Boron-containing high-temperature resistant near-stoichiometric silicon carbide fiber and preparation method thereof

Abstract

The present invention discloses a boron-containing, high-temperature-resistant, near-stoichiometric silicon carbide fiber and a preparation method thereof. The preparation method includes a spinning stage, an infusibility stage, a pre-sintering stage, a densification sintering stage, and a nitriding stage, and is characterized in that: in the infusibility stage, the metal-doped polycarbosilane precursor fiber obtained in the spinning stage is subjected to a boron-doping reaction in an atmosphere containing boron trichloride and a cross-linking reaction in an atmosphere of a gaseous hydrocarbon having a carbon-carbon double bond. The method is simple to operate, has high production efficiency, low production cost, and is easy to use for large-scale industrial production. The prepared boron-containing, high-temperature-resistant, near-stoichiometric silicon carbide fiber has the advantages of low oxygen content, high degree of densification, few defects, stable structure, high tensile strength modulus, large grain size, and good high-temperature resistance, oxidation resistance, and creep resistance.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic fibers, and in particular to a boron-containing, high-temperature-resistant, near-stoichiometric silicon carbide fiber and a preparation method thereof. Background Art

[0002] SiC fibers offer exceptional properties such as high strength, high modulus, high-temperature resistance, oxidation resistance, and high-temperature creep resistance. They can surpass the temperature limits of high-temperature alloys and withstand long-term use at higher temperatures. Furthermore, SiC fibers exhibit excellent compatibility with ceramic matrices, making them ideal reinforcements for ceramic-based composites. They hold broad application prospects in aerospace, military, and other fields.

[0003] At present, the preparation of SiC fibers by precursor conversion method has been fully commercialized. It has developed into the first, second and third generation SiC fibers. Among them, the third generation SiC fibers with high temperature resistance and near stoichiometric ratio are the most difficult to prepare and have the best temperature resistance. There are two main routes for preparing near stoichiometric SiC fibers. One is the preparation route represented by Hi-Nicalon-S, which uses electron beam irradiation to infusibility and high temperature sintering with hydrogen to remove excess carbon. The other is the preparation route represented by TyrannoSA, which introduces the densification sintering element Al, infusibility through air, and sintering at around 1300℃ to obtain Si-CO-Al fibers. The excess carbon and oxygen elements are then removed at a high temperature above 1700℃ to achieve densification sintering.

[0004] Boron, another very effective sintering aid for SiC, can also densify the fiber at high temperatures, enabling dense sintering of the fiber. However, introducing boron during the precursor synthesis process to achieve dense sintering at high temperatures is difficult. When the introduced boron content is too low, the densification and sintering effect is limited. When the introduced boron content is too high, the spinnability of the precursor is greatly reduced, and industrial-grade continuous SiC fibers cannot be obtained. Chinese patent CN114560704 A discloses a boride-containing silicon carbide composite ceramic fiber and its preparation method. The method utilizes the active silicon-hydrogen bond of polymetallic carbosilane and reacts with boron trichloride gas under the excitation state of an electron beam to introduce boron during the infusible treatment process. The fiber is then subjected to pyrolysis and high-temperature sintering to obtain a metal boride-containing silicon carbide fiber. Although the composite ceramic fiber prepared by this method has certain mechanical properties and high-temperature resistance, its oxygen content cannot be effectively controlled. Excessive oxygen content will reduce its antioxidant capacity, structural strength, thermal conductivity and physical properties, thereby affecting its application in high-temperature and oxygen environments. At the same time, this method requires expensive electron beam irradiation equipment, resulting in high production costs. Therefore, it is necessary to find other ways to introduce boron to achieve fiber densification and sintering at high temperatures. Summary of the Invention

[0005] To address the shortcomings of existing boron-containing silicon carbide fibers and their preparation methods, the first objective of the present invention is to provide a method for preparing high-temperature-resistant, near-stoichiometric boron-containing silicon carbide fibers. This method uses metal-doped polycarbosilane as a raw material. Boron and a gaseous hydrocarbon with carbon-carbon double bonds are introduced during the infusible phase to achieve crosslinking between the boron doping and the fibers. The boron element densifies and sinters the fibers at high temperatures. This method offers advantages such as a simple preparation process, high crystallinity, and low cost.

