Preparation method of SiC / SiBCN ceramic matrix composite box with inner boss

Abstract

The invention relates to a preparation method of a composite material box body with an inner boss, in particular to a preparation method of a SiC / SiBCN ceramic matrix composite material box body with an inner boss. In order to overcome the defects that in the prior art, the preparation process of a composite box body with an inner boss is complex, holes are formed in areas with different thicknesses, and hole filling fiber bundles are prone to deformation and dislocation after being pressed, so that the structure is unstable. The preparation method of the SiC / SiBCN ceramic matrix composite box with the inner boss sequentially comprises the steps of SiC fiber prefabricated body preparation, high-temperature treatment, boron nitride interface layer preparation, Si3N4 matrix deposition, SiBCN matrix preparation, Si3N4 matrix deposition and the like, the SiC fiber prefabricated body is prepared from a U-shaped prefabricated body, a concentric-square-shaped prefabricated body and an exterior prefabricated body, and the stability of the mounting boss is improved.

Description

Technical Field

[0001] This invention relates to a method for preparing a composite material box with an inner boss, specifically a method for preparing a SiC / SiBCN ceramic matrix composite material box with an inner boss. Background Technology

[0002] In aerospace, flame stabilizers are commonly located at the engine's exhaust nozzle, serving to stabilize the flame flow. Since flame stabilizers are typically exposed outside the engine, they must also possess wave-absorbing capabilities to support electromagnetic radiation. Furthermore, the working parts of the flame stabilizer must be heat-resistant and oxidation-resistant. SiC fiber-reinforced SiBCN ceramic matrix composites have great potential for application in high-temperature engine components requiring wave absorption due to their heat resistance, oxidation resistance, tunable dielectric properties, and electromagnetic wave absorption capabilities. Common wave-absorbing ceramic matrix composites primarily absorb electromagnetic waves by introducing absorbents into the ceramic matrix or by alternating layers of ceramics with different dielectric properties on the surface of the composite. However, their fabrication process is complex due to issues such as uniform absorbent dispersion and weak interlayer bonding.

[0003] Flame stabilizers are typically box-shaped structures with internal bosses. When made using SiC fiber-toughened ceramic matrix composites, in areas of unequal thickness within the box, due to the continuity of fiber cloth layup, there are areas where the thickness of the unequal thickness exceeds that of other areas, making it impossible to lay the fiber cloth and creating holes. To solve this problem, existing methods fill the hole areas with fiber bundles. However, the fiber bundles deform and misalign during the extrusion process, failing to completely fill the holes and resulting in significant internal defects in the parts, leading to structural instability. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies, such as the complex preparation process of composite material boxes with internal bosses, the formation of holes in areas of unequal thickness, and the easy deformation and misalignment of fiber bundles filled with these holes under pressure, leading to structural instability. This invention provides a method for preparing SiC / SiBCN ceramic matrix composite material boxes with internal bosses.

[0005] To achieve the above objectives, the technical solution provided by this invention is as follows: A method for preparing a SiC / SiBCN ceramic matrix composite box with an inner boss, wherein the SiC / SiBCN ceramic matrix composite box with an inner boss includes a hollow shell and mounting bosses disposed on its inner wall; the method is characterized by including the following steps: Step 1: Obtain a SiC fiber preform of a SiC / SiBCN ceramic matrix composite box with an inner boss; The SiC fiber preform includes an inner U-shaped preform, a spiral preform, and a hollow outer preform. The inner U-shaped preform and the spiral preform are embedded into the outer preform from top to bottom. The bottom of the inner U-shaped preform is attached to the top of the spiral preform. Molds are provided for support. The attached parts of each preform are sewn together. The molds are removed and the attached parts of the bottom of the inner U-shaped preform and the spiral preform are processed to obtain mounting bosses, thereby obtaining the SiC fiber preform. Corresponding molds are set in the SiC fiber preform. Step 2: High-temperature treatment of the SiC fiber preform; Step 3: Prepare a boron nitride interface layer on the surface of the preform fiber; Step 4: Deposit Si3N4 matrix on the surface of SiC fiber preform with boron nitride interface layer to obtain semi-densified preform; Step 5: Remove the mold supporting the semi-dense preform; Step 6: Prepare a SiBCN matrix on a semi-densified preform using a precursor impregnation pyrolysis process to obtain a box structure of SiC / SiBCN ceramic matrix composite material; Step 7: Deposit Si3N4 matrix on the surface of the SiC / SiBCN ceramic matrix composite box structure to fill the pores in the SiBCN matrix, thereby obtaining a densified SiC / SiBCN ceramic matrix composite box with internal bosses.

