Production and processing technology of a high-strength ceramic matrix composite bolt

Abstract

This application relates to the field of the preparation of ceramic matrix composite bolts, and specifically relates to a production and processing technology for high-strength ceramic matrix composite bolts. The technology includes: obtaining a rod-shaped preform with a cladding structure and a core structure, suspending it in a chemical vapor deposition furnace, depositing a pyrolytic carbon interface layer on the fiber surface of the rod-shaped preform, and performing high-temperature treatment; placing the treated rod-shaped preform in a vacuum impregnation barrel; pumping a ceramic precursor slurry into the barrel, taking it out after being pressurized with argon, heated, kept warm, and cooled with the furnace, and performing vacuum pyrolysis treatment under low-temperature and high-temperature conditions respectively, and naturally cooling to room temperature in an argon atmosphere after keeping warm; preparing a silicon carbide matrix and obtaining segmented bars; grinding and processing the segmented bars; preparing a ceramic coating on the surface of the bolt with external threads processed, and the ceramic coating is silicon carbide, so as to obtain a ceramic matrix composite bolt. This application aims to optimize the pyrolysis temperature during the pyrolysis treatment of the ceramic matrix composite bolt.

Description

Technical Field

[0001] This application relates to the field of preparation of ceramic matrix composite bolts, and particularly to a production and processing technology for high-strength ceramic matrix composite bolts. Background Art

[0002] Ceramic matrix composites are a class of composites in which ceramics are used as the matrix and various fibers are compounded. They have excellent properties such as high temperature resistance, high strength and stiffness, relatively light weight, and corrosion resistance. As a type of connecting piece, ceramic matrix composite bolts have broad application prospects in the fields of aerospace, automotive, energy, and military, etc. They can not only improve the safety of related equipment but also show excellent reliability in extreme environments. Therefore, the research and application of ceramic matrix composite bolts are of great significance.

[0003] In the process of preparing ceramic matrix composite bolts, pyrolysis treatment is required. This process can convert ceramic precursors into ceramic matrices with good mechanical properties and high-temperature stability, improve the stability of materials in high-temperature environments, and optimize the mechanical and thermal properties of materials by controlling the crystal phase and microstructure of the materials. However, it is difficult for the existing technology to accurately analyze the heat distribution uniformity and thermal response stability characteristics inside the preform, and thus it is impossible to provide scientific data support for the adjustment of pyrolysis temperature, which may cause the drawback that the performance of ceramic matrix composite bolts is damaged due to improper pyrolysis temperature. Summary of the Invention

[0004] In view of the above, it is necessary to provide a production and processing technology for high-strength ceramic matrix composite bolts to solve the above problems.

[0005] An embodiment of this application provides a production and processing technology for high-strength ceramic matrix composite bolts, and the technology includes:

[0006] S1: Obtain a rod-shaped preform with a cladding structure and a core structure using silicon carbide fibers and perform pretreatment.

[0007] S2: Subject the rod-shaped preform obtained in S1 to vacuum pyrolysis treatment successively under low-temperature and high-temperature conditions, and after heat preservation, naturally cool it to room temperature in an argon atmosphere to obtain a densified rod. Among them, during the vacuum pyrolysis at high temperature:

[0008] S201: After pyrolyzing at high temperature for a preset time, obtain the thermal imaging diagram of the ceramic matrix composite bolt at each moment.

[0009] S202: According to the heat distribution difference between each pixel and the pixels in the neighborhood range in the thermal imaging diagram of the ceramic matrix composite bolt, as well as the temperature gradient distribution characteristics, obtain the pyrolysis characteristic factor of each pixel.

[0010] S203: Cluster the pixels in the thermal image based on the cracking characteristic factors, and obtain the temperature adjustment factor through the boundary distribution of each clustering cluster in the thermal image and the stability of the temperature change within a preset time period;

[0011] S204: Evaluate the cracking sufficiency of the ceramic matrix composite bolt through the temperature adjustment factor, and adjust the cracking temperature;

[0012] S3: Prepare a silicon carbide matrix by chemical vapor infiltration method, and cut the densified bar into segmented bars with a preset length according to the bolt length requirement;

[0013] S4: Stop grinding the outer circle of the segmented bar after meeting the outer diameter condition, and machine it according to the requirements of the external thread of the bolt;

[0014] S5: Use chemical vapor deposition method to prepare a ceramic coating on the surface of the bolt after the external thread is machined. The ceramic coating is silicon carbide, and a ceramic matrix composite bolt is obtained.

[0015] Among them, the process of performing pretreatment in S1 is as follows:

[0016] S101: Suspend the rod-shaped preform in the chemical vapor deposition furnace, deposit a pyrolytic carbon interface layer on the fiber surface of the rod-shaped preform, and perform high-temperature treatment;

[0017] S102: Place the treated rod-shaped preform in a vacuum impregnation barrel; then, pump the ceramic precursor slurry into the barrel, take it out after argon pressurization, heating, heat preservation, and furnace cooling;

[0018] S103: Drain the slurry on the impregnated rod-shaped preform, perform heat preservation and then cool and take it out.

[0019] Among them, the core structure is a cylinder formed by arranging multiple fiber bundles in the same direction, and the silicon carbide fibers account for 40% - 50% of the volume fraction of the entire cylinder.

[0020] Among them, the cladding structure is a tubular fiber bundle braided layer wrapped around the outer peripheral surface of the core structure, and the silicon carbide fibers account for 40% - 50% of the volume fraction of the tubular fiber bundle braided layer.

[0021] Among them, the thickness of the pyrolytic carbon interface layer is: ; The conditions for the high-temperature treatment are: 1700 - 1900 °C, heat preservation for 1 - 1.5 h.

