SiC nanowire in-situ modified ceramic matrix composite connecting fastener and preparation method thereof

Abstract

The application discloses a SiC nanowire in-situ modified ceramic matrix composite connecting fastener and a preparation method thereof, and belongs to the technical field of ceramic matrix composite materials. The preparation method comprises the following steps: firstly, performing heat treatment on a fiber preform; then, performing CVD or CVI deposition on the fiber preform by using boron trichloride and ammonia gas / ethylene as a precursor; then, performing catalyst solution impregnation and drying; finally, performing CVI deposition on the composite preform by using trichloromethylsilane as a precursor, so that the composite preform is prepared; firstly, performing CVD or CVI deposition on the composite preform by using silicon tetrachloride and ammonia gas as a precursor; then, performing precursor solution impregnation and drying; then, performing vacuum pyrolysis treatment; finally, performing CVI deposition on the composite preform by using silicon tetrachloride and ammonia gas as a precursor, processing threads, and the connecting fastener is prepared. The application realizes rapid densification while reinforcing and toughening by means of in-situ growth of SiC nanowires, and has the advantages of short preparation period, good mechanical properties of products, high connecting efficiency and the like.

Description

Technical Field

[0001] This invention relates to the field of ceramic matrix composites technology, specifically to a SiC nanowire in-situ modified ceramic matrix composite fastener and its preparation method. Background Technology

[0002] To meet the application needs of CMC-SiC materials in aerospace, aviation, aero-engine, and deep space exploration, CMC-SiC components are mostly large, complex, thin-walled components with irregular shapes. Traditional integral fiber weaving techniques for forming and processing these components suffer from problems such as poor mechanical properties in the bent areas of the woven fibers, the need for complete replacement of damaged components in small areas, poor maintainability, long manufacturing cycles, and high manufacturing costs. Therefore, employing a disassembly and assembly process to fabricate large, complex CMC-SiC thin-walled components is a preferred general technology for integrated manufacturing and an essential path to achieving serialization, standardization, and modularization of this material and its components.

[0003] Practice has shown that in the integrated manufacturing process of disassembly and assembly, the joints of ceramic matrix composite materials are the weakest links in the integrated assembly components. The strength, temperature resistance, and environmental adaptability of the fasteners at these joints all have a certain impact on the overall performance of the component. Currently, the main connecting materials for the integrated assembly manufacturing of CMC-SiC components fall into two categories: metallic materials represented by high-temperature alloys and inorganic non-metallic materials represented by CMC-SiC. Considering the problems of high-temperature alloy materials, such as their low temperature resistance (<1100℃), large mass, and mismatched coefficients of thermal expansion, CMC-SiC materials are gradually becoming the preferred material for connectors. Therefore, there is an urgent need for fasteners based on both materials (C / SiC, SiC / SiC) and both types (bolts, screws). Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a SiC nanowire in-situ modified ceramic matrix composite fastener and its preparation method, thereby solving the problems of existing high-temperature alloy materials having low temperature resistance (<1100℃), large mass, and mismatched thermal expansion coefficients.

[0005] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0006] A method for preparing SiC nanowire-modified ceramic matrix composite fasteners includes the following steps:

[0007] (1) First, heat-treat the fiber preform, then use boron trichloride and ammonia or boron trichloride and ethylene as precursors to perform CVD or CVI deposition to prepare an interface layer, then impregnate and dry it in a catalyst solution, and finally use trichloromethylsilane as a precursor to perform CVI deposition to obtain a composite material preform.

[0008] (2) First, CVD or CVI deposition is performed on the composite material preform obtained in step (1) using silicon tetrachloride and ammonia as precursors to prepare a pre-processed sample. Then, the sample is immersed in the precursor solution, dried, and then subjected to vacuum pyrolysis treatment. Finally, CVI deposition is performed again using silicon tetrachloride and ammonia as precursors, and then the threads are processed to obtain the preform.

[0009] The beneficial effects of this invention are as follows: The SiC nanowire in-situ modified ceramic matrix composite fastener prepared by this invention is composed of fibers, interfaces, SiC nanowires, and a matrix, establishing a global load-sharing mechanism. Simultaneously, the introduction of SiC nanowires can serve as a second reinforcing phase, working together with the fibers to enhance strength and toughness, effectively improving the connection efficiency of CMC-SiC fasteners.

[0010] Furthermore, the fiber preform is a C-fiber preform, including any one of two-dimensional fiber fabric laminates, three-dimensional needle-punched preforms, and fine-knitted puncture preforms.

[0011] Furthermore, before heat treatment of the fiber preform in step (1), the fiber preform is cleaned in acetone.

[0012] Furthermore, the heat treatment temperature in step (1) is 400-600℃ and the time is 2-4h.

[0013] Preferably, the heat treatment temperature in step (1) is 500°C and the time is 3 hours.

