FIELD

[0001] The present disclosure relates to woven fabrics prepared from spread tows of ceramic fibers. Both oxide and non-oxide ceramic fibers may be used.

SUMMARY

[0002] Briefly, in one aspect, the present disclosure provides a fabric comprising a warp comprising a plurality of first spread tows of first ceramic fibers; and a first fill. Each first spread tow is aligned with a first axis and the fill is aligned with a second axis and interlaced with the plurality first spread tows such that the angle between the second axis and the first axis is between 5 degrees and 90 degrees, inclusive.

In some embodiments, the first ceramic fibers comprise oxide ceramic fibers. In some embodiments, the first ceramic fibers comprise non-oxide ceramic fibers.

[0003] In some embodiments, the first spread tows have a first aspect ratio of no greater than 0.04, e.g., between 0.01 and 0.03, inclusive. In some embodiments, the first spread tows have a denier of at 10,000 grams per meter square. In some embodiments, an areal density of the fabric in units of grams per meter squared divided by a denier of first spread tows in units of grams per 9000 meters is between 50 and 500 m-l, inclusive.

[0004] In some embodiments, the first fill comprises a plurality of second spread tows of second ceramic fibers; wherein each second spread tow is aligned with the second axis and interlaced with the plurality first spread tows. In some embodiments, the second ceramic fibers comprise oxide ceramic fibers. In some embodiments, the second ceramic fibers comprise non-oxide ceramic fibers. In some embodiments, the second spread tows have a second aspect ratio of no greater than 0.04, e.g., between 0.01 and 0.03, inclusive. In some embodiments, the second spread tows have a denier of at least 10,000 grams per meter square. In some embodiments, an areal density in units of grams per meter squared divided by an average denier of first spread tows and the second spread tows in units of grams per 9000 meters is between 50 and 500 m-l, inclusive.

[0005] In some embodiments, the angle between the second axis and the first axis is between 85 degrees and 90 degrees, inclusive; e.g., between 40 degrees and 80 degrees, inclusive.

[0006] The above summary of the present disclosure is not intended to describe each embodiment of the present invention. The details of one or more embodiments of the invention are also set forth in the description below. Other features, objects, and advantages of the invention will be apparent from the description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] FIG. 1 illustrates substantially circular tows of ceramic fibers of the prior art.

[0008] FIG. 2 illustrates a woven fabric prepared from the substantially circular tows of ceramic fibers of the prior art. [0009] FIGS. 3A and 3B are images of two exemplary spread tows of ceramic fibers according to some embodiments of the present disclosure.

[0010] FIG. 4 illustrates an exemplary woven fabric of spread tows of ceramic fibers according to some embodiments of the present disclosure.

[0011] FIG. 5 illustrates an exemplary unidirectional fabric of spread tows of ceramic fibers according to some embodiments of the present disclosure.

[0012] FIGS. 6A-6D show images of fabrics prepared from spread tows of ceramic fibers according to some embodiments of the present disclosure.

DETAILED DESCRIPTION

[0013] Ceramic fibers are well-known and available from a variety of commercial sources. Oxide- based ceramic fibers include, e.g., alumina fibers and alumina-silica fibers. Oxide-based ceramic fibers may include additional components such as boria, alkaline earth oxides, alkali metal oxides, and metals. Nonoxide-based ceramic fibers are based on carbides and nitrides, including oxynitrides, oxycarbides, and oxycarbonitrides. Exemplary nonoxide-based ceramic fibers include silicon carbide, silicon nitride, silicone oxycarbides, and silicon oxycarbonitrides fibers. Such nonoxide -based ceramic fibers may include additional components such as metals or carbon

[0014] Ceramic fibers are useful in many demanding situations, particularly those requiring high temperature and high strength performance. For example, ceramic fibers can be used in applications requiring continuous temperatures of 750°C or even l000°C. In contrast carbon fibers are typically limited to use temperatures of less than 300°C. Ceramic fibers also have a crystalline structure, providing superior mechanical properties compared to amorphous glass fibers.

