Due to its excellent properties of high strength, high modulus, high thermal stability and high oxidation resistance, SiC fiber has great advantages in ultra-high temperature resistant reinforced materials, and the preparation of ultra-high temperature resistant SiC fiber has become a research hotspot in the field of national defense. At present, chemical vapor deposition (CVD) and precursor transformation are the main methods to prepare SiC fibers.

Preparation of SiC fiber by CVD
The advantages of SiC fibers prepared by CVD method are high temperature stability, but the disadvantages are large diameter, poor flexibility, difficult weaving, which is not conducive to the preparation of complex shape components, and expensive, so its application is greatly limited. The precursor conversion method for SiC fiber has a good processability, can be fired at low temperature, and the prepared fiber has a series of advantages, such as small diameter, easy to prepare, easy to realize industrial production and so on, which makes the precursor method more advantageous in the selection of SiC fiber preparation methods.

Preparation of SiC fiber by precursor conversion
The companies that develop and produce SiC fibers by precursor conversion are mainly concentrated in a few developed countries such as Japan and the United States. Researchers from Northeastern University of Japan first successfully developed the precursor conversion method to prepare SiC fiber. The process includes four steps: precursor synthesis (Polycarbosilane), melt spinning, non melt treatment and high-temperature sintering. However, the initial fibers have low density, and the properties of the fibers decrease sharply when the temperature is higher than 1250 ℃. The first generation of commercial SiC fiber is NICALON 200 produced by Nippon carbon company in Japan and tyranolox-m produced by Ube company in Japan. Due to the introduction of oxygen in the process of cross-linking, the two kinds of commercial fibers prepared by precursor conversion have sicxoy composite phase and free carbon, so the mechanical properties of the two kinds of SiC fibers decrease obviously after 1200 ℃. In order to improve its high temperature stability and obtain SiC fiber with better performance, Nippon carbon company of Japan obtained hi NICALON products through PCs precursor spinning, electron beam crosslinking and pyrolysis in hydrogen atmosphere. In this process, the surplus carbon was further removed, making the final SiC fiber with tensile strength of 2.6-3gpa and elasticity The modulus is up to 420 GPA, the diameter of the fiber is 14 μ m, and the maximum service temperature can be as high as 1600 ℃. Therefore, the SiC fiber prepared after improvement has the advantages of high modulus, high creep resistance, high oxidation resistance and high thermal stability. At the same time, the first generation SiC fiber preparation process has been improved by Ube company of Japan, which adopts PACS precursor, after spinning and air crosslinking, it is hot The si-al-c-o fiber was obtained by pyrolysis, and the latest product tyranosa was obtained by high temperature sintering. Its tensile strength is 3-3.3gpa, elastic modulus can be up to 420gpa, fiber diameter is 11 μ m, and the maximum service temperature can be up to 1800 ℃. After improvement, the high temperature performance of the two improved significantly, but the cost increased significantly. In addition, the SiC fiber produced by Corning company of the United States with methylpolysiloxane and hydrogenated polysiloxane as precursors has a tensile strength of 3.2 GPA, an elastic modulus of 380 GPA, a fiber diameter of 10 μ m, and a maximum service temperature of 1500 ℃. A large number of basic researches have been carried out in China. Zheng chunman et al. From polyaluminosilane, prepared Continuous SiC (AL) fiber by precursor conversion method, with diameter of 12 μ m and average strength of 1.4gpa. Due to the low content of sicxoy composite phase and free carbon in the fiber, the fiber has excellent ultra-high temperature resistance. After being treated in argon at 1800 ℃ for 1h, the strength of the fiber does not change much, and the cost is effectively reduced. At the same time, Xie Zhengfang et al. Synthesized the precursor PMCs containing heterogeneous elements by mcl5 and LPS. The SiC fibers containing heterogeneous elements (Nb, Mo, re) were prepared by melting spinning, air non melting treatment and sintering at 1200 ℃ in inert atmosphere. The average diameter of the SiC fibers was 12 μ m, the average strength was 2 GPa, and they had excellent high temperature resistance and high temperature oxidation resistance, 1250 ℃ in air still has high strength. In conclusion, for the preparation of SiC fiber by precursor synthesis method, researchers in various countries have improved the technology by introducing heterogeneous elements into the precursor preparation process, so as to carry out physical and chemical modification of precursor Polycarbosilane, and prepare a new SiC fiber with excellent performance.