[0014] Further, the conditions for CVD or CVI deposition in step (1) using boron trichloride and ammonia or boron trichloride and ethylene as precursors are as follows: the dilution gas is argon, the catalyst gas is hydrogen, the flow rate of boron trichloride is 0.15-0.3 L / min, the flow rate of ammonia or ethylene is 0.25-0.5 L / min, the flow rate of argon is 0.6-2 L / min, the flow rate of hydrogen is 0.5-1 L / min, the furnace pressure is 2-5 kPa, the deposition temperature is 650-900℃, the deposition time is 10-50 h, and the interface layer thickness is 200-1500 nm.

[0015] Preferably, the conditions for CVD or CVI deposition in step (1) using boron trichloride and ammonia or boron trichloride and ethylene as precursors are as follows: the dilution gas is argon, the catalyst gas is hydrogen, the flow rate of boron trichloride is 0.225 L / min, the flow rate of ammonia or ethylene is 0.4 L / min, the flow rate of argon is 1.3 L / min, the flow rate of hydrogen is 0.75 L / min, the furnace pressure is 3.5 kPa, the deposition temperature is 750 °C, the deposition time is 30 h, and the interface layer thickness is 1000 nm.

[0016] Furthermore, the interface layer is either a PyC interface or a BN interface.

[0017] Further, in step (1), the catalyst includes any one of ferrocene, ferric phenylacetate, nickel ferrocene, nickel acetate, nickel nitrate and nickel chloride; the mass ratio of catalyst to water in the catalyst solution is (5-20):(80-95); the immersion time in the catalyst solution is 30-60 min; the drying temperature is 70-80℃ and the time is 3-5 h.

[0018] Preferably, the catalyst in step (1) includes any one of ferrocene, ferric phenylacetate, nickel ferrocene, nickel acetate, nickel nitrate and nickel chloride; the mass ratio of catalyst to water in the catalyst solution is 10:900; the immersion time in the catalyst solution is 45 min; the drying temperature is 75 °C and the drying time is 4 h.

[0019] Furthermore, the impregnation environment pressure is -0.1 MPa.

[0020] Furthermore, the conditions for CVI deposition in step (1) using trichloromethylsilane as a precursor are as follows: the dilution gas is argon, the catalyst gas is hydrogen, the argon flow rate is 2.5-10 L / min, the hydrogen carrier gas flow rate is 1.5-5 L / min, the hydrogen dilution gas flow rate is 2.5-5 L / min, the furnace pressure is 0.3-0.6 kPa, the deposition temperature is 700-1000℃, and the deposition time is 5-50 h.

[0021] Preferably, the conditions for CVI deposition in step (1) using trichloromethylsilane as a precursor are as follows: the dilution gas is argon, the catalyst gas is hydrogen, the argon flow rate is 6 L / min, the hydrogen carrier gas flow rate is 3 L / min, the hydrogen dilution gas flow rate is 4 L / min, the furnace pressure is 0.45 kPa, the deposition temperature is 850 °C, and the deposition time is 20 h.

[0022] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: This invention uses chemical vapor deposition and impregnation with a catalyst solution containing Fe or Ni to grow SiC nanowires, which can obtain SiC nanowire micro / nano modified carbon fiber / pyrolytic carbon (SiC) nw -C f PyC composite preforms can effectively improve the poor mechanical properties in weak areas of C / C composites.

[0023] Further, the conditions for CVD or CVI deposition in step (2) using silicon tetrachloride and ammonia as precursors are as follows: argon is used as the dilution gas, hydrogen is used as the catalyst gas, the flow rate of silicon tetrachloride is 100-500 mL / min, the flow rate of ammonia is 150-1000 mL / min, the flow rate of argon is 300-2500 mL / min, the flow rate of hydrogen is 750-2500 mL / min, the furnace pressure is 1-5 kPa, the deposition temperature is 700-1100℃, the deposition time is 8-200 h, and the deposition is carried out until the density of the composite material reaches 1.55-1.75 g / cm³. 3 .

[0024] Preferably, the conditions for CVD or CVI deposition in step (2) using silicon tetrachloride and ammonia as precursors are as follows: argon as the dilution gas, hydrogen as the catalyst gas, silicon tetrachloride flow rate of 300 mL / min, ammonia flow rate of 500 mL / min, argon flow rate of 1200 mL / min, hydrogen flow rate of 1200 mL / min, furnace pressure of 3 kPa, deposition temperature of 900 °C, deposition time of 50 h, and deposition until the composite material density reaches 1.65 g / cm³. 3 .

[0025] Further, in step (2), the mass ratio of precursor material, solvent and catalyst in the precursor solution is 35-50:50-65:3-7; the precursor material is at least one of polycarbosilane, polysilazane, polyzirconane and polyboronzirconane; the catalyst is at least one of ferrocene, ferric phenylacetate, nickel dicene, nickel acetate, nickel nitrate and nickel chloride; the impregnation time is 30-60 min, the drying temperature is 70-80℃ and the time is 3-5 h.

