WO2024119186A1 - Tps material with enhanced toughness and interlaminar strength - Google Patents

Tps material with enhanced toughness and interlaminar strength Download PDF

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Publication number
WO2024119186A1
WO2024119186A1 PCT/US2023/082365 US2023082365W WO2024119186A1 WO 2024119186 A1 WO2024119186 A1 WO 2024119186A1 US 2023082365 W US2023082365 W US 2023082365W WO 2024119186 A1 WO2024119186 A1 WO 2024119186A1
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mwcnt
composite
carbon
tps
preformed
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PCT/US2023/082365
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French (fr)
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Arthur J. Gavrin
Stephen SCHOENHOLTZ
Douglas W. Freitag
Feng Wang
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Triton Systems, Inc.
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/15—Nano-sized carbon materials
    • C01B32/158—Carbon nanotubes
    • C01B32/168—After-treatment
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B32/00—Carbon; Compounds thereof
    • C01B32/20—Graphite
    • C01B32/205—Preparation
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
    • C08K3/00—Use of inorganic substances as compounding ingredients
    • C08K3/02—Elements
    • C08K3/04—Carbon

Definitions

  • TPS Thermal Protection Systems
  • Carbon-carbon composites are a family of advanced composite materials. They are the most advanced form of carbon and consist of a fiber based on carbon precursors embedded in a carbon matrix. This unique composition gives them such properties as low density, high thermal conductivity and shock resistance, low thermal expansion, and high modulus. Carboncarbon composites are mostly used in aerospace applications, mainly for aircraft disc brakes, rocket re-entry nose tips, and for parts of rocket nozzles.
  • TPS thermal protection system
  • MWCNT- C/C multi-walled carbon nanotube reinforced, carbon-carbon composite
  • PY preformed yarn
  • TPS material described herein has both the thermal protection and loadbearing capabilities integrated into one structured
  • FIGURE 1 Triton’s proposed method for low cost, quicker fabrication of enhanced flexural strength, toughness, interlaminar shear strength, impact strength, and thermal performance TPS materials for high Mach vehicles.
  • the proposed method utilizes MWCNT containing pyrocarbon in the Preformed Yam method. Once the yam is fabricated, the yarn is laid-up and pressed into a green part, which is then carbonized/graphitized to make the C/C TPS.
  • FIGURE 2 Mechanical properties of CNTs C/C composite. Left: flexure strength and Right: Interlaminar shear strength
  • FIGURE 3 Flow Chart for C-C Composite synthesis by the PY method.
  • FIGURE 4 Timeline of PY method vs. conventional method for C/C composite manufacturing.
  • FIGURE 5 Illustration of Triton’s MWCNT-C/C Composite.
  • FIGURE 6 Dispersion process of MWCNT in PyC precursor solution.
  • FIGURE 7 MWCNT-C/C preformed yam fabrication process.
  • the pyrocarbon matrix precursor consists of a pitch binder, MWCNTs, and coke powder
  • the MWCNT-C/C TPS materials made by PY, shown in Figure 1 provides an innovative approach to achieve low-cost, high efficiency production of a robust TPS material with enhanced thermal, mechanical, and weight characteristics that will satisfy the MDA need.
  • the PY method has been made in consideration of the problems involved in the conventional techniques.
  • a novel preformed yam which is useful as a precursor for fiber-reinforced carbon composites, is excellent in workability and processability in the fabrication of composite articles, and gives highly heat-resistant composite articles exhibiting high and uniform mechanical properties.
  • Table 1 presents the range of properties that can be achieved and, for comparison, those of ferritic steel and titanium alloys.
  • the properties for carbon-carbon are given in the fiber direction. Perpendicular to the fibers, the properties are much less superior.
  • the mechanical properties are much superior to those of conventional graphite.
  • three- dimensional carbon-carbon composites can be tailored to withstand damage and minimum delamination crack growth under interlaminar shearing.
  • the tensile strength increases above 1200°C when conventional superalloy components start to weaken; the density is only about 1.9 g/cm 3 compared with 8 g/cm 3 for superalloys and in the event of failure the material does not disintegrate catastrophically, but goes through a gradual failure that has been called graceful failure, which made C/C composites the material of choice as a thermal protection material for hypersonic vehicle applications.
  • CNTs carbon nanotubes
  • thermosetting pitch or resin Here impregnation is accomplished with fluid impregnates: like coal tar, oil pitches, and other high char yielding thermosetting resins.
