Preparation method of carbon fiber toughened graphite throat liner material

Abstract

The application discloses a preparation method of carbon fiber toughened graphite throat lining material, which comprises a toughened fiber pretreatment process, a mixing and batching process, a dry pressing forming process, a multi-cycle densification process and a high-temperature graphitization treatment process. Compared with the existing carbon / carbon composite material preparation method, the production cycle is significantly shortened, and the cost is effectively reduced.

Description

Technical Field

[0001] This invention mainly relates to the field of thermal protection materials for solid rocket engine nozzles and the preparation technology of high-temperature special carbon-based composite materials, and particularly to a method for preparing carbon fiber toughened graphite throat liner material. Background Technology

[0002] Solid rocket motors are core propulsion devices that convert the chemical energy of propellant into the thermal energy of high-temperature, high-pressure combustion gases, and then convert this thermal energy into high-speed jet kinetic energy through the nozzle assembly, thereby generating thrust to propel the aircraft. The nozzle throat liner, as the smallest cross-sectional area and the hottest component in a solid rocket motor, operates in an extremely harsh environment. During engine ignition and power stroke, the surface temperature of the throat liner's inner wall typically spikes to over 3000°C instantaneously. It must withstand not only the extremely high thermal shock from the combustion gas flow but also the intense mechanical erosion and shearing of high-speed solid particles within the combustion gas. If the throat liner material experiences macroscopic cracking, large-scale spalling, or excessive ablation under extreme thermal loads, it will directly lead to an enlargement of the engine nozzle throat diameter or even structural failure, resulting in decreased thrust, trajectory deviation, or even catastrophic launch mission failure.

[0003] In the existing technology, throat liner materials that can meet the above-mentioned harsh working conditions are mainly divided into two major development routes: pure graphite materials and carbon / carbon composite materials.

[0004] The first type of pure graphite materials, including isostatically pressed graphite and molded graphite, is the earliest and most widely used throat liner material system in the aerospace field. Its core advantages lie in the abundant raw material sources, relatively mature preparation processes, and low manufacturing costs. Furthermore, graphite crystals themselves possess high melting points and sublimation temperatures, low coefficients of thermal expansion, and good ablation resistance. However, pure graphite materials are typical brittle inorganic non-metallic materials with weak interfacial bonding at the microscopic cleavage planes, resulting in generally low macroscopic tensile and flexural strengths (typically flexural strength below 45 MPa) and extremely poor fracture toughness. Under the intense thermal shock of milliseconds during the initial stage of engine ignition, the huge temperature gradient generated between the inner and outer walls of the throat liner easily induces thermal stress microcracks within the graphite matrix. Coupled with the powerful scouring of high-temperature, high-pressure combustion gases, these microcracks rapidly destabilize and propagate, ultimately leading to catastrophic macroscopic spalling and fracture of the graphite throat liner. This has become the biggest bottleneck limiting the application of pure graphite materials in high-performance tactical missiles and large solid-propellant launch vehicles.

[0005] The second category comprises carbon / carbon composites developed to overcome the brittleness of pure graphite. Traditional carbon / carbon composite throat liners typically employ a pre-woven three-dimensional continuous carbon fiber skeleton (such as 2.5D, 3D, or multi-directional braids) as a preform, followed by multi-cycle densification via chemical vapor deposition or pitch impregnation-carbonization (PIC) processes. This material system fully leverages the high strength and high modulus properties of carbon fibers, exhibiting exceptional fracture toughness, pseudoplastic fracture characteristics, and extremely low linear ablation rate (typically controllable within a high standard range of ≤0.05 mm / s). However, carbon / carbon composites face extremely severe manufacturing engineering challenges: First, the process is extremely complex. For example, chemical vapor deposition is subject to a "bottleneck effect" (the surface is first deposited and crusted, making it difficult to fill the internal pores), resulting in a very slow deposition rate. It requires multiple tedious cycles of deposition, machining to remove the crust, and re-deposition, making the preparation cycle of a single throat liner as long as six months. Second, the extremely long production cycle, high fiber weaving costs, and huge equipment energy consumption result in extremely high manufacturing costs for carbon / carbon composites (usually 5 to 10 times higher than that of pure graphite of the same volume). This not only severely restricts its promotion in the cost-sensitive commercial aerospace field, but also makes it difficult to meet the strategic needs of large-scale rapid mass production of tactical weapons and rapid wartime resupply.