[0026] Preferably, in step (2), the mass ratio of precursor material, solvent and catalyst in the precursor solution is 40:60:5; the precursor material is at least one of polycarbosilane, polysilazane, polyzirconane and polyboronzirconane; the catalyst is at least one of ferrocene, ferric phenylacetate, nickel dicene, nickel acetate, nickel nitrate and nickel chloride; the impregnation time is 45 min, the drying temperature is 705 °C and the time is 4 h.

[0027] Furthermore, the solvent includes xylene, divinylbenzene, or cyclohexane.

[0028] Furthermore, the impregnation environment pressure is -0.1 MPa.

[0029] Further, the conditions for vacuum pyrolysis treatment in step (2) are as follows: the vacuum degree is 0.08-0.1MPa, the temperature is first raised to 1200-1500℃ at a heating rate of 3-10℃ / min, held for 1-3h, and then cooled to 500-700℃ at a cooling rate of 3-10℃ / min, and then cooled with the furnace.

[0030] Preferably, the conditions for vacuum pyrolysis treatment in step (2) are as follows: the vacuum degree is 0.09 MPa, the temperature is first raised to 1350°C at a heating rate of 5°C / min, held for 2 hours, and then cooled to 600°C at a cooling rate of 5°C / min, and then cooled with the furnace.

[0031] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: The present invention uses polymer conversion combined with high-temperature pyrolysis method to grow SiC nanowires in situ inside and on the surface of the sample. At the same time, some polymers inside the composite material are also converted into SiC matrix, which helps to rapidly densify while strengthening and toughening the threads.

[0032] Furthermore, in step (2), the conditions for CVI deposition using silicon tetrachloride and ammonia as precursors are as follows: the dilution gas is argon, the catalyst gas is hydrogen, the argon flow rate is 2.5-10 L / min, the hydrogen carrier gas flow rate is 1.5-5 L / min, the hydrogen dilution gas flow rate is 2.5-5 L / min, the furnace pressure is 1-5 kPa, the deposition temperature is 700-1100℃, and the deposition time is 8-200 h.

[0033] Preferably, the conditions for CVI deposition in step (2) using silicon tetrachloride and ammonia as precursors are as follows: the dilution gas is argon, the catalyst gas is hydrogen, the argon flow rate is 6 L / min, the hydrogen carrier gas flow rate is 3 L / min, the hydrogen dilution gas flow rate is 4 L / min, the furnace pressure is 3 kPa, the deposition temperature is 900 °C, and the deposition time is 50 h.

[0034] Furthermore, the final sample density obtained in step (2) is 2.05-2.35 g / cm³. 3 The porosity is 10-15%.

[0035] A SiC nanowire in-situ modified ceramic matrix composite fastener was prepared using the above-mentioned method.

[0036] The present invention has the following beneficial effects:

[0037] (1) In the ceramic matrix composite fastener prepared by the present invention, SiC nanowires are distributed non-directionally in the composite material, and pyrolytic carbon is deposited in a ring around it. SiC nanowires can serve as a second reinforcing phase to reinforce the C / C composite material together with the fiber. Some SiC nanowires grow outward in a radial manner perpendicular to the fiber, which can effectively improve the interfacial bonding between the carbon fiber and the PyC matrix. In addition, SiC nanowires are connected in series between the PyC layers, which can not only reduce the defects of the pyrolytic carbon layer, but also enhance the cohesion of the pyrolytic carbon.

[0038] (2) In this invention, SiC nanowires play a bridging role in defects, which can effectively alleviate crack propagation; SiC nanowires play a filling role, which can repair defects and enhance the load bearing capacity between defects; SiC nanowires are interspersed between pyrolytic carbon matrix, which can toughen and strengthen pyrolytic carbon; SiC nanowires will break and absorb fracture energy during the stress process, thereby improving the load bearing capacity of the material.

[0039] (3) The SiC nanowires grown in situ on the surface of the composite bolt thread obtained by the present invention can effectively bear the load. The energy released by the thread tooth loss and pull-out can be borne by the nanowires. The introduction of nanowires can also improve the density of the thread teeth and studs, which is beneficial to improving the tensile and shear resistance of the bolt. Attached Figure Description

[0040] Figure 1 This is a process flow diagram for the preparation of the SiC nanowire in-situ modified ceramic matrix composite fastener of the present invention;

[0041] Figure 2 SiC prepared in Example 1 of this invention nw -C f Microscopic morphology images of PyC composite preforms, pre-processed specimens with nanowires, and SiC nanowires in-situ modified ceramic matrix composite fasteners, wherein (a) shows the microstructure of SiC nanowires. nw -C f / PyC composite preform, (b) is a pre-processed sample with nanowires, (c) and (d) are SiC nanowire in-situ modified ceramic matrix composite connecting fasteners;

[0042] Figure 3 This is a fracture analysis diagram of the SiC nanowire in-situ modified ceramic matrix composite fastener prepared in Example 1 of the present invention. Detailed Implementation

[0043] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0044] Example 1:

[0045] A method for preparing SiC nanowire-modified ceramic matrix composite fasteners (process route diagram as shown) Figure 1 (As shown), including the following steps:

[0046] (1) Pretreatment of fiber preform

[0047] Two-dimensional carbon fiber fabric laminate was selected as the preform. The fiber preform was cleaned in acetone to remove surface contaminants. Then, the cleaned fiber preform was placed in a muffle furnace (air atmosphere) for heat treatment. The temperature was raised to 500℃, held for 3 hours, and then cooled with the furnace to remove the adhesive coating on the fiber surface.