[0015] Ceramic fibers are useful in a wide variety of applications. For example, composites may be formed by embedding ceramic fibers in a variety of matrices including polymers (i.e., polymer matrix composites,“PMC”), metals (i.e., metal matrix composites“MMC”), and ceramics (i.e., ceramic matrix composites“CMC”). In some embodiments, ceramic matrix composites, which comprise reinforcing ceramic fibers embedded in a ceramic matrix, can provide superior performance including high- temperature resistance and stability, mechanical strength, hardness, and corrosion resistance.

[0016] Ceramic fibers have been available as individual fibers (sometimes referred to as filaments) or as tows. A tow (sometimes referred to as a strand or roving) is a bundle of fibers aligned along a common axis. The fibers may be held together using, e.g., a sizing agent.

[0017] Generally, individual ceramic fibers may have a dimeter of about 5 to 20 micrometers, e.g., at least 8 microns to less than 15 microns. Tows of such fibers may have a nominal fiber count of at least 200, e.g., at least 400 fibers. In some embodiments, the nominal fiber count may be as high as 1125,

2550, 5100, or even greater. Examples of some commercially available ceramic fibers and their properties are summarized in Table 1. Tows of ceramic fibers are also available as yams consisting of multiple tows twisted together. Table 1: Summary of commercially available 3M NEXTEL Ceramic tows.

[0018] Matrix composites are formed by combining the ceramic fibers with a matrix material, e.g., a ceramic matrix. The tow (or yam) of fibers is generally impregnated with the matrix material, then formed into a desired shape for further processing. In some embodiments, the sizing material may be removed before or during the impregnation step. For example, the tow may be washed to remove the sizing, or the sizing may be burned off. In some embodiments, the sizing is removed during the impregnation process itself.

[0019] Referring to FIG. 1, with substantially circular tows (10) comprise a loose bundle of aligned fibers (20). Each tow has a major axis (Al) and a minor axis (A2), where the length of the minor axis is less than or equal to the length of the major axis. If the tow were circular, the ratio of the minor axis (A2) over the major axis (Al) would be 1. When the tows are wound or otherwise formed into shapes, there can be significant compression in the thickness direction (T) and corresponding expansion in the width direction (W). This may lead in a reduction in the minor axis of the tow and possibly an increase in the major axis of the tow, leading to a more elliptically-shaped cross-section. The resulting tows would have an aspect ratio (A2/A1) of less than 1. For example, the ratio of A2/A1 may be less than 0.5, less than 0.2 or even less than 0.1.

[0020] The impregnated fiber tows can be formed using standard fiber handling techniques such as filament winding and advanced fiber placement. In either process, the tows are laid down substantially parallel to each other. As layers of tows are built, the orientation of the tows may vary between layers.

As shown in FIG. 1, the substantially-circular cross-section of the tows (10) results in gaps (30) between tows which must be filled with matrix material.

[0021] Ceramic fibers are also available as woven fabrics. Such fabrics are prepared by weaving tows. The fabrics may be impregnated with a matrix material (e.g., polymer, metal, or ceramic matrix) and then cut to shape and laid-up to form the desired part for further processing. As shown in FIG. 2, the use of the substantially-circular tows (110, 112) to form fabric (100) still leads to significant gaps (130) between fiber tows that must be filled with resin (140). This results in large resin-rich regions lacking fiber support.

[0022] The present disclosure relates to ceramic fiber bundles with a new form factor. Rather than the traditional circularly-shaped tows, the present disclosure uses spread tows of ceramic fibers. Beginning with traditional, circular-shaped tows, spread tows may be formed using any known methods including those suitable for use with carbon fibers, e.g., the use of spreader bars. Such techniques spread the fibers of the bundle, significantly increasing the width of the tow while reducing the thickness.

[0023] As used herein a“spread tow” refers to a tow of fibers having an aspect ratio (A2/A1) of no greater than 0.05. In some embodiments, the aspect is no greater than 0.04, e.g., no greater than 0.03 or even no greater than 0.02. In some embodiments, the aspect is greater than 0.002, e.g., greater than 0.005. In some embodiments, the aspect ratio is between 0.005 and 0.04, e.g., between 0.01 and 0.03, e.g., between 0.01 and 0.02, wherein all ranges are inclusive of the end points.

