Ceramic matrix composite structures with controlled microstructures fabricated using chemical vapor infiltration (CVI)

A method comprising:

• associating a plurality of preform plies to define a preform, wherein a first preform ply and a second preform ply of the plurality of preform plies have different average pore sizes, the first preform ply having a first average pore size, the second preform ply having a second average pore size and wherein the second average pore size is greater than the first average pore size;
• and
• subjecting the preform to chemical vapor infiltration (CVI) to define a densified ceramic matrix composite (CMC) structures;
• wherein the preform comprises at least one of the following:
• a) a solid structure, wherein the plurality of preform plies includes a center preform ply, a first set of preform plies from the center preform ply to a preform ply defining a first outer surface of the preform having increasing average pore sizes, and a second set of preform plies from the center preform ply to a preform ply defining a second outer surface of the preform having increasing average pore sizes, or
• b) a hollow structure preform, wherein the plurality of preform plies of the preform define a sidewall of the hollow structure preform, wherein the plurality of preform plies includes a center preform ply, a first set of preform plies from the center preform ply to a preform ply defining an outer surface of the hollow structure preform having increasing average pore sizes, and a second set of preform plies from the center preform ply to a preform ply defining an inner surface of the hollow structure preform having decreasing average pore sizes, or
• c) the preform is a hollow structure preform, wherein the plurality of preform plies of the preform define a sidewall of the hollow structure preform, wherein a certain preform ply of the plurality of preform plies that defines an inner surface of the hollow structure preform has a smallest average pore size of the plurality of preform plies, and wherein preform plies of the plurality of preform plies in a succession of locations from a location of the certain preform ply to a location of a preform ply that defines an outer surface of the hollow structure preform have increasing average pore sizes.