[0006] The second object of the present invention is to provide a boron-containing, high-temperature resistant, near-stoichiometric silicon carbide fiber, which has low oxygen content, high degree of densification, few defects, stable structure, high tensile strength modulus, large grain size, and good high-temperature resistance, oxidation resistance and creep resistance.

[0007] In order to achieve the above technical objectives, the present invention provides a method for preparing boron-containing high-temperature resistant near-stoichiometric silicon carbide fibers, which includes a spinning stage, an infusibility stage, a pre-sintering stage, a densification sintering stage and a nitriding stage. In the infusibility stage, the metal-doped polycarbosilane precursor fibers obtained in the spinning stage are sequentially subjected to a boron doping reaction in an atmosphere containing boron trichloride and a cross-linking reaction in an atmosphere of gaseous hydrocarbons having carbon-carbon double bonds.

[0008] The present invention uses polycarbosilane doped with metal elements as a raw material. The metal elements introduced into the polycarbosilane precursor can inhibit the abnormal growth of SiC grains at high temperatures and refine the grains. At the same time, the boron element is introduced in the non-melting stage and gaseous hydrocarbons with carbon-carbon double bonds are introduced to achieve cross-linking, further inhibiting the abnormal growth of SiC grains at high temperatures. The boron element is used to help the fiber achieve densification and sintering at high temperatures. Finally, heating and insulation are performed in a nitrogen atmosphere to convert the free boron in the fiber into a stable boron nitride structure, forming a thin in-situ boron nitride coating on the fiber surface, thereby improving the high-temperature creep resistance of the fiber.

[0009] Another key aspect of the present invention lies in the introduction of a gaseous hydrocarbon with carbon-carbon double bonds into the crosslinking reaction. This crosslinking prevents melt stranding during the subsequent inorganic sintering process. Furthermore, the dual effects of boron trichloride and the reactive gas with carbon-carbon double bonds reduce the oxygen content in the finished silicon carbide pre-sintered fiber, making densification and sintering easier and improving the finished fiber's strength.

[0010] As a preferred embodiment, the metal-doped polycarbosilane precursor fibers are obtained by melt-spinning metal-doped polycarbosilane at a temperature of 60-100°C above the melting point of the metal-doped polycarbosilane and a pressure of 0.3-0.8 MPa. The precursor fibers have a diameter of 12-20 μm. In the present invention, a precursor fiber with a diameter that is too small can affect the wear resistance and durability of the silicon carbide fiber, while a larger diameter can affect the strength and stiffness of the silicon carbide fiber.

[0011] As a preferred solution, the metal-doped polycarbosilane of the present invention needs to be heated under the protection of an inert gas, and the inert gas used can be at least one of nitrogen, argon and helium.

[0012] As a preferred solution, the metal is at least one of Ti, Zr, Hf, Al and Y. The metal doping of the present invention can suppress abnormal growth of grains and refine the grains.

[0013] As a preferred solution, the mass of the metal doping metal is 0.5-3%.

[0014] As a preferred solution, the process of the infusibility stage is as follows: the metal-doped polycarbosilane precursor fiber is placed in a sealed infusibility device, filled with nitrogen for protection, and first a gas containing boron trichloride is introduced to carry out the boron doping reaction, and then a gaseous hydrocarbon containing carbon-carbon double bonds is introduced to carry out the cross-linking reaction. In the present invention, since the added boron trichloride and the gaseous hydrocarbon with carbon-carbon double bonds have different reaction temperature ranges, they need to be introduced into the system step by step, and the temperature needs to be controlled in stages. The reaction temperature of boron trichloride and fiber is relatively low. By introducing boron trichloride at a lower temperature, the sintering aid boron element can be introduced into the fiber in advance, achieving the purpose of uniformly controlling grain growth and achieving microstructural densification. The gaseous hydrocarbon with carbon-carbon double bonds requires a temperature above 200°C to react with the fiber. The introduction of the gaseous hydrocarbon with carbon-carbon double bonds at high temperature allows the fiber to produce crosslinks, so that the fiber will not melt and sew during the subsequent inorganic sintering process. As a preferred solution, the gaseous hydrocarbon compound having a carbon-carbon double bond is at least one of cyclohexene, ethylene and acetylene.

