Powder Compositions Including Chopped Coated Silicon Carbide Fibers and Method of Producing or Repairing a Fiber-Reinforced Ceramic Matrix Composite

A method of producing or repairing a fiber-reinforced ceramic matrix composite comprises delivering a powder composition comprising SiC particles and chopped coated SiC fibers into or onto a powder receptacle configured for composite fabrication or repair. After delivering the powder composition into or onto the powder receptacle, the SiC particles are densified to form a SiC matrix reinforced with the chopped coated SiC fibers, thereby producing or repairing a fiber-reinforced ceramic matrix composite.

TECHNICAL FIELD

This disclosure relates generally to ceramic matrix composites and more particularly to a method of producing or repairing a fiber-reinforced ceramic matrix composite.

BACKGROUND

Gas turbine engines include a compressor, combustor and turbine in flow series along a common shaft. Compressed air from the compressor is mixed with fuel in the combustor to generate hot combustion gases that rotate the turbine blades and drive the compressor. Improvements in the thrust and efficiency of gas turbine engines are linked to increasing turbine entry temperatures, which places a heavy burden on turbine engine components. Ceramic matrix composites (CMCs), which include continuous ceramic fibers embedded in a ceramic matrix, exhibit a combination of properties that make them promising candidates for gas turbine engine components and other industrial applications that demand excellent thermal and mechanical properties along with low weight. A ceramic matrix composite that includes a silicon carbide (SiC) matrix reinforced with continuous SiC fibers may be referred to as a fiber-reinforced ceramic matrix composite, or more particularly as a SiC/SiC composite.

DETAILED DESCRIPTION

Described herein are novel powder and slurry compositions and a method of producing or repairing a fiber-reinforced ceramic matrix composite utilizing such compositions. The fiber-reinforced ceramic matrix composite may form part or all of a component of a gas turbine engine, such as a blade, vane, combustor liner or seal segment.

Referring toFIG.1, the powder composition102comprises silicon carbide (SiC) particles104and chopped coated SiC fibers106, that is, chopped SiC fibers108having a surface coating110. For use in making or repairing a composite, the powder composition may comprise a mixture (preferably a homogeneous mixture) of the SiC particles104and the chopped coated SiC fibers106. Such a mixture may be formed by manual mixing or sonication of the powder composition102.

Importantly, the chopped coated SiC fibers106may be produced from continuous SiC fibers208that include an interface or interphase coating210. Such coated continuous SiC fibers206, as shown inFIG.2, are widely used as reinforcements in ceramic matrix composites. Excess or scrap coated continuous SiC fibers206not utilized in ceramic matrix composite production may be chopped up, as illustrated inFIG.3, to form the chopped coated SiC fibers106. The chopping may be carried out with a diamond blade or wire, for example, or by laser or water jet machining, shearing, tumbling, or pulverization via volume grinding. In some examples, the chopped coated SiC fibers106may be produced from other sources of coated continuous SiC fibers206. Typically, the interface or interphase coating210on the continuous SiC fibers206, and thus the surface coating110on the chopped coated SiC fibers106, comprises boron nitride, silicon-doped boron nitride, and/or pyrolytic carbon. Generally speaking, carbide, nitride, oxide and/or carbon coatings may be suitable for the interface and surface coatings210,110. Because the coating210is applied to the fibers206prior to chopping, ends of each chopped coated SiC fiber106may be uncoated, as illustrated inFIG.3. That is, the surface coating110may be present only on the cylindrical portion of the fibers108extending between the ends.

The chopped coated SiC fibers106may account for from 1 vol. % to 99 vol. %, e.g., at least 1 vol. %, at least 20 vol. %, or at least 40 vol. %, and/or up to 99 vol. %, up to 75 vol. %, or up to 50 vol. %, of the powder composition102. In some examples, the powder composition102may further include a small amount of silicon particles. For example, the powder composition102may include the silicon particles at a concentration from 1 vol. % to 10 vol. %. Also or alternatively, the powder composition102may include other particulate additives, such as carbon particles. The SiC particles104may account for the balance, e.g., from 1 vol. % to 99 vol. % of the powder composition102. More specifically, the SiC particles104may account for at least 1 vol. %, at least 40 vol. %, or at least 60 vol. %, and/or up to 99 vol. %, up to 80 vol. %, up to 50 vol. %, or up to 30 vol. % of the powder composition102.