  • C/C composite manufacturers may infiltrate a preform to set the dimensions, followed by hot isostatic pressing at temperatures 750 °C and 100 MPa pressure. This is followed via carbonization at 1000°C and graphitization at 2750 °C.
  • Preformed Yarn (PY) Method (flow diagram shown in Figure 3): aPreformed Y arn (PY) of 3 to 4mm width and 200 to 1000 mm long was utilized by N. Hirotaka et al. in the PY strategy ⁇ .
  • PY has PAN-based carbon fiber as the support, coke powder and oil mesophase pitch (cover) as grid antecedent and polypropylene globules as the polymer that coats the carbon fiber and framework forerunner.
  • a PY square was made by unidirectionally adjusting PY sheets which were set up by the stacking up of PY s. Hot pressing of the PY in a metal mold was completed at 600 °C (10 °C/min) which was then subjected to carbonization at 800°C and graphitization at 2000 °C to yield the final C/C composite.
  • the PY method has at least the following advantages:
  • the conventional manufacturing method (impregnation method and CVD method) requires complicated steps and requires very long times to manufacture (as steps need to be repeated to remove porosity). As a result, it is extremely expensive.
  • the preformed yarn method (PY method) successfully demonstrated advantages in a process simplification, shortening delivery time, and reducing costs.
  • the industry seeks methods to produce thermal protection materials with complex shapes that are light weight and resistant to erosion, impact damage, and interlaminate blistering when at high Mach flight conditions. Further, reduction in manufacturing time and waste are desired.
  • the goal of the methods described herein is the development of a thin shell Carbon-Carbon thermal protection system (TPS) material with high toughness and erosion resistance. The material solution developed will be quicker and less expensive production with a reduced scraping rate.
  • TPS Carbon-Carbon thermal protection system
  • Proposed herein is a methodology to produce a thin shell TPS structure with high strength/high density and short manufacturing time.
  • the proposed method can yield a sample that is greater than inches thick and of an area greater than % square foot. It is contemplated that the process can produce larger C-C shells. The reduction in manufacturing time of a full- scale part will be demonstrated. Samples will be arc tested and mechanical properties tested at a high Mach test facility. Further, ablation performance of the reinforced TPS shells will be demonstrated.
  • MWCNT-C/C scalable carbon nanotube reinforced carbon-carbon composites
  • PY preformed yam method
  • CNT interface reinforcement in C/C composite
  • a scalable manufacturing process of the MWCNT-C/C composite will be folly characterized to verify the achievement of reinforced interlaminar shearing strength and physical characteristics.
  • the MWCNT-C/C by PY method ensures better penetration of the carbon fiber bundles into the carbon matrix, ensuring uniform properties in the composite and higher strength than conventional C/C composites.
  • CNT C/C Low Cost High Efficiency Fabrication of MWCNT-Reinforced C/C TPS Composite by PY Method
  • the fabrication of a CNT C/C involves (a) dispersion of CNT in PyC matrix precursor, (b) fabrication of preformed yarn, (c) preparation of green body from preformed yam and (d) graphitization to achieve final MWCNT-C/C composite.
  • Preformed yam (PY) method is a low-cost manufacturing process to fabricate C/C composites.
  • the preformed yam consists of a bundle of carbon fibers in a matrix of coke and pitch binder powders.
  • the yam is encased in a flexible thermoplastic sleeve.
  • the sleeved preformed yam is woven into sheets, layered, and then hot-pressed in a mold to form a green part, which is then graphitized at 2000 °C in an inert gas environment to form a C/C composite.
  • the preformed yam may be fabricated using a prewoven carbon fiber fabric, which is then impregnated with the coke and pitch matrix.
  • the PY method produces C/C composites with substantially shorter processing time, l/3 ⁇ l/6 of that by conventional methods (impregnation or the CVD method).
  • the standard composition of C/C composites manufactured by the PY method is 40 ⁇ 50% carbon fiber content by volume, however, after graphitization at 2000 °C, the constituent element is 100% carbon.
  • the MWCNT-C/C approach is based on the incorporation of CNT in the precursor of the pyrocarbon (PyC), which acts as both carbon fiber interlaminar nanostitching phase and mechanical enhancement for the PyC matrix in the final C/C composite, as shown in Figure 5.
