Process optimization for high performance SiC fibers from polymer-driven Pre-ceramics

SiC
_f
/SiC composites are one of the most promising advanced fusion reactor materials especially for the first wall/blanket because of their low induced radioactivity and excellent mechanical properties. There is no doubt that the performance of SiCf/SiC composite is much more dependent on the properties of SiC fiber. The synthesis process of SiC fibers from polycarbosilane (PCS) by pyrolysis process is a common processing method up to the present. By the conversion process of organomentallic polymer into inorganic compounds, PCS is converted into beta-SiC phase over 1500degC with suitable control of the time. Among the various conditions of heat-treatment, notably temperature and time are very important factor to understand the crystallized SiC fiber. Though many papers are investigated on the dependence on parameter of conversion process, research on extremely high performance crystallization has few papers. In this study, process speed, especially high speed process for crystallized SiC fiber is investigated. Fiber morphology is investigated by Field Emission-Scanning Electron Microscopy (FE-SEM). Due to examining fiber reliability, Weibull distribution using fiber strength of crystallized SiC fiber will be also discussed. Heat-treatment of Pre-ceramic fiber was carried out from 1 min at elevated temperature in order to examine the time and temperature dependency. In case of the heat-treated SiC fiber at around 1900degC for 1 min, grain size was very small but at around 2000degC, the grain size was around 150 nm which was relatively larger than formal one and both cases has rough lateral-surface. The tensile strength of heat treated SiC fiber for 1 min is less than 2 GPa at both 1900degC and 2000degC temperatures. The rough lateral-surface, residual stress and residual of raw material in the fibers due to the rapid conversion reaction likely caused the result of low tensile strength. Therefore the heat-treated SiC fiber for 1 min, as a result, shows increase of tensile strength to approximately 2 GPa and by the recrystallization the grain size also grew up.