[0022] Among them, being placed in the vacuum impregnation barrel includes evacuating to -0.5 to -0.05 MPa and maintaining for 60 minutes; the argon gas pressurization, heating, and heat preservation specifically mean pressurizing to 0.8 to 1 MPa, heating to 50 °C and maintaining for 1 to 1.5 hours; among them, the way to obtain the ceramic precursor slurry is: placing polycarbosilane and xylene in a water bath according to a mass ratio of 2:1, and mechanically stirring at a rotation speed of 60 r / min at 70 °C for 3 to 5 h to mix evenly and then obtaining it.

[0023] Among them, obtaining the pyrolysis characteristic factor of each pixel includes:

[0024] Taking each pixel as the center to establish a pixel window, and obtaining the temperature extreme difference of each pixel in the pixel window of each thermal imaging map at each moment; calculating the temperature difference between each pixel and other pixels in its pixel window, and combining the temperature extreme difference to obtain the neighborhood temperature difference of each pixel;

[0025] Obtaining the negative correlation mapping result of the distance between each pixel and any pixel in its pixel window, fusing the negative correlation mapping result with the temperature difference between the corresponding two pixels to obtain the temperature gradient between each pixel and the any pixel in its pixel window; taking the average level of all the temperature gradients of each pixel as the temperature change index of each pixel;

[0026] Based on the neighborhood temperature difference and temperature change index of each pixel, obtaining the pyrolysis characteristic factor of each pixel.

[0027] Among them, obtaining the temperature adjustment factor includes:

[0028] Taking the absolute value of the difference in pyrolysis characteristic factors between pixels as the distance measurement method between pixels, and clustering all pixels in the thermal imaging map at each moment; performing edge detection on the thermal imaging map at each moment;

[0029] For each clustering cluster in the thermal imaging map, fusing the temperature differences between each clustering cluster and the clustering centers of all the other clustering clusters to obtain the comprehensive temperature difference index of each clustering cluster; obtaining the fusion result of the temperature differences between each boundary pixel in each clustering cluster and all the pixels in its neighborhood to obtain the boundary temperature difference value of each boundary pixel; taking the negative correlation mapping result after fusing the boundary temperature difference values of all the boundary pixels in each clustering cluster and the comprehensive temperature difference index as the thermal response factor of each clustering cluster;

[0030] Arranging the thermal response factors of all the clustering clusters in the thermal imaging map at each moment in order to form the thermal response feature vector of the thermal imaging map at each moment; taking the preset time period as a pyrolysis temperature adjustment interval;

[0031] For each pyrolysis temperature adjustment interval, according to the distance metric between the thermal response eigenvectors at each moment and those at the remaining moments, combined with the degree of chaos of the thermal response eigenvectors at each moment, the temperature eigenvalue at each moment is obtained; the sum of the temperature eigenvalues at all moments in each pyrolysis temperature adjustment interval is normalized to obtain the temperature adjustment factor for each pyrolysis temperature adjustment interval.

[0032] Among them, the adjustment of the pyrolysis temperature includes:

[0033] Set a pyrolysis sufficiency threshold. When the temperature adjustment factor obtained in real time is greater than or equal to the pyrolysis sufficiency threshold, no temperature adjustment is performed; otherwise, the temperature is increased by a preset value based on the current pyrolysis temperature.

[0034] Among them, the specific steps for preparing the silicon carbide matrix are as follows:

[0035] Place the bolt of the ceramic matrix composite material after pyrolysis treatment in a chemical vapor infiltration furnace. Using trichlorosilane as the precursor, hydrogen as the carrier gas and reducing gas, argon as the dilution gas, the deposition temperature is 800 - 900 °C, the deposition time is 80 - 100 h, the deposition pressure is set to 15 kPa, the molar ratio of the reducing gas to trichlorosilane is 15:1, the precursor flow rate is 4 g / min, the dilution gas flow rate is 10 L / min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, and the carrier gas flow rate is 100 mL / min, until the final density of the material after the ceramic matrix is prepared is: .

[0036] This application has at least the following beneficial effects:

[0037] This application obtains the pyrolysis characteristic factors by acquiring the thermal imaging map during the pyrolysis process of the ceramic matrix composite material bolt, and analyzing the heat distribution and temperature gradient characteristics in the vicinity of the preform. Based on the analysis of the heat distribution uniformity in the vicinity of the preform, the sharpness of the temperature change is considered, which more accurately reflects the ideal pyrolysis treatment effect at the pixel position; clustering the pixels in the thermal imaging map based on the pyrolysis characteristic factors, and obtaining the temperature adjustment factor through the boundary distribution of each clustering cluster in the thermal imaging map and the stability of the temperature change within a preset time period, so as to evaluate the pyrolysis sufficiency of the ceramic matrix composite material bolt, and use it as the data basis for pyrolysis temperature adjustment. Considering the internal thermal response characteristics and the consistency of the thermal response change trend of the preform material during the pyrolysis process, it more accurately quantifies the pyrolysis sufficiency of the ceramic matrix composite material bolt, provides scientific data support for the optimization and adjustment of the pyrolysis temperature during the pyrolysis treatment process of the ceramic matrix composite material bolt, and avoids uneven heat inside the preform and insufficient pyrolysis inside the preform, which affects the performance of the prepared ceramic matrix composite material bolt. Description of the Drawings

[0038] Figure 1 Flow chart of a production and processing process for a high-strength ceramic matrix composite bolt provided for this application;

[0039] Figure 2 Flow chart of preprocessing the rod-shaped preform provided for this application;