[0048] (2) Interface layer preparation

[0049] A PyC interface was prepared in the fiber preform after pretreatment in step (1) using the CVI process to prepare a composite material with weak interfacial bonding. The fiber preform material was suspended on a sample holder in a vacuum furnace, with the fiber preform material located at the center of the isothermal zone inside the furnace. Boron trichloride, ethylene, dilution gas argon, and catalytic gas hydrogen were simultaneously introduced. The flow rates of boron trichloride, ethylene, argon, and hydrogen were 0.225 L / min, 0.4 L / min, 1.3 L / min, and 0.75 L / min, respectively. The furnace pressure was 3.5 kPa, the deposition temperature was 750 °C, and the deposition time was 30 h, resulting in a preform with an interfacial layer thickness of 1000 nm.

[0050] (3) Preparation of a preform containing a catalyst solution

[0051] First, 10% ferrocene and 90% deionized water by mass were mixed and stirred at 500 rpm for 45 min to obtain a catalyst solution. Then, the preform obtained after the CVI process in step (2) was immersed in the catalyst solution under a pressure of -0.1 MPa using a vacuum impregnation method. After 60 min, it was taken out and dried at 70°C for 4 h to obtain a preform containing the catalyst solution.

[0052] (4) Preparation of SiC nanowire modified carbon fiber / pyrolytic carbon (SiC nw -C f / PyC) Composite Preform

[0053] The preform containing the catalyst solution obtained in step (3) was deposited using the CVI process to generate SiC nanowires inside and on its surface. The deposition conditions were as follows: the precursor was trichloromethylsilane, the dilution gas was argon, the catalyst gas was hydrogen, the argon flow rate was 6 L / min, the hydrogen carrier gas flow rate was 3 L / min, the hydrogen dilution gas flow rate was 4 L / min, the furnace pressure was 0.45 kPa, the deposition temperature was 850 °C, and the deposition time was 20 h. SiC nanowires were then obtained. nw -C f / PyC composite preform.

[0054] (5) Preparation of matrix materials

[0055] The SiC obtained in step (4) using the CVI processnw -C f A dense Si3N4 matrix and coating were prepared on the interior and surface of the PyC composite preform. The precursors were silicon tetrachloride and ammonia, the dilution gas was argon, and the catalyst gas was hydrogen. The flow rates of silicon tetrachloride, ammonia, argon, and hydrogen were all 300 mL / min, 500 mL / min, 1200 mL / min, and 1200 mL / min, respectively. The furnace pressure was 3 kPa, the deposition temperature was 900 °C, and the deposition time was 50 h, until the composite density reached 1.65 g / cm³. 3 The matrix material was prepared, and the fasteners were cut into strips and ground into rounds according to the size standards to obtain pre-processed samples.

[0056] (6) Fabrication of nanowires

[0057] First, polycarbosilane and xylene are mixed at a mass ratio of 40%:50%, and then ferrocene with a total mass fraction of 5% of polycarbosilane and xylene is added and stirred evenly to obtain a precursor solution. Then, the pre-processed sample obtained in step (5) is immersed in the precursor solution under a vacuum environment of -0.1MPa for 60 min and then taken out and dried at 70℃ for 4 h. Finally, the dried pre-processed sample is placed in a vacuum tube furnace for pyrolysis to grow nanowires. The vacuum degree in the furnace is 0.09MPa. The pyrolysis conditions are: first, the temperature is raised to 1350℃ at a heating rate of 5℃ / min and held for 2 h, and then the temperature is lowered to 600℃ at a cooling rate of 5℃ / min and cooled with the furnace. Argon gas is introduced as a protective atmosphere during the pyrolysis process to obtain a pre-processed sample with nanowires.

[0058] (7) Preparation of SiC nanowire in-situ modified ceramic matrix composite fasteners

[0059] A SiC protective layer was deposited on the surface of the pre-processed sample with nanowires prepared in step (6) using the CVI process. The deposition conditions were as follows: the precursors were silicon tetrachloride and ammonia, the dilution gas was argon, the catalyst gas was hydrogen, the argon flow rate was 6 L / min, the hydrogen carrier gas flow rate was 3 L / min, the hydrogen dilution gas flow rate was 4 L / min, the furnace pressure was 3 kPa, the deposition temperature was 900℃, and the deposition time was 50 h, resulting in a density of 2.2 g / cm³. 3 Pre-processed samples of nanowire-reinforced ceramic matrix composites with an open porosity of 12% were obtained, and then screws, studs, nuts and pins were processed according to the thread specifications to obtain SiC nanowire-modified ceramic matrix composite fasteners.

