Ceramic matrix composites having unimodal pore size distribution and low fiber volume fraction
阅读说明：本技术 具有单峰孔径分布和低纤维体积分数的陶瓷基质复合物 (Ceramic matrix composites having unimodal pore size distribution and low fiber volume fraction ) 是由 G.S.科曼 J.H.维弗 K.L.卢思拉 于 2017-03-23 设计创作，主要内容包括：本发明公开了陶瓷基质复合物制品(10),包括例如在具有单峰孔径分布的基质(30)中的纤维丝束(20)的多个单向阵列,以及约15百分比至约35百分比的纤维体积分数。制品可通过方法(100)形成,例如,其包括提供成形预制件(110),该成形预制件包括纤维丝束的单向阵列的预浸料带叠层、基质前体和成孔剂,固化成形预制件(120)以热解基质前体并烧尽成孔剂,使得成形预制件包括纤维丝束的单向阵列和具有单峰孔径分布的多孔基质,并且使固化的成形预制件经历化学气相渗透(130)以使多孔基质致密化,使得陶瓷基质复合物制品具有约15百分比至约35百分比的纤维体积分数。(A ceramic matrix composite article (10) includes a plurality of unidirectional arrays of fiber tows (20), such as in a matrix (30) having a unimodal pore size distribution, and a fiber volume fraction of about 15 percent to about 35 percent. The article may be formed by the method (100), for example, which includes providing a shaped preform (110) including a prepreg tape layup of a unidirectional array of fiber tows, a matrix precursor, and a pore former, curing the shaped preform (120) to pyrolyze the matrix precursor and burn off the pore former such that the shaped preform includes the unidirectional array of fiber tows and a porous matrix having a monomodal pore size distribution, and subjecting the cured shaped preform to chemical vapor infiltration (130) to densify the porous matrix such that the ceramic matrix composite article has a fiber volume fraction of about 15 percent to about 35 percent.)
1. A ceramic matrix composite article, the ceramic matrix composite article comprising:
a plurality of unidirectional arrays of fiber tows in a matrix having a monomodal pore size distribution; and
wherein the ceramic matrix composite article comprises a fiber volume fraction of about 15 percent to about 35 percent.
2. The ceramic matrix composite article according to claim 1, wherein the ceramic matrix composite article comprises a fiber volume fraction of about 15 percent to about 30 percent.
3. The ceramic matrix composite article according to claim 1, wherein the matrix comprises a uniform spatial porosity distribution.
4. The ceramic matrix composite article according to claim 1, wherein the ceramic matrix composite article comprises an interlaminar tensile strength in excess of 6 ksi.
5. The ceramic matrix composite article according to claim 1, wherein the ceramic matrix composite article comprises a volume porosity of about 5 percent to about 20 percent.
6. The ceramic matrix composite article according to claim 1, wherein the ceramic matrix composite article comprises a monomodal pore size distribution having a median pore size from about 1 micron to about 20 microns.
7. The ceramic matrix composite article according to claim 1, wherein the ceramic matrix composite article comprises at least one first portion having a first fiber volume percentage and at least one second portion having a second fiber volume percentage different than the first fiber volume percentage.
8. The ceramic matrix composite article according to claim 1, wherein the unidirectional array of fiber tows comprises silicon carbide.
9. The ceramic matrix composite article according to claim 1, wherein the matrix comprises silicon carbide.
10. The ceramic matrix composite article according to claim 1, wherein the ceramic matrix composite article comprises a turbine component or a turbine component repair.
Technical Field
The present disclosure relates generally to ceramic matrix composites and, more particularly, to articles and methods for forming ceramic matrix composite articles having a unimodal pore size distribution and an optimal fiber volume fraction.
Background
Ceramic Matrix Composites (CMCs) generally comprise a ceramic fiber reinforcement material embedded in a ceramic matrix material. In the event of matrix rupture, the reinforcement serves as a load bearing constituent of the CMC, while the ceramic matrix protects the reinforcement, maintains its fiber orientation, and acts to dissipate the load on the reinforcement. Of particular interest for high temperature applications (e.g., in gas turbines) are silicon-based composites (SiC) that include silicon carbide (SiC) as a matrix and/or reinforcement material.
