High-temperature-resistant silicon carbide fiber for aerospace and preparation method of high-temperature-resistant silicon carbide fiber

Abstract

The invention discloses a high-temperature-resistant silicon carbide fiber for aerospace, which comprises a three-layer gradient composite structure: a core layer inhibits beta-Si C grain growth through boron-carbon synergistic doping, a middle layer adopts an A < 2 > O < 3 > / Y < 2 > O < 3 > / graphene ternary composite system to construct a compact grain boundary network, and an outer layer is a 0.5 [mu] m BN coating to form a chemical bonding anti-oxidation barrier; according to the preparation method, uniform dispersion of nano-powder is realized through electrostatic self-assembly, and the strength retention rate of the fiber in an air environment of 1650 DEG C breaks through 80% in combination with a Y2O3 liquid phase filling pore technology in a stepped sintering process, and the strength of the fiber is still kept to be 75% or above after an instantaneous high temperature test at 1800 DEG C; through cooperative control of technological parameters, excellent high-temperature stability is achieved under the condition that the total addition amount is only 8-12 wt%, and the performance limit of the aerospace hot end component material is remarkably improved.

Description

Technical Field

[0001] This invention relates to the field of heat-resistant materials technology, and in particular to a high-temperature resistant silicon carbide fiber for aerospace applications and its preparation method. Background Technology

[0002] In the aerospace field, extremely high-temperature performance requirements for materials are present. Silicon carbide (SiC) fibers, due to their advantages such as low density and high strength, have broad application prospects in high-temperature structural components and engine hot-end parts. However, at temperatures above 1200℃, the β-SiC grains of traditional SiC fibers coarsen and microcracks are generated, leading to a sharp drop in strength. This severely affects their performance and reliability in high-temperature environments, limiting their application in even higher-temperature scenarios. To address this issue, existing technologies introduce sintering aids such as aluminum (Al) and boron (B) to improve high-temperature strength by inhibiting the growth of β-SiC grains.

[0003] However, single sintering aids have significant drawbacks: on the one hand, their distribution in SiC fibers is uneven, with excessively high concentrations in some areas potentially leading to abnormally large grains, while insufficient concentrations in others fail to effectively inhibit grain growth; on the other hand, the content is difficult to control precisely, with insufficient content resulting in limited inhibition, and excessive content introducing impurity phases, or even reacting with SiC to degrade fiber performance. Especially in scenarios requiring instantaneous high-temperature operation at 1800℃, such as hot-end components of aerospace hypersonic vehicles, existing SiC fibers containing single sintering aids cannot meet the requirements, becoming a key obstacle to their further promotion and application. Therefore, it is essential to develop high-temperature resistant silicon carbide fibers that meet these high-temperature requirements and their preparation methods. Summary of the Invention

[0004] The purpose of this invention is to overcome the above-mentioned technical deficiencies and propose a high-temperature resistant silicon carbide fiber for aerospace applications, thereby solving the problems mentioned in the background art.

[0005] To achieve the above-mentioned technical objectives, the present invention provides a high-temperature resistant silicon carbide fiber for aerospace applications, comprising a three-layer core-shell structure:

[0006] Core layer (70-75wt%): composed of β-SiC microcrystals with a particle size ≤50nm, doped with 0.5-1wt% boron (B) and 1-2wt% carbon (C);

[0007] Intermediate layer (20-25wt%): composed of amorphous SiC matrix and heat-resistant additives, wherein the heat-resistant additives include, by weight: 5-8 parts of Al2O3 nanopowder, 3-5 parts of Y2O3 nanopowder, and 2-4 parts of graphene.

[0008] Outer layer (5wt%): 0.5μm thick continuous BN coating.

[0009] Furthermore, a method for preparing high-temperature resistant silicon carbide fibers for aerospace applications includes the following steps:

[0010] S1. Precursor synthesis: Al2O3 / Y2O3 / graphene nanoparticles (particle size ≤100nm) were ultrasonically dispersed in xylene solvent and stirred with polycarbosilane (PCS) at 60℃ for 6h to form a composite precursor;

[0011] S2. Melt spinning: spinning at 280-320℃ with a draw ratio of 1.5-2.0 to obtain fiber precursors with a diameter of 10-15μm;

[0012] S3. Non-melting treatment: cross-linking is performed by electron beam irradiation at an energy of 2 MeV and a dose of 150-200 kGy;

[0013] S4. Step sintering: In an inert atmosphere, the temperature is successively maintained at 800-1000℃ for 1 hour, 1300℃ for 0.5 hours, and 1600℃ for 1 hour.

[0014] S5.BN coating deposition: A 0.5μm BN coating was formed by deposition at 850℃ for 30 min using CVD with a molar ratio of BCl3:NH3 = 1:3.

[0015] Furthermore, the graphene is a few-layer graphene grown by chemical vapor deposition, with ≤5 layers.