[0060] Example 2:

[0061] A method for preparing SiC nanowire-modified ceramic matrix composite fasteners includes the following steps:

[0062] (1) Pretreatment of fiber preform

[0063] Three-dimensional needle-punched carbon fiber preforms were selected as the preforms. The fiber preforms were cleaned in acetone to remove surface contaminants. Then, the cleaned fiber preforms were placed in a muffle furnace (air atmosphere) for heat treatment. The temperature was raised to 500°C and held for 3 hours before being cooled with the furnace to remove the adhesive coating on the fiber surface.

[0064] (2) Interface layer preparation

[0065] A PyC interface was prepared in the fiber preform after pretreatment in step (1) using the CVI process to prepare a composite material with weak interfacial bonding. The fiber preform material was suspended on a sample holder in a vacuum furnace, with the fiber preform material positioned at the center of the isothermal zone inside the furnace. Boron trichloride, ethylene, dilution gas argon, and catalytic gas hydrogen were simultaneously introduced. The flow rates of boron trichloride, ethylene, argon, and hydrogen were 0.225 L / min, 0.4 L / min, 1.3 L / min, and 0.75 L / min, respectively. The furnace pressure was 3.5 kPa, the deposition temperature was 900 °C, and the deposition time was 25 h, resulting in a preform with an interfacial layer.

[0066] (3) Preparation of a preform containing a catalyst solution

[0067] First, 15% ferric phenylacetate and 85% deionized water were mixed and stirred at 500 rpm for 45 min to obtain a catalyst solution. Then, the preform obtained after the CVI process in step (2) was immersed in the catalyst solution under a pressure of -0.1 MPa using a vacuum impregnation method. After 60 min, it was taken out and dried at 70°C for 4 h to obtain a preform containing the catalyst solution.

[0068] (4) Preparation of SiC nanowire modified carbon fiber / pyrolytic carbon (SiC nw -C f / PyC) Composite Preform

[0069] The preform containing the catalyst solution obtained in step (3) was deposited using the CVI process to generate SiC nanowires inside and on its surface. The deposition conditions were as follows: the precursor was trichloromethylsilane, the dilution gas was argon, the catalyst gas was hydrogen, the argon flow rate was 6 L / min, the hydrogen carrier gas flow rate was 3 L / min, the hydrogen dilution gas flow rate was 4 L / min, the furnace pressure was 0.45 kPa, the deposition temperature was 800 °C, and the deposition time was 25 h. SiC nanowires were then obtained. nw -C f / PyC composite preform.

[0070] (5) Preparation of matrix materials

[0071] The SiC obtained in step (4) using the CVI process nw -C f A dense Si3N4 matrix and coating were prepared on the interior and surface of the PyC composite preform. The precursors were silicon tetrachloride and ammonia, the diluent gas was argon, and the catalyst gas was hydrogen. The flow rates of silicon tetrachloride, ammonia, argon, and hydrogen were all 300 mL / min, 500 mL / min, 1200 mL / min, and 1200 mL / min, respectively. The furnace pressure was 3 kPa, the deposition temperature was 1000 °C, and the deposition time was 50 h, until the composite density reached 1.65 g / cm³. 3 The matrix material was prepared, and the fasteners were cut into strips and ground into rounds according to the size standards to obtain pre-processed samples.

[0072] (6) Fabrication of nanowires

[0073] First, polycarbosilane and divinylbenzene were mixed at a mass ratio of 45%:55%, and then ferric phenylacetate with a total mass fraction of 5% of polycarbosilane and xylene was added and stirred evenly to obtain a precursor solution. Then, the pre-processed sample obtained in step (5) was immersed in the precursor solution under a vacuum environment of -0.1 MPa for 60 min and then taken out and dried at 70°C for 4 h. Finally, the dried pre-processed sample was placed in a vacuum tube furnace for pyrolysis to grow nanowires. The vacuum degree in the furnace was 0.09 MPa, and the pyrolysis conditions were as follows: first, the temperature was raised to 1500°C at a heating rate of 5°C / min and held for 2 h, and then the temperature was lowered to 600°C at a cooling rate of 5°C / min and cooled with the furnace. Argon gas was introduced as a protective atmosphere during the pyrolysis process to obtain a pre-processed sample with nanowires.