[0040] Figure 3 Schematic diagram of the change in the internal porosity and densification degree of the preform during the high-temperature pyrolysis process provided for this application;

[0041] Figure 4 Specific flow chart of adjusting the high-temperature pyrolysis temperature provided for this application. Specific embodiments

[0042] In the description of the embodiments of this application, words such as "exemplary", "or", "for example", etc. are used to indicate examples, illustrations or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of this application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Rather, the use of words such as "exemplary", "or", "for example" is intended to present related concepts in a specific manner.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs. The terms used in the description of the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0044] In addition, it should be noted that the terms "first" and "second" in this application and its drawings are used to distinguish similar objects and are not used to describe a specific order or sequence. For the methods disclosed in the embodiments of this application or the methods shown in the flow charts, including one or more steps for implementing the methods, without departing from the scope of protection of this application, the execution order of multiple steps can be interchanged with each other, and some steps can also be deleted.

[0045] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs.

[0046] The embodiments of this application propose a production and processing process for a high-strength ceramic matrix composite bolt, which is applied to the field of ceramic matrix composite bolt preparation. Referring to the attached Figure 1 , the process includes:

[0047] S1: Obtain a rod-shaped preform with a cladding structure and a core structure using silicon carbide fibers and perform preprocessing.

[0048] (1)Determine the size of the fiber preform and design the fiber preform structure.

[0049] According to the size requirements of the ceramic matrix composite bolt, design the size of its fiber preform. The fiber preform includes a core structure and a cladding structure. The core structure is a cylinder formed by arranging multiple fiber bundles in the same direction; the cladding structure is a tubular fiber bundle braided layer wrapped around the outer peripheral surface of the core structure. Among them, the fiber is a silicon carbide fiber. The size of the prepared ceramic matrix composite bolt is: minor diameter 6 mm, major diameter 8 mm. Using silicon carbide fiber as the material of the fiber preform, design the diameter of the core structure of the carbon fiber preform to be 5.5 mm, and the outer diameter of the cladding to be 8.5 mm.

[0050] (2)Prepare the core structure.

[0051] Prepare fiber bundles with a length of 1500 mm, and use a round bar with a length of 1485 mm and a diameter of 5.5 mm as the bundling mold; disperse multiple fiber bundles onto the surface of the round bar in such a way that each fiber bundle extends along the axial direction of the round bar and multiple fiber bundles are closely arranged along the circumferential direction of the round bar until the entire round bar is wrapped. Tie one end of the fiber bundle that extends beyond the end face of the round bar with a 1K silicon carbide fiber bundle, then remove the metal round bar, straighten all the fiber bundles, and tie the other end with a 1K silicon carbide fiber bundle. Keep the tension of the fiber bundles and tie them in a spiral direction with molten glass filaments to form a core structure of unidirectional fiber bundles and keep it in a straightened state. Among them, in the core structure of this embodiment, the silicon carbide fiber accounts for 40% of the volume fraction of the entire cylinder; in the core structure of other embodiments, the silicon carbide fiber accounts for 43% of the volume fraction of the entire cylinder; in the core structure of some other embodiments, the silicon carbide fiber accounts for 50% of the volume fraction of the entire cylinder.

[0052] (3)Weave the cladding structure.

[0053] While the unidirectional fiber bundle core structure is kept straightened, use a three-dimensional four-directional weaving method to weave a fiber bundle cladding on its surface, and set the fiber bundle weaving tension so that the unidirectional fiber bundle core structure preform is under compressive stress from the cladding weaving preform. Among them, in the cladding structure of this embodiment, the silicon carbide fiber accounts for 40% of the volume fraction of the tubular fiber bundle braided layer; in the cladding structure of other embodiments, the silicon carbide fiber accounts for 45% of the volume fraction of the tubular fiber bundle braided layer; in the cladding structure of some other embodiments, the silicon carbide fiber accounts for 50% of the volume fraction of the tubular fiber bundle braided layer.

[0054] (4)Sew the core and cladding structures to obtain a rod-shaped preform.

[0055] Using fine molten glass filaments, under the guidance of a metal needle, stitch once along the 0° and 90° directions of the cross-section of the preform obtained in (3), and then continue to stitch once along the 0° and 90° directions of the cross-section after setting a length at intervals along the axial direction. Repeat the above stitching steps to form a rod-shaped preform with a cladding of a cylindrical fiber bundle braided layer structure and a core of a cylindrical structure formed by arranging multiple fiber bundles in the same direction.

[0056] Perform pretreatment on the rod-shaped preform, and the process of the pretreatment includes:

[0057] S101: Suspend the rod-shaped preform in a chemical vapor deposition furnace, deposit a pyrolytic carbon interface layer on the fiber surface of the rod-shaped preform, and perform high-temperature treatment.

[0058] Suspend the rod-shaped preform in a chemical vapor deposition furnace, and use the CVI deposition process to deposit a pyrolytic carbon interface layer on the fiber surface of the rod-shaped preform. The thickness range of the pyrolytic carbon interface layer is: ; Perform high-temperature treatment on the rod-shaped preform with the pyrolytic carbon interface layer deposited. In this embodiment, the high-temperature treatment conditions are: 1700 °C, hold for 1.5 h; in other embodiments, the high-temperature treatment conditions are: 1750 °C, hold for 1.5 h; in some other embodiments, the high-temperature treatment conditions are: 1900 °C, hold for 1 h.

[0059] S102: Place the treated rod-shaped preform in a vacuum impregnation barrel; then, pump the ceramic precursor slurry into the barrel, and take it out after pressurizing with argon, heating up, holding, and cooling down with the furnace.