Different processing methods have been employed in forming CMCs. For example, one method includes Chemical Vapor Infiltration (CVI). CVI is a process of forming fiber reinforced composites by infiltrating a matrix material into a fiber preform at elevated temperature using a reactive gas. For example, conventional cloth-based CMCs formed from CVI typically have a porosity of 10 to 20 percent, a fiber volume fraction of 35 to 40 percent, and an interlaminar tensile (ILT) strength of 1 to 3 ksi, as measured by the standard 1 inch diameter button pull test. CVI composite substrates generally do not have a free silicon phase and therefore have good creep resistance and the possibility of operating at temperatures above 2,570 degrees fahrenheit.
Another method includes Melt Infiltration (MI), which uses molten silicon to infiltrate into a fiber-containing preform. For example, conventional unidirectional tape base CMCs formed from MI typically have a porosity of 3 percent or less, a fiber volume fraction of 20 to 33 percent, and an interlaminar tensile (ILT) strength of 5 to 9 ksi. The matrix of the MI composite contains a free silicon phase (i.e., elemental silicon or silicon alloy) that limits the use of CMC to below the melting point of silicon or silicon alloy or to about 2,550 degrees fahrenheit to 2,570 degrees fahrenheit. In addition, the free silicon phase provides the MI SiC matrix with relatively poor creep resistance.
Another approach employs a partial CVI process followed by an MI process, and is commonly referred to as "slurry cast MI". This process typically achieves an intermediate porosity between the MI and CVI composites of typically about 6 percent, a fiber volume fraction of 35 to 40 percent, an interlaminar tensile (ILT) strength of 2 to 4 ksi, and also contains residual free silicon phase within the composite matrix.
Disclosure of Invention
The shortcomings of the prior art are overcome and additional advantages are provided through the provision of, in one embodiment, a method for forming a ceramic matrix composite article. The method includes, for example, providing a shaped preform comprising a prepreg tape layup of a unidirectional array of fiber tows, a matrix precursor, and a pore former, curing the shaped preform to pyrolyze the matrix precursor and burn off the pore former such that the shaped preform comprises the unidirectional array of fiber tows and a porous matrix skeleton having a unimodal pore size distribution, and subjecting the cured shaped preform to chemical vapor infiltration to densify the porous matrix skeleton such that the ceramic matrix composite article has a fiber volume fraction of about 15 percent to about 35 percent.
In another embodiment, a method for forming a ceramic matrix composite article includes, for example, providing a shaped preform, the shaped preform comprising a prepreg tape layup of a unidirectional array of fiber tows, a matrix precursor for forming a ceramic matrix, particulate filler, and a pore former, curing the shaped preform to pyrolyze the matrix precursor and burn off the pore former, such that the shaped preform comprises a unidirectional array of fiber tows and a porous ceramic matrix skeleton having a monomodal pore size distribution having a median pore diameter from about 1 micron to about 30 microns, and subjecting the solidified shaped preform to chemical vapor infiltration, partial chemical vapor infiltration and melt infiltration using a gaseous ceramic, or partial chemical vapor infiltration, slurry casting, and melt infiltration, to densify the porous ceramic matrix skeleton, such that the ceramic matrix composite article has a fiber volume fraction of about 15 percent to about 35 percent.
In another embodiment, a ceramic matrix composite article includes a plurality of unidirectional arrays of fiber tows, for example, in a matrix having a unimodal pore size distribution, and wherein the ceramic matrix composite article comprises a fiber volume fraction of about 15 percent to about 35 percent.
The technical scheme 1: a method for forming a ceramic matrix composite article, the method comprising:
providing a shaped preform comprising a prepreg tape layup of a unidirectional array of fiber tows, a matrix precursor, and a pore former;
curing the shaped preform to pyrolyze the matrix precursor and burn off the pore former such that the shaped preform comprises a unidirectional array of fiber tows and a porous matrix skeleton having a monomodal pore size distribution; and
subjecting the cured shaped preform to chemical vapor infiltration to densify the porous matrix skeleton such that the ceramic matrix composite article has a fiber volume fraction of about 15 percent to about 35 percent.
The technical scheme 2 is as follows: the method of claim 1, wherein the ceramic matrix composite article has a fiber volume fraction of about 15 percent to about 30 percent.
Technical scheme 3: the method of claim 1, wherein the porous matrix skeleton comprises a uniform spatial porosity distribution.
The technical scheme 4 is as follows: the method of claim 1, wherein the porous matrix skeleton comprises a ceramic.
The technical scheme 5 is as follows: the method of claim 4, wherein the porous matrix skeleton comprises silicon carbide.
