Method of making a fiber preform for ceramic matrix composite (CMC) fabrication
A method of making a fiber preform for ceramic matrix composite (CMC) fabrication that utilizes a fugitive binder and a machining step is described. The method includes, according to one embodiment, laying up a plurality of plies to form a stack, where each ply comprises an arrangement of fibers. The stack is infiltrated with a polymer at an elevated temperature to form an infiltrated stack that is cooled to form a rigid preform. The rigid fiber preform is machined to have a predetermined shape, such that a machined fiber preform is formed. A composite assembly including the machined fiber preform is formed and then the composite assembly is heated at a sufficient temperature to pyrolyze the polymer. Thus, a porous preform of a predetermined geometry is formed for further processing into a CMC.
1. A method of making a fiber preform for ceramic matrix composite (CMC) fabrication, the method comprising:
laying up a plurality of plies to form a stack, each ply comprising an arrangement of fibers;
infiltrating the stack with a polymer at an elevated temperature sufficient to soften or melt the polymer to form an infiltrated stack;
cooling the infiltrated stack to form a rigid preform;
machining the rigid preform to have a predetermined shape, thereby forming a machined preform;
forming a composite assembly comprising the machined preform; and
heating the composite assembly at a sufficient temperature to pyrolyze the polymer, thereby forming a porous preform of a predetermined geometry for further processing.
2. The method of claim 1 , further comprising:
coating the porous preform with a fiber interphase material to form a coated preform;
rigidizing the coated preform to form a rigidized preform; and
infiltrating the rigidized preform with a slurry comprising a particulate matrix material to form an impregnated preform; and
melt infiltrating the impregnated preform with a molten metal or alloy, thereby fabricating a CMC.
3. The method of claim 1 , wherein infiltrating the stack with the polymer comprises placing a polymeric sheet comprising the polymer on the stack and heating the polymeric sheet to the elevated temperature, thereby inducing flow of the polymer into interstices of the stack.
4. The method of claim 1 , wherein the elevated temperature is in a range from about 80° C. to about 200° C.
5. The method of claim 1 , wherein the infiltrated stack is cooled to room temperature, and further comprising, prior to cooling to room temperature, pressing the infiltrated stack to a predetermined thickness.
6. The method of claim 5 , wherein the pressing comprises a pressure in a range from about 0.3 MPa to about 0.7 MPa.
7. The method of claim 1 , wherein the composite assembly further comprises an additional preform selected from the group consisting of: a second machined preform and a first rigid preform.
8. The method of claim 1 , wherein the composite assembly further comprises one or more infiltrated plies, each of the one or more infiltrated plies comprising a fiber arrangement embedded in a polymer.
9. The method of claim 1 , wherein the sufficient temperature to pyrolyze the polymer is in a range from about 200° C. to about 1000° C.
10. The method of claim 1 , wherein the polymer is selected from the group consisting of polyethylene, polyethylene carbonate, polypropylene carbonate, and polyvinyl alcohol.
11. The method of claim 1 , wherein the fibers comprise a ceramic selected from the group consisting of silicon carbide and silicon nitride.