[0060] Place the rod-shaped preform treated in S101 in a vacuum impregnation barrel. In this embodiment, evacuate to -0.5 MPa and hold for 60 min; in other embodiments, evacuate to -0.05 MPa; in some other embodiments, evacuate to -0.4 MPa.

[0061] Then pump the ceramic precursor slurry into the vacuum impregnation barrel to completely submerge the rod-shaped preform in the precursor slurry, introduce the protective gas argon, pressurize to 0.8 MPa in this embodiment, slowly heat up to 50 °C, hold for 1 h, and take it out after cooling down to room temperature with the furnace; in other embodiments, pressurize to 1 MPa, slowly heat up to 50 °C, hold for 1.5 h, and take it out after cooling down to room temperature with the furnace; in some other embodiments, pressurize to 1 MPa, slowly heat up to 50 °C, hold for 1 h, and take it out after cooling down to room temperature with the furnace.

[0062] The above-mentioned ceramic precursor slurry is obtained by: placing polycarbosilane and xylene in a water bath at a mass ratio of 2:1, and mechanically stirring at a speed of 60 r / min at 70 °C. In this embodiment, it is obtained after stirring for 3 h to mix evenly; in other embodiments, stirring for 3.5 h; in some other embodiments, the stirring duration is 5 h.

[0063] S103: Drain the slurry on the impregnated rod-shaped preform, keep it warm and then take it out after cooling.

[0064] Drain the slurry on the impregnated rod-shaped preform, put it into a preheated oven. In this embodiment, keep it at 120°C for 7 h at a heating rate of 10°C / min; in other embodiments, keep it at 120°C for 5 h at a heating rate of 10°C / min; in some other embodiments, keep it at 180°C for 4 h at a heating rate of 10°C / min; then take it out after natural cooling to room temperature in the furnace.

[0065] Among them, the flow chart of the pretreatment of the rod-shaped preform is as Figure 2 shown.

[0066] S2: Perform vacuum pyrolysis treatment on the rod-shaped preform obtained in S1 successively under low temperature and high temperature conditions, keep it warm and then natural cool to room temperature in an argon atmosphere to obtain a densified rod.

[0067] Low-temperature pyrolysis: Place the above-mentioned solidified rod-shaped preform in a sintering furnace. In this embodiment, evacuate to 60 Pa, heat up to 800°C at a heating rate of 10°C / min, keep it warm for 3 h, and take it out after natural cooling to room temperature in an argon atmosphere; in some other embodiments, evacuate to 90 Pa, heat up to 1000°C at a heating rate of 10°C / min, keep it warm for 3 h; in some other embodiments, evacuate to 100 Pa, heat up to 1000°C at a heating rate of 10°C / min, keep it warm for 2 h.

[0068] High-temperature pyrolysis: Place the rod-shaped preform after low-temperature pyrolysis in a sintering furnace. In this embodiment, evacuate to 60 Pa, heat up to 1100°C at a heating rate of 10°C / min, keep it warm for 3 h, and take it out after natural cooling to room temperature in an argon atmosphere; in some other embodiments, evacuate to 80 Pa, heat up to 1100°C at a heating rate of 10°C / min, keep it warm for 3 h; in some other embodiments, evacuate to 100 Pa, heat up to 1300°C at a heating rate of 10°C / min, keep it warm for 2 h.

[0069] Among them, during the vacuum pyrolysis at high temperature:

[0070] S201: After the preset time of high-temperature pyrolysis, obtain the thermal imaging diagrams of the ceramic matrix composite bolts at each moment.

[0071] In order to analyze the cracking treatment effect of the ceramic matrix composite bolt during the cracking process and provide a scientific basis for cracking temperature control, this application collects relevant data during the cracking process of the ceramic matrix composite bolt through a SCADA (Supervisory Control And Data Acquisition) system. The specific collection method is as follows: After the rod-shaped preform after low-temperature cracking is placed in a sintering furnace and subjected to high-temperature cracking treatment for 30 minutes, an infrared thermal imager is used to obtain the thermal imaging diagram of the ceramic matrix composite bolt. The time interval for obtaining the thermal imaging diagram is 5 s; the implementer can adjust it according to the actual situation; to prevent serious noise interference in the obtained thermal imaging diagram of the ceramic matrix composite bolt from seriously affecting subsequent analysis, the histogram equalization method is used to perform image enhancement processing on the collected thermal imaging diagram. Since the histogram equalization method is a well-known technology, the specific acquisition process will not be elaborated too much.

[0072] The thermal imaging diagram of the ceramic matrix composite bolt is referred to as the thermal imaging diagram for subsequent description, and the thermal imaging diagram obtained through the above method is transmitted to the data statistical analysis module of the SCADA system.

[0073] S202: According to the heat distribution difference between each pixel and the pixels in the neighborhood range in the thermal imaging diagram of the ceramic matrix composite bolt, and the temperature gradient distribution characteristics, the cracking characteristic factor of each pixel is obtained.

[0074] Under the ideal state of the cracking process of the ceramic matrix composite bolt, as the temperature slowly rises, the heat distribution at each position of the ceramic matrix composite bolt shows a uniform phenomenon; when the temperature difference between the corresponding position and the adjacent position in the thermal imaging diagram of the ceramic matrix composite bolt during the cracking process is more significant, it indicates that the cracking treatment effect of the preform is worse, and it is more likely to reduce the performance of the ceramic matrix composite bolt obtained in the subsequent preparation.

[0075] Based on the above analysis, a pixel window is established with each pixel as the center, and the temperature extreme difference in the pixel window of each pixel in the thermal imaging diagram at each moment is obtained; the temperature difference between each pixel and other pixels in its pixel window is calculated, and combined with the temperature extreme difference, the neighborhood temperature difference of each pixel is obtained.