[0006] To find the optimal engineering balance between "low cost / short cycle time" and "high performance / high reliability," materials scientists both domestically and internationally have attempted to develop carbon fiber-reinforced graphite composites, which involve directly incorporating short-cut carbon fibers into a graphite powder matrix to achieve toughening. However, in practical application, this approach has encountered significant obstacles. This is because carbon fibers exhibit strong chemical inertness (low surface energy, hydrophobic properties), and their individual filaments are extremely fine with a large specific surface area. During mechanical mixing with graphite powder and binders (such as pitch or resin), severe electrostatic adsorption and physical entanglement easily occur. These fibers often aggregate into clumps, failing to uniformly disperse in the matrix to form an effective three-dimensional stress transfer network. Furthermore, because the agglomerates cannot be wetted by the binder liquid phase, numerous macroscopic dry spots, voids, and structural defects form after high-temperature calcination. These defects become stress concentration sources when the material is under stress, resulting in negligible toughening effects, and even making the overall strength and ablation resistance of the material inferior to pure graphite materials.

[0007] In recent years, there have been cases of introducing carbon fibers to improve mechanical strength in the field of isostatic graphite manufacturing for semiconductors. For example, patent application CN119797953A discloses a method for producing isostatic graphite for semiconductors. This method involves grafting organic functional groups onto the surface of carbon fibers using isocyanate, followed by pitch impregnation and separate high-temperature graphitization to obtain "modified carbon fibers." These modified carbon fibers are then mixed with graphene oxide, chitosan-modified pitch, and coke to prepare isostatic graphite. While this technology effectively alleviates fiber agglomeration and achieves a flexural strength of 73 MPa in the final product, its process route has significant limitations for the aerospace throat liner field. On the one hand, the modification treatment using highly toxic chemical reagents such as isocyanate not only significantly increases raw material processing costs and environmental pressure but also makes the process extremely cumbersome. On the other hand, the calcination cycle in this scheme requires six months. This extremely long heat treatment cycle essentially fails to overcome the high time cost inherent in traditional special graphite manufacturing, and is completely unable to meet the core requirements of rapid iteration and efficient mass production of key heat-resistant components in aerospace propulsion systems.

[0008] Therefore, under the premise of low cost, easy processing, and short cycle in aerospace engineering, how to abandon complex and highly polluting chemical modification methods and rely solely on the synergistic regulation of process fluid dynamics and physical interfaces to overcome the core engineering technical problems of uneven dispersion and weak interfacial bonding of carbon fibers (or silicon carbide fibers) in graphite matrix, and thus prepare a new toughened throat liner material that combines the economic advantages of pure graphite with the excellent performance of carbon / carbon composite materials, has become a technical pain point that urgently needs to be solved in the field of solid rocket thermal protection structural materials. Summary of the Invention

[0009] In view of the technical difficulties in existing technologies, such as the brittle fracture failure of pure graphite throat liners, the lengthy and costly preparation cycle of carbon / carbon composite materials, and the macroscopic defects caused by fiber agglomeration due to traditional direct blending methods, this invention aims to provide a carbon fiber toughened graphite throat liner material and its preparation method. This invention is based on the physical reshaping of the fiber's microstructure and the interface pre-coating technology of high-viscosity fluid wetting, combined with cold isostatic pressing and a multi-cycle pressurization and heating densification system, aiming to fundamentally solve the problems of agglomeration and interface debonding in fiber-toughened matrix materials.

[0010] To achieve the above objectives, this invention provides a method for preparing carbon fiber-reinforced graphite throat liner material. This method scientifically and systematically integrates pretreatment, batching, molding, and densification processes, and specifically includes the following steps:

[0011] Step S1: Pretreatment of toughening fibers

[0012] First, the toughening fiber is cut into a length of 5 to 20 mm, then mechanically crushed into short fiber bundles of 1 to 5 mm, and then mixed with the first binder at high temperature in a kneading device to make the surface of the toughening fiber uniformly coated with a layer of binder film, thus obtaining pretreated fiber.

