Present Status and Future Trends on the Development and Application of Continuous SiC Fibers

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Polymer-derived SiC fiber Nicalon has been produced commercially and widely used as a reinforcement of Polymer Matrix Composites (PMCs) and Ceramic Matrix Composites (CMCs). Main applications of Nicalon fibers are PMC for structural materials of aerospace and CMC for high temperature components of aerospace engine. In recent years, it has been increasing in demand for high performance CMC for high temperature application. Ceramic matrix composites are most promising materials for high temperature structural materials of gas turbines for aerospace and power generation. Mechanical performances of CMCs are highly dependent on properties of the reinforcement. We have been improving fiber properties for CMCs by reducing oxygen content and excess carbon in chemical composition of the SiC fibers. The oxygen free SiC fiber (Hi-Nicalon) was developed and has been commercially produced using an electron beam curing process. By reducing oxygen, this fiber has a higher elastic modulus and creep resistance, and thermal stability up to 1,600°C than those of Nicalon fiber. High temperature mechanical properties of CMCs using Hi-Nicalon have significant improved. However, creep resistance of Hi-Nicalon CMC is not satisfactory as structural materials at high temperature, because Hi-Nicalon mainly consists of SiC micro-crystals and excess carbon. Recently, the SiC fiber (Hi-Nicalon type S) having stoichiometric SiC composition and high crystallinity have been developed by Nippon Carbon. By reducing excess carbon and putting C/Si ratio close to stoichiometric composition, Type S fiber has high elastic modulus of 420 GPa, high thermal conductivity, and excellent creep resistance. In this paper, the recent development of these oxygen free SiC fibers and results of physical and mechanical properties, thermal stability, and an environmental resistance are reported. Hi-Nicalon Type S fibers should be the best candidates for the reinforcement of ceramic matrix composites. Application of SiC fibers is introduced. Now, Nicalon fiber/ceramic matrix composites are used for the exhaust flaps and seals of jet engine. Hi-Nicalon Type S fiber/BN/SiC composites are being developed as the components of gas turbine for aerospace and power generation such as shrouds and combustor.