[0006] Further, in step 1, the outer side of the corners of the inner U-shaped prefabricated body and the inner side of the connecting part of the U-shaped prefabricated body is a right angle transition and the inner side is an R-angle transition, which is defined as an area of ​​unequal thickness. Specifically, it is achieved by the following method: the inner side of the corner near the R-angle transition area is formed by laying multiple layers of whole fabric continuously with the flat part to obtain the R-angle, while the outer right angle transition area is formed by laying two pieces of fiber fabric horizontally and vertically to create the right angle. The middle area between the R-angle transition area and the right angle transition area is increased by laying continuous layers of fiber fabric horizontally and vertically to increase the wall thickness.

[0007] Furthermore, step 6 specifically includes: Step 6.1, impregnation of the precursor; The SiC fiber preform with boron nitride interface layer is completely immersed in a polyborosilicate precursor solution. A vacuum is drawn, with a vacuum pressure not exceeding -0.08 MPa, and the vacuum is continued until no more bubbles emerge from the polyborosilicate precursor solution. Step 6.2, precursor curing; The impregnated SiC fiber preform is pre-cured by holding it at 80~100℃ for 3~12h, and then the temperature is raised to 180~200℃ and held for 1~2h to complete the preform curing. Step 6.3, exhaust the precursor gas; The SiC fiber preform that has completed precursor curing is vented under vacuum to remove the gas generated during curing. The vacuum pressure is no greater than -0.08 MPa, and the venting is continued for 30~60 minutes. Step 6.4, precursor lysis; In a nitrogen atmosphere, the SiC fiber preform after exhaust is heated to 900~1000℃ and held at that temperature for 1~2h for pyrolysis, and then cooled to room temperature at a rate of 2~3℃ / min to obtain a box structure of SiC / SiBCN ceramic matrix composite material.

[0008] Furthermore, in step 6.1, the mass concentration of the polyborosilicate precursor solution is 20%~30%.

[0009] Furthermore, step 6 also includes step 6.5, repeating steps 6.1-6.4 multiple times, so that the density of the SiC / SiBCN ceramic matrix composite material reaches 2.1~2.2 g / cm³. 3 .

[0010] Furthermore, in step 1, the planar portions of the inner U-shaped precast body, the loop-shaped precast body, and the outer precast body are all provided with equal wall thickness.

[0011] Furthermore, step 2 specifically involves: The SiC fiber preform is held at 1200℃~1350℃ in an inert gas atmosphere for 1~2 hours, and then cooled down in the furnace to complete the high-temperature treatment.

[0012] Furthermore, step 4 specifically involves: A Si3N4 matrix was deposited on the surface of a SiC fiber preform with a boron nitride interface layer using chemical vapor deposition. Through multiple rounds of deposition, the density of the semi-densified preform was reduced to 1.6–1.7 g / cm³. 3 .

[0013] Furthermore, in step 3, the boron nitride interface layer is prepared by chemical vapor deposition, and the thickness of the interface layer is 300~500 nm.

[0014] Furthermore, in step 7, a Si3N4 matrix is ​​deposited using chemical vapor deposition to achieve a density of 2.3 g / cm³ for the SiC / SiBCN ceramic matrix composite material. 3 above.

[0015] The beneficial effects of this invention are: 1. In this invention, the SiC / SiBCN ceramic matrix composite box with an inner boss is disassembled into U-shaped preforms, U-shaped preforms, and external preforms, and then combined to obtain the corresponding SiC fiber preforms, so that the mounting boss and the box are integrated into one structure, improving the stability of the mounting boss and making it easy to form complex structures.

