Preparation method of crack-free coating fiber

Abstract

The invention relates to a preparation method of a crack-free coating fiber, and belongs to the technical field of preparation of a composite material. After initial tensile stress sigma o is exerted to continuous single fibers or fiber bundles, an anti-oxidation coating is evenly deposited on the surface by using a CVD (chemical vapor deposition) method and the like under the condition of tensile stress; the initial tensile stress sigma o is unloaded under the condition that the initial tensile stress is greater than or equal to the crack generating temperature TC of the coating after deposition is ended; the anti-oxidation coating is integrally cooled to room temperature after the initial tensile stress sigma o is unloaded, so as to obtain the crack-free coating fiber. By adopting the preparation method, a thermal stress crack caused by mismatching of thermal expansion of the fiber and the coating is avoided; a channel of an oxidizing medium is cut off; the fiber is prevented from being oxidized; anti-oxidation protection of a full-temperature section is achieved. Thus, the integrality, the safety and the reliability of the composite material are improved; the preparation method is suitable for preparation of heat-resistant, anti-oxidation and high-temperature creep-resistant reinforced composites. Therefore, the preparation method is continuous and simple in preparation technology, and convenient to industrially produce.

Description

technical field [0001] The invention relates to a preparation method of a crack-free coating fiber, belonging to the technical field of composite material preparation. Background technique [0002] C fiber-reinforced SiC-based ceramic composites (CMC—SiC), the performance is obvious to all, but due to the thermal expansion mismatch between the C fiber and the SiC matrix, the SiC matrix cracks, and it has very good anti-oxidation performance and protection at high temperatures. Functional SiC matrix, however, due to the cracks in the matrix, the oxidizing medium can be exploited. Due to the oxidation channels provided by the cracks, the performance of CMC-SiC is seriously affected. In order to prevent the C fiber from being oxidized, researchers have thought of various methods, and the more effective methods are: ① Crack closing method, which is to use the difference in thermal expansion coefficient between the fiber and the matrix to heal the crack, so that the oxidizing me...

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Problems solved by technology

The above method is good, but Academician Zhang Litong of Northwestern Polytechnical University pointed out 【2】 , since there are fewer reinforcing fibers available for selection, and the C base is not resistant to oxidation, a better method is still needed

②The CMC-MS method is the multi-layer self-healing method, and its effect is also very good; but the disadvantages are: 1) Due to B 2 o 3 The temperature at which the fiber becomes viscous is above 650°C, while the C fiber has begun to oxidize at 370°C, that is, the matrix cracks in the temperature range of 370°C to 650°C cannot be formed by the liquid B 2 o 3 To fill, and CMC-SiC has relatively many cracks in this temperature range, making its oxidation resistance very poor

2)B 2 o 3 Very sensitive to water vapor, easy to make B 2 o 3 Layer peeling off, in addition, when the temperature reaches 815°C, B 2 o 3 The diffusion rate of oxygen is very high. When the temperature is above 1000℃, B 2 o 3 The vapor pressure is too high, the oxygen diffusion rate is too high, and it is no longer protective 【3】 , and the higher the temperature, the more serious the volatilization

3) SiO2 2 The high-temperature vapor pressure is small, and the diffusion rate of oxygen is small, but SiO 2 Only when the temperature is above 1000 ℃ can there be a liquid seal function, so simply use SiO 2 Liquid seal, in the temperature range of 370°C to 1000°C, it has no protective effect

such as B 4 C, SiC and other coatings, but still due to thermal mismatch, the tensile stress of these coatings in the fiber axis is too large, resulting in cracks in the coating and substrate perpendicular to the fiber axis, and then unable to protect the C fiber. C f / The C fiber in SiC cannot be protected, so the C fiber has to be replaced by SiC fiber, but SiC f / SiC creep resistance becomes very poor at temperatures above 1600°C f The creep resistance of SiC is much higher than that of SiC f / SiC

Current SiC f The long-term use temperature of SiC is 1450℃, C f / SiC's long-term use temperature reaches 1650 ° C, so it is f C in / SiC f The oxidation resistance is C f / Key technology of SiC ceramics 【11】 , that is, to solve the thermal stress problem that the axial direction of the C fiber does not match the expansion coefficient of the coating or the substrate, resulting in cracking of the coating or the substrate; but there is no ideal method to close or eliminate thermal stress cracks to prevent the C fiber and PyC The interface is oxidized

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