Rapid preparation method of ceramic matrix composite large-size sunk screw

Abstract

The invention discloses a rapid preparation method of a ceramic matrix composite large-size countersunk head screw, and relates to the technical field of countersunk head screw preparation. The method sequentially comprises the following steps that CVI is conducted on a plate; processing a strip material; performing CVI (chemical vapor infiltration) deposition; turning a bar material; pIP-C is adopted; rMI-Si is adopted; turning threads; and performing CVI deposition to obtain a finished product. The PIP + RMI + CVI combined forming process technology is provided, the advantages of each single process technology are integrated, the preparation period of the countersunk head screw is short, the technology is suitable for machining countersunk head screws with various countersunk head angles and especially suitable for preparing large-specification countersunk head screws with the thread specification of M10 or above, and the integrity of the machined appearance is better. The problems that an existing ceramic matrix composite large-size sunk screw is long in preparation period and poor in performance are solved.

Description

Technical Field

[0001] This invention relates to the field of countersunk screw manufacturing technology, specifically to a rapid manufacturing method for large-size countersunk screws made of ceramic matrix composite materials. Background Technology

[0002] Ceramic matrix composites are a new type of strategic material with characteristics such as high temperature resistance, low density, high specific strength, high specific modulus, oxidation resistance, ablation resistance, insensitivity to cracks, and non-catastrophic damage. They have wide applications in aviation, aerospace, satellite spaceflight, nuclear energy, and photovoltaic fields.

[0003] Due to limitations in the preform molding process of ceramic matrix composite countersunk screws, the current fabrication method for large-size countersunk screw preforms is mostly three-dimensional needle-punched (carbon fiber) flat plates. It is difficult to achieve conformal fabrication of countersunk screws. The common CVI process has poor gas deposition permeability, long deposition preparation cycle, and obvious density unevenness for large-size countersunk screws. Countersunk screws have defects such as sharp edge appearance defects (chipping, notch), uneven density in the countersunk area, and damage when tightening the countersunk area, which makes it difficult to meet the online connection accuracy requirements of ceramic matrix composites. Therefore, it is crucial to adopt certain measures and methods to improve the preparation cycle and quality of large-size countersunk screws made of ceramic matrix composites. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a rapid preparation method for large-size countersunk screws made of ceramic matrix composite materials, thereby solving the problems of long preparation cycles and poor performance of existing large-size countersunk screws made of ceramic matrix composite materials.

[0005] The technical solution of this invention to solve the above-mentioned technical problems is as follows: A rapid preparation method for large-size countersunk screws made of ceramic matrix composite materials is provided, comprising the following steps: (1) Plate CVI: A silicon carbide matrix is ​​deposited on a flat ceramic matrix preform using CVI until the density by drainage method is 1.3-1.4 g / cm³. 3 This yields a flat preform; (2) Processing strips: Along the layup direction of the ceramic matrix composite preform, the flat preform is processed into strips. The length of the strip is 10-12 mm longer than the total length of the countersunk screw, and the thickness and width of the strip are 0.4-0.8 mm greater than the maximum countersunk diameter of the countersunk screw. (3) CVI deposition: Silicon carbide substrate is deposited on the strip using CVI until the density by drainage method is 1.55-1.65 g / cm³. 3 The strip preform is obtained; (4) Turning bar stock: On a CNC lathe, the strip preform is processed into round bar stock, and then processed into "convex" shaped stepped round bar stock. The diameter of the large diameter section of the stepped round bar stock is the same as the maximum diameter of the countersunk head of the countersunk screw. The diameter of the small diameter section of the stepped round bar stock is 0.2-0.5mm larger than the nominal diameter of the countersunk screw. The length of the small diameter section of the stepped round bar stock is the length of the countersunk screw. The length of the stepped round bar stock is 10mm more than the total length of the countersunk screw. (5) PIP-C: Stepped round bars are impregnated with phenolic resin impregnation solution, then cured, pyrolyzed and pyrolyzed to obtain ceramic matrix composite parts; (6) RMI-Si: The ceramic matrix composite parts are impregnated with silicon using RMI; (7) Thread cutting: On a CNC lathe, the threads, nominal diameter of the screw, total length, screw length and countersunk head are machined to obtain a semi-finished product; (8) CVI deposition: Silicon carbide is deposited on the semi-finished product using CVI to obtain the finished product.

