Patent Publication Number: US-2017348876-A1

Title: Thin ply high temperature composites

Description:
BACKGROUND 
     The field of the disclosure relates generally to gas turbine engine components, and more particularly, to high temperature composite materials for gas turbine engine components. 
     In order to increase the efficiency and the performance of gas turbine engines so as to provide increased thrust-to-weight ratios, lower emissions and improved specific fuel consumption, engine components have been made from lighter composite materials able to withstand higher operating temperatures, including ceramic matrix composites (CMCs), which provide an improved temperature and density advantage over most metals. The composite materials are typically made from layers, or plies, of fibrous strands, or tows. The composite plies are first formed into thin sheets (prepreg process), and then the plies are cut into shape, stacked, pressed and laminated together at a higher temperature curing process to create the desired engine component. 
     During the prepreg process, the tows can tend to clump together especially when trying to create very thin prepregs, even while being spread by machinery. The clumping phenomenon results in the individual plies being thicker and non-uniform. Finished components made from thicker ply materials can experience greater degrees of delamination and micro-cracking at the edges, ply drops, and/or open holes of the components, as the laminated edges are subjected to repeated fatigue loading and tensile stresses. For some low temperature composites, nylon binders have been used to maintain thinner plies during prepreg process. These nylon binders though, melt and degrade at lower temperatures than are required for fabrication of most high temperature (&gt;400° F. process) materials, that is, at about 400° F. or greater. Such high temperature materials include bismaleimides (BMI), polyimides (PI), carbon-carbon, and CMCs such as silicon carbides (SiC) and aluminum oxides (Al 2 O 3 ). 
     BRIEF DESCRIPTION 
     In one aspect, a method of fabricating a laminar composite article, includes steps of spreading a plurality of continuous fiber tows from a spool to form a first ply layer having a substantially consistent layer thickness, applying a binder to the spread plurality of continuous fiber tows, curing the plurality of continuous fiber tows and applied binder at a cure temperature less than a thermal decomposition temperature of the binder, and processing the cured plurality of continuous fiber tows at a post-cure temperature greater than the cure temperature. 
     In another aspect, a laminar composite article, includes a cured, reinforced matrix of composite material. The matrix includes a plurality of individual ply layers laminated together. Each ply layer of the plurality of individual ply layers includes a plurality of continuous tows extending substantially parallel to each other through the ply layer. Each of the plurality of continuous tows includes a plurality of individual fibers. Each ply layer further includes an average minimum fiber spacing between adjacent ones of the plurality of individual fibers equal to or greater than half of a diameter of the individual fibers. 
     In yet another aspect, a gas turbine engine includes a combustion section, a cold section forward of the combustion section, and a hot section aft of the combustion section. The hot section includes a laminar composite article fabricated of a cured, reinforced matrix of composite material. The matrix includes a plurality of individual ply layers laminated together. Each ply layer of the plurality of individual ply layers includes a plurality of continuous tows extending substantially parallel to each other through the ply layer. Each of the plurality of continuous tows includes a plurality of individual fibers. Each ply layer further includes an average minimum fiber spacing between adjacent ones of the plurality of individual fibers equal to or greater than half of a diameter of the individual fibers. 
    
    
     
       DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein: 
         FIG. 1  is a schematic illustration of an exemplary gas turbine engine in accordance with an exemplary embodiment of the present disclosure. 
         FIG. 2  is a perspective illustration of an exemplary composite engine component that can be utilized with the gas turbine engine depicted in  FIG. 1 . 
         FIG. 3  is an exploded perspective view illustrating the layered construction of the engine component depicted in  FIG. 2 . 
         FIGS. 4A and 4B  illustrate partial sectional views of the fiber tows that form the individual ply layers depicted in  FIG. 3 . 
         FIGS. 5A-5C  illustrate partial sectional views of the thin tow spread of fibers depicted in  FIG. 4B , at successive processing steps. 
         FIG. 6  illustrates a partial sectional view of a woven fiber thin tow spread. 
         FIG. 7  is a flow chart diagram of an exemplary laminate article manufacturing process. 
         FIG. 8  illustrates a partial perspective view of an alternative binder application to the fiber tows depicted in  FIGS. 4A-4B . 
         FIG. 9  illustrates a partial perspective view of an alternative binder application to the arrangement depicted in  FIG. 8 . 
         FIG. 10  is a schematic illustration of an alternative binder application to the arrangements depicted in  FIGS. 8 and 9 . 
     
    
    
     Unless otherwise indicated, the drawings provided herein are meant to illustrate features of embodiments of this disclosure. These features are believed to be applicable in a wide variety of systems including one or more embodiments of this disclosure. As such, the drawings are not meant to include all conventional features known by those of ordinary skill in the art to be required for the practice of the embodiments disclosed herein. 