[0016] Furthermore, the particle size ratio of Al2O3 to Y2O3 nanoparticles in the intermediate layer is 1:1.2-1.5.

[0017] Furthermore, the heating rate of the stepped sintering is 5°C / min.

[0018] Furthermore, the tensile strength of the fiber is ≥2.8 GPa, and the strength retention rate in air at 1650°C is >80%.

[0019] Furthermore, the electron beam irradiation is carried out in an inert atmosphere chamber with an oxygen content of <10ppm.

[0020] Compared with the prior art, the beneficial effects of the present invention include:

[0021] 1. This invention utilizes a gradient composite structure, introducing a boron-carbon synergistic doping mechanism in the core layer to effectively suppress the abnormal growth of β-SiC grains under high-temperature conditions. The intermediate layer employs an Al2O3 / Y2O3 / graphene ternary composite system, leveraging the pinning effect of nanoparticles and the two-dimensional barrier effect of graphene to construct a dense grain boundary network. The outer 0.5μm BN coating not only forms an antioxidant barrier, but its chemical bonding structure with the intermediate layer significantly enhances the interfacial bonding strength. This design enables the fiber to retain over 80% of its strength in an air environment at 1650℃, nearly doubling that of traditional products, making it particularly suitable for components such as turbine blades of aero-engines that require long-term operation in oxidizing, high-temperature environments.

[0022] 2. This invention employs electrostatic self-assembly technology to uniformly disperse Al2O3 / Y2O3 nanoparticles in the precursor. Combined with a rapid heating phase of 10℃ / min in the stepped sintering process, this promotes the formation of a liquid-phase filling pore structure in Y2O3 at 1300℃. The combined application of electron beam irradiation crosslinking and HF etching pretreatment processes increases the bonding strength between the BN coating and the fiber matrix to 45N, a 50% improvement over conventional processes. This process route achieves excellent high-temperature stability by precisely controlling the sintering aid content (total addition only 8-12wt%), avoiding performance degradation caused by excessive addition, and significantly improving product yield and batch consistency. Attached Figure Description

[0023] Figure 1 This is a cross-sectional schematic diagram of a high-temperature resistant silicon carbide fiber for aerospace applications provided by the present invention;

[0024] Figure 2 This is a process flow diagram of the preparation process of high-temperature resistant silicon carbide fiber for aerospace applications provided by the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0026] Reference Figure 1 This invention provides a high-temperature resistant silicon carbide fiber for aerospace applications, comprising a three-layer core-shell structure:

[0027] The core layer 1 (70-75wt%) is composed of β-SiC microcrystals with a particle size ≤50nm, doped with 0.5-1wt% boron (B) and 1-2wt% carbon (C);

[0028] The intermediate layer 2 (20-25wt%) is composed of an amorphous SiC matrix and heat-resistant additives. The heat-resistant additives include, by weight, 5-8 parts of Al2O3 nanopowder, 3-5 parts of Y2O3 nanopowder, and 2-4 parts of graphene.

[0029] The outer layer 3 (5wt%) is a continuous BN coating with a thickness of 0.5μm.

[0030] Reference Figure 2 The preparation process of this silicon carbide fiber is as follows:

[0031] 1. Raw material pretreatment

[0032] (1) β-SiC microcrystals with an average particle size of 40nm (core layer substrate) are selected and surface hydroxylation treatment is performed to enhance the interfacial bonding with dopants.

[0033] (2) Few-layer graphene nanosheets with ≤5 layers were prepared by chemical vapor deposition and the surface residual catalyst was removed by plasma treatment.

[0034] (3) Prepare Al2O3 (10nm) / Y2O3 (12nm) composite powder (particle size ratio 1:1.2) and achieve uniform dispersion of nanoparticles through electrostatic self-assembly process.

[0035] 2. Precursor Synthesis

[0036] (1) 5 wt% Al2O3 / Y2O3 composite powder and 3 wt% graphene nanosheets were added to xylene solvent and treated with an ultrasonic cell disruptor (20 kHz, 30 min) to form a stable suspension.

[0037] (2) Add polycarbosilane (PCS, molecular weight 1500-2000) and stir at 300 rpm for 6 h in a constant temperature magnetic stirrer at 60℃ to obtain a composite precursor with a viscosity of 800-1200 mPa·s.

[0038] 3. Melt spinning

[0039] (1) A twin-screw extrusion spinning machine was used, with the spinning temperature set at 300℃ and the spinneret orifice diameter at 0.3mm.

[0040] (2) Control the draw ratio to 1.8 to obtain a continuous fiber filament with a diameter of 12μm, and monitor the temperature distribution of the spinning line in real time by using an infrared thermometer.

[0041] 4. Non-melting treatment

[0042] Vacuum degree ≤ 5 × 10 -3The irradiation crosslinking was carried out in the electron accelerator chamber of Pa, with an electron beam energy of 2MeV and a dose of 180kGy. High-purity argon gas (oxygen content ≤8ppm) was continuously introduced during the irradiation process, and the atmosphere in the chamber was monitored in real time by a residual gas analyzer.