[0006] Based on the above technical solution, the present invention can be further improved as follows: Furthermore, in step (4), the part of the stepped round bar that is 10mm longer than the length is the process head for subsequent thread cutting.

[0007] Furthermore, in step (5), the phenolic resin impregnation solution is prepared by dissolving phenolic resin in ethanol, then adding hexamethylenetetramine, then adding acetone, and finally ball milling.

[0008] Furthermore, the mass-to-volume ratio of phenolic resin, hexamethylenetetramine, ethanol, and acetone is 43g:3.44g:100mL:20mL.

[0009] Furthermore, the ball was milled for 8 hours at 200 r / min. Furthermore, the viscosity of the aldehyde resin impregnation solution is 30-40 mPa·s.

[0010] Furthermore, in step (5), the sample is immersed for 20 minutes under a pressure of 0.5-1 MPa.

[0011] Furthermore, in step (5), the curing process is completed by keeping the temperature at 180℃ for 2 hours.

[0012] Furthermore, in step (5), the temperature is kept at 1080-1120℃ for 2 hours to complete the pyrolysis process.

[0013] Furthermore, in step (5), the temperature is maintained at 1880-1920℃ for 4 hours to complete the pyrolysis process.

[0014] Further, in step (6), the small diameter of the ceramic matrix composite part is coated with boron nitride, the large diameter is facing down and embedded in the powder, and RMI impregnation with silicon is performed.

[0015] Furthermore, the powder is prepared by mixing silicon powder and silicon carbide powder in a mass ratio of 3:4.

[0016] Furthermore, in step (6), the silicon is impregnated at 1480-1520℃ for 4 hours to complete the RMI impregnation. Furthermore, in step (8), deposition lasts for 30-35 hours.

[0017] The present invention has the following beneficial effects: 1. This invention proposes a combined PIP+RMI+CVI molding process technology, integrating the advantages of each individual process technology, resulting in a short manufacturing cycle for countersunk screws. The PIP process effectively solves the problem of poor deposition and penetration effect of the traditional CVI process on thick preforms. RMI-Si introduces molten silicon phase to quickly fill the pores of the preform fiber bundles, achieving rapid densification. Furthermore, the molten silicon reacts with the carbon source introduced by PIP-C to generate SiC matrix protective fiber bundles, preventing fiber bundle damage caused by excessive molten silicon filling the pores in the single RMI process. This balances rapid densification and mechanical properties of the countersunk part. After rapid densification to near the required density of the finished product through capillary adsorption, dimensional finishing is performed. Finally, CVI-SiC is used to fill and finish the surface micropores, ensuring that the appearance of large countersunk screws meets the requirements.

[0018] 2. This technology is applicable to the processing of countersunk screws with various countersunk angles (90°, 60°, and 55°), and is especially suitable for the preparation of large-size countersunk screws with thread specifications of M10 and above, and the processing morphology is more complete. Attached Figure Description

[0019] Figure 1 This is a process flow diagram of the present invention; Figure 2 Schematic diagram of a prefabricated flat countersunk screw; Figure 3 Schematic diagram of countersunk screw strips; Figure 4 Schematic diagram of countersunk screw bar stock; Figure 5 This is a schematic diagram of the precision machining of countersunk screws. Detailed Implementation

[0020] 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.

[0021] Figures 2-4 In this diagram, Dk is the maximum countersunk diameter; D is the nominal diameter of the screw; L is the total length; B is the screw length; E is the thread length; α is the countersunk angle; and M is the thread specification.

[0022] CVI: Chemical Vapor Deposition, PIP: Precursor Impregnation Pyrolysis, RMI: Reactive Melt Infiltration.

[0023] Example 1: A large-size countersunk screw made of ceramic matrix composite material has a thread specification of M12, a total length L of 20 mm, a screw length B of 16 mm, a thread length E of 10 mm, a countersunk angle α of 90°, a maximum countersunk diameter Dk of 20 mm, and a nominal screw diameter D of 12 mm.