  • PyC pyrocarbon
  • Unidirectional carbon fiber bundles or woven carbon fiber fabric will be wet and infiltrated by being pulled through the CNT loaded PyC precursor hot bath, followed by encasing with thermoplastics (nylon, for example) to form preformed yams.
  • the resulting preformed yarns will then be hand chopped and hand laid up in a mold, followed by a hot press process at moderate processing temperature, around 600 °C, to burn off the thermoplastic sleeve materials and form a green body composite.
  • Impregnated carbon fiber fabric may be hand laid up in a mold, followed by a hot press process at moderate processing temperature, around 600 °C, to burn off the thermoplastic sleeve materials and form a green body composite.
  • Final MWCNT-C/C composites will be obtained by graphitize the green body at 2000 °C and above. This novel approach will realize the MWCNT-C/C TPS composite design with a practical, low cost, high efficiency, fabrication process.
  • a mature CNT dispersion approach is used to prepare homogenously dispersed CNT in the PyC precursor solution that will be used in the PY method.
  • a MWCNTs/isopropanol solution will be stirred for one hour using a homogenizer, then the solution will be vibrated using ultrasonication for another two hours to enable the CNTs to evenly disperse in the isopropanol solution.
  • the CNTs/isopropanol solution will be mixed with pitch binder and coke for one hour using a mechanical mixer. The mixture will then be further mixed by a heated ultrasonication bath for 60 min.
  • the resulting CNT loaded PyC precursor solution will then be extracted by using a vacuum pump to remove isopropanol and other low molecular weight solvents in the solution that may cause voids in next steps.
  • the obtained CNT/PyC precursor solution will be used for fabricating the preformed yarn.
  • the PY method has been made in consideration of the problems involved in the conventional techniques by fabricating a novel preformed yam that is used as a precursor for fiber-reinforced carbon composites, which is excellent in workability and processability in the fabrication of composite articles.
  • the resulting composites have high heat-resistance with high and uniform mechanical properties.
  • the PY method provides a process for the preparation of a preformed yam useful in forming composite articles, comprising the steps of: continuously passing a bundle of carbon fibers (or carbon fiber fabric) through a bed of the previously prepared MWCNT loaded PyC precursor solution (pitch binder and coke) so that the mixed solution is taken in the interstices between carbon fibers; mixed solution-carrying carbon fibers will then form a tow with mixed solution being held between carbon fibers (or a prepreg fabric when carbon fiber fabric is utilized); followed by extruding a thermoplastic resin over the tow or prepreg to form a sleeve surrounding the tow or prepreg, which will be wind up as the MWCNT-C/C preformed yarn for composite articles fabrication.
  • the sleeve is preferably formed of an easily decomposable and vaporizable, low softening point thermoplastic resin such as polyamide, polyethylene, polypropylene, polyester or polyvinylidene fluoride. Above all, the use of a polyethylene or polypropylene is preferred for reasons of inexpensiveness and capability of forming a thin sleeve.
  • the thickness of the sleeve is not specifically limited. However, as long as the workability or processability of the preformed yarn is not adversely affected, the use of a thinner sleeve is more preferred for improving the properties of composite articles. The use of a sleeve with a thickness of 7-30 um is typically recommended.
  • the preformed yarn according to the proposed approach can be utilized to produce inorganic fiber-reinforced composite articles that are to be used under high temperature and high mechanical stress conditions.
  • Such composite articles may be easily prepared by, for example, filament winding or hot pressing in a simple manner.
  • the proposed MWCNT-C/C preformed yarn is subjected to hot pressing at a temperature of 400 °C or higher, especially close to 600 °C, the shaped body produced is almost free of volatile substances. Therefore, the succeeding carbonizing or graphitizing treatment can be performed without encountering problems of generation of gases.
  • the composite articles obtained with the use of the proposed preformed yarns is substantially free of pores.
  • the CNT loaded PyC precursor solution is homogeneously distributed in the interstices of the reinforcing carbon fibers (in other words, the reinforcing carbon fibers are homogeneously dispersed in the matrix of CNT loaded PyC), the resulting composite articles therefrom are uniform in physical properties.
  • the preformed yarn is also very suited for the production of composite articles having complex shapes and small radii of curvature.