[0015] As a preferred embodiment, the boron trichloride concentration in the boron trichloride-containing gas is 1-10% by volume, with the remainder of the gas serving as a carrier. The boron trichloride concentration in the present invention directly impacts the high-temperature performance and fiber strength of the produced silicon carbide. If the boron trichloride concentration is too high, excessive boron is introduced, affecting the high-temperature resistance of the final fiber. On the other hand, if the boron trichloride concentration is too low, insufficient boron is introduced, resulting in poor high-temperature sintering and lower fiber strength.

[0016] As a preferred solution, the carrier gas is at least one of nitrogen, argon and helium.

[0017] As a preferred embodiment, the boron doping reaction is carried out at a temperature of 150-180°C for 0.5-6 hours. The cross-linking reaction is carried out at a temperature of 400-500°C for 1-6 hours. The temperatures of the two heating and holding steps in the present invention are determined by the reaction temperature of the boron trichloride gas and the gaseous hydrocarbon compound having a carbon-carbon double bond.

[0018] As a preferred solution, the densification sintering stage comprises: heating to 1000-1400°C in a hydrogen atmosphere, holding for 0.5-5 hours for pre-sintering, and then heating to 1700-1850°C in an argon atmosphere and holding for 0.5-2 hours for densification. The present invention performs pre-sintering in a hydrogen atmosphere in the early stages of the densification sintering stage to remove excess carbon from the fiber, reduce defects caused by high-temperature thermal decomposition of the fiber, and reduce resistance to densification sintering. At the same time, it ensures that the fiber after sintering at temperatures above 1700°C is near stoichiometric, which is conducive to obtaining higher-strength third-generation SiC fibers.

[0019] As a preferred solution, the volume concentration of hydrogen in the hydrogen-containing atmosphere is 40-80%, and the remainder is nitrogen.

[0020] As a preferred solution, the temperature of the nitriding stage is greater than 1600°C and the duration is 0.5 to 2 hours. The nitriding stage converts the free boron in the fiber into a stable BN structure, forming a thin in-situ BN coating on the fiber surface, thereby improving the fiber's high-temperature creep resistance.

[0021] The present invention also provides a boron-containing, high-temperature resistant, near-stoichiometric silicon carbide fiber. The silicon carbide fiber has a low oxygen content, a high degree of densification, few defects, a stable structure, a high tensile strength modulus, a large grain size, and excellent high-temperature resistance, oxidation resistance, and creep resistance. The silicon carbide fiber prepared by the present invention has a C / Si atomic ratio close to 1.00, an oxygen content of less than 0.41 wt.%, a boron content of 1-3 wt.%, a nitrogen content of 1-3 wt.%, an average grain size greater than 35 nm, and a bulk density of 2.90-3.20 g / cm. 3 , the fiber tensile strength is greater than 2.5GPa, and the fiber tensile modulus is greater than 363GPa.

[0022] Compared with the prior art, the technical solution of the present invention brings the following beneficial technical effects:

[0023] 1) The preparation method provided by the present invention does not require the use of expensive electron beam irradiation equipment, is simple to operate, has high production efficiency, low production cost, and is easy to use for large-scale industrial production.

[0024] 2) The preparation method provided by the present invention achieves the purpose of uniformly controlling grain growth and realizing microstructure densification by introducing metal elements during precursor synthesis and boron elements as a sintering aid during non-melting, thereby avoiding the introduction of too many heterogeneous elements during precursor synthesis, resulting in a decrease in spinnability and poor quality of the resulting raw silk.

[0025] 3) The preparation method provided by the present invention realizes fiber crosslinking through BCl3 and active gas, and at the same time controls the oxygen content of Si-COMB fiber to an extremely low range through the synergistic effect of the added gaseous hydrocarbons with carbon-carbon double bonds. In addition, H2 is used to remove excess carbon in the fiber, thereby reducing the defects generated by the fiber during high-temperature thermal decomposition and the resistance to densification sintering. At the same time, it ensures that the fiber after sintering at above 1700°C is near the stoichiometric ratio, which is conducive to obtaining higher strength third-generation SiC fiber.

[0026] 4) The silicon carbide fiber provided by the present invention has low oxygen content, high degree of densification, few defects, stable structure, high tensile strength modulus, large grain size, and good high temperature resistance, oxidation resistance and creep resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is the SEM cross-sectional image of the silicon carbide fiber prepared in Example 1.

