Method of processing a ceramic matrix composite (CMC) component

1. A method of processing a CMC component, the method comprising:

preparing a fiber preform having a predetermined shape;

positioning the fiber preform with tooling having holes facing one or more surfaces of the fiber preform;

after the positioning, applying a clamping pressure to the tooling to force portions of the one or more surfaces of the fiber preform into the holes, thereby forming protruded regions of the fiber preform;

during the application of the clamping pressure, exposing the fiber preform to gaseous reagents at an elevated temperature, thereby depositing a matrix material onto the fiber preform and forming a rigidized preform including surface protrusions opposite to the holes in the tooling;

removing the tooling; and

infiltrating the rigidized preform with a melt for densification, thereby forming a CMC component having surface bumps.

2. The method of claim 1 , further comprising forming an assembly comprising the CMC component and a metal component, wherein only the surface bumps of the CMC component are in contact with the metal component, thereby minimizing diffusion between the CMC component and the metal component at elevated temperatures.

3. The method of claim 2 , further comprising, prior to forming the assembly, depositing an isolation layer comprising a material non-reactive with silicon on the metal component.

4. The method of claim 1 , wherein the tooling includes one or more flow passages in fluid communication with the holes, and

wherein exposing the fiber preform to the gaseous reagents comprises flowing the gaseous reagents through the one or more flow passages and out the holes.

5. The method of claim 1 , wherein the fiber preform comprises silicon carbide fibers, and wherein the CMC component includes a matrix comprising silicon carbide reinforced with the silicon carbide fibers.

6. The method of claim 1 , wherein the holes are uniformly spaced apart on a surface of the tooling.

7. The method of claim 1 , wherein the clamping pressure is in a range from about 69 kPa to about 690 kPa.

8. The method of claim 1 , wherein the surface bumps have a height in a range from about 0.01 cm to about 0.08 cm.

9. The method of claim 1 , wherein the holes have a width in a range from about 0.25 cm to about 1.3 cm.

10. The method of claim 1 , wherein the predetermined shape is an airfoil shape,

wherein the fiber preform comprises an internal cavity,

wherein the tooling includes internal tooling positioned within the cavity and external tooling placed adjacent to an external surface of the fiber preform, the internal tooling comprising the holes, and

wherein the CMC component is a CMC airfoil formed with internal surface bumps, and the metal component is a metal spar.

11. The method of claim 10 , wherein the CMC airfoil is a vane for a gas turbine engine.

12. The method of claim 1 , wherein the surface bumps comprise a reduced amount of free silicon of about 5 vol. % or less.

13. The method of claim 12 , wherein preparing the CMC component with the surface bumps having the reduced amount of free silicon comprises:

applying a surface formulation comprising a resin and/or a preceramic polymer to the fiber preform prior to melt infiltration;

curing the surface formulation to form a surface coating; and

pyrolyzing the surface coating to convert the resin to carbon and/or the preceramic polymer to silicon carbide,

wherein, during melt infiltration of the fiber preform, the carbon reacts with silicon to form silicon carbide, and the silicon carbide at a surface of the component prevents unreacted silicon from accessing the surface.

14. The method of claim 13 , wherein the preceramic polymer comprises an organosilicon polymer and/or an inorganic silicon polymer.

15. The method of claim 13 , wherein the resin comprises a phenolic resin.

16. The method of claim 13 , wherein the pyrolysis is carried out at a temperature in a range from about 850° C. to about 1300° C.

17. The method of claim 12 , wherein preparing the CMC component with the surface bumps having the reduced amount of free silicon comprises:

extracting silicon from a surface of the CMC component after melt infiltration.

18. The method of claim 17 , wherein the extraction comprises contacting the surface of the CMC component with a wicking medium comprising an element reactive with silicon and having the form of a felt or powder.

19. The method of claim 18 , wherein the element reactive with silicon is selected from the group consisting of carbon, molybdenum, and tungsten.

20. The method of claim 17 , further comprising, prior to extracting silicon, depositing a coating comprising boron nitride on the surface of the CMC component.