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Abstract

Disclosed herein are methods for preparing a MWCNT-C/C TPS material, from a pitch binder, MWCNTs, and coke powder to produce a MWCNT-C/C preformed yarn which is then used to produce CNT reinforced C/C composite articles. In some embodiments, the articles are formed by filament winding or hot pressing. Disclosed are materials comprising such pre-formed yarns, and articles made therefrom.

Description

TPS MATERIAL WITH ENHANCED TOUGHNESS AND INTERLAMINAR STRENGTH
CROSS-REFERENCE WITH RELATED APPLICATIONS
10001] This application claims the benefit of priority to U.S. Provisional Patent Application No. 63/385,820 filed December 2, 2022.
GOVERNMENT INTERESTS
[0002] This invention was made with government support from the Missile Defense Agency (MDA) under Contract No. HQ0860-21-C-7041. The U.S. Government has certain rights in this invention.
BACKGROUND
[0003] High energy, high velocity flights through the atmosphere lead to extremely severe aerodynamic heating and pressures on the vehicle exteriors. The vehicle structure needs to be protected from damage due to this heating. Design features incorporated into a vehicle to withstand this aerodynamic heating and protect it from damage are known as Thermal Protection Systems or TPS.
[0004] Discovery of carbon-carbon composites by Chance Vought Aircraft in 1958 created an opportunity to use these materials for heat shielding appliances due to their high strength and thermal resistance.
[0005] Carbon-carbon composites are a family of advanced composite materials. They are the most advanced form of carbon and consist of a fiber based on carbon precursors embedded in a carbon matrix. This unique composition gives them such properties as low density, high thermal conductivity and shock resistance, low thermal expansion, and high modulus. Carboncarbon composites are mostly used in aerospace applications, mainly for aircraft disc brakes, rocket re-entry nose tips, and for parts of rocket nozzles.
[0006] There is a need for methods to produce thermal protection system (TPS) materials with complex shapes that are light weight and resistant to erosion, impact damage, and interlaminar blistering when used at high Mach flight conditions. Also desired is a reduction in manufacturing time and waste. Disclosed herein are scalable, multi-walled carbon nanotube reinforced, carbon-carbon composite (MWCNT- C/C) TPS materials fabricated using the preformed yarn (PY) method that will demonstrate one or more of enhanced flexural strength, toughness, interlaminar shear strength and impact strength, as well as thermal performance.
[0007] The TPS material described herein has both the thermal protection and loadbearing capabilities integrated into one structured
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIGURE 1. Triton’s proposed method for low cost, quicker fabrication of enhanced flexural strength, toughness, interlaminar shear strength, impact strength, and thermal performance TPS materials for high Mach vehicles. The proposed method utilizes MWCNT containing pyrocarbon in the Preformed Yam method. Once the yam is fabricated, the yarn is laid-up and pressed into a green part, which is then carbonized/graphitized to make the C/C TPS.
[0009] FIGURE 2. Mechanical properties of CNTs C/C composite. Left: flexure strength and Right: Interlaminar shear strength
[0010] FIGURE 3. Flow Chart for C-C Composite synthesis by the PY method.
[0011] FIGURE 4. Timeline of PY method vs. conventional method for C/C composite manufacturing.
[0012] FIGURE 5. Illustration of Triton’s MWCNT-C/C Composite.
[0013] FIGURE 6. Dispersion process of MWCNT in PyC precursor solution.
[0014] FIGURE 7. MWCNT-C/C preformed yam fabrication process.
DETAILED DESCRIPTION
[0015] To achieve MWCNT-C/C TPS composites with desirable thermal, strength, and weight characteristics, a unique low-cost high efficiency PY method will be adopted. As illustrated in Figure 1, the proposed development of the novel MWCNT-C/C TPS by PY technology is designed to fundamentally improve the interphase strength in C/C composites by a CNT reinforcement mechanism with a novel modified PY method that follows the steps of:
[0016] i) The preparation of MWCNT loaded pyrocarbon (PyC) matrix precursor solution
(the pyrocarbon matrix precursor consists of a pitch binder, MWCNTs, and coke powder); [0017] ii) Production of MWCNT-C/C preformed yam with excellent workability and processability for the fabrication of composite articles;
[0018] iii) The preformed yam according to the proposed approach can be utilized to produce CNT reinforced C/C composite articles by fdament winding or hot pressing followed by carbonization and graphitization.
[0019] iv) The resulting MWCNT- C/C composite will be comprehensively tested to verify the increase in interlaminar shear strength and toughness while maintaining other key performance properties.
