CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Patent Application Number 61 /779,590, filed 13 March 2013, the disclosure of which is now expressly incorporated herein by reference.

FIELD OF THE DISCLOSURE

[0002] The present disclosure relates generally to composite materials including fibers suspended in a matrix material. More specifically, the present disclosure relates to coatings for fibers included in ceramic matrix composites that are used in high-temperature mechanical systems such as gas turbine engines.

BACKGROUND

[0003] A gas turbine engine, such as an aircraft engine, operates in severe environments. Ceramic matrix composite (CMC) components have desirable high temperature mechanical, physical, and chemical properties which allow gas turbine engines to operate at much higher temperatures than current engines with

superalloy components. For example, CMC components exhibit a significant amount of damage tolerance when under an applied load when compared to superalloy components. This damage tolerance is due in part to the formation of multiple matrix cracks that aid in the redistribution of stresses.

[0004] An issue with CMC components, however, is their lack of

environmental durability in combustion environments. For example, the formation of matrix cracks may result in environmental exposure to the fiber and fiber interface coating (typically boron nitride (BN)), which over time, may cause environmental degradation of the CMCs. The environmental degradation of CMCs is temperature and environment dependent. For example, at low temperatures (e.g., below 1000 ^Q C) oxygen may ingress to the fiber unimpeded causing environmental attack at the interface and resulting in embrittlement. At high temperatures (e.g., greater than 1000 ^Q C), silicon dioxide (Si0 ₂ ) may be formed, which may impede oxygen transport and slow down the degradation of the fiber and the fiber interface. However, the formation of Si0 ₂ may be hindered if water vapor (a combustion reaction product) is present. SUMMARY

[0005] The present application discloses one or more of the features recited in the appended claims and/or the following features which, alone or in any

combination, may comprise patentable subject matter.

[0006] According to the present disclosure, a method of making a

reinforcement for a composite component includes depositing an oxide coating onto a fiber. The method also includes depositing a silicon-containing coating onto the oxide coating.

[0007] In some embodiments, the method may also include heating the coated fiber to a predetermined temperature. Heating the coated fiber may form a predetermined amount of silicate in the silicon-containing coating at the interface of the oxide coating and the silicon-containing coating.

[0008] In some embodiments, heating the coated fiber to a predetermined temperature to form a predetermined amount of silicate at the interface of the oxide coating and the silicon-containing coating may be performed for a predetermined amount of time in a furnace. The predetermined temperature may be between about 800 and 1500 degrees Celsius.

[0009] In some embodiments, the silicate formed at the interface of the oxide coating and the silicon-containing coating may include silicon dioxide. The silicon- containing coating may have a porosity by volume of between about 10 percent and 20 percent. The oxide coating may have a porosity by volume of between about 10 percent and 20 percent. The fiber may include silicon carbide and the silicon- containing coating may include silicon carbide.

[0010] According to another aspect of the present disclosure, a reinforcement for a composite component may include a fiber and a multilayer coating. The multilayer coating may include an oxide coating and a silicon-containing coating in contact with the oxide coating to form an interface between the oxide coating and the silicon-containing coating.

[0011] In some embodiments, a silicate may be formed at the interface of the oxide coating and the silicon-containing coating. The silicate may be formed by heating of the fiber, the oxide coating, and the silicon-containing coating to a predetermined temperature so that a predetermined amount of silicate is produced. [0012] In some embodiments, the predetermined temperature may be greater than 800 degrees Celsius. The silicate formed at the interface of the oxide coating and the silicon-containing coating may include silicon dioxide.

[0013] In some embodiments, the silicon-containing coating may have a porosity by volume of between about 10 percent and 20 percent. The oxide coating may have a porosity by volume of between about 10 percent and 20 percent. In some embodiments, the fiber may include silicon carbide and the silicon-containing coating may include silicon carbide.

[0014] According to another aspect of the present disclosure, a method of making a composite component may include preparing reinforcements and suspending the reinforcements in a matrix material. Preparing reinforcements may be performed byby depositing an oxide coating and depositing a silicon-containing coating onto the oxide coating.

[0015] In some embodiments, the method may include heating the

reinforcements to a predetermined temperature to form a controlled amount of silicate. The silicate may be formed at the interface of the oxide coating and the silicon-containing coating.

