Patent Publication Number: US-2023159397-A1

Title: Ceramic matrix composite article and method of making the same

Description:
BACKGROUND 
     A gas turbine engine typically includes a fan section, a compressor section, a combustor section and a turbine section. Air entering the compressor section is compressed and delivered into the combustion section where it is mixed with fuel and ignited to generate a high-speed exhaust gas flow. The high-speed exhaust gas flow expands through the turbine section to drive the compressor and the fan section. The compressor section may include low and high pressure compressors, and the turbine section may also include low and high pressure turbines. 
     Ceramic matrix composites (“CMC”) are being considered for certain gas turbine engine components, and have usefulness in other fields as well. For instance, CMCs can be employed for airfoils in the compressor or turbine sections of a gas turbine engine. Among other attractive properties, CMCs have high temperature resistance. Despite this attribute, however, there are unique challenges to implementing CMCs in airfoils. 
     SUMMARY 
     A method of making a ceramic matrix composite component according to an exemplary embodiment of this disclosure, among other possible things includes forming a ceramic matrix composite component by infiltrating an array of ceramic-based reinforcements with a ceramic-based matrix, applying filler particles to a surface of the ceramic matrix composite component such that the filler particles fill in gaps between adjacent ones of the ceramic-based reinforcements, and infiltrating the filler particles with a filler matrix. 
     In a further example of the foregoing, the reinforcements are fibers. 
     In a further example of any of the foregoing, the fibers are woven or braided to form the array. 
     In a further example of any of the foregoing, the filler particles are disposed in a liquid carrier to form a slurry. The applying step includes applying the slurry to the surface of the ceramic matrix composite component. 
     In a further example of any of the foregoing, the method includes the step of evaporating the liquid carrier after the applying step. 
     In a further example of any of the foregoing, after the applying step, the filler particles are at the surface of the ceramic matrix composite component but not in the array of ceramic-based reinforcements. 
     In a further example of any of the foregoing, after the applying step, the filler particles fill more than 30% of the volume of the gaps. 
     In a further example of any of the foregoing, after the step of infiltrating the filler particles with the filler matrix, the filler matrix is disposed over the ceramic-based reinforcements and ceramic-based matrix, and is in the gaps. 
     In a further example of any of the foregoing, the filler particles are oxide, carbide, or boride particles. 
     A ceramic matrix composite component according to an exemplary embodiment of this disclosure, among other possible things includes an array of ceramic-based reinforcements disposed in a ceramic-based matrix. The ceramic-based reinforcements are arranged in an array. There are gaps between adjacent ones of the ceramic-based reinforcements at a surface of the ceramic matrix composite component. The ceramic matrix composite also includes a filler composition disposed in the gaps. The filler composition includes filler particles disposed in a filler matrix. 
     In a further example of the foregoing, the reinforcements are fibers. 
     In a further example of any of the foregoing, the fibers are woven or braided to form the array. 
     In a further example of any of the foregoing, the filler particles are not within the array of ceramic-based reinforcements. 
     In a further example of any of the foregoing, the filler matrix is the same material as the ceramic-based matrix and the filler matrix and ceramic-based matrix are continuous with one another. 
     In a further example of any of the foregoing, the filler matrix is disposed over the ceramic-based reinforcements and ceramic-based matrix, and is in the gaps. 
     In a further example of any of the foregoing, the filler matrix is a different material than the ceramic-based matrix. 
     In a further example of any of the foregoing, the filler matrix provides at least one of mechanical, thermal, and environmental protection to the ceramic matrix composite component. 
     In a further example of any of the foregoing, the filler particles fill more than 30% of the volume of the gaps. 
     In a further example of any of the foregoing, the filler particles have a uniform distribution of particle size between 0.5 and 100 microns. 
     In a further example of any of the foregoing, the ceramic matrix composite component is a component of a gas turbine engine. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    schematically shows an example gas turbine engine. 
         FIG.  2    schematically shows a detail view of woven fibers for a ceramic matrix composite component. 
         FIG.  3    schematically shows a detail view of a ceramic matrix composite component. 
         FIG.  4    shows a detail view of the ceramic matrix composite component of  FIG.  2    with filler particles. 