[0076] In this embodiment, for subsequent analysis, an example of the thermal imaging diagram at any moment is taken. A pixel window is constructed with each pixel in the thermal imaging diagram as the center, and the size of the pixel window is ; the implementer can adjust it according to the actual situation, and this application does not limit it.

[0077] For the neighborhood temperature difference of the i-th pixel, it can be calculated through the following method: ; where is the neighborhood temperature difference of the i-th pixel in the thermal imaging diagram; is the temperature extreme difference value in the pixel window corresponding to the i-th pixel in the thermal image; is the cumulative result of the absolute values of the temperature differences between the i-th pixel in the thermal image and all pixels in its pixel window.

[0078] It should be understood that when the cracking treatment effect of the ceramic matrix composite bolt is more ideal, the heat distribution inside the preform is more uniform, the temperature difference within the neighborhood range is smaller, that is, the difference between the maximum temperature value and the minimum temperature value in the pixel window is smaller, and the temperature difference between all pixels in the pixel window and the central pixel is smaller.

[0079] Under normal circumstances, during the cracking process of the ceramic matrix composite bolt, when the phenomenon of sharp change in the temperature gradient inside the preform is more significant, it indicates that the cracking treatment effect of the preform is less ideal, and the discontinuity of heat transfer is more likely to affect the performance of the obtained ceramic matrix composite bolt.

[0080] Based on the above analysis, the negative correlation mapping result of the distance between each pixel and any pixel in its pixel window is obtained, and fused with the temperature difference between the corresponding two pixels to obtain the temperature gradient between each pixel and any pixel in its pixel window; the average level of all the temperature gradients of each pixel is used as the temperature change index of each pixel.

[0081] In this embodiment, the distance between pixels is measured by the Euclidean distance, and the negative correlation mapping result of the variable is specifically the reciprocal of the variable; the method of multiplication is used to fuse multiple variables, that is, the temperature gradient is specifically the absolute value of the temperature difference between each pixel and any pixel in its pixel window divided by the distance between the corresponding two pixels. Specifically, the sharpness of temperature change of the i-th pixel can be calculated as follows: ; where is the temperature change index of the i-th pixel in the thermal image; is the total number of pixels in the pixel window; is the absolute value of the temperature difference between the i-th pixel and the j-th pixel in its pixel window in the thermal image; is the Euclidean distance between the i-th pixel and the j-th pixel in its pixel window in the thermal image; represents the temperature gradient between the i-th pixel and the j-th pixel in the thermal image.

[0082] It should be understood that during the cracking process of the ceramic matrix composite bolt, when the heat transfer effect inside the preform is better, the temperature gradient within the neighborhood range of the preform is smaller, and the phenomenon of sharp temperature change is more blurred, that is, the cumulative result of the ratio of the temperature difference and the distance difference between all pixels in the pixel window and the central pixel is smaller.

[0083] Under normal circumstances, when the heat distribution in the ceramic matrix composite bolt is more uniform during the pyrolysis process and the sharpness of the temperature change phenomenon is more blurred, it can better reflect the characteristics of sufficient pyrolysis treatment inside the preform. Based on the neighborhood temperature difference and temperature change index of each pixel, the pyrolysis characteristic factor of each pixel is obtained.

[0084] In this embodiment, the product of the neighborhood temperature difference and the temperature change index of each pixel is calculated, and the reciprocal of the product is used as the pyrolysis characteristic factor of each pixel; it should be noted that in order to avoid the situation where the denominator is zero, a preset value needs to be added to the denominator, and the value of the preset value in the embodiment is 0.1.

[0085] It should be understood that when the pyrolysis treatment effect of the ceramic matrix composite bolt is more ideal, the heat distribution in the neighborhood of the preform is more uniform, the temperature gradient is smaller, the heat transfer is smoother, and the pyrolysis characteristic factor is larger, that is, the neighborhood temperature difference is smaller and the temperature change degree is smaller.

[0086] S203: Cluster the pixels in the thermal imaging map based on the pyrolysis characteristic factor, and obtain the temperature adjustment factor through the boundary distribution of each cluster in the thermal imaging map and the stability of the temperature change within a preset time period.

[0087] Taking all the pixels in the thermal imaging map at any moment as the input, the K-mediods clustering algorithm is used to obtain each cluster and the cluster center in the thermal imaging map. Among them, the number of cluster centers is set to 10, and the absolute value of the difference in the pyrolysis characteristic factors between pixels is used as the distance measurement method between pixels. Since the K-mediods clustering algorithm is a well-known technology, the specific acquisition process will not be elaborated too much. The purpose of using the K-mediods clustering algorithm in this application is to obtain the most data-representative cluster center in the clusters with similar pyrolysis characteristics in the thermal imaging map at any moment through the clustering algorithm, which is convenient for further analyzing the sufficient pyrolysis characteristics of the ceramic matrix composite bolt within the cluster, and thus providing accurate data support for pyrolysis temperature control.

[0088] During the pyrolysis treatment process of the ceramic matrix composite bolt, the porosity inside the preform will gradually decrease, thereby improving the density inside the preform. When the pyrolysis treatment of the ceramic matrix composite bolt is more sufficient, the thermal response characteristics inside the preform are more obvious, that is, the temperature difference between different regions is more slight, and due to the more uniform temperature distribution, the thermal boundary phenomenon between different regions inside the preform is more slight.