[0024] A rapid preparation method for large-size countersunk screws made of ceramic matrix composite materials includes the following steps: (see process flow diagram) Figure 1 ) (1) Plate CVI: A flat ceramic matrix composite preform (see Figure 2 , Figure 2 (From top to bottom, the images are a top view and a front view.) A silicon carbide substrate was deposited using CVI, with a density of 1.4 g / cm³ obtained by the drainage method. 3 This yields a flat preform; (2) Processing strips: Along the layup direction of the ceramic matrix composite preform, the flat preform is processed into strips. The length of the strip is 12 mm longer than the total length of the countersunk screw, and the thickness and width of the strip are both 0.5 mm greater than the maximum countersunk diameter of the countersunk screw. The strips are then obtained (see...). Figure 3 , Figure 3 (From left to right, the front view and the side view are arranged as follows). Specifically: 2.1. Machining the upper and lower surfaces of the ceramic matrix composite preform plate on a surface grinder, with the allowance evenly distributed on both sides, ensuring that the thickness of the ceramic matrix composite preform plate is 20.5mm; 2.2 The ceramic matrix composite preform plate is processed into strips along the orthogonal direction of its shape. The strips are 32mm long, and the thickness and width of the strips are both 20.5mm. (3) CVI deposition: Silicon carbide substrate is deposited on the strip using CVI until the density by drainage method is 1.65 g / cm³. 3 The strip preform is obtained; (4) Turning bar stock: On a CNC lathe, the bar stock preform is installed on a four-jaw chuck, the dial indicator is used for alignment, and diamond tools are used to chamfer the bar stock into φ20.5mm round bar stock; Then, the round bar is mounted onto the three-jaw chuck of the CNC lathe, aligned using a dial indicator, and machined into a "convex" shaped stepped round bar. The diameter of the major diameter section of the stepped round bar is the same as the maximum countersunk diameter of the countersunk screw, φ20mm. The diameter of the minor diameter section of the stepped round bar is φ12.5mm, which is 0.5mm larger than the nominal diameter of the countersunk screw. The length of the minor diameter section of the stepped round bar is 16mm, which is the length of the countersunk screw. The length of the stepped round bar is 30mm, which is 10mm longer than the total length of the countersunk screw. The portion of the stepped round bar that is 10mm longer than the total length is the process head for clamping during subsequent threading (see...). Figure 4 ); (5) PIP-C: The stepped round bar is impregnated with a phenolic resin impregnation solution. The vacuum requirement is -0.03 MPa. The impregnation pressure is 1 MPa and held for 20 min. Then, it is cured (the impregnated ceramic matrix composite part is drained, placed in an oven, and kept at 180℃ for 2 h), pyrolyzed (vacuum requirement: 20 Pa, RT is raised to 1080℃ and held for 2 h, then cooled to RT in the furnace), and pyrolyzed (vacuum requirement: 20 Pa, RT is raised to 1900℃ and held for 4 h, then cooled to RT in the furnace) to obtain ceramic matrix composite parts; The phenolic resin impregnation solution was prepared by the following method: phenolic resin was dissolved in ethanol, then hexamethylenetetramine was added, followed by acetone, and finally the mixture was ball-milled at 200 r / min for 8 h to obtain a phenolic resin impregnation solution with a viscosity of 30 mPa·s; wherein the mass-volume ratio of phenolic resin, hexamethylenetetramine, ethanol and acetone was 43 g: 3.44 g: 100 mL: 20 mL; (6) RMI-Si: The small diameter of the ceramic matrix composite part is coated with boron nitride, the large diameter is facing down and embedded in the powder (silicon powder and silicon carbide powder are mixed in a mass ratio of 3:4), and the powder is compacted. RMI impregnation with silicon is performed. The vacuum degree requirement is 40 Pa. After the RT temperature is raised to 1480℃, it is kept at the temperature for 4 hours. Then it is cooled down to RT with the furnace and the appearance is cleaned. (7) Thread cutting: On a CNC lathe, clamp the process head on a three-jaw fixture, use a dial indicator to align, and machine the thread, nominal diameter of the screw, total length, screw length, and countersunk head to obtain a semi-finished product (see...). Figure 5 , Figure 5 In the middle, from left to right, are the front view and the side view. (8) CVI deposition: The semi-finished product is deposited with silicon carbide by CVI for 30 hours to obtain the finished product.

