阅读说明：本技术 一种陶瓷基复合材料螺柱及其制备方法 (Ceramic matrix composite material stud and preparation method thereof ) 是由 张东生 吴恒 曹伟 魏庆勃 姚栋嘉 刘喜宗 潘广镇 于 2021-01-27 设计创作，主要内容包括：本发明属于紧固件的制备技术领域,具体公开一种陶瓷基复合材料螺柱及其制备方法。(1)、根据螺柱的设计尺寸加工纤维预制体；(2)、在纤维预制体表面制备界面层,所述界面层为复合界面层或梯度界面层；(3)、浸渍-固化-低温裂解步骤重复3～6次；(4)、浸渍-固化-高温裂解重复1～3次；(5)、机械精加工；(6)、加工螺纹：(7)、重复上述浸渍-固化-高温裂解步骤1～2次；(8)、精修螺纹；(9)、CVI-SiC致密化,即得陶瓷基复合材料螺柱。本发明方法制备周期短,所制备的螺柱芯部强度较高,力学性能优异。(The invention belongs to the technical field of fastener preparation, and particularly discloses a ceramic matrix composite stud and a preparation method thereof. (1) Processing the fiber preform according to the design size of the stud; (2) preparing an interface layer on the surface of the fiber preform, wherein the interface layer is a composite interface layer or a gradient interface layer; (3) repeating the steps of dipping, curing and low-temperature cracking for 3-6 times; (4) repeating the dipping, curing and pyrolysis for 1-3 times; (5) performing mechanical finish machining; (6) and processing threads: (7) repeating the steps of dipping, curing and pyrolysis for 1-2 times; (8) finishing the threads; (9) and performing CVI-SiC densification to obtain the ceramic matrix composite stud. The method has the advantages of short preparation period, high strength of the prepared stud core part and excellent mechanical property.)

1. A ceramic matrix composite stud is characterized in that: the fiber reinforced composite material consists of a fiber preform, an interface layer and a ceramic matrix, wherein the density of the fiber preform is gradually reduced from inside to outside; the interface layer is a composite interface layer or a gradient interface layer; the composite interface layer is any two or three of a pyrolytic carbon interface layer, a boron nitride interface layer and a silicon carbide interface layer; the gradient interface layer is an interface layer with a silicon-carbon ratio in gradient distribution, and the silicon-carbon ratio is gradually increased from inside to outside; the ceramic matrix is a silicon carbide matrix containing nano-fibers.

2. The ceramic matrix composite stud according to claim 1, wherein: the nano-fiber is nano-carbon fiber, carbon nano-tube, graphene, nano-SiC fiber, nano-Si₃N₄Any one or more of fiber, nanometer ZrC fiber, nanometer TiC fiber and nanometer TiN fiber.

3. A method for preparing a ceramic matrix composite stud according to claim 1 or 2, characterized in that the steps are as follows:

(1) preparing a fiber preform: preparing the fiber into a fiber preform which has the same shape as the final stud product, has the size with allowance and has density gradient; the density gradient means that the density of the fiber preform is gradually reduced from inside to outside;

(2) preparing an interface layer: preparing an interface layer for the fiber preform obtained in the step (1), wherein the interface layer is a composite interface layer or a gradient interface layer; the composite interface layer is any two or three of a pyrolytic carbon interface layer, a boron nitride interface layer and a silicon carbide interface layer; the gradient interface layer is an interface layer with a silicon-carbon ratio in gradient distribution, and the silicon-carbon ratio is gradually increased from inside to outside;

(3) dipping, curing and low-temperature cracking: repeating the processes of dipping, curing and low-temperature cracking for 3-6 times; the low-temperature cracking process comprises the following steps: putting the product obtained by curing into a sintering furnace, heating to a low-temperature cracking temperature of 850-1300 ℃ at a heating rate of 5-10 ℃/min under a vacuum state or a micro-positive pressure state in the furnace, preserving heat for 2-10 h, naturally cooling to room temperature under a protective gas atmosphere, and taking out; the vacuum degree in the vacuum state is below 200 Pa; the micro-positive pressure state is that protective gas is introduced, the pressure in the furnace is adjusted to be 100-200 kPa, and the gas flow is 4-10L/min;

(4) dipping, curing and pyrolysis: repeating the processes of dipping, curing and pyrolysis for 1-3 times; the high-temperature cracking process is the same as the low-temperature cracking process in the step (3), except that the temperature of the high-temperature cracking process is 1300-1500 ℃;

(5) and (3) mechanical finish machining: processing the product obtained in the step (4) into the design size of a stud;

(6) and processing threads: machining threads on the product obtained in the step (5);

(7) dipping, curing and pyrolysis: repeating the dipping-curing-pyrolysis process in the step (4) for 1-2 times on the product obtained in the step (6);

(8) finishing the threads: polishing the product obtained in the step (7) to the final size precision;

(9) CVI-SiC densification: and (5) performing chemical vapor infiltration SiC on the product obtained in the step (8) for further densification to obtain the ceramic matrix composite stud.

4. The method of making a ceramic matrix composite stud according to claim 3, wherein: in the step (1), the fiber is carbon fiber or silicon carbide fiber; the fiber preform is prepared by molding fibers in a 2.5D needling or 2.5D puncturing mode, and the needling density of the fiber preform is 20-40 needles/cm²The puncture density of the fiber preform is 15-30 needles/cm²。

5. The method of making a ceramic matrix composite stud according to claim 3, wherein: in the step (2), the pyrolytic carbon interface layer, the boron nitride interface layer, the silicon carbide interface layer and the gradient interface layer are respectively prepared according to the following methods:

the pyrolytic carbon interface layer is prepared by isothermal CVI: the deposition temperature is 800-1300 ℃, carbon source gas is introduced at the flow rate of 5-15L/min, the pressure in the furnace is adjusted to be 0.5-20 kPa, and the temperature is kept for 1-60 h; the carbon source gas is selected from any one or more of methane, propane and propylene;

the boron nitride interface layer is formed by nitrogen source precursorThe body and the boron source precursor are prepared by adopting an isothermal CVI technology under the hydrogen atmosphere: the deposition temperature is 600-1100 ℃, the pressure in the furnace is 10-25 kPa, the total flow of the nitrogen source and the boron source precursor gas is 200-1000 sccm, the flow ratio of the nitrogen source to the boron source is 10-20: 1, the flow ratio of the hydrogen gas to the nitrogen source is 50-100: 1, and the temperature is kept for 1-30 h; the nitrogen source precursor is NH₃、B₃N₃H₆Or Cl₃B₃N₃H₃The boron source precursor is BH₃、BCl₃、BF₃、B₂H₆、B₄H₁₀、B₃N₃H₆Or Cl₃B₃N₃H₃One of (1);

the silicon carbide interface layer is prepared by adopting an isothermal CVI technology: introducing a silicon source, the carrier gas, the diluent gas and the reducing gas into a vacuum degree of less than 200Pa by taking hydrogen as the carrier gas, argon as the diluent gas and hydrogen as the reducing gas, regulating the pressure in the furnace to be 5-20 kPa, controlling the deposition temperature to be 1000-1500 ℃ and keeping the temperature for 1-25 h; wherein the molar ratio of the reducing gas to the silicon source is 8-20: 1, the flow rate of the silicon source is 1-15 g/min, the flow rate of the diluting gas is 2-20L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, and the flow rate of the carrier gas is 100-200 mL/min; the silicon source is methyl trichlorosilane;