     DETAILED DESCRIPTION 
     In the following specification and the claims, reference will be made to a number of terms, which shall be defined to have the following meanings. 
     The singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. 
     “Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where the event occurs and instances where it does not. 
     Approximating language, as used herein throughout the specification and claims, may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. Accordingly, a value modified by a term or terms, such as “about,” “approximately,” and “substantially,” are not to be limited to the precise value specified. In at least some instances, the approximating language may correspond to the precision of an instrument for measuring the value. Here and throughout the specification and claims, range limitations may be combined and/or interchanged; such ranges are identified and include all the sub-ranges contained therein unless context or language indicates otherwise. 
       FIG. 1  is a schematic cross-sectional view of a gas turbine engine  100  in accordance with an exemplary embodiment of the present disclosure. In the exemplary embodiment, gas turbine engine  100  is embodied in a high-bypass turbofan jet engine. As shown in  FIG. 1 , gas turbine engine  100  defines an axial direction A (extending parallel to a longitudinal axis  102  provided for reference) and a radial direction R. In general, gas turbine engine  100  includes a fan section  104  and a core engine  106  disposed downstream from fan section  104 . 
     In the exemplary embodiment, core engine  106  includes an approximately tubular outer casing  108  that defines an annular inlet  110 . Outer casing  108  encases, in serial flow relationship, a compressor section  112  and a turbine section  114 . Compressor section  112  includes, in serial flow relationship, a low pressure (LP) compressor, or booster,  116 , a high pressure (HP) compressor  118 , and a combustion section  120 . Turbine section  114  includes, in serial flow relationship, a high pressure (HP) turbine  122 , a low pressure (LP) turbine  124 , and a jet exhaust nozzle section  126 . A high pressure (HP) shaft, or spool,  128  drivingly connects HP turbine  122  to HP compressor  118 . A low pressure (LP) shaft, or spool,  130  drivingly connects LP turbine  124  to LP compressor  116 . Compressor section  112 , combustion section  120 , turbine section  114 , and nozzle section  126  together define a core air flowpath  132 . Compressor section  112  is also sometimes referred to as the “cold section,” and turbine section  114  is sometimes referred to as the “hot section.” 
     In the exemplary embodiment, fan section  104  includes a variable pitch fan  134  having a plurality of fan blades  136  coupled to a disk  138  in a spaced apart relationship. Fan blades  136  extend radially outwardly from disk  138 . Each fan blade  136  is rotatable relative to disk  138  about a pitch axis P by virtue of fan blades  136  being operatively coupled to a suitable pitch change mechanism (PCM)  140  configured to vary the pitch of fan blades  136 . In other embodiments, PCM  140  is configured to collectively vary the pitch of fan blades  136  in unison. Fan blades  136 , disk  138 , and PCM  140  are together rotatable about longitudinal axis  102  by LP shaft  130  across a power gear box  142 . Power gear box  142  includes a plurality of gears (not shown) for adjusting the rotational speed of variable pitch fan  134  relative to LP shaft  130  to a more efficient rotational fan speed. 
     Disk  138  is covered by a rotatable front hub  144  that is aerodynamically contoured to promote airflow through fan blades  136 . Additionally, fan section  104  includes an annular fan casing, or outer nacelle,  146  that circumferentially surrounds variable pitch fan  134  and/or at least a portion of core engine  106 . In the exemplary embodiment, annular fan casing  146  is configured to be supported relative to core engine  106  by a plurality of circumferentially-spaced outlet guide vanes  148 . Additionally, a downstream section  150  of annular fan casing  146  may extend over an outer portion of core engine  106  so as to define a bypass airflow passage  152  therebetween. 
     During operation of gas turbine engine  100 , a volume of air  154  enters gas turbine engine  100  through an associated inlet  156  of annular fan casing  146  and/or fan section  104 . As volume of air  154  passes across fan blades  136 , a first portion  158  of volume of air  154  is directed or routed into bypass airflow passage  152  and a second portion  160  of volume of air  154  is directed or routed into core air flowpath  132 , or more specifically into LP compressor  116 . A ratio between first portion  158  and second portion  160  is commonly referred to as a bypass ratio. The pressure of second portion  160  is then increased as it is routed through high pressure (HP) compressor  118  and into combustion section  120 , where it is mixed with fuel and burned to provide combustion gases  162 . 