The chopped coated SiC fibers106may have a nominal length in a range from about 1 micron to about 100 microns, and more typically from about 10 microns to about 30 microns. Preferably, for some applications, the chopped coated SiC fibers106may have a length comparable to a linear dimension (e.g., diameter or width) of the SiC particles104. Generally speaking, the SiC particles104may have a linear dimension in a range from about 1 micron to about 100 microns, and more typically from about 10 microns to about 30 microns. Also or alternatively, the chopped coated SiC fibers106may have a length comparable to the pore size (e.g., the spacing between adjacent fiber tows) of a fiber preform comprising continuous SiC fibers, since in some examples the chopped coated SiC fibers106may be used for slurry infiltration of such fiber preforms, as described below.

The surface coating110may have a thickness determined by the coating method used to form the interface or interphase coating210on the continuous SiC fibers208. Normally, the coating method is chemical vapor deposition (CVD) or chemical vapor infiltration (CVI), which may entail delivering gaseous reactants into a heated process chamber that contains the continuous SiC fibers, followed by chemical reactions which lead to deposition of the desired coating. In one example, the gaseous reactants may comprise BX3and NH3, where X is selected from the group consisting of F and CI, to produce a coating comprising boron nitride (BN). In another example, the gaseous reactants may comprise boron trichloride (BCl3), ammonia (NH3) and a silicon precursor such as dichlorosilane (H2Cl2Si), trichlorosilane (HCl3Si), silicon tetrachloride (SiCl4), and/or silane (SiH4) to produce a coating comprising silicon-doped boron nitride. In yet another example, the gaseous reactants may comprise methane (CH4), propane (C3H8), and/or propylene (C3H6) to produce a coating comprising pyrolytic carbon. In the process chamber, the gaseous reactants diffuse through interstices between fibers or fiber tows, and reaction products deposit on exposed surfaces of the fibers, such that the interface or interphase coating is formed. CVD or CVI may lead to conformal coatings of uniform thickness in the nano- to microscale range. Consequently, the surface coating110on the chopped coated SiC fibers106typically has a uniform thickness in a range from about 0.1 micron (100 nm) to about 1 micron.

The powder composition102as described in this disclosure may be dispersed in a liquid114to form a slurry112, as indicated inFIG.1. The liquid114may include water and/or may be an aqueous solution. It is also contemplated that the liquid114may comprise an organic solvent. The chopped coated SiC fibers106may account for from 1 vol. % to 99 vol. % of the solids content of the slurry. For example, the chopped coated SiC fibers106may account for at least 1 vol. %, at least 20 vol. %, or at least 40 vol. %, and/or up to 99 vol. %, up to 75 vol. %, or up to 50 vol. % of the solids content of the slurry. The SiC particles104and any other solid-phase constituents, e.g., the silicon particles or carbon particles mentioned above, and/or any other slurry additives, such as a dispersant or surfactant, may account for the remainder of the solids content. In particular, the SiC particles104may account for over 50 vol. % of the solids content of the slurry112. Silicon particles may be present at a concentration from about 1 vol. % to about 10 vol. %, and carbon particles may be present at a concentration from about 1 vol. % to about 10 vol. %. Any other slurry additives may be included individually at a concentration up to about 5 vol. %.

The powder composition102and/or slurry112described above may be used to produce or repair a composite according to the method represented in the flow chart ofFIG.4, which is illustrated according to various examples inFIGS.5A-8C. The method may include delivering400the powder composition102, which includes the SiC particles104and the chopped coated SiC fibers106described above, into or onto a powder receptacle116which is configured for fabrication or repair of a fiber-reinforced ceramic matrix composite. The powder receptacle116may comprise: (1) a fiber preform including continuous silicon carbide fibers; (2) a mold having a predetermined shape; (3) a repair region of the fiber-reinforced ceramic matrix composite; or (4) a substrate. In some examples, to promote flowability and ease of delivery, a slurry112containing the powder composition102(where the SiC particles104and the chopped coated SiC fibers106are dispersed in a liquid114) may be delivered into or onto the powder receptacle116. As will be discussed in more detail below, delivery of the powder composition102into or onto the powder receptacle116may entail slurry infiltration, pouring or conveying, or additive fabrication (e.g., layer-by-layer processing), depending at least in part on whether the powder receptacle116takes the form of a fiber preform, a mold, a repair region, or a substrate.

