Patent Description:
Ceramic matrix composites (CMC) have high temperature capability and are light weight. The composites are an attractive material for various applications in which high temperature durability and light weight are desired. Ceramic matrix composites can be formed by infiltrating a preform with a vapor (chemical vapor infiltration) to form the matrix. While current methods and materials may be adequate improved methods and materials are desired. <CIT> discloses a woven preform for a ceramic composite. <CIT> discloses a method of making composite material parts comprising preparing a fiber substrate with holes. <CIT> discloses a method for making a ceramic preform. <CIT> discloses a SiC/SiC CMC comprising elongated channels.

Disclosed is a preform for a ceramic matrix composite (e.g. as disclosed herein and/or as made by the method disclosed herein) including or comprising direct channels extending from an exterior surface of the preform to an interior space of the preform wherein the direct channels are free of char and each direct channel is an open space having no variations in direction of more than five degrees, wherein at least two of the direct channels are perpendicular to each other and lie in the same plane and at least one additional direct channel is perpendicular to the plane.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the direct channels extend from a first exterior surface to a second exterior surface.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the direct channels have a diameter at the interior space of the preform that is less than the diameter at the exterior surface of the preform.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the direct channels have substantially the same diameter throughout the channel.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the direct channels have a diameter of <NUM> to <NUM> micrometers.

Also disclosed is a method of making a ceramic matrix composite (e.g. as disclosed herein) including: forming a preform (e.g. as disclosed herein) having direct channels extending from an exterior surface of the preform to an interior space of the preform wherein the direct channels are free of char and each direct channel is an open space having no variations in direction of more than five degrees; and infiltrating the preform having direct channels with matrix materials, wherein at least two of the direct channels are perpendicular to each other and lie in the same plane and at least one additional direct channel is perpendicular to the plane.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, forming a preform having direct channels includes or comprises removing at least one tow per layer to make a gap in each layer.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, further including or comprising aligning the gap in each layer on an alignment device.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, infiltrating includes or comprises chemical vapor infiltration.

Also disclosed is a ceramic matrix composite as made by the method disclosed herein comprising direct matrix channels extending from an exterior surface of the composite to an interior space of the composite wherein the direct matrix channels are free of char and each direct matrix channel is an open space having no variations in direction of more than five degrees, wherein at least two of the direct matrix channels are perpendicular to each other and lie in the same plane and at least one additional direct matrix channel is perpendicular to the plane.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the direct matrix channels extend from a first exterior surface to a second exterior surface.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the direct matrix channels have a diameter at the interior space of the ceramic matrix composite that is less than the diameter at the exterior surface of the ceramic matrix composite.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the direct matrix channels have substantially the same diameter throughout the channel.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the direct matrix channels have a diameter of <NUM> to <NUM> micrometers.

In addition to one or more of the features described above, or as an alternative to any of the foregoing embodiments, the ceramic matrix composite includes or comprises a matrix and reinforcing fiber. In some embodiments the matrix may include silicon carbide, silicon nitride or a combination thereof and the reinforcing fiber may include silicon carbide. In some embodiments the matrix and reinforcing fiber include or comprise oxide materials such as aluminum oxide, silicon dioxide, yttrium aluminum garnet, aluminosilicates, zirconium dioxide, zinc oxide, and mixtures thereof.

A ceramic matrix composite can be made by infiltrating a preform using chemical vapor infiltration. In chemical vapor infiltration the reaction product of the infiltrating gases deposits on the surface of the reinforcing fibers. Gradually the open spaces in the preform are reduced. The ceramic matrix forms faster closer to the exterior surface of the preform and can completely fill the spaces between the reinforcing fibers close to the exterior surface before infiltrating the interior of the preform, resulting in a non-uniform microstructure in the final composite and less desirable physical properties.

This problem can be addressed by employing a preform having direct channels extending from an exterior surface of the preform to an interior space of the preform. The direct channels allow the chemical infiltration gas to more completely and uniformly permeate the preform which will make the infiltration process quicker. The resulting composite has a more uniform and dense microstructure.

The term "direct" channel describes an open space having no variations in direction of more than five degrees. The channel may have any cross section shape. The diameter (or width) of the channel may be the same (vary by less than <NUM>%) at the exterior and interior or the channel may be tapered - having width at the exterior surface which is greater than the width at an interior space. The width of the channel may be <NUM> to <NUM> micrometers, or, <NUM> to <NUM> micrometers, or <NUM> to <NUM> micrometers. The fiber volume fraction of the preform is <NUM> to <NUM> vol%.