     Combustion gases  162  are routed through HP turbine  122  where a portion of thermal and/or kinetic energy from combustion gases  162  is extracted via sequential stages of HP turbine stator vanes  164  that are coupled to outer casing  108  and a plurality of HP turbine rotor blades  166  that are coupled to HP shaft  128 , thus causing HP shaft  128  to rotate, which then drives a rotation of HP compressor  118 . Combustion gases  162  are then routed through LP turbine  124  where a second portion of thermal and kinetic energy is extracted from combustion gases  162  via sequential stages of a plurality of LP turbine stator vanes  168  that are coupled to outer casing  108 , and a plurality of LP turbine rotor blades  170  that are coupled to LP shaft  130  and drive a rotation of LP shaft  130  and LP compressor  116  and/or rotation of variable pitch fan  134 . 
     Combustion gases  162  are subsequently routed through jet exhaust nozzle section  126  of core engine  106  to provide propulsive thrust. Simultaneously, the pressure of first portion  158  is substantially increased as first portion  158  is routed through bypass airflow passage  152  before it is exhausted from a fan nozzle exhaust section  172  of gas turbine engine  100 , also providing propulsive thrust. HP turbine  122 , LP turbine  124 , and jet exhaust nozzle section  126  at least partially define a hot gas path  174  for routing combustion gases  162  through core engine  106 . Composite engine components disposed within hot gas path  174 , i.e., hot section  114  are required to withstand a considerably greater temperature range than engine components forward of hot gas path  174 , i.e., within cold section  112 . 
     Gas turbine engine  100  is depicted in  FIG. 1  by way of example only. In other exemplary embodiments, gas turbine engine  100  may have any other suitable configuration including for example, a turboprop engine. Gas turbine engine  100  could also be a steam engine configuration, or an engine requiring lightweight, durable components in a high-temperature dynamic environment. 
       FIG. 2  is a perspective illustration of an exemplary composite engine component that can be utilized with gas turbine engine  100 , depicted in  FIG. 1 . In this example, the engine component is illustrated as an uncoated, i.e., uncooled, airfoil  200 . According to the exemplary embodiment, airfoil  200  is formed from a CMC material, such as SiC. In alternative embodiments, airfoil  200  is formed from other high temperature composite materials, such as BMI, SiO, PI, quartz, and aluminum oxide. 
     Airfoil  200  includes a forward portion  202  against which a flow of gas is directed, e.g., hot gas path  174 . Airfoil  200  is mounted to a disk (not shown) by a dovetail  204  that extends downwardly as viewed in  FIG. 2  from forward portion  202  and engages a slot (not shown) of complimentary geometry on the disk. According to the exemplary embodiment, airfoil  200  does not include an integral platform, and a separate platform can be provided to minimize the exposure of dovetail  204  to the surrounding environment, if desired. In alternative embodiments, the complex geometry of airfoil  200  may include an integral platform. Airfoil  200  further includes a leading edge section  206  and a trailing edge section  208 . As discussed further below with respect to  FIG. 3 , the complex geometry of airfoil  200  is fabricated of a plurality of cured, reinforced, high temperature, thin ply composite layers. 
       FIG. 3  is an exploded perspective view illustrating the layered construction of airfoil  200  depicted in  FIG. 2 . In an exemplary embodiment, airfoil  200  is fabricated of a plurality of ply layers  300  arranged around a centerplane  302 . For the particular geometry of airfoil  200 , the layered construction includes a plurality of root plies  304  and short plies  306  arranged between long plies  308 . In this example, the smaller plies  304 ,  306  allow airfoil  200  to have a dovetail geometry when all the plies  304 ,  306 ,  308  are laminated together and cured in the layered order shown. 
     As described herein, the term “fiber” describes a smallest unit of fibrous material, having a high aspect ratio and a diameter that is relatively small in comparison with its length. The term fiber is also used interchangeably with filament. Additionally, a “tow” refers to a bundle of continuous fibers or filaments, and a “matrix” refers to an essentially homogenous material into which other materials, compounds, polymers, fibers, or tows are embedded. In some instances, individual plies are referred to as a “prepreg” layer, which refers to a sheet of unidirectional tow, or short lengths of discontinuous fiber, impregnated with matrix material. Prepreg layers are typically a fabric which has been pre-impregnated with a curing agent, which allows the multiple ply layers to be laminated together and cured in a mold without the addition of further agents. As described herein, a “pre-form” is a lay-up of prepreg plies, which may include additional inserts, into a predetermined shape prior to final curing of the prepreg plies. 
