Abstract:
A method of creating a tackified prepreg includes steps of providing a fiber weave that have unidirectional fibers and woven sections spaced apart from one another to provide unidirectional fiber sections, applying a tackifier to the fiber weave, and separating the uni-directional fiber section from the woven sections.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/878,994, which was filed on Sep. 17, 2013 and is incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    This disclosure relates to a method of manufacturing a gas turbine engine airfoil from a CMC. 
         [0003]    Gas turbine engines typically include a compressor section, a combustor section and a turbine section. During operation, air is pressurized in the compressor section and is mixed with fuel and burned in the combustor section to generate hot combustion gases. The hot combustion gases are communicated through the turbine section, which extracts energy from the hot combustion gases to power the compressor section and other gas turbine engine loads. 
         [0004]    Both the compressor and turbine sections may include alternating series of rotating blades and stationary vanes that extend into the core flow path of the gas turbine engine. For example, in the turbine section, turbine blades rotate and extract energy from the hot combustion gases that are communicated along the core flow path of the gas turbine engine. The turbine vanes, which generally do not rotate, guide the airflow and prepare it for the next set of blades. 
         [0005]    It is desirable to provide fiber-based articles for their lightweight and durability in high temperature applications. One example process wraps a resin impregnated ceramic matrix composite (CMC) cloth about a mandrel to form an article to provide a desired shape. The article and resin are heated to high temperatures to pyrolyze the structure and form a crystalline ceramic metal matrix. 
       SUMMARY 
       [0006]    In one exemplary embodiment, a method of creating a tackified prepreg includes steps of providing a fiber weave that have unidirectional fibers and woven sections spaced apart from one another to provide unidirectional fiber sections, applying a tackifier to the fiber weave, and separating the unidirectional fiber section from the woven sections. 
         [0007]    In a further embodiment of the above, the woven sections are in alternating relationship to the unidirectional fiber sections. The woven sections include cross fibers arranged transverse to the unidirectional fibers. 
         [0008]    In a further embodiment of any of the above, the separating step includes cutting the unidirectional sections from the woven sections. 
         [0009]    In a further embodiment of any of the above, the method includes the step of feeding the fiber weave between rollers. 
         [0010]    In a further embodiment of any of the above, the fiber weave is fed through a bath of the tackifier. 
         [0011]    In a further embodiment of any of the above, the rollers include a feed direction. The unidirectional fibers are arranged in the same direction as the feed direction. 
         [0012]    In a further embodiment of any of the above, the method includes the step of arranging layers of the unidirectional fiber sections onto one another to provide a stack. 
         [0013]    In a further embodiment of any of the above, the fibers are ceramic. 
         [0014]    In a further embodiment of any of the above, the tackifier is a pre-ceramic polymer. 
         [0015]    In a further embodiment of any of the above, the tackifier is a solid at room temperature. 
         [0016]    In a further embodiment of any of the above, the tackifier is an amorphous solid. 
         [0017]    In another e exemplary embodiment, a method of creating a tackified prepreg, includes steps of providing a fiber weave having unidirectional fibers and woven sections spaced apart from one another to provide unidirectional fiber sections, applying a tackifier to the fiber weave, arranging layers of the fiber weave onto one another to provide a stack, and wrapping the stack around a form to provide an article having a desired shape. 
         [0018]    In a further embodiment of the above, the method includes the step of applying a resin to the article in a mold. 
         [0019]    In a further embodiment of any of the above, the resin is a liquid at room temperature. 
         [0020]    In a further embodiment of any of the above, the resin is a ceramic-based. 
         [0021]    In a further embodiment of any of the above, the tackifier and resin are silicon carbide-based. 
         [0022]    In a further embodiment of any of the above, the method includes the step of heating and curing the article. 
         [0023]    In a further embodiment of any of the above, the method includes the step of machining the cured article. 
         [0024]    In a further embodiment of any of the above, the method includes the step of pyrolyzing the article, including the tackifier and the resin, subsequent to the machining step. 
         [0025]    In another exemplary embodiment, a CMC article for a gas turbine engine includes a wall that has multiple tacks joined to one another. Each stack includes multiple layers. The layers consist of unidirectional fibers that form a ceramic matrix composite with a resin and a tackifier that are different than one another. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0026]    The disclosure can be further understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
           [0027]      FIG. 1  is a flow chart of an example method of manufacturing a CMC article. 
