Patent Application
20240109223
The present invention relates to chemical vapor infiltration (CVI), and more particularly to improved tooling for CVI.
In the processing of ceramic matrix composites (CMCs), there is a need to infiltrate matrix within and around fibrous tow bundles to replace pore volume with dense matrix material. In a woven system, large voids often exist between adjacent tows of a preform. Such voids can become large defects after infiltration of the composite that are detrimental to composite properties. The pore network through a woven system is often highly tortuous for infiltrating reactant vapors, which leads to uneven deposition through the thickness of the preform, with, higher concentrations tending to deposit on preform surfaces and edges. This leads to an overall slower and less uniform matrix infiltration process resulting in composites with undesirably porous midplanes. Thus, a need exists for means to facilitate even matrix infiltration.
A tooling assembly for perforating a fibrous preform comprises a tooling fixture comprising a plurality of receiving holes, and a spiked array comprising a plate and a plurality of metallic spikes projecting away from the plate and toward the tooling fixture, each of the plurality of metallic spikes corresponding to and extending towards one of the plurality of receiving holes. The spiked array is engageable with the tooling fixture such that the plurality of spikes extend at least partially into respective ones of the plurality of receiving holes.
A method of preparing a fibrous preform for use in a ceramic matrix composite comprises supporting the preform with a tooling fixture, and perforating the preform with a spiked array to form a perforated preform, the spiked array comprising a plate with a plurality of metallic spikes projecting away from the plate. When perforating the preform, the plurality of metallic spikes extend at least partially into a plurality of respective receiving holes in the tooling fixture.
While the above-identified figures set forth one or more embodiments of the present disclosure, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features and components not specifically shown in the drawings.
This disclosure presents means for perforating a fibrous ceramic preform prior to densification via chemical vapor infiltration (CVI). Multiple embodiments of perforating tooling can be used to create holes through the thickness of the preform. Such holes facilitate access to the interior of the preform by reactant vapors such that matrix deposits in a more even manner compared to non-perforated preforms.
Spiked array 16 includes multiple spikes 18 arranged in rows and columns on and extending from generally planar plate 20. Spikes 18 can be spaced apart a distance, or length L1, which can be measured from the center point of one spike 18 to the center point of the adjacent spike 18. L1 can range from 1.0 mm to 10 mm. Each spike 18 can have a short to medium taper in an exemplary embodiment (e.g., as shown in
In one embodiment, fixture 12 can be formed from graphite, while spiked array 16 can be formed from a metallic material and manufactured, for example, via additive manufacturing. Metallic spikes 18 can further be coated with a ceramic, such as SiC, such that any contaminants left in preform 14 after the removal of spikes 18 would be from the ceramic coating and beneficially incorporated into the densified component. In an alternative embodiment, fixture 12 can also be formed from a metallic material and formed via traditional or additive manufacturing.
Prior to insertion of spikes 18 into preform 14, a lubricating solution can be applied to preform 14 to prevent damage to preform 14 from sticking/catching of spikes 18. Exemplary solutions can include water with polyvinyl alcohol (PVA), or alcohol with polyvinyl butyral (PVB). The lubricating solution can be applied (e.g., via spraying, pipetting, dipping, etc.) to preform 14, to individual plies of preform 14, and/or to individual tows prior to weaving. With spikes 18 inserted into preform 14, preform 14 can undergo a stabilization process, which in an exemplary embodiment, can be a drying step to remove the solvent (i.e., water or alcohol) of the lubricant solution. Stabilization can further include removal of/burning-off the PVA or PVB by, for example, heating preform 14 in an inert environment. Stabilization of preform 14 in this manner helps prevent warping of holes 26 after removal of spikes 18 during subsequent processing, such as debulking.
In one embodiment, preform 14 can be transferred to CVI tooling after the removal of spikes, and any intervening processing. This may be necessary where fixture 12 is formed from metal, thus preform 14 can be transferred to graphite tooling. Further, even if a graphite fixture 12 was used during perforation with no upper plate 22, a graphite upper plate (e.g., upper plate 22) can be placed over perforated preform 14 after removal of spikes 18. Suitable CVI tooling should include infiltration holes aligned with holes 26 in preform 14, which gives reactant vapors access to holes 26. Holes 26 can provide a less tortuous path for reactant vapors to diffuse and deposit matrix throughout preform 14.