[0013] Step S1 is the core of solving the persistent problem of fiber agglomeration in existing technologies. Traditionally, directly sheared carbon fibers have flat ends, smooth surfaces, and are bundled together. This invention first cuts the fibers and then "mechanically crushes" them. The mechanical shearing and compressive stress during the crushing process forces the tightly packed carbon fiber bundles to loosen radially, increasing the gaps between the filaments. Furthermore, it causes microscopic fibrillation and splitting at the ends of the carbon fibers, significantly increasing the fiber roughness and specific surface area. Immediately afterwards, the fibers are vigorously mixed with a binder within a specific temperature range of 120 to 160°C (at which point the binder, such as medium-temperature coal tar pitch, reaches an excellent rheological state, exhibiting Newtonian fluid characteristics). Under the action of capillary osmotic pressure, the high-viscosity fluid rapidly penetrates into the loose fiber bundles and the splitting gaps at the ends, forming a strong physical anchoring and mechanical interlocking effect. Through this composite process combining mechanical splitting and fluid pre-wetting, a uniform binder isolation film is constructed on the fiber surface. This isolation membrane not only utilizes the steric hindrance effect to isolate the electrostatic adsorption and entanglement between dry fibers, eliminating the risk of agglomeration at the source; more importantly, this adhesive membrane is transformed in situ into an isotropic pyrolytic carbon transition phase rich in microcrystalline structure during the subsequent high-temperature calcination stage, constructing a modulus gradient buffer layer with a thermal expansion coefficient between the fiber (reinforcing phase) and graphite powder (matrix phase), which greatly alleviates the interfacial thermal stress under extreme thermal shock conditions and prevents premature debonding failure of the interface.

[0014] Step S2, Mixing and Batching Process

[0015] The pretreated fibers obtained in step S1 are mixed with graphite powder at a mass ratio of (10 to 30): (70 to 90), a second binder is added, and the mixture is thoroughly mixed in a kneader to obtain a mixture.

[0016] In step S2, graphite powder and toughening fibers construct a dual / multi-scale toughening system within the material, significantly improving its toughness, strength, and crack propagation resistance. The core of this result lies in altering the driving force and path of crack propagation, thereby enhancing the material's fracture toughness by consuming the energy required for crack propagation. According to Griffith theory, the fracture strength of a material depends on its elastic modulus, fracture surface energy, and critical crack size. Microparticle-based toughening achieves this by increasing the energy required to overcome crack propagation (i.e., the effective fracture surface energy). The fracture toughness of the composite material can be expressed as:

[0017]

[0018] Where Ec is the Young's modulus of the composite material, Jm is the matrix crack propagation energy, and J is the additional crack propagation energy due to the introduction of the second phase. Microparticle toughening significantly increases the J value through various mechanisms.

[0019] By introducing high-strength, high-modulus carbon fibers or SiC fibers, multiple toughening mechanisms can be synergistically achieved. These mainly include: fiber debonding (crack propagation along weak interfaces), fiber pull-out (frictional energy is consumed when fibers are pulled out of the matrix), and fiber bridging (unbroken fibers connect crack surfaces). These mechanisms work together to make crack propagation require overcoming enormous resistance, thereby transforming the material's fracture behavior from brittle fracture to non-brittle fracture.

[0020] Once a crack forms, this spatial structure can deflect and bridge the crack, thereby increasing its strength and preventing brittle fracture.

[0021] Crack deflection: When a crack propagates into high-strength, high-toughness fiber particles, the crack tip may deviate from its original propagation direction and bend or change direction due to the obstruction of the particles and / or the residual stress at the particle-matrix interface. This process increases the crack propagation path length, thus consuming more energy.

[0022] Crack bridging: During crack propagation, unbroken fiber particles act as "bridges," connecting the two surfaces of the crack and generating closure stress between them. This bridging effect directly reduces the stress intensity factor at the crack tip, preventing further crack opening and propagation. The toughening effect of bridging is related to factors such as the particle size of the bridging units.

[0023] Step S3, Dry pressing process

[0024] The mixture obtained in step S2 is loaded into a molding mold, sealed, and placed in a hydraulic cylinder for dry pressing. After depressurization and demolding, an isotropic green body is obtained.

[0025] Step S4: Multi-cycle densification process (three baking and three soaking)

[0026] The green body prepared in step S3 is subjected to impregnation and firing cycles to fill the internal pores of the green body;

[0027] Step S5, High-Temperature Graphitization Process

[0028] The preform after the multi-cycle densification treatment is subjected to high-temperature graphitization treatment to finally obtain toughened graphite throat liner material.