     In the exemplary embodiment, each of the plies  304 ,  306 ,  308  is fabricated of a flattened layer of fibers or tows of the particular high temperature composite material desired, and each is oriented in a single, predetermined direction for the individual ply, as shown below in  FIGS. 4A-4B , described further below. Plies  308  extend the full length or substantially the full length of airfoil  200 , and the orientation of each of plies  304 ,  306 ,  308  is determined to provide the desired mechanical properties for airfoil  200 . Accordingly, a 0° orientation describes a ply that is laid up so that its line of fiber tows is substantially parallel to a preselected plane of the component, for example the long dimension or axis (not shown) of a turbine blade. A 90° orientation describes a ply oriented at substantially 90° to the preselected plane. The remaining plies may be laid up in an altering formation, such as ±45° to the preselected plane of the part. Thus, in the exemplary embodiment, a sequence of ply layers  300  is laid up in a sequence of 0°, +45°, −45°, 90°, 45°, +45°, 0° so that airfoil  200  has tensile strength in directions other than along the airfoil&#39;s axis. 
     In the exemplary embodiment, the composite component is formed of a lay-up of substantially continuous plies, each ply in the lay-up of substantially continuous plies having a plurality of tows extending substantially parallel to each other in an uncured matrix material, each ply being positioned so that the tows extend at a preselected angle to the tows in an adjacent ply. In areas where complex features are present, non-ply ceramic inserts are incorporated into the component, so that the turbine component is a combination of prepreg layers and non-ply ceramic inserts such that the inserts are modeled into the component to replace a substantial number of the small prepreg plies that previously were cut to size to provide for a change in thickness or a change in contour, the replacement of which provides a predetermined shape. The reinforced ceramic matrix composite is then cured to form the article. 
     The number of continuous fiber thin plies that extend along the substantially full length of the component, e.g., long plies  308 , is maximized for structural stability of the laminate, particularly where the plies meet at edges and holes. The thinner ply layers experience less edge/hole microcracking and delamination over time than relatively thicker layers. In some embodiments, inserts are utilized, and a slurry paste or putty can be applied into cavities of the article as the article is laid up, forming an uncured insert, which then cures on drying or subsequent curing processes. 
     In the exemplary embodiment, the final cured airfoil  200  is a CMC component having tows extending in preselected orientations, and having a majority of plies  300  extending substantially the full length of airfoil  200 . Alternatively, airfoil  200  is a component fabricated from a different high temperature material such as CF/BMI, SiO, PI, quartz, or aluminum oxide fibers. In CMCs having a plurality of plies, the cured component yields a plurality of groups of continuous tows, the tows in each group extending substantially parallel to each other in a matrix, each group oriented at a preselected angle to the tows in at least one other group and each group having substantially anisotropic properties. In alternative embodiments, each of ply layers  300  includes a tow of a different predetermined orientation than an immediately adjacent ply in order to maximize strength of the finished laminate, or one or more immediately adjacent ply layers  300  are oriented parallel to one another. In another alternative embodiment, at least one discontinuously reinforced composite insert (not shown) having substantially isotropic properties is incorporated into the component between adjacent ply layers  300 . The insert may also extend substantially the length of the component, or may be modeled to replace specially cut, smaller prepreg plies at contours and at changes in discontinuously reinforced composite part thickness. 
       FIGS. 4A and 4B  illustrate partial sectional views of the fiber tows that form the individual ply layers depicted in  FIG. 3 . In prepreg processing, for example, spools of fiber tows, or yarns, are typically spread over rollers to form a uniform wide tape. The thinness of the spread fiber is limited by the strength of the material and its adhesion. The uniform material can become unstable when spread too thin.  FIG. 4A  depicts a “thick” tow spread  400  of individual fibers  402  shown clumped, or coalesced, together off of the spool.  FIG. 4B  depicts a “thin” tow spread  404  of fibers  402  that have been flattened and spread, prior to a curing process, to prepare a fiber pre-form into the desired shape for an individual ply layer, e.g., ply layer  300 ,  FIG. 3 . 
     Conventional manufacturers apply chemical sizings to the fibers of spools of fiber tows prior to shipping. The chemical sizings protect the individual fibers during shipment and handling, and are typically burned off prior to or during a fiber coating operation at temperatures exceeding 400° F. With the loss of the chemical sizing, the individual fiber tows tend to coalesce. As described below with respect to  FIGS. 5A-5C  (for a unidirectional spread) and  6  (for a woven structure), a binder is applied to the fiber tows prior to formation of the finished article to maintain the thin tow spread, i.e., tow spread  404 ,  FIG. 4B , throughout the manufacturing process until the fibers exhibit minimal relative movement during later curing steps. 