[0089] Among them, the schematic diagram of the change in porosity and density inside the preform during the high-temperature pyrolysis process is as Figure 3As shown in the figure, the abscissa is time, with the unit of min, the left ordinate is the porosity, and the right ordinate is the densification degree, both with the unit of %. Among them, as the pyrolysis treatment of the preform progresses, the pores inside the preform gradually decrease, and the densification degree increases. When the pyrolysis temperature is inappropriate, it may cause the pore closure in the ceramic matrix composite inside the preform to be blocked, resulting in a rebound of the porosity. At this time, the pyrolysis temperature of the ceramic matrix composite bolt should be adjusted in time to avoid affecting the pyrolysis treatment effect of the preform.

[0090] Based on the above analysis, now take any moment as an example for subsequent analysis. Screen the boundary pixels in each clustering cluster of the thermal image. The screening method is as follows: Take the thermal image as the input, and use the edge detection algorithm based on the Canny operator to obtain all the edges in the thermal image. Denote the edge farthest from the clustering center within each clustering cluster as the thermal boundary of each clustering cluster, and denote all the pixels on the thermal boundary as the boundary pixels of the corresponding clustering cluster. Among them, the Canny edge detection is a well-known existing technology and will not be elaborated in this application. Implementers can choose other edge detection algorithms, and this application does not limit this.

[0091] For each clustering cluster in the thermal image, fuse the temperature differences between each clustering cluster and the clustering centers of all the other clustering clusters to obtain the comprehensive temperature difference index of each clustering cluster; obtain the fusion result of the temperature differences between each boundary pixel within each clustering cluster and all the pixels in its neighborhood to obtain the boundary temperature difference value of each boundary pixel; use the negative correlation mapping result after fusing the boundary temperature difference values of all the boundary pixels in each clustering cluster and the comprehensive temperature difference index as the thermal response factor of each clustering cluster.

[0092] In this embodiment, the comprehensive temperature difference index is specifically the sum of the absolute values of the temperature differences between each clustering cluster and the clustering centers of all the other clustering clusters; the boundary temperature difference value of each boundary pixel is specifically the sum of the absolute values of the temperature differences between each boundary pixel within each clustering cluster and all the pixels in its neighborhood; the thermal response factor is specifically: calculate the sum of the boundary temperature difference values of all the boundary pixels in each clustering cluster, and use the reciprocal of the product of the sum value and the comprehensive temperature difference index as the thermal response factor of each clustering cluster.

[0093] It should be understood that when the pyrolysis treatment of the ceramic matrix composite bolt is more sufficient, the thermal response characteristics inside the preform are more obvious, the temperature difference between different regions is more slight, the thermal boundary phenomenon is more slight, and the thermal response factor is larger, that is, the temperature difference between the corresponding clustering centers of different clustering clusters is smaller, and the temperature difference situation between all the boundary pixels in the clustering cluster and all the pixels within its neighborhood range is more slight.

[0094] Under normal circumstances, when the ceramic matrix composite bolt is cracked more fully, over time, the stable characteristics of the thermal response inside the preform become more prominent, that is, over time, the consistency of the change trend of the thermal response characteristics inside the preform becomes more prominent.

[0095] Based on the above analysis, the sequence formed by arranging the thermal response factors of all clustering clusters in the thermal imaging map at any moment in ascending order is used as the thermal response feature vector of the thermal imaging map at the corresponding moment. Every 30 minutes is used as a cracking temperature adjustment interval, and the implementer can adjust the length of the cracking temperature adjustment interval according to the actual situation; now, take any cracking temperature adjustment interval as an example for subsequent analysis.

[0096] For each cracking temperature adjustment interval, according to the distance metric between the thermal response feature vectors of each moment and the remaining moments, combined with the degree of chaos of the thermal response feature vectors of each moment, the temperature characteristic value of each moment is obtained; the sum value of the temperature characteristic values of all moments in each cracking temperature adjustment interval is normalized to obtain the temperature adjustment factor of each cracking temperature adjustment interval.

[0097] Specifically, for the temperature adjustment factor of the q-th cracking temperature adjustment interval, it can be calculated as follows: ; where is the temperature adjustment factor of the q-th cracking temperature adjustment interval; is the total number of moments in the cracking temperature adjustment interval; is the cumulative result of the DTW distances between the thermal response feature vector of the h-th moment and the thermal response feature vectors of all the remaining moments in the q-th cracking temperature adjustment interval; is the information entropy of the thermal response feature vector of the h-th moment in the q-th cracking temperature adjustment interval; norm[] is a normalization function, making the value range of which is between [0, 1].

[0098] It should be understood that when the ceramic matrix composite bolt is cracked more fully, over time, the consistency of the change trend of the thermal response characteristics inside the preform is stronger, the difference between the thermal response feature vectors at different moments in the cracking temperature adjustment interval is smaller, and the difference in the thermal response characteristics between different clustering clusters in the thermal imaging map corresponding to each moment in the cracking temperature adjustment interval is smaller, that is, the cumulative result of the DTW distances between the thermal response feature vectors of all moments and the thermal response feature vectors of the remaining moments in the cracking temperature adjustment interval is smaller, and the information entropy of the thermal response feature vectors of all moments in the cracking temperature adjustment interval is smaller. At this time, there is no need to adjust the cracking temperature of the ceramic matrix composite bolt to avoid uneven heat inside the preform caused by improper cracking temperature and insufficient cracking inside the preform, which affects the performance of the subsequent prepared ceramic matrix composite bolt.

[0099] S204: Evaluate the degree of pyrolysis completion of the ceramic matrix composite bolt through the temperature adjustment factor and adjust the pyrolysis temperature.

