Patent Publication Number: US-2023145812-A1

Title: 3d woven space filler

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims the benefit of U.S. Provisional Application No. 63/276,040 filed Nov. 5, 2021 for “3D WOVEN SPACE FILLER” by K. Read. 
    
    
     BACKGROUND 
     The present invention relates to ceramic matrix composites and, more particularly, space filling inserts for use in ceramic matrix composite preforms. 
     Many ceramic matrix composite (CMC) components for gas turbine engines have regions of variable wall thickness. Some of these regions are too small to form with standard ply(s) of woven cloth but too large to form using individual fiber tows. In such cases, space filling inserts can be used to build upon and prevent large voids in the body of the CMC. As with other locally-thickened regions of CMCs, these inserts can often present challenges in achieving a high and/or uniform density through the chemical vapor infiltration (CVI) process. 
     SUMMARY 
     A ceramic fiber preform includes a plurality of ceramic fiber plies arranged to define a wall, a void adjacent the wall, and an insert positioned within the void. The insert includes a first region having a first porosity and a second region in physical contact with the first region and having a second porosity. The first region and second region are formed from a woven ceramic material, the wall has a wall porosity, and the first porosity is less than at least one of the second porosity and the wall porosity. 
     A ceramic fiber preforms includes a woven ceramic insert having a first porosity and a plurality of ceramic fiber plies surrounding the insert to form an outer layer. The outer layer has a second porosity greater than the first porosity. 
     An insert for inclusion in a void of a ceramic fiber preform includes a first region having a first porosity and a second region in physical contact with the first region and having a second porosity. The first region and the second region are formed from a woven ceramic material, and the first porosity is different from the second porosity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a simplified perspective view of a preform structure with a triangular insert shown in close-up. 
         FIG.  2    is simplified cross-sectional view of an airfoil preform with an I-shaped insert shown in close-up. 
         FIG.  3    is a simplified cross-sectional view of a preform structure with a T-shaped core insert. 
     
    
    