Returning again toFIG.4, after delivery400of the powder composition102into or onto the powder receptacle116, the SiC particles104undergo densification410to form—either from the fiber preform, within the mold, within the repair region, or on the substrate—a SiC matrix118reinforced with the chopped coated SiC fibers106. Accordingly, upon densification of the SiC particles104, a fiber-reinforced ceramic matrix composite120is fabricated or repaired420. In examples where the powder receptacle116is a fiber preform comprising continuous SiC fibers208(e.g., coated continuous SiC fibers206, as shown inFIG.2) the SiC matrix118formed upon densification is reinforced with both the chopped coated SiC fibers106and the coated continuous SiC fibers206. As discussed in more detail below, densification may be effected by melt infiltration, polymer infiltration and pyrolysis, chemical vapor deposition or infiltration, or sintering/melting. When a slurry112is employed for delivery of the powder composition102into or onto the powder receptacle116, some or all of the liquid114may be removed from the slurry112prior to or during densification. The SiC matrix118formed by densification of the SiC particles104may be understood to have a residual porosity level of no greater than about 10 vol. %.

Referring now toFIGS.5A and5B, when the powder receptacle116comprises a fiber preform516, delivery of the powder composition102may entail infiltrating a slurry112comprising the powder composition102into the fiber preform516, a process known as slurry infiltration. The fiber preform may be produced by laying up plies comprising the continuous SiC fibers to have a shape of a desired composite component. To effect slurry infiltration of the fiber preform516, a vacuum may be applied to the fiber preform516prior to exposure to the slurry and then removed during infiltration to create a pressure gradient (e.g., about 1 atm) that may enhance capillary forces. The fiber preform516may be exposed to the slurry at room temperature (e.g., from about 15° ° C. to about 25° C.). After exposure to the slurry and infiltration, the fiber preform516may be dried to remove some or all of the liquid. Drying may be carried out at room temperature or at an elevated temperature (e.g., from about 40° ° C. to about 150° C.). After infiltration with the slurry112, the SiC particles104may be densified to form a SiC matrix118reinforced with the chopped coated SiC fibers106, as illustrated inFIG.5C, using an approach described below.

Referring now toFIGS.6A-6C and7A-7C, when the powder receptacle116comprises either a mold616having a predetermined shape or a repair region716of the composite, delivery of the powder composition102may comprise pouring or conveying a slurry112including the powder composition102into the mold616(FIGS.6A-6B) or the repair region716(FIGS.7A-7B). Alternatively, the powder composition102may be poured or conveyed into the mold616or repair region716in the form of a dry powder mixture. It is noted that the predetermined shape of the mold may be an inverse of the desired shape of the composite to be produced. In addition, the repair region716may include a damaged region of a composite that is optionally further machined to produce the repair region716in a size and shape configured to receive the powder composition102. After delivery of the powder composition102into the mold616or repair region716, the SiC particles104may be densified to form a SiC matrix118reinforced with the chopped coated SiC fibers106, as illustrated inFIGS.6C and7C, using one of the approaches described below.

Referring now toFIGS.8A-8C, when the powder receptacle116comprises a substrate816, delivery of the powder composition102may entail depositing a slurry112comprising the powder composition102on the substrate816in an additive, e.g., layer-by-layer, process. For example, the slurry112may be extruded through a nozzle818moving relative to the substrate816to deposit the powder composition102in a desired 2D or 3D pattern on the substrate816, as illustrated inFIG.8B. After deposition of the powder composition102onto the substrate816, partial or complete drying may optionally be carried out to remove some or all of the liquid, and the SiC particles104may be densified to form a SiC matrix118reinforced with the chopped coated SiC fibers106, as illustrated inFIG.8C, using one of the densification approaches described below.