[0074] (7) Preparation of SiC nanowire in-situ modified ceramic matrix composite fasteners

[0075] A SiC protective layer was deposited on the surface of the pre-processed sample with nanowires obtained in step (6) using the CVI process. The deposition conditions were as follows: the precursors were silicon tetrachloride and ammonia, the dilution gas was argon, the catalyst gas was hydrogen, the argon flow rate was 6 L / min, the hydrogen carrier gas flow rate was 3 L / min, the hydrogen dilution gas flow rate was 4 L / min, the furnace pressure was 3 kPa, the deposition temperature was 800℃, and the deposition time was 50 h. The pre-processed sample of nanowire-reinforced ceramic matrix composite material was obtained. Then, the screw, stud, nut and pin were processed according to the thread specifications to obtain the SiC nanowire in-situ modified ceramic matrix composite material fastener.

[0076] Example 3:

[0077] A method for preparing SiC nanowire-modified ceramic matrix composite fasteners includes the following steps:

[0078] (1) Pretreatment of fiber preform

[0079] Select a finely woven carbon fiber puncture preform as the preform. The fiber preform is cleaned in acetone to remove surface contaminants. Then, the cleaned fiber preform is placed in a muffle furnace (air atmosphere) for heat treatment. The temperature is raised to 500℃, held for 3 hours, and then cooled with the furnace to remove the adhesive coating on the fiber surface.

[0080] (2) Interface layer preparation

[0081] A PyC interface was prepared in the fiber preform after pretreatment in step (1) using the CVI process to prepare a composite material with weak interfacial bonding. The fiber preform material was suspended on a sample holder in a vacuum furnace, with the fiber preform material positioned at the center of the isothermal zone inside the furnace. Boron trichloride, ethylene, dilution gas argon, and catalytic gas hydrogen were simultaneously introduced. The flow rates of boron trichloride, ethylene, argon, and hydrogen were 0.225 L / min, 0.4 L / min, 1.3 L / min, and 0.75 L / min, respectively. The furnace pressure was 3.5 kPa, the deposition temperature was 700 °C, and the deposition time was 35 h, resulting in a preform with an interfacial layer.

[0082] (3) Preparation of a preform containing a catalyst solution

[0083] First, 5% nickel acetate and 95% deionized water were mixed and stirred at 500 rpm for 45 min to obtain a catalyst solution. Then, the preform obtained after the CVI process in step (2) was immersed in the catalyst solution under a pressure of -0.1 MPa using a vacuum impregnation method. After 60 min, it was taken out and dried at 70°C for 4 h to obtain a preform containing the catalyst solution.

[0084] (4) Preparation of SiC nanowire modified carbon fiber / pyrolytic carbon (SiC nw -C f / PyC) Composite Preform

[0085] The preform containing the catalyst solution obtained in step (3) was deposited using the CVI process to generate SiC nanowires inside and on its surface. The deposition conditions were as follows: the precursor was trichloromethylsilane, the dilution gas was argon, the catalyst gas was hydrogen, the argon flow rate was 6 L / min, the hydrogen carrier gas flow rate was 3 L / min, the hydrogen dilution gas flow rate was 4 L / min, the furnace pressure was 0.45 kPa, the deposition temperature was 900 °C, and the deposition time was 20 h. SiC nanowires were then obtained. nw -C f / PyC composite preform.

[0086] (5) Preparation of matrix materials

[0087] The SiC obtained in step (4) using the CVI process nw -C f A dense Si3N4 matrix and coating were prepared on the interior and surface of the PyC composite preform. The precursors were silicon tetrachloride and ammonia, the dilution gas was argon, and the catalyst gas was hydrogen. The flow rates of silicon tetrachloride, ammonia, argon, and hydrogen were all 300 mL / min, 500 mL / min, 1200 mL / min, and 1200 mL / min, respectively. The furnace pressure was 3 kPa, the deposition temperature was 800 °C, and the deposition time was 50 h, until the composite density reached 1.65 g / cm³. 3 The matrix material was prepared, and the fasteners were cut into strips and ground into rounds according to the size standards to obtain pre-processed samples.

[0088] (6) Fabrication of nanowires

[0089] First, polyzirconium carbide and cyclohexane were mixed at a mass ratio of 35%:65%, and then nickel acetate with a total mass fraction of 5% of polycarbosilane and xylene was added and stirred evenly to obtain a precursor solution. Then, the pre-processed sample obtained in step (5) was immersed in the precursor solution under a vacuum environment of -0.1 MPa for 60 min and then taken out and dried at 70°C for 4 h. Finally, the dried pre-processed sample was placed in a vacuum tube furnace for pyrolysis to grow nanowires. The vacuum degree in the furnace was 0.09 MPa, and the pyrolysis conditions were as follows: first, the temperature was raised to 1200°C at a heating rate of 5°C / min and held for 2 h, and then the temperature was lowered to 600°C at a cooling rate of 5°C / min and cooled with the furnace. Argon gas was introduced as a protective atmosphere during the pyrolysis process to obtain a pre-processed sample with nanowires.