The technical scheme 6 is as follows: the method of claim 4, wherein the porous matrix skeleton comprises a ceramic derived from pyrolysis of a matrix precursor.
The technical scheme 7 is as follows: the method according to claim 1, wherein the matrix precursor is based on polycarbosilane and/or polysilazane chemistry.
The technical scheme 8 is as follows: the method of claim 1, wherein subjecting comprises subjecting the solidified shaped preform to a gaseous mixture of deposited silicon carbide.
Technical scheme 9: the method of claim 5, wherein subjecting the solidified shaped preform to chemical vapor infiltration comprises subjecting the solidified shaped preform to a gaseous mixture that deposits silicon carbide.
Technical scheme 10: the method of claim 1, wherein the ceramic matrix composite article comprises an interlaminar tensile strength of greater than about 6 ksi.
Technical scheme 11: the method of claim 1, wherein the cured preform has a median value of the unimodal pore size distribution of from about 1 micron to about 30 microns.
Technical scheme 12: the method of claim 1, wherein the cured preform has a median value of the unimodal pore size distribution of from about 1 micron to about 20 microns.
Technical scheme 13: the method of claim 1, wherein the chemical vapor infiltration comprises partial chemical vapor infiltration, and further comprising subjecting the partially chemical vapor infiltration densified ceramic matrix composite article to melt infiltration.
Technical scheme 14: the method of claim 13, wherein the melt infiltration comprises silicon, a silicon alloy, or an oxide.
Technical scheme 15: the method of claim 13, wherein the ceramic matrix composite article comprises less than about 5 percent porosity after the ceramic matrix composite article undergoes melt infiltration.
Technical scheme 16: the method of claim 1, wherein the chemical vapor infiltration comprises partial chemical vapor infiltration, and further comprising subjecting the partially chemical vapor infiltration densified ceramic matrix composite article to slurry casting and melt infiltration.
Technical scheme 17: the method of claim 16, wherein the slurry casting comprises a slurry comprising silicon carbide, boron carbide, one or more oxides, and/or combinations thereof.
Technical scheme 18: the method of claim 1, wherein the cured shaped preform comprises a volume porosity of about 35 percent to about 65 percent.
Technical scheme 19: the method of claim 1, wherein the ceramic matrix composite article comprises a volume porosity of about 5 percent to about 20 percent.
The technical scheme 20 is as follows: the method of claim 1, the ceramic matrix composite article comprising at least one first portion having a first fiber volume percent and at least one second portion having a second fiber volume percent different from the first fiber volume percent.
Technical scheme 21: the method of claim 1, wherein the pore former comprises polyethylene, polypropylene, polyamide, nylon, polytetrafluoroethylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, or cellulose powder.
Technical scheme 22: the method of claim 1, wherein the shaped prepreg further comprises silicon carbide particles, boron carbide particles, oxide particles, and/or combinations thereof.
Technical scheme 23: the method of claim 1, wherein the fiber tow comprises a silicon carbide fiber tow.
Technical scheme 24: a method for forming a ceramic matrix composite article, the method comprising:
providing a shaped preform comprising a prepreg tape layup of a unidirectional array of fiber tows, a matrix precursor for forming a ceramic matrix, and a pore former;
curing the shaped preform to pyrolyze the matrix precursor and burn off the pore former such that the shaped preform comprises a unidirectional array of fiber tows and a porous ceramic matrix skeleton having a monomodal pore size distribution having a median pore size of from about 1 micron to about 30 microns; and
subjecting the solidified shaped preform to chemical vapor infiltration, partial chemical vapor infiltration and melt infiltration, or partial chemical vapor infiltration, slurry casting and melt infiltration with a gaseous ceramic to densify the porous ceramic matrix skeleton such that the ceramic matrix composite article has a fiber volume fraction of about 15 percent to about 35 percent.
Technical scheme 25: a ceramic matrix composite article, the ceramic matrix composite article comprising:
a plurality of unidirectional arrays of fiber tows in a matrix having a monomodal pore size distribution; and
wherein the ceramic matrix composite article comprises a fiber volume fraction of about 15 percent to about 35 percent.
Technical solution 26: the ceramic matrix composite article according to claim 25, having a fiber volume fraction of about 15 percent to about 30 percent.
Technical scheme 27: the ceramic matrix composite article according to claim 25, the matrix comprising a uniform spatial porosity distribution.