the gradient interface layer is prepared by adopting an isothermal CVI technology, and the specific process is as follows:

method (i): using hydrogen as a carrier gas, argon as a diluent gas, using hydrogen as a reducing gas, introducing a silicon source, the carrier gas, the diluent gas and the reducing gas under the vacuum degree of below 200Pa, adjusting the pressure in the furnace to be 0.5-20 kPa, raising the deposition temperature to 1150-1500 ℃, preserving the temperature for 1-5 h, then cooling at the speed of 1-2 ℃/min, preserving the temperature for 1-5 h every 100 ℃, and cooling to 850-1150 ℃; wherein the molar ratio of the reducing gas to the silicon source is 5-20: 1, the flow rate of the silicon source is 1-20 g/min, the flow rate of the diluting gas is 2-20L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, and the flow rate of the carrier gas is 100-200 mL/min; the silicon source is methyl trichlorosilane;

method (ii): introducing a silicon source, the carrier gas, the diluent gas and the reducing gas into a vacuum degree of less than 200Pa by taking hydrogen as the carrier gas, argon as the diluent gas and hydrogen as the reducing gas, regulating the pressure in the furnace to be 0.5-20 kPa, controlling the deposition temperature to be 800-1500 ℃ and keeping the temperature for 1-50 h; wherein the molar ratio of the reducing gas to the silicon source is gradually increased to 20-25: 1 from 5-10: 1, the flow rate of the silicon source is 1-20 g/min, the flow rate of the diluting gas is 2-20L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, and the flow rate of the carrier gas is 100-200 mL/min; the silicon source is methyl trichlorosilane.

6. The method of making a ceramic matrix composite stud according to claim 3, wherein: in the step (3) and the step (4), the impregnation is vacuum impregnation; the vacuum impregnation process comprises the following steps: putting the product into a vacuum impregnation barrel, vacuumizing until the vacuum degree is below 100Pa, keeping the vacuum for 0.5-1 h, injecting ceramic precursor slurry, keeping the vacuum for 1-5 h, and breaking the vacuum and taking out.

7. The method of making a ceramic matrix composite stud according to claim 6, wherein: the ceramic precursor slurry is prepared by mixing a ceramic precursor, a solvent and nano fibers according to the mass ratio of 10: 3-8: 0.5-2; the ceramic precursor is polysilane containing one or more of carbon, nitrogen, boron and oxygen; the solvent is divinylbenzene, xylene, toluene, dimethyl sulfoxide, n-hexane, cyclohexane, tetrahydrofuran, chloroform or chlorobenzene; the nano-fiber is nano-carbon fiber, carbon nano-tube, graphene, nano-SiC fiber, nano-Si₃N₄Any one or more of fiber, nanometer ZrC fiber, nanometer TiC fiber and nanometer TiN fiber.

8. The method of making a ceramic matrix composite stud according to claim 7, wherein: the ceramic precursor is polysilane, polycarbosilane, polysilazane, polysiloxane, polyborosilazane or polycarbosilazane.

9. The method of making a ceramic matrix composite stud according to claim 6, wherein: in the step (3) and the step (4), vacuum impregnation is carried out, and then pressure impregnation is carried out, wherein the pressure impregnation process comprises the following steps: and (3) putting the product subjected to vacuum impregnation into a pressure impregnation tank, heating to 50-70 ℃, introducing protective gas until the pressure in the pressure impregnation tank is 1-6 MPa, preserving the heat for 1-5 h, naturally cooling to room temperature, and taking out.

10. The method for preparing a ceramic matrix composite stud according to claim 3, wherein in step (9), the CVI-SiC densification process is: the method comprises the following steps of (1) further densifying a product through CVI by taking methyltrichlorosilane as a precursor, hydrogen as a carrier gas, argon as a diluent gas and hydrogen as a reducing gas; wherein, the parameter conditions of CVI are as follows: the deposition temperature is 800-1200 ℃, the deposition pressure is 1-20 kPa, and the deposition time is 5-200 h; the molar ratio of the reducing gas to the precursor is 8-20: 1, the flow rate of the precursor is 1-15 g/min, the flow rate of the diluting gas is 2-20L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the precursor, and the flow rate of the carrier gas is 100-200 mL/min.

Technical Field

The invention belongs to the technical field of fastener preparation, and particularly relates to a ceramic matrix composite stud and a preparation method thereof.

Background

The ceramic matrix composite connecting piece is used for connecting aerospace structural members, can be used for a long time at about 1650 ℃, and has the short-time use temperature as high as 2000 ℃. With the development of science and technology, the environment applied to aerospace is more complex and harsh, and has higher requirements on the strength, variety and structure of the connecting piece.

At present, the ceramic matrix composite connecting piece has the defects of insufficient core strength and less connecting piece types, most of the existing preparation technologies can only prepare small-size connecting pieces, and the preparation of connecting pieces with larger diameters or complicated structures is difficult.

The Chinese invention patent (patent publication No. CN 101265935A) discloses a preparation method of a ceramic matrix composite bolt, which comprises the steps of preparing a preform by laying fibers, depositing a pyrolytic carbon interface layer on the preform, preparing a semi-finished ceramic matrix composite plate by depositing a SiC matrix on the pyrolytic carbon interface layer by adopting a CVI method, cutting a bolt blank on the plate and tapping a thread, finally carrying out PIP method for multiple dipping and cracking on the semi-finished bolt, and continuously depositing a SiC oxidation resistant layer by adopting the CVI method to obtain the bolt with higher strength. The invention adopts CVI and PIP technology to prepare ceramic matrix composite products, the cost is reduced, but the invention adopts a fiber laying structure, and the layering is easy during processing. According to the invention, the SiC matrix is prepared by using the CVI, the process is difficult to control, closed pores are easy to form, and when the PIP method is used for impregnation and cracking, slurry is not easy to soak into the interior of the preform, so that the number of internal voids is large, the strength of the obtained material core is low, and the cost is high when the CVI technology is used for preparing the SiC matrix.

The invention discloses a method for preparing a SiC/SiC composite material pin by a precursor impregnation cracking method, which overcomes the defect of layering of a fiber layering structure, adopts 2D weaving to prepare a pin preform, adopts CVI to deposit a pyrolytic carbon interface layer, and adopts a PIP method to prepare a substrate, so that the SiC/SiC composite material pin has high strength and good toughness, and the process of processing threads by bolts is reduced when the pin is prepared. The invention adopts a PIP method to prepare the pin, the diameter of the prepared pin is less than 5mm, and the preparation of a connecting piece with a larger diameter required by the standard can not be met. In addition, this method is not suitable for threaded connection preparation, which also limits the usefulness of ceramic matrix composite high temperature connections.

In conclusion, the prefabricated body interlayer combination used in the prior art is weaker, the diameter range of the prepared member is smaller, and the practicability range is not large.

Disclosure of Invention

In order to solve the problems that the CVI technology in the prior art is high in cost, closed holes are easy to form, the preparation efficiency is low, a two-dimensional paving component is easy to layer, the diameter range of a connecting piece is small, and the like, the invention aims to provide the ceramic matrix composite stud with high strength, good toughness, a large diameter range and high preparation efficiency and the preparation method thereof.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a ceramic matrix composite stud consists of a fiber preform, an interface layer and a ceramic matrix, wherein the density of the fiber preform is gradually reduced from inside to outside; the interface layer is a composite interface layer or a gradient interface layer; the composite interface layer is any two or three of a pyrolytic carbon interface layer, a boron nitride interface layer and a silicon carbide interface layer; the gradient interface layer is an interface layer with a silicon-carbon ratio in gradient distribution, and the silicon-carbon ratio is gradually increased from inside to outside; the ceramic matrix is a silicon carbide matrix containing nano-fibers.