[0028] Figure 2 This is the SEM cross-sectional image of the silicon carbide fiber prepared in Comparative Example 1. DETAILED DESCRIPTION

[0029] The following examples are only specific descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of implementation of the present invention. For those skilled in the art, any improvements made without departing from the present invention should be considered to be within the scope of protection of the present invention.

[0030] Example 1

[0031] S1: Zr-doped polycarbosilane with a softening point of 208°C was heated to 285°C under a nitrogen atmosphere, with the pressure maintained at 0.4 MPa and a spinning speed of 560 m / min, for melt spinning to obtain a raw yarn with an average diameter of 15 μm.

[0032] S2: Place the raw silk into a sealed infusible device, evacuate and fill with nitrogen repeatedly for 3 times, introduce a mixture of 2% BCl3 and N2, heat it to 150℃ and keep it warm for 6 hours, evacuate and fill with nitrogen repeatedly for 3 times, introduce hexyne, heat it to 450℃ and keep it warm for 2 hours to obtain boron-containing low-oxygen infusible Zr-doped fiber.

[0033] S3: The infusible Zr-doped fiber is pre-sintered at 1200°C in a H2 / N2 mixture with a H2 concentration of 50% for 1 hour to obtain Si-CO-Zr-B fiber, and then the temperature is increased to 1800°C in an argon atmosphere and kept for 1 hour for densification sintering to obtain highly crystalline near-stoichiometric SiC fiber.

[0034] S4: The fiber obtained in S3 is placed in a nitrogen atmosphere, heated to 1750°C and kept warm for 1 hour to obtain a fiber with an in-situ grown BN coating on the surface.

[0035] The silicon carbide fiber prepared in this embodiment has a C / Si atomic ratio of 1.07, an oxygen content of 0.41 wt.%, a boron content of 1.52 wt.%, a nitrogen content of 1.83 wt.%, an average grain size of 35 nm, and a bulk density of 2.99 g / cm 3 , fiber tensile strength 2.6GPa, fiber tensile modulus 375GPa.

[0036] Example 2

[0037] S1: Ti-doped polycarbosilane with a softening point of 213°C was heated to 289°C in a nitrogen atmosphere, with the pressure maintained at 0.4 MPa and a spinning speed of 560 m / min, for melt spinning to obtain a raw yarn with an average diameter of 14 μm.

[0038] S2: Place the raw silk into a sealed infusible device, evacuate and fill with nitrogen repeatedly for 3 times, introduce a mixture of BCl3 and N2 with a concentration of 5%, heat it to 170℃ and keep it warm for 3 hours, evacuate and fill with nitrogen repeatedly for 3 times, introduce cyclohexene, heat it to 480℃ and keep it warm for 3 hours to obtain boron-containing low-oxygen infusible Ti-doped fiber.

[0039] S3: The infusible Ti-doped fiber is pre-sintered at 1000°C in a H2 / N2 mixture with a H2 concentration of 60% for 3 hours to obtain Si-CO-Ti-B fiber, and then the temperature is increased to 1700°C in an argon atmosphere and kept for 2 hours for densification sintering to obtain highly crystalline near-stoichiometric SiC fiber.

[0040] S4: The fiber obtained in S3 is placed in a nitrogen atmosphere, heated to 1650° C. and kept warm for 2 h to obtain a fiber with an in-situ grown BN coating on the surface.

[0041] The silicon carbide fiber prepared in this embodiment has a C / Si atomic ratio of 1.09, an oxygen content of 0.32 wt.%, a boron content of 2.35 wt.%, a nitrogen content of 2.07 wt.%, an average grain size of 39 nm, and a bulk density of 3.03 g / cm 3 , fiber tensile strength 3.1GPa, fiber tensile modulus 387GPa.

[0042] Example 3

[0043] S1: Hf-doped polycarbosilane with a softening point of 217°C was heated to 296°C in a nitrogen atmosphere, with the pressure maintained at 0.4 MPa and a spinning speed of 560 m / min, for melt spinning to obtain a raw yarn with an average diameter of 16 μm.

[0044] S2: Place the raw silk into a sealed infusible device, evacuate and fill with nitrogen repeatedly for 3 times, introduce a mixture of BCl3 and N2 with a concentration of 6%, heat it to 180℃ and keep it warm for 1 hour, evacuate and fill with nitrogen repeatedly for 3 times, introduce ethylene, heat it to 490℃ and keep it warm for 2 hours to obtain boron-containing low-oxygen infusible Hf-doped fiber.