[0025] Example 2: A large-size countersunk screw made of ceramic matrix composite material has a thread specification of M14, a total length L of 22 mm, a screw length B of 18 mm, a thread length E of 10 mm, a countersunk angle α of 60°, a maximum countersunk diameter Dk of 18.6 mm, and a nominal screw diameter D of 14 mm.

[0026] A rapid preparation method for large-size countersunk screws made of ceramic matrix composite materials includes the following steps: (see process flow diagram) Figure 1 ) (1) Plate CVI: A plate-shaped ceramic matrix composite preform is deposited with silicon carbide matrix using CVI until the density by drainage method is 1.3 g / cm³. 3 This yields a flat preform; (2) Processing strips: Along the layup direction of the ceramic matrix composite preform, the flat preform is processed into strips. The length of the strip is 10 mm longer than the total length of the countersunk screw, and the thickness and width of the strip are both 0.4 mm greater than the maximum countersunk diameter of the countersunk screw. Specifically: 2.1. Machining the upper and lower surfaces of the ceramic matrix composite preform plate on a surface grinder, with the allowance evenly distributed on both sides, to ensure that the thickness of the ceramic matrix composite preform plate is 19mm; 2.2 The ceramic matrix composite preform plate is processed into strips along the orthogonal direction of its shape. The strips are 32mm long, and the thickness and width of the strips are both 19mm. (3) CVI deposition: Silicon carbide substrate is deposited on the strip using CVI until the density by drainage method is 1.55 g / cm³. 3 The strip preform is obtained; (4) Turning bar stock: On a CNC lathe, the bar stock preform is installed on a four-jaw chuck, the dial indicator is used for alignment, and diamond tools are used to chamfer the bar stock into φ19mm round bar stock; Then, the round bar is installed onto the three-jaw chuck of the CNC lathe, aligned with a dial indicator, and machined into a "convex" shaped stepped round bar. The diameter of the major diameter section of the stepped round bar is the same as the maximum countersunk diameter of the countersunk screw, which is φ18.6mm. The diameter of the minor diameter section of the stepped round bar is φ14.2mm, which is 0.2mm larger than the nominal diameter of the countersunk screw. The length of the minor diameter section of the stepped round bar is 18mm, which is the length of the countersunk screw. The length of the stepped round bar is 10mm longer than the total length of the countersunk screw, which is 32mm. The part of the stepped round bar that is 10mm longer than the total length is the clamping head for subsequent thread cutting. (5) PIP-C: The stepped round bar is impregnated with a phenolic resin impregnation solution. The vacuum requirement is -0.02 MPa. The impregnation pressure is 0.8 MPa and held for 20 min. Then, it is cured (the impregnated ceramic matrix composite part is drained, placed in an oven, and kept at 180℃ for 2 h), pyrolyzed (vacuum requirement: 20 Pa, RT is raised to 1100℃ and held for 2 h, then cooled to RT in the furnace), and pyrolyzed (vacuum requirement: 20 Pa, RT is raised to 1920℃ and held for 4 h, then cooled to RT in the furnace) to obtain ceramic matrix composite parts; The phenolic resin impregnation solution was prepared by the following method: phenolic resin was dissolved in ethanol, then hexamethylenetetramine was added, followed by acetone, and finally the mixture was ball-milled at 200 r / min for 8 h to obtain a phenolic resin impregnation solution with a viscosity of 40 mPa·s; wherein the mass-volume ratio of phenolic resin, hexamethylenetetramine, ethanol and acetone was 43 g: 3.44 g: 100 mL: 20 mL; (6) RMI-Si: The small diameter of the ceramic matrix composite part is coated with boron nitride, the large diameter is facing down and embedded in the powder (silicon powder and silicon carbide powder are mixed in a mass ratio of 3:4), and the powder is compacted. RMI impregnation with silicon is performed. The vacuum degree requirement is 40Pa. After the RT temperature is raised to 1520℃, it is kept at the temperature for 4 hours. Then it is cooled down to RT with the furnace and the appearance is cleaned. (7) Thread cutting: On a CNC lathe, install the clamping process head on a three-jaw tooling, use a dial indicator to align, and process the thread, nominal diameter of the screw, total length, screw length and countersunk head to obtain a semi-finished product; (8) CVI deposition: The semi-finished product is deposited with silicon carbide by CVI for 35 hours to obtain the finished product.

