Patent Application
20240400467
The present invention relates to ceramic matrix composites (CMCs), and more particularly, to the preparation of ceramic materials for use in ceramic matrix composites.
In the processing of CMCs, there is a need to infiltrate matrix within and around fibrous tows of a preform. Depending on the preform architecture, there can be large voids between adjacent tows of a preform that can become large defects after matrix infiltration. Such defects diminish interlaminar properties of the composite structure. Accordingly, a need exists for means of reducing such voids.
A method of forming a ceramic matrix composite includes preparing a plurality of fibrous ceramic plies by applying a binder solution loaded with ceramic particles to each of a first subset of plies, and applying the binder solution without ceramic particles to each of a second subset of plies. The method further includes arranging the plurality of plies to form a preform with a gradient along a thickness direction of the preform by stacking the first subset of plies to form a first zone of the preform, and stacking individual ones of the second subset of the plies on both sides of the first zone to form a second zone on each side of the first zone. Loading of the ceramic particles is higher in the first zone than in the second zones. The method further includes densifying the preform with a ceramic matrix.
A gradient preform includes a stacking arrangement of fibrous ceramic plies including a first zone having a first subset of plies, and a second zone disposed on each side of the first zone, each second zone having a second subset of plies. The preform further includes ceramic particles dispersed throughout the first zone such that loading of the ceramic particles is higher in the first zone than in the second zones.
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 a particle-loaded preform used to form a CMC component (e.g., for a gas turbine engine). More specifically, a gradient approach to particle loading creates the highest particle loading concentration at the midplane region of the preform and transitions to a particle-free surface (i.e., outer) region to allow for a more uniform infiltration of reactant vapors during chemical vapor infiltration (CVI). The resulting CMC component can have a more uniformly deposited matrix.
During preforming, a number of plies 10 can be laid up in a stack.
Particles 20 can be formed from one or more of silicon carbide, boron carbide, hafnium oxide, hafnium boride, aluminum oxide, ytterbium oxide, or zirconium boride, to name a few non-limiting examples. Particles 20 can be a homogeneous or heterogenous mixture of generally spherical, elongate, or otherwise irregularly shaped particles (e.g., short ceramic fibers). Particle size for an individual particle 20 can range from 0.5 microns to 100 microns, and particles 20 can further be a homogeneous or heterogenous mixture of such particle sizes. The number and/or size of particles 20 can be used to control particle loading throughout preform 16.
Preform 16 can be divided into a plurality of zones (collectively “zones Z”) defining the gradient microstructure. Particle loading can be highest at midplane zone ZA, which, as shown in
In alternative embodiments, any zone Z can include more or fewer plies 10 than depicted in
At step 104, particle-loaded plies can be laid up to form the midplane and intermediate zones. More specifically, plies with the highest particle loading can be stacked in the midplane zone. Plies with relative lower particle loading can be stacked and disposed on either side of the midplane zone to form intermediate zones. At step 106, the partially formed preform can be debulked/consolidated using one or a combination of mechanical and vacuum compressive force along with heat. This can nominally reduce the thickness of the preform and also remove at least some of the solvent from the binder solution. At step 108, plies prepared with only the binder solution (i.e., particle-free plies) can be laid up in contact with the intermediate zone(s) of the partially formed preform to form the surface zones of the gradient preform. Laying up particle-free plies after step 106 helps reduce the migration of particles from the intermediate and/or midplane zones into the surface zones. At step 110, debulking can be repeated on the entire gradient preform. Any loosely-adhered particles that migrate to the surface zones (i.e., migrant particles) between steps 106 and 110 can be optionally removed using a light brushing technique, the application of a lightly pressurized stream of air, etc.
In an alternative embodiment, the plies can be laid up in a different order, such as from one surface zone to the other. More specifically, a subset of particle-free plies intended for the inner surface of the preform can be laid up first. Layup can proceed with the plies of first intermediate zone, the midplane zone, the second intermediate zone, and finally, the outer surface zone plies. Debulking can occur repeatedly and at various stages in such an embodiment, such that steps 104-110 are differently ordered and some may be repeated. Such a layup can be necessary for non-planar preforms with inner plies becoming inaccessible during preforming, such as airfoils. In yet another alternative embodiment, all plies laid up can come from a stock of particle-loaded plies, which can be more economical with fewer manufacturing errors as it simplifies ply preparation. In such an embodiment, surface plies can be treated with brushing and/or pressurized air to remove at least a majority of the particles. Such removal techniques should be carried out more robustly/extensively than for the optional removal of migrant particles discussed above.