[0020] The MWCNT-C/C TPS materials made by PY, shown in Figure 1, provides an innovative approach to achieve low-cost, high efficiency production of a robust TPS material with enhanced thermal, mechanical, and weight characteristics that will satisfy the MDA need.
[0021] The design presents a novel system with the following key benefits:
[0022] Easy tailorable properties. In the proposed efforts, we will investigate the CNT length, volume fraction, effects on the physical properties, the shear strength, and modulus of the interphase of the MWCNT-C/C TPS composite. The systematic investigation will enable fast estimation and fine tuning of targeted C/C TPS composite properties.
[0023] Fast, Cost effective, scalable, fabrication process. We adopted a novel preformed yam method for the fabrication of MWCNT-C/C TPS composite in this program. Compared to conventional methods, the PY method has successfully demonstrated advantages in process simplification, shortening delivery time, and reducing costs.
[0024] Highly uniform geometry C/C TPS composite. When subjected to hot pressing at a temperature of 400 °C or higher, especially close to 600 °C, the shaped green body produced from the proposed PY method is free of volatile substances. Therefore, the succeeding carbonizing or graphitizing treatment can be performed without encountering problems of the generation of gases. Thus, the composite articles obtained with PY are substantially free of voids.
[0025] Excellent workability and processability. The PY method has been made in consideration of the problems involved in the conventional techniques. At its core is a novel preformed yam, which is useful as a precursor for fiber-reinforced carbon composites, is excellent in workability and processability in the fabrication of composite articles, and gives highly heat-resistant composite articles exhibiting high and uniform mechanical properties.
[0026] In the Phase I effort our team demonstrated the feasibility of the MWCNT-C/C by PY solution as a superior robust TPS material with enhanced thermal, mechanical, and weight characteristics suitable for next generation high Mach vehicle applications. The proposed method was used to provide a sample that is greater than 14 inches thick with an area greater than !4 square foot, and key material properties were tested to verify it met the materials property requirements.
[0027] In the Phase II project, the process will be scaled to produce larger representative CNT-C/C TPS shells. The reduction in manufacturing time of a full-scale part (<6 months) will be demonstrated. Samples will be arc tested and mechanical properties tested at a high Mach test facility. Further, ablation performance of the reinforced TPS shells will be demonstrated.
[0028] Table 1 presents the range of properties that can be achieved and, for comparison, those of ferritic steel and titanium alloys. The properties for carbon-carbon are given in the fiber direction. Perpendicular to the fibers, the properties are much less superior. The mechanical properties are much superior to those of conventional graphite. In particular, three- dimensional carbon-carbon composites can be tailored to withstand damage and minimum delamination crack growth under interlaminar shearing. The tensile strength increases above 1200°C when conventional superalloy components start to weaken; the density is only about 1.9 g/cm3 compared with 8 g/cm3 for superalloys and in the event of failure the material does not disintegrate catastrophically, but goes through a gradual failure that has been called graceful failure, which made C/C composites the material of choice as a thermal protection material for hypersonic vehicle applications.
Table 1. Range of properties for C/C composites
Figure imgf000006_0001
[0029] Compared with carbon fibers, carbon nanotubes (CNTs) possess theoretical strengths that are up to an order of magnitude higher. These excellent properties, combined with the high specific surface area, make carbon nanotubes a promising substitute for carbon fibers to meet the challenges of the next generation aerospace technologies.
[0030] Ming-Chuen Yip and coworkers reported on the mechanical properties of CNT reinforced C/C Composites. In their study, the CNTs-reinforced carbon/carbon composites with 4 different proportions of CNT at 0.5wt%, 1.0wt%, 1.2wt%, and 1.5wt% were fabricated and investigated. The flexure strength, interlaminar shear strength, and impact resistance were tested, and the results were compared with those of CNTs-unadded carbon/carbon composites.