         FIG.  5    shows a detail view of the ceramic matrix composite component of  FIG.  2    with filler particles and a filler matrix. 
         FIG.  6    shows a method of making the ceramic matrix composite component of  FIGS.  3 - 5   . 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1    schematically illustrates a gas turbine engine  20 . The gas turbine engine  20  is disclosed herein as a two-spool turbofan that generally incorporates a fan section  22 , a compressor section  24 , a combustor section  26 , and a turbine section  28 . The fan section  22  may include a single-stage fan  42  having a plurality of fan blades  43 . The fan blades  43  may have a fixed stagger angle or may have a variable pitch to direct incoming airflow from an engine inlet. The fan  42  drives air along a bypass flow path B in a bypass duct  13  defined within a housing  15  such as a fan case or nacelle, and also drives air along a core flow path C for compression and communication into the combustor section  26  then expansion through the turbine section  28 . A splitter  29  aft of the fan  42  divides the air between the bypass flow path B and the core flow path C. The housing  15  may surround the fan  42  to establish an outer diameter of the bypass duct  13 . The splitter  29  may establish an inner diameter of the bypass duct  13 . Although depicted as a two-spool turbofan gas turbine engine in the disclosed non-limiting embodiment, it should be understood that the concepts described herein are not limited to use with two-spool turbofans as the teachings may be applied to other types of turbine engines including three-spool architectures. The engine  20  may incorporate a variable area nozzle for varying an exit area of the bypass flow path B and/or a thrust reverser for generating reverse thrust. 
     The exemplary engine  20  generally includes a low speed spool  30  and a high speed spool  32  mounted for rotation about an engine central longitudinal axis A relative to an engine static structure  36  via several bearing systems  38 , It should be understood that various bearing systems  38  at various locations may alternatively or additionally be provided, and the location of bearing systems  38  may be varied as appropriate to the application. 
     The low speed spool  30  generally includes an inner shaft  40  that interconnects, a first (or low) pressure compressor  44  and a first (or low) pressure turbine  46 . The inner shaft  40  is connected to the fan  42  through a speed change mechanism, which in the exemplary gas turbine engine  20  is illustrated as a geared architecture  48  to drive the fan  42  at a lower speed than the low speed spool  30 . The inner shaft  40  may interconnect the low pressure compressor  44  and low pressure turbine  46  such that the low pressure compressor  44  and low pressure turbine  46  are rotatable at a common speed and in a common direction. In other embodiments, the low pressure turbine  46  drives both the fan  42  and low pressure compressor  44  through the geared architecture  48  such that the fan  42  and low pressure compressor  44  are rotatable at a common speed. Alternatively, the low pressure compressor  44  includes a forward hub  45 A and an aft hub  45 B driven by the inner shaft  40 . 
     Although this application discloses geared architecture  48 , its teaching may benefit direct drive engines having no geared architecture. The high speed spool  32  includes an outer shaft  50  that interconnects a second (or high) pressure compressor  52  and a second (or high) pressure turbine  54 . A combustor  56  is arranged in the exemplary gas turbine  20  between the high pressure compressor  52  and the high pressure turbine  54 . A mid-turbine frame  57  of the engine static structure  36  may be arranged generally between the high pressure turbine  54  and the low pressure turbine  46 . The mid-turbine frame  57  further supports bearing systems  38  in the turbine section  28 . In the illustrated example, the mid-turbine frame  57  only includes a bearing system  38  that supports the high spool  50  and the mid-turbine frame  57  does not support the low speed spool  30 . Additionally, a pair of bearing systems  38 E are located adjacent a downstream end of the low speed spool  30  adjacent an exhaust outlet of the gas turbine engine to support the low speed spool  30 . Furthermore, a bearing assembly  38 C can be located radially inward from the combustor  56  and supported by a diffuser case and be used in place of or in addition to the bearing system  38  associated with the mid-turbine frame  57 . The inner shaft  40  and the outer shaft  50  are concentric and rotate via bearing systems  38  about the engine central longitudinal axis A which is collinear with their longitudinal axes. 