At step 112, the gradient preform can be densified with a matrix using CVI to form a CMC component. During densification, the plies are infiltrated by reactant vapors, and a gaseous precursor deposits on the ceramic tows. The matrix material can be silicon carbide or other suitable ceramic material. Densification is carried out until the resulting CMC has reached the desired residual porosity. Interface coating(s) (e.g., of boron nitride) can be deposited prior to the matrix to ensure that the composite fails in a non-brittle manner. In an alternative embodiment, densification can additionally and/or alternatively include other methodologies such as, but not limited to, melt infiltration (MI) and polymer infiltration and pyrolysis (PIP).
Because of the gradient microstructure of the preform, the matrix can deposit in an inside-out manner, referring directionally from the midplane to each outer surface 18, in a uniform manner. The increasing porosity from the midplane out prevents “canning off” of the preform region near the midplane, where the matrix deposits too quickly near the outer surface of the preform and prevents reactant vapors from accessing the midplane region. This can lead to asymmetrical densification with an undesirably porous midplane region compared to sufficiently densified outer surfaces. The inclusion of inorganic particles also provides additional surface area upon which the matrix deposits. The use of particle-free plies at the preform outer surfaces can be more cost effective than depositing particles throughout the preform thickness because fewer materials are needed to prepare surface plies.
After densification with matrix, additional particles (e.g., particles 20) can be applied to the outer surface of the CMC component in an optional smoothing step. Such a step can be carried out using a seal coating process suitable for ceramic substrates.
A CMC component formed from the disclosed gradient preform 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 method of forming a ceramic matrix composite includes preparing a plurality of fibrous ceramic plies by applying a binder solution loaded with ceramic particles to each of a first subset of plies, and applying the binder solution without ceramic particles to each of a second subset of plies. The method further includes arranging the plurality of plies to form a preform with a gradient along a thickness direction of the preform by stacking the first subset of plies to form a first zone of the preform, and stacking individual ones of the second subset of the plies on both sides of the first zone to form a second zone on each side of the first zone. Loading of the ceramic particles is higher in the first zone than in the second zones. The method further includes densifying the preform with a ceramic matrix.
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 steps:
The above method can further include applying the binder solution with the ceramic particles to a third subset of plies, and stacking individual ones of the third subset of plies on both sides of the first zone and between the first and second zones to form third zones on each side of the first zone.
In any of the above methods, arranging the preform can include forming the first zone, subsequently, forming the third zones, and debulking the first zone and the third zones.
Any of the above methods can further include subsequently, forming the second zones, and debulking the first zone, the second zones, and the third zones.
In any of the above methods, arranging the preform can include forming one of the second zones, subsequently, forming one of the third zones, subsequently, forming the first zone, subsequently, forming an other of the third zones, and subsequently, forming an other of the second zones.
Any of the above methods can further include debulking the first zone, the second zones, and the third zones.
Any of the above methods can further include removing migrant ceramic particles from the second zones using one of a brushing and blowing technique.
In any of the above methods, the step of densifying the preform with a ceramic matrix can include one or a combination of chemical vapor infiltration, melt infiltration, and polymer infiltration and pyrolysis.
In any of the above methods, the binder solution can include a solvent, a dispersant, and one of polyvinyl alcohol and polyvinyl butyral.
In any of the above methods, the ceramic particles can include one or a combination of silicon carbide, boron carbide, hafnium oxide, hafnium boride, aluminum oxide, ytterbium oxide, or zirconium boride.
In any of the above methods, the step of applying the binder solution to each of the first subset and the second subset of plies can include one of a spraying and pipetting technique.
In any of the above methods, each of the first subset and the second subset of plies can be impregnated with the binder solution.
A gradient preform includes a stacking arrangement of fibrous ceramic plies including a first zone having a first subset of plies, and a second zone disposed on each side of the first zone, each second zone having a second subset of plies. The preform further includes ceramic particles dispersed throughout the first zone such that loading of the ceramic particles is higher in the first zone than in the second zones.
The preform 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 preform, the plies can be formed from tows of silicon carbide.
In any of the above preforms, a tow architecture of each of the plies can be one of harness-satin, plain, twill, braid, and unidirectional.
In any of the above preforms, the ceramic particles can include one or a combination of silicon carbide, boron carbide, hafnium oxide, hafnium boride, aluminum oxide, ytterbium oxide, or zirconium boride.
In any of the above preforms, a size of the ceramic particles can range from 0.5 microns to 100 microns.
In any of the above preforms, a particle loading of the first zone can range from 5 wt % to 15 wt %.
In any of the above preforms, a particle loading of each of the second zones can be less than 5 wt %.
Any of the above preforms can further include a third zone disposed on both sides of the first zone and between the first zone and each of the second zone, each of the third zones having a third subset of plies.
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.