[0045] S3: The infusible Hf-doped fiber is pre-sintered at 1300°C in a H2 / N2 mixture with a H2 concentration of 70% for 0.5 h to obtain Si-CO-Hf-B fiber, and then the temperature is increased to 1800°C in an argon atmosphere for 0.5 h for densification sintering to obtain highly crystalline near-stoichiometric SiC fiber.

[0046] S4: The fiber obtained in S3 is placed in a nitrogen atmosphere, heated to 1700° C. and kept warm for 2 h to obtain a fiber with an in-situ grown BN coating on the surface.

[0047] The silicon carbide fiber prepared in this embodiment has a C / Si atomic ratio of 1.05, an oxygen content of 0.23 wt.%, a boron content of 1.84 wt.%, a nitrogen content of 1.75 wt.%, an average grain size of 45 nm, and a bulk density of 3.05 g / cm 3 , fiber tensile strength 2.5GPa, fiber tensile modulus 363GPa.

[0048] Example 4

[0049] S1: Al-doped polycarbosilane with a softening point of 207°C was heated to 283°C in a nitrogen atmosphere, with the pressure maintained at 0.4 MPa and a spinning speed of 560 m / min, for melt spinning to obtain a raw fiber with an average diameter of 14 μm.

[0050] S2: Place the raw silk into a sealed infusible device, evacuate and fill with nitrogen three times repeatedly, introduce a mixture of BCl3 and N2 with a concentration of 8%, heat it to 170℃ and keep it warm for 3 hours, evacuate and fill with nitrogen three times repeatedly, introduce hexene, heat it to 450℃ and keep it warm for 5 hours to obtain boron-containing low-oxygen infusible Al-doped fiber.

[0051] S3: The infusible Al-doped fiber is pre-sintered at 1200°C in a H2 / N2 mixture with a H2 concentration of 65% for 1 hour to obtain Si-CO-Al-B fiber, and then the temperature is increased to 1750°C in an argon atmosphere and kept for 2 hours for densification sintering to obtain highly crystalline near-stoichiometric SiC fiber.

[0052] S4: The fiber obtained in S3 is placed in a nitrogen atmosphere, heated to 1750° C. and kept warm for 2 h to obtain a fiber with an in-situ grown BN coating on the surface.

[0053] The silicon carbide fiber prepared in this embodiment has a C / Si atomic ratio of 1.08, an oxygen content of 0.21 wt.%, a boron content of 2.89 wt.%, a nitrogen content of 2.47 wt.%, an average grain size of 48 nm, and a bulk density of 3.04 g / cm 3 , fiber tensile strength 2.8GPa, fiber tensile modulus 379GPa.

[0054] Example 5

[0055] S1: Ti-doped polycarbosilane with a softening point of 218°C was heated to 292°C under a nitrogen atmosphere, with the pressure maintained at 0.4 MPa and a spinning speed of 560 m / min, for melt spinning to obtain a raw yarn with an average diameter of 13 μm.

[0056] S2: Place the raw silk into a sealed infusible device, evacuate and fill with nitrogen repeatedly for 3 times, introduce a mixture of BCl3 and N2 with a volume concentration of 8%, heat it to 170℃ and keep it warm for 3 hours, evacuate and fill with nitrogen repeatedly for 3 times, introduce cyclohexene, heat it to 460℃ and keep it warm for 3 hours to obtain boron-containing low-oxygen infusible Ti-doped fiber.

[0057] S3: The infusible Ti-doped fiber is pre-sintered at 1000°C in a H2 / N2 mixture with a H2 concentration of 65% for 3 hours to obtain Si-CO-Ti-B fiber, and then the temperature is increased to 1800°C in an argon atmosphere and kept for 1.5 hours for densification sintering to obtain highly crystalline near-stoichiometric SiC fiber.

[0058] S4: The fiber obtained in S3 is placed in a nitrogen atmosphere, heated to 1800° C. and kept warm for 2 h to obtain a fiber with an in-situ grown BN coating on the surface.

[0059] The silicon carbide fiber prepared in this embodiment has a C / Si atomic ratio of 1.08, an oxygen content of 0.22 wt.%, a boron content of 2.52 wt.%, a nitrogen content of 2.67 wt.%, an average grain size of 43 nm, and a bulk density of 3.05 g / cm 3 , fiber tensile strength 3.3GPa, fiber tensile modulus 392GPa.