[0024] A spread tow could be as thin as a single layer of fibers. However, in some embodiments, the spread tow has an average thickness of at least 5 fibers, e.g., at least 10 fibers. In some embodiments, the thickness of the spread tow will be no greater than 25 fibers, e.g., no greater than 20 fibers, or even no greater than 15 fibers.

[0025] Preparation of Sample ST-l. A water-sized, 10,000 denier NEXTEL 610 ceramic fiber tow (available from 3M Company, St. Paul, Minnesota, U.S.A.) having a nominal filament count of 2550 was unwound and passed through a tube furnace at 900 °C to dry off the water. The tow was then passed through a series of three spreader bars, evenly spaced apart 7.6 cm horizontally and 5.1 cm vertically.

This caused the tow to spread. The resulting spread tow was then coated with polyethylene glycol (20,000 gm/mol, from Alfa Aesar), dried at 140 °C using a hot air gun, and wound on a core. The resulting spread tow had an average width of 7.6 mm, thickness of 0.10 mm. The coating content was 1.5 wt.%, based on the total weight of the coated tow.

[0026] Preparation of Sample ST-2. A water-sized 20,000 denier NEXTEL 610 ceramic fiber tow (3M Company) having a nominal filament count of 5100 was unwound and passed through a tube furnace at 900 °C to dry off the water. The tow was then passed through a series of three spreader bars, evenly spaced apart 7.6 cm horizontally and 5.1 cm vertically. This caused the tow to spread. The resulting spread tow was then coated with polyethylene oxide (100,000 gm/mol, from Alfa Aesar), dried at 140 °C using a hot air gun, and wound on a core. The resulting spread tow had an average width of 12.7 mm, thickness of 0.19 mm. The coating content was 1.5 wt.%, based on the total weight of the coated tow.

[0027] Preparation of Sample ST-3. A water-sized 10,000 denier NEXTEL 610 ceramic fiber tow (3M Company) having a nominal filament count of 2550 was unwound and passed through a tube furnace at 900 °C to dry off the water. The tow was then passed through a series of three spreader bars, evenly spaced apart 7.6 cm horizontally and 5.1 cm vertically. This caused the tow to spread. The resulting spread tow was then coated with 20,000 g/mol molecular weight polyethylene oxide (Alfa Aesar), dried at 140 °C using a hot air gun, and wound on a core. The resulting spread tow had an average width of 6.1 mm, thickness of 0.09 mm, and coating content of 3.4 wt%.

[0028] Preparation of Sample ST-4. A water-sized 20,000 denier NEXTEL 610 ceramic fiber tow (3M Company) having a nominal filament count of 5100 was unwound and passed through a tube furnace at 900 °C to dry off the water. The tow was then passed through a series of three spreader bars, evenly spaced apart 7.6 cm horizontally and 5.1 cm vertically. This caused the tow to spread. The resulting spread tow was then coated with a low molecular weight 26,000 g/mol polyvinyl alcohol (Alfa Aesar), dried at 140 °C using a hot air gun, and wound on a core. The resulting spread tow had an average width of 12.6 mm, thickness of 0.17 mm, and coating content of 0.2 wt%.

[0029] Preparation of Sample ST-5. A water-sized 20,000 denier NEXTEL 610 ceramic fiber tow (3M Company) having a nominal filament count of 5100 was unwound and passed through a tube furnace at 900 °C to dry off the water. The tow was then passed through a series of three spreader bars, evenly spaced apart 7.6 cm horizontally and 5.1 cm vertically. This caused the tow to spread. The resulting spread tow was then coated with a 40,000 g/mol polyvinylpyrrodliodone (Sigma Aldrich), dried at 140 °C using a hot air gun, and wound on a core. The resulting spread tow had an average width of 12.4 mm, thickness of 0.20 mm, and coating content of 0.7 wt%.

[0030] The width (major axis Al) and thickness (minor axis A2) of these spread tows, and the ratio of A2/A1 are summarized in Table 2.

Table 2: Dimensions of the spread tows prepared from NEXTEL 610 ceramic tows.

[0031] Two exemplary spread tows are shown in FIGS. 3A (Spread Tow ST-l) and 3B (Spread Tow ST-2).