Preferably, the nano-fiber is nano-carbon fiber, carbon nano-tube, graphene, nano-SiC fiber, nano-Si₃N₄In fiber, nano ZrC fiber, nano TiC fiber and nano TiN fiberAny one or more.

A preparation method of the ceramic matrix composite stud comprises the following steps:

(1) preparing a fiber preform: preparing the fiber into a fiber preform which has the same shape as the final stud product, has the size with allowance and has density gradient; the density gradient means that the density of the fiber preform is gradually reduced from inside to outside;

(2) preparing an interface layer: preparing an interface layer for the fiber preform obtained in the step (1), wherein the interface layer is a composite interface layer or a gradient interface layer; the composite interface layer is any two or three of a pyrolytic carbon interface layer, a boron nitride interface layer and a silicon carbide interface layer; the gradient interface layer is an interface layer with a silicon-carbon ratio in gradient distribution, and the silicon-carbon ratio is gradually increased from inside to outside;

(3) dipping, curing and low-temperature cracking: repeating the processes of dipping, curing and low-temperature cracking for 3-6 times; the low-temperature cracking process comprises the following steps: putting the product obtained by curing into a sintering furnace, heating to a low-temperature cracking temperature of 850-1300 ℃ at a heating rate of 5-10 ℃/min under a vacuum state or a micro-positive pressure state in the furnace, preserving heat for 2-10 h, naturally cooling to room temperature under a protective gas atmosphere, and taking out; the vacuum degree in the vacuum state is below 200 Pa; the micro-positive pressure state is that protective gas is introduced, the pressure in the furnace is adjusted to be 100-200 kPa, and the gas flow is 4-10L/min;

(4) dipping, curing and pyrolysis: repeating the processes of dipping, curing and pyrolysis for 1-3 times; the high-temperature cracking process is the same as the low-temperature cracking process in the step (3), except that the temperature of the high-temperature cracking process is 1300-1500 ℃;

(5) and (3) mechanical finish machining: processing the product obtained in the step (4) into the design size of a stud;

(6) and processing threads: machining threads on the product obtained in the step (5);

(7) dipping, curing and pyrolysis: repeating the dipping-curing-pyrolysis process in the step (4) for 1-2 times on the product obtained in the step (6);

(8) finishing the threads: polishing the product obtained in the step (7) to the final size precision;

(9) CVI-SiC densification: and (5) performing chemical vapor infiltration SiC on the product obtained in the step (8) for further densification to obtain the ceramic matrix composite stud.

Preferably, in the step (1), the fiber is carbon fiber or silicon carbide fiber; the fiber preform is prepared by molding fibers in a 2.5D needling or 2.5D puncturing mode, and the needling density of the fiber preform is 20-40 needles/cm²The puncture density of the fiber preform is 15-30 needles/cm²。

Preferably, in the step (2), the pyrolytic carbon interface layer, the boron nitride interface layer, the silicon carbide interface layer and the gradient interface layer are respectively prepared according to the following methods:

the pyrolytic carbon interface layer is prepared by isothermal CVI: the deposition temperature is 800-1300 ℃, carbon source gas is introduced at the flow rate of 5-15L/min, the pressure in the furnace is adjusted to be 0.5-20 kPa, and the temperature is kept for 1-60 h; the carbon source gas is selected from any one or more of methane, propane and propylene;

the boron nitride interface layer is prepared by adopting isothermal CVI technology under hydrogen atmosphere through a nitrogen source precursor and a boron source precursor: the deposition temperature is 600-1100 ℃, the pressure in the furnace is 10-25 kPa, the total flow of the nitrogen source and the boron source precursor gas is 200-1000 sccm, the flow ratio of the nitrogen source to the boron source is 10-20: 1, the flow ratio of the hydrogen gas to the nitrogen source is 50-100: 1, and the temperature is kept for 1-30 h; the nitrogen source precursor is NH₃、B₃N₃H₆Or Cl₃B₃N₃H₃The boron source precursor is BH₃、BCl₃、BF₃、B₂H₆、B₄H₁₀、B₃N₃H₆Or Cl₃B₃N₃H₃One of (1);

the silicon carbide interface layer is prepared by adopting an isothermal CVI technology: introducing a silicon source, the carrier gas, the diluent gas and the reducing gas into a vacuum degree of less than 200Pa by taking hydrogen as the carrier gas, argon as the diluent gas and hydrogen as the reducing gas, regulating the pressure in the furnace to be 5-20 kPa, controlling the deposition temperature to be 1000-1500 ℃ and keeping the temperature for 1-25 h; wherein the molar ratio of the reducing gas to the silicon source is 8-20: 1, the flow rate of the silicon source is 1-15 g/min, the flow rate of the diluting gas is 2-20L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, and the flow rate of the carrier gas is 100-200 mL/min; the silicon source is methyl trichlorosilane;

the gradient interface layer is prepared by adopting an isothermal CVI technology, and the specific process is as follows:

method (i): using hydrogen as a carrier gas, argon as a diluent gas, using hydrogen as a reducing gas, introducing a silicon source, the carrier gas, the diluent gas and the reducing gas under the condition that the vacuum degree is below 200Pa, adjusting the pressure in the furnace to be 0.5-20 kPa, raising the deposition temperature to 1150-1500 ℃, preserving the temperature for 1-5 h, cooling at the rate of 1-2 ℃/min, and preserving the temperature for 1-5 h every time when the temperature is lowered by 100 ℃ until the temperature is lowered to 850-1150 ℃; wherein the molar ratio of the reducing gas to the silicon source is 5-20: 1, the flow rate of the silicon source is 1-20 g/min, the flow rate of the diluting gas is 2-20L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, and the flow rate of the carrier gas is 100-200 mL/min; the silicon source is methyl trichlorosilane;

method (ii): introducing a silicon source, the carrier gas, the diluent gas and the reducing gas into a vacuum degree of less than 200Pa by taking hydrogen as the carrier gas, argon as the diluent gas and hydrogen as the reducing gas, regulating the pressure in the furnace to be 0.5-20 kPa, controlling the deposition temperature to be 800-1500 ℃ and keeping the temperature for 1-50 h; wherein the molar ratio of the reducing gas to the silicon source is gradually increased to 20-25: 1 from 5-10: 1, the flow rate of the silicon source is 1-20 g/min, the flow rate of the diluting gas is 2-20L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, and the flow rate of the carrier gas is 100-200 mL/min; the silicon source is methyl trichlorosilane.

Preferably, in the step (3) and the step (4), the impregnation is vacuum impregnation; the vacuum impregnation process comprises the following steps: putting the product into a vacuum impregnation barrel, vacuumizing until the vacuum degree is below 100Pa, keeping the vacuum for 0.5-1 h, injecting ceramic precursor slurry, keeping the vacuum for 1-5 h, and breaking the vacuum and taking out.