[0016] 2. In this invention, the SiC / SiBCN ceramic matrix composite material is prepared by using a precursor impregnation pyrolysis process to create the SiBCN matrix, followed by the preparation of a Si3N4 matrix to fill the voids generated during the precursor impregnation pyrolysis process. The resulting box-shaped structure exhibits good compositional uniformity and will play a more important role in future aero-engine applications. This invention selects both the boron nitride interface layer and the Si3N4 matrix as the main components of the SiC / SiBCN ceramic matrix composite material, avoiding the introduction of other components that could disrupt the material's uniformity.

[0017] 3. In this invention, a special fiber layup method is used at the corner of the mounting boss to achieve a right-angle transition on the outside of the corner, a rounded corner transition on the inside, and a uniform transition in areas of unequal thickness. This ensures the continuous setting of the mounting boss and the fiber cloth as much as possible, improving structural stability. At the same time, this invention uses an alternating layering method of fiber cloth on both sides in areas of unequal thickness, which effectively solves the problem of voids caused by unstable fiber bundles.

[0018] 4. This invention uses a boron nitride interface layer as a transition layer between SiC fibers and the matrix. The boron nitride interface layer has a self-healing function, which can repair microcracks generated in the material during use, improve the service life of the material, and the boron nitride interface has the same composition as the matrix material, so it will not affect the microwave absorption performance of the matrix material.

[0019] 5. This invention adds the preparation of a Si3N4 matrix by chemical vapor deposition before the precursor impregnation and pyrolysis process, so that the SiC fiber preform reaches a semi-densified state. This allows the mold to be removed during the precursor impregnation and pyrolysis process, reducing the number of repetitions of the precursor impregnation and pyrolysis process and improving the mechanical properties of the product.

[0020] 6. In the precursor impregnation pyrolysis process, the present invention adopts segmented curing and adds a pre-curing stage. The pre-curing stage has a lower temperature and a longer duration, which allows the impregnated precursor to undergo a slow chemical reaction, so that the generated small molecule gas can escape from the surface of the precursor, reducing the gas inside the precursor after curing. Then the temperature is raised to reach the curing temperature of the precursor, so that the precursor is completely cured.

[0021] 7. In the SiBCN matrix precursor impregnation and pyrolysis process of this invention, vacuum impregnation, segmented curing, degassing of the precursor after curing, and low-temperature short-time pyrolysis are employed. After the SiBCN matrix is ​​prepared, Si3N4 matrix is ​​used to fill the gaps generated by the precursor pyrolysis. All of these measures are aimed at reducing the generation of large pores inside the SiBCN matrix during the preparation process. By reducing the large pores, the large pores are divided into smaller micropores, increasing the density of the absorbing material and increasing the number of micropores in the SiBCN matrix. This increases the multiple scattering and reflection of electromagnetic waves, extends the propagation path, and enhances absorption. The more micropores there are, the more reflections occur, which is more conducive to the absorption of low-frequency electromagnetic waves. This invention broadens the low-frequency absorption band of SiC / SiBCN ceramic matrix composites, enabling SiC / SiBCN ceramic matrix composites to have absorption performance in the 1~18GHz frequency range. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the flame stabilizer in an embodiment of the present invention; Figure 2 This is an exploded view of the prefabricated components of the flame stabilizer in an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure of the SiC fiber preform of the flame stabilizer in an embodiment of the present invention; Figure 4 This is a schematic diagram of the uneven thickness region of the flame stabilizer in an embodiment of the present invention; wherein, (a) is a cross-sectional view of the SiC fiber preform, and (b) is a schematic diagram of the layup at point A in (a); Figure 5 This is a process flow diagram of an embodiment of the present invention; Figure 6 The image shows the test results of the material absorption performance of the flame stabilizer in an embodiment of the present invention.

[0023] Explanation of reference numerals in the attached figures: 1-Flame stabilizer, 2-Inner U-shaped preform, 3-U-shaped preform, 4-Outer preform. Detailed Implementation

[0024] This invention provides a method for preparing a box-shaped structure with an internal boss made of SiC / SiBCN ceramic matrix composite material. This embodiment takes the flame stabilizer 1 of an aero-engine as an example to illustrate the specific preparation method steps.

