Abstract:
An article comprising a ceramic material having a ceramic matrix composite backing adapted for use in a gas turbine engine is provided. The article comprises a structural ceramic material having a hot side facing toward a high temperature environment and a cold side facing away from the high temperature environment; and a ceramic matrix composite composition having a strength greater than the strength of the ceramic material attached to the back of the cold side of the ceramic material, whereby crack initiation and propagation are inhibited by the ceramic matrix composition to a greater degree than by the ceramic material.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Serial No. 60/408,642, filed Sep. 6, 2002. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to the field of temperature resistant components and in particular, to an article comprising a structural ceramic material having a ceramic matrix composite backing and used as a component of a gas turbine engine such as a combustion liner.  
         BACKGROUND OF THE INVENTION  
         [0003]    Gas turbine engines are known to include a compressor section for supplying a flow of compressed combustion air, a combustor section for burning fuel in the compressed combustion air, and a turbine section for extracting thermal energy from the combustion air and converting that energy into mechanical energy in the form of a rotating shaft. Many components that form the combustor and turbine sections are directly exposed to hot combustion gases, for example, the combustor liner, the transition duct between the combustor and turbine sections, and the turbine stationary vanes and rotating blades and surrounding ring segments.  
           [0004]    It is also known that increasing the firing temperature of the combustion gas can increase the power and efficiency of the combustion turbine. Modern high efficiency combustion turbines have firing temperatures that exceed temperatures of about 1,600° C., and even higher firing temperatures are expected as the demand for more efficient engines continues. Thus, the cobalt and nickel based superalloy materials traditionally used to fabricate the structural gas turbine components must be aggressively cooled and/or insulated from the hot gas flow in order to survive long term operation in the aggressive high temperature combustion environment. Additionally, certain combustion turbine components and configurations demand that the insulating material also provide structural mechanical support and strength. For example, it is known to use ceramic tiles to form the combustion liner within the combustion section of the engine.  
           [0005]    An issue associated with these structural ceramic tiles, however, is that they are known to crack when operational local stresses exceed the ceramic material properties. To further complicate matters, these cracks are caused by a variety of factors and formed in a variety of locations. If left unresolved, these cracks can propagate and expand until the tile fails. Thus, expense and time consuming periodic inspections are frequently required to ensure the tile are not cracked.  
           [0006]    Accordingly, there is a need to reduce the time and cost associated with cracked ceramic combustion liner tiles. There is also a need to reduce the formation of cracks on ceramic combustion liner tiles.  
         SUMMARY OF THE INVENTION  
         [0007]    A combustion turbine component comprising a structural ceramic material having a ceramic matrix composite backing for use in a high temperature environment is provided, as well as a method of manufacturing this hybrid material.  
           [0008]    One aspect of the present invention involves an article of manufacture comprising: a structural ceramic material having a hot side facing toward a high temperature environment and a cold side facing away from the high temperature environment; and a ceramic matrix composite composition having a strength greater than the strength of the ceramic material attached to the back of the cold side of the ceramic material, whereby crack initiation and propagation are inhibited by the ceramic matrix composite to a greater degree than by the ceramic material.  
           [0009]    Another aspect of the present invention involves a component of a gas turbine engine comprising: a structural ceramic material having a hot side facing toward a high temperature environment and a cold side facing away from the high temperature environment; a ceramic matrix composite backing having a strength greater than the strength of the ceramic material; and an adhesive arranged between the ceramic material and the ceramic matrix composite adapted to bond the back of the cold side of the ceramic material to the ceramic matrix composite, whereby crack initiation and propagation are inhibited by the ceramic matrix composite to a greater degree than by the ceramic material.  
           [0010]    Another aspect of the present invention involves a method of manufacturing a combustion liner tile adapted for use in a combustion turbine engine comprising: providing a structural ceramic material having a hot side facing toward a high temperature environment and a cold side facing away from the high temperature environment; applying a layer of green ceramic matrix composite composition onto the structural ceramic material; and heating the ceramic matrix composite composition and the ceramic material to a temperature in excess of about 1100° C. to form the combustion liner tile having a strength greater than the strength of the ceramic material. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    These and other advantages of the invention will be more apparent from the following description in view of the drawings that include:  
         [0012]    [0012]FIG. 1 is a perspective view of an exemplary gas turbine combustion liner of the present invention;  
         [0013]    [0013]FIG. 2 is a detail cross-sectional view of the combustion liner of FIG. 1 formed of a structural ceramic material having an adhesively attached ceramic matrix composite backing.  