       FIGS. 5A-5C  illustrate partial sectional views of the thin tow spread of fibers depicted in  FIG. 4B , at successive processing steps. CMC manufacture, for example, typically require steps of: (1) preparing the fibers for coating deposition and/or sizing removal; (2) applying a fiber coating; and (3) infiltration of a matrix material. Step (2) may be optionally removed for PMC materials. Conventionally, the mechanical spreading of fiber tows into thin ply layers renders such thin plies difficult to handle during manufacturing of the finished component (e.g., airfoil  200 ), even with automated equipment. Thin ply layers that do not have sufficient strength, i.e., flexibility, and adhesion can wrinkle during manufacturing, or experience other defects that can negatively affect the mechanical properties of the article or lead to ply separation. The present embodiments realize significantly thinner ply layers than conventional fabrication processes, yet maintain strength and adhesion through successive curing processes such that the finished component achieves greater durability in the thermodynamically robust environment of the hot section of a gas turbine engine. 
       FIG. 5A  depicts thin tow spread  404  after an application of a binder  500 , prior to fiber coating deposition on thin tow spread  404 , such as during an autoclave cycle. In an exemplary embodiment, fiber coalescence is inhibited during curing by application of binder  500  having a thermal decomposition point greater than that of the curing temperature. Where chemical sizing, e.g., polyvinyl alcohol, is applied to the fiber tows prior to shipping, binder  500  may be applied over the chemical sizing as well as the fiber. In the exemplary embodiment, the polyvinyl alcohol decomposes during the fiber coating deposition process, or other high temperature processes if an intermediate fiber coating is not deposited. Curing is performed at temperature ranges between 300 and 400° F. 
     In the exemplary embodiment, binder  500  is applied using a solution-based process prior to subsequent processing such as chemical vapor deposition (CVD) or chemical vapor infiltration (CVI), which are employed to deposit a fiber coating  502  on fibers  402 , as shown in  FIG. 5C , below, prior to introducing a matrix material (not shown). Referring back to  FIG. 5A , in an alternative embodiment, curing may be performed prior to fiber coating deposition as two polymer application substeps. In the first polymer application substep, binder  500  is applied to fibers  402  by spraying or drawing fibers  402  through a solution containing binder  500 . Thin tow spread  500  is subsequently dried prior to subsequent processing in fiber coaters. The second polymer application substep introduces a polymer to the dried binder/spread  500 / 404  in a solution-based process, described further below. In an exemplary embodiment, the second polymer application substep draws the fibers  402 , coated with dried binder  500 , through a matrix solution to form a prepreg ply, prior to lay up. 
       FIG. 5B  depicts thin tow spread  404  at an intermediate stage during the CVD/CVI process. For a CMC material, an SiC fiber pre-form is exposed to a gas mixture at standard pressure and a temperature above 1800° F. The gas decomposes, depositing a material, such as boron nitride (BN), as fiber coating  502 , i.e.,  FIG. 5C , below, on and between fibers  402 . The temperature of the deposition/infiltration process is such that binder  500  thermally decomposes fully prior to the deposition of fiber coating  502  on fibers  402 . In the exemplary embodiment, binder  500  is polyethylene oxide, which has a melting point around 150° F. but a thermal decomposition point around 800° F. This relatively low melting point renders polyethylene oxide convenient to apply prior to or during curing, and allows the fiber pre-form, e.g., tow spread  404 , to maintain the desired spacing between individual fibers  402  during subsequent CVI/CVD processing, as shown in  FIG. 5B . Polyethylene oxide as binder  500  would thus be substantially removed entirely from a CMC material. 
     Binder  500  serves to fill the spaces between individual fibers  402  during the higher temperature processing to inhibit fibers  402  from clumping back together, but can be fully removed, as depicted in  FIG. 5B , by thermal decomposition during the same higher temperature processing. In the exemplary embodiment, removal of binder  500  ( FIG. 5B ) and deposition of fiber coating  502  ( FIG. 5C ) occur during the same first CVI/CVD high-temperature processing step. Alternatively, binder decomposition and fiber coating deposition can be arranged in successive heat zones. Tow spread  404  may be pulled, e.g., off of spools, through a continuous CVD reactor vessel, and binder  500  is thermally removed as tow spread  404  enters the CVD chamber (not shown). Fiber spacing is maintained by holding tow spread  404  under tension while binder  500  is thermally decomposed and replaced by fiber coating  502 . 
     In an alternative embodiment, non-carbide materials, such as silicon oxide, glass, and aluminum fibers, may not employ a fiber coating on individual fibers prior to matrix densification processing. In this alternative, a matrix-compatible binder is utilized similar to the processing described above, except that binder  500  thermally decomposes at a temperature greater than the curing temperature, but less than the temperature of matrix densification, which may be 2000° F. or greater. In this alternative, binder  500  is selected such that it exhibits no/low char to avoid leaving gaps in the matrix from the thermally decomposed binder. 
