Method of producing an internal cavity in a ceramic matrix composite and mandrel therefor
A process for producing an internal cavity in a CMC article and mandrels used therewith. The process entails incorporating a mandrel made of a material that is substantially absorbed during thermal treatment of a preform to form the CMC article. The mandrel material is preferably reactive with one or more constituents of the CMC preform during the thermal treatment. The material is preferably silicon or a silicon alloy.
1. A method of forming a CMC article with at least one internal cavity, the method comprising:
coating at least one mandrel with a coating that is impervious to constituents of the CMC preform;
wrapping ceramic composite precursor prepreg plies over the coating of the at least one mandrel, wherein each mandrel comprises silicon;
curing the ceramic composite precursor prepreg plies into a laminate CMC preform, wherein the laminate CMC preform comprises resinous components;
after curing, heating the laminate CMC preform and the at least one mandrel to above 500° C. to remove the resinous components to yield a porous CMC preform from the laminate CMC preform; and
after heating, subjecting the porous CMC preform to a thermal treatment, wherein the silicon of each mandrel melts to yield molten silicon that wets the CMC preform, and is reacted with and/or absorbed into the CMC porous preform leaving behind at least one internal cavity within the CMC preform.
2. The method according to claim 1 , wherein the at least one mandrel consists of silicon or a silicon alloy.
3. The method according to claim 1 , wherein the thermal treatment comprises a melt-infiltration step.
4. The method according to claim 1 , wherein the at least one internal cavity comprises multiple internal cavities and the at least one mandrel comprises multiple mandrels.
5. The method according to claim 1 , wherein the at least one mandrel contains a material that is chemically reactive with a constituent of the CMC preform.
6. The method according to claim 1 , wherein the mandrel comprises a powder silicon material.
7. The method according to claim 1 , wherein the ceramic composite precursor prepreg plies are based on silicon compounds.
8. The method according to claim 7 , wherein the silicon compound is SiC.
9. The method according to claim 1 , wherein the at least one mandrel consists of elemental silicon.
10. The method according to claim 1 , further comprising:
after coating the at least one mandrel with the coating and prior to wrapping the ceramic composite precursor prepreg plies over the at least one mandrel, sintering the at least one mandrel.
11. The method according to claim 1 , wherein the coating comprises an acrylic resin.
12. The method according to claim 1 , wherein the acrylic resin is methyl methacrylate.
13. The method according to claim 1 , wherein subjecting the porous CMC preform to a thermal treatment is performed within a vacuum furnace.