         [0014]    [0014]FIG. 3 is a detail cross-sectional view of the combustion liner of FIG. 1 formed of a structural ceramic material having a co-processed ceramic matrix composite backing.  
         [0015]    [0015]FIG. 4 is another embodiment of the combustion liner of FIG. 1 formed of a structural ceramic material having a co-processed ceramic matrix composite backing. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0016]    The invention described herein employs several basic concepts. For example, one concept relates to a high temperature and crack resistant gas turbine engine component. Another concept relates to forming a hybrid material comprising a structural ceramic having a ceramic matrix composite backing adapted for use in a combustion turbine engine. Another concept relates to method of manufacturing such a hybrid material.  
         [0017]    The present invention is disclosed in context of use as a combustion liner  2  within a gas turbine engine. The principles of the present invention, however, are not limited to combustion liners  2  or even gas turbine engine components. For example, the principles of the present invention can be used to fabricate other gas turbine components, such as transition ducts, blades, vanes and ring segments. For another example, the principles of the present invention can be used with aerospace applications, such as airplanes with turbine engines and reentry space vehicles having heat shields. For another example, the principles of the present invention can be used with materials other than ceramics. One skilled in the art may find additional applications for the apparatus, processes, systems, components, configurations, methods, and applications disclosed herein. Thus, the illustration and description of the present invention in context of an exemplary combustion liner  2  within a gas turbine engine is merely one possible application of the present invention.  
         [0018]    Referring now to FIGS. 1 and 2, an exemplary combustion liner  10  is provided. The illustrated combustion liner is shown  2  surrounded by an annular combustor  18  and connected to the combustor  18  by a plurality of clips  20 , although many other combustor configurations and connection methods could be used as will be understood by those skilled in the art. The combustion liner  10  is advantageously formed from a plurality of ceramic tiles  12  with a ceramic matrix composite (CMC)  14  backing. The CMC  14  may be applied onto the ceramic  12  by a variety of techniques, as explained in more detail below. By this configuration, the CMC  14  resists crack formation and crack propagation on the ceramic tile  12 .  
         [0019]    The combustion liner  10  is advantageously formed of a plurality of ceramic tiles  12  that provide the requisite mechanical strength and thermal protection to withstand the thermal and mechanical stresses placed upon the combustion liner  10  during gas turbine engine operation and cycling. The ceramic tiles are advantageously capable of withstanding mechanical stresses of up to about 6 MPa and operating temperatures of up to about 1500° C. However, as will be understood by those skilled in the art, depending on the context of use, this range of mechanical stress and operating temperature could be appreciably greater or less. The ceramic material  12  may be formed of any ceramic, although it has been found advantageous to include alumina, silcia, zirconia, other binary oxides, and combinations thereof due to their strength and temperature resistance as well as their oxidation, corrosion and thermal shock resistance in aggressive high temperature environments. Also, the ceramic material  12  is illustrated as a plurality of tiles that can be formed of any size, shape, and thickness suitable to perform its structural and temperature resistant function, as well as formed as a monolith.  
         [0020]    The CMC  14  is advantageously applied as a backing onto the ceramic tile  12  to provide resistance to crack formation and to crack propagation on the ceramic tile  12  during gas turbine engine operation and cycling. The CMC material  14  may be of the type described in U.S. pending patent application Ser. No. 09/631,097 filed Aug. 2, 2000, Ser. No. 09/962,733 filed Sep. 24, 2001, and Ser. No. 09/963,278 filed Sep. 26, 2001, each of the pending patent applications which are incorporated by reference in their entirely herein, or may be of the type described in U.S. patent application Ser. No. 5,854,154 which is incorporated by reference in its entirety herein.  