     Airflow in the core flow path C is compressed by the low pressure compressor  44  then the high pressure compressor  52 , mixed and burned with fuel in the combustor  56 , then expanded through the high pressure turbine  54  and low pressure turbine  46 . The mid-turbine frame  57  includes airfoils  59  which are in the core flow path C. The turbines  46 ,  54  rotationally drive the respective low speed spool  30  and high speed spool  32  in response to the expansion. It will be appreciated that each of the positions of the fan section  22 , compressor section  24 , combustor section  26 , turbine section  28 , and fan drive gear system  48  may be varied. For example, gear system  48  may be located aft of the low pressure compressor, or aft of the combustor section  26  or even aft of turbine section  28 , and fan  42  may be positioned forward or aft of the location of gear system  48 . 
     The low pressure compressor  44 , high pressure compressor  52 , high pressure turbine  54  and low pressure turbine  46  each include one or more stages having a row of rotatable airfoils. Each stage may include a row of vanes adjacent the rotatable airfoils. The rotatable airfoils are schematically indicated at  47 , and the vanes are schematically indicated at  49 . In one example, the low pressure compressor  44  includes at least 4 stages and no more than 7 stages and in another example, the low pressure compressor  44  includes at least 5 stages and no more than 7 stages. In both examples, the high pressure compressor  52  includes more stages than the low pressure compressor. 
     The engine  20  may be a high-bypass geared aircraft engine. The bypass ratio can be greater than or equal to 10.0 and less than or equal to about 18.0, or more narrowly can be less than or equal to 16.0. The geared architecture  48  may be an epicyclic gear train, such as a planetary gear system or a star gear system. The epicyclic gear train may include a sun gear, a ring gear, a plurality of intermediate gears meshing with the sun gear and ring gear, and a carrier that supports the intermediate gears. With the planetary gear system, the ring gear is fixed from rotation relative to the engine static structure  36  and the carrier rotates with the fan  42 . With the star gear system, the carrier is fixed from rotation relative to the engine static structure  36  and the ring gear rotates with the fan  42 . The sun gear may provide an input to the gear train. The ring gear (e.g., star gear system) or carrier (e.g., planetary gear system) may provide an output of the gear train to drive the fan  42 . A gear reduction ratio may be greater than or equal to 2.3, or more narrowly greater than or equal to 3.0, and in some embodiments the gear reduction ratio is greater than or equal to 3.4, The gear reduction ratio may be less than or equal to 4.0 4.2. The fan diameter is significantly larger than that of the low pressure compressor  44 . The low pressure turbine  46  can have a pressure ratio that is greater than or equal to 8.0 and in some embodiments is greater than or equal to 10.0. The low pressure turbine pressure ratio can be less than or equal to 13.0, or more narrowly less than or equal to 12.0. Low pressure turbine  46  pressure ratio is pressure measured prior to an inlet of low pressure turbine  46  as related to the pressure at the outlet of the low pressure turbine  46  prior to an exhaust nozzle. It should be understood, however, that the above parameters are only exemplary of one embodiment of a geared architecture engine and that the present invention is applicable to other gas turbine engines including direct drive turbofans. All of these parameters are measured at the cruise condition described below. 
     A significant amount of thrust is provided by the bypass flow B due to the high bypass ratio. The fan section  22  of the engine  20  is designed for a particular flight condition—typically cruise at about 0.8 Mach and about 35,000 feet (10,668 meters). The flight condition of 0.8 Mach and 35,000 ft (10,668 meters), with the engine at its best fuel consumption—also known as “bucket cruise Thrust Specific Fuel Consumption (′TSFC)”—is the industry standard parameter of lbm of fuel being burned divided by lbf of thrust the engine produces at that minimum point, The engine parameters described above, and those in the next paragraph are measured at this condition unless otherwise specified. 
     “Fan pressure ratio” is the pressure ratio across the fan blade  43  alone, without a Fan Exit Guide Vane (“FEGV”) system. A distance is established in a radial direction between the inner and outer diameters of the bypass duct  13  at an axial position corresponding to a leading edge of the splitter  29  relative to the engine central longitudinal axis A. The fan pressure ratio is a spanwise average of the pressure ratios measured across the fan blade  43  alone over radial positions corresponding to the distance. The fan pressure ratio can be less than or equal to 1.45, or more narrowly greater than or equal to 1.25, such as between 1.30 and 1.40, “Corrected fan tip speed” is the actual fan tip speed in ft/sec divided by an industry standard temperature correction of [(Tram ° R)/(518.7° R)]0.5, The corrected fan tip speed can be less than or equal to 1150.0 ft/second (350.5 meters/second), and can be greater than or equal to 1000.0 ft/second (304.8 meters/second). 