Technical solution 28: the ceramic matrix composite article according to claim 25, comprising an interlaminar tensile strength in excess of 6 ksi.
Technical scheme 29: the ceramic matrix composite article according to claim 25, comprising a volume porosity of about 5 percent to about 20 percent.
The technical scheme 30: the ceramic matrix composite article according to claim 25, comprising a monomodal pore size distribution having a median pore size from about 1 micron to about 20 microns.
Technical scheme 31: the ceramic matrix composite article according to claim 25, comprising at least one first portion having a first fiber volume percentage and at least one second portion having a second fiber volume percentage different than the first fiber volume percentage.
Technical solution 32: the ceramic matrix composite article of claim 25, the unidirectional array of fiber tows comprising silicon carbide.
Technical scheme 33: the ceramic matrix composite article according to claim 25, the matrix comprising silicon carbide.
Technical scheme 34: the ceramic matrix composite article according to claim 25, comprising a turbine component or a turbine component repair.
Drawings
The foregoing and other features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description of various aspects of the present disclosure when considered in conjunction with the accompanying drawings in which:
FIG. 1 is a cross-sectional view of a ceramic matrix composite article according to one embodiment of the present disclosure;
FIG. 2 is a flow diagram of a method for forming the ceramic matrix composite article of FIG. 1 according to one embodiment of the present disclosure;
FIG. 3 is a cross-sectional view of an uncured preform having a plurality of unidirectional prepreg strips used to form the ceramic matrix composite article of FIG. 1;
FIG. 4 is a cross-sectional view of a cured preform formed from the uncured preform of FIG. 3;
FIG. 5 shows a schematic of a conventional CVI preform made from braided fiber tows;
FIG. 6 is an idealized representation of the pore size distribution of a preform and final CVI densified composite article formed according to the present disclosure, as compared to a preform and CVI densified composite formed using a woven fiber layup as is commonly used for conventional CVI;
FIG. 7 is a flow diagram of a method for forming a ceramic matrix composite article according to one embodiment of the present disclosure;
FIG. 8 is a flow diagram of a method for forming a ceramic matrix composite article according to one embodiment of the present disclosure; and
fig. 9 is a flow diagram of a method for forming a ceramic matrix composite article according to one embodiment of the present disclosure.
Detailed Description
Embodiments of the present disclosure and certain features, advantages and details thereof are explained more fully hereinafter with reference to the non-limiting examples that are illustrated in the accompanying drawings. Descriptions of well-known materials, processing techniques, and the like are omitted so as not to unnecessarily obscure the detailed disclosure. It should be understood, however, that the detailed description and the specific examples, while indicating embodiments of the present disclosure, are given by way of illustration only, and not by way of limitation. Various substitutions, modifications, additions and/or arrangements within the spirit and/or scope of the inventive concept will be apparent to those skilled in the art in light of this disclosure.
FIG. 1 illustrates a portion of a Ceramic Matrix Composite (CMC) article 10 according to one embodiment of the present disclosure. The CMC article 10 may include a ceramic fiber reinforcement in a ceramic matrix material. As described in more detail below, in some embodiments, the CMC article 10 may be formed by a process that results in a CMC article 10 having a plurality of unidirectional arrays of fiber tows 20 and a densified matrix 30. Such CMC articles may be tailored to have improved properties such as, but not limited to, mechanical properties (e.g., Interlaminar (ITL) strength and ratio limit (PL)) and oxidation resistance.
As described further below, for example, pre-coated fiber tows, pre-pregging, ply laying, consolidation, and burn-out may result in a cured preform for subsequent densification. A slurry with, for example, matrix precursors along with particulate fillers and pore formers such as polymeric pore formers may be used in the prepreg process to adjust fiber spacing and pore size distribution and to give a separate preform for CVI densification. After solidification of the preform, e.g. pyrolysis of the matrix precursor and burnout of the pore former, a single CVI may be used, with a portion of the CVI, followed by silicon, silicon alloy or an oxide, e.g. a rare earth disilicate (RE)2Si2O7) Or using slurry infiltration prior to melt infiltration to densify the solidified preform. The advantage of using a tow-based unidirectional layer preform may give a more uniform pore structure for densification, resulting in more uniformityThe CMC microstructure of (a). The feel of the fibers and continuous coating can be eliminated, thereby improving the mechanical properties and oxidation resistance of the CMC article. This technique of the present disclosure may be advantageously applied to silicon bearing ceramic turbine components (e.g., turbine blades, vanes, nozzles, shrouds, combustors, etc.) and repairs thereof.
