coating selected from the group consisting of oxides of aluminum, yttrium, titanium, zirconium, beryllium, silicon, precious metals and mixtures thereof. Depositing at least one silicon-doped boron nitride (B (Si) N) coating on the silicon carbide-containing fibrous material, wherein the coating substantially covers the outer surface of the fibrous material; Mixing the particulate material with the fibrous material comprising infiltrating-promoting particles selected from the group consisting of carbon, silicon carbide and mixtures thereof; Molding the mixture into a preform; Infiltrating the preform with a wetting agent comprising substantially molten silicon; And Cooling the infiltrated preform to produce a silicon-silicon carbide matrix composite, Wherein the weight percent of silicon in the B (Si) N coating is from about 5 to about 40 weight percent, the method of producing a silicon-silicon carbide matrix composite having improved properties in oxidative and wet environments.