Method of producing an internal cavity in a ceramic matrix composite
A process for producing an internal cavity in a CMC article and mandrels used therewith. The process entails incorporating a mandrel made of a fusible material that is melted and drained during a thermal treatment of a CMC preform to form the CMC article. The mandrel material is preferably non-wetting and non-reactive with any constituents of the CMC preform during the thermal treatment. The mandrel is preferably tin or an alloy of tin.
1. A method of forming a CMC article to have at least one internal cavity, the method comprising:
incorporating at least one mandrel into a CMC preform via laying the CMC preform on the at least one mandrel, wherein the CMC preform comprises multiple prepreg layers in the form of a tape-like structure comprising a reinforcement material, a precursor of a CMC matrix material, and binders, wherein the at least one internal cavity comprises multiple cavities and the at least one mandrel comprises multiple mandrels; and
subjecting the CMC preform to a thermal treatment wherein the at least one mandrel melts to form a molten material that drains from the CMC preform to leave behind at least one internal cavity within the CMC preform.
2. The method according to claim 1 , wherein the mandrel consists of tin or a tin alloy.
3. The method according to claim 1 , wherein the thermal treatment is a burn-out process.
4. The method according to claim 1 , wherein the at least one mandrel is free of materials that are wetting and/or reactive to constituents of the CMC preform.
5. The method according to claim 1 , the method further comprising recovering the molten material and forming another mandrel from the molten material.
6. The method according to claim 1 , the method further comprising coating the at least one internal cavity with a slurry comprising a ceramic material.
7. The method according to claim 6 , wherein the ceramic material is boron nitride.
8. The method according to claim 7 , wherein the average particle size of boron nitride is about 0.5 to 1.0 micrometer.
9. A method of forming a CMC article to have at least one internal cavity, the method comprising:
incorporating at least one mandrel into a CMC preform via laying the CMC preform on the at least one mandrel, wherein the CMC preform comprises multiple prepreg layers in the form of a tape-like structure comprising a reinforcement material, a precursor of a CMC matrix material, and binders, the at least one mandrel consisting of a material that is non-wetting and non-reactive with any constituents of the CMC preform, wherein the at least one internal cavity comprises multiple cavities and the at least one mandrel comprises multiple mandrels;
subjecting the CMC preform to a burn-out process wherein the at least one mandrel melts to form a molten material that does not wet the CMC preform, does not react with constituents of the CMC preform, and drains from the CMC preform to leave behind at least one internal cavity in the CMC preform; and
melt-infiltrating the CMC preform with an infiltrant to form the CMC article which has the at least one internal cavity.
10. The method of claim 9 , wherein the material of the at least one mandrel is elemental tin.
11. The method of claim 9 , wherein the material of the at least one mandrel is a tin alloy.
12. The method of claim 9 , the method further comprising coating the at least one internal cavity with a slurry of a ceramic material prior to the melt infiltration step, the ceramic material not being wettable by the infiltrant.
13. The method of claim 12 , wherein the ceramic material is boron nitride.
14. The method of claim 13 , wherein the average particle size of boron nitride is about 0.5 to 1.0 micrometer.
15. The method of claim 9 , wherein the at least one internal cavity is a cooling slot or hole.
16. The method of claim 9 , wherein the CMC article is an airfoil component.
17. The method of claim 9 , wherein the CMC article is based on at least one silicon compound.
18. The method of claim 17 , wherein the infiltrant is silicon and the at least one silicon compound is SiC.
19. The method of claim 1 , wherein the CMC perform in the incorporating step is uncured and is laid on a surface of the at least one mandrel.