     In the exemplary embodiment, binder  500  is a polymer, e.g., polyethylene oxide, that remains thermally stable during, i.e., withstand, a consolidation process, such as which occurs in an autoclave cycle, e.g., below 400° F. For PMC materials, binder  500  may remain thermally stable throughout the entire manufacturing process of the finished article after the consolidation process. For CMC materials, binder  500  is selected such that binder  500  will thermally decompose during a fiber coating deposition process, or for CMC materials that do not incorporate fiber coatings, during subsequent pyrolysis or higher temperature processing steps after the consolidation process. In the embodiment illustrated in  FIG. 5A , binder  500  may be applied by spraying fibers  402 , or by drawing fibers  402  through a solution containing binder  500 . Alternatively, binder  500  is applied to tow spread  404  by over-winding a grid of fibers  402  with binder  500  and melting binder  500  on the grid to tack the tows together, as described further below with respect to  FIGS. 8 and 9 . 
     In an alternative embodiment, binder  500  is a polymer exhibiting higher temperature characteristics, such as polysilazane or polycarbosilane, which do not vaporize at high temperatures, but instead may form ceramic materials such as silicon nitride, silicon carbide, and carbon when exposed to temperatures ranging from about 1300° F. through 2200° F. In such alternative embodiments, the binder material is selected such that binder  500  does not decompose during high temperature processing steps, but instead integrally mates with the high-temperature matrix material with which it is compatible. In an example of this alternative embodiment, oxide fibers are prepared with an oxide binder that exhibit similar temperature characteristics to one another. 
     Conventional CMC components fabricated from SiC matrix composites containing fibrous material infiltrated with molten silicon, sometimes known as the Silcomp process, have been limited to ply layers greater than about 0.013 inches, or 13 mils, for woven CMC articles, and greater than 0.008 inches, or 8 mils, for unidirectional tapes. Finished component shapes from such thicker ply materials, utilizing a minimum of three plies together, are thus typically limited to thicknesses of approximately 0.039 inches, or 39 mils, for woven materials, and 0.025 inches, or 25 mils, for unidirectional materials. Similar thickness limitations have been experienced with standard prepreg plies, which normally have an uncured thickness in the range of about 0.009 inch to about 0.011 inch. Finished articles according to the embodiments described above though, are able to reduce the thickness of the finished ply layers by up to several mils per layer, which result in finished articles having much greater durability. 
     Thin ply layers have been achieved for conventional carbon fiber articles, but these articles are not generally utilized in thermodynamic environments exceeding 600-650° F. In contrast, the embodiments described herein achieve comparable thin ply laminates capable of withstanding significantly higher temperatures. For example, glass fibers such as SiO and quartz are useful in environments of about 900° F. Aluminum oxide articles are used up to 1800° F. CMC materials such as SiC are utilized for temperatures exceeding 2000-2400° F. 
     These finished plies use thin, unidirectional tows, allowing initial ply thicknesses of less than 10 mils, generally from 7 mils to 9 mils, depending on the material being laminated. Higher temperature materials generally result in thicker final ply layers after curing than do lower temperature materials, particularly where stiffer fiber materials and fiber coatings are utilized. According to the advantageous embodiments described herein, finished CMC and oxide ply layers survive higher temperature post processing and achieve a thickness less than about 11-13 mils for woven materials, and less than about 7-8 mils for unidirectional materials utilizing the CVI and PIP processes described above. Similarly, BMI and PI layers, as well as phthalonitrile ply composites, according to the present embodiments can be successfully realized at thicknesses ranging from 2-3 mils. 
     Thinner plies are difficult to handle during manufacturing and fabrication of the finished article. Accordingly, the plies can be best accommodated by the manufacturing process when the plies, or at least a substantial majority thereof, are full length plies that are laid up against a full length insert. Nevertheless, the high-temperature plies fabricated according to the embodiments herein experienced significantly greater durability even prior to lamination into the finished article. 
       FIG. 6  illustrates a partial sectional view of a woven fiber tow spread  600 . Woven fiber tow spread  600  includes fibers  402  woven together with cross fibers  602  in a warp and fill pattern, prior to formation into a thin ply layer, e.g., ply layer  300 ,  FIG. 3 . In the exemplary embodiment, binder  500  is applied to fibers  402  and cross fibers  602  prior to weaving in order to inhibit damage to the individual fibers during the weaving process. For woven fiber tow spread  600 , each “thread” is a single tow of fibers containing a plurality of individual fiber filaments  402  and  602 . The woven “fabric” is then shaped into a pre-form, and layers of individual woven plies are cut into final shapes formed on a tool or mandrel. The resultant pre-form shape may then be held in a clamping tool in the CVI/CVD reactor during fiber coating deposition (or other matrix densification), and then processed similarly to the non-woven, unidirectional embodiments described above with respect to  FIGS. 5A-5C . 