10031] As shown in Figure 2 left, the flexure strength of CNTs-added reinforced C/C composite was significantly increased by 13.44% and up to 62.56MPa when the CNTs content increases to 0.5wt%. As CNTs content increases up to 1.2wt%, the highest flexure strength was reached and up to 67.78MPa, and enhancement was increased by 23%. The interlaminar shear strength of CNTs-unadded C/C composite laminate reached around 4.834MPa. As the CNTs content exceeds 0.5wt% (Figure 2 right), the enhancement of the interlaminar shear strength of CNTs-added C/C composite laminate increased with the increase of the CNTs content. When the CNTs content increased to 1.2wt%, the highest interlaminar shear strength was reached at 6.27MPa, and the enhancement was an increase of 30% when compared 0% MWCNT-C/C composite. However, the shear strength starts to decrease as CNTs content increases up to 1.5wt%. This phenomenon was attributed to CNT agglomeration. When the CNT concentration reaches a high enough amount for agglomeration, the decrease of contacted area between CNTs and matrix decreases the effect of resistance to delamination.
[0032] Fabrication Processing of C/C Composites
[0033] Conventional Fabrication Processes
[0034] The gas phase route using chemical vapor deposition process: In CVD, risky hydrocarbons like methane, propane, benzene, and other different low molecular weight chemicals are used as precursors. Thermal decay of the hydrocarbons takes place in the heated chamber containing carbon fibers and deposition of carbon takes place.
[0035] The liquid route using thermosetting pitch or resin: Here impregnation is accomplished with fluid impregnates: like coal tar, oil pitches, and other high char yielding thermosetting resins. C/C composite manufacturers may infiltrate a preform to set the dimensions, followed by hot isostatic pressing at temperatures 750 °C and 100 MPa pressure. This is followed via carbonization at 1000°C and graphitization at 2750 °C.
[0036] Advanced Fabrication Method
[0037] Preformed Yarn (PY) Method (flow diagram shown in Figure 3): aPreformed Y arn (PY) of 3 to 4mm width and 200 to 1000 mm long was utilized by N. Hirotaka et al. in the PY strategy^. PY has PAN-based carbon fiber as the support, coke powder and oil mesophase pitch (cover) as grid antecedent and polypropylene globules as the polymer that coats the carbon fiber and framework forerunner. At that point, a PY square was made by unidirectionally adjusting PY sheets which were set up by the stacking up of PY s. Hot pressing of the PY in a metal mold was completed at 600 °C (10 °C/min) which was then subjected to carbonization at 800°C and graphitization at 2000 °C to yield the final C/C composite.
[0038] Compared to conventional C/C composite fabrication processes, the PY method has at least the following advantages:
[0039] Reducing the manufacturing time by up to 1/3 (see Figure 4 for a comparison of PY and conventional fabrication processes)
[0040] Dramatic cost reductions for the manufacturing of C/C composites
[0041] 3-point twisting tests demonstrated enhanced flexural quality and modulus than that achieved by conventional techniques, by a factor of 1.3.
10042] Small-scale basic investigations displayed good fiber/lattice densification, yielding a minimal number of pores.
[0043] Although the C/C composite has excellent performance, the conventional manufacturing method (impregnation method and CVD method) requires complicated steps and requires very long times to manufacture (as steps need to be repeated to remove porosity). As a result, it is extremely expensive. Compared to conventional methods, the preformed yarn method (PY method) successfully demonstrated advantages in a process simplification, shortening delivery time, and reducing costs. [0044] The industry seeks methods to produce thermal protection materials with complex shapes that are light weight and resistant to erosion, impact damage, and interlaminate blistering when at high Mach flight conditions. Further, reduction in manufacturing time and waste are desired. The goal of the methods described herein is the development of a thin shell Carbon-Carbon thermal protection system (TPS) material with high toughness and erosion resistance. The material solution developed will be quicker and less expensive production with a reduced scraping rate.
[0045] Proposed herein is a methodology to produce a thin shell TPS structure with high strength/high density and short manufacturing time. The proposed method can yield a sample that is greater than inches thick and of an area greater than % square foot. It is contemplated that the process can produce larger C-C shells. The reduction in manufacturing time of a full- scale part will be demonstrated. Samples will be arc tested and mechanical properties tested at a high Mach test facility. Further, ablation performance of the reinforced TPS shells will be demonstrated.
[0046] Disclosed herein are scalable carbon nanotube reinforced carbon-carbon composites (MWCNT-C/C) TPS using the preformed yam method (PY) that will demonstrate enhanced physical performance in flexural strength, toughness, interlaminar shear strength, and impact strength; as well as thermal performance. Disclosed herein is the use of CNT as interface reinforcement in C/C composite, and a scalable manufacturing process of the MWCNT-C/C composite. The resultant MWCNT-C/C composite will be folly characterized to verify the achievement of reinforced interlaminar shearing strength and physical characteristics. The MWCNT-C/C by PY method ensures better penetration of the carbon fiber bundles into the carbon matrix, ensuring uniform properties in the composite and higher strength than conventional C/C composites.