[0090] (7) Preparation of SiC nanowire in-situ modified ceramic matrix composite fasteners

[0091] A SiC protective layer was deposited on the surface of the pre-processed sample with nanowires prepared in step (6) using the CVI process. The deposition conditions were as follows: the precursors were silicon tetrachloride and ammonia, the dilution gas was argon, the catalyst gas was hydrogen, the argon flow rate was 6 L / min, the hydrogen carrier gas flow rate was 3 L / min, the hydrogen dilution gas flow rate was 4 L / min, the furnace pressure was 3 kPa, the deposition temperature was 1000℃, and the deposition time was 50 h. The pre-processed sample of nanowire-reinforced ceramic matrix composite material was obtained. Then, the screw, stud, nut and pin were processed according to the thread specifications to obtain the SiC nanowire in-situ modified ceramic matrix composite material fastener.

[0092] Experimental example:

[0093] (1) The SiC obtained in step (4) of Example 1 nw -C f The microstructure of the PyC composite preform, the pre-processed sample with nanowires obtained in step (6), and the SiC nanowires in the in-situ modified ceramic matrix composite fastener obtained in step (7) were observed by scanning electron microscopy. The experimental results are as follows: Figure 2 As shown.

[0094] Figure 2 Figure (a) shows the SiC nanowires grown on the surface and inside of the carbon fiber / pyrolytic carbon composite preform after a pyrolytic carbon interface layer is prepared on the carbon fiber preform and impregnated with a catalyst using the CVI method. As shown in the figure, SiC nanowires growing radially and perpendicularly to the fiber outwards along the outer diameter of the carbon fiber can be observed. The nanowires are coiled, which can effectively improve the cross-sectional bonding between the carbon fiber and the PyC matrix. In addition, the SiC nanowires are connected in series between the PyC layers, which can not only reduce the defects between the pyrolytic carbon layers, but also increase the cohesive force of the pyrolytic carbon.

[0095] Figure 2 Figure (b) shows the morphology of SiC nanowires grown inside a semi-densified composite material through polymer conversion combined with high-temperature pyrolysis. It can be observed that the SiC nanowire layer is wrapped between the fiber bundles that have been deposited in the SiC matrix. The SiC nanowires play a role in filling gaps, repairing defects, enhancing the load-bearing capacity between defects, and having a toughening effect.

[0096] Figure 2 Figure (c) shows SiC nanowires observed at the tip and bottom of the thread after machining. This indicates that SiC nanowires have good growth effect and strong permeability, which can strengthen and toughen the bolt thread. The energy released by thread tooth loss and pull-out can be borne by the nanowires. The introduction of nanowires can also improve the density of the thread and bolt, which is beneficial to improving the tensile and shear properties of the bolt.

[0097] Figure 2 Figure (d) shows the magnified morphology of the SiC nanowires at the threaded teeth, which shows that the nanowires are linear in shape and have a bent shape, further indicating their good strength and toughness.

[0098] (2) The fracture structure of the SiC nanowire in-situ modified ceramic matrix composite fastener prepared in Example 1 was characterized, and the experimental results are as follows: Figure 3 As shown.

[0099] according to Figure 3 As shown in Figures (a)-(c), the prepared SiC nanowires effectively filled the inter-beam pores of the sample. Figure 3As shown in Figure (d), the growth of SiC nanowires on the sample surface did not affect the effective penetration of the SiC matrix in the later stage, nor did it cause a crust to form on the sample surface. Figure 3 This demonstrates that the nanowire preparation process of the present invention can effectively improve the performance of fasteners. The SiC nanowires grown in situ on the surface of bolt threads can effectively bear the load, and the energy released by thread chipping and pull-out can be borne by the nanowires. The introduction of nanowires can also improve the density of the thread teeth and studs, which is beneficial to improving the tensile and shear properties of bolts. At the same time, the preparation of nanowires by polymer conversion combined with high-temperature pyrolysis can also generate some SiC matrix, which helps to improve the densification of the sample (SiC nanowires and SiC matrix jointly reinforce each other), effectively reducing the number of densification deposition furnaces and saving costs.

[0100] (3) The room temperature tensile strength and shear strength of the M6 ​​and M8 bolts processed from the SiC nanowire in-situ modified ceramic matrix composite material prepared in Example 1 were characterized. The experimental results are shown in Table 1.

[0101] Table 1. Room temperature tensile strength and shear strength of M6 and M8 bolts obtained in Example 1 of the present invention.