     Specifically, woven fiber tow spread  600  includes binder  500  selected to be compatible with a matrix material subsequently introduced to the pre-form. Similar to the embodiments described above, woven fiber tow spread  600  utilizes binder  500  that may exhibit a relatively lower temperature characteristics such that clumping of fibers  402  and  602  is inhibited during a curing step, and is substantially decomposed and removed by CVI/CVD processes that introduce a fiber coating, e.g., fiber coating  502 , or matrix phase introduction, as described above for CMC articles. 
     The article resulting from a first CVI/CVD process will exhibit significant porosity with respect to fiber coating  502 . Nevertheless, a sufficient quantity of fiber coating  502  is deposited during this first deposition/infiltration process to hold the fibers  402 ,  602  together in the desired woven fiber tow spread  600 . Resultant porosity of the article from the CVI/CVD process is reduced by subsequent infiltrations/depositions, and the article can then be infiltrated by the matrix material. Fiber coating  502  thus holds the desired fiber spacing between fibers  402 ,  602  throughout later processing due to the fact that the thickness of fiber coating  502  builds and bridges adjacent fibers to lock them in place, irrespective of subsequent final matrix densification or deposition steps. According to this embodiment, a minimum fiber spacing can be maintained between generally all fibers in the structure, thereby significantly strengthening the finished article, while also allowing for thinner woven structures. 
     Conventional woven structures exhibit significant numbers of fibers in direct contact with one another, and particularly where fibers and cross fibers meet in the weave. By utilizing the binder materials disclosed herein, the present embodiments are capable of maintaining a minimum fiber spacing between all fibers, thereby allowing for a reduction in the overall thickness of the material without sacrificing strength or durability of the finished article. In the exemplary embodiment, an average minimum fiber spacing between individual fibers  402 ,  602  is greater than half the fiber diameter. 
       FIG. 7  is a flow chart diagram of a laminate article manufacturing process  700  that may be implemented with the above-described embodiments. Process  700  begins at step  702 . In step  702 , fibers  402  are spread as they are unwound from the spool (not shown), and then maintained as thin tow spread  404 ,  FIG. 4B . Process  700  then proceeds to step  704 , in which binder  500  is applied to mechanically-held tow spread  404 , as shown in  FIG. 5A , described above. Binder  500  then functions to physically maintain the relative spread of fibers  402  as thin tow spread  404  moves through additional processing steps where the original mechanical maintenance structures do not follow. For CMC materials, step  704  optionally includes a second substep of depositing fiber coating  502  while removing binder  500 , as described above with respect to  FIGS. 5A-5C . Once bound by binder  500  (for PMC materials and CMC materials not utilizing fiber coatings) or fiber coating  502  (for CMC materials), process  700  proceeds to step  706 , in which thin tow spread  404  is impregnated with matrix material to create prepreg plies. 
     Once prepreg plies are formed, process  700  continues similarly to the processing steps described above with respect to  FIG. 3 . In step  708 , the prepreg plies are cut into shapes, e.g., plies  304 ,  306 ,  308 ,  FIG. 3 . Step  710  is a consolidation step. In step  710 , the cut ply shapes are stacked and laminated together into the desired shape of the finished article, e.g., article  200 ,  FIGS. 2-3 . The laminated article is then cured in step  712 , and then post-processed, sometimes referred to as “post-cured”, in step  714 . Post-processing step  714  is performed at a significantly higher temperature than curing step  712 . For example, where the composite material is BMI, curing step  712  is performed at approximately 350-375° F., whereas post-processing step  714  is performed at temperatures of approximately 450° F. or greater. PI, on the other hand, is cured at temperatures exceeding 600-700° F. CMC materials can be cured at even higher temperatures. In an exemplary embodiment, steps  710  and  712  are performed together. 
       FIG. 8  illustrates a partial perspective view of an alternative binder application  800  to thin tow spread  404 . In this embodiment, binder  500  is applied to thin tow spread  404  by over-winding the generally linear fibers  402  with a substantially linear distribution of binder  500  in a direction substantially parallel to the direction of fibers  402 . Binder  500  can then be melted on thin tow spread  404  to tack fibers  402  together during subsequent processing steps. For PMC materials, binder  500  is selected of a material that is compatible with the material of fibers  402  such that binder  500  will adhere to the matrix and not degrade during further processing steps. Binder  500  may thus exhibit a relatively higher temperature characteristic, and/or be of a compatible material, such that binder  500  is integrated into the composite matrix material of the finished article. In this example, binder  500  may remain in the finished composite article, e.g., article  200 ,  FIGS. 2-3 . Materials for binder  500  in this example may include thermoplastic polyimide, polyphenylsulfone, or polysilazane. 
