A continuous method for preparing a BN coating on a SiC fiber

Abstract

The application discloses a method for continuously preparing a BN coating on the surface of SiC fibers, and comprises the following steps: firstly, a carbon coating is arranged on the surface of SiC fibers; then, the SiC fibers are discharged from a wire discharging device, and are firstly immersed in a boron-containing solution to obtain SiC fibers wrapped by a boron-containing film; then, the SiC fibers wrapped by the boron-containing film are continuously passed through a high-temperature furnace to form a BN coating on the surface of the SiC fibers, and a mixed atmosphere of nitrogen and ammonia is introduced into the high-temperature furnace; and finally, the SiC fibers are collected by a wire collecting device. The method has the advantages of high temperature for preparing the BN coating on the SiC fibers, good crystallinity of the coating, high stability, and effective protection of the fibers in the preparation process of composite materials.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of fiber surface interface layer preparation, and particularly relates to a method for continuously preparing a BN coating on the surface of a SiC fiber bundle. BACKGROUND

[0002] SiC fiber reinforced ceramic matrix composite has excellent characteristics of high temperature resistance, oxidation resistance, corrosion resistance, light weight and high strength, and has great application prospect in the fields of aerospace and military industry. Fiber interface coating has the important functions of protecting the fiber and adjusting the bonding force between the fiber and the matrix, and is the key to preparing composite materials with excellent performance.

[0003] The BN coating has the following advantages as the interface coating of the SiC fiber: 1. The BN coating has weak interface bonding like the C coating, can better exert the load bearing capacity of the brittle SiC fiber, and improve the strength and fracture toughness of the SiC fiber reinforced ceramic matrix composite; 2. The BN coating has excellent oxidation resistance, and the generated B2O3 after oxidation of the BN has self-healing function and can prevent further oxidation; 3. The BN coating has strong corrosion resistance and can well protect the fiber during the preparation of the composite material.

[0004] At present, the conventional method for preparing the BN interface layer on the surface of the SiC fiber is as follows: the SiC fiber is first woven into a shape, and then deposition is performed in a closed deposition furnace. However, since the woven body has a certain thickness, the deposition speed of the outer layer is different from that of the inner layer, and the uniformity of the coating has great difference, and the surface coating is thick while the core coating is thin. In addition, the BN coating prepared by the chemical vapor deposition has amorphous state at a low temperature, is easy to decompose, and needs to be further treated at a high temperature in other equipment to convert the amorphous BN into crystalline BN. During the transfer process, the coating is easy to decompose, which is not conducive to obtaining the high crystalline BN coating.

[0005] Zhou Xinguie et al. use the dip coating method, immerse the SiC fiber in the boric acid and urea solution, and perform pyrolysis under ammonia, and the BN coating is prepared on the surface of the SiC fiber through multiple cycles. However, the preparation temperature is only 1000℃, the crystallinity of the prepared BN coating is poor, and there is a hidden danger of corroding the fiber. Yang Haitang et al. adopt the chemical vapor deposition method to continuously deposit the BN coating on the SiC fiber, and supplement the high temperature heat treatment, and obtain the continuous BN coating with good crystallinity. However, the equipment has high requirements, the by-product has strong corrosion, and the equipment is easy to be damaged.

[0006] It is necessary to further develop the process preparation method to develop a BN coating with low cost, high production efficiency, and good uniformity and stability. SUMMARY

[0007] In view of the deficiencies of the prior art, the present application aims to provide a method for continuously preparing a BN coating on the surface of a SiC fiber bundle, which is simple and efficient, and the prepared BN interface layer can be uniformly distributed on the surface of the SiC fiber, and the fiber is prepared in a BN coating under tension, and the obtained SiC fiber bundle with a BN coating has good flatness and strong weavability, and can be used to prepare high-performance ceramic matrix composites.

[0008] In order to achieve the above-mentioned purpose, the technical scheme of the present application is as follows:

[0009] The present application is a method for continuously preparing a BN coating on the surface of a SiC fiber, which comprises the following steps: first, a carbon coating is provided on the surface of the SiC fiber, and then the SiC fiber is discharged from a yarn discharge device, is first immersed in a boron-containing solution to obtain SiC fiber wrapped with a boron-containing film, and then the SiC fiber wrapped with the boron-containing film is continuously passed through a high-temperature furnace to form a BN coating on the surface of the SiC fiber, and is then collected by a yarn collection device.

[0010] The high-temperature furnace is provided with a mixed atmosphere of nitrogen and ammonia.

[0011] The boron-containing solution comprises, by mass percentage, 2-10% of boron oxide, 85-96% of anhydrous ethanol, and 0.5-5% of PVB.