The direct channels are free from char. Char is residual material resulting from pyrolysis and the like. Char can function as scaffolding for matrix deposition and facilitate deposition in the channels before deposition between the fibers.

The preform can have direct channels that extend parallel to each other and may have channels that extend in multiple directions such as parallel and perpendicular. The channels may also extend in directions of varying angles. In some embodiments at least two of the direct channels are perpendicular to each other and lie in the same plane and at least one additional direct channel is perpendicular to the plane. The direct channels may extend between two exterior surfaces or may extend from an exterior surface and end at an interior space.

The direct channels can be formed in the preform by removing a tow from the reinforcing material to form a direct channel in one direction and removing a tow from the reinforcing material in a perpendicular direction to form another direct channel. The intersection of the direct channels in the two directions can then be aligned to form a direct channel in a third direction. Alternatively, the reinforcing may be woven with direct channels in desired locations.

Turning now to <FIG>, a preform <NUM> is shown having fibers running in an X direction <NUM> and fibers running in a Y direction <NUM>. The direct channels <NUM> in the X direction intersect with the direct channels <NUM> in the Y direction to form the direct channels <NUM> in the Z direction (coming out of the page in <FIG>). For simplicity the cross over points are not shown.

<FIG> shows a cross section of a preform through direct channels <NUM> in the Y direction. Fibers running in the X direction between X direction direct channels are not shown individually for simplicity. The intersection of the Y direction direct channel <NUM> with the X direction direct channel <NUM> forms a direct channel in the Z direction <NUM>. Alignment devices <NUM> may be used to align the intersections of the X and Y direction direct channels to form the Z direction direct channel. Exemplary alignment devices include pins, optical laser alignment and the like. Infiltrating gas may enter and/or exit the preform through the direct channels in any of the three directions, providing a significantly higher amount of edge surfaces to facilitate matrix deposition and result in a ceramic matrix composition having a more uniform microstructure. The direct channels in the preform result in the direct matrix channels in the ceramic matrix composite.

<FIG> shows a Z direction direct channel <NUM> having a varying diameter over the length of the channel.

Exemplary CMC materials are silicon-containing, or oxide containing matrix and reinforcing materials. Some examples of CMCs include, but are not limited to, materials having a matrix and reinforcing fibers comprising non-oxide silicon-based materials such as silicon carbide, silicon nitride, silicon oxycarbides, silicon oxynitrides, silicides, and mixtures thereof. Examples include, but are not limited to, CMCs with a silicon carbide matrix and silicon carbide fiber; silicon nitride matrix and silicon carbide fiber; and silicon carbide/silicon nitride matrix mixture and silicon carbide fiber. Furthermore, CMCs can have a matrix and reinforcing fibers comprised of oxide ceramics. Specifically, the oxide-oxide CMCs may be comprised of a matrix and reinforcing fibers comprising oxide-based materials such as aluminum oxide (Al<NUM>O<NUM>), silicon dioxide (SiO<NUM>), yttrium aluminum garnet (YAG), aluminosilicates, zirconium dioxide (ZnO<NUM>), zinc oxide (ZnO), and mixtures thereof. Aluminosilicates can include crystalline materials such as mullite (3Al<NUM>O<NUM> 2SiO<NUM>), as well as glassy aluminosilicates. Other ceramic composite materials that are not comprised of either silicon or oxygen may be used, including carbon, zirconium carbide, hafnium carbide, boron carbide, or other ceramic materials, alone or in combination with the materials noted above.

The method described herein can be used to prepare a variety of components comprising ceramic matrix composites such as components in the aviation industry, marine industry and energy industry. Exemplary components include components for gas turbine engines, such as in high pressure compressors (HPC), fans, boosters, high pressure turbines (HPT), and low pressure turbines (LPT). More specifically exemplary components include combustion liners, shrouds, nozzles, stators, vanes, and blades.

Claim 1:
A preform for a ceramic matrix composite comprising direct channels extending from an exterior surface of the preform to an interior space of the preform wherein the direct channels are free of char and each direct channel is an open space having no variations in direction of more than five degrees;
wherein at least two of the direct channels are perpendicular to each other and lie in the same plane and at least one additional direct channel is perpendicular to the plane.