[0060] Comparative Example 1

[0061] The only difference between this comparative example and Example 5 is that the polycarbosilane used is not doped with metal, and the other conditions are the same.

[0062] The silicon carbide fiber prepared in this comparative example has a C / Si atomic ratio of 1.09, an oxygen content of 0.18 wt.%, a boron content of 1.32 wt.%, a nitrogen content of 1.27 wt.%, an average grain size of 50 nm, and a bulk density of 2.96 g / cm 3 , fiber tensile strength 1.5GPa, fiber tensile modulus 343GPa. After the final densification sintering, although the fiber still has a certain strength, but has greatly decreased, its microscopic morphology is as follows Figure 2 As shown, there are many hole defects in the fiber cross section.

[0063] Comparative Example 2

[0064] The only difference between this comparative example and Example 1 is that no carbon-carbon double bond active gas is added. The fibers melt and spun during the inorganic sintering, and normal fibers cannot be produced.

[0065] Comparative Example 3

[0066] The only difference between this comparative example and Example 1 is that the volume concentration of BCl3 is 15%, and the other conditions are the same.

[0067] The silicon carbide fiber prepared in this embodiment has a C / Si atomic ratio of 1.04, an oxygen content of 0.62 wt.%, a boron content of 3.7 wt.%, a nitrogen content of 3.9 wt.%, an average grain size of 30 nm, and a bulk density of 2.95 g / cm 3 , fiber tensile strength 1.9GPa, fiber tensile modulus 343GPa. In this comparative example, when the volume concentration of BCl3 is too high, due to the excessive introduction of boron elements, the high temperature resistance of the final fiber is reduced and the fiber strength is reduced.

Claims

1. A method for preparing high-temperature resistant, near-stoichiometric boron-containing silicon carbide fiber, comprising a spinning stage, an infusibility stage, a pre-sintering stage, a densification sintering stage, and a nitriding stage, characterized in that: The process of the infusibility stage is as follows: placing the metal-doped polycarbosilane precursor fiber into a sealed infusibility device, filling it with nitrogen for protection, first introducing a gas containing boron trichloride to carry out a boron doping reaction, and then introducing a gaseous hydrocarbon containing a carbon-carbon double bond to carry out a cross-linking reaction; The metal is at least one of Ti, Zr, Hf, Al and Y; The boron doping reaction conditions are: temperature of 150-180°C and time of 0.5-6h; The cross-linking reaction conditions are: temperature of 400-500°C and time of 1-6 hours; The volume concentration of boron trichloride in the boron trichloride-containing gas is 1-10%, and the remaining gas is carrier gas.

2. The method for preparing a high-temperature-resistant, near-stoichiometric boron-containing silicon carbide fiber according to claim 1, characterized in that: The metal-doped polycarbosilane precursor fiber is obtained by heating the metal-doped polycarbosilane to a temperature 60-100° C. above the melting point of the metal-doped polycarbosilane and performing melt spinning under a pressure of 0.3-0.8 MPa.

3. The method for preparing a high-temperature-resistant, near-stoichiometric boron-containing silicon carbide fiber according to claim 2, characterized in that: The gaseous hydrocarbon compound containing a carbon-carbon double bond is at least one of cyclohexene, ethylene and acetylene.

4. The method for preparing a high-temperature-resistant, near-stoichiometric boron-containing silicon carbide fiber according to claim 3, characterized in that: The carrier gas is at least one of nitrogen, argon and helium.

5. The method for preparing a high-temperature-resistant, near-stoichiometric boron-containing silicon carbide fiber according to claim 3 or 4, characterized in that: The densification sintering stage is as follows: heating to 1000-1400° C. in a hydrogen atmosphere, keeping the temperature for 0.5-5 hours for pre-sintering, and then heating to 1700-1850° C. in an argon atmosphere, keeping the temperature for 0.5-2 hours for densification.

6. The method for preparing high-temperature-resistant, near-stoichiometric boron-containing silicon carbide fiber according to claim 5, characterized in that: The volume concentration of hydrogen in the hydrogen-containing atmosphere is 40-80%, and the rest is carrier gas, which is nitrogen.

7. A boron-containing, high-temperature-resistant, near-stoichiometric silicon carbide fiber, characterized by: Prepared by the preparation method described in any one of items 1 to 6.

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