[0016] In some embodiments, heating the coated fiber to a predetermined temperature to form a predetermined amount of silicate at the interface of the oxide coating and the silicon-containing coating may be performed for a predetermined amount of time in a furnace. The predetermined temperature may be greater than 800 degrees Celsius.

[0017] In some embodiments, heating the reinforcements to a predetermined temperature may be performed before suspending the reinforcements in a matrix material. The silicon-containing coating may include silicon carbide and the fiber may include silicon carbide. The matrix material may also include silicon carbide.

[0018] According to another aspect of the present disclosure, a composite component may include a matrix material and a plurality of reinforcements. Each reinforcement may include a fiber, an oxide coating, and a silicon-containing coating.

[0019] In some embodiments, the silicon-containing coating may be arranged in contact with the oxide coating to form an interface. A silicate may be formed at the interface by heating of the fiber, the oxide coating, and the silicon-containing coating to a predetermined temperature so that a predetermined amount of silicate is produced.

[0020] In some embodiments, the predetermined temperature may be greater than 800 degrees Celsius. The silicate formed at the interface of the oxide coating and the silicon-containing coating may include silicon dioxide.

[0021] In some embodiments, the silicon-containing coating may have a porosity by volume of between about 10 percent and 20 percent. The oxide coating may have a porosity by volume of between about 10 percent and 20 percent. In some embodiments, the matrix material, the fiber, and/or the silicon-containing coating may each include silicon carbide.

[0022] These and other features of the present disclosure will become more apparent from the following description of the illustrative embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Fig. 1 is a perspective view of a composite component including a plurality of reinforcements suspended in a cured matrix material;

[0024] Fig. 2 is a cross-sectional view of a reinforcements included in the composite component suspended in the cured matrix material of Fig. 1 illustrating that the reinforcement includes a fiber coated with a multilayer interface coating;

[0025] Fig. 3 is a block diagram of a method of making the composite component of Figs. 1 and 2 showing that the method includes preparing

reinforcements for use in the composite component; and

[0026] Fig. 4 is a block diagram showing a method of preparing

reinforcements for use in the method of making the composite component illustrated in Fig. 3 showing that the method of preparing reinforcements includes depositing an oxide coating and a silicon-containing coating onto a fiber and heating the coated fiber to form a silicate in the silicon-containing coating at the interface of the silicon- containing coating and the oxide coating.

DETAILED DESCRIPTION OF THE DRAWINGS

[0027] For the purposes of promoting an understanding of the principles of the disclosure, reference will now be made to a number of illustrative embodiments illustrated in the drawings and specific language will be used to describe the same. [0028] An illustrative composite component 10 adapted for use in high temperature applications such as a gas turbine engine is shown in Fig. 1 . The composite component 10 illustratively includes a matrix material 12 and a plurality of reinforcements 14. The matrix material 12 illustratively comprises silicon carbide (SiC) so that the exemplary composite component 10 is a ceramic matrix composite (CMC). Each of the reinforcements 14 illustratively includes a fiber 16 comprising silicon carbide (SiC) so that the exemplary composite component 10 is a silicon- carbide silicon-carbide (SiC-SiC) component. The composition of the composite component 10 provides high temperature capability.

[0029] In addition to a fiber 16, each reinforcement 14 includes a multilayer coating 18 applied to a corresponding fiber 16 as shown in Fig. 2. The multilayer coating 18 is formulated and treated during production of the composite component 10 so that a predetermined amount of silicate 20 (illustratively silicon dioxide (Si0 ₂ )) is formed at an interface 25 of two coating layers 21 , 22 included in the multilayer coating 18 before the reinforcement 14 is incorporated into the composite

component 10. The silicate 20 formed in the multilayer coating 18 improves the water vapor stability of the reinforcements 14 to extend the life of the composite component 10 if a crack 24 forming in the composite component 10 extends through the matrix material 12 and into the reinforcements 14 during use of the composite component 10.

[0030] In order to produce the silicate 20, the illustrative multilayer coating 18 includes a first layer of coating 21 that comprises an oxide and a second layer of coating 22 that comprises a silicon-containing compound as suggested in Figs. 2 and 4. The first layer 21 is deposited directly onto the fiber 16 and provides a weak interface with the fiber 16 to allow for fiber debonding. The second layer 22 is deposited onto the first layer of coating 21 so that the interface 25 is created between the first and second layers of coating 21 , 22.