[0025] Figure 1The diagram shows the structure of flame stabilizer 1, which is a U-shaped three-sided box, including a hollow shell and mounting bosses on its inner wall. The mounting bosses facilitate the connection and assembly of flame stabilizer 1 with the engine. The flame stabilizer prefabrication body is formed by piercing two-dimensional plain-weave SiC fiber cloth. The mounting bosses are the docking points between flame stabilizer 1 and the engine. Since the force transmission between flame stabilizer 1 and the engine mainly occurs through the bosses, the material strength requirements between the mounting bosses and the hollow shell are high. The connection strength of the ceramic matrix composite material is mainly provided by the fiber reinforcement. To improve the material strength between the mounting bosses and the hollow shell, the fiber cloth of the mounting bosses must be continuously arranged with the fiber cloth of the hollow shell.

[0026] Figure 2 The diagram shows the structure of each preform in the process of manufacturing the flame stabilizer 1, including an inner U-shaped preform 2, a spiral preform 3, and a hollow outer preform 4. In this embodiment, the outer preform 4 is set as a U-shaped preform. Each preform is made of two-dimensional plain weave SiC fiber cloth. Finally, the inner U-shaped preform 2 and the spiral preform 3 are embedded into the outer preform 4 from top to bottom. The bottom of the inner U-shaped preform 2 is attached to the top of the spiral preform 3. The attached parts of the three preforms are sewn together with fiber bundles of the same material. Finally, the excess material on the attached parts of the inner U-shaped preform 2 and the spiral preform 3 is processed and removed to obtain the mounting boss, thereby obtaining the complete SiC fiber preform of the flame stabilizer 1.

[0027] Figure 3 The image shows the SiC fiber preform of the flame stabilizer 1. The inner U-shaped preform 2 and the U-shaped preform 3 meet at the surface where the mounting boss is located. By using the inner U-shaped preform 2 and the U-shaped preform 3, the continuity of the fibers between the mounting boss and the stabilizer body is ensured, thereby guaranteeing the strength of the mounting boss. During the fabrication of the SiC fiber preform, except for the machining of the mounting boss, molds are always placed inside each part of the preform to ensure that its shape meets the design requirements.

[0028] Figure 4 The inner U-shaped precast body 2, the loop-shaped precast body 3, and the outer precast body 4 shown have uniform wall thickness in their planar portions. At the corners where the inner U-shaped precast body 2 and the loop-shaped precast body 3 meet, the outer side has a right-angle transition, while the inner side has an R-angle transition, creating areas of unequal thickness. To address these unequal thickness areas using two-dimensional plain-weave SiC fiber cloth, local padding is used in areas with thicker walls, such as... Figure 4As shown, the inner side of the corner near the R-corner transition area is formed by laying out multiple layers of fabric continuously with the flat part to obtain the R-corner. The outer right-angle transition area is formed by laying out two pieces of fiber fabric horizontally and vertically to create the right angle. The middle area between the R-corner transition area and the right-angle transition area is formed by stacking fiber fabric laid from the two sides with the same wall thickness to increase the wall thickness. This method achieves unequal thickness fiber lay-up in the inner rounded corner and the outer right-angle area.

[0029] Figure 5 The flowchart shown is a process for preparing the SiC / SiBCN ceramic matrix composite box with an inner boss according to the present invention. Taking the flame stabilizer 1 mentioned above as an example, the specific steps include: Step 1: Obtain the SiC fiber preform of flame stabilizer 1; Step 2, high-temperature treatment; The SiC fiber preform with mold is kept at 1200℃~1350℃ in an inert gas atmosphere for 1~2 hours, and then cooled in the furnace to complete the high-temperature treatment of the preform.

[0030] Step 3, preparation of the interface layer; A boron nitride interface layer with a thickness of 300-500 nm was prepared on the surface of SiC fiber preforms by chemical vapor deposition.

[0031] Step 4, Si3N4 substrate deposition; A Si3N4 matrix was deposited on the surface of a SiC fiber preform with a boron nitride interface layer using chemical vapor deposition. Multiple deposition cycles were performed to increase the density of the SiC fiber preform, achieving a density of 1.6–1.7 g / cm³. 3 A semi-densified preform is obtained; Step 5, demolding; Remove the mold that supports the semi-dense preform.