An array of spikes 118 can extend from each plate 120. Spikes 118 can be inserted into and through preform 114 to form a perforated preform 114. Accordingly, inner fixture 112 includes receiving holes 124 corresponding to spikes 188, which can have various dimensions depending on the dimensions of spike 118 and the thickness of preform 114. Like tooling assembly 10, inner fixture 112 can be formed from graphite or a metal, and spiked array 116 can be at least partially metallic, with ceramic coated metallic spikes. Spikes 118 can be spaced apart from adjacent spikes a distance L3 ranging from 0.1 mm to 1.0 mm. Each spike 118 can further have a short to medium taper, and a diameter D3 ranging from 0.1 mm to 1.0 mm. L3 and D3 create corresponding spacing and dimensions of holes (not visible in
Tooling assemblies 10, 110 can be used when infiltrating preforms 14, 114, via CVI, to deposit interface coatings (e.g., layers of BN, SiC, silicon-doped BN, etc.) and/or to form a matrix (e.g., SiC) to create a CMC part. Such CMC parts can be incorporated into aerospace, maritime, or industrial equipment, to name a few, non-limiting examples.
The following are non-exclusive descriptions of possible embodiments of the present invention.
A tooling assembly for perforating a fibrous preform comprises a tooling fixture comprising a plurality of receiving holes, and a spiked array comprising a plate and a plurality of metallic spikes projecting away from the plate and toward the tooling fixture, each of the plurality of metallic spikes corresponding to and extending towards one of the plurality of receiving holes. The spiked array is engageable with the tooling fixture such that the plurality of spikes extend at least partially into respective ones of the plurality of receiving holes.
The tooling assembly of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
In the above tooling assembly, each spike of the plurality of spikes can be spaced apart from an adjacent one of the plurality of spikes a distance ranging from 1.0 mm and 10 mm.
In any of the above tooling assemblies, each spike of the plurality of spikes can have a diameter ranging from 0.1 mm to 1.0 mm.
In any of the above tooling assemblies, each spike of the plurality of spikes can have a short taper or a medium taper.
In any of the above tooling assemblies, each spike of the plurality of spikes can be coated with a ceramic material.
In any of the above tooling assemblies, the tooling fixture can further include a plate in which the plurality of receiving holes are disposed.
In any of the above tooling assemblies, the plate of the spiked array and the plate of the tooling fixture can be planar.
In any of the above tooling assemblies, the tooling fixture can be formed from one of graphite or a metallic material.
In any of the above tooling assemblies, the spiked array can include a plurality of plates, each of the plurality of plates including a plurality of metallic spikes projecting therefrom.
In any of the above tooling assemblies, at least one of the plurality of plates can be curved.
In any of the above tooling assemblies, at least one plate of the plurality of plates can further include a plurality of guide holes extending completely through the at least one plate.
In any of the above tooling assemblies, at least a subset of the plurality of metallic spikes can be removably attached to the plurality of plates.
A method of preparing a fibrous preform for use in a ceramic matrix composite comprises supporting the preform with a tooling fixture, and perforating the preform with a spiked array to form a perforated preform, the spiked array comprising a plate with a plurality of metallic spikes projecting away from the plate. When perforating the preform, the plurality of metallic spikes extend at least partially into a plurality of respective receiving holes in the tooling fixture.
The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:
The above method can further include prior to perforating the preform, applying a lubricant solution to the preform.
In any of the above methods, the lubricant solution can include at least one of water with polyvinyl alcohol, and alcohol with polyvinyl butyral.
In any of the above methods, when perforating the preform, the plurality of metallic spikes can be inserted into the preform such that they extend fully through a thickness of the preform.
Any of the above methods can further include with the plurality of spikes still inserted into the perforated preform, stabilizing the perforated preform via a drying process to remove the water or the alcohol of the lubricant solution.
In any of the above methods, stabilizing the preform can further include removing the polyvinyl alcohol or the poly vinyl butyral via a heating process.
A perforated preform formed via any of the above methods can further include a plurality of cylindrical holes extending through a thickness of the preform. Each hole of the plurality of holes can be spaced apart from an adjacent hole of the plurality of holes a distance ranging from 1.0 mm to 10 mm, and each hole of the plurality of holes can have a diameter ranging from 0.1 mm to 1.0 mm.
In the above perorated preform, the preform can be formed from tows of silicon carbide.
While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.