[0032] Individual spread tows of ceramic fibers may be used with the same materials (e.g., sizings and matrix materials) and in the same manner as traditional circular tows. For example, such spread tows may be applied using filament winding and advanced fiber placement equipment. Modifications may need to be made to handle the width of the spread tows; however, such modifications would be similar to those already required for tapes prepared from parallel rows of traditional circular spread tows.

[0033] The significantly lower aspect ratio achieved with spread tows results in much more compact packing of the ceramic fibers, less open volume between tows, and as a result, a significant reduction or elimination of the matrix-rich regions associated with circular spread tow constructions. Some advantages of the very low aspect ratio of spread tows of ceramic fibers can be realized when using individual spread tows using fiber placement mechanisms such as filament winding and advanced fiber placement. However, even greater benefits can be achieved when use a woven fabric.

[0034] The use of spread tows of ceramic fibers to produce woven fabrics can offer significant advantages over similar fabrics made from traditional circular tows. For example, the combination of greater width and lower thickness for the same fiber count will lead to much less undulation in thickness produced by the weaving pattern. Also, the spread tow will result in lower weight fabrics based on weight per unit area. Higher fiber to matrix ratios can be obtained as gaps leading to matrix-rich regions can be reduced or eliminated. In some embodiments, matrix material will more easily penetrate through the full thickness of the spread tow allowing contact with all fibers as compared to the thicker, circular spread tows.

[0035] Generally, any known weaving pattern may be used to create the fabrics of the present disclosure. For illustration purposes, a plain weave is shown in FIG. 4. Woven fabric (400) comprises warp (440) and fill (or weft) (450).

[0036] Warp (440) comprises a plurality of first spread tows (410). Each first spread tow comprises a plurality of first ceramic fibers (415) substantially aligned along a common axis. The plurality of first spread tows are spaced apart and aligned with first axis (XI). Fill (450) comprises a plurality of second spread tows (420). Each second spread tow comprises a plurality of second ceramic fibers (425) substantially aligned along a common axis. The plurality of second spread tows are spaced apart and aligned with second axis (X2).

[0037] As shown, the second spread tows (420) of fill (450) are interlaced with the first spread tows (410) of warp (440) in a plain weave pattern. First axis XI is aligned parallel to fabric direction F.

Generally, this orientation is referred to as 0 degrees. Second axis X2 is aligned perpendicular to fabric direction F. Generally, this orientation is referred to as 90 degrees. First axis XI and second axis X2 intersect at angle B. In the plain weave pattern of FIG. 4, the axes are approximately perpendicular, i.e., B is about 90 degrees.

[0038] Other weaving patterns, resulting in other angles of intersection can be used. When two axes intersect at an angle other than 90 degrees, they will form both an acute angle and an opposite obtuse angle. For clarity, all intersection angles, regardless of the spread tow orientations will be referred to by the acute angle. Therefore, all intersection angles will range from great than 0 to 90 degrees. For example, the angle of intersection may be Due to normal manufacturing variations, the angle of intersection (B) may vary by about +/- 5 degrees. Therefore, as used herein, all intersection angles allow for such variation. For example, if the stated intersection angle is 45 degrees this would cover intersection angles ranging from 40 to 50 degrees.

[0039] In some embodiments, the first axis XI and second axis X2 intersect at angle B, where B is greater than 40 degrees, e.g., greater than 50 degrees, or even greater than 60 degrees. In some embodiments, angle B will be no greater than 80 degrees, e.g., no greater than 70 degrees, or even no greater than 50 degrees. For example, in some embodiments, angle B will be between 40 and 80 degrees, for example, between 50 and 70 degrees, e.g., about 60 degrees (i.e., 60 +/- 5 degrees). In some embodiments, angle B will be between 40 and 60 degrees, e.g., between 40 and 50 degrees, e.g., about 45 degrees (i.e., 45 +/- 5 degrees).

[0040] Generally, any weave pattern may be used including, e.g., twill and satin weaves. In some embodiments, the warp axis is aligned with the fabric axis. However, in some embodiments, the warp axis may form an angle relative to the fabric axis. For example, in some embodiments, the warp axis forms an angle of +45 degrees relative to the fabric axis. The fill axis may then form any angle relative to the warp axis. For example, the fill axis may form an angle of -45 degrees relative to the fabric axis.