         [0021]    The CMC material  14  advantageously includes any fiber reinforced matrix material or metal reinforced matrix material as may be known or later developed in the art, such as that commercially available from the COI Ceramics company under the name AS-N720. If a fiber reinforced material is used, the fibers may be oxide ceramics, non-oxide ceramics, or a combination thereof. For example, the oxide ceramic fiber composition can include those commercially available from the Minnesota Mining and Manufacturing company under the trademark Nextel, including Nextel 720 (alumino-silicate), Nextel 610 (alumina), and Nextel 650 (alumina and zirconia). For another example, the non-oxide ceramic fiber composition can include those commercially available from the COI Ceramics company under the trademark Sylramic (silicon carbide), and from the Nippon Carbon corporation limited under the trademark Nicalon (silicon carbide). The matrix material composition that surrounds the fibers may be made of an oxide or non-oxide material, such as alumina, mullite, aluminosilicate, ytrria alumina garnet, silicon carbide, silicon nitride, silicon carbonitride, and the like. A CMC material  14  that combines a matrix composition with a reinforcing phase of a different composition (such as mulite/silica) or of the same composition (alumina/alumina or silicon carbide/silicon carbide) could also be used. The fibers may be continuous or long discontinuous fibers, and may be oriented in a direction generally parallel, perpendicular or otherwise disposed relative to the major length of the CMC material  14 . The matrix composition may further contain whiskers, platelets, particulates, or fugitives therein. The reinforcing fibers may be disposed in the matrix material in layers, with the plies of adjacent layers being directionally oriented to achieve a desired mechanical strength.  
         [0022]    Although it is possible to apply the CMC  14  backing onto the ceramic  12  tile in a variety of ways, due care should be made to suitably match the thermal expansion of these two materials in order to reduce interface stresses and strains.  
         [0023]    Applicants have found two approaches of joining the ceramic and CMC to be preferable, although many other approaches could be used. One approach involves bonding the fully fired CMC material  14  onto the finished ceramic material  12 . The other approach involves processing and finishing the green CMC material  14  onto the finished structural ceramic material  12 .  
         [0024]    Referring to FIG. 2, the ceramic tile  12  and the CMC  14  are independently formed. During this independent formation, care should be taken to ensure that the tile  12  and CMC  14  have a similar, if not substantially similar or even exact, surface profile (e.g. length, width, curvature, perimeter, geometry) to facilitate attachment. The CMC material  14  is advantageously formed by laying up a series of pre-impregnated laminates, vacuum bagging the laminates to compress the laminates, drying the compressed laminates, autoclaving the dried compressed laminates, and then curing the laminate structure to form a finished profiled CMC  14  panel. Although the CMC  14  could be formed via other techniques, such as those described in more detail in the patents and patents applications previously incorporated by reference, and may include difference, additional or less processing steps. The ceramic material  12  is advantageously formed by pressing or casting green body particles and then firing the green body to a predetermined sintering temperature to form the finished ceramic tile  12 .  
         [0025]    The finished CMC  14  is then attached to the finished ceramic  12  (or vice-versa) by an adhesive  16  or bonding agent. Suitable adhesives  16  include fine powder ceramics such as mullite, alumina, silica and combinations thereof mixed or otherwise combined with a liquid binder such as silica sol, oxychloride solution and combinations thereof, although the ceramic need not be in fine powder form and the binder need not be in liquid form. Also, other types of adhesives  16  could also be used, such as those commercially available from the Cotronics corporation under the tradename Resbond and from the Aremco Products Inc under the tradename Ceramabond. The adhesive  16  is advantageously applied in a slurry form to the surface of the ceramic tile  12  (or CMC  14  or both  12 ,  14 ) and then the CMC panel  14  is applied to the slurry coated surface of the tile  14  and allowed to air dry. The hybrid structure is then advantageously further dried and heat treated to about 1000-1200° C. for about 1-3 hours to form a refractory bond between the two suitably thermally matched materials  12 ,  14 . Using this type of ceramic adhesive  16 , strengths of up to 6.2 MPa have been observed, although greater or less adhesive strengths could be achieved and used.  