[0029] In extreme high-temperature fields above 2300℃, the carbon atoms of amorphous carbon (i.e., pitch coke produced by the pyrolysis of the binder) exhibiting a disordered layered structure within the system acquire sufficient activation energy to break through the potential barrier and undergo lattice rearrangement, gradually developing into a three-dimensional long-range ordered hexagonal graphite microcrystalline network. This crystallization process not only eliminates residual grain boundary defects and microscopic residual thermal stress within the material, greatly improving its thermal conductivity and thermal shock resistance; but also, thanks to the buffering effect of the S1 pretreatment interface, the volume shrinkage stress of the toughening fibers at extremely high temperatures is effectively absorbed by the interface layer, preventing the matrix from being torn by thermal stress and ensuring the structural integrity of the finished product.

[0030] Preferably, the toughening fiber is polyacrylonitrile-based carbon fiber with a fiber diameter of 5 to 8 μm and a tensile strength ≥3000 MPa.

[0031] Preferably, the toughening fiber is silicon carbide fiber with a fiber diameter of 0.1 to 15 μm, a tensile strength ≥2.5 GPa, and an elastic modulus of 176.4 to 400 GPa.

[0032] More preferably, the silicon carbide fiber is pretreated before use. When the silicon carbide fiber is used as a composite material reinforcement, the sizing agent of the silicon carbide fiber is thermally decomposed by baking at 180 to 220°C for 2 to 4 hours to improve the interfacial bonding performance with the matrix material.

[0033] Preferably, the first and second binders are asphalt, which is medium-temperature coal tar pitch or high-temperature coal tar pitch with a softening point of 80 to 120°C; the kneading temperature in step S1 is 120 to 160°C, the kneading time is 30 to 60 minutes, and the mass ratio of asphalt to toughening fiber is (0.3 to 0.5):1.

[0034] Preferably, the graphite powder in step S2 is natural flake graphite or artificial graphite, with a particle size of 50 to 200 μm and a carbon content of ≥99.9%.

[0035] More preferably, the artificial graphite is a pulverized material of isostatically pressed graphite for semiconductors, obtained by mixing coke, modified pitch, isocyanate-modified carbon fiber and graphene oxide, followed by isostatic pressing, calcination and graphitization treatment.

[0036] Preferably, in step S3, the forming mold is a special metal mold, the dry pressing forming pressure is 200 to 350 MPa, and the holding time is 60 to 120 min.

[0037] Preferably, the multi-cycle densification in step S4 is a three-baking, three-immersion densification process, and the specific operation flow includes:

[0038] Step S41, First Impregnation-Caking Stage: The green billet is first impregnated in medium-temperature coal tar pitch at an impregnation temperature of 180 to 220°C, an impregnation pressure of 1.5 to 2.5 MPa, and an impregnation time of 2 to 4 hours; then it is calcined under inert gas protection at a calcination temperature of 800 to 1000°C, a heating rate of 5 to 10°C / h, and a holding time of 2 to 4 hours.

[0039] Step S42, Second Impregnation-Caking Stage: The green body treated in Step S41 is impregnated for the second time in medium-temperature coal tar pitch, with the impregnation temperature increased to 190 to 230°C, the impregnation pressure increased to 1.8 to 2.8 MPa, and the impregnation time to 2 to 4 hours; then, it is calcined under inert gas protection, with the calcination temperature increased to 850 to 1050°C, the heating rate to 5 to 10°C / h, and the holding time to 2 to 4 hours;

[0040] Step S43, Third Impregnation-Caking Stage: The green blank treated in step S42 is impregnated for the third time in medium-temperature coal tar pitch, the impregnation temperature is further increased to 200 to 240°C, the impregnation pressure is further increased to 2.0 to 3.0 MPa, and the impregnation time is 2 to 4 hours; then, it is calcined under inert gas protection, the calcination temperature is further increased to 900 to 1100°C, the heating rate is 5 to 10°C / h, and the holding time is 2 to 4 hours.

[0041] During the initial calcination, the binder asphalt undergoes intense thermal dehydrogenation and condensation reactions, releasing small-molecule volatiles and inevitably leaving a large network of pores within the matrix. This step employs a process with a dual-gradient increase in temperature and pressure. As the impregnation cycle increases, the effective radius of the pores remaining inside the green body continuously decreases, and the friction resistance of fluid penetration increases exponentially. In subsequent cycles, this invention progressively increases the impregnation temperature to further reduce the viscosity of the asphalt liquid phase; and progressively increases the impregnation pressure to increase the penetration driving force overcoming the capillary resistance of the pores, thereby ensuring that even micro- and nano-sized deep closed blind pores can be effectively filled. Simultaneously, the stepwise increase in calcination temperature (from 800℃ to 850℃ and finally to 900℃) promotes deep depurification and aromatization reactions of macromolecular fused-ring compounds that were not completely debonded in the early stages, improving the quality of the asphalt coke precursor. By strictly controlling the conservative heating rate of 5 to 10°C / h, volatile gases are ensured to seep out slowly from the narrow pores, preventing microcracks and fragmentation of the matrix induced by a sudden increase in internal pressure. Compared to the single ultra-long calcination cycle of more than half a year in existing technologies, the stepped densification of this invention greatly improves mass transfer efficiency.

[0042] Preferably, the high-temperature graphitization process in step S5 is carried out in an inert gas protection or vacuum environment, with a graphitization temperature of 2300 to 2800°C and a holding time of 2 to 6 hours.

[0043] Compared with the prior art, the present invention has achieved unexpected beneficial effects:

[0044] 1. The preparation method of the present invention uses physical and mechanical mechanisms to replace expensive and complex chemical modification methods, prefabricating a buffer interface layer on the fiber surface, blocking fiber agglomeration, realizing a three-dimensional equidistant and uniform distribution of high-strength skeleton in graphite matrix, and making stress transmission within the material unobstructed.

[0045] 2. The throat liner material prepared by this invention benefits from its three-dimensional fiber network structure. When the material generates initial microcracks under ignition thermal shock, the crack tip encounters a fiber interface with moderate interfacial bonding strength, resulting in frequent crack deflection, crack blunting, and crack bridging effects. Simultaneously, the interfacial layer allows the fibers to overcome enormous frictional forces during pull-out. These multiple mechanisms can absorb a large amount of fracture surface energy, causing the material to transition to a "pseudo-plastic fracture mode" with high damage tolerance. Both tensile strength and flexural strength are significantly improved.

[0046] 3. The entire process cycle of this invention is compressed to approximately 10 to 15 days, significantly shortening the production cycle compared to traditional chemical vapor deposition (CVD) processes for preparing carbon / carbon composite materials. The manufacturing equipment utilizes mature carbon industry equipment, eliminating the need for expensive deposition furnaces or fiber weaving machines. The final product cost is only about 40 to 50% of that of carbon / carbon materials of the same volume. The process window is wide, and batch stability is extremely high, making it highly suitable for the aerospace equipment sector's demand for large-scale, streamlined production of cost-effective heat-resistant components. Detailed Implementation

[0047] To make the technical objectives, core technical solutions, and resulting technical benefits of this patent application clearer, the technical path of the present invention will be analyzed in more depth and detail below, in conjunction with several non-limiting specific embodiments and comparative examples for comparison. It should be understood that the specific embodiments described and disclosed herein are for illustrative purposes only and should not be construed as limiting the scope of protection of this patent. Any equivalent alternative material selections, parameter adjustments, and process variations made by engineers skilled in the art after understanding the inventive concept, without departing from the guiding principles of the present invention, should be considered to fall within the scope of protection of the claims of this invention.

[0048] Example 1

[0049] This embodiment details a method for preparing a carbon fiber toughened graphite throat liner material, specifically including the following steps:

[0050] Step S1, Pretreatment of toughening fibers

[0051] The toughening fiber is made of aerospace-grade high-strength polyacrylonitrile-based T300 continuous carbon fiber tow. Key indicators: single filament diameter 7μm, nominal tensile strength 3500MPa.

[0052] First, the continuous filaments are cut using a special mechanical cutter to a length of 10mm. Then, the cut fibers are fed into a twin-screw mechanical pulverizer equipped with counter-rotating blades for high-intensity mechanical pulverization until the average fiber length is reduced to 2 to 3mm, and under a microscope, the fiber bundle ends are observed to exhibit a clear fibrillation, branching, and loose state.

[0053] Weigh 1.0 kg of the above-mentioned chopped fibers and 0.4 kg of medium-temperature coal tar pitch with a softening point of 85℃. Add both simultaneously to a jacketed high-temperature kneader preheated to 140℃ (within this temperature range, the viscosity of this type of pitch is extremely low, exhibiting excellent Newtonian fluid properties). Maintain this temperature and knead vigorously for 45 minutes. Utilize the enormous mechanical shear force generated by the mixing paddle to knead and break up the fiber bundles, causing the liquid pitch not only to coat the fiber surface but also to penetrate deeply into the fiber's internal gaps through capillary action. After cooling and mechanical crushing, pretreated fiber particles with good flowability and no electrostatic adsorption are obtained. This step has no significant loss, and the yield is 1.4 kg.

[0054] Step S2, mixing and batching process

[0055] All the pretreated carbon fiber components obtained in step S1 were premixed with 9.0 kg of pre-weighed natural flake graphite powder (powder physical properties: median particle size D50 of 80 to 150 μm, fixed carbon content as high as 99.95%) in a high-speed dry powder mixer for 5 minutes. Then, the mixture was transferred to a thermal kneader, and 2.0 kg of medium-temperature coal tar pitch was added as a matrix binder and lubricant phase. The entire system was heated to 120°C, and the kneader was started for continuous, thorough mixing for 1.5 hours. In the temperature-controlled fluid shear field, the pitch macromolecular chains fully expanded and impregnated each graphite crystal and the pretreated fiber network, ultimately obtaining a mixture with uniform color and excellent plastic deformation capacity.

[0056] Step S3, dry pressing process

[0057] While the mixture temperature has not dropped significantly and it still retains good micro-rheological properties, it is quantitatively and uniformly spread into a specially made metal mold. The mold is placed in a hydraulic cylinder and held at a molding pressure of 200 MPa for 60 minutes. After depressurization and demolding, an isotropic green body is obtained.

[0058] Step S4, multi-cycle densification process

[0059] Impregnation Stage 1: The green body is transferred to a high-temperature, high-pressure impregnation autoclave. A rotary vane vacuum pump is started to evacuate the chamber to an absolute pressure ≤1 kPa and maintain this pressure for 30 minutes to remove adsorbed gases from the capillary channels of the green body. A medium-temperature coal tar pitch impregnating agent, preheated to 200℃ and in a molten state, is then injected, followed by high-pressure nitrogen to pressurize to 2.0 MPa. The pressure is maintained for 3 hours for impregnation.

[0060] First stage of roasting: The green billets, after initial impregnation, are deeply buried in carbonization saggers filled with reducing metallurgical coke (which serves a dual purpose of oxygen isolation, oxidation prevention, and support to prevent deformation), and then pushed into a ring-type roasting kiln. High-purity nitrogen is circulated throughout the kiln as a protective gas, and the temperature is slowly increased to 900℃ at a controlled rate of 8℃ / h, and held at this depth for 3 hours. This slow ramp-up curve ensures that the large amount of volatile alkane produced by pitch pyrolysis escapes smoothly, preventing bubbling and cracking defects caused by a sudden increase in vapor pressure inside the billet.

[0061] Impregnation Stage 2 and Calcination Stage 2: Due to the sharp reduction in the residual pore size of the matrix after the first calcination, the second impregnation process was intensified to overcome the greater capillary penetration resistance: impregnation temperature 210℃, impregnation pressure 2.3MPa, and holding time 4h. The slope of the second calcination heating curve remained unchanged, but the highest calcination temperature was set to 950℃ and held for 3h to promote further dehydrogenation and aromatization of the polycyclic aromatic hydrocarbons that were not fully condensed in the early stage.

[0062] Impregnation and calcination stages three: final pore filling. Impregnation conditions were increased to: impregnation temperature 220℃, impregnation pressure 2.5MPa, and impregnation time 4h. The maximum calcination temperature was set at 1000℃, with a holding time of 3h.

[0063] After undergoing this rigorous three-dip and three-baking thermodynamic evolution cycle, the nested network of pitch coke is deposited and solidified inside the pores, resulting in a densed green body.

[0064] Step S5, High-temperature graphitization process

[0065] The densified preform was transferred into an Atchison-type high-temperature graphitization furnace, surrounded by conductive coke particles. Electricity was applied, utilizing the resistance of the matrix and its surroundings to generate heat. After tens of hours of slow energy accumulation, the core temperature reached 2450°C and was held at this temperature for 4 hours. Driven by the thermal activation energy exceeding the threshold, the amorphous pitch coke macromolecules underwent long-range spatial rotation and three-dimensional lattice rearrangement, ultimately evolving into a graphite microcrystalline structure with a perfect hexagonal grid feature. After the furnace was de-energized and allowed to cool naturally to room temperature, the material was machined using diamond tools to obtain the carbon fiber-reinforced graphite throat liner.

[0066] Example 2

[0067] This embodiment adjusts the relevant processes of embodiment 1 as follows:

[0068] In step S1, the cutting length of the toughening fiber is 15 mm, and the average length of the short fiber bundle after mechanical crushing is 3 to 4 mm. At the same time, in order to meet the specific surface area wetting requirements of longer fibers, the macroscopic viscosity of the kneading system is reduced, and the mass ratio of medium-temperature coal tar pitch to carbon fiber is increased to 1:0.5, that is, 1.0 kg of the above-mentioned short fiber is mixed with 0.5 kg of medium-temperature coal tar pitch with a softening point of 85°C to obtain 1.5 kg of pretreated fiber.

[0069] In step S2, the mass ratio of fiber to natural flake graphite powder is reduced to 2:8, that is, 24.0 kg of natural flake graphite powder is added.

[0070] In step S4, the three firing temperatures are lowered to 850℃, 900℃, and 950℃ respectively.

[0071] In step S5, the temperature is set to 2300℃.

[0072] Other process parameters shall be executed in accordance with Example 1.

[0073] Example 3

[0074] The specific process adjustments in this embodiment are as follows:

[0075] In step S1, special carbon fibers with a finer monofilament diameter (nominal diameter of only 5μm) are selected, with an initial cutting length of 5mm. The fibers are mechanically sheared and crushed for a longer period of time, aiming to impart a higher density three-dimensional micro-interwoven stress dissipation network to the matrix.

[0076] In step S2, high-purity artificial graphite powder (precisely sieved to a particle size of 50 to 100 μm) with better equiaxed properties and a richer microporous structure is used. The porous geological features on the surface of artificial graphite particles are extremely beneficial for deeper mechanical interlocking and anchoring with the binder bitumen.

[0077] In step S4, the maximum permeation pressure of the high-pressure impregnation autoclave is increased to 2.8 MPa.

[0078] In step S5, the temperature is set to 2800℃ and the heat treatment is carried out at a constant temperature for 2 hours.

[0079] Other process parameters shall be executed in accordance with Example 1.

[0080] Through the above three embodiments, Embodiment 1 fully demonstrates the core process path of the present invention. The fiber agglomeration problem was successfully solved by physically reshaping the fibers and pre-coating the interface. The gradient densification process ensured that the internal pores of the preform were effectively filled. After graphitization at 2450℃, the final product formed a three-dimensional fiber network structure transitioned by a pre-treated interface layer. When subjected to thermal shock, this material can absorb a large amount of energy through mechanisms such as crack deflection, fiber pull-out, and bridging, thereby achieving a transformation from brittle fracture to pseudo-plastic fracture. It possesses good thermal shock resistance, high strength, and moderate fracture toughness, while its production cycle (approximately 10-15 days) and cost are far lower than traditional carbon / carbon composite materials.

[0081] Example 2 verifies the versatility of the process window. By adjusting the binder ratio to accommodate the specific surface area of ​​longer fibers, the pretreatment effect was ensured. Even with relatively low calcination and graphitization temperatures, a toughened material with balanced performance could still be obtained due to proper pretreatment and the subsequent densification process. This demonstrates that the method is well-adaptable to different fiber lengths and ratios, and can be flexibly adjusted according to specific performance requirements (such as whether toughness or cost is prioritized).

[0082] Example 3 explores the performance potential of the present invention. Finer fibers mean a greater number of fibers per unit volume, resulting in a more significant toughening effect. The porous surface of the artificial graphite and higher impregnation pressure further enhance the bonding strength between the matrix and the fiber / binder interface. Ultra-high temperature graphitization at 2800°C allows amorphous carbon to be more thoroughly transformed into highly ordered graphite microcrystals, greatly improving the material's thermal conductivity and thermal shock resistance, and eliminating internal stress. The material prepared in this example maintains a lower cost advantage while its mechanical properties and ablation resistance are closer to those of high-end carbon / carbon composites, making it suitable for more demanding working conditions.

[0083] In summary, the three embodiments verified the feasibility, broad process window, and adjustable performance of the present invention from different perspectives. Through unique physical pretreatment and interface control techniques, the challenges of fiber agglomeration and interfacial bonding in fiber-reinforced graphite-based composites were successfully solved with extremely short production cycles and significantly reduced costs. This achieved the goal of low-cost, high-efficiency preparation of high-performance throat liner materials, finding an excellent engineering balance between pure graphite and carbon / carbon composites.