Fig. 2 illustrates a method 100 for forming the ceramic matrix composite article 10 (fig. 1) according to one embodiment of the present disclosure. In the exemplary embodiment, method 100 generally includes providing a shaped preform comprising a prepreg tape layup of a unidirectional array of fiber tows, a matrix precursor, and a pore former at 110, curing the shaped preform to pyrolyze the matrix precursor and burn off the pore former at 120 such that the shaped preform comprises the unidirectional array of fiber tows and a porous matrix skeleton having a monomodal pore size distribution, and subjecting the cured shaped preform to chemical vapor infiltration to densify the porous matrix skeleton at 130 such that the ceramic matrix composite article has a fiber volume fraction of about 15 percent to about 35 percent.
FIG. 3 shows an uncured shaped preform 200 fabricated with a plurality of prepreg layers 210 in the form of a tape-like structure of unidirectionally aligned tows impregnated with a slurry 214 to produce a generally two-dimensional laminate. Prepregs may be formed from reinforcement materials such as the desired CMC and a slurry that may include a matrix precursor, a pore former, particulate filler and a carrier, as described below. The slurry may be roll milled to deagglomerate (deglomerate) and disperse the powder. The slurry can penetrate into the coated tow by passing the tow through a slurry bath. The tow may then be wound onto a drum and may include partial drying of the slurry, such that a tape is formed. The belt may be taken off the drum and the unidirectional preform layer may be cut to form the belt.
The material for the tows may include silicon carbide (SiC) fibers, polycrystalline SiC fibers, or other suitable fibers. An example of a material suitable for the tow is HI-NICALON from NGS Advanced Fibers Co. LTD. A suitable range for fiber diameters is about five to about twenty microns, however fibers having larger and smaller diameters are also within the scope of the present disclosure. The fibers may preferably be coated with a material, such as a carbon or boron nitride interface layer (not shown), to impart certain desired properties to the CMC article, such as allowing slippage between the coating and the matrix material of the formed CMC article. For example, the fiber tow may be a single tow of about 500 individual fibers.
The slurry may include a matrix precursor, such as an organic or inorganic material, which leaves a char/residue after being burned out, e.g., pyrolyzed or calcined. In some embodiments, the matrix precursor may include a silicon-containing precursor that may be used to form a porous silicon-containing precursor, such as silicon carbide, in the cured preform, as described below. Examples of matrix precursors include Tetraethylorthosilicate (TEOS), polycarbosilanes, polysilazanes, polysiloxanes, phenolics, and furan compounds. The pore former may include particles or other species that may remain present through the consolidation process but may disappear during burn-out or pyrolysis resulting in pores. Examples of pore formers may include polyethylene, polypropylene, polyamide, nylon, Polytetrafluoroethylene (PTFE), polystyrene, polyvinyl acetate, polyvinyl alcohol, and/or cellulose powder. The filler may comprise oxide or non-oxide particles or whiskers that help control shrinkage. Examples of the filler include SiC and B4C、SiO2、HfC、HfB2、ZrC、ZrB2、MoSi2、Si3N4、Al2O3Rare earth silicates and rare earth silicides. The carrier may comprise an organic or inorganic liquid in which the matrix precursor and other ingredients are dissolved or carried. Examples of the carrier include water, isopropyl alcohol, toluene and acetone.
The particles included in the pore former may include a monomodal particle size distribution for a collection of particles having a single clearly discernible maximum on a particle size distribution curve as compared to a collection of particles having a bimodal particle size distribution with two clearly discernible maxima on a particle size distribution curve or a multimodal particle size distribution with three or more clearly discernible maxima on a particle size distribution curve. The particles included in the pore former may include a median particle diameter in a range of about 1 micron to about 30 microns, may include a median particle diameter in a range of about 1 micron to about 20 microns, may include a median particle diameter in a range of about 3 microns to about 10 microns, and/or may include a median particle diameter in a range of about 3.5 microns to about 8 microns. The slurry including the matrix precursor, the pore former, the particulate filler, and the carrier may be combined and mixed prior to passing the tow through the slurry bath until a uniform mixture of pore former with uniform spatial distribution is obtained.