[0032] Step 6, precursor impregnation and lysis; For the preform obtained by puncturing two-dimensional plain-weave SiC fiber fabric, this embodiment selects polyborosilazane as a precursor and prepares a SiBCN matrix on the semi-densified SiC fiber preform through a precursor impregnation and pyrolysis process to obtain a box structure of SiC / SiBCN ceramic matrix composite material.

[0033] The precursor impregnation and pyrolysis process for preparing SiBCN matrix mainly includes four steps: precursor impregnation, precursor curing, precursor degassing, and precursor pyrolysis. Specifically: Precursor impregnation: Vacuum-assisted impregnation is used to completely impregnate the SiC fiber preform with the mold in a 20%~30% polyborosilicate precursor solution. Then, a vacuum is drawn with a pressure not exceeding -0.08 MPa. The vacuum is continued until no obvious bubbles emerge from the precursor solution. After impregnation is completed, the precursor is cured.

[0034] Precursor curing: The impregnated SiC fiber preform with mold is placed in an oven and heated to 80~100℃ for precuring and kept at that temperature for 3~12h. Then, the temperature is raised to 180~200℃ and kept at that temperature for 1~2h to complete the precursor curing.

[0035] Precursor venting: Small molecule gases formed by the solidification of the precursor will exist inside the preform. The solidified preform is placed in a pyrolysis furnace, and the gases generated during solidification are vented by continuously drawing a vacuum for 30-60 minutes. The vacuum pressure throughout the process does not exceed -0.08 MPa. Precursor pyrolysis: The pyrolysis furnace is heated to 900~1000℃ and held for 1~2 hours, then cooled to room temperature at a rate of 2~3℃ / min. The entire pyrolysis process requires nitrogen flow protection to prevent oxidation of the precursor during pyrolysis.

[0036] The aforementioned precursor impregnation and pyrolysis process was repeated 3-5 times to increase the density of the SiC / SiBCN ceramic matrix composite material. Each repetition maintained the same process as described above. After the precursor impregnation and pyrolysis process was completed, the box-like structure density of the SiC / SiBCN ceramic matrix composite material reached 2.1-2.2 g / cm³. 3 .

[0037] Step 7, Si3N4 substrate deposition; A Si3N4 matrix was deposited on the surface of a SiC / SiBCN ceramic matrix composite box structure using chemical vapor deposition (CVD) to fill the pores in the SiBCN matrix, achieving a SiC / SiBCN ceramic matrix composite density of 2.3 g / cm³. 3 The above yields flame stabilizer 1.

[0038] Figure 6 The image shows the radar reflectivity test results of the flame stabilizer 1 prepared in this embodiment in the 1~18GHz frequency band. In the frequency range of 1~18GHz, the SiC / SiBCN ceramic matrix composite material has wave absorption performance.

Claims

1. A method for preparing a SiC / SiBCN ceramic matrix composite box with an inner boss, wherein the SiC / SiBCN ceramic matrix composite box with an inner boss comprises a hollow shell and mounting bosses disposed on its inner wall; characterized in that, Includes the following steps: Step 1: Obtain a SiC fiber preform of a SiC / SiBCN ceramic matrix composite box with an inner boss; The SiC fiber preform includes an inner U-shaped preform (2), a spiral preform (3), and a hollow outer preform (4). The inner U-shaped preform (2) and the spiral preform (3) are embedded into the outer preform (4) from top to bottom. The bottom of the inner U-shaped preform (2) is attached to the top of the spiral preform (3). Molds for support are provided in each part to sew the attached parts of each part of the preform together. The molds are removed and the attached parts of the bottom of the inner U-shaped preform (2) and the spiral preform (3) are processed to obtain the mounting boss, and then the SiC fiber preform is obtained. A corresponding mold is set in the SiC fiber preform. Step 2: High-temperature treatment of the SiC fiber preform; Step 3: Prepare a boron nitride interface layer on the surface of the preform fiber; Step 4: Deposit Si3N4 matrix on the surface of SiC fiber preform with boron nitride interface layer to obtain semi-densified preform; Step 5: Remove the mold supporting the semi-dense preform; Step 6: Prepare a SiBCN matrix on a semi-densified preform using a precursor impregnation pyrolysis process to obtain a box structure of SiC / SiBCN ceramic matrix composite material; Step 7: Deposit Si3N4 matrix on the surface of the SiC / SiBCN ceramic matrix composite box structure to fill the pores in the SiBCN matrix, thereby obtaining a densified SiC / SiBCN ceramic matrix composite box with internal bosses.