Preferably, the ceramic precursor slurry is prepared from a ceramic precursor, a solvent and nano-fibers according to the ratio of 10: 3-8: 1(0.5-2) by mass; the ceramic precursor is polysilane containing one or more of carbon, nitrogen, boron and oxygen; the solvent is divinylbenzene, xylene, toluene, dimethyl sulfoxide, n-hexane, cyclohexane, tetrahydrofuran, chloroform or chlorobenzene; the nano-fiber is nano-carbon fiber, carbon nano-tube, graphene, nano-SiC fiber, nano-Si₃N₄Any one or more of fiber, nanometer ZrC fiber, nanometer TiC fiber and nanometer TiN fiber.

Preferably, the ceramic precursor is polysilane, polycarbosilane, polysilazane, polysiloxane, polyborosilazane, or polycarbosilazane.

Preferably, in step (3) and step (4), vacuum impregnation is followed by pressure impregnation, and the pressure impregnation process is as follows: and (3) putting the product subjected to vacuum impregnation into a pressure impregnation tank, heating to 50-70 ℃, introducing protective gas until the pressure in the pressure impregnation tank is 1-6 MPa, preserving the heat for 1-5 h, naturally cooling to room temperature, and taking out.

Preferably, in the step (3) and the step (4), the curing is: and heating the product obtained after dipping to 120-250 ℃ at the heating rate of 5-10 ℃/min, preserving the heat for 3-10 h, naturally cooling to room temperature, and taking out.

Preferably, in step (9), the CVI-SiC densification process is: the method comprises the following steps of (1) further densifying a product through CVI by taking methyltrichlorosilane as a precursor, hydrogen as a carrier gas, argon as a diluent gas and hydrogen as a reducing gas; wherein, the parameter conditions of the CVI technology are as follows: the deposition temperature is 800-1200 ℃, the deposition pressure is 1-20 kPa, and the deposition time is 5-200 h; the molar ratio of the reducing gas to the precursor is 8-20: 1, the flow rate of the precursor is 1-15 g/min, the flow rate of the diluting gas is 2-20L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the precursor, and the flow rate of the carrier gas is 100-200 mL/min.

Has the advantages that:

(1) according to the invention, the prefabricated body structure with the density gradually reduced from inside to outside is adopted, on one hand, pores at the core part of the prefabricated body are preferably filled in the dipping and cracking process, the densification effect of the core part can be improved, and the prepared material has higher core part strength and more uniform density; on the other hand, after multiple times of dipping and cracking, the density of the surface layer is small, the fiber volume fraction of the prefabricated body is small, the pores are large, the pores of the surface layer are not easy to be blocked in the dipping and cracking process, the bottleneck effect is not easy to form, the processing times of the surface layer can be reduced or no processing is needed, and further the damage to the material reinforced structure is reduced; the method can be used for preparing standard studs with different diameters ranging from 5mm to 48mm, and large-size ceramic matrix composite studs can be prepared;

(2) according to the invention, a plurality of composite interface layers or gradient interface layers are adopted, so that a crack propagation path is increased, and the toughness, thermal shock resistance and oxidation resistance of the material are improved; the inner layer of the gradient interface layer has more carbon content, and the outer layer has more silicon content, so that the difference of thermal expansion coefficients between the interface layer and the fibers and the matrix can be reduced, and the thermal shock resistance at high temperature is better; the composite interface layer and the gradient interface layer are beneficial to improving the thermal matching between the interface layers and improving the thermal shock resistance, the interface layers realize continuous weak bonding, the deflection is easier to occur when a crack passes through, the energy of the crack can be quickly consumed, and the crack is effectively prevented from extending to the fiber to generate brittle fracture;

(3) according to the invention, a high-low temperature circulating impregnation-curing-cracking process is adopted, a low-temperature cracking process is firstly adopted to generate amorphous SiC ceramic, then the amorphous SiC ceramic is fully converted into polycrystalline SiC ceramic through high-temperature cracking, some decomposition products escape in the conversion process to form pores, the next impregnation-curing-cracking process is facilitated, the impregnation efficiency of the stud can be improved, and the preparation period can be shortened; the high-low temperature circulating impregnation-solidification-cracking process can effectively avoid the problems of obvious expansion and shrinkage of the prefabricated body, large influence on the gaps of the matrix and large size deformation caused by direct high-temperature cracking when the material density is low;

(4) the invention adopts the ceramic precursor slurry containing the nano-fiber, which can improve the dipping efficiency and reduce the preparation period; secondly, the toughness of the material can be improved by adding the nano fibers, so that the bending and shearing resistance of the stud is improved; thirdly, the nano-fiber is added, so that the wear resistance of the material can be improved;

(5) the density of the product obtained by high-low temperature cyclic dipping-curing-cracking is 1.45-1.7 mm/cm3, the density is low, tapping is carried out at low density, screw thread cracking caused by high material hardness and brittleness is avoided, the thread machining precision can be improved, the abrasion of the diamond grinding wheel is reduced, and the cost is reduced;

(6) the invention recycles the product after the thread is processed for 1-2 times of dipping-curing-pyrolysis processes, and can carry out hole sealing densification on the product so as to meet the requirements on the density and the strength of the ceramic matrix composite stud;

(7) according to the invention, a comprehensive preparation method combining CVI and PIP is adopted, the advantages of good effect of sealing and filling large holes and high preparation efficiency of the PIP method are fully exerted, the advantage of good effect of filling small holes is utilized again by the CVI technology, and the prepared material is low in porosity and low in cost;

(8) the invention adopts near net shape, consumes less material, and can save material and cost.

Detailed Description

The present invention will be further described with reference to the following specific examples. It should be understood that the following examples are illustrative only and are not intended to limit the scope of the present invention.

Example 1

A ceramic matrix composite stud is composed of a fiber preform, a gradient interface layer and a ceramic substrate, wherein the fiber preform adopts carbon fiber, 0/90-degree laid fabric/mesh tire laminated layer is formed into a 2.5D preform by needling, the layer number ratio of the laid fabric/mesh tire in the preform is 10: 1, and the layer number ratio of the laid fabric to the mesh tire from inside to outside is gradually reduced to 2: 1; the gradient interface layer is a silicon carbide gradient interface layer with the silicon-carbon ratio gradually increasing from inside to outside; the ceramic matrix is a silicon carbide matrix containing nano carbon fibers.

The preparation method comprises the following steps:

(1) preparing a fiber preform: the design diameter of the stud is 10mm, and according to the design size of the stud, a fiber preform which is consistent with the shape of the stud, has a processing allowance of 1mm and has a density gradient is prepared by adopting carbon fibers; the fiber preform is 0/90 DEG non-woven cloth/a 2.5D prefabricated body is formed by needle punching of laminated layers of net tires, and the needle punching density is 20 needles/cm²The layer ratio of the non-woven cloth/the net tire in the prefabricated body is 10: 1, and the layer ratio of the non-woven cloth to the net tire from inside to outside is gradually reduced to 2: 1;

(2) preparing an interface layer: preparing a gradient interface layer for the prefabricated body obtained in the step (1): introducing a silicon source, the carrier gas, the diluent gas and the reducing gas under the vacuum degree of 100Pa by taking hydrogen as the carrier gas, argon as the diluent gas and hydrogen as the reducing gas, and adjusting the pressure in the furnace to be 10kPa, the deposition temperature to be 1000 ℃ and the heat preservation time to be 35 hours; wherein, the mol ratio of the reducing gas to the silicon source is gradually increased from 10: 1 to 20: 1, the flow rate of the silicon source is 2g/min, the flow rate of the diluting gas is 18L/min, the flow rate of the reducing gas is determined by the mol ratio of the reducing gas to the silicon source, and the flow rate of the carrier gas is 150 mL/min; the silicon source is methyl trichlorosilane;