The densification of the SiC particles104that occurs after delivery of the powder composition into or onto the powder receptacle116may entail, in one example, infiltrating the powder receptacle116with a melt comprising silicon, and then the cooling the melt. In some examples, the melt may comprise pure silicon (“silicon metal,” that is, silicon with only incidental impurities) or a silicon alloy. Alloying elements that may be added to the melt may include carbon, boron, and/or transition metal elements. During melt infiltration, the melt flows through the powder receptacle (e.g, a fiber preform or mold) and reacts with any reactive elements, such as carbon particles, in the flow path. Typically, melt infiltration is carried out at a temperature at or near the melting temperature Tmof silicon (1414° C.), which may be from about 1410° C. to about 1500° C., depending on the composition of the melt. Melt infiltration may be carried out for a time duration from several minutes up to several hours, depending on the size and complexity of the powder receptacle116. Upon cooling of the melt, the SiC particles104in or on the powder receptacle116are densified and a SiC matrix118reinforced with the chopped coated SiC fibers106is formed. If the powder receptacle116is a fiber preform516, as illustrated inFIG.5B, the SiC matrix118is also reinforced with the coated continuous SiC fibers206from the preform516. Accordingly, a fiber-reinforced ceramic matrix composite120may be produced or repaired.

In a second example, to effect densification after delivery of the powder composition102into or onto the powder receptacle116, polymer infiltration and pyrolysis may be employed. In this example, the powder receptacle116may be infiltrated with a formulation comprising a silicon-based polymer, and the formulation may be pyrolyzed to convert the silicon-based polymer to silicon carbide. The silicon-based polymer may thus be understood to function as a silicon carbide ceramic precursor. Examples of suitable silicon-based polymers may include polysilane, polycarbosilane, polysiloxane, and/or polysilazane. To pyrolyze the silicon-based polymer formulation, the powder receptacle116may be heated to a temperature in a range from about 850° C. to about 1300° C., causing the silicon-based polymer to be converted to silicon carbide. Typically, pyrolysis is conducted in an inert gas and/or a vacuum environment, such as in a vacuum chamber that has been evacuated and backfilled with a desired pressure of inert gas (e.g., argon, helium and/or nitrogen). As a consequence of pyrolysis, the SiC particles104in or on the powder receptacle116may be densified and a SiC matrix118reinforced with the chopped coated SiC fibers106may be formed. Accordingly, a fiber-reinforced ceramic matrix composite120may be fabricated or repaired.

In a third example, to effect densification after delivery of the powder composition102into or onto the powder receptacle116, the powder receptacle116may be infiltrated with silicon- and carbon-containing gaseous reactant(s), and a solid-phase reaction product comprising SiC may be deposited within or on the powder receptacle116. Such an approach is typically referred to as chemical vapor deposition (CVD) or chemical vapor infiltration (CVI), and may be carried out as discussed above using, for example, methyltrichlorosilane (CH3SiCl3) and H2as the silicon-containing gaseous reactants. The amount of SiC deposited may depend on the time duration of gaseous infiltration and reaction product deposition. Due to the deposition of silicon carbide, the SiC particles104in or on the powder receptacle116may be densified and a SiC matrix118reinforced with the chopped coated SiC fibers106may be formed. Accordingly, a fiber-reinforced ceramic matrix composite120may be produced or repaired.

In a fourth example, to effect densification after delivery of the powder composition102, heat and optionally pressure may be applied to induce sintering of the SiC particles104in or on the powder receptacle116. Typical sintering temperatures are in a range from about 1800° C. to about 2200° C., and optional pressures may lie in a range from about 10 MPa to about 100 MPa. For powder compositions102that include silicon particles and optionally carbon particles, the temperature at which the SiC particles104undergo sintering may induce melting of the silicon particles, which may react with the carbon particles and produce additional SiC. Due to the sintering/melting, the SiC particles104in or on the powder receptacle116may be densified and a SiC matrix118reinforced with the chopped coated SiC fibers106may be formed. Accordingly, a fiber-reinforced ceramic matrix composite120may be produced or repaired.

