Method for combined desizing and interface coating of fibers for ceramic matrix composites

Abstract

A method of preparing a fiber for use in forming a ceramic matrix composite material comprises the steps of removing an organic sizing from a fiber to provide pyrolyzed remnants on the fiber, and using the pyrolyzed remnants as a reactant to provide an interface coating on the fiber.

Claims

1. A method of preparing a fiber for use in forming a ceramic matrix composite material comprising the steps of: removing an organic sizing from a fiber to provide pyrolyzed remnants on the fiber, the pyrolyzed remnants including residual carbon; using the pyrolyzed remnants as a reactant to provide an interface coating on the fiber; and performing a heat treatment to create the interface coating, wherein the heat treatment occurs in a vacuum or in nitrogen.

2. The method according to claim 1 wherein the organic sizing comprises a polymer based coating.

3. The method according to claim 1 including providing the heat treatment with a material comprising a solid species that includes at least boron to provide the interface coating.

4. The method according to claim 3 wherein the heat treatment occurs in the vacuum.

5. The method according to claim 4 wherein the heat treatment occurs approximately at 100 mTorr pressure or less.

6. The method according to claim 4 wherein the heat treatment occurs approximately at 1450 Celsius or less.

7. The method according to claim 4 including providing an additional heat treatment in nitrogen to provide a boron carbide, a boron nitride coating, and/or a boron nitride coating that includes carbon.

8. A method of preparing a fiber for use in forming a ceramic matrix composite material comprising the steps of: removing an organic sizing from a fiber to provide pyrolyzed remnants on the fiber, wherein the organic sizing comprises a polymer based coating, and wherein the polymer based coating further comprises carbon nanotubes; and using the pyrolyzed remnants as a reactant to provide an interface coating on the fiber.

9. The method according to claim 8 including subsequently forming a layer that includes boron nitride nanotubes.

10. A method of preparing a fiber for use in forming a ceramic matrix composite material comprising the steps of: removing an organic sizing from a fiber to provide pyrolyzed remnants on the fiber, wherein the organic sizing comprises a polymer based coating, and wherein the polymer based coating further comprises select inorganic additives or catalysts; and using the pyrolyzed remnants as a reactant to provide an interface coating on the fiber.

11. A method of preparing a fiber for use in forming a ceramic matrix composite material comprising the steps of: removing an organic sizing from a fiber to provide pyrolyzed remnants on the fiber; using the pyrolyzed remnants as a reactant to provide an interface coating on the fiber; performing a heat treatment with a material comprising a solid species that includes at least boron to create the interface coating, and wherein the heat treatment occurs in nitrogen.

12. The method according to claim 11 wherein the heat treatment occurs approximately at 1450 Celsius or less.

13. The method according to claim 11 including providing an additional heat treatment in nitrogen with silicon oxide to provide a boron nitride coating, a boron nitride coating that includes carbon, and/or silicon nitride coating.

14. A method of forming a ceramic matrix composite material comprising the steps of: removing an organic sizing from a fiber to provide pyrolyzed remnants on the fiber, wherein the pyrolyzed remnants include residual carbon; using the pyrolyzed remnants as a reactant to provide an interface coating on the fiber; performing a heat treatment with a boron based solid species to create the interface coating, wherein the heat treatment occurs in a vacuum or in nitrogen; and forming a ceramic matrix composite from fibers having the interface coating.

15. A method of preparing a fiber for use in forming a ceramic matrix composite material comprising the steps of: removing a polymer based sizing from a ceramic fiber to provide residual carbon on the fiber; using the residual carbon as a reactant to provide an interface coating on the fiber; and performing a heat treatment to produce the interface coating, wherein the heat treatment occurs in a vacuum.

16. The method according to claim 15 including providing the heat treatment with a boron based solid species to provide the interface coating.

17. The method according to claim 16 wherein the heat treatment occurs in the vacuum approximately at 100 mTorr pressure or less, and at a temperature of approximately 1450 Celsius or less, to form the interface coating as a boron carbide coating.

18. A method of preparing a fiber for use in forming a ceramic matrix composite material comprising the steps of: removing a polymer based sizing from a ceramic fiber to provide residual carbon on the fiber; using the residual carbon as a reactant to provide an interface coating on the fiber; and performing a heat treatment with a boron based solid species to create the interface coating, wherein the heat treatment occurs in nitrogen at a temperature of approximately 1450 Celsius or less to form the interface coating as a boron (carbon) nitrogen coating.

19. The method according to claim 18 including providing an additional heat treatment in nitrogen with silicon oxide, and at a temperature of approximately 1600 Celsius or less, to provide a boron nitride coating, a boron nitride coating that includes carbon, and/or silicon nitride coating.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a method of forming a fiber with an interface coating to be used to form a CMC material.

DETAILED DESCRIPTION

(2) FIG. 1 shows a method for preparing a fiber for use in forming a ceramic matrix composite (CMC) material. As discussed above, CMC materials are typically formed from a process that includes the steps of: lay-up and fixation of glass or ceramic fibers to form a preform; infiltration of a matrix material into the preform to form a CMC structure; and final processing of the CMC structure.

(3) The CMC materials are formed from high temperature ceramic fibers, such as silicon carbide (SiC) fibers, siliconborocarbonitride (SiBCN) fibers, silicon nitride (Si.sub.3N.sub.4) fibers, boron carbide (B.sub.4C) fibers, etc. The diameter of such fibers may range between 5 and 150 microns. FIG. 1 shows an example of such a fiber 10 that is provided with a polymeric fiber coating or sizing 12, which prevents fiber breakage and damage during handling.