[0100] Set the pyrolysis completion threshold V. Through the data acquisition and analysis module in the SCADA system, obtain the temperature adjustment factor for any pyrolysis temperature adjustment interval according to the above steps, and transmit the real-time obtained temperature adjustment factor to the early warning management module in the SCADA system to evaluate the degree of pyrolysis completion of the ceramic matrix composite bolt in real time. The specific evaluation method is as follows:

[0101] When the real-time obtained temperature adjustment factor is greater than or equal to the pyrolysis completion threshold V, it is determined that the internal heat distribution of the preform is uniform and the thermal response characteristics are stable within the current pyrolysis temperature adjustment interval, and there is no need to adjust the pyrolysis temperature of the ceramic matrix composite bolt; when the real-time obtained temperature adjustment factor is less than the pyrolysis completion threshold V, it is determined that the internal heat distribution of the preform is uneven, the heat transfer is not smooth, and the stable characteristics of the thermal response at each position inside the preform are not obvious. It is necessary to increase the temperature by R °C on the basis of the current pyrolysis temperature to further promote the pyrolysis completion of the ceramic matrix composite bolt;

[0102] The value range of the pyrolysis completion threshold V is between [0, 1]. The larger V is, the higher the pyrolysis requirement for the ceramic matrix composite bolt. In this application, the pyrolysis completion threshold V and the preset value R are taken as 0.6 and 30 respectively. Implementers can set the sizes of the pyrolysis completion threshold V and the preset value R according to the actual situation.

[0103] Among them, the specific flow chart for adjusting the high-temperature pyrolysis temperature is as Figure 4 shown.

[0104] S3: Prepare a silicon carbide matrix by chemical vapor infiltration method. According to the bolt length requirement, cut the densified bar into segmented bars with a preset length.

[0105] The silicon carbide matrix is prepared by chemical vapor infiltration to seal the internal pores of the rod-shaped preform after the above pyrolysis treatment, and further densify the ceramic matrix. The specific treatment method is as follows: The ceramic matrix composite bolt after pyrolysis treatment is placed in a chemical vapor infiltration furnace. Trichlorosilane is used as the precursor, hydrogen is used as the carrier gas and reducing gas, and argon is used as the dilution gas. In this embodiment, the deposition temperature is 800 °C and the deposition time is 100 h; in some other embodiments, the deposition temperature is 800 °C and the deposition time is 80 h; in some other embodiments, the deposition temperature is 900 °C and the deposition time is 80 h; the deposition pressure is set to 15 kPa, the molar ratio of the reducing gas to trichlorosilane is 15:1, the precursor flow rate is 4 g / min, the dilution gas flow rate is 10 L / min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, and the carrier gas flow rate is 100 mL / min. Until the final density of the material after the ceramic matrix is prepared is 2.4 - 2.8 , complete the matrix densification treatment to obtain a densified rod.

[0106] According to the bolt length requirement, use a diamond tool to cut the densified rod into segmented rods with a length of 80 mm.

[0107] S4: Stop grinding the outer circle of the segmented rod after meeting the outer diameter condition, and machine it according to the requirements of the external thread of the bolt.

[0108] Use a centerless grinder to grind the outer circle of the segmented rod until the outer diameter of the rod is equal to the major diameter of the bolt. Use a diamond tool to machine the segmented rod with a qualified outer circle to the qualified size according to the requirements of the external thread of the bolt.

[0109] S5: Use chemical vapor deposition to prepare a ceramic coating on the surface of the bolt after the external thread is machined. The ceramic coating is silicon carbide to obtain a ceramic matrix composite bolt. In this embodiment, the coating thickness is 100 .

[0110] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to embodiments of the present application. In this regard, each block in the flowchart or block diagram may represent a module, a segment of a program, or a part of code, which contains one or more executable instructions for implementing the specified logical function. In some alternative implementations, the functions noted in the blocks may occur in a different order than noted in the accompanying drawings. For example, two consecutive blocks may actually be executed substantially in parallel, or they may sometimes be executed in the reverse order, depending on the functions involved. In the description corresponding to the flowcharts and block diagrams in the accompanying drawings, the operations or steps corresponding to different blocks may also occur in a different order than disclosed in the description, and sometimes there is no specific order between different operations or steps. For example, two consecutive operations or steps may actually be executed substantially in parallel, or they may sometimes be executed in the reverse order, depending on the functions involved. Each block in the block diagram and / or flowchart, and combinations of blocks in the block diagram and / or flowchart, can be implemented by a dedicated hardware-based system that performs the specified functions or actions, or can be implemented by a combination of dedicated hardware and computer instructions.

