Effects of molecular weight of raw material and heat-treatment temperature on mechanical properties of dry-spun SiC fibers

Abstract

SiC fiber reinforced SiC matrix composites (SiC/SiC composites) are a kind of ceramic matrix composites (CMC) and have attracted attention as a new material for aerospace engines because of their high strength, high temperature resistance, and oxidation resistance. The dry-spinning method for SiC fibers is one of approach to reduce the fabrication cost of SiC/SiC composites. In the dry-spinning method, the raw material, polycarbosilane (PCS) is dissolved in a volatile solvent and spun. This method can skip the curing process, which is the cause of high cost. In this study, dry-spun SiC fibers were fabricated by changing molecular weight of PCS and heat-treatment temperature. The mechanical properties of SiC fibers were determined by monofilament tensile tests. The highest tensile strength and elastic modulus of the dry-spun SiC fibers were 2.88 GPa and 270 GPa, respectively. These mechanical properties strongly effected the molecular weight of PCS, the heat-treatment temperature, and the fiber diameter. As the molecular weight of PCS was higher than a certain threshold, the excessive crystallization was observed causing the decrease of mechanical properties. In addition, the defects inside the fiber increase when molecular weight is higher. The heat-treatment temperature also affected the crystallization and the increase of defects with depending on the molecular weight of PCS. The crystal size enlarged with increasing the heat-treatment temperature, while the fracture morphology remained unchanged.

Keywords

• sic fiber
• dry spinning method
• dry spun fiber
• ceramic matrix composite
• sic/sic composite
• mechanical properties
• monofilament tensile test