     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. 
     DETAILED DESCRIPTION 
     This disclosure presents various space filling inserts, sometimes referred to as “noodles,” for incorporation into a CMC preform. The inserts can be formed using a three-dimensional (3D) weaving technique to create a structure with a gradient porosity through its thickness. More specifically, two or more regions of differing porosity can be incorporated into an insert depending on factors such as its thickness and shape. The gradient arrangement enables a more even matrix infiltration of the insert and encompassing preform structure. 
       FIG.  1    is a simplified perspective view of preform  10  with an enlarged view of insert  12 . Preform  10  can be used to form a CMC component for use in a gas turbine engine combustor, compressor, and/or turbine section, to name a few non-limiting examples. Preform  10  is formed from multiple plies  14  laid up in such a manner as to form a structure with a desired shape and thickness. Plies  14  can be formed from braided, woven, and/or chopped ceramic fibers or tows. The ceramic material can be silicon carbide or another suitable ceramic material. As shown in  FIG.  1   , plies  14  can be laid up to form walls  16  with curved regions  18 . The bending of plies  14  to form curved region  18  can create a void  20  between a subset of plies  14 . Void  20  can be too small to effectively fill with additional plies  14 , and too large to fill with individual ceramic tows or tow bundles. Thus, insert  12  can be formed to have a shape and size generally complementary to void  20 . More specifically, insert  12  can be formed to have a complementary triangular cross-sectional geometry, a thickness or width defined in one or a combination of the x and y-axes, and a length extending alone the z-axis. Generally speaking, insert  12  is sized to fill void  20  along the x, y, and z-axes. 
     Insert  12  can be formed from woven ceramic fibers, as is discussed in greater detail below. As can be seen in the enlarged view, insert  12  includes regions  22 ,  24 , and  26  in the concentrically innermost to outermost direction. Insert  12  can include just two or four regions in an alternative embodiment. Each region is associated with a different material porosity. In an exemplary embodiment, innermost (first) region  22  has a first porosity, middle (second) region  24  has a second porosity, and outermost (third) region  26  has a third porosity. The porosity gradient of insert  12  is such that first porosity&lt;second porosity&lt;third porosity. Material porosity can be a function of the fiber volume fraction of the woven ceramic material in each region  22 ,  24 , and  26 . Each of these regions can be formed to have a fiber volume fraction (i.e., the fraction of fiber volume to total volume of the insert) and a void/pore fraction (i.e., the fraction of void/pore volume to total volume of the insert) that differs from the other regions. In a preform (e.g., preform  10 ), fiber volume fraction and pore volume fraction are generally inversely proportional such that a region with low porosity will have a high fiber volume fraction relative to the other regions. In the embodiment shown, the fiber volume fraction of region  22  (first fiber volume fraction)&gt;the fiber volume fraction of region  24  (second fiber volume fraction)&gt;the fiber volume fraction of region  26  (third fiber volume fraction). In general, the fiber volume fraction of each region will differ from the immediately adjacent region by at least 1%. More specifically, region  22  can have a fiber volume fraction ranging from 40% to 45%, region  24  can have a fiber volume fraction ranging from 35% to 40%, and region  26  can have a fiber volume fraction ranging from 30% to 35%. Walls  16  abutting void  20 /insert  12  can also have a wall porosity and fiber volume fraction different from most or all of sections  22 ,  24 ,  26 . In the embodiment shown, walls  16  can have a porosity and fiber volume fraction generally equal to or slightly less than immediately adjacent region  26 . More specifically, the fiber volume fraction of walls  16  can range from 32% to 40%. 
     Insert  12  can be formed by 3D (i.e., Jacquard) weaving, having fiber components in three, generally orthogonal (x, y, z) axes. As with two-dimensional (2D) woven structures (e.g., plies  14 ), insert  12  can have warp and weft fibers (tows), but can further include z-fibers orthogonal to and crossing over layers of warp and/or weft fibers. The various fibers can be formed from the same ceramic (e.g., silicon carbide) material, or from combinations of different ceramics. In an alternative embodiment, polymer fibers or yarns can be included at some positions on the loom and incorporated into the insert. In such an embodiment, the polymer fibers can be decomposed (e.g., thermally or chemically) during subsequent processing to help locally control the fiber volume fraction/porosity of the insert, as these fugitive polymer fibers leave behind open spaces when decomposed. Certain embodiments can be formed such that each section  22 ,  24 ,  26  is separately woven from and joined with the other sections. More specifically, first section  22  can be woven, then second section  24  can be woven around first section  22 , then third section  26  can be woven around section  24 . In order to achieve the porosity gradient across sections  22 ,  24 , and  26 , material characteristics such as fiber length, shape, and/or cross-sectional area can be varied to achieve different fiber volume fractions. It is alternatively and/or additionally possible to modify the weaving technique/pattern from section to section to vary fiber spacing and number of interlacements between yarns. For example, increased fiber spacing can lead to a decrease in fiber volume fraction, and a greater number of interlacements can lead to an increase in fiber volume fraction. 
       FIG.  2    is a simplified cross-sectional view of airfoil preform  110  with an enlarged view of insert  112 . Like preform  10 , preform  110  is formed from various plies  114 , which can be substantially similar to plies  14 . Insert  112  has an I-shaped cross-sectional geometry and is incorporated into an airfoil structural rib spanning between outer walls  116  formed by plies  114 . Although not visible in  FIG.  2   , insert  112  occupies a complementary void between rib walls  116  also formed by plies  114 . 
     Instead of multiple concentric regions, insert  112  has abutting regions  122 ,  124 ,  126 , and  128 . In the embodiment shown, the porosity gradient is such that first region  122 &lt;second region  124 &lt;third region  126 =fourth region  128 . That is, the distal ends (regions  126  and  128 ) of insert  112  can have equal porosities. In an alternative embodiment, all four regions  122 ,  124 ,  126 ,  128  can have different porosities. In another alternative embodiment, insert  112  can have only three regions, for example, with one on each end and one larger section (e.g., a combination of regions  122  and  124 ) disposed between the two ends. Other arrangements are contemplated herein. The fiber volume fraction of each region can be substantially similar to the ranges discussed above with respect to insert  12 . That is, the fiber volume fraction of region  122  can range from 40% to 45%, region  124  can have a fiber volume fraction ranging from 35% to 40%, and regions  126  and  128  can each have a fiber volume fraction ranging from 30% to 35%. Walls  116  can have a fiber volume fraction ranging from 32% to 40%. Like insert  12 , insert  112  can be formed by 3D weaving. Each section can be individually woven and joined together using, for example, using a stitching technique to secure each section to the abutting section, or various adhesives can be used. 