[0027] Example 3: A large-size countersunk screw made of ceramic matrix composite material has a thread specification of M14, a total length L of 22 mm, a screw length B of 18 mm, a thread length E of 10 mm, a countersunk angle α of 55°, a maximum countersunk diameter Dk of 18.2 mm, and a nominal screw diameter D of 14 mm.

[0028] A rapid preparation method for large-size countersunk screws made of ceramic matrix composite materials includes the following steps: (see process flow diagram) Figure 1 ) (1) Plate CVI: A silicon carbide matrix is ​​deposited on a flat ceramic matrix preform using CVI until the density by drainage method is 1.35 g / cm³. 3 This yields a flat preform; (2) Processing strips: Along the layup direction of the ceramic matrix composite preform, the flat preform is processed into strips. The length of the strip is 11 mm longer than the total length of the countersunk screw, and the thickness and width of the strip are both greater than the maximum countersunk diameter of the countersunk screw by 0.8 mm. Specifically: 2.1. Machining the upper and lower surfaces of the ceramic matrix composite preform plate on a surface grinder, with the allowance evenly distributed on both sides, to ensure that the thickness of the ceramic matrix composite preform plate is 19mm; 2.2 The ceramic matrix composite preform plate is processed into strips along the orthogonal direction of its shape. The strips are 33mm long, and the thickness and width of the strips are both 19mm. (3) CVI deposition: Silicon carbide substrate is deposited on the strip using CVI until the density by drainage method is 1.55 g / cm³. 3 The strip preform is obtained; (4) Turning bar stock: On a CNC lathe, the bar stock preform is installed on a four-jaw chuck, the dial indicator is used for alignment, and diamond tools are used to chamfer the bar stock into φ19mm round bar stock; Then, the round bar is installed onto the three-jaw chuck of the CNC lathe, aligned with a dial indicator, and machined into a "convex" shaped stepped round bar. The diameter of the major diameter section of the stepped round bar is the same as the maximum countersunk diameter of the countersunk screw, which is φ18.2mm. The diameter of the minor diameter section of the stepped round bar is φ14.3mm, which is 0.3mm larger than the nominal diameter of the countersunk screw. The length of the minor diameter section of the stepped round bar is 18mm, which is the length of the countersunk screw. The length of the stepped round bar is 10mm longer than the total length of the countersunk screw, which is 32mm. The part of the stepped round bar that is 10mm longer than the total length is the clamping head for subsequent thread cutting. (5) PIP-C: The stepped round bar is impregnated with a phenolic resin impregnation solution. The vacuum requirement is -0.01 MPa. The impregnation pressure is 0.5 MPa and held for 20 min. Then, it is cured (the impregnated ceramic matrix composite part is drained, placed in an oven, and kept at 180℃ for 2 h), pyrolyzed (vacuum requirement: 20 Pa, RT is raised to 1120℃ and held for 2 h, then cooled to RT in the furnace), and pyrolyzed (vacuum requirement: 20 Pa, RT is raised to 1880℃ and held for 4 h, then cooled to RT in the furnace) to obtain ceramic matrix composite parts; The phenolic resin impregnation solution was prepared by the following method: phenolic resin was dissolved in ethanol, then hexamethylenetetramine was added, followed by acetone, and finally the mixture was ball-milled at 200 r / min for 8 h to obtain a phenolic resin impregnation solution with a viscosity of 35 mPa·s; wherein the mass-volume ratio of phenolic resin, hexamethylenetetramine, ethanol and acetone was 43 g: 3.44 g: 100 mL: 20 mL; (6) RMI-Si: The small diameter of the ceramic matrix composite part is coated with boron nitride, the large diameter is facing down and embedded in the powder (silicon powder and silicon carbide powder are mixed in a mass ratio of 3:4), and the powder is compacted. RMI impregnation with silicon is performed. The vacuum degree requirement is 40 Pa. After the RT temperature is raised to 1500℃, it is kept at the temperature for 4 hours. Then it is cooled down to RT with the furnace and the appearance is cleaned. (7) Thread cutting: On a CNC lathe, install the clamping process head on a three-jaw tooling, use a dial indicator to align, and process the thread, nominal diameter of the screw, total length, screw length and countersunk head to obtain a semi-finished product; (8) CVI deposition: The semi-finished product is deposited with silicon carbide by CVI for 32 hours to obtain the finished product.

