Patent Publication Number: US-11021971-B2

Title: CMC blade with monolithic ceramic platform and dovetail

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 61/890,005, which was filed on Oct. 11, 2013 and is incorporated herein by reference. 
    
    
     BACKGROUND 
     This disclosure relates to a ceramic matrix composite blade with a monolithic ceramic portion. 
     Gas turbine engines may be made more efficient, in part, by increasing engine operating temperatures. Exotic metallic components within the engine are already near their maximum operating temperatures. To further increase temperatures within the engine, both monolithic ceramic and fiber reinforced ceramic matrix composite (CMC) components are increasingly used and have higher temperature capabilities than more conventional materials. 
     Ceramic composite blades have been proposed in which CMC layers extend from the root to the airfoil tip. The CMC layers are encased in a monolithic ceramic that extends from the dovetail (root) to the airfoil tip. The monolithic ceramic also provides the platform. 
     SUMMARY 
     In one exemplary embodiment, a blade for a gas turbine engine includes a fiber reinforced ceramic matrix composite structure that provides an airfoil with an exposed exterior airfoil surface and a refractory structure that provides at least an outer portion of a root secured relative to the airfoil. 
     In a further embodiment of the above, the ceramic matrix composite structure includes an inner root. The outer portion of the root is secured over the inner root. The refractory structure includes substantially isotropic, monolithic refractory material including but not limited to silicon nitride, silicon carbide, aluminum nitride, molybdenum silicide, molybdenum-silicon-boron alloy, and admixtures thereof. 
     In a further embodiment of any of the above, the outer portion includes angled walls that provide a dovetail. 
     In a further embodiment of any of the above, the inner root includes a root end that extends beyond the angled walls. 
     In a further embodiment of any of the above, the refractory structure includes a platform. 
     In a further embodiment of any of the above, the refractory structure has a neck interconnecting the outer portion to the platform. 
     In a further embodiment of any of the above, the platform includes an aperture through which the airfoil extends. 
     In a further embodiment of any of the above, the platform surrounds a perimeter of airfoil. 
     In a further embodiment of any of the above, the ceramic matrix composite structure provides a fillet arranged about the perimeter and overlaps the platform and the airfoil. 
     In a further embodiment of any of the above, the refractory structure includes an integral fillet that is arranged about the perimeter. 
     In another exemplary embodiment, a rotating assembly for a gas turbine engine includes a rotor including a slot, a blade that has a fiber reinforced ceramic matrix composite structure that provides an airfoil with an exposed exterior airfoil surface, and a refractory structure that provides at least an outer portion of a root that is secured relative to the airfoil and received in the slot. 
     In a further embodiment of the above, the ceramic matrix composite structure includes an inner root. The outer portion is secured over the inner root. The refractory structure includes substantially isotropic, monolithic refractory material including but not limited to silicon nitride, silicon carbide, aluminum nitride, molybdenum silicide, molybdenum-silicon-boron alloy, and admixtures thereof. 
     In a further embodiment of any of the above, the outer portion includes angled walls that provide a dovetail. The dovetail engages the rotor within the slot. 
     In a further embodiment of any of the above, the inner root includes a root end that extends beyond the angled walls. 
     In a further embodiment of any of the above, the refractory structure includes a platform that extends circumferentially to opposing mate faces. The mate face is arranged proximate to adjacent mate faces of adjacent blades supported by the rotor. 
     In a further embodiment of any of the above, the refractory structure has a neck that interconnects the outer portion to the platform. 
     In a further embodiment of any of the above, the platform includes an aperture through which the airfoil extends. 
     In a further embodiment of any of the above, the platform surrounds a perimeter of airfoil. 
     In a further embodiment of any of the above, the ceramic matrix composite structure provides a fillet arranged about the perimeter and overlaps the platform and the airfoil. 
     In a further embodiment of any of the above, the refractory structure includes an integral fillet that is arranged about the perimeter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1  is a schematic side view of an example turbine blade. 
         FIG. 2  is a highly schematic cross-sectional view of the blade shown in  FIG. 1  arranged in a rotor slot. 
         FIG. 3  is a top view of the blade shown in  FIG. 1 . 
         FIG. 4  is one example of a fillet provided between a platform and an airfoil. 
         FIG. 5  is another example of a fillet provided between the platform and the airfoil. 
     
    
    
     The embodiments, examples and alternatives of the preceding paragraphs, the claims, or the following description and drawings, including any of their various aspects or respective individual features, may be taken independently or in any combination. Features described in connection with one embodiment are applicable to all embodiments, unless such features are incompatible. 
     DETAILED DESCRIPTION 
     A turbine blade  10  is schematically shown in  FIG. 1 . The blade  10  includes an airfoil  12  extending in a radial direction from a platform  14  to a tip  18 . The platform  14  is supported by a root  16 , which is received in a slot  42  of a rotor  40  of gas turbine engine, as shown in  FIG. 2 . With continuing reference to  FIG. 1 , a neck  22  is provided between the root  16  and the platform. The airfoil  12  includes an exterior airfoil surface  20 , and the root  16  includes an exterior root surface  24 . 
     The blade  10  is constructed from a fiber reinforced ceramic matrix composite structure and a refractory structure secured to one another. In the example, the ceramic matrix composite structure provides the airfoil  12 , and the refractory structure provides the platform  14 . The ceramic matrix composite structure together with the refractory structure provides the root  16 . In one example, the refractory structure is an isotropic material such as monolithic ceramics and Mo-SIB. 
     Referring to  FIG. 2 , a ceramic matrix composite structure provides the airfoil  12  connected to an inner root  32  by an inner neck. Although not needed for certain ceramic blade applications, cooling flow inlet  36  may be provided in the inner root  32  to supply a cooling fluid to a cooling passage  38  in the airfoil  12 . 
     The ceramic matrix composite portion of the structure is typically constructed from multiple composite layers. In one example method of manufacture, silicon-carbide fibers are coated with a pre-ceramic polymer resin to provide a layer. In one example, multiple layers are stacked into plies, and the plies are arranged about a form in the shape of an article. The pre-ceramic polymer is pyrolyzed to produce ceramic matrix composite structure of, for example, silicon carbide, silicon oxycarbide, and silicon oxy carbonitride. The matrix of ceramic matrix composite structure can be formed by other methods if desired, for example, by chemical vapor infiltration (CVI) or melt infiltration using glasses or silicon metal. Multiple types of matrix infiltration may be used if desired. 
     The ceramic matrix composite structure provides the exterior airfoil surface  20 , which can better withstand impact from foreign object debris than, for example, a monolithic ceramic. In the example, the entire airfoil  12  is made from ceramic matrix composite. The ceramic matrix composite structure also provides the strength and durability needed to transfer centrifugal loads on the blade  10  to the rotor  40 . 
     The refractory structure provides an outer portion or outer root  23 , the outer neck  22  and the platform  14 . More complex platform shapes can be formed of the refractory structure than ceramic matrix composite. The outer root  23  is provided by angled walls  19  that form a dovetail, which engages the rotor  40  within the slot  42 . A root end  34  of the inner root  32  extends beyond the angled walls  29 . The refractory structure is easier to machine than ceramic matrix composite and can be machined, for example, by diamond grinding, to tighter tolerances. When machining CMCs to high tolerance, exposing or grinding through fibers is undesirable due to creation of stress concentrations and exposure of the fiber/matrix interface to environmental effects. 
     Referring to  FIGS. 2 and 3 , circumferential sides of the platform  16  include mating faces  26  that are arranged adjacent to the platforms of adjacent blades. The platform  14 , which provides the inner flow path surface of the engine&#39;s core flow path, is relatively free of foreign object debris such that the additional strength provided by the fibers in the CMC structure should not be needed. 
     The refractory structure provides an aperture  30 , shown in  FIGS. 2 and 3 , through which the airfoil  12  extends. As a result, the refractory structure surrounds a perimeter  48  of the airfoil  12 . 
     It may be desirable to provide a fillet  46  between the platform  14  and the airfoil  12  for aerodynamic efficiency. The “airfoil” is the portion that extends beyond the platform or platform fillet, if used. As shown in  FIG. 4 , overlapping layers  44  of ceramic matrix composite, for example, are arranged about the perimeter  48  and over the ceramic matrix composite layers  43  of the airfoil  12  to provide a smooth transition between the airfoil  12  and the platform  14 . In another example shown in  FIG. 5 , the fillet  146  is integral with the refractory structure and provided by the platform  114 . 
     It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom. Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention. 
     Although the different examples have specific components shown in the illustrations, embodiments of this invention are not limited to those particular combinations. It is possible to use some of the components or features from one of the examples in combination with features or components from another one of the examples. 
     Although an example embodiment has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of the claims. For that reason, the following claims should be studied to determine their true scope and content.