[0031] In some embodiments, additional paired coating layers (not shown) of oxide coating and silicon-containing coating may be applied over the first and second paired layers 21 , 22 to create additional interfaces at which silicate is formed during preparation of a reinforcement 14 as suggested in Fig. 4. In some embodiments, up to fifty layers of paired coating layers may be included in the multilayer coating 18. Further, in some embodiments, other coating layers may be applied to the fiber 16 before the first layer 21 and/or at regular or irregular intervals between paired oxide/silicon-containing coating layers in the multilayer interface coating 18. For example, other coating layers included in multilayer coating 18 may comprise boron nitride. However, the outermost layer of the multilayer interface coating 18 is not boron nitride.

[0032] The first layer 21 illustratively includes a stable rare earth oxide and may be selected from the group including Yttrium(lll), Ytterbium oxide, Erbium(lll), Lutetium(lll), and Dysprosium(lll). The first layer 21 has a thickness of between about 25 nanometers and 100 nanometers. In some embodiments, the first layer 21 may include a single phase transition metal oxide. Exemplary single phase transition metal oxides may include transition metals such as Zirconium, Halfnium, etc. along with oxygen (e.g. Zr02, Hf02, etc.). In some embodiments, the first layer 21 may include a mixed oxide (e.g. Y203-Zr02, Yb203-Hf02, etc.).

[0033] The oxide-containing first layer of coating 21 illustratively has a porosity of between about 10 to 20 percent by volume. The porosity of the first layer 21 encourages deflection of a crack 24 that extends through the matrix material 12 and into the reinforcements 14 during use of the composite component 10. In other embodiments, the first layer 21 may be dense (non-porous).

[0034] The oxide-containing first layer 21 of multilayer coating 18 may impede and/or prevent the formation of oxide products (e.g., oxidation) during use of the composite component 10 in environments between about 800 and 1000 degrees Celsius. Thus, the first layer 21 of multilayer coating 18 may prevent and/or reduce embrittlement of the reinforcements 14 when the composite component 10 is in use.

[0035] The second layer 22 illustratively includes silicon carbide deposited onto the first layer 21 to create the interface 25 as shown in Fig. 2. The second layer 22 has a thickness of between about 25 nanometers and 100 nanometers. In some embodiments, the second layer 22 may include other silicon-containing compounds.

[0036] The silicon-containing second layer of coating 22 illustratively has a porosity of between about 10 to 20 percent by volume. The porosity of the second layer 22 encourages deflection of a crack 24 that extends through the matrix material 12 and into the reinforcements 14 during use of the composite component 10. In other embodiments, the second layer 22 may be dense (non-porous). [0037] The silicate 20 is formed in the second layer 22 as a result of heating the multilayer coating 18 included in the reinforcement 14 to cause the silicon- containing second layer 22 to react with the oxide-containing first layer 21 at the interface 25 as shown in Fig. 2. As noted above, the silicate 20 formed in the exemplary embodiment includes silicon dioxide (Si02) that improves the water vapor stability of the reinforcements 14. The silicate 20 is formed by heating the fiber 16 and the multilayer coating 18 to a predetermined temperature for a predetermined amount of time so that a predetermined (desired) amount of silicate is formed at the interface 25 prior to incorporation of the reinforcements 14 into the composite component 10. In the illustrative embodiment, the silicate 20 is formed by heating the multilayer coating 18 to a temperature between about 800 degrees Celsius and 1500 degrees Celsius for more than one hour.

[0038] In the illustrative embodiment, the fibers 16 are chopped fibers as shown in Fig. 1 . In other embodiments, the fibers 16 may be woven, braided, or otherwise processed in addition to being coated by the multilayer coating 18. For purposes of this disclosure, "fiber" or "fibers" may refer to fibers, filaments, whiskers, tows, cloth and combinations thereof.

[0039] Turning now to Fig. 3 a method 310 for making the composite component 10 is shown. In a step 312 of method 310, the reinforcements 14 are prepared as shown in more detail in Fig. 4. In a step 314, the reinforcements 14 are arranged in a mold. In a step 316, the matrix material 12 is poured into the mold to preliminarily suspend the reinforcements 14. The order of step 314 and step 316 may be reversed and the steps may be repeated a number of times to distribute the reinforcements 14 as desired. In a step 316, the matrix material 12 is cured to harden/finish the composite component 10. Curing the matrix material 12 in step 316 is illustratively performed by heating the matrix material 12 to a temperature generally under 800 degrees Celsius in a controlled-atmosphere furnace.

