Densification method for woven preform

Abstract

The invention discloses a densification method for weaving a prefabricated body. The densification method comprises the following steps: S1, preparing the prefabricated body; s2, primary vapor deposition: carrying out primary deposition coating on the preform by adopting a vapor deposition process; s3, primary rough machining, wherein the surface of the prefabricated body subjected to primary deposition coating is polished; s4, secondary vapor deposition: carrying out secondary deposition coating on the prefabricated body subjected to primary rough machining by adopting a vapor deposition process; s5, secondary rough machining, wherein the surface of the prefabricated body subjected to secondary deposition coating is polished; s6, circulating the steps S2-S5 until the thickness and the density of the prefabricated body are qualified; and S7, performing PIP circulation to obtain a finished product. According to the method, the density of the prefabricated body can reach the maximum value through the steps of multiple times of cyclic deposition and rough machining, and gaps caused by weaving can be basically filled. And the problem of high porosity caused by the vapor deposition process can be further solved by simultaneously using the PIP process for multiple times, so that the performances such as density, hardness and strength of the finished product are improved.

Description

Technical Field

[0001] The invention relates to the technical field of production of ceramic-based composite material products, and in particular to a densification method for a braided preform. Background Art

[0002] CVI / CVD is a commonly used chemical vapor deposition method, which is a process of generating solid thin films by introducing one or more gaseous precursors containing the required elements into the reaction chamber, causing chemical reactions on the collective surface. These gaseous precursors undergo chemical reactions such as decomposition and reduction under conditions such as high temperature, plasma excitation or light radiation, thereby depositing the required thin film material on the surface of the substrate, which can form a uniform and consistent coating on a relatively complex preform, increase the density of the preform, and make the subsequent solidification and cracking molding more stable.

[0003] At present, ceramic-based composite products are usually made by molding a single part and then assembling and riveting it. For parts with higher strength requirements or main load-bearing parts, multiple parts are generally stacked to form an assembly (an assembly refers to a stacked structure with ≥2 parts in the wall thickness direction) to improve the overall strength of the ceramic-based composite products.

[0004] When assembling an assembly, the surfaces of each part of the assembly need to be polished and repaired. After polishing, the density of a single part decreases significantly. The final density and uniformity are crucial to the final performance of the ceramic-based composite assembly. Uneven density of the assembly is difficult to meet production requirements, and it is imperative to increase density uniformity. Summary of the invention

[0005] The purpose of the present invention is to provide a method for densifying a braided preform, which can achieve a maximum density of the preform through multiple cycles of deposition and rough processing steps, and can basically fill the gaps caused by braiding. The use of multiple PIP processes at the same time can further solve the problem of high porosity caused by the vapor deposition process, thereby improving the density, hardness and strength of the finished product.

[0006] In order to solve the above technical problems, the present invention adopts the following solutions:

[0007] A densification method for a braided preform comprises the following steps:

[0008] S1: preparing a preform, using a ceramic-based fiber bundle to form a preform by twill weaving;

[0009] S2: initial vapor deposition, using a vapor deposition process to deposit a coating on the preform;

[0010] S3: initial rough machining, grinding the surface of the preform after the initial deposition coating;

[0011] S4: secondary vapor deposition, using a vapor deposition process to perform secondary deposition coating on the preform after the initial rough processing;

[0012] S5: secondary rough processing, grinding the surface of the preform after secondary deposition coating;

[0013] S6: loop S2-S5 until the thickness and density of the preform meet the requirements;

[0014] S7: PIP cycle to obtain the finished product.