Claims

1. A method for preparing a carbon fiber-reinforced graphite throat liner material, Its features are, Includes the following steps: Step S1: Pretreatment of toughening fibers First, the toughening fiber is cut into a length of 5 to 20 mm, then mechanically crushed into short fiber bundles of 1 to 5 mm, and then mixed with the first binder at high temperature in a kneading device to make the surface of the toughening fiber uniformly coated with a layer of binder film, thus obtaining pretreated fiber. Step S2, Mixing and Batching Process The pretreated fibers obtained in step S1 are mixed with graphite powder at a mass ratio of (10 to 30): (70 to 90), a second binder is added, and the mixture is thoroughly mixed in a kneader to obtain a mixture. Step S3, Dry pressing process The mixture obtained in step S2 is loaded into a molding mold, sealed, and placed in a hydraulic cylinder for dry pressing. After depressurization and demolding, an isotropic green body is obtained. Step S4, Multi-cycle densification process The green body prepared in step S3 is subjected to impregnation and firing cycles to fill the internal pores of the green body; Step S5, High-Temperature Graphitization Process The preform after the multi-cycle densification treatment is subjected to high-temperature graphitization treatment to finally obtain toughened graphite throat liner material.

2. The preparation method according to claim 1, characterized in that, The toughening fiber is a polyacrylonitrile-based carbon fiber with a fiber diameter of 5 to 8 μm and a tensile strength of ≥3000 MPa.

3. The preparation method according to claim 1, characterized in that, The toughening fiber is silicon carbide fiber with a fiber diameter of 0.1 to 15 μm, a tensile strength ≥2.5 GPa, and an elastic modulus of 176.4 to 400 GPa.

4. The preparation method according to claim 3, characterized in that, The silicon carbide fibers are pretreated by baking at 180 to 220°C for 2 to 4 hours before use.

5. The preparation method according to claim 1, characterized in that, The first and second binders are asphalt, and the asphalt is medium-temperature coal tar pitch or high-temperature coal tar pitch with a softening point of 80 to 120°C. In step S1, the kneading temperature is 120 to 160°C, the kneading time is 30 to 60 minutes, and the mass ratio of asphalt to toughening fiber is (0.3 to 0.5):

1.

6. The preparation method according to claim 1, characterized in that, In step S2, the graphite powder is natural flake graphite or artificial graphite, with a particle size of 50 to 200 μm and a carbon content of ≥99.9%.

7. The preparation method according to claim 6, characterized in that, The artificial graphite is a pulverized material of isostatically pressed graphite for semiconductors, obtained by mixing coke, modified pitch, isocyanate-modified carbon fiber and graphene oxide, followed by isostatic pressing, calcination and graphitization.

8. The preparation method according to claim 1, characterized in that, In step S3, the forming mold is a special metal mold, the dry pressing forming pressure is 200 to 350 MPa, and the holding time is 60 to 120 min.

9. The preparation method according to claim 1, characterized in that, The multi-cycle densification process in step S4 is a three-baking, three-immersion densification process, and the specific operation flow includes: Step S41, First Impregnation-Caking Stage: The green billet is first impregnated in medium-temperature coal tar pitch at an impregnation temperature of 180 to 220°C, an impregnation pressure of 1.5 to 2.5 MPa, and an impregnation time of 2 to 4 hours; then it is calcined under inert gas protection at a calcination temperature of 800 to 1000°C, a heating rate of 5 to 10°C / h, and a holding time of 2 to 4 hours. Step S42, Second Impregnation-Caking Stage: The green body treated in Step S41 is impregnated for the second time in medium-temperature coal tar pitch, with the impregnation temperature increased to 190 to 230°C, the impregnation pressure increased to 1.8 to 2.8 MPa, and the impregnation time to 2 to 4 hours; then, it is calcined under inert gas protection, with the calcination temperature increased to 850 to 1050°C, the heating rate to 5 to 10°C / h, and the holding time to 2 to 4 hours; Step S43, Third Impregnation-Caking Stage: The green blank treated in Step S42 is impregnated for the third time in medium-temperature coal tar pitch, the impregnation temperature is further increased to 200 to 240℃, the impregnation pressure is further increased to 2.0 to 3.0 MPa, and the impregnation time is 2 to 4 hours; then, it is calcined under inert gas protection, the calcination temperature is further increased to 900-1100℃, the heating rate is 5 to 10℃ / h, and the holding time is 2 to 4 hours.

10. The preparation method according to claim 1, characterized in that, In step S5, the high-temperature graphitization process is carried out in an inert gas protection or vacuum environment, with a graphitization temperature of 2300 to 2800°C and a holding time of 2 to 6 hours.

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