[0029] 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 rapid preparation method for large-size countersunk screws made of ceramic matrix composite materials, characterized in that, The steps are as follows: (1) Plate CVI: A silicon carbide matrix is ​​deposited on a flat ceramic matrix preform using CVI until the density by drainage method is 1.3-1.4 g / cm³. 3 This yields a flat preform; (2) Processing strips: Along the layup direction of the ceramic matrix composite preform, the flat preform is processed into strips. The length of the strip is 10-12 mm longer than the total length of the countersunk screw, and the thickness and width of the strip are 0.4-0.8 mm greater than the maximum countersunk diameter of the countersunk screw. (3) CVI deposition: Silicon carbide substrate is deposited on the strip using CVI until the density by drainage method is 1.55-1.65 g / cm³. 3 The strip preform is obtained; (4) Turning bar stock: On a CNC lathe, the strip preform is processed into round bar stock, and then processed into "convex" shaped stepped round bar stock. The diameter of the large diameter section of the stepped round bar stock is the same as the maximum diameter of the countersunk head of the countersunk screw. The diameter of the small diameter section of the stepped round bar stock is 0.2-0.5mm larger than the nominal diameter of the screw of the countersunk screw. The length of the small diameter section of the stepped round bar stock is the length of the screw of the countersunk screw. The length of the stepped round bar stock is 10mm more than the total length of the countersunk screw. (5) PIP-C: Stepped round bars are impregnated with phenolic resin impregnation solution, then cured, pyrolyzed and pyrolyzed to obtain ceramic matrix composite parts; (6) RMI-Si: The ceramic matrix composite parts are impregnated with silicon using RMI; (7) Thread cutting: On a CNC lathe, the threads, nominal diameter of the screw, total length, screw length and countersunk head are machined to obtain a semi-finished product; (8) CVI deposition: Silicon carbide is deposited on the semi-finished product using CVI to obtain the finished product.

2. The rapid preparation method for large-size countersunk screws made of ceramic matrix composite material according to claim 1, characterized in that, In step (5), the phenolic resin impregnation solution is prepared by dissolving phenolic resin in ethanol, then adding hexamethylenetetramine, then adding acetone, and finally ball milling.

3. The rapid preparation method for large-size countersunk screws made of ceramic matrix composite material according to claim 2, characterized in that, The mass-to-volume ratio of phenolic resin, hexamethylenetetramine, ethanol, and acetone was 43 g: 3.44 g: 100 mL: 20 mL.

4. The rapid preparation method for large-size countersunk screws made of ceramic matrix composite material according to claim 2, characterized in that, Ball milling was performed at 200 r / min for 8 hours.

5. The rapid preparation method for large-size countersunk screws made of ceramic matrix composite material according to claim 1, characterized in that, In step (5), the sample is immersed for 20 minutes at 0.5-1 MPa.

6. The rapid preparation method for large-size countersunk screws made of ceramic matrix composite material according to claim 1, characterized in that, In step (6), the small diameter of the ceramic matrix composite part is coated with boron nitride, the large diameter is facing down and embedded in the powder, and RMI impregnation with silicon is performed.

7. The rapid preparation method for large-size countersunk screws made of ceramic matrix composite material according to claim 6, characterized in that, The powder is prepared by mixing silicon powder and silicon carbide powder in a mass ratio of 3:

4.

8. The rapid preparation method of large-size countersunk screws made of ceramic matrix composite material according to claim 1, characterized in that, In step (6), the temperature is kept at 1480-1520℃ for 4 hours to complete the RMI impregnation of silicon.

9. The rapid preparation method of large-size countersunk screws made of ceramic matrix composite material according to claim 1, characterized in that, In step (8), deposition takes 30-35 hours.

10. A ceramic matrix composite large-size countersunk screw prepared by the rapid preparation method of the ceramic matrix composite large-size countersunk screw according to any one of claims 1-9.

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