[0015] In this method, first, high-quality ceramic-based fiber bundles are selected and woven into a preform with a predetermined structure and shape through precise twill weaving technology. This step ensures the basic strength and structural stability of the preform. The woven body formed by the weaving process will produce weaving gaps, which can also be called pores. Then, the vapor phase deposition technology is used to perform the initial coating deposition on the surface of the preform. This step forms a uniform coating by precisely controlling the vapor phase composition and deposition conditions to enhance the surface properties and interface bonding strength of the preform. However, the weaving gaps cannot be completely filled. Then, the preform after the initial coating deposition is polished, and the unfilled weaving gaps will be exposed. Then, the vapor phase deposition technology is used again to perform the coating deposition on the preform. Secondary coating deposition, secondary vapor deposition will fill the exposed weaving gaps, further enhancing the density and strength of the preform, and then the preform after the secondary coating deposition will be polished again until the unfilled weaving gaps are exposed, followed by vapor deposition for the third time, and then polished again, so that vapor deposition and polishing are continuously cycled until there is no weaving gap position in the preform after polishing, and then the coating is applied to the required thickness. At this time, the thickness and density of the preform are qualified. After completing the predetermined number of deposition and rough processing cycles, PIP cycle treatment is performed. This step further fills the weaving gaps (pores) inside the preform through polymer impregnation and cracking processes, improves the overall density and strength of the material, and finally obtains a finished product that meets the requirements. Through multiple cycles of deposition and rough processing steps, the density of the preform can reach the maximum value, and the gaps caused by weaving can be almost filled. The use of multiple PIP processes can also further solve the problem of high porosity caused by the vapor deposition process, thereby improving the density, hardness and strength of the finished product.

[0016] Optionally, when the preform is subjected to initial rough machining, it is ground until all pores on the preform are exposed, and the preform is densely filled for a second time through secondary interface sedimentation.

[0017] Optionally, in S3, during the secondary rough machining of the preform, the preform is polished again until all pores on the preform are exposed, and the interface is settled again to densely fill the preform again.

[0018] Optionally, in S3, when the preform is rough-machined, the grinding thickness is the thickness of the deposited coating.

[0019] Optionally, in S3 and S6, vapor deposition and rough machining are repeated multiple times until there are no pores on the surface of the preform after grinding, and the wall thickness of the preform is measured to see whether it meets the requirements. If so, the subsequent process is carried out. If not, the interface is again sedimented to the designed thickness before the subsequent process is carried out.

[0020] Optionally, in S3, the area, thickness and weight of the preform are measured, the density value is calculated, and compared with the theoretical density value, and within the measurement error range, it is determined whether there are pores on the surface of the preform.

[0021] Optionally, in S3, the vapor deposited material of the initial vapor deposition is boron nitride, the boron nitride vapor deposition process is 700-800℃ / 10±5h, the atmosphere gas is BCl3, the gas delivery rate is 1.5-2.5L / min, NH3, the gas delivery rate is 1.5-2.5L / min, argon, the gas delivery rate is 1.5-3.5L / min, and hydrogen gas delivery rate is 1.5-3.5L / min.

[0022] Optionally, in S3, the vapor deposit of the secondary vapor deposition is silicon nitride, the silicon nitride interface deposition process is 900-1100°C / / 30±10h, the atmosphere gas is methyltrichlorosilane, the gas delivery rate is 1-5L / min, nitrogen, the gas delivery rate is 1-5L / min, and hydrogen, the gas delivery rate is 1-5L / min.

[0023] Optionally, in S3, the PIP cycle includes impregnation, cracking, and curing. An impregnation liquid needs to be prepared before impregnation. The impregnation liquid reacts and bonds with the preform. The impregnation and curing are both carried out in a vacuum high-pressure impregnation tank. The cracking adopts a vacuum atmosphere box-type resistance furnace and a double-chamber horizontal oil-extracted gas-cooled vacuum furnace.

[0024] Optionally, in S3, the impregnation liquid is prepared in a ratio of xylene: polycarbosilane: DVB = 5:2:1, and the preform with qualified thickness and density is placed in the impregnation liquid to start the PIP process, the impregnation temperature is 30-60°C, the time is 1-1.5h, the pressure impregnation is 4±2Mpa, and then solidification is carried out, the curing temperature is 180-240°C / 4±1h, the curing pressure is 5.0±2.0Mpa, and finally cracking is carried out, the cracking temperature is 900-1300°C, and the cracking pressure is 0.05-0.07Mpa. The PIP process needs to be cycled multiple times.

[0025] The present invention has the beneficial effects:

[0026] 1. In the present invention, the density of the preform can reach the maximum value through multiple cycles of deposition and rough processing steps, and the gaps caused by weaving can be almost filled. The use of multiple PIP processes can further solve the problem of high porosity caused by the vapor deposition process, thereby improving the density, hardness, strength and other properties of the finished product. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic diagram of the process of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0029] In the description of the present invention, it should be noted that the terms "center", "up", "down", "left", "right", "vertical", "longitudinal", "lateral", "horizontal", "inside", "outside", "front", "back", "top", "bottom" and the like indicate directions or positional relationships based on the directions or positional relationships shown in the accompanying drawings, or are the directions or positional relationships in which the inventive product is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore should not be understood as a limitation on the present invention.