[0047] A cost-effective process for coupon size interlaminar shearing strength enhanced high-temperature MWCNT-C/C TPS composite fabrication is also contemplated. Scale-up methods will be investigated for large area usage.
[0048] Low Cost High Efficiency Fabrication of MWCNT-Reinforced C/C TPS Composite by PY Method [0049] The fabrication of a CNT C/C involves (a) dispersion of CNT in PyC matrix precursor, (b) fabrication of preformed yarn, (c) preparation of green body from preformed yam and (d) graphitization to achieve final MWCNT-C/C composite.
[0050] Preformed yam (PY) method is a low-cost manufacturing process to fabricate C/C composites. The preformed yam consists of a bundle of carbon fibers in a matrix of coke and pitch binder powders. The yam is encased in a flexible thermoplastic sleeve. The sleeved preformed yam is woven into sheets, layered, and then hot-pressed in a mold to form a green part, which is then graphitized at 2000 °C in an inert gas environment to form a C/C composite. Alternatively, the preformed yam may be fabricated using a prewoven carbon fiber fabric, which is then impregnated with the coke and pitch matrix. The PY method produces C/C composites with substantially shorter processing time, l/3±l/6 of that by conventional methods (impregnation or the CVD method). The standard composition of C/C composites manufactured by the PY method is 40±50% carbon fiber content by volume, however, after graphitization at 2000 °C, the constituent element is 100% carbon.
[0051] Material Design of MWCNT Reinforced C/C TPS Composites
[0052] To take advantage of the interlaminar reinforcement and physical enhancement of CNT for C/C composite, a low-risk, scalable route to reinforce the mechanical and interlaminating strength of C/C material that is suitable for TPS applications is contemplated herein. The mechanism of the reinforced MWCNT- C/C composite is illustrated in Figure 5.
[0053] The MWCNT-C/C approach is based on the incorporation of CNT in the precursor of the pyrocarbon (PyC), which acts as both carbon fiber interlaminar nanostitching phase and mechanical enhancement for the PyC matrix in the final C/C composite, as shown in Figure 5. Unidirectional carbon fiber bundles (or woven carbon fiber fabric) will be wet and infiltrated by being pulled through the CNT loaded PyC precursor hot bath, followed by encasing with thermoplastics (nylon, for example) to form preformed yams. For the unidirectional fiber bundles, the resulting preformed yarns will then be hand chopped and hand laid up in a mold, followed by a hot press process at moderate processing temperature, around 600 °C, to burn off the thermoplastic sleeve materials and form a green body composite. Impregnated carbon fiber fabric may be hand laid up in a mold, followed by a hot press process at moderate processing temperature, around 600 °C, to burn off the thermoplastic sleeve materials and form a green body composite. Final MWCNT-C/C composites will be obtained by graphitize the green body at 2000 °C and above. This novel approach will realize the MWCNT-C/C TPS composite design with a practical, low cost, high efficiency, fabrication process.
[00541 Preparation of Multiwalled Carbon Nanotubes Pyrocarbon (MWCNTs/PyC) Precursor Solution.
[0055] A mature CNT dispersion approach is used to prepare homogenously dispersed CNT in the PyC precursor solution that will be used in the PY method. First, a MWCNTs/isopropanol solution will be stirred for one hour using a homogenizer, then the solution will be vibrated using ultrasonication for another two hours to enable the CNTs to evenly disperse in the isopropanol solution. Then the CNTs/isopropanol solution will be mixed with pitch binder and coke for one hour using a mechanical mixer. The mixture will then be further mixed by a heated ultrasonication bath for 60 min. The resulting CNT loaded PyC precursor solution will then be extracted by using a vacuum pump to remove isopropanol and other low molecular weight solvents in the solution that may cause voids in next steps. The obtained CNT/PyC precursor solution will be used for fabricating the preformed yarn.
[00561 Fabrication of MWCNT-C/C Preformed Yarn
[0057] The PY method has been made in consideration of the problems involved in the conventional techniques by fabricating a novel preformed yam that is used as a precursor for fiber-reinforced carbon composites, which is excellent in workability and processability in the fabrication of composite articles. The resulting composites have high heat-resistance with high and uniform mechanical properties.