The resulting multiple layers of prepreg are laid up or stacked in a desired pattern and shape, and are typically arranged such that the tows of a prepreg layer are oriented parallel, transverse (e.g., perpendicular), or at an angle relative to the other tows of the prepreg layer in the other layers. The multiple layers may typically undergo consolidation or debulking (debulking) under the application of pressure and elevated temperature (e.g., in a vacuum or in an autoclave or with localized application of pressure and heat).
The consolidated multiple stack layers are subjected to burnout, e.g., pyrolysis, or heating in vacuum or in an inert or reactive atmosphere, in order to decompose the matrix precursor to form a ceramic or ceramic char, and where the pore former, for example, volatilizes and produces a porous preform for chemical vapor infiltration, resulting in the cured preform 300 shown in fig. 4. The porosity of the resulting precursor matrix can have a predominantly monomodal pore size distribution and a predominantly uniform spatial distribution. For example, the local maxima in the pore size distribution of the cured porous silicon-containing precursor can be from about 1 micron to about 30 microns, from about 1 micron to about 20 microns, from about 3 microns to about 10 microns, and/or from about 3.5 microns to about 8 microns. The cured preform may have a volume porosity of about 35 percent to about 65 percent.
The solidified preform is then subjected to chemical vapor infiltration, for example using an externally supplied source of gaseous silicon carbide. The source of gaseous silicon carbide infiltrates into the pores and reacts to deposit SiC on the interior pore surfaces of the porous layer to form a densified silicon carbide matrix of the CMC article 10 as shown in fig. 1, and may be free of free Si metal. Suitable chemical vapor infiltration gases may include methyltrichlorosilane, dimethyl-dichlorosilane, silane + methane, tetrachlorosilane + methane, and other suitable gases.
The porosity of the resulting CMC article 10 may have a monomodal pore size distribution. For example, the median pore size of the CVI densified CMC article may be from about 1 micron to about 20 microns, or from about 1 micron to about 15 microns. The CMC article 10 may have a volume porosity of about 5 percent to about 20 percent. The CMC article may have a uniform spatial distribution of fiber volume percentages. For example, the CMC article may have a fiber volume of about 15 percent to about 35 percent. In other embodiments, the CMC article may be customized to have different fiber volumes throughout the CMC based on lay-up and tape prepregs. For example, a CMC article may include at least one first portion having a first fiber volume percentage and at least one second portion having a second fiber volume percentage different than the first fiber volume percentage.
Those skilled in the art will appreciate that the teachings of the present disclosure are also applicable to other CMC material combinations, and such combinations are within the scope of the present disclosure. Suitable materials for the chemical vapor infiltration process may include silicon carbide, silicon nitride, silicon oxynitride, silicon oxycarbide, silicon dioxide, aluminum nitride, aluminum oxide, boron carbide, zirconium carbide, hafnium carbide, zirconium diboride, hafnium diboride, molybdenum silicide, and other suitable materials.
Testing of CMC articles formed in accordance with the techniques of the present disclosure, including a predominantly unimodal pore size distribution, showed an interlaminar tensile (ILT) strength value of about 6 ksi to about 12 ksi for a CMC having an 0/90 architecture, and a fiber volume fraction of about 18 percent ([ 0:90]2s architecture, 0.1 "thick) to 28 percent ([ 0:90]2s architecture, 0.065" thick) that was significantly higher than the ILT value of conventional CVI composites made from woven fibers and comparable (comparable to) or better than the typical value of MI-type ceramic composites.
Fig. 5 shows a schematic representation of the microstructure of a conventional CVI composite preform made from woven fibers. The crossing of the fiber tows in the weave pattern tends to compress the tows into a tight bundle. In addition, the fiber layer tends to pack inefficiently due to the surface roughness of the woven fiber cloth. The microstructure of a conventional CVI preform therefore has two different types of porosity; the first is a small interfiber hole within the fiber tow and the second is a larger interfiber hole caused by the weave pattern and the degree of mismatching of the pattern at the layer boundaries.