[0030] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "disposed", "opened", "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] Example

[0032] A densification method for a braided preform comprises the following steps:

[0033] S1: preparing a preform, using a ceramic-based fiber bundle to form a preform by twill weaving;

[0034] S2: initial vapor deposition, using a vapor deposition process to deposit a coating on the preform;

[0035] S3: initial rough machining, grinding the surface of the preform after the initial deposition coating;

[0036] S4: secondary vapor deposition, using a vapor deposition process to perform secondary deposition coating on the preform after the initial rough processing;

[0037] S5: secondary rough processing, grinding the surface of the preform after secondary deposition coating;

[0038] S6: loop S2-S5 until the thickness and density of the preform meet the requirements;

[0039] S7: PIP cycle to obtain the finished product.

[0040] In this embodiment, Figure 1 As shown, first, high-quality ceramic-based fiber bundles are selected and woven into a preform with a predetermined structure and shape through precise twill weaving technology. This step ensures the basic strength and structural stability of the preform. The woven body formed by the weaving process will produce weaving gaps, which can also be called pores. Then, the vapor phase deposition technology is used to perform the initial coating deposition on the surface of the preform. This step forms a uniform coating by precisely controlling the vapor phase composition and deposition conditions to enhance the surface properties and interface bonding strength of the preform. However, the weaving gaps cannot be completely filled. Then, the preform after the initial coating deposition is polished, and the unfilled weaving gaps will be exposed. Then, the vapor phase deposition technology is used again to perform the second coating deposition on the preform. The second coating is deposited, and the second vapor deposition is used to fill the exposed weaving gaps, further enhancing the density and strength of the preform. The preform after the second coating deposition is then polished again until the unfilled weaving gaps are exposed. Then vapor deposition is performed for the third time, and then polished again. The vapor deposition and polishing are continuously cycled until there is no weaving gap position in the preform after polishing, and then the coating is applied to the required thickness. At this time, the thickness and density of the preform are qualified. After completing the predetermined number of deposition and rough processing cycles, the PIP cycle treatment is performed. This step further fills the weaving gaps (pores) inside the preform through the polymer impregnation and cracking process, improves the overall density and strength of the material, and finally obtains a finished product that meets the requirements. Through multiple cycles of deposition and rough processing steps, the density of the preform can reach the maximum value, and the gaps caused by the weaving can be almost filled. The use of multiple PIP processes can also further solve the problem of high porosity caused by the vapor deposition process, thereby improving the density, hardness and strength of the finished product.

[0041] Furthermore, when the preform is subjected to the initial rough machining, it is ground until all pores on the preform are exposed, and the preform is densely filled for a second time through secondary interface sedimentation.

[0042] Furthermore, in S3, during the secondary rough machining of the preform, the preform is polished again until all pores on the preform are exposed, and the interface is settled again to densely fill the preform again.

[0043] Furthermore, in S3, when the preform is rough-machined, the grinding thickness is the thickness of the deposited coating.

[0044] Specifically, high-quality ceramic-based fiber bundles are used to weave into a preform with a predetermined structure and shape through precise twill weaving technology. The vapor phase deposition technology is used to deposit the initial coating on the surface of the preform to form a uniform and dense coating. The preform after the initial coating deposition is polished until all pores are completely exposed. The pores are equivalent to the weaving gaps. The purpose of this step is to prepare for the subsequent secondary dense filling to ensure that the coating can penetrate into every pore of the preform. The grinding thickness should be equal to or slightly greater than the thickness of the initial deposition coating to ensure that the coating is completely removed without damaging the basic structure of the preform. A secondary coating is deposited on the preform after the initial rough machining. The vapor deposition technology is used to precisely control the deposition parameters and process conditions to achieve further optimization and enhancement of the coating. The preform is densely filled for a second time, which can fill a part of the pores. The preform after the secondary coating deposition is polished again until all the pores are completely exposed. The purpose of this step is to ensure that the tertiary coating can also penetrate into every pore of the preform, further improving the density and strength of the preform. The grinding thickness should also be equal to or slightly greater than the thickness of the secondary deposition coating to ensure that the coating is completely removed while keeping the overall structure of the preform intact. According to the final thickness and density requirements of the preform, steps S2 to S5 are repeated until the predetermined performance indicators are reached. Each cycle includes coating deposition, rough machining and pore exposure to ensure the overall performance and uniformity of the preform. After completing the predetermined deposition and rough machining cycles, PIP cycle treatment is performed. Through the polymer impregnation and cracking process, the pores inside the preform are further filled, the overall density and strength of the material are improved, and finally a finished product that meets the requirements is obtained.