(3) dipping, curing and low-temperature cracking:

(3a) and vacuum impregnation: putting the prefabricated body obtained in the step (2) into a vacuum impregnation barrel, firstly vacuumizing until the vacuum degree is 80Pa, keeping the vacuum for 1h, injecting ceramic precursor slurry, keeping the vacuum for 3h, and then breaking the vacuum and taking out; the ceramic precursor slurry is prepared by mixing a ceramic precursor, a solvent and nano-fibers according to the mass ratio of 10: 5: 0.5; the ceramic precursor is polycarbosilane; the solvent is xylene; the nano-fibers are nano-carbon fibers; the slurry mixing is to mechanically stir the ceramic precursor and the solvent in a 50 ℃ water bath kettle at the rotating speed of 50r/min for 2h, then add the nano carbon fiber, and ball-mill the mixture for 8h at the rotating speed of 280r/min by a ball mill;

(3b) pressure impregnation: putting the prefabricated body obtained in the step (3 a) into a pressure impregnation tank, heating to 50 ℃, introducing protective gas, adjusting the pressure in the pressure impregnation tank to 3MPa, preserving the heat for 3 hours, naturally cooling to room temperature, and taking out;

(3c) and curing: heating the prefabricated body obtained in the step (3 b) to 120 ℃ at the heating rate of 10 ℃/min, preserving the heat for 8 hours, naturally cooling to room temperature, and taking out;

(3d) and low-temperature cracking: putting the prefabricated body obtained in the step (3 c) into a sintering furnace, keeping the furnace in a vacuum state, heating to the low-temperature cracking temperature of 1000 ℃ at the heating rate of 5 ℃/min, preserving the heat for 2 hours, introducing argon after the heat preservation is finished, naturally cooling to the room temperature in the argon atmosphere, and taking out;

(3e) repeating the steps (3 a) - (3 d) for 5 times on the product obtained in the step (3 d);

(4) dipping, curing and pyrolysis:

(4a) and vacuum impregnation: replacing the prefabricated body obtained in the step (2) in the step (3 a) with the product obtained in the step (3 e), and performing other operations as in the step (3 a);

(4b) pressure impregnation: replacing the prefabricated body obtained in the step (3 a) in the step (3 b) with the product obtained in the step (4 a), and performing the same operation as the step (3 b);

(4c) and curing: replacing the prefabricated body obtained in the step (3 b) in the step (3 c) with the product obtained in the step (4 b), and performing the same operation as the step (3 c);

(4d) and pyrolysis: replacing the product obtained in the step (4 c) with the preform obtained in the step (3 c) in the step (3 d), simultaneously replacing low-temperature cracking with high-temperature cracking at 1400 ℃, and performing other operations in the same step (3 d);

(4e) repeating the steps (4 a) - (4 d) for 1 time on the product obtained in the step (4 d);

(5) and (3) mechanical finish machining: processing the product obtained in the step (4 e) into the design size of a screw column;

(6) and processing threads: manually processing threads on the product obtained in the step (5) by adopting a diamond cutter;

(7) dipping, curing and pyrolysis: repeating the steps (4 a) - (4 d) for 2 times on the product obtained in the step (6);

(8) finishing the threads: polishing the product obtained in the step (7) by using 2000-mesh abrasive paper until the final size precision is reached;

(9) CVI-SiC densification: taking methyltrichlorosilane as a precursor, hydrogen as a carrier gas, argon as a diluent gas and hydrogen as a reducing gas for the product obtained in the step (8), and penetrating SiC into the small holes of the product to realize densification of the product; wherein, the parameter conditions of CVI are as follows: the deposition temperature is 1100 ℃, the deposition pressure is 10kPa, and the deposition time is 30 h; the molar ratio of the reducing gas to the precursor is 8: 1, the flow rate of the precursor is 8g/min, the flow rate of the diluting gas is 10L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the precursor, and the flow rate of the carrier gas is 110 mL/min; and (5) obtaining the ceramic matrix composite stud after CVI-SiC densification.

Comparative example 1

The difference from example 1 is that: in step (3 a), the ceramic precursor slurry does not contain nanofibers, and the rest is the same as in example 1.

Example 2

The utility model provides a ceramic matrix composite stud comprises fibre preform, compound interface layer, ceramic base member, the fibre preform adopts carbon fiber, puncture shaping 2.5D preform to the preform reduces gradually from inside to outside fibre density, and inside fibre density is 0.70g/cm³The external fiber density was 0.55g/cm³(ii) a The composite interface layer is a pyrolytic carbon interface layer and a silicon carbide interface layer from inside to outside of the surface of the prefabricated body in sequence; the ceramic matrix is a silicon carbide matrix containing nano-fibers; the nano-fiber is a nano-fiber which is a carbon nano-tube and a nano SiC fiber with the mass ratio of 1: 1.

The preparation method comprises the following steps:

(1) preparing a fiber preform: the design diameter of the stud is 38mm, and according to the design size of the stud, a fiber preform which is consistent with the shape of the stud, has a machining allowance of 0.5mm and has a density gradient is prepared by adopting carbon fibers; the fiber preform is a 2.5D preform formed by puncture, and the puncture density is 25 needles/cm²And the fiber density of the preform gradually decreases from inside to outside, the internal fiber density being 0.70g/cm³The external fiber density was 0.55g/cm³；

(2) Preparing an interface layer: preparing a composite interface layer from the preform obtained in the step (1), wherein the composite interface layer sequentially comprises a pyrolytic carbon interface layer and a silicon carbide interface layer from inside to outside of the surface of the preform;

the pyrolytic carbon interface layer is prepared by isothermal CVI: the deposition temperature is 1150 ℃, carbon source gas is introduced at the flow rate of 8L/min, the pressure in the furnace is adjusted to be 5kPa, and the temperature is kept for 20 h; the carbon source gas is propylene;

the silicon carbide interface layer is prepared by isothermal CVI: introducing a silicon source, the carrier gas, the diluent gas and the reducing gas into a furnace with hydrogen as the carrier gas, argon as the diluent gas and hydrogen as the reducing gas under the vacuum degree of below 200Pa, adjusting the pressure in the furnace to 12kPa, the deposition temperature to 1200 ℃ and the heat preservation time to 15 h; wherein, the molar ratio of the reducing gas to the silicon source is 16: 1, the flow rate of the silicon source is 5g/min, the flow rate of the diluting gas is 10L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, and the flow rate of the carrier gas is 110 mL/min; the silicon source is methyl trichlorosilane;

(3) dipping, curing and low-temperature cracking:

(3a) and vacuum impregnation: putting the prefabricated body obtained in the step (2) into a vacuum impregnation barrel, firstly vacuumizing until the vacuum degree is 60Pa, keeping the vacuum for 1h, injecting ceramic precursor slurry, keeping the vacuum for 5h, and then breaking the vacuum and taking out; the ceramic precursor slurry is prepared by mixing a ceramic precursor, a solvent and nano-fibers according to the mass ratio of 10: 8: 1; the ceramic precursor is polysilazane; the solvent is tetrahydrofuran; the nano-fiber is a carbon nano-tube and nano-SiC fiber with the mass ratio of 1: 1; the slurry mixing is to mechanically stir the ceramic precursor and the solvent in a 70 ℃ water bath kettle at the rotating speed of 60r/min for 2h, then add the carbon nano tube and the nano SiC fiber, and ball mill the mixture for 8h at the rotating speed of 280r/min by a ball mill;