[0102]

[0103] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for producing a SiC nanowire in-situ modified ceramic matrix composite connecting fastener, characterized by, The method comprises the following steps: (1) heat treating the fiber preform, then depositing an interface layer by CVD or CVI using boron trichloride and ammonia or boron trichloride and ethylene as precursors, then dipping in a catalyst solution, drying, and finally depositing by CVI using trichloromethylsilane as a precursor to obtain a composite preform; (2) depositing by CVD or CVI using silicon tetrachloride and ammonia as precursors on the composite preform obtained in step (1) to obtain a pre-processed sample, then dipping in a precursor solution, drying, and then performing vacuum pyrolysis, and finally depositing by CVI using silicon tetrachloride and ammonia as precursors, and then processing threads to obtain a product; The catalyst in step (1) comprises any one of ferrocene, iron phenylacetate, nickelocene, nickel acetate, nickel nitrate and nickel chloride; In step (2), the mass ratio of the precursor material, the solvent and the catalyst in the precursor solution is 35-50:50-65:3-7; the precursor material is at least one of polycarbosilane, polysilazane, polyzirconocarbosilane and polyborozirconocarbosilane; the catalyst is at least one of ferrocene, iron phenylacetate, nickelocene, nickel acetate, nickel nitrate and nickel chloride; the dipping time is 30-60 min, the drying temperature is 70-80℃, and the drying time is 3-5 h.

2. The method for preparing SiC nanowire in-situ modified ceramic matrix composite fasteners according to claim 1, characterized in that, In step (1), the heat treatment temperature is 400-600℃, and the heat treatment time is 2-4 h.

3. The method for preparing the SiC nanowire in-situ modified ceramic matrix composite fastener according to claim 1, characterized in that, In step (1), the CVD or CVI deposition conditions using boron trichloride and ammonia or boron trichloride and ethylene as precursors are as follows: the dilution gas is argon, the catalyst gas is hydrogen, the boron trichloride flow rate is 0.15-0.3 L / min, the ammonia or ethylene flow rate is 0.25-0.5 L / min, the argon flow rate is 0.6-2 L / min, the hydrogen flow rate is 0.5-1 L / min, the furnace pressure is 2-5 kPa, the deposition temperature is 650-900℃, the deposition time is 10-50 h, and the interface layer thickness is 200-1500 nm.

4. The method for preparing SiC nanowire in-situ modified ceramic matrix composite fasteners according to claim 1, characterized in that, In step (1), the mass ratio of the catalyst and water in the catalyst solution is (5-20):(80-95); the dipping time in the catalyst solution is 30-60 min; the drying temperature is 70-80℃, and the drying time is 3-5 h.

5. The method for preparing the SiC nanowire in-situ modified ceramic matrix composite fastener according to claim 1, characterized in that, In step (1), the CVI deposition conditions using trichloromethylsilane as a precursor are as follows: the dilution gas is argon, the catalyst gas is hydrogen, the argon flow rate is 2.5-10 L / min, the hydrogen carrier gas flow rate is 1.5-5 L / min, the hydrogen dilution gas flow rate is 2.5-5 L / min, the furnace pressure is 0.3-0.6 kPa, the deposition temperature is 700-1000℃, and the deposition time is 5-50 h.

6. The method of claim 1, wherein the SiC nanowire in-situ modified ceramic matrix composite fastener is prepared by the steps of: providing a SiC nanowire in-situ modified ceramic matrix composite fastener; and coating the SiC nanowire in-situ modified ceramic matrix composite fastener with a coating layer. The conditions for the step (2) of CVD or CVI deposition using silicon tetrachloride and ammonia as precursors are as follows: argon as dilution gas, hydrogen as catalytic gas, silicon tetrachloride flow rate of 100-500 mL / min, ammonia flow rate of 150-1000 mL / min, argon flow rate of 300-2500 mL / min, hydrogen flow rate of 750-2500 mL / min, furnace pressure of 1-5 kPa, deposition temperature of 700-1100℃, deposition time of 8-200 h, and deposition to a composite density of 1.55-1.75 g / cm 3 .

7. The method of claim 1, wherein the SiC nanowire in-situ modified ceramic matrix composite fastener is prepared by the steps of: providing a SiC nanowire in-situ modified ceramic matrix composite fastener; and coating the SiC nanowire in-situ modified ceramic matrix composite fastener with a coating layer. In step (2), the vacuum pyrolysis conditions are as follows: the vacuum degree is 0.08-0.1 MPa, first heating at a heating rate of 3-10℃ / min to 1200-1500℃, holding for 1-3 h, then cooling at a cooling rate of 3-10℃ / min to 500-700℃, and then cooling with the furnace.

8. The method of claim 1, wherein the SiC nanowire in-situ modified ceramic matrix composite fastener is prepared by the steps of: providing a SiC nanowire in-situ modified ceramic matrix composite fastener; and coating the SiC nanowire in-situ modified ceramic matrix composite fastener with a coating layer. The conditions for the step (2) of CVI deposition using silicon tetrachloride and ammonia as precursors are as follows: argon as dilution gas, hydrogen as catalytic gas, argon flow rate of 2.5-10 L / min, hydrogen carrier gas flow rate of 1.5-5 L / min, hydrogen dilution gas flow rate of 2.5-5 L / min, furnace pressure of 1-5 kPa, deposition temperature of 700-1100℃, and deposition time of 8-200 h.

9. A SiC nanowire in-situ modified ceramic matrix composite joining fastener, characterized by, The preparation method of any one of claims 1-8 is used.

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