     Referring now to both  FIGS.  1  and  2   , preforms  10  and  110  can undergo matrix formation and densification using a CVI process in which plies  14 ,  114  and inserts  12 ,  112  are infiltrated by reactant vapors, and a gaseous precursor deposits on the ceramic fibers. The matrix material can be a silicon carbide or other suitable ceramic material. Densification is carried out until the resulting CMC has reached the desired residual porosity. The gradient arrangement of inserts  12 ,  112  with respect to the abutting walls  16 ,  116  allows for a more even distribution of matrix precursor material within preforms  10 ,  110 . This occurs because sufficient amounts of precursor can reach the inner (i.e., less porous) regions before the walls or outer regions seal off/become too densely packed with precursor due to their relatively greater porosity. With respect to inserts  12 ,  112 , the regions can be arranged in any desired manner based on the expected direction of flow of the gaseous precursor in the reactor, for example, with regions more exposed to the gaseous precursor being more porous than those shielded by other preform structures. The porosity/fiber volume fraction gradient of insert  12 , for example, can produce a uniform density to the final workpiece (i.e., post-densification) by facilitating infiltration through higher porosity regions and providing higher fiber volume fraction in regions more difficult to infiltrate. More generally, the porosity gradient of any insert (e.g.,  112 ) can be selected to produce desired densities in different portions of the completed workpiece by providing locally increased preform density or locally enhanced infiltration via increased porosity. 
       FIG.  3    is simplified cross-sectional view of preform  210  having T-shaped core insert  212  surrounded by plies  214 . Instead of being inserted into a void created by the lay-up of plies  214 , core insert  212  can serve as a scaffolding on which to lay up plies  214 . Core insert  212  can further make up the majority (greater than 50%) of the total volume of preform  210 . Plies  214  form a wall or outer layer  216  surrounding core insert  212 . Plies  214  are substantially similar in composition to plies  14  and  114 . Core insert  212  is similar to inserts  12  and  112  in composition and method of formation. However, core insert  212  can have a generally uniform porosity while a porosity gradient is created across preform  210  by making core insert  212  less porous (having a higher fiber volume fraction) than surrounding outer layer  216 . In an alternative embodiment, core insert  212  can be formed to have regions of varying porosity. Preform  210  can undergo matrix formation in the same manner as preforms  10  and  110  such that a porosity gradient permits more even matrix distribution. 
     It should be understood that various other insert shapes, such as rectangular, circular, elliptical, “U,” and “V” can alternatively and/or additionally be formed for incorporation into the disclosed preforms without departing from the scope of the invention. A CMC component formed with the disclosed inserts can be incorporated into aerospace, maritime, or industrial equipment, to name a few, non-limiting examples. 
     DISCUSSION OF POSSIBLE EMBODIMENTS 
     The following are non-exclusive descriptions of possible embodiments of the present invention. 
     A ceramic fiber preform includes a plurality of ceramic fiber plies arranged to define a wall, a void adjacent the wall, and an insert positioned within the void. The insert includes a first region having a first porosity and a second region in physical contact with the first region and having a second porosity. The first region and second region are formed from a woven ceramic material, the wall has a wall porosity, and the first porosity is less than at least one of the second porosity and the wall porosity. 
     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 ceramic fiber plies and the woven ceramic material can be formed from silicon carbide. 
     In any of the above preforms, the insert can further include a third region in physical contact with at least one of the first or second region and having a third porosity. 
     In any of the above preforms, the first porosity can be less than the second porosity, and the second porosity can be less than the third porosity and the wall porosity. 
     In any of the above preforms, the first region can have a first fiber volume fraction, the second region can have a second fiber volume fraction, the third region can have a third fiber volume fraction, and the wall can have a wall fiber volume fraction. 
     In any of the above preforms, the first fiber volume fraction can be greater than the second fiber volume fraction, and the second fiber volume fraction can be greater than the third fiber volume fraction and the wall fiber volume fraction. 
     In any of the above preforms, the insert can have a one of a triangular cross-sectional shape and an “I” cross-sectional shape. 
     A gas turbine engine component can include any of the above preforms and a ceramic matrix deposited onto and within the preform. 
     A ceramic fiber preforms includes a woven ceramic insert having a first porosity and a plurality of ceramic fiber plies surrounding the insert to form an outer layer. The outer layer has a second porosity greater than the first porosity. 
     In the above preform, the insert can have a “T” cross-sectional shape. 
     In any of the above preforms, the insert can be 50% or more of the total volume of the preform. 
     An insert for inclusion in a void of a ceramic fiber preform includes a first region having a first porosity and a second region in physical contact with the first region and having a second porosity. The first region and the second region are formed from a woven ceramic material, and the first porosity is different from the second porosity. 
     In the above insert, the woven ceramic material can include tows of silicon carbide. 
     Any of the above inserts can further include woven polymer fibers. 
     Any of the above inserts can further include a third region in physical contact with at least one of the first or second region and having a third porosity, and the third region can be formed from the woven ceramic material. 
     In any of the above inserts, the first region can be positioned concentrically within the second region, the second region can be positioned concentrically within the third region, the first porosity can be less than the second porosity, and the second porosity can be less than the third porosity. 
     In any of the above inserts, the first region can have a first fiber volume fraction, the second region can have a second fiber volume fraction less than the first fiber volume fraction, and the third region can have a third fiber volume fraction less than the second fiber volume fraction. 
     Any of the above inserts can have a triangular cross-sectional shape. 
     Any of the above inserts can further include a fourth region in physical contact with at least one of the first, second, or third regions and having a fourth porosity. The fourth region can be formed from the woven ceramic material, and the fourth porosity can be greater than at least one of the first porosity, the second porosity, and the third porosity. 
     Any of the above inserts can have a “I” cross-sectional shape. 
     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.