(4) Before an interface coating, such as boron carbide for example, can be applied to the fiber 10, the sizing 12 must be removed. In one example, the sizing 12 comprises an organic sizing made from a polymer based material. To remove the sizing 12, a first step 20 is performed where the fiber 10 with the sizing 12 is subjected to a heat treatment in a vacuum or inert atmosphere (argon (Ar), nitrogen (N2), helium (He), etc.). This heat treatment occurs for a predetermined amount of time at a temperature of approximately 1000 C. (1832 F.) or less.

(5) Once this step 20 is completed, the sizing 12 has been removed from the fiber 10. However, the heat treatment causes pyrolysis of the sizing 12 which results in a remnant material that is left on the outer surface of the fiber 10. This material comprises a layer 22 of residual carbon from the pyrolyzed organic sizing on the fiber 10. The pyrolyzed remnants serve as a reactant to provide an interface coating on the fiber. This will be explained in greater detail below.

(6) Next, a heat treatment step 30a or 30b is provided for the fiber 10 with the layer 22 of residual carbon in order to form the interface coating. This heat treatment step is utilized with a material that comprises a solid species that includes at least boron. In one example, the boron-containing solid species is placed in a reactor vessel or furnace chamber. In one example, the boron-containing solid species comprises boron oxide (B.sub.2O.sub.3). This solid is heated such that it substantially or fully melts during the heat treatment step to supply a significant vapor pressure. This provides a gaseous reactant source for the residual carbon layer 22, which then produces a boron nitride, carbide, or a mixed nitride/carbide layer. In one example, this heat treatment step occurs simultaneously or concurrently with the desizing heat treatment step 20 within the same reactor vessel or furnace chamber during a single heat treatment cycle. Two different examples of heat treatment are discussed below.

(7) In one example, a heat treatment step 30a occurs in a vacuum at approximately 100 mTorr pressure or less, and at a temperature of approximately 1450 Celsius (2642 F.) or less. The boron oxide (B.sub.2O.sub.3) melts as described above and provides a gaseous reactant that reacts with the residual carbon to produce a fiber 10 with an interface coating 32a that is comprised of boron carbide (e.g. B.sub.4C). This boron carbide interface coating may be subjected to an additional heat treatment step 40a in nitrogen to convert the boron carbide layer in part, or fully, to a boron nitride layer 42a or a combination thereof. Thus, the layer resulting from the heat treatment step 40a could be a fully boron nitride layer, or could be a layer that comprises a carbon-containing BN. In one example, this additional heat treatment step 40a occurs for a predetermined amount of time at a temperature of approximately 1600 Celsius (2912 F.) or less.

(8) In another example, a heat treatment step 30b is applied to the fiber 10 with the residual carbon layer 22. This alternative heat treatment step 30b occurs in nitrogen (1 atmosphere or partial pressure) at a temperature of approximately 1450 Celsius or less. The boron oxide (B.sub.2O.sub.3) melts as described above and provides a gaseous reactant that reacts with the residual carbon to produce a fiber 10 with an interface coating 32b that is comprised of a boron (carbon) nitrogen layer, which is fully boron nitride (BN) or substantially boron nitride (BN) with some carbon in solution. This boron (carbon) nitrogen interface coating 32b may be subjected to an additional heat treatment step 40b in nitrogen with silicon oxide (SiO) solid in the reaction chamber to convert the boron carbide layer in part, or fully, to a layer or layers 42b that include boron (carbon) nitrogen (fully or substantially boron nitride (BN) with some carbon in solution) and silicon nitride (Si.sub.3N.sub.4), or a combination thereof. In one example, this additional heat treatment step 40b occurs for a predetermined amount of time at a temperature of approximately 1600 Celsius or less.

(9) Next, in either embodiment, once the interface coating has been provided, a ceramic matrix composite (CMC) material is formed from fibers having the interface coating, as indicated at 50. Finally, the CMC material is then used to form a component 60 for a gas turbine engine. The component 60 formed in these ways may be for use in a gas turbine engine, in one example, and could be a turbine blade, vane, blade outer air seal, combustor liner, etc.

(10) Optionally, the sizing 12 that is originally provided on the fibers 10 could be selected to include selected organic and inorganic additives to enhance the formation or functionality of the subsequently formed layers, such as carbon nanotubes (which may convert to boron nitride nanotubes), or small amounts of catalysts for these reactions such as iron, nickel, etc. Using carbon nanotubes in the sizing can lead to formation of BN nanotubes. Using catalysts in the sizing can facilitate lower temperature growth of BN.

(11) The subject invention provides in one heat treatment cycle the opportunity for both desizing of high temperature ceramic fibers and an in-situ formation of an interface coating of desired chemistry. As discussed above, the preferred reaction schemes are those which occur first under vacuum, which will facilitate vaporization of the gaseous reactant species and encourage a more uniform reaction (i.e. under the low pressure of the vacuum the gaseous species should be distributed throughout the reaction chamber vs. a flowing gas).

(12) Additional benefits of the invention include an enhancement in surface roughness on the fiber, formation of uniform, conformal coatings, and formation of more highly crystalline coating phases, i.e. hexagonal BN vs. amorphous or turbostratic. The invention also avoids the use of hazardous materials (or byproducts), such as those found in typical chemical vapor deposition processes for interface coatings.

(13) Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.