(3b) pressure impregnation: putting the prefabricated body obtained in the step (3 a) into a pressure impregnation tank, heating to 60 ℃, introducing protective gas until the pressure in the pressure impregnation tank is 2MPa, preserving the heat for 4 hours, naturally cooling to room temperature, and taking out;

(3c) and curing: heating the prefabricated body obtained in the step (3 b) to 150 ℃ at the heating rate of 8 ℃/min, preserving the heat for 5 hours, naturally cooling to room temperature, and taking out;

(3d) and low-temperature cracking: putting the prefabricated body obtained in the step (3 c) into a sintering furnace, keeping the furnace in a vacuum state, heating to the low-temperature cracking temperature of 1300 ℃ at the heating rate of 5 ℃/min, preserving the heat for 2 hours, introducing argon after the heat preservation is finished, naturally cooling to the room temperature in the argon atmosphere, and taking out;

(3e) repeating the steps (3 a) - (3 d) for 5 times on the product obtained in the step (3 d);

(4) dipping, curing and pyrolysis:

(4a) and vacuum impregnation: replacing the prefabricated body obtained in the step (2) in the step (3 a) with the product obtained in the step (3 e), and performing other operations as in the step (3 a);

(4b) pressure impregnation: replacing the prefabricated body obtained in the step (3 a) in the step (3 b) with the product obtained in the step (4 a), and performing the same operation as the step (3 b);

(4c) and curing: replacing the prefabricated body obtained in the step (3 b) in the step (3 c) with the product obtained in the step (4 b), and performing the same operation as the step (3 c);

(4d) and pyrolysis: replacing the product obtained in the step (4 c) with the preform obtained in the step (3 c) in the step (3 d), simultaneously replacing low-temperature cracking with high-temperature cracking, wherein the high-temperature cracking temperature is 1500 ℃, and performing other operations in the same step (3 d);

(4e) repeating the steps (4 a) - (4 d) for 1 time on the product obtained in the step (4 d);

(5) and (3) mechanical finish machining: processing the product obtained in the step (4 e) into the design size of a screw column;

(6) and processing threads: manually processing threads on the product obtained in the step (5) by adopting a diamond cutter;

(7) dipping, curing and pyrolysis: repeating the steps (4 a) - (4 d) for 2 times on the product obtained in the step (6);

(8) finishing the threads: polishing the product obtained in the step (7) by using 2000-mesh abrasive paper until the final size precision is reached;

(9) CVI-SiC densification: taking methyltrichlorosilane as a precursor, hydrogen as a carrier gas, argon as a diluent gas and hydrogen as a reducing gas for the product obtained in the step (8), and infiltrating SiC into small holes of the product through CVI to realize product densification; wherein, the parameter conditions of CVI are as follows: the deposition temperature is 1100 ℃, the deposition pressure is 10kPa, and the deposition time is 30 h; the molar ratio of the reducing gas to the precursor is 20: 1, the flow rate of the precursor is 15g/min, the flow rate of the diluting gas is 10L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the precursor, and the flow rate of the carrier gas is 110 mL/min; and (5) performing CVI-SiC densification to obtain the ceramic matrix composite stud.

Example 3

The ceramic matrix composite stud consists of a fiber preform, a composite interface layer and a ceramic substrate, wherein the fiber preform adopts silicon carbide fibers, the fibers are punctured to form a 2.5D preform, the fiber density of the preform is gradually reduced from inside to outside, and the internal fiber density is 0.65g/cm³The external fiber density was 0.5g/cm³；

The composite interface layer is a pyrolytic carbon interface layer and a boron nitride interface layer from the inside to the outside of the surface of the prefabricated body in sequence; the ceramic matrix is a silicon carbide matrix containing nano-fibers; the nanofiber is graphene.

The preparation method comprises the following steps:

(1) preparing a fiber preform: the design diameter of the stud is 20mm, and according to the design size of the stud, a fiber preform which is consistent with the shape of the stud, has a machining allowance of 2mm and has a density gradient is prepared by adopting silicon carbide fibers; the fiber preform is a fiber puncture molding 2.5D preform, and the puncture density is 15 needles/cm²And the fiber density of the preform is gradually reduced from inside to outside, and the internal fiber density is 0.65g/cm³The external fiber density was 0.5g/cm³；

(2) Preparing an interface layer: preparing a composite interface layer from the preform obtained in the step (1), wherein the composite interface layer sequentially comprises a pyrolytic carbon interface layer and a boron nitride interface layer from inside to outside of the surface of the preform;

the pyrolytic carbon interface layer is prepared by isothermal CVI: the deposition temperature is 1050 ℃, carbon source gas is introduced at the flow rate of 8L/min, the pressure in the furnace is adjusted to 8kPa, and the temperature is kept for 15 h; the carbon source gas is propane;

the boron nitride interface layer is formed by a nitrogen source precursor and a boron sourceThe precursor is prepared by isothermal CVI under hydrogen atmosphere: the deposition temperature is 700 ℃, the pressure in the furnace is 30kPa, the heat preservation time is 30H, the total flow of the nitrogen source and the boron source precursor gas is 1000sccm, the flow ratio of the nitrogen source to the boron source is 20: 1, H is₂The flow ratio of the nitrogen source to the nitrogen source is 50: 1; the nitrogen source precursor is NH₃The boron source precursor is BCl₃；

(3) Dipping, curing and low-temperature cracking:

(3a) and vacuum impregnation: putting the prefabricated body obtained in the step (2) into a vacuum impregnation barrel, firstly vacuumizing until the vacuum degree is 50Pa, keeping the vacuum for 0.5h, then injecting ceramic precursor slurry, keeping the vacuum for 1h, and then breaking the vacuum and taking out; the ceramic precursor slurry is prepared by mixing a ceramic precursor, a solvent and nano-fibers according to the mass ratio of 10: 5: 0.5; the ceramic precursor is polysilane; the solvent is toluene; the nano-fibers are graphene; the slurry mixing is to mechanically stir the ceramic precursor and the solvent in a water bath kettle at 55 ℃, stir the mixture for 3 hours at the rotating speed of 55r/min, add the graphene, and ball-mill the mixture for 8 hours at the rotating speed of 250r/min by a ball mill;

(3b) pressure impregnation: putting the prefabricated body obtained in the step (3 a) into a pressure impregnation tank, heating to 70 ℃, introducing protective gas, adjusting the pressure in the pressure impregnation tank to 1MPa, preserving the heat for 1h, naturally cooling to room temperature, and taking out;

(3c) and curing: heating the prefabricated body obtained in the step (3 b) to 200 ℃ at the heating rate of 5 ℃/min, preserving the heat for 3h, naturally cooling to room temperature, and taking out;

(3d) and low-temperature cracking: putting the prefabricated body obtained in the step (3 c) into a sintering furnace, keeping the furnace in a vacuum state, heating to the low-temperature cracking temperature of 1000 ℃ at the heating rate of 5 ℃/min, preserving the heat for 2 hours, introducing argon after the heat preservation is finished, naturally cooling to the room temperature in the argon atmosphere, and taking out;

(3e) repeating the steps (3 a) - (3 d) for 5 times on the product obtained in the step (3 d);

(4) dipping, curing and pyrolysis:

(4a) and vacuum impregnation: replacing the prefabricated body obtained in the step (2) in the step (3 a) with the product obtained in the step (3 e), and performing other operations as in the step (3 a);