Fig. 6 shows an idealized representation of the pore size distribution of a CVI preform and final densified composite prepared using a conventional woven fiber-based CVI process and by the techniques of the present disclosure. The two hole populations shown in fig. 5 and described in the previous paragraph result in bimodal or multimodal pore size distributions for conventional woven fiber CVI preforms. By using the method outlined in the present invention and described in fig. 7-9, a preform microstructure as shown in fig. 1 with a monomodal pore size distribution was obtained. After densification via CVI or a combination of CVI and MI methods, the amount of porosity is reduced and the average of the peaks in the pore size distribution can shift, but the multimodal or unimodal nature of the distribution is retained. It is a relatively large pore, e.g., over 30 microns in size, that is primarily responsible for limiting the interlaminar tensile strength and proportional ultimate strength of conventional cloth-based CVI composites. Composites made from the present disclosure eliminate or minimize the amount of this undesirable macroporosity, resulting in improved interlaminar tensile strength.
Work by the inventors indicates that for samples of constant thickness, the interlaminar tensile (ILT) strength is inversely proportional to the fiber volume fraction, as long as the fibers remain uniformly dispersed within the matrix, and as long as the porosity predominantly remains unimodal. On the other hand, Ultimate Tensile Strength (UTS) and Proportional Limit (PL) are directly related to fiber volume fraction.
Thus, an optimal balance of properties for a particular application may include a CMC article in accordance with the present disclosure having a fiber volume of about 15 percent to about 35 percent compared to 35 percent to 40 percent fiber volume typically used for conventional CVI composites. In some embodiments as noted above, portions of the ceramic matrix composite article may have different fiber volume percentages based on the desired properties of the different portions of the ceramic matrix composite article. For example, some ceramic matrix composite articles may have portions or regions with a lower fiber volume percentage than other portions or regions with a higher fiber volume percentage.
Fig. 7 illustrates a method 500 for forming a ceramic matrix composite article according to one embodiment of the present disclosure. In the exemplary embodiment, method 500 generally includes coating fiber tows at 510, performing tow prepreg at 520 to form a prepreg tape, and cutting the prepreg tape and laying down an uncured preform used to form an article at 530. At 540, the preform is consolidated under heat and pressure, for example in an autoclave. At 550, the preform undergoes a burnout process such that, for example, the resulting preform has a unimodal pore size distribution. At 560, the cured preform undergoes chemical vapor infiltration to densify the cured preform to form a finished ceramic matrix composite article at 570. The ceramic matrix composite article formed by method 500 may have an optimal Interlaminar (ILT) strength range and ratio limit (PL), have a fiber volume of about 15 percent to 35 percent, and a volume porosity of about 8 percent to about 20 percent. The ceramic matrix of the ceramic matrix composite may have a monomodal pore size distribution having a median pore size of from about 3 microns to about 30 microns. The ceramic matrix of the ceramic matrix composite may have a uniform spatial pore distribution. Such ceramic matrix composite articles may be advantageously applied to silicon bearing ceramic turbine components (e.g., turbine blades (blades), vanes (vans), nozzles, shrouds, combustors, etc.) and repairs thereof.
In a Chemical Vapor Infiltration (CVI) process, a matrix material, such as silicon carbide, is infiltrated into a fiber preform by using a reactive gas at elevated temperature. Generally, the limitations caused by the diffusion of the reactants into the preform and the diffusion of the byproduct gases away from the preform result in a relatively high residual porosity in the composite of about 12 percent to about 15 percent. In forming CMCs using CVI, the inner portion of the composite formed by CVI typically has a porosity that is higher than the porosity of the outer portion. CVI composite matrices generally contain no free silicon phase, have good creep resistance, and the potential to operate at temperatures above 2,570 degrees fahrenheit.
Fig. 8 illustrates a method 600 for forming a ceramic matrix composite article according to one embodiment of the present disclosure. In the exemplary embodiment, method 600 generally includes coating fiber tows at 610, performing tow prepreg at 620 to form a prepreg tape, and cutting the prepreg tape and laying down an uncured preform used to form an article at 630. At 640, the preform is consolidated under heat and pressure, for example in an autoclave. At 650, the preform undergoes a burnout process such that, for example, the preform matrix has a unimodal pore size distribution. At 660, the cured preform undergoes chemical vapor infiltration to densify the cured preform, resulting in a volume porosity of about 12 percent to about 35 percent. Further densification may occur in a melt infiltration process at 665 to form a finished ceramic matrix composite article at 570. The melt infiltration may include silicon, silicon alloys, silicides, oxides, or combinations thereof. In method 600, the step of chemical vapor infiltration may be partial or complete chemical vapor infiltration, as compared to the chemical vapor infiltration process of method 500 (FIG. 6). The ceramic matrix composite article formed by the method 600 may have a volume porosity of less than about 5 percent. The ceramic matrix of the ceramic matrix composite may have a monomodal pore size distribution having a median pore size of from about 1 micron to about 20 microns. The ceramic matrix of the ceramic matrix composite may have a uniform spatial pore distribution. Such ceramic matrix composite articles may be advantageously applied to silicon bearing ceramic turbine components (e.g., turbine blades (blades), vanes (vans), nozzles, shrouds, combustors, etc.) and repairs thereof.