[0058] As illustrated in Figure 7, the PY method provides a process for the preparation of a preformed yam useful in forming composite articles, comprising the steps of: continuously passing a bundle of carbon fibers (or carbon fiber fabric) through a bed of the previously prepared MWCNT loaded PyC precursor solution (pitch binder and coke) so that the mixed solution is taken in the interstices between carbon fibers; mixed solution-carrying carbon fibers will then form a tow with mixed solution being held between carbon fibers (or a prepreg fabric when carbon fiber fabric is utilized); followed by extruding a thermoplastic resin over the tow or prepreg to form a sleeve surrounding the tow or prepreg, which will be wind up as the MWCNT-C/C preformed yarn for composite articles fabrication. [0059] The sleeve is preferably formed of an easily decomposable and vaporizable, low softening point thermoplastic resin such as polyamide, polyethylene, polypropylene, polyester or polyvinylidene fluoride. Above all, the use of a polyethylene or polypropylene is preferred for reasons of inexpensiveness and capability of forming a thin sleeve. The thickness of the sleeve is not specifically limited. However, as long as the workability or processability of the preformed yarn is not adversely affected, the use of a thinner sleeve is more preferred for improving the properties of composite articles. The use of a sleeve with a thickness of 7-30 um is typically recommended.
[0060] Hot Press Molding and Graphitization.
[0061] The preformed yarn according to the proposed approach can be utilized to produce inorganic fiber-reinforced composite articles that are to be used under high temperature and high mechanical stress conditions. Such composite articles may be easily prepared by, for example, filament winding or hot pressing in a simple manner.
[0062] When the proposed MWCNT-C/C preformed yarn is subjected to hot pressing at a temperature of 400 °C or higher, especially close to 600 °C, the shaped body produced is almost free of volatile substances. Therefore, the succeeding carbonizing or graphitizing treatment can be performed without encountering problems of generation of gases. Thus, the composite articles obtained with the use of the proposed preformed yarns is substantially free of pores. Moreover, since the CNT loaded PyC precursor solution is homogeneously distributed in the interstices of the reinforcing carbon fibers (in other words, the reinforcing carbon fibers are homogeneously dispersed in the matrix of CNT loaded PyC), the resulting composite articles therefrom are uniform in physical properties. The preformed yarn is also very suited for the production of composite articles having complex shapes and small radii of curvature.
[0063] To fabricate the specimens with dimension of no less than 6”x6”xl/4”, we will hand chop the prepared preformed yarn, lay up the yarn in a metal mold, followed by hot press the mold at 600 °C (10 °C/min), which will then be subjected to carbonization at 800 °C and graphitization at 2000 °C to get the final MWCNT-C/C composite.
[0064] Characterization
[0065] Comprehensive performance evaluation will be conducted on the fabricated MWCNT-C/C composite to demonstrate the improvement in interlaminar strength and physical properties of CCC by the MWCNT- C/C by PY technology. The interlaminar shear strengths of will be determined by following the ASTM D3846 standard as a guide and will be performed at Intertek. Tensile and compression strengths and moduli according to ASTM D3039 and ASTM D695 will also be performed on MWCNT-C/C composite panels to evaluate the trade off or improvement in key properties. Standard test method ASTM E 399 is used to measure the fracture toughness.
[0066] Scanning electron microscopy (SEM) will be performed throughout the efforts to exam the morphology of interphase and fractured sections of MWCNT-C/C composite.

Claims

CLAIMS What is claimed is:
1. A method for preparing a MWCNT-C/C TPS material, the method comprising: i) preparing a MWCNT loaded pyrocarbon (PyC) matrix precursor solution comprising a pitch binder, MWCNTs, and coke powder; ii) producing a MWCNT-C/C preformed yam from the matrix precursor solution; iii) using the preformed yam to produce CNT reinforced C/C composite articles.
2. The method of claim 1, wherein the articles are formed by filament winding or hot pressing followed by carbonization and graphitization.
3. A TPS material comprising:
A MWCNT-C/C pre-formed yam.
4. The TPS material of claim 3, wherein the preformed yam is shaped into an article.
5. The TPS material of claim 3 produced by the method of claim 1.
PCT/US2023/082365 2022-12-02 2023-12-04 Tps material with enhanced toughness and interlaminar strength WO2024119186A1 (en)

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Citations (2)

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