(4b) pressure impregnation: replacing the prefabricated body obtained in the step (3 a) in the step (3 b) with the product obtained in the step (4 a), and performing the same operation as the step (3 b);

(4c) and curing: replacing the prefabricated body obtained in the step (3 b) in the step (3 c) with the product obtained in the step (4 b), and performing the same operation as the step (3 c);

(4d) and pyrolysis: replacing the product obtained in the step (4 c) with the preform obtained in the step (3 c) in the step (3 d), simultaneously replacing low-temperature cracking with high-temperature cracking at 1400 ℃, and performing other operations in the same step (3 d);

(4e) repeating the steps (4 a) - (4 d) for 1 time on the product obtained in the step (4 d);

(5) and (3) mechanical finish machining: processing the product obtained in the step (4 e) into the design size of a screw column;

(6) and processing threads: manually processing threads on the product obtained in the step (5) by adopting a diamond cutter;

(7) dipping, curing and pyrolysis: repeating the steps (4 a) - (4 d) for 2 times on the product obtained in the step (6);

(8) finishing the threads: polishing the product obtained in the step (7) by using 2000-mesh abrasive paper until the final size precision is reached;

(9) CVI-SiC densification: taking methyltrichlorosilane as a precursor, hydrogen as a carrier gas, argon as a diluent gas and hydrogen as a reducing gas for the product obtained in the step (8), and infiltrating SiC into small holes of the product through CVI to realize product densification; wherein, the parameter conditions of CVI are as follows: the deposition temperature is 1000 ℃, the deposition pressure is 8kPa, and the deposition time is 30 h; the molar ratio of the reducing gas to the precursor is 11: 1, the flow rate of the precursor is 12g/min, the flow rate of the diluting gas is 10L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the precursor, the flow rate of the carrier gas is 110mL/min, and the ceramic matrix composite stud is obtained after CVI-SiC densification.

Example 4

A ceramic matrix composite stud is composed of a fiber preform, a gradient interface layer and a ceramic substrate, wherein the fiber preform adopts carbon fiber, 0/90-degree laid cloth/mesh tire laminated layer is subjected to needling to form a 2.5D preform, and the layer ratio of the laid cloth/mesh tire of the preform from inside to outside is 15: 1 and is gradually reduced to 5: 2; (ii) a The gradient interface layer is a silicon carbide gradient interface layer with the silicon-carbon ratio gradually increasing from inside to outside; the ceramic matrix is a silicon carbide matrix containing nano-fibers; the nano-fibers are nano-SiC fibers.

The preparation method comprises the following steps:

(1) preparing a fiber preform: the design diameter of the stud is 8mm, and according to the design size of the stud, a fiber preform which is consistent with the shape of the stud, has a processing allowance of 1mm and has a density gradient is prepared by adopting carbon fibers; the fiber preform is a 0/90-degree laid fabric/net tire laminated layer laminated needling forming 2.5D preform, and the needling density is 40 needles/cm²And the layer ratio of the non-woven cloth/the net tire of the prefabricated body from inside to outside is 15: 1 and is gradually reduced to 5: 2;

(2) preparing an interface layer: preparing a gradient interface layer for the prefabricated body obtained in the step (1): using hydrogen as a carrier gas, argon as a diluent gas, using hydrogen as a reducing gas, introducing a silicon source, the carrier gas, the diluent gas and the reducing gas under the condition that the vacuum degree is below 150Pa, adjusting the pressure in the furnace to be 10kPa, raising the deposition temperature to 1400 ℃, preserving heat for 5h, then gradually lowering the temperature at the rate of 2 ℃/min, preserving heat for 3h when the temperature is lowered to 100 ℃ until the temperature is lowered to 850 ℃, and preserving heat for 3 h; wherein, the molar ratio of the reducing gas to the silicon source is 15: 1, the flow rate of the silicon source is 1g/min, the flow rate of the diluting gas is 20L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, and the flow rate of the carrier gas is 180 mL/min; the silicon source is methyl trichlorosilane;

(3) dipping, curing and low-temperature cracking:

(3a) and vacuum impregnation: putting the prefabricated body obtained in the step (2) into a vacuum impregnation barrel, firstly vacuumizing until the vacuum degree is 80Pa, keeping the vacuum for 1h, injecting ceramic precursor slurry, keeping the vacuum for 3h, and then breaking the vacuum and taking out; the ceramic precursor slurry is prepared by mixing a ceramic precursor, a solvent and nano-fibers according to the mass ratio of 10: 5: 1.5; the ceramic precursor is polycarbosilane; the solvent is xylene; the nano-fibers are nano SiC fibers; the slurry mixing is to mechanically stir the ceramic precursor and the solvent in a water bath kettle at 65 ℃, stir for 1h at the rotating speed of 60r/min, add the nano SiC fiber, and ball-mill for 8h at the rotating speed of 300r/min by a ball mill;

(3b) pressure impregnation: putting the prefabricated body obtained in the step (3 a) into a pressure impregnation tank, heating to 55 ℃, introducing protective gas until the pressure in the pressure impregnation tank is 5MPa, preserving the heat for 2 hours, naturally cooling to room temperature, and taking out;

(3c) and curing: heating the prefabricated body obtained in the step (3 b) to 250 ℃ at the heating rate of 6 ℃/min, preserving the heat for 3h, naturally cooling to room temperature, and taking out;

(3d) and low-temperature cracking: putting the prefabricated body obtained in the step (3 c) into a sintering furnace, keeping the furnace in a vacuum state, heating to the low-temperature cracking temperature of 1000 ℃ at the heating rate of 5 ℃/min, preserving the heat for 2 hours, introducing argon after the heat preservation is finished, naturally cooling to the room temperature in the argon atmosphere, and taking out;

(3e) repeating the steps (3 a) - (3 d) for 5 times on the product obtained in the step (3 d);

(4) dipping, curing and pyrolysis:

(4a) and vacuum impregnation: replacing the prefabricated body obtained in the step (2) in the step (3 a) with the product obtained in the step (3 e), and performing other operations as in the step (3 a);

(4b) pressure impregnation: replacing the prefabricated body obtained in the step (3 a) in the step (3 b) with the product obtained in the step (4 a), and performing the same operation as the step (3 b);

(4c) and curing: replacing the prefabricated body obtained in the step (3 b) in the step (3 c) with the product obtained in the step (4 b), and performing the same operation as the step (3 c);

(4d) and pyrolysis: replacing the product obtained in the step (4 c) with the preform obtained in the step (3 c) in the step (3 d), simultaneously replacing low-temperature cracking with high-temperature cracking at 1400 ℃, and performing other operations in the same step (3 d);

(4e) repeating the steps (4 a) - (4 d) for 1 time on the product obtained in the step (4 d);

(5) and (3) mechanical finish machining: processing the product obtained in the step (4 e) into the design size of a screw column;

(6) and processing threads: manually processing threads on the product obtained in the step (5) by adopting a diamond cutter;

(7) dipping, curing and pyrolysis: repeating the steps (4 a) - (4 d) for 2 times on the product obtained in the step (6);

(8) finishing the threads: polishing the product obtained in the step (7) by using 2000-mesh abrasive paper until the final size precision is reached;

(9) CVI-SiC densification: taking methyltrichlorosilane as a precursor, hydrogen as a carrier gas, argon as a diluent gas and hydrogen as a reducing gas for the product obtained in the step (8), and penetrating SiC into the small holes of the product to realize densification of the product; wherein, the parameter conditions of CVI are as follows: the deposition temperature is 1150 ℃, the deposition pressure is 10kPa, and the deposition time is 30 h; the molar ratio of the reducing gas to the precursor is 15: 1, the flow rate of the precursor is 20g/min, the flow rate of the diluting gas is 10L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the precursor, and the flow rate of the carrier gas is 110 mL/min; and (5) obtaining the ceramic matrix composite stud after CVI-SiC densification.