     Some of the components of the gas turbine engine  20 , such as airfoils in the turbine section  28 , can be made of ceramic matrix composite (CMC) materials. In general, CMC components include ceramic-based reinforcements, such as fibers, in a ceramic-based matrix. CMC components optionally include coatings that can provide mechanical, thermal, and/or environmental protection to the underlying CMC material. 
     In the example where the reinforcements are fibers, the fibers can be arranged in a variety of ways that are known in the art, such as unidirectionally, in various weaves including three-dimensional weaves, braids, etc. In some more particular examples, the fibers can be arranged in bundles or tows. However, it should be understood that other non-fiber reinforcements such as grains or particles are also contemplated. 
     Moreover, the CMC components can include several plies or layers of CMC material stacked and bonded to one another to form a three-dimensional component. 
       FIG.  2    shows a detail top-down view of an example fiber array for a CMC component  100 . In this example, the fiber array includes a first set of fibers  102   a  and a second set of fibers  102   b  that are woven together. The fibers  102   a / 102   b  comprise a ceramic-based material. Though the sets of fibers  102   a / 102   b  in this example are oriented perpendicular to one another, it should be understood that other weaves, other nonwoven fiber configurations, or non-fiber reinforcements are also contemplated for the component  100 . Additionally, in  FIG.  2   , the first and second sets of fibers  102   a / 102   b  comprise individual fibers. In other examples, the first and second sets of fibers  102   a / 102   b  can comprise bundles or tows of fibers in place of the individual fibers. 
     In the particular weave pattern of  FIG.  2   , the first set of fibers  102   a  are arranged generally in a horizontal direction and each have an extent that lays on top of the second set of fibers  102   b , which are arranged generally in a vertical direction. The first set of fibers  102   a  is therefore nearest the surface of the component  100  in the example of  FIG.  2   . As shown therein, there are various gaps G at the surface between adjacent ones of the fibers  102   a . Some gaps G′ are due to spacing between adjacent ones of the first set of fibers  102   a . Other gaps G″ are the result of spaces formed due to the weave pattern of the first set of fibers  102   a  with the second set of fibers  102   b.    
       FIG.  3    schematically shows a cutaway view of a surface  106  of the component  100  including several of the first set of fibers  102   a  infiltrated with a matrix material  104 . The matrix material  104  comprises a ceramic-based material. Though in this example only certain of the first set of fibers  102   a  are shown, it should be understood that in other examples the surface  106  of the component  100  could also or alternatively include fibers of the second set of fibers  102   b , depending on the weave pattern or other arrangement of fibers  102   a / 102   b . The surface  106  of the component  100  includes gaps G between adjacent ones of the fibers  102   a / 102   b  which could be either of the gaps G′ and G″ discussed above. The gaps G cause the surface  106  of the component  100  to be rough. Reducing the surface  106  roughness improves the aerothermal, aerodynamic, and durability performance of the component  100 . To that end, as shown in  FIGS.  4 - 5   , a filler composition  108  is disposed in gaps G. The filler composition  108  fills in the gaps G to smooth the surface  106  of the component  100 . 
     The filler composition  108  includes filler particles  110  disposed in a filler matrix  112 . The filler particles  110  can be oxide, carbide, or boride particles including but not limited to silicon carbide (SiC), silicon oxycarbide (SiOC), boron carbide (B 4 C), hafnium boride (HfB 2 ), zirconium boride (ZrB 2 ), ytterbium oxide (Yb 2 O 3 ), aluminum oxide (Al 2 O 3 ), and hafnium oxide (HfO 2 ). 
     In some examples, the filler particles  110  have a size (diameter) between about 0.5 and about 100 microns. In a particular example, the filler particles  110  have a size (diameter) between about 5 and about 50 microns. In a further example, the filler particles  110  have a size (diameter) between about 5 and about 30 microns. A ratio of a diameter of the fibers  102   a / 102   b  to the size (diameter) of the filler particles  110  can be between about 0.1 and about 24. The filler particles  110  can have a single modal or uniform size distribution, e.g., the majority (more than half) of the particles have a size within about 5% of a selected particle size. In other examples, however, the filler particles  110  can have bi- or other multi-modal size distributions. As used herein, the term “about” has the typical meaning in the art, however in a particular example “about” can mean deviations of up to 10% of the values described herein. 
