Additive manufacturing methods for forming high-temperature composite structures and related structures

A method of forming a high-temperature carbon-carbon or ceramic matrix composite structure, the method comprising:

• operating a robotic 3D printing machine to form a 3D precursor structure defining at least one void between substantially-nonporous portions, the operating comprising:
• drawing a filament from a spool on which the filament is wound to deposit an amount of filament material, the filament material comprising a precursor matrix material having embedded therein a fiber reinforcing material;
• laying the filament along an axis;
• and
• drawing more of the filament from the spool to deposit an additional amount of the filament material on the amount of the filament material;
• pyrolyzing the 3D precursor structure at a temperature exceeding about 932° F. to solidify at least some of the precursor matrix material and form a porous intermediate structure;
• introducing, into pores of the porous intermediate structure, a liquid resin comprising carbon or a preceramic material to impregnate the porous intermediate structure with the liquid resin to add the carbon or a ceramic material to the porous intermediate structure and form a densified and impregnated intermediate structure;
• and
• heating the densified and impregnated intermediate structure at a temperature between about 932° F. and about 5432° F.