[0043] 5. Stepped sintering

[0044] A three-stage heating program is used:

[0045] First stage: Hold at 800℃ for 1 hour (heating rate 3℃ / min, to remove organic matter and avoid micropore formation);

[0046] Second stage: Hold at 1300℃ for 0.5h (heating rate 10℃ / min, β-SiC crystal nuclei form);

[0047] Third stage: Hold at 1600℃ for 1 hour (heating rate 8℃ / min, Y2O3 liquid phase fills the pores, density reaches 2.83 g / cm³). 3 );

[0048] The temperature uniformity of the fiber axial direction is monitored by a thermocouple array, and the temperature difference is controlled to be ≤±10℃.

[0049] 6. BN coating deposition

[0050] A plasma-enhanced chemical vapor deposition (PECVD) system was used, with the reaction temperature set at 850℃. BCl3 (flow rate 30 sccm) and NH3 (flow rate 90 sccm) were introduced, the CVD reaction chamber pressure was 200 Pa, the BCl3:NH3 ratio was 1:3, and the carrier gas Ar flow rate was 100 sccm.

[0051] Performance verification:

[0052] 1. Microstructure characterization

[0053] (1) Observation by transmission electron microscopy showed that the core layer β-SiC grain size was controlled at 45±5nm, the intermediate layer formed a uniformly distributed nanocomposite structure, and the BN coating showed continuous columnar crystal growth characteristics.

[0054] (2) Energy dispersive spectroscopy analysis confirmed that boron was uniformly distributed in the core layer and carbon existed in the form of nano whiskers at the grain boundaries.

[0055] 2. High-temperature mechanical property testing

[0056] (1) Tensile strength test (ASTM C1359 standard): The average strength at room temperature is 3.1 GPa, and the strength retention rate is 82% after being kept in an air environment at 1650℃ for 1 hour.

[0057] (2) High-temperature creep test (1700℃, 50MPa): steady-state creep rate is less than 8×10 -7 s -1 It is significantly superior to traditional SiC fibers.

[0058] 3. Thermal shock resistance performance assessment

[0059] After 20 cycles of water quenching at 1800℃ to room temperature, the fiber strength retention rate still reached 78%, and no visible crack propagation was found during microscopic observation.

[0060] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A high temperature resistant silicon carbide fiber for aerospace applications, characterized by: The silicon carbide fiber comprises a three-layer core-shell structure: Core layer (70-75wt%): composed of β-SiC microcrystals with a particle size ≤50nm, doped with 0.5-1wt% boron (B) and 1-2wt% carbon (C); Intermediate layer (20-25wt%): composed of an amorphous SiC matrix and heat-resistant additives, the heat-resistant additives including, by weight parts: Al2O3 nano powder 5-8 parts, Y2O3 nano powder 3-5 parts, graphene 2-4 parts; Outer layer (5wt%): a continuous BN coating with a thickness of 0.5μm.

2. A method of producing high temperature resistant silicon carbide fibers for aerospace applications according to claim 1, characterized in that The method comprises the following steps: S1. Precursor synthesis: ultrasonic dispersion of Al2O3 / Y2O3 / graphene nano powder (particle size ≤100nm) in a xylene solvent, stirring with polycarbosilane (PCS) at 60℃ for 6h to form a composite precursor; S2. Melt spinning: spinning at 280-320℃ with a draw ratio of 1.5-2.0 to produce a fiber precursor with a diameter of 10-15μm; S3. Non-melting treatment: electron beam irradiation crosslinking, energy 2MeV, dose 150-200kGy; S4. Step sintering: in an inert atmosphere, sequentially at 800-1000℃ for 1h→1300℃ for 0.5h→1600℃ for 1h; S5. BN coating deposition: CVD method, BCl3:NH3=1:3 molar ratio, 850℃ for 30min to form a 0.5μm BN coating.

3. A method of producing high temperature resistant silicon carbide fibers for aerospace applications according to claim 2, wherein: The graphene is few-layer graphene grown by chemical vapor deposition, with a layer number ≤5.

4. The high temperature resistant silicon carbide fiber for aerospace of claim 1, wherein: The particle size ratio of Al2O3 to Y2O3 nano powder in the intermediate layer is 1:1.2-1.

5.

5. The method for preparing high-temperature resistant silicon carbide fiber for aerospace applications according to claim 2, characterized in that: The heating rate of the step sintering is 5℃ / min.

6. The high temperature resistant silicon carbide fiber for aerospace of claim 1, wherein: The tensile strength of the fiber is ≥2.8GPa, and the strength retention rate in air at 1650℃ is >80%.

7. The method of claim 2, wherein the method further comprises: The electron beam irradiation is carried out in an inert atmosphere chamber with an oxygen content <10ppm.

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