     In one example, the filler particles  110  are located primarily, or fully, in the gaps G at the surface  106 , and are not within the fiber array  102   a / 102   b  or existing matrix  104 . 
     In one example, the filler particles  110  fill more than 30% of the volume of the gaps G. In a further example, the filler particles  110  fill more than 50% of the volume of the gaps G. In general, the higher the percentage of volume of gaps G filled with filler particles  110 , the lower the surface roughness of the component  100 . 
     In the example of  FIG.  5   , the filler matrix  112  is disposed over substantially the entire surface  106 , e.g., it is disposed on the fibers  102   a / 102   b  and matrix  104  as well as in the gaps G. In some examples, the material of the filler matrix  112  is selected such that the filler matrix  112  serves as a coating or barrier layer for the component  100 . In another example, the filler matrix  112  is the same material as the matrix  104  of the component  100  such that in the final component  100  the filler matrix  112  is continuous with the matrix  104 . 
       FIG.  6    shows an example method  200  for making the component  100 . In step  202 , a CMC component  100  having ceramic-based reinforcements, such as fibers  102   a / 102   b , disposed in a matrix  104  is formed by any known method. For instance, the fibers  102   a / 102   b  are arranged in an array in a desired configuration, and the fiber array is infiltrated with the matrix  104 . The matrix  104  infiltration can be accomplished by any known method such as chemical vapor deposition (CVD), chemical vapor infiltration (CVI), polymer infiltration pyrolysis (PIP), or melt infiltration (MI). Step  202  can also include densification or curing steps as are known in the art. 
     In step  204 , the filler particles  110  are applied to the surface  106  and fill in the gaps G as shown in  FIG.  4    discussed above. As noted above, in some examples, the filler particles  110  are primarily, or fully, in the gaps and do not migrate into the fiber array  102   a / 102   b , after the applying step  204 . The filler particles  110  can be applied to the surface  106  by painting, injecting, air spraying, pipetting or dropping, or another suitable method. 
     In one example, the filler particles  110  are dispersed in a liquid carrier to form a slurry for the applying step  204 . The liquid carrier can be aqueous or alcohol, for instance. The slurry may also include dispersants or polymer additives such as poly vinyl alcohol (PVA), poly vinyl butyral (PVB), poly ethylene glycol (PEG), or a preceramic polymer, which can assist in binding the filler particles  110  to the surface  106  of the component  100  until the filler matrix  112  matrix can be deposited (as discussed below). In this example, the component  100  is subjected to an evaporation step to evaporate off the liquid carrier, leaving the filler particles  110  in the gaps G. The evaporation step can include heating or another method, depending on the liquid carrier used. 
     In step  206 , the filler particles  110  are infiltrated with the filler matrix  112  as shown in  FIG.  5    discussed above. As noted above, the filler matrix  112  may be disposed over substantially the entire surface  106 , including over the fiber array  102   a / 102   b  and matrix  104  and in the gaps G. The infiltration step  206  can be performed by any suitable method, such as the methods discussed above for infiltrating the fiber array  102   a / 102   b  with the matrix  104 . 
     In some examples, the filler particles  110  can act as nucleation sites for the filler matrix  112 , encouraging the formation of a uniform filler matrix  112 . 
     In some examples, optional processing steps may be performed after the infiltration step  206 , such as densification or curing steps to harden the filler matrix  112  and trap the filler particles  110  in the gaps G. 
     As noted above, reducing the surface  106  roughness of the component  100  improves the aerothermal, aerodynamic, and durability performance of the component  100 . Because the underlying component  100  is unaltered by the application of the filler composition  108  according to the above-described method  200 , the surface  106  roughness is reduced without debiting the characteristics of the reinforcements such as fibers  102   a / 102   b , e.g., by changing their shape or size. Moreover, above-described method  200  can be employed to improve existing CMC components because there is no need to alter the underlying material. 
     Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.