[0040] Fig. 4 shows a method 410 of preparing the reinforcements 14 for use in the method 310 shown in Fig. 3. In a step 412 of method 410, the first layer 21 is deposited onto the fiber 16. In a step 414 of method 410, the second layer 22 is deposited onto first layer 21 . After the first two layers 21 , 22 are deposited, it is determined if additional coating layers are desirable in a decision step 416. [0041] When additional layers are found to be desired in decision step 416, an additional inner coating layer including an oxide is deposited in a step 418 and an additional outer coating layer including a silicon-containing compound is deposited in a step 420. After step 420, the decision step 416 is repeated and additional paired layers are deposited onto the fiber 16 until no additional layers are desired.

[0042] In some embodiments, additional steps for depositing intervening layers of coating may also be performed as part of the method 410. For example, coating layers comprising boron nitride (or other materials) may be deposited as part of the multilayer coating 18.

[0043] When additional layers are not found to be desired in decision step 416, the coated fiber is heated in a step 422 to a predetermined temperature for a predetermined amount of time in a furnace as shown in Fig. 4. Heating the coated fiber forms a predetermined amount of silicate 20 in the silicon-containing second layer 22 at the interface 25 with the oxide-containing first layer 21 . Additional silicate is formed at the interface of additional silicon-containing layers and oxide-containing layers deposited onto the fiber 16. In some embodiments of the method 410, step 422 may be omitted on account of expected silicate formation during use of the composite component 10.

[0044] During use of the composite component 10 in a high temperature environment, silicate formation can take place when a crack 24 in the matrix material 12 propagates to the multilayer coating 18 of the reinforcements 14 and when temperatures are above 1000 degrees Celsius. Particularly, when operating temperatures of the composite component 10 are above 1000 degrees Celsius and the multilayer coating 18 is exposed to the high-temperature environment as a result of a crack 24, a silicate 20 containing silicon dioxide (Si0 ₂ ) may be formed in the silicon-containing second layer 22 of the multilayer coating 18. The silicate 20 formed in the silicon-containing second layer 22 may be added to silicate 20 formed during preparation of the reinforcements 14. Any silicate 20 included in the multilayer coating 18 may slow down the propagation of oxygen to the fiber 16 or the fiber interface with the multilayer coating 18 prolonging the life of the composite component 10. In addition, the silicate 20 may improve the water vapor stability of the reinforcement 14 and, as a result, may improve life of the composite component [0045] In step 412, the first layer 21 is illustratively deposited using a chemical vapor infiltration technique. Standard chemical vapor infiltration, metal organic chemical infiltration, ultraviolet assisted chemical vapor infiltration, physical vapor deposition, or directed vapor deposition are all contemplated methods of depositing oxide-containing layers onto the fiber 16.

[0046] In a related embodiments, during step 412, the first layer 21 may be formed by deposition of a carbide, nitride, or carbonitride of the transition metal or rare earth material, or a combination thereof (e.g. ZrC, ZrC _x Ni- _x , HfC _x Ni _-x , YC ₂ , YN, YbN, Hf _x Y _y C _z N _-z , etc) and a subsequent heat treatment to form a dense or porous oxide layer. The non-oxide coating could also be oxidized (usually forming a porous layer) through normal use at temperatures below 1000 degrees Celsius.

[0047] In step 414, the second layer 22 is illustratively deposited using a chemical vapor infiltration technique. Standard chemical vapor infiltration, metal organic chemical infiltration, ultraviolet assisted chemical vapor infiltration, physical vapor deposition, or directed vapor deposition are all contemplated methods of depositing oxide-containing layers onto the first layer 21 .

[0048] In step 422, heating of the coated fibers is illustratively performed at temperatures between about 800 degrees Celsius and 1500 degrees Celsius.

Further, the coated fibers are heated for more than one hour.

[0049] In some embodiments, prior to use of the composite component 10 in a high-temperature application, the component 10 may be machined into a particular shape for use as a turbine blade track, a turbine blade, a combustion liner, a heat shield tile or the like. In some embodiments, the composite component 10 may be shaped in the mold to for use in its final application.

[0050] While the disclosure has been illustrated and described in detail in the foregoing drawings and description, the same is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments thereof have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected.