Patent Publication Number: US-10309230-B2

Title: Co-formed element with low conductivity layer

Description:
BACKGROUND 
     The present disclosure is directed to a co-formed element having a core structure formed from a high thermal conductivity ceramic matrix composite material and a low thermal conductivity layer. 
     Gas turbine engines operate over a large temperature range. The internal flowpath is exposed to high gas pressures, velocities and temperature variations. Additionally, gas turbine engines are capable of accelerating and decelerating very quickly. The net result is flowpath exposed parts, such as blades, vanes, and shrouds can see large transient heat loads. High thermal conductivity (hi-K) ceramic matrix composites (CMC) are required to quickly dissipate the transient thermal gradients, and reduce the transient thermal stresses. 
     Parts made from CMC materials offer the ability to operate at temperatures above the melting temperature of their metallic counterparts. For hi-K CMC&#39;s, heat conduction into a metallic attachment part could overheat the metal in the attachment part. In these situations, the metal attachment part may have to be cooled, even though the CMC part does not require cooling. Adding cooling flow could create damaging local thermal gradients in the CMC part. 
     SUMMARY 
     There is provided in accordance with the present disclosure, an element which broadly comprises a core structure which has a root portion and is formed from a high thermal conductivity ceramic matrix composite material; and a low thermal conductivity layer co-formed with the core structure and surrounding the root portion of the core structure. 
     In another and alternative embodiment, the core structure is a turbine blade. 
     In another and alternative embodiment, the core structure is a vane. 
     In another and alternative embodiment, the core structure is a shroud. 
     In another and alternative embodiment, the low thermal conductivity layer includes a platform. 
     In another and alternative embodiment, the high thermal conductivity ceramic matrix composite material comprises silicon carbide fiber in a fully densified silicon carbide matrix material having a residual porosity of less than 10%. 
     In another and alternative embodiment, the residual porosity is less than 5.0%. 
     In another and alternative embodiment, the low thermal conductivity layer is formed from silicon carbide fibers in a matrix material. 
     In another and alternative embodiment, the low conductivity matrix material is selected from the group consisting of a silicon nitride, silicon-nitrogen-carbon material, at least one glassy material, or a combination thereof dispersed in a silicon carbide matrix. 
     Further in accordance with the present disclosure, there is provided a gas turbine engine system which broadly comprises a metal support structure, and a co-formed element having a core structure formed from a high thermal conductivity ceramic matrix composite material and an attachment layer formed from a low thermal conductivity ceramic matrix composite material surrounding a root portion of the core structure and contacting the metal support structure. 
     In another and alternative embodiment, the core structure is a turbine blade and the metal support structure is a disk. 
     In another and alternative embodiment, the core structure is a vane and the metal support structure is a metal hook. 
     In another and alternative embodiment, the core structure is a shroud. 
     In another and alternative embodiment, the attachment layer has a platform structure. 
     In another and alternative embodiment, the high thermal conductivity ceramic matrix composite material comprises silicon carbide fiber in a fully densified silicon carbide matrix material having a residual porosity of less than 10%. 
     In another and alternative embodiment, the residual porosity is less than 5.0%. 
     In another and alternative embodiment, the low thermal conductivity layer is formed from silicon carbide fibers in a matrix material. 
     In another and alternative embodiment, the low thermal conductivity matrix material is selected from the group consisting of a silicon nitride material, silicon-nitrogen-carbon material, at least one glassy material, and combination of these materials dispersed in a silicon carbide matrix. 
     Further in accordance with the present disclosure, there is provided a process for forming a co-formed element which broadly comprises the steps of placing a core structure formed from a fully densified, high thermal conductivity ceramic matrix material having a residual porosity of less than 10% into a mold, placing a three dimensional woven material into the mold so that the three dimensional woven material surrounds a root portion of the core structure, injecting a matrix material into the mold so that the three dimensional woven material is infiltrated with the matrix material; and allowing the matrix material to solidify to form the co-formed element. 
     In another and alternative embodiment, the residual porosity is less than 5.0%. 
     In another and alternative embodiment, the injecting step comprises injecting a matrix material selected from the group consisting of a silicon nitride material, at least one glassy material, a silicon-nitrogen-carbon material, and a combination of the materials dispersed in a silicon carbide matrix. 
     In another and alternative embodiment, the process further comprises forming the core structure from silicon carbide fiber in a silicon carbide matrix material. 
     In another and alternative embodiment, the process further comprises forming the three dimensional woven material from silicon carbide fibers. 
     Other details of the co-formed element with a low conductivity layer is set forth in the following detailed description and the accompanying drawing wherein like reference numerals depict like element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic representation of a turbine blade having a high thermal conductivity ceramic matrix composite material core structure and a low thermal conductivity layer; 
         FIG. 2  is a schematic representation of the low thermal conductivity layer of  FIG. 1  having a platform structure. 
         FIG. 3  is a flow chart showing the process of forming the turbine blade of  FIG. 1 ; 
         FIG. 4  is a schematic representation of a turbine engine component having a thermal conductivity ceramic matrix composite material core structure and a low thermal conductivity layer; and 
         FIG. 5  is a flow chart showing the process of forming the turbine engine component of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION 
     There are a number of turbine engine components which come into contact with a metallic support structure. For example, turbine blades are mounted to a metallic rotor disk typically formed from a nickel based alloy. Similarly, vanes and shrouds are mounted to hooks formed from a metallic material. 
     In order to avoid the transfer of heat from the turbine engine component to the metallic support structure, it is proposed to form the turbine engine component, such as a turbine blade, vane or shroud, with a core structure formed from a strong hi-K (high thermal conductivity) CMC material, and co-form a low thermal conductivity (low-K) CMC insulating layer which surrounds those surfaces of the core structure that interact with the metallic support structure, such as a nickel-alloy disk, a case, or a support. 
     Referring now to  FIG. 1 , there is shown a turbine blade  10  which is to be mounted to a metallic rotor disk  12 . The turbine blade  10  has a core structure  11  which may be formed from a hi-K CMC such as silicon carbide fiber (SiC) in a fully densified silicon carbide (SiC) matrix (SiC/SiC) material having a residual porosity of less than 10%. In a non-limiting embodiment, the residual porosity may be of less than 5.0%. The core structure  11  may have an airfoil portion  24 . The metallic rotor disk  12  may be formed from a nickel based alloy. 
     In order to minimize the transfer of heat from the turbine blade  10  to the disk  12 , an attachment layer  14  is co-formed around the surfaces  16  of the turbine blade  10  that interact with the metallic disk  12 . The surfaces  16  are located in the root portion  18  of the core structure  11 . The attachment layer  14  is formed from a low-K CMC material and has a thickness in the range of from 0.02 inches to 0.06 inches. The low-K CMC material may be formed from a three dimensional woven material. A suitable low-K CMC material which may be used for the attachment layer  14  is a material having SiC fibers in a silicon nitride (Si3N4), silicon-nitrogen-carbon (SiNC) or a glassy matrix. Alternatively, the silicon nitride, silicon-nitrogen-carbon (SiNC), and/or at least one glassy material may be combined and added to the SiC matrix to lower its thermal conductivity. In a non-limiting embodiment, the low-K CMC material forming the attachment layer  14  should have a thermal conductivity of less than one-tenth of the thermal conductivity of the metal material forming the disk  12 . 
     As can be seen from  FIG. 1 , the attachment layer  14  surrounds a root portion  18  of the core structure  11 . If desired, as shown in  FIG. 2 , the attachment layer  14  may include a platform structure  20 . The platform structure  20  may be in the form of a three dimensional (3D) woven material infiltrated by a matrix material. As described below, the attachment layer  14  is co-formed with the core structure  11 . 
     To form a turbine blade  10  with an insulating attachment layer  14 , the process shown in  FIG. 3  may be used. As shown in step  102 , a fully densified, melt infiltration (MI) SiC/SiC core structure  11 , having a residual porosity of less than 10%, in the form of a turbine blade  10  may be placed in a mold. If desired, the residual porosity may be less than 5.0%. In step  104 , the woven 3D fibers of the attachment layer  14 , which can have a 3D woven platform structure  20  forming part of the attachment layer  14 , are placed over a portion of the core structure  11  including the blade root portion  18 . In step  106 , a matrix material, such as glass, is injected into the mold using a glass—transfer process. The attachment layer is thus infused with the matrix material. In step  108 , the mold is allowed to cool. As a result, the matrix material solidifies and a fully, co-formed CMC turbine blade  10  is created with a low-K attachment layer  14  and a hi-K core structure having an airfoil portion  24 . 
     In another and alternative embodiment, in step  106 , a matrix precursor material, such as Si3N4 and/or SiNC, or in combination with SiC matrix precursor material, is injected into the mold using a resin transfer process. The attachment layer is thus infused with the matrix precursor material. The material is heated and the matrix precursor is converted into the matrix material. In step  108 , the mold is allowed to cool. As a result, the matrix solidifies and a fully co-formed CMC turbine blade  10  is created with a low-K attachment layer  14  and a high-K core structure  11  having an airfoil portion  24 . 
     In another and alternative embodiment, in step  106 , a matrix material, such as Si3N4 and/or SiNC is deposited into the woven fibers in the mold using a chemical vapor infiltration (CVI) process. The attachment layer is thus infused with the matrix material. In step  108 , the mold is allowed to cool. As a result, the matrix has formed a fully, co-formed CMC turbine blade  10  created with a low-K attachment layer  14  and a high-K core structure having an airfoil portion. 
     Referring now to  FIG. 4 , there is illustrated, a turbine engine component  50  such as a vane or a shroud, an attachment layer  52  surrounding a root portion  54  of the turbine engine component  50 , and a metal support  56 , such as a metal hook, for securing the turbine engine component  50  in position. The turbine engine component  50  has a core structure  51  which may be formed from a high-K CMC material such as a fully densified, melt infiltration SiC fiber in a SiC matrix material having a residual porosity of less than 10%. In another and alternative embodiment, the residual porosity is less than 5.0%. The attachment layer  52  may be formed from a low-K CMC material. The attachment layer  52  may include a platform structure if needed. The attachment layer may be formed from a woven three dimensional (3D) SiC fiber material in a matrix material selected from the group consisting of silicon-nitrogen-carbon (SiNC) and a glassy matrix. 
     Referring now to  FIG. 5 , as shown in step  120 , the core structure  51  of the turbine engine component  50 , formed from the high-K CMC material, is placed into a mold. In step  122 , the woven three dimensional fiber material is placed in the mold and positioned around the root portion  54  of the core structure  11  to cover all attachment surfaces with the metal support  56 . In step  124 , a matrix material, such as at least one glass material, is injected into the mold. This causes a hook region  60  of the attachment layer  52  to be locally infused with the matrix material. In step  126 , the mold is allowed to cool. As a result, the matrix material solidifies and a fully, co-formed CMC turbine engine component  50  is created with the desirable characteristic of a low-K contact point with the metal support  56 . 
     Alternatively in step  124 , a matrix precursor material, such as Si3N4 and/or SiNC or a combination with SiC matrix precursor, is injected into the mold using a resin transfer process. The attachment layer is thus infused with the matrix precursor material. The material is heated and the matrix precursor is converted into the matrix material. In step  126 , the mold is allowed to cool. As a result, the matrix solidifies and a fully, co-formed CMC turbine engine component  50  is created with the desirable characteristic of a low-K contact point with the metal support  56 . 
     In another alternative embodiment, in step  124 , a matrix material, such as Si3N4 and/or SiNC is deposited into the woven fibers in the mold using a chemical vapor infiltration (CVI) process. The attachment layer is thus infused with the matrix material. In step  126 , the mold is allowed to cool. As a result, the matrix has formed a fully co-formed CMC turbine engine component  50  created with the desirable characteristics of a low-K contact point with the metal support  56 . 
     The presence of the low thermal conductivity attachment layer  14  or  52  helps break the conduction path from the high-K CMC core structure of the particular component to the metallic support structure. Compared to a thermal barrier coating, a glassy CMC used for the attachment layer has equal strength to the high thermal conductivity CMC core structure. Thus, no structural penalty is created by using the low-K attachment layer  14  or  52 . 
     There has been provided a co-formed element with a low thermal conductivity layer. While the co-formed element with a low thermal conductivity layer has been described in the context of specific embodiments thereof, other unforeseen alternatives, modifications, and variations may become apparent to those skilled in the art having read the foregoing description. Accordingly, it is intended to embrace those alternatives, modifications, and variations as fall within the broad scope of the appended claims.