This would result in a 90 degree angle between the warp and fill axes.

[0041] Unidirectional fabric (500) is shown in FIG. 5. Unidirectional fabric (500) comprises with warp (540) and fill (550). Warp (540) comprises a plurality of first spread tows (510) aligned along axis Yl. Each first spread tow comprises a plurality of ceramic fibers (515) substantially aligned along a common axis. Fill (550) comprises a plurality of fibers or yams (530) aligned along axis Y2. As a result, axes Yl and Y2 intersect forming intersection angle B, which is about 90 degrees.

[0042] Fibers (530) are interlaced with first spread tows (510) stitching them together to form unidirectional fabric (500). The material used to form fiber (530) is not particularly limited. In some embodiments, fiber (530) is a ceramic fiber. In some embodiments, the fiber may be a traditional (i.e., circular) tow of fibers, e.g., ceramic fibers. In some embodiments, glass fiber may be used. In some embodiments, polymeric fibers, e.g., polyamide fibers, may be used.

[0043] Generally, the compositions of the first and second ceramic fibers are not limited, and may be independently selected. In some embodiments, the ceramic fibers will be oxide-based ceramic fibers. In some embodiments, the oxide-based ceramic fibers will comprise alumina fibers or alumina-silica fibers. Such oxide-based ceramic fibers may include additional components such as boria, alkaline earth oxides, alkali metal oxides, and metals.

[0044] In some embodiments, the ceramic fibers will be nonoxide-based ceramic fibers. Exemplary nonoxide-based ceramic fibers include silicon carbide, silicon nitride, silicone oxycarbides, and silicon oxycarbonitrides fibers. Such nonoxide -based ceramic fibers may include additional components such as metals or carbon.

[0045] In some embodiments, the compositions of the first ceramic fibers and the second ceramic fibers are the same. In some embodiments, their compositions may be different. In addition, the ceramic fibers of each first spread tow may be independently selected from the ceramic fibers composing any other first spread tow. Similarly, the ceramic fibers of each second spread tow may be independently selected from the ceramic fibers composing any other second spread tow.

[0046] Examples.

[0047] Spread tows were prepared from 10,000 Denier NEXTEL 610 ceramic fiber were prepared.

The spread tows were similar to tow ST-1 of FIG. 3A. Spread tows of ceramic fibers are available from 3M Company, St. Paul, Minnesota, USA.) The spread tows were sized with polyethylene glycol.

[0048] Three fabrics were prepared from the spread tows. A first fabric was prepared in a plain weave pattern (EX-l). A second fabric was prepared in a 2/2 twill pattern (EX-2). A third fabric was a unidirectional fabric, with the spread tows stitched together with 150 denier copolyamide fiber at three fibers per centimeter (EX-3). The copolyimide was EMS GRILTEC K85 copolyamide.

[0049] Images of the three fabrics of spread tow are shown in FIGS. 6B-6D. An image of comparative fabric (CE-l) prepared from convention tows of 1500 denier NEXTEL 610 ceramic fiber (Fabric DF-l 1 from 3M Company) is shown in FIG. 6A. Properties of these fabrics are summarized in Table 3.

Table 3. Properties of woven fabrics of spread tows of ceramic fibers.

[0050] As shown, the spread tow fabrics were prepared from much higher denier materials than the comparative, traditional tow fabric (10,000 give?· compared 1500 give?). However, the spread tow fabrics of Ex. 1 and 2 had about the same thickness as the standard fabric (about 260 microns) while providing a

25% reduction areal weigh (280 give? compared to 370 give?). The areal density divided by denier is a more representative measure of the weight reduction. As shown, the woven fabrics using spread tows show an almost 9x reduction. As a result, low weight, high denier fabrics may be prepared using spread tows of ceramic fibers.

[0051] In some embodiments, the areal density in units of grams per meter squared divided by an average denier of first spread tows and the second spread tows in units of grams per 9000 meters is less than 500 m l. In some embodiments, the areal density divided by the average denier is at least 50 m l.

In some embodiments, the areal density divided by the average denier is between 50 and 500 m L between 100 and 400 m l, or even between 100 and 300 m l, where all ranges are inclusive of their endpoints.

[0052] Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope and spirit of this invention.