The subject-matter of the disclosure may also relate, among others, to the following aspects:

A first aspect relates to a powder composition comprising: SiC particles; and chopped coated SiC fibers comprising chopped SiC fibers with a surface coating thereon.

A second aspect relates to the powder composition of the first aspect, further comprising silicon particles.

A third aspect relates to the powder composition of the first or the second aspect, wherein the surface coating comprises a carbide, a nitride, an oxide, and/or pyrolytic carbon.

A fourth aspect relates to the powder composition of any preceding aspect, wherein ends of each chopped coated SiC fiber are uncoated with the surface coating.

A fifth aspect relates to the powder composition of any preceding aspect, wherein the chopped coated SiC fibers are included at a concentration from 1 vol. % to 99 vol. %.

A sixth aspect relates to the powder composition of any preceding aspect, wherein the chopped coated SiC fibers have a nominal length in a range from about 1 micron to about 100 microns.

A seventh aspect relates to a slurry comprising the powder composition of any preceding claim dispersed in a slurry.

An eighth aspect relates to a method of producing or repairing a fiber-reinforced ceramic matrix composite, the method comprising: delivering a powder composition comprising SiC particles and chopped coated SiC fibers into or onto a powder receptacle configured for composite fabrication or repair; after delivering the powder composition into or onto the powder receptacle, densifying the SiC particles to form a SiC matrix reinforced with the chopped coated SiC fibers, thereby producing or repairing a fiber-reinforced ceramic matrix composite.

A ninth aspect relates to the method of the preceding aspect, wherein the powder receptacle comprises: a fiber preform including continuous SiC fibers; a mold having a predetermined shape; a repair region of the fiber-reinforced ceramic matrix composite; or a substrate.

A tenth aspect relates to the method of any preceding aspect, wherein the powder composition further comprises silicon particles.

An eleventh aspect relates to the method of any preceding aspect, wherein a slurry comprising the powder composition dispersed in a liquid is delivered into or onto the powder receptacle.

A twelfth aspect relates the method of any preceding aspect, wherein the delivering the powder composition into or onto the powder receptacle comprises: slurry infiltration; pouring or conveying; or additive processing.

A thirteenth aspect relates to the method of any of the ninth through the twelfth aspects, wherein the powder receptacle comprises the fiber preform, and wherein delivering the powder composition comprises infiltrating a slurry comprising the powder composition into the fiber preform.

A fourteenth aspect relates to the method of any of the ninth through the thirteenth aspects, wherein the powder receptacle comprises the mold or the repair region, and wherein delivering the powder composition comprises pouring or conveying the powder composition, or pouring or conveying a slurry comprising the powder composition, into the mold or the repair region.

A fifteenth aspect relates to the method of any of the ninth through the fourteenth aspects, wherein delivering the powder composition comprises depositing a slurry comprising the powder composition onto the substrate in a layer-by-layer process.

A sixteenth aspect relates to the method of any preceding aspect, wherein densifying the SiC particles comprises: infiltrating the powder receptacle with a melt comprising silicon, and cooling the melt.

A seventeenth aspect relates to the method of any preceding aspect, wherein densifying the SiC particles comprises: infiltrating the powder receptacle with a formulation comprising a silicon-based polymer, and pyrolyzing the formulation to convert the silicon-based polymer to silicon carbide.

An eighteenth aspect relates to the method any preceding aspect, wherein densifying the silicon carbide particles comprises: infiltrating the powder receptacle with silicon- and carbon-containing gaseous reactant(s); and depositing a solid-phase reaction product comprising SiC within and/or on the powder receptacle.

A nineteenth aspect relates the method of any preceding aspect, wherein densifying the SiC particles comprises: heating the powder receptacle to induce sintering of the SiC particles.

A twentieth aspect relates to the method of any preceding aspect, wherein the powder composition further comprises silicon particles, and wherein the heating induces melting of the silicon particles.

In addition to the features mentioned in each of the independent aspects enumerated above, some examples may show, alone or in combination, the optional features mentioned in the dependent aspects and/or as disclosed in the description above and shown in the figures.