[0012] In the present application, the SiC fiber provided with a carbon coating is discharged from the yarn discharge device in the continuous device, is first moved to the boron-containing solution, is immersed in the boron-containing solution to obtain SiC fiber wrapped with a boron-containing film, and is then continuously passed through the high-temperature tube furnace, and the mixed atmosphere of nitrogen and ammonia is introduced into the high-temperature tube furnace, so that the carbon coating on the SiC fiber serves as a reaction substrate, the carbon reacts with the boron oxide in the boron-containing film in the ammonia environment to generate BN, and thus the BN coating on the surface of the SiC fiber is obtained.

[0013] The inventor found that, in order to finally obtain a uniform BN coating, the formula of the boron-containing solution is crucial, and replacing any ingredient or any ingredient out of the present application range will not be able to obtain a uniform BN coating. In the actual exploration process, the present application also tried other boron sources such as boric acid, which not only corroded the fiber but also damaged the furnace. In addition, regarding the ingredient content, if too much PVB is added, the boron-containing substance coated on the fiber is not uniform enough, which affects the uniformity of the coating, and if too little PVB is added, the boron-containing substance adhered to the fiber is less, and the coating thickness is too thin.

[0014] In addition, the formation of the carbon coating is also crucial. If the carbon coating is not provided, the BN coating is directly made afterwards, which will corrode the fiber and cause a decrease in strength. The coating of the present application not only can avoid the corrosion of the fiber but also serves as a reaction substrate, which is conducive to the growth of the BN coating.

[0015] Preferably, the SiC fiber comprises monofilament SiC fiber and SiC fiber bundle.

[0016] Preferably, the SiC fiber is placed in a heating furnace, and a chlorine gas atmosphere is introduced, and the SiC fiber is kept at 500-800°C for 1-5 hours to obtain the SiC fiber with carbon coating. In actual operation, after the SiC fiber is placed in the heating furnace, inert gas is first introduced, and vacuum is repeatedly applied for three times, then chlorine gas is introduced, and the pressure in the furnace is kept at a slightly positive pressure, and then the temperature is raised to the holding temperature, and a thin layer of in-situ grown carbon coating is formed on the surface of the SiC fiber.

[0017] The method for forming the carbon coating of the present application is to etch the Si in the SiC under a chlorine gas atmosphere at high temperature to become SiCl4 gas which runs away, and the C in the SiC remains to form the carbon coating on the surface. Through the above method, the in-situ grown carbon coating not only has extremely high bonding performance, but also has very good uniformity.

[0018] In actual exploration, the inventor tried to use chemical vapor deposition to form a pyrolytic carbon interface layer, and found that not only the bonding performance was reduced, but also the uniformity was far inferior to that of the present application.

[0019] Preferably, the boron-containing solution comprises 3-9% boron oxide, 90-96% anhydrous ethanol, and 1-2% PVB.

[0020] Preferably, the wire speed of the SiC fiber is 0.3-3 m / min, and preferably 0.5-2 m / min.

[0021] In the present application, the wire speed of the SiC fiber or SiC fiber bundle refers to the linear speed of the moving single SiC fiber or SiC fiber bundle under the guidance of the wire laying device. Controlling the wire speed within the range of the present application can efficiently obtain a uniform BN coating.

[0022] Preferably, the flow volume ratio of nitrogen gas to ammonia gas is 0.8-3:0.5-5. Controlling the flow volume ratio of nitrogen gas to ammonia gas within the above range has the highest efficiency.

[0023] Preferably, the temperature of the high-temperature furnace is 1200-1500°C.

[0024] Preferably, the thickness of the obtained BN coating is 100-800 nm, and the grain size is 5-50 nm.

[0025] Preferably, after the BN coating is formed on the surface of the SiC fiber, the SiC fiber is first passed through anhydrous ethanol, and then is collected by a wire collecting device.

[0026] Preferably, the continuous device comprises a yarn releasing device, a container A, a high-temperature furnace, a container B, and a yarn collecting device; the container A and the container B are located on both sides of the high-temperature furnace and are connected with the high-temperature furnace; the container A is filled with a boron-containing solution, and the container B is filled with anhydrous ethanol.

[0027] Advantages of the present application:

[0028] 1. The BN coating prepared on the SiC fiber has a uniform and controllable thickness, and the obtained SiC fiber bundle has good straightness and strong weaving property, which can greatly improve the performance and uniformity of the ceramic matrix composite.

[0029] 2. The BN coating prepared on the SiC fiber has a high temperature, good crystallinity and high stability, which can effectively protect the fiber during the preparation of the composite material.

[0030] 3. The device used in the present application is simple, the raw material cost is low, and the efficiency is high. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 The schematic diagram of the equipment for preparing the BN coating of the present application.