[0045] Further, in S3 and S6, vapor deposition and rough machining are repeated for multiple cycles until there are no pores on the surface of the preform after grinding, and the wall thickness of the preform is measured to see whether it meets the requirements. If so, the subsequent process is carried out. If not, the interface is again sedimented to the designed thickness before the subsequent process is carried out.

[0046] Furthermore, in S3, the area, thickness and weight of the preform are measured, the density value is calculated, and compared with the theoretical density value, and within the measurement error range, it is determined whether there are pores on the surface of the preform.

[0047] Specifically, in step S3, the vapor deposition and rough processing of the preform are mainly carried out, and the surface quality and dimensional parameters of the preform are paid attention to in the process. In step S3, a vapor deposition process is firstly carried out for multiple cycles to ensure the compactness of the internal structure of the preform. Subsequently, rough processing is carried out, including removing excess material and preliminary grinding. In this process, it is necessary to continuously observe and check the surface state of the preform to ensure that there are no more pores on the surface of the preform after multiple grindings. After grinding, the wall thickness of the preform is measured using a precision measuring tool to ensure that it meets the design requirements. In addition, in step S3, the area, thickness and weight of the preform need to be accurately measured. According to these measured values, the actual density value of the preform is calculated and compared with the theoretical density value. Within the allowable measurement error range, if the actual density value is consistent with the theoretical density value, it is further judged that the surface of the preform is completely free of pores. The purpose of this step is to ensure that the overall quality and performance of the preform meet the requirements of subsequent processes. In step S6, if the preform wall thickness after step S3 still does not meet the design requirements, additional adjustments are required. The specific method is to perform interface sedimentation treatment again until the preform wall thickness reaches the design thickness. This process needs to be repeated until all size and quality requirements are met before subsequent processing can be carried out.

[0048] Furthermore, in S3, the vapor deposited material of the initial vapor deposition is boron nitride, the boron nitride vapor deposition process is 700-800℃ / 10±5h, the atmosphere gas is BCl3, the gas delivery rate is 1.5-2.5L / min, NH3, the gas delivery rate is 1.5-2.5L / min, argon, the gas delivery rate is 1.5-3.5L / min, and hydrogen gas delivery rate is 1.5-3.5L / min.

[0049] Furthermore, in S3, the vapor deposit of the secondary vapor deposition is silicon nitride, the silicon nitride interface deposition process is 900-1100°C / / 30±10h, the atmosphere gas is methyltrichlorosilane, the gas delivery rate is 1-5L / min, nitrogen, the gas delivery rate is 1-5L / min, and hydrogen, the gas delivery rate is 1-5L / min.

[0050] Furthermore, in S3, the PIP cycle includes impregnation, cracking, and solidification. Before impregnation, an impregnation liquid needs to be prepared. The impregnation liquid reacts and bonds with the preform. The impregnation and solidification are both carried out in a vacuum high-pressure impregnation tank. The cracking adopts a vacuum atmosphere box-type resistance furnace and a double-chamber horizontal oil-extracted gas-cooled vacuum furnace.

[0051] Further, in S3, the impregnation liquid is prepared in the ratio of xylene: polycarbosilane: DVB = 5:2:1, and the preform with qualified thickness and density is placed in the impregnation liquid to start the PIP process, the impregnation temperature is 30-60°C, the time is 1-1.5h, the pressure impregnation is 4±2Mpa, and then solidification is performed, the solidification temperature is 180-240°C / 4±1h, the solidification pressure is 5.0±2.0Mpa, and finally cracking is performed, the cracking temperature is 900-1300°C, the cracking pressure is 0.05-0.07Mpa, and the PIP process needs to be cycled multiple times. Using multiple PIP processes can also further solve the problem of high porosity caused by the vapor deposition process, thereby improving the density, hardness and strength of the finished product.