Example 5

The ceramic matrix composite stud consists of a fiber preform, a composite interface layer and a ceramic substrate, wherein the fiber preform adopts silicon carbide fibers, the fibers are punctured to form a 2.5D preform, the fiber density of the preform is gradually reduced from inside to outside, and the internal fiber density is 0.6g/cm³External fiber density of 0.4g/cm³(ii) a The composite interface layer is sequentially a boron nitride interface layer, a pyrolytic carbon interface layer and a silicon carbide interface layer from inside to outside of the surface of the prefabricated body; the ceramic matrix is a silicon carbide matrix containing nano-fibers; the nano-fibers are nano-carbon fibers.

The preparation method comprises the following steps:

(1) preparing a fiber preform: design of studThe diameter is 20mm, and according to the design size of the stud, a fiber preform which is consistent with the shape of the stud, has a machining allowance of 0.5mm and has a density gradient is prepared by adopting silicon carbide fibers; the fiber preform is a fiber puncture molding 2.5D preform, and the puncture density is 30 needles/cm²And the fiber density of the preform gradually decreases from inside to outside, the internal fiber density being 0.6g/cm³External fiber density of 0.4g/cm³；

(2) Preparing an interface layer: preparing a composite interface layer for the prefabricated body obtained in the step (1); the composite interface layer is sequentially a boron nitride interface layer, a pyrolytic carbon interface layer and a silicon carbide interface layer from inside to outside of the surface of the prefabricated body;

the boron nitride interface layer is prepared by a nitrogen source precursor and a boron source precursor by adopting isothermal CVI: the deposition temperature is 650 ℃, the heat preservation time is 3H, the pressure in the furnace is 15kPa, the total flow of the nitrogen source and the boron source precursor gas is 200 sccm, the flow ratio of the nitrogen source to the boron source is 8: 1, H is₂The flow ratio of the nitrogen source to the nitrogen source is 60: 1; the nitrogen source precursor is NH₃The boron source precursor is BF₃；

The pyrolytic carbon interface layer is prepared by isothermal CVI: the deposition temperature is 850 ℃, carbon source gas is introduced at the flow rate of 5L/min, the pressure in the furnace is adjusted to be 5kPa, and the temperature is kept for 8 h; the carbon source gas is methane;

the silicon carbide interface layer is prepared by isothermal CVI: introducing a silicon source, the carrier gas, the diluent gas and the reducing gas into a furnace with the vacuum degree below 200Pa by taking hydrogen as the carrier gas, argon as the diluent gas and hydrogen as the reducing gas, wherein the pressure in the furnace is 5kPa, the deposition temperature is 1350 ℃ and the heat preservation time is 3 h; wherein, the molar ratio of the reducing gas to the silicon source is 14: 1, the flow rate of the silicon source is 10g/min, the flow rate of the diluting gas is 13L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, and the flow rate of the carrier gas is 100 mL/min; the silicon source is methyl trichlorosilane;

(3) dipping, curing and low-temperature cracking:

(3a) and vacuum impregnation: putting the prefabricated body obtained in the step (2) into a vacuum impregnation barrel, firstly vacuumizing until the vacuum degree is 70Pa, keeping the vacuum for 1h, injecting ceramic precursor slurry, keeping the vacuum for 3h, and then breaking the vacuum and taking out; the ceramic precursor slurry is prepared by mixing a ceramic precursor, a solvent and nano-fibers according to the mass ratio of 10: 5: 0.8; the ceramic precursor is polycarbosilane; the solvent is toluene; the nano-fiber is nano-carbon fiber; the slurry mixing is to mechanically stir the ceramic precursor and the solvent in a 60 ℃ water bath kettle at a rotating speed of 60r/min for 3h, then add the nano carbon fiber, and ball-mill the mixture for 4h at a rotating speed of 200r/min by a ball mill;

(3b) pressure impregnation: putting the prefabricated body obtained in the step (3 a) into a pressure impregnation tank, heating to 70 ℃, introducing protective gas until the pressure in the pressure impregnation tank is 6MPa, preserving the heat for 1h, naturally cooling to room temperature, and taking out;

(3c) and curing: heating the prefabricated body obtained in the step (3 b) to 220 ℃ at a heating rate of 10 ℃/min, preserving heat for 6h, naturally cooling to room temperature, and taking out;

(3d) and low-temperature cracking: putting the prefabricated body obtained in the step (3 c) into a sintering furnace, keeping the furnace in a vacuum state, heating to the low-temperature cracking temperature of 1000 ℃ at the heating rate of 5 ℃/min, preserving the heat for 2 hours, introducing argon after the heat preservation is finished, naturally cooling to the room temperature in the argon atmosphere, and taking out;

(3e) repeating the steps (3 a) - (3 d) for 5 times on the product obtained in the step (3 d);

(4) dipping, curing and pyrolysis:

(4a) and vacuum impregnation: replacing the prefabricated body obtained in the step (2) in the step (3 a) with the product obtained in the step (3 e), and performing other operations as in the step (3 a);

(4b) pressure impregnation: replacing the prefabricated body obtained in the step (3 a) in the step (3 b) with the product obtained in the step (4 a), and performing the same operation as the step (3 b);

(4c) and curing: replacing the prefabricated body obtained in the step (3 b) in the step (3 c) with the product obtained in the step (4 b), and performing the same operation as the step (3 c);

(4d) and pyrolysis: replacing the product obtained in the step (4 c) with the preform obtained in the step (3 c) in the step (3 d), simultaneously replacing low-temperature cracking with high-temperature cracking at 1400 ℃, and performing other operations in the same step (3 d);

(4e) repeating the steps (4 a) - (4 d) for 1 time on the product obtained in the step (4 d);

(5) and (3) mechanical finish machining: processing the product obtained in the step (4 e) into the design size of a screw column;

(6) and processing threads: manually processing threads on the product obtained in the step (5) by adopting a diamond cutter;

(7) dipping, curing and pyrolysis: repeating the steps (4 a) - (4 d) for 2 times on the product obtained in the step (6);

(8) finishing the threads: polishing the product obtained in the step (8) to thread accuracy by using 2000-mesh abrasive paper;

(9) CVI-SiC densification: taking methyltrichlorosilane as a precursor, hydrogen as a carrier gas, argon as a diluent gas and hydrogen as a reducing gas for the product obtained in the step (7), and infiltrating SiC into small holes of the product through CVI to realize product densification; wherein, the parameter conditions of CVI are as follows: the deposition temperature is 950 ℃, the deposition pressure is 10kPa, and the deposition time is 100 h; the molar ratio of the reducing gas to the precursor is 8: 1, the flow rate of the precursor is 5g/min, the flow rate of the diluting gas is 10L/min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the precursor, the flow rate of the carrier gas is 110mL/min, and the ceramic matrix composite stud is obtained through CVI-SiC densification.

Samples of the random positions of the ceramic matrix composite studs obtained in examples 1 to 5 and comparative example 1 were cut out, and the properties of the cut samples were tested, with the results shown in table 1.