[0032] 1. Yarn releasing device, 2. Boron-containing solution (filled in container A), 3. Process gas inlet, 4. High-temperature tubular furnace, 5. Tail gas outlet, 6. Anhydrous ethanol solution (filled in container B), 7. Yarn collecting device.

[0033] Figure 2 The SEM microstructure diagram of the BN coating prepared by the present application. DETAILED DESCRIPTION

[0034] In order to better show the purpose, technical scheme and advantages of the present application, the present application will be further described in detail below in combination with examples. It should be understood that the specific examples described herein are only used to explain the present application and are not used to limit the present application.

[0035] The preparation in the examples is carried out in a continuous device, which comprises a yarn releasing device, a container A, a high-temperature furnace, a container B, and a yarn collecting device; the container A and the container B are located on both sides of the high-temperature furnace and are connected with the high-temperature furnace; the container A is filled with a boron-containing solution, and the container B is filled with anhydrous ethanol.

[0036] The SiC fiber provided with a carbon coating is discharged from the yarn releasing device, first runs into the container A, so that the SiC fiber is immersed in the boron-containing solution in the container A, then continues to run through the high-temperature tubular furnace, and then enters the container B, is soaked in the anhydrous ethanol, and finally is collected by the yarn collecting device.

[0037] Example 1

[0038] First, the SiC fiber is placed in a heating furnace, filled with inert gas, vacuumed, and repeated three times. Then, chlorine gas is introduced, and the pressure in the furnace is kept at a slightly positive pressure. Then, the temperature is raised to 550°C for 2 hours, and a thin layer of in-situ grown carbon coating is prepared on the surface of the SiC fiber.

[0039] The boron oxide, anhydrous ethanol, and PVB are mixed in a ratio of 3:96:1 to prepare a boron-containing solution. The SiC fiber is taken out from the wire releasing device, immersed in the prepared boron-containing solution, and passed through the high-temperature tube furnace at a speed of 2 m / min. The temperature of the high-temperature tube furnace is set to 1400°C, and the flow ratio of nitrogen to ammonia is 1:1. Finally, the BN-coated SiC fiber bundle is collected by the wire collecting device, with a coating thickness of 200 nm and a grain size of 7 nm.

[0040] Example 2

[0041] First, the SiC fiber is placed in a heating furnace, filled with inert gas, vacuumed, and repeated three times. Then, chlorine gas is introduced, and the pressure in the furnace is kept at a slightly positive pressure. Then, the temperature is raised to 650°C for 3 hours, and a thin layer of in-situ grown carbon coating is prepared on the surface of the SiC fiber.

[0042] The boron oxide, anhydrous ethanol, and PVB are mixed in a ratio of 5:93.5:1.5 to prepare a boron-containing solution. The SiC fiber is taken out from the wire releasing device, immersed in the prepared boron-containing solution, and passed through the high-temperature tube furnace at a speed of 1.2 m / min. The temperature of the high-temperature tube furnace is set to 1450°C, and the flow ratio of nitrogen to ammonia is 1:2. Finally, the BN-coated SiC fiber bundle is collected by the wire collecting device, with a coating thickness of 400 nm and a grain size of 10 nm.

[0043] Example 3

[0044] First, the SiC fiber is placed in a heating furnace, filled with inert gas, vacuumed, and repeated three times. Then, chlorine gas is introduced, and the pressure in the furnace is kept at a slightly positive pressure. Then, the temperature is raised to 750°C for 4 hours, and a thin layer of in-situ grown carbon coating is prepared on the surface of the SiC fiber.

[0045] The boron oxide, anhydrous ethanol, and PVB are mixed in a ratio of 8:90:2 to prepare a boron-containing solution. The SiC fiber is taken out from the wire releasing device, immersed in the prepared boron-containing solution, and passed through the high-temperature tube furnace at a speed of 0.6 m / min. The temperature of the high-temperature tube furnace is set to 1500°C, and the flow ratio of nitrogen to ammonia is 1:3. Finally, the BN-coated SiC fiber bundle is collected by the wire collecting device, with a coating thickness of 700 nm and a grain size of 35 nm.

[0046] Example 4

[0047] First, the SiC fiber was placed in a heating furnace, filled with inert gas, vacuumed, repeated three times. Then the chlorine was introduced, the pressure in the furnace was kept at a slightly positive pressure. Then the temperature was raised to 600°C for 3h, a thin layer of in-situ grown carbon coating was prepared on the surface of the SiC fiber.

[0048] The boron oxide, absolute ethanol, PVB were mixed uniformly according to the ratio of 6:92:2 to prepare the boron-containing solution. The SiC fiber was taken out from the wire releasing device, immersed in the prepared boron-containing solution, and walked through the high-temperature tube furnace at a speed of 0.8 m / min. The temperature of the high-temperature tube furnace was set to 1400°C, the flow ratio of nitrogen to ammonia was 1:3, and finally the BN-coated SiC fiber bundle was wound through the wire collecting device. The coating thickness was 550 nm, and the grain size was 27 nm.