Fig. 9 illustrates a method 700 for forming a ceramic matrix composite article according to one embodiment of the present disclosure. In the exemplary embodiment, method 700 generally includes coating fiber tows at 710, performing tow prepreg at 720 to form a prepreg tape, and cutting the prepreg tape and laying down an uncured preform for forming an article at 730. At 740, the preform is consolidated under heat and pressure, for example in an autoclave. At 750, the preform undergoes a burnout process such that, for example, the preform matrix has a unimodal pore size distribution. At 760, the cured preform undergoes chemical vapor infiltration to densify the cured preform. Further, densification may occur by applying slurry casting at 763 followed by melt infiltration at 767 to form a finished ceramic matrix composite article at 770. The slurry casting may include silicon carbide, silicon nitride, molybdenum silicide, boron carbide, HfC, ZrC, HfB2, ZrB2, rare earth silicates, and the melt infiltration may include silicon, silicon alloys, silicides, oxides, or combinations thereof. The ceramic matrix composite article formed by method 700 may have a volume porosity of less than about 5 percent. The ceramic matrix of the ceramic matrix composite may have a monomodal pore size distribution having a median pore size of from about 1 micron to about 20 microns. The ceramic matrix of the ceramic matrix composite may have a uniform spatial pore distribution. Such ceramic matrix composite articles may be advantageously applied to silicon bearing ceramic turbine components (e.g., turbine blades (blades), vanes (vans), nozzles, shrouds, combustors, etc.) and repairs thereof.
Further densification in methods 600 and 700 using melt infiltration may result in a fully dense ceramic matrix composite article, for example, generally having zero or less than about 5 or less than about 3 percent residual porosity by volume. This very low porosity gives the composite the desired mechanical properties, such as high proportional ultimate strength as well as interlaminar tensile and shear strength, high thermal conductivity and good oxidation resistance. The matrix may have a free silicon phase (i.e., elemental silicon or silicon alloy) that may limit the service temperature of the ceramic matrix composite article to below the melting point of silicon or silicon alloy, or about 2,550 degrees fahrenheit to 2,570 degrees fahrenheit. The free silicon phase may result in lower creep resistance compared to densification by chemical vapor infiltration alone.
It is to be understood that the above description is intended to be illustrative, and not restrictive. Numerous changes and modifications may be made herein by one of ordinary skill in the art without departing from the general spirit and scope of the disclosure as defined by the following claims and the equivalents thereof. For example, the above-described embodiments (and/or aspects thereof) may be used in combination with each other. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the various embodiments without departing from their scope. While the dimensions and types of materials described herein are intended to define the parameters of the various embodiments, they are by no means limiting and are exemplary only. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of various embodiments should, therefore, be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. In the appended claims, the terms "including" and "in which" are used as the plain-English equivalents of the respective terms "comprising" and "in which" (where), respectively. Furthermore, in the following claims, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. In addition, the term "operable" in conjunction with terms such as coupling, connecting, engaging, sealing, and the like, is used herein to refer to both connections being made of separate and distinct components that are directly or indirectly coupled, as well as being made of integrally formed components (i.e., one-piece, unitary, or one-piece). Furthermore, the limitations of the following claims are not written in a device-plus-function fashion, and are not intended to be interpreted based on 35 u.s.c. § 112, paragraph six, unless and until such claim limitations explicitly use the phrase "means for. It is to be understood that not necessarily all such objects or advantages described above may be achieved in accordance with any particular embodiment. Thus, for example, those skilled in the art will recognize that the systems and techniques described herein may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other objects or advantages as may be taught or suggested herein.
While the disclosure has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the disclosure is not limited to such disclosed embodiments. Rather, the disclosure can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the disclosure. Additionally, while various embodiments have been described, it is to be understood that aspects of the disclosure may include only some of the described embodiments. Accordingly, the disclosure is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
This written description uses examples to include the best mode, and also to enable any person skilled in the art to practice the disclosure, 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 languages of the claims.