         [0026]    Of course, alternate bonding adhesive systems could be used such as glass frits, where a slurry of particulate glass particles are applied to the ceramic tile  12  surface and then the CMC  14  panel is applied to the glass slurry. The hybrid structure is then dried and heated to about 1000-1200° C. for about 1-3 hours such that the glass melts and wets the surface of the CMC  14 . During cool down, and at the approximate anticipated operating use temperature, the glass forms a bond between the ceramic tile  12  and the CMC panel  14 . Using this type of bond, strengths of up to 5.8 MPa have been observed, although greater or less bond strengths could be achieved and used.  
         [0027]    The adhesive bonding agent  16  is shown completely covering the CMC  14  and ceramic  12  interface. However, the adhesive  16  need not be applied such that it completely covers the entire contact area between the cold side of the ceramic  12  and the CMC  14 . For example, the adhesive  16  can be applied to selected portions of the cold side of the ceramic  12  such that the non-adhesive-applied portions of the ceramic  14  is physically decoupled from the CMC  14 , which can help disseminate strain energy. Also, more than one type of adhesive  16  can be used, for example, bonding agents  16  with different strengths can be applied to different portions of the ceramic  14  and/or CMC  14  to assist with strain tolerance at or along selected portions of the ceramic  12 .  
         [0028]    Referring to FIG. 3, another aspect of the invention is provided where the nascent CMC  14  is processed and finished onto the finished structural ceramic  12 . During this co-processing formation, the fibers of the CMC layer are first cut and applied to the tile surface and the matrix material is infiltrated around the fibers. This fiber application and matrix material infiltration may be repeated to build up the CMC material  14 . Alternatively, a number of fabric plies of CMC prepreg material  14  (matrix material pre-impregnated with the fibers) may be cut to the surface profile of the tile and then stacked onto the backside of the tile  12 . The stacked plies can then be vacuum bagged or otherwise compressed to compact the plies to the desired thickness. The finished tile  12  with green CMC backing is then preferably autoclaved and fired. Using this type of co-processing formation, strengths of up of 2.8 Mpa have been observed, although greater or less bonding strengths could be achieved and used. Suitable co-processing techniques are provided in more detail in U.S. patent application Ser. No. 10/245,528, titled “Composite Structure Formed By CMC-On-Insulation Process,” which is incorporated herein by reference in its entirety.  
         [0029]    An advantage of this co-processing application method is that it allows the CMC material  14  to conform to the contours of a shaped ceramic  12 . Another advantage of this method is that minimal shrinkage of the CMC  14  occurs during co-processing, which provides an overall slight compressive force on the tile which assists in inhibiting crack propagation in the tile  12 . Since the co-processed CMC  14  can be formed to partially or wholly encapsulate, sheath or trap the ceramic, it provides additional strength and reinforcement. Further, the co-processed CMC  14  could be applied such that the CMC  14  is thicker and thus stronger at certain high stress areas of the ceramic. An adhesive  16  or bonding system may also be used between the ceramic  12  and CMC  14  backing during the co-processing application to further secure the CMC  14  to the structural ceramic  12 .  
         [0030]    Referring to FIG. 4, another example of a co-processed CMC  14  on ceramic tile  12  combustion liner  10  is provided. In this embodiment, the CMC material  14  is applied on the upstream and downstream sides of the ceramic tile  12 . This upstream and downstream application may be used in combination with either of the above-described CMC backing methods. Thus, the CMC  14  may be disposed on or along one or more edges or side surfaces of the ceramic tile  14  instead of or in additional to the backside of the ceramic tile  14 .  
         [0031]    Those skilled in the art will understand other suitable techniques to attach the CMC  14  and ceramic  12 , such as structural means. For example, a clamp or dovetail groove. Also, the CMC  14  fibers or laminates can be oriented at different angles with respect to each other or the ceramic tile  12 , for example, orienting the laminates at an angle of about 45° relative to the major axis of the ceramic tile  12  tends to provide increased ductility and strain tolerance, thereby inhibiting cracks and crack propagation in the tile  12 .  
         [0032]    During typical gas turbine operation, the combustion gas temperature is about 1400-1700° C. or greater, with the ceramic tile  12  normally reaching temperatures of about 1200-1500° C. and the CMC material  14  normally reaching temperatures of about 600-1100° C.  
         [0033]    While the preferred embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Aspects of one embodiment can be used or combined with aspects of one or more other embodiments. Numerous variations, changes and substitutions will occur to those of skill in the art without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.