[0049] Example 5

[0050] First, the SiC fiber was placed in a heating furnace, filled with inert gas, vacuumed, repeated three times. Then the chlorine was introduced, the pressure in the furnace was kept at a slightly positive pressure. Then the temperature was raised to 700°C for 5h, a thin layer of in-situ grown carbon coating was prepared on the surface of the SiC fiber.

[0051] The boron oxide, absolute ethanol, PVB were mixed uniformly according to the ratio of 7:91:2 to prepare the boron-containing solution. The SiC fiber was taken out from the wire releasing device, immersed in the prepared boron-containing solution, and walked through the high-temperature tube furnace at a speed of 0.5 m / min. The temperature of the high-temperature tube furnace was set to 1450°C, the flow ratio of nitrogen to ammonia was 1:3.5, and finally the BN-coated SiC fiber bundle was wound through the wire collecting device. The coating thickness was 600 nm, and the grain size was 21 nm.

[0052] Comparative Example 1

[0053] Other conditions were the same as in Example 1, except that the boron oxide was replaced by an equal weight of boric acid, and it was found that the BN coating thickness was thinned to about 80 nm, and the fiber strength was damaged.

[0054] Comparative Example 2

[0055] Other conditions were the same as in Example 1, and the proportion of PVB was reduced. The boron oxide, absolute ethanol, PVB were mixed uniformly according to the ratio of 3:96.7:0.3 to prepare the boron-containing solution. The viscosity of the obtained boron-containing solution was too low, and it failed to adhere enough boron-containing substances on the fiber. The BN coating thickness was thinned to 50 nm.

[0056] Comparative Example 3

[0057] Other conditions were the same as in Example 1, and the proportion of ammonia was reduced. The flow ratio of nitrogen to ammonia was changed to 1:0.1. The BN coating thickness was thinned to 70 nm.

[0058] Comparative Example 4

[0059] Other conditions are the same as example 1, the wire speed is increased to 5 m / min, the BN coating thickness is thinned to 60 nm, and the grain size is reduced to 2 nm.

Claims

1. A method for continuously preparing a BN coating on the surface of SiC fibers, characterized in that: A carbon coating is first applied to the surface of SiC fibers, and then the fibers are placed in a continuous equipment. The SiC fibers are released from the feeding device and first immersed in a boron-containing solution to obtain SiC fibers wrapped with a boron-containing film. Then, the SiC fibers wrapped with the boron-containing film are passed through a high-temperature furnace to form a BN coating on the surface of the SiC fibers, and then the fibers are taken in by the winding device. The method of pre-setting carbon coating on the surface of SiC fiber is as follows: place SiC fiber in a heating furnace, introduce chlorine atmosphere, and keep it at 500~800℃ for 1~5 hours. A mixed atmosphere of nitrogen and ammonia is introduced into the high-temperature furnace; The boron-containing solution has the following composition by mass percentage: 2-10% boron oxide, 85-96% anhydrous ethanol, and 0.5-5% PVB.

2. The method for continuously preparing a BN coating on the surface of SiC fibers according to claim 1, characterized in that: The SiC fiber comprises monofilament SiC fibers and SiC fiber bundles.

3. The method for continuously preparing a BN coating on the surface of SiC fibers according to claim 1, characterized in that: The SiC fiber has a fiber feeding speed of 0.3~3m / min.

4. The method for continuously preparing a BN coating on the surface of SiC fibers according to claim 1, characterized in that: The flow rate volume ratio of nitrogen and ammonia is 0.8~3:0.5~5.

5. The method for continuously preparing a BN coating on the surface of SiC fibers according to claim 1, characterized in that: The temperature of the high-temperature furnace is 1200~1500℃.

6. The method for continuously preparing a BN coating on the surface of SiC fibers according to claim 1, characterized in that: The thickness of the obtained BN coating is 100~800nm, and the grain size is 5~50nm.

7. The method for continuously preparing a BN coating on the surface of SiC fibers according to claim 1, characterized in that: After forming a BN coating on the surface of SiC fibers, the fibers are first passed through anhydrous ethanol and then through a winding device.

8. The method for continuously preparing a BN coating on the surface of SiC fibers according to claim 1, characterized in that: The continuous processing equipment includes a feeding device, container A, a high-temperature furnace, container B, and a winding device; container A and container B are located on both sides of the high-temperature furnace and are in communication with the high-temperature furnace; container A contains a boron-containing solution, and container B contains anhydrous ethanol.

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