           [0028]      FIG. 2  is a schematic view of a prepregging process. 
           [0029]      FIG. 3  is a side view of the prepregging process shown in  FIG. 2 . 
           [0030]      FIG. 4  is a schematic view of multiple layers of fiber material kitted into stacks. 
           [0031]      FIG. 5  is an example cross-sectional view of the stacks wrapped about a mandrel providing an article having a desired shape. 
       
    
    
       [0032]    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 
       [0033]    Referring to  FIG. 1 , a method  10  is disclosed of manufacturing ceramic matrix composite (CMC) articles. The method  10  includes prepregging a CMC fiber weave that includes unidirectional fiber sections with a tackifier, as indicated at block  12 . Referring to  FIG. 2 , the fiber weave  28  includes unidirectional fibers  30  woven with cross fibers  32  to provide spaced apart woven sections  34 . Unidirectional fiber sections  38  are provided between the woven sections  34 . The woven sections  34  provide stability to the unidirectional fibers  30  during the prepregging process to hold the unidirectional fibers  30  in alignment with one another during the tackifying process. The fiber weave  28  is fed through rollers, for example, first and second rollers  42 ,  44  with the unidirectional fibers  30  oriented in a same direction as a feed direction F of the rollers  42 ,  44 . 
         [0034]    Referring to  FIG. 3 , the tackifier  40  may be applied to the fiber weave  28  in a bath. The second rollers  44  are arranged with respect to one another to provide a desired thickness  46  of the tackified fiber weave. Once the fiber weave  28  has been tackified, the unidirectional fibers  30  in the unidirectional sections  38  may be separated from the woven sections  34  at cut lines  36  shown in  FIG. 2  (block  14  in  FIG. 1 ). The unidirectional fibers  30  are sufficiently adhered to one another with the tackifier, such that they can be handled and trimmed without falling apart or frying the tow. 
         [0035]    In one example, the tackifier is a pre-ceramic polymer material, for example, a silicon carbide. The tackifier is melt processable polymer solid at room temperature, for example, an amorphous solid that readily flows at moderate temperatures. In order to not compromise the integrity of the CMC, a tackifier was chosen that has the same chemical backbone as the matrix that material used, polycarbosilane. Upon pyrolyzing of the tackifier it is incorporated into the matrix of the CMC. The tackifier can also be loaded with filler particles to aid in processing in addition to altering desired CMC properties. 
         [0036]    The degree of “tack” that is provided by the tackifier enables the layers of the unidirectional fibers  38  to be kitted and stuck to one another to produce stacks  50 , as shown in  FIG. 4  (block  16  in  FIG. 1 ). The layers  48  are sufficiently sticky such that the layers will stick to one another at room temperature using hand pressure only or low levels of heat. 
         [0037]    The tackifier process will provide the fabric/fiber to which it is applied with the appropriate handling characteristics that allow the fabric to be cut, handled and kitted while maintaining edge, ply integrity and fiber alignment. The fabric/fiber can then be utilized in RTM processing of complex shapes while maintaining handling characteristics. This process is suitable for the processing of unidirectional fiber tows. 
         [0038]    Returning to  FIG. 1 , block  18 , the stacks  50  are wrapped about a form  52 , such as a mandrel shown in  FIG. 5 , to provide an article  54  having a desired shape. With continuing reference to  FIG. 1 , the article is arranged into a mold and a pre-ceramic polymer resin is injected into the mold. The resin and tackifier are different than one another. In one example, the resin is a liquid at room temperature. In one example, the tackifier has a greater carbon content than the resin. 
         [0039]    The article is heated within the mold, as indicated at block  20 . The article is allowed to cool and cure, enabling the resin and tackifier to set and the article to sufficiently take its shape for subsequent handling, as indicated at block  22 . The article then may be machined to a finished shape, as indicated at block  24 . Finally, the article may be arranged in a fixture to maintain its shape and heated to high temperatures, for example, 1000-1600° C., to pyrolized the article including the tackifier and resin, to form a crystalline ceramic matrix composite. The CMC article includes multiple stacks, each having multiple layers. The layers consist of unidirectional fibers that form a ceramic matrix composite with the resin and the tackifier. 
         [0040]    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. 
         [0041]    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. 
         [0042]    Although example embodiments have 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 and other reasons, the following claims should be studied to determine their true scope and content.