       FIG. 9  illustrates a partial perspective view of an alternative binder application  900  to thin tow spread  404 . In this embodiment, binder  500  is applied to thin tow spread  404  by over-winding the generally linear fibers  402  in a planar cross-weave distribution. The direction of individual linear portions of the binder in the cross-weave pattern should be oblique to the linear direction of fibers  402  to further inhibit fiber clumping in more than one direction. Similar to the embodiment described with respect to  FIG. 8 , binder  500  can then be melted on thin tow spread  404  to tack fibers  402  together during subsequent processing steps. 
       FIG. 10  is a schematic illustration of an alternative binder application  1000 . In this embodiment, first fibers  402 (A) are fed from a first fiber spool  1002  and through rollers  1004  to mechanically spread first fibers  402 (A) into first tow spread  404 (A). Simultaneously, binder  500  is fed from binder spool  1006 , also through rollers  1004 , to create a binder underlayer on a surface (not numbered) of first tow spread  404 (A). In this embodiment, binder  500  is a thermally activated adhesive web material applied to the undersurface of first tow spread  404 (A), and the combined first tow spread  404 (A)/binder  500  is subjected to heat and pressure  1008  to create a composite bound spread  1010  for further processing. 
     In an alternative embodiment, second fibers  402 (B) are fed from a second fiber spool  1012  simultaneously with first fibers  402 (A) and binder  500 , through rollers  1004 , and on a surface (not numbered) of the web of binder  500  opposite to first fibers  402 (A). Rollers  1004  thus function to also mechanically spread second fibers  402 (B) into second tow spread  404 (B), which, upon application of heat and pressure  1008 , results in composite bound spread being formed of two thin tow spreads sandwiching binder  500  therebetween. 
     Thin ply layers having fibers spaced according to the embodiments described above yield additional advantages over the conventional thicker ply materials where most adjacent filaments are in direct contact with one another. Increased fiber density in a thicker ply material, such as a fiber volume of 40%, for example, may exhibit greater in-plane strength, yet experience lower structural efficiency. Lower structural efficiency can result from difficulties in infiltrating matrix material to maximize the material density, or minimize residual matrix porosity. In the exemplary embodiment, fibers  402  are approximately 10-15 microns in diameter, for silicon carbide fibers. At a fiber volume of 25%, spacing between individual fibers within a finished article can be maintained on the order of a fiber diameter, or as low as approximately a 10 microns gap on average. For PMC fibers having average diameters of 5-7 microns, fiber volume is approximately 55%. 
     Thin ply composite articles formed according the embodiments herein also realize significantly greater uniformity of spacing between individual fibers in the finished article than are seen in conventional composite articles. Conventional processes do not sufficiently control the uniformity of spacing within an individual ply layer, which can further result in reduced durability of the finished article. Protective sizings applied to conventional fiber spools do not provide sufficient fiber spreading control to result in consistent uniformity of spacing in a thin ply layer. Thin ply layers according to the present embodiments are capable of maintaining uniformity of fiber spacing with an average deviation within 0.0005 inches, or a half mil, where the average maximum fiber spacing is a function of the fiber diameter. 
     The present embodiments have been described with respect to an airfoil section of a narrow chord turbine blade. However, the present embodiments are not limited to only this particular use, but they also can be readily adapted to other hot section components, such as liners, vanes, ducts, cases, external articles, center bodies, and the like, as well as other sections of complex geometries in the hot section of a gas turbine engine, such as platforms and dovetails, in which small multiple plies are cut to size to account for a contour change or a thickness change, particularly over a short distance. 
     Exemplary embodiments of high temperature, thin ply composite material components for gas turbine engines are described above in detail. The components and methods of fabricating such components are not limited to the specific embodiments described herein, but rather, the components and/or steps of their fabrication may be utilized independently and separately from other components and/or steps described herein. Additionally, the exemplary embodiments can be implemented and utilized in connection with many other engine types that utilize high temperature, light weight components. 
     This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims. 
     Although specific features of various embodiments of the disclosure may be shown in some drawings and not in others, this is for convenience only. In accordance with the principles of the disclosure, any feature of a drawing may be referenced and/or claimed in combination with any feature of any other drawing. 
     This written description uses examples to disclose the embodiments, including the best mode, and also to enable any person skilled in the art to practice the embodiments, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.