[0111] The above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A production and processing technology for high-strength ceramic-based composite bolts, characterized in that: The process includes: S1: A rod-shaped preform having a cladding structure and a core structure is obtained by using silicon carbide fiber, and pre-treated; S2: The rod-shaped preform obtained in S1 is subjected to vacuum cracking treatment at low temperature and high temperature in turn, and after heat preservation, it is naturally cooled to room temperature in an argon atmosphere to obtain a densified rod; wherein, during the high temperature vacuum cracking process: S201: After a preset time of high temperature cracking, obtaining a thermal image of the ceramic matrix composite material bolt at each time; S202: establishing a pixel window with each pixel in the thermal image as the center, obtaining the temperature extreme difference value in the pixel window of each pixel in the thermal image at each moment; calculating the temperature difference between each pixel and other pixels in its pixel window, and combining the temperature extreme difference value to obtain the neighborhood temperature difference of each pixel; Obtain a negative correlation mapping result of the distance between each pixel and any pixel in its pixel window, fuse the negative correlation mapping result with the temperature difference between the corresponding two pixels, and obtain a temperature gradient between each pixel and any pixel in its pixel window; and use the average level of all the temperature gradients of each pixel as the temperature change index of each pixel; Based on the neighborhood temperature difference and temperature change index of each pixel, the cracking characteristic factor of each pixel is obtained; S203: taking all pixels in the thermal image at any moment as input, taking the absolute value of the difference of the cracking characteristic factors between the pixels as the distance measurement method between the pixels, and using the K-mediods clustering algorithm to obtain each cluster and the cluster center in the thermal image; performing edge detection on the thermal image at each moment, recording the edge farthest from the cluster center in each cluster as the thermal boundary of each cluster, and recording all pixels on the thermal boundary as the boundary pixels of the corresponding cluster; For each cluster in the thermal imaging image, the temperature difference between each cluster and the cluster center of all other clusters is fused to obtain the comprehensive temperature difference index of each cluster; the fusion result of the temperature difference between each boundary pixel in each cluster and all pixels in its neighborhood is obtained to obtain the boundary temperature difference value of each boundary pixel; the negative correlation mapping result after the boundary temperature difference value of all boundary pixels of each cluster is fused with the comprehensive temperature difference index is used as the thermal response factor of each cluster; The thermal response factors of all clusters in the thermal imaging image at each moment are arranged in order to form a thermal response feature vector of the thermal imaging image at each moment; the preset time period is used as a cracking temperature adjustment interval; For each cracking temperature adjustment interval, the temperature characteristic value of each moment is obtained according to the distance measurement between the thermal response characteristic vectors of each moment and the rest of the moments, combined with the degree of disorder of the thermal response characteristic vectors of each moment; the sum of the temperature characteristic values ​​of all moments in each cracking temperature adjustment interval is normalized to obtain the temperature adjustment factor of each cracking temperature adjustment interval; S204: evaluating the degree of cracking sufficiency of the ceramic matrix composite material bolt by a temperature adjustment factor, and adjusting the cracking temperature; S3: The silicon carbide matrix is ​​prepared by chemical vapor infiltration, and the densified rod is cut into segmented rods of preset length according to the bolt length requirements; S4: Grinding the outer circle of the segmented bar stops when it meets the outer diameter conditions, and the processing is carried out according to the requirements of the bolt external thread; S5: A ceramic coating is prepared on the surface of the bolt after external thread processing by chemical vapor deposition, wherein the ceramic coating is silicon carbide, and a ceramic matrix composite material bolt is obtained.

2. The production and processing technology of a high-strength ceramic matrix composite material bolt according to claim 1, characterized in that: The pre-processing process described in S1 is: S101: suspending the rod-shaped preform in a vapor deposition furnace, depositing a pyrolytic carbon interface layer on the fiber surface of the rod-shaped preform, and performing high temperature treatment; S102: placing the processed rod-shaped preform in a vacuum impregnation barrel; then, pumping the ceramic precursor slurry into the barrel, and taking it out after being pressurized by argon gas, heated, kept warm, and cooled with the furnace; S103: drain the slurry on the rod-shaped preform after the immersion, keep it warm, and then cool it down and take it out.

3. The production and processing technology of a high-strength ceramic matrix composite material bolt according to claim 1, characterized in that: The core structure is a cylinder formed by multiple fiber bundles arranged in the same direction, wherein silicon carbide fibers account for 40% to 50% of the volume fraction of the entire cylinder.

4. The production and processing technology of a high-strength ceramic matrix composite material bolt according to claim 1, characterized in that: The cladding structure is a tubular fiber bundle braided layer wrapped around the outer peripheral surface of the core structure, wherein the volume fraction of silicon carbide fibers in the tubular fiber bundle braided layer is 40% to 50%.

5. The production and processing technology of a high-strength ceramic matrix composite material bolt according to claim 2, characterized in that: The thickness of the pyrolytic carbon interface layer is: The high temperature treatment conditions are: 1700~1900℃, keeping warm for 1~1.5h.

6. The production and processing technology of a high-strength ceramic matrix composite material bolt according to claim 2, characterized in that: The method of placing the ceramic precursor slurry in a vacuum impregnation barrel includes evacuating to -0.5~-0.05MPa and maintaining it for 60 minutes; the method of pressurizing, heating and keeping warm with argon gas includes pressurizing to 0.8~1MPa, heating to 50°C and keeping warm for 1~1.5 hours; wherein, the method of obtaining the ceramic precursor slurry is: polycarbosilane and xylene are placed in a water bath at a mass ratio of 2:1, and mechanically stirred at a speed of 60r / min for 3~5h at 70°C to mix them evenly.

7. The production and processing technology of a high-strength ceramic matrix composite material bolt according to claim 1, characterized in that: The step of adjusting the cracking temperature comprises: Set a sufficient cracking threshold. When the temperature adjustment factor obtained in real time is greater than or equal to the sufficient cracking threshold, no temperature adjustment is performed; otherwise, the temperature of the preset value is increased based on the current cracking temperature.

8. The production and processing technology of a high-strength ceramic matrix composite material bolt according to claim 1, characterized in that: The specific steps of preparing the silicon carbide substrate are: The ceramic matrix composite bolts after cracking treatment are placed in a chemical vapor infiltration furnace, with trichlorosilane as the precursor, hydrogen as the carrier gas and reducing gas, argon as the diluent gas, the deposition temperature is 800-900 ° C, the deposition time is 80-100 h, the deposition pressure is set to 15 kPa, the molar ratio of the reducing gas to trichlorosilane is 15:1, the precursor flow rate is 4 g / min, the dilution gas flow rate is 10 L / min, the flow rate of the reducing gas is determined by the molar ratio of the reducing gas to the silicon source, the carrier gas flow rate is 100 mL / min, until the final density of the material after the ceramic matrix is ​​prepared is: .

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