2. The method for preparing a SiC / SiBCN ceramic matrix composite box with an inner boss according to claim 1, characterized in that: In step 1, the outer side of the corners of the inner U-shaped prefabricated body (2) and the inner side of the U-shaped prefabricated body (3) is a right angle transition and the inner side is an R-angle transition, which is defined as an area of ​​unequal thickness. Specifically, it is achieved by the following method: the inner side of the corner is close to the R-angle transition area by using a multi-layer whole fabric continuous with the flat part to obtain the R-angle, and the outer right angle transition area is made by using two pieces of fiber cloth horizontally and vertically to lay out the right angle. The middle area between the R-angle transition area and the right angle transition area is increased by stacking fiber cloth with continuous horizontal and vertical layers.

3. The method for preparing a SiC / SiBCN ceramic matrix composite box with an inner boss according to claim 1 or 2, characterized in that, Step 6 specifically involves: Step 6.1, impregnation of the precursor; The SiC fiber preform with boron nitride interface layer is completely immersed in a polyborosilicate precursor solution. Vacuum is drawn, and the vacuum pressure is no greater than -0.08 MPa. The vacuum is continued until no more bubbles emerge from the polyborosilicate precursor solution. Step 6.2, precursor curing; The impregnated SiC fiber preform is pre-cured by holding it at 80~100℃ for 3~12h, and then the temperature is raised to 180~200℃ and held for 1~2h to complete the preform curing. Step 6.3, exhaust the precursor gas; The SiC fiber preform that has completed precursor curing is vented under vacuum to remove the gas generated during curing. The vacuum pressure is no greater than -0.08 MPa, and the venting is continued for 30~60 minutes. Step 6.4, precursor lysis; In a nitrogen atmosphere, the SiC fiber preform after exhaust is heated to 900~1000℃ and held at that temperature for 1~2h for pyrolysis, and then cooled to room temperature at a rate of 2~3℃ / min to obtain a box structure of SiC / SiBCN ceramic matrix composite material.

4. The method for preparing a SiC / SiBCN ceramic matrix composite box with an inner boss according to claim 3, characterized in that: In step 6.1, the mass concentration of the polyborosilicate precursor solution is 20%~30%.

5. The method for preparing a SiC / SiBCN ceramic matrix composite box with an inner boss according to claim 4, characterized in that: Step 6 also includes step 6.5, repeating steps 6.1-6.4 multiple times to achieve a density of 2.1~2.2 g / cm³ for the SiC / SiBCN ceramic matrix composite material. 3 .

6. The method for preparing a SiC / SiBCN ceramic matrix composite box with an inner boss according to claim 1, characterized in that: In step 1, the planar parts of the inner U-shaped precast body (2), the U-shaped precast body (3), and the outer precast body (4) are set with equal wall thickness.

7. The method for preparing a SiC / SiBCN ceramic matrix composite box with an inner boss according to claim 6, characterized in that, Step 2 is as follows: The SiC fiber preform is held at 1200℃~1350℃ in an inert gas atmosphere for 1~2 hours, and then cooled down in the furnace to complete the high-temperature treatment.

8. The method for preparing a SiC / SiBCN ceramic matrix composite box with an inner boss according to claim 7, characterized in that, Step 4 is as follows: A Si3N4 matrix was deposited on the surface of a SiC fiber preform with a boron nitride interface layer using chemical vapor deposition. Through multiple rounds of deposition, the density of the semi-densified preform was reduced to 1.6–1.7 g / cm³. 3 .

9. The method for preparing a SiC / SiBCN ceramic matrix composite box with an inner boss according to claim 8, characterized in that: In step 3, the boron nitride interface layer is prepared by chemical vapor deposition, and the thickness of the interface layer is 300~500nm.

10. The method for preparing a SiC / SiBCN ceramic matrix composite box with an inner boss according to claim 9, characterized in that: In step 7, a Si3N4 matrix is ​​deposited using chemical vapor deposition to achieve a density of 2.3 g / cm³ for the SiC / SiBCN ceramic matrix composite material. 3 above.

Images