[0052] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any form. According to the technical essence of the present invention, within the spirit and principles of the present invention, any simple modification, equivalent replacement and improvement made to the above embodiment still falls within the protection scope of the technical solution of the present invention.

Claims

1. A densification method for a braided preform, characterized in that: The following steps are involved: S1: preparing a preform, using a ceramic-based fiber bundle to form a preform by twill weaving; S2: initial vapor deposition, using a vapor deposition process to deposit a coating on the preform; S3: initial rough machining, grinding the surface of the preform after the initial deposition coating; S4: secondary vapor deposition, using a vapor deposition process to perform secondary deposition coating on the preform after the initial rough processing; S5: secondary rough processing, grinding the surface of the preform after secondary deposition coating; S6: loop S2-S5 until the thickness and density of the preform meet the requirements; S7: PIP cycle to obtain the finished product.

2. A densification method for a braided preform according to claim 1, characterized in that: When the preform is subjected to the initial rough machining, it is ground until all the pores on the preform are exposed, and the preform is filled with secondary density through secondary interface sedimentation.

3. A densification method for a braided preform according to claim 1, characterized in that: In S3, during the secondary rough machining of the preform, the preform is polished again until all pores on the preform are exposed, and the interface is settled again to densely fill the preform again.

4. A densification method for a braided preform according to claim 1, characterized in that: In S3, when the preform is rough-machined, the grinding thickness is the thickness of the deposited coating.

5. A densification method for a braided preform according to claim 1, characterized in that: In S3 and S6, vapor deposition and rough machining are repeated for multiple times until there are no pores on the surface of the preform after grinding, and the wall thickness of the preform is measured to see whether it meets the requirements. If so, the subsequent process is carried out. If not, the interface is again deposited to the designed thickness before the subsequent process is carried out.

6. A densification method for a braided preform according to claim 5, characterized in that: In S3, the area, thickness and weight of the preform are measured, the density value is calculated, and compared with the theoretical density value. Within the measurement error range, it is determined whether there are pores on the surface of the preform.

7. A densification method for a braided preform according to claim 1, characterized in that: In S3, the vapor deposited material of the initial vapor deposition is boron nitride, the boron nitride vapor deposition process is 700-800℃ / 10±5h, the atmosphere gas is BCl3, the gas delivery rate is 1.5-2.5L / min, NH3, the gas delivery rate is 1.5-2.5L / min, argon, the gas delivery rate is 1.5-3.5L / min, and hydrogen gas delivery rate is 1.5-3.5L / min.

8. A densification method for a braided preform according to claim 1, characterized in that: In S3, the vapor deposit of the secondary vapor deposition is silicon nitride, the silicon nitride interface deposition process is 900-1100°C / / 30±10h, the atmosphere gas is methyltrichlorosilane, the gas delivery rate is 1-5L / min, nitrogen, the gas delivery rate is 1-5L / min, and hydrogen, the gas delivery rate is 1-5L / min.

9. A densification method for a braided preform according to claim 1, characterized in that: In S3, the PIP cycle includes impregnation, cracking, and solidification. The impregnation liquid needs to be prepared before impregnation. The impregnation liquid reacts with the preform and bonds them together. The impregnation and solidification are both carried out in a vacuum high-pressure impregnation tank. The cracking adopts a vacuum atmosphere box-type resistance furnace and a double-chamber horizontal oil-extracted gas-cooled vacuum furnace.

10. A densification method for a braided preform according to claim 9, characterized in that: In S3, the impregnation liquid is prepared in a ratio of xylene: polycarbosilane: DVB = 5:2:1, and the preform with qualified thickness and density is placed in the impregnation liquid to start the PIP process. The impregnation temperature is 30-60°C, the time is 1-1.5h, the pressure impregnation is 4±2Mpa, and then solidification is carried out. The curing temperature is 180-240°C / 4±1h, and the curing pressure is 5.0±2.0Mpa. Finally, cracking is carried out. The cracking temperature is 900-1300°C and the cracking pressure is